Another smile was raised by an aside in a description of how centre-locks work by Wilson McComb attributed to a North American writer. Large diameter wire wheels were an uncommon sight in post-war America, but with a number of early MG T-series cars having been brought back by American Forces personnel after WWII, they were christened 'coffins riding on four harps'.

Care needs to be taken with all original types of wheel if having them balanced at modern tyre fitters with computer balancing machines - it is crucial how the wheel is supported on the machine. Modern wheels are relatively high-precision items compared to original MGB wheels, indeed I've heard it said that Rostyle wheels were often neither round nor concentric and they rejected many! Unlike the Dunlop V8 alloys which were (centre hole excepted) very accurate and very strong - the factory apparently never managed to break one in early tests with massive over-loads.

Modern wheels are mounted on computer balancers using the centre hole and a quick-release spinner as this is much quicker to mount and demount than using studs and nuts. All MGB wheels have these centre holes as well, but on disc, Rostyle and V8 alloys the hole was intended simply to clear the hub nut and so its positioning wasn't precise. Mount one of these wheels on its centre hole and the tyre fitter is likely to advise you that it is so out of balance/out of round that is unsafe. Centre-lock wheels have to be mounted on the centre hole of course, but the adapters used are crucial, they need to be held at the same machined surfaces as they on the hub, but these are rarely available. Speaking to the MGOC they told me they had to purchase their own balancing machine and get a suitable adapter made as no-one else was able to do them properly. This Dayton Wire Wheel document on taper angles seems to be saying that their centre-lock wheels manufactured since 1990 have had a fully machined hub and as such will mount correctly on a modern tyre balancing machine using two inside cones of 70 degrees (as measured on screen) as opposed to an inner cone of 60 degrees and an outer of 20 degrees (both stated) that are needed for earlier wheels, and presumably those from other manufacturers.

Personally I reckon on-car balancing would be the answer, for all types of wheel, as was the norm in the 70s and 80s. However tyre places with those machines are now few and far between. Another possibility is the home static (anything that spins the wheel is a 'dynamic' balancer) balancer that uses an air-bubble, but I've read these are a bit hit and miss.

Incidentally 'Rostyle' is actual 'R-O style' abbreviated from 'Rubery-Owen style' after the manufacturer of the wheel.

Stud-mounted: These wheels all have stud holes and if the tyre fitter has a four-stud adapter plate for his balancing machine then ask that it be used. If not then you are better off going somewhere else that does, even to pay extra for balancing only. But I'm still not convinced that is the whole answer, see below for my V8 balance problems.

V8 Balance Problems: From being fine when I first bought the car I started getting problems as soon as I replaced the fronts. They lasted the life of one particular pair of tyres despite repeated rebalancing even with the 4-stud adapter plate (see above), so it was obviously the tyres that were at fault. But along the way I read that the wheel nuts used with the V8 cast-alloy wheels can cause a little imbalance and of a way to avoid it.

Unlike Rostyles the V8 wheels and nuts do not have the conical seat to aid location. The shank of the nut goes right through the wheel and a flat washer as a shoulder does the clamping, therefore right up until the time the nuts are fully tightened the wheel can move up and down and side to side a little way, which means that when they are fully tightened the wheel can be in one of a small range but infinite number of positions in relation to the hub. Unless the wheel is exactly concentric with the hub some imbalance is inevitable. The recommendation was to use a pair of Rostyle wheel nuts on opposite studs and lightly tighten them. The taper on these nuts, even though it is bearing against a parallel-sided hole, will always locate the wheel in the same position on the hub. The first two V8 nuts are then replaced and tightened, then the Rostyle nuts are removed and the final two V8 nuts replaced and tightened. The Rostyle nuts are a different size 'across the flats' to the V8 nuts, so I welded a strip of metal around the Rostyle nuts to build them up to the same size as the V8 nuts to avoid having to use separate wrenches or spanners for each type. I also mark one hub stud and one hole in each wheel to ensure each wheel goes onto its hub in the same position each time as well as ensuring each wheel goes back onto its own hub (I never rotate my tyres around the car, it leads to premature replacement and all four, or five, wear out together). Since doing that (and junking the dodgy tyres it has to be said) I had no more problems with wheel balance, although after replacing the front tyres again (normal wear) the wobble has come back, and again I have been unable to get rid of it.

Update July 2009: It has been quite significant for a long time now, despite repeated rebalancing, more new tyres, and swapping fronts and backs over. It's not a steady vibration, but fades in and out at a regular rate, as if both are out of balance, one is rotating at a slightly different speed to the other, so they are alternately cancelling each other out and adding to each other. Also on a long curve on a motorway one way the rate of fading in and out speeds up, and the other way it slows down, also tending to confirm that both are out of balance. As all four wheels are doing the same it could well be that the so-called balancing machine is actually leaving them all unbalanced by the same amount when the machine says they are balanced. A couple of months ago on one trip it seemed particularly bad, which made me do another Google search, and this time I found a reference to BMTR in Birmingham having a special 'Road Force Measurement' machine, and also Vibration Free in Bicester who are balancing specialists, any rotating machinery, and do have on-car balancing facilities. At the MOT the other week the tester made a verbal observation that the rack is showing some play, which it is in the straight-ahead position, so almost certainly due to this wobble over a long time. I don't want to replace that while I still have the problem, so it really is time to do something about the vibration. £55 (plus the dreaded VAT) per hour for Vibration Free and usually a minimum of 2 hours required for four wheels, as compared to £15 per wheel at BMTR, so that was my first port of call.

I had great hopes of it as they tested the wheels with the existing weights first and both were out, one by a long way, whereas other places have just ripped the old weights off and started from there. They were also mounted on the machine much more securely. Ordinarily places will simply mount them by the centre hole against a cone, but MGB wheels were never made accurately enough for that, pre-dating those machines by several aeons. Some fitters including the one I usually go to have a gadget which holds them by the stud holes, but it consists of a hub with four arms which can be swung out to fit any stud spacing, and I've never been convinced that method is accurate enough. BMTR have a set of circular plates with holes drilled at gradually increasing distances from the centre. Pins are put into these holes that engage with the stud holes in the wheel. Instead of a cone on the back of the wheel there is a cylinder, which fits inside the hole in the wheel with some play and a shoulder that butts up to the back of the wheel. That just supports the back of the wheel same as the hub, whilst the four pins with tapered ends are clamped onto the front of the wheel in the stud holes and do the accurate positioning. This method of mounting is used on all wheels, so obviously the machine manufacturer doesn't think location by the centre hole is a good idea on any wheel! As soon as I drove out of the place I was amazed to find it felt smoother even at low speeds, but then dismissed that as probably wishful thinking. When I was finally able to get on some open road (this place is in the middle of Birmingham frustratingly) I was able to do two or three sprints of 70+ with no wobble - marvellous after all this time. Shan't be totally sure though until I can get on a longer run at those sorts of speeds.

Update May 2010: Will this saga ever end? True enough the balance remained good. But on removing the drivers front on various occasions the very large weight (the only weight) that was on the inside was obviously coming loose, and eventually at the annual service last month I found it was missing altogether, but had noticed no wobble. Thinking it was possible that it had come off on the last outing I took it for a fast run, but on that, and on subsequent longer motorway journeys, the balance was still perfect - very weird! Even weirder had the fronts replaced this week and got them to assess the balance before removing the weights or tyres, and whilst the left font had 10 grams too much on their machine the right front (lost weight remember) was a massive 160 grams out! He couldn't explain why the balance was the same with and without, and I suspect he thought I didn't know what I was talking about, but to be honest I doubt I would believe me either. Had the new tyres balanced as normal, and whilst they are nowhere near as bad as before there seems to be a very slight tremor some times, but not consistently fading in and out as it did originally. On an 80 mile motorway run the only tremor seems to be on concrete surfaces, on new tarmac it is fine. So now that raises questions about the balance machine at the tyre place I have been using for years, as I got these somewhere else.

Incidentally, I noticed that when replacing the wheels the fitter used an air-gun to do up the nuts and only used a torque wrench to check they they weren't under torqued. Correct torque is 60 ft lb, and back home I used my torque wrench to loosen a couple on the rears (tightened by myself previously) and they needed about 70 ft lb to undo. One of the fronts got up to 100 ft lb before it started to move, very slowly, needing torque to keep it moving whereas they usually loosen quite quickly, another got up to 120 ft lb and then the torque wrench (bendy bar type) broke! I had to use a breaker bar on the rest, and they were very variable in how much force was required. This place (National Tyre and Autowreck) also use a different method of raising the car - you drive over a short ramp that the wheels straddle, then they place rubber blocks under the body and lift it with those, which I really didn't like. I may take wheels there for tyre replacement in future, but I would never take a car again.

Centre-lock: Centre-lock wheels must be held by the inner and outer tapers just as they are by the hub and locking-cap or they will not be centralised, with similar comments to mounting studded wheels by the centre hole as above. Modern balance machines usually have a set of tapered adapters of different sizes that are slid onto the balancer machine shaft so as to mount wheels with different sized holes. All the ones I have seen are conical in shape with the contact surface for the wheel on its outer angled surface. These are fine for the inner face of the wheel as it is similar to the hub, but because the quick-release spinner presents a flat surface to the wheel it doesn't hold the outer face of the wheel properly. I've seen them slide another taper onto the shaft and then the quick-release spinner, but this utilises the inside surface of the hole in the wheel and not its taper with the same results as before. Unless your fitter has a taper of the correct type i.e. one with a conical hole then again don't have them balanced. When first fitting chrome wire wheels the last thing I wanted was weights attached, especially to the outside, so opted to try them unbalanced first. Maybe I was just lucky, but I have never had any balance problems.

Updated January 2010: Following a discussion on the MG Enthusiasts bulletin board Richard Davidson emailed to anyone who was interested details of an adapter that will mount centre-lock wheels correctly on balancing machines. I'm sure he won't mind if I make his documents available here. He is going to have some made up by a friend with the necessary CNC facilities, making further copies relatively easy to obtain. Unfortunately he lives in South Africa, so postage to places like the UK and North America is likely to be an issue! I'm making enquiries locally to me in the UK about having some made here. However, it occurs to me that maybe only the outer cone that replicates the spinner may be needed, one of the balancer standard cones being adequate for the inner taper. Come to that, maybe an old spinner could have the end machined off to slide onto the balancer shaft. Or even an old hub and spinner modified to clamp the wheel correctly and slide onto the balancer as an assembly.

Updated April 2010: Son-in-law found me a machinist in Birmingham who quoted me £35 to make an outer cone, and £30 for an inner (collected prices), had one set made and collected them this month. I replaced two rear tyres last year and since then have felt some body vibration at typical wheel imbalance speeds of 65mph and greater. Put these on the fronts and had severe vibration. Took them and the cones to my local tyre place, and first had them assessed using how they would normally mount them (test 1), then with just my outer cone (test 2), then with my inner and outer cones (test 3). A noticeable improvement in run-out using my cones, and more balance weight required, in tests 2 and 3 over test 1. Had them weighted up using my cones, and back on the car they are as right as ninepence (which is more than it cost me to have them done (apart from a bung), which is why I'm reluctant to say who did them in case they get into trouble). Incidentally these are Cooper tyres and one needed 110grams and the other 150grams, which are large amounts. As the first tyres I put on when changing from Rostyles to wires needed no weights, I rather suspect these tyres are the problem instead of my wheels. I need new tyres for the front soon, so it will be interesting to have the wheels checked with the tyres off first, then again with the new tyres on, and I shan't be buying Coopers!.

There was no difference between tests 2 and 3, which indicates that the standard cones used on the inside of the wheel is perfectly adequate on its own, hence only the outer cone is required. However offering the stabdard cone up to the wheel shows that it is contacting the taper right at the inner edge of the taper, i.e. right where the splines start. If there were any damage i.e. burrs in this area then it would hold the wheel incorrectly. By contrast my inner cone contacts the wheel right in the middle of the taper. This inner cone sat exctly square in the wheel, however the outer cone exhibited a slight rock on all five of my wheels. As the axis of the rock stayed with the wheel as I tried the cone in different positions it can only be a slightly warped hub. Perhaps not surprising, it is only a pressing (India Dunlops anyway), this taper is right at the edge and not in the middle as with the inner cone, with spokes close by under significant and variable tension. On the car the spinner is banged up pretty tight which probably helps to overcome this, on a balance machine it won't be as tight. Nevertheless my wheels came up with zero after balancing, and feel perfect on the car, so that is proof enough.

If you want to obtain the cones then I have left the drawings with the machinist for him to use as and when he wishes. He is:

Self-tightening? Or not? The theory is that centre-lock spinners, or locking-caps, are self-tightening, although some poo-poo it. Certainly the threads are different from side to side - with left-hand threads on the right-hand side of the car and vice-versa. With seized spinners the advice is usually to drive in reverse in a tight circle, and towing advice is never tow a centre-lock equipped car backwards with any wheels on the ground. Definitely mine take more effort to undo than I put in to doing them up, and that is when clean and lubricated and after only a short journey, so no seizing there. I came across a description of the self-locking action on a TR web-site, reprinted by permission from Safety Fast (MG Car Club), written by Wilson McComb, which he attributes to The Autocar Handbook of 1918! I reproduce the guts of what he wrote here, I hope none of the aforementioned object.

The crucial components consist of the centre part of the wheel, known as 'the wheel centre', the axle hub it slides onto and the spinner or 'locking cap' that secures it. The wheel centre is not pressed up against the brake drum as with a conventional wheel with four or five studs and nuts per wheel, but there is a gap of 1/8" or so. It is the inner taper of the wheel centre which contacts a corresponding taper on the inner part of the hub that achieves this. The wheel centre has another taper on its outside surface, which contacts a similar taper on the locking cap. When the three components are assembled and the locking cap tightened the wheel is held firmly between these two tapers, which centralises it with a small clearance over the splined section. These splines don't support the wheel but only provide driving and braking forces, and there has to be a small clearance between the two splined surfaces or you would need to press the wheel on and off the hub - not really convenient when you get a puncture. Moving out from the wheel centre we have the spokes, which are prevented from pulling out of the centre by a nipple bearing on the inside surface. At the other end of the spoke we have an adjuster to control the tension in the spoke. Because of this the wheel centre only ever hangs on the upper spokes the lower spokes are never in compression - if they were loose enough the nipple on the wheel centre end would be pushed free of the wheel.

Because the weight is always carried by the upper half of the wheel it means the forces on the upper part of each pair of tapers is different to that on the lower half. And as the wheel rotates these forces move along the pairs of tapers and hence round the wheel about its axis. The effect of this is to cause the locking cap (which is the only part than can move any significant distance in relation to the other two parts) to turn relative to the other two, and the physics involved means it turns in the opposite direction to the movement of the forces around the tapers. Exactly the same effect can be seen by spinning a plate (not your wife's best china given to her by your Mother-in-Law ...) on a flat surface - the plate starts off at right-angles to the flat surface, but as it slows its angle gradually flattens and approaches the horizontal. As it gets close to the horizontal, and if the plate is coming to rest upside down, compare the direction of movement of the point of contact with the ground with the rotation of the plate about its own axis, and you will see it is always opposite. An untightened centre-lock wheel locking-cap is similar to the plate in the flattest part of its spin i.e. shortly before it comes to a stop, except the wheel cannot rotate relative to the hub but the locking cap rotates relative to the wheel and the hub. This contra-rotating action of the locking cap combined with the direction of the threads means this is always a tightening motion when the car is travelling forwards.

This effect is nothing to do with a quirk of wire-wheels e.g. their flexibility, it applies equally to alloys which are very rigid. On the other hand I have read that one North American motor manufacturer used left-hand threads on studded disc wheels believing that the same principle applies with these too. I don't believe they do - the forces involved in a disc wheel do not rotate around the centre-line of each stud and nut but move across them from one stud to the next around the wheel. And I think we have been living with right-hand threads on studs and nuts on both sides of the car now to dispose of that theory.

How tight? McComb says the earliest instruction he came across was never more than finger-tight. However the looser they are the more the one set of splines is likely to fret against its opposite number, causing wear, and instructions for many years have been to hammer them up then check after 20 miles and retighten if necessary. 'Hammering' means with a copper, hide, lead or similar mallet (see below) and not beating the living daylights out of it with a steel sledge-hammer. Manually overtightening could well distort the wheel centre affecting the tightness of the spokes and the 'true' of the wheel, hence causing balance problems. The recheck after 20 miles can only be a belt-and-braces check maybe against having left it finger tight or less when refitting, given the self-tightening action 20 miles will probably have tightened it up anyway. I bought the MGOC 'lead-faced' hammer with my wire wheels but the 'lead' seemed far too hard to me one tentative whack confirmed my fears by marking my brand-new chrome spinner, so I had to resort to using a block of wood as a buffer for several years. Then I discovered a Thor hammer in my local Halfords that had nylon one side and aluminium the other, and in 10 years or so of use it (the nylon end) hasn't left a single mark on the spinners. Click here for the Thor web site for UK sales, although I can't currently see a picture of the exact hammer I have. Anglo American are agents for Thor hammers, see here for North American stockists. Thor also do the correct (for older MGs really) copper and leather hammer but is very expensive.

Lubrication: Essential to avoid the wheel, hub and locking-cap seizing together, with the aforementioned difficulties in the event of a puncture. Splines, locking cap and hub threads to aid self-tightening as well as removal and the surfaces of the tapers. When first fitting new wheels and hubs one probably puts on too much as it fills up the grooves in the splines and the threads, the excess working its way out into the wheel centre. Once on the spoke nipples it will work its way through the wheel centre and along the spokes. I've seen a recommendation to use silver grease so it doesn't show, but in my experience it is the dust and dirt that stick to the grease that you can see on the spokes, and this is always black or very dark brown, making the original colour of the grease immaterial. In the 15 years and 40k miles since fitting my wire wheels I haven't had to re-grease the splines or threads since first fitting, and once I'd cleaned the excess out of the centre of the hub, where the spoke holes are, I very rarely get any up the spokes. At each service I just wipe the thinnest smear over the tapers, and usually this comes from the area between the taper and the splines. The tapers should keep dirt out of the splines and threads in normal use, make sure you don't introduce any when removing wheels.

Spline wear: Because the splines have some clearance, and even when the centre-cap is fully tightened, it is inevitable that there is very slight rotational movement between wheel centre and hub when repeatedly accelerating (rear wheels only) and braking. Initially this is very slight but each time the one does move relative to the other the faces of the splines are brought together with a bit of an impact. This 'hammering' gradually deforms the splines, making them thinner, which increases: the gap between the faces of the splines; the distance each spline travels when it changes direction; the impact when it finally reaches its opposite number; and the rate of wear. Initially and with lubricated splines, this movement and impact is inaudible, but eventually wear increases to the point of causing an audible 'clonk' (not to be confused with a similar noise from the diff which is caused by worn thrust washers). New splines have a cross section that looks like a triangle with the top cut off. As they wear i.e. the splines get thinner the flat top narrows, until the top of the triangle is pointed again, and the triangle may lean to one side. Further wear will eventually cause the triangle to bend right over and the two sets of splines can wedge on top of one another seizing the wheel to the hub. Alternatively, i.e. under sudden heavy braking, the tops of the splines can be snapped off and then the wheels can rotate independently of the hub, which can be a bit traumatic! I'm told that new hubs have a diameter at the splines of 2.440", fairly worn (sharp point instead of flat top) may be greater than this, stripped splines will be less than this.

The following drawings have been taken from British Wire Wheel. However in my opinion the flat top to an unworn spline is much more evident than shown in their drawings, as shown here:

Updated July 2010: There also seems to be some confusion caused by slight rotational movement of the wheel and tyre, when the tyre is grasped and turned, with the brakes on, wheel off the ground, and the spinner hammered up tight. Look carefully at the brake drum as the wheel moves back and fore, and if this moves with the wheel, that is not spline wear, but the shoes moving against the back-plate. As such this has no effect when running as the handbrake is off. If however the brake drum remains stationary as the wheel turns, that is indeed play in the splines. As stated above there must be some play in the splines or you would never get the wheel on and off without a press or puller, it's clonks from the wheels that indicate spline wear. Some is inevitable as the wheels and hubs get older, and when you start hearing clonks that is when you start keeping an eye on the shape of the splines, and definitely replace both (unfortunately) at the latest when the splines develop a sharp point, if not before. You may well find that it's the brake drum that turns initially, but then with increased force on the tyre, especially if you are hearing clonks from the wheel, that the wheel moves further but the drum doesn't. It's this second movement that is spline wear, and with correctly tightened spinners should be quite a bit harder to obtain than the initial movement with the drum.

Originally radial tyres for the 4-cylinder would have been marked '155SR14' for the roadster, '165SR14' for the 4-cylinder GT and '175HR14' for the V8. '155/165/175' is the width of the tyre in millimeters, 'S' and 'H' are the speed rating (113MPH and 130MPH respectively), 'R' signifies Radial construction, and '14' is the rim diameter in inches. No aspect ratio is given as most tyres were 80s, i.e. the sidewall height is 80% of the tread width. 80 profile tyres aren't commonly available these days, so it is quite normal to see 70 or 75 profile tyres used with an increased tread width to keep speedo accuracy. No load rating given either. Modern tyres, for the V8 for example, will be marked '185/70 R14 H88' i.e. 185mm tread width, 70 profile, radial construction, 14" rims, H speed rated, 88 load rated.

It's interesting to note that with the change from crossply to radial the tread width units changed from Imperial to metric, even though it was long before general metrification in the UK. This may well have been to give a clearer indication of construction than a simple code letter, as crossply and radial must never be mixed on the same axle, nor can their be radials on the front with crossplies on the rear. However the rim diameter continues to be in inches, because there are few exact, round number conversions between metric and Imperial, and the rim diameter needs to be to very close tolerances or you won't get it on, it will leak, or even worse come off the rim, and there is little point in specifying tyres for a 14" wheel as '355.6mm' just so as you can use metric units. Why do UK wheels continue to have rim diameter in inches when they could be metric? Probably because tyre manufacturers for the UK market would then have to produce tyres in both Imperial and metric, with only tiny differences between some of them.

Speed ratings:

Load ratings:

Those figures are for the roadster, for completeness 4-cylinder GT figures are 20 or 21 front (cross-ply or radial) 24 rear, V8 21 front and 25 rear. At maximum weight increase the rear pressures by 2psi, and for sustained high-speeds increase front and rear by about 6psi.

The original tyres for the roadster were 5.60-14 (crossply) or 155-14 (radial) as an option. The first number is the tread width - 5.60 inches in the case of the crossply, 155mm for the radial, even though 5.6" converts to 142mm! '14' is the wheel diameter at the tyre bead. When the GT was introduced its tyres were 165-14. At the time the sidewall height (which is the major factor in rolling radius) wasn't specified, but was always '80', which represents 80% of the tread width. It was the same for both 155 roadster tyres and 165 GT tyres, which means the GT has a slightly higher rolling radius, which will have a small effect on speedo reading. Wheel width was something else altogether, at 4" for roadster disc wheels, 5" for GT disc wheels, but 4.5" for wire wheels on both! It's this difference (in disc wheels) that accounts for the different tread widths. When Rostyles replaced disc wheels both models used 5". The alloy wheels used on some special models late on were also 5", but had 185 width tyres, with 70 profile instead of 80, and RV8s used a 65 profile! Confused? You have every right to be. Speedo reading isn't as much as an issue as you might think, as most markets accept speedos that fit into a band where they don't under-read, but can over-read (i.e. show you are going faster than you really are) by up to 10%. 5mm increase in the width for the same profile results in about an extra half inch (in typical MGB tyres) of radius, which equates to about 2%, so well inside the 10%. Germany was the exception and required much more accurate speedos, so GTs had a different speedo to roadsters to cope with the wider tyre with the same profile and hence the larger rolling radius, with a lower turns per mile - 640 as opposed to 660mm (which is actually turns per kilometre not turns per mile). Speedo operation is governed by a number of factors including tyre rolling radius, axle ratio, speedo drive gears in the gearbox, as well as the gearing inside the speedo.

Added October 2009:
As well as width, profile and wheel size speed rating is also important. Neither the Leyland Workshop Manual nor Haynes specify a speed rating for the 4-cylinder cars, but Clausager states it was SR, but today the 'R' seems to have been dropped and the rating is just 'S' which is good for up to 112mph, comfortably over what a standard car should be able to achieve. However the MGOC seems to only be offering MGB tyres in T and H ratings, and T is only rated up to 106mph which is cutting things very fine even for a standard car. They also offer them in 15", which is the MGC diameter, which should definitely have H rated. Originally V8 tyres were specced as 'HR' ('H' in today's parlance) which is good for up to 130mph, which doesn't give much leeway. Of course any increase in performance that even reaches these figures, let alone exceeds it, means that the appropriate higher rating must be fitted. Beware those websites that show speed ratings with column graphs, as well as being pointless and taking up far more screen space they are confusing if not downright inaccurate as they appear to show each rating as having a lower speed than they actually have. You are better-off with a simple table from the likes of BlackCircles.com or the RAC.

Added July 2009:
Table of standard tyres, plus various options for 4-cylinder cars as compared to the original 155/80 roadster radials:

Since writing this someone has posted to the V8 Register BBS their experiences with Solent Wheels. Their chrome was in fairly bad condition and for £50 Solent stripped and powder-coated the whole wheel - rim and alloy centre - silver then top-coated the alloy part in satin black, finally polishing the areas round the cut-outs. Photo looks pretty good and had my chrome been any worse a better bet then spending eight hours per wheel!

Update July 2010 In December 2007 I added a paragraph about someone in the West Midlands who would split and rechrome V8 wheels. I've recently had an email from someone who has had a very poor experience with rechromed Rostyles from this person, commenting on a crude technique for splitting and reassembling, severe balance problems afterwards, and chrome that rusted over winter in a dry garage. So on balance, link deleted!

Note: 22mm offset is mentioned in various places, but my 5" Rostyles measure 27mm positive offset. So does it vary with wheel width? To keep the same track, the offset would be the same, which would reduce the clearances both side of the tyre. But if the track was originally made as wide as possible with narrow tyres with a minimum clearance to the outer part of the well, then with wider wheels a bigger positive offset would be needed to retain that clearance, which would reduce the track, and the clearance to the inner part of the well would reduce by the whole of the increase in wheel width.

And what about wire-wheels? Stud wheels are easy - you simply measure the distance from the centre-line of the wheel to the face of the wheel hub that contacts the face of the brake drum. But for wire wheels is it measured from the back of the wheel hub or to the inner taper? And if at the inner taper is it the wider edge? The narrower edge? Or between the two? Wire wheel axles are 1.75" (banjo) or 1.5" (Salisbury) narrower than stud axles, and the tyres are at much the same position in the arch, so the brake drum face is 3/4" (for a Salisbury wire wheel) closer to the middle of the car than a Salisbury stud axle. The back of the wheel hub is 13mm out from the brake drum, the middle of the inner taper is 14mm further out from that, i.e. 27mm out from the brake drum. This puts the centre of the wire wheel inline with the face of the brake drum, and not 27mm behind it as with the Rostyle, so it either could be considered to have zero offset using the same axle reference point i.e. the drum face) or 27mm positive offset if using the mounting face i.e. mid-way on the inner taper. The upshot is the track with a 4.5J wire wheel is actually 20mm wider than a 5J Rostyle, but because of the narrower width the outer rim is only 4mm closer to the arch. See this drawing showing other wheel dimensions.

Update summer 2007. Had the other wheel with three broken spokes completely replaced with polished stainless after the May Tamar Valley and June New Forest runs. These were more highly polished than the ones I had seen earlier, the only real difference being a slight grey tinge to the stainless whereas the chrome have a slight blue tinge. We shall see how they go. As far as the other wheels go I shall get a handful of stainless spokes with a view to replacing them myself as and when they break. Getting the tyre bead off the rim will be interesting, the tyre shouldn't need complete removal as the broken spokes have always been in the outer edge of the rim, not in the well. I have a couple of ideas, including using the weight of the V8!

Update May 2008. Following the rash of breakages found early last year I only had one broken spoke at the end of the season, and so far about 700 miles this year with no more. Quite why that should be with so many last year I don't know, but I've decided to proceed with the experiment of replacing them myself.

As mentioned I found that by jacking up the V8, laying the wire-wheel down under it (on some thick padding to protect the rim edge on the back of the wheel), and jacking the V8 tyre down on the sidewall of the wire-wheel tyre, the bead came free easily.
With the bead off the rim very little pressure on the sidewall presses it down far enough to get at the nipples of the short spokes (these are the only ones that break in my experience), cut the protective tape and remove the nipple complete with broken spoke through the rim. Cutting the protective tape over the short spokes doesn't matter as the tyre bead covers them and stops the tube coming into contact with any sharp edges.
I took a good spoke as well as a broken one to Central Wheel Components at Coleshill in Warwickshire to have 10 made up at £1.50 each, and they also had a suitable spanner. This has two jaws capable of fitting six different sizes of nipple, the largest one had to be ground out very slightly to fit the MGB nipples, and the edges ground down slightly to get enough 'swing' on it as the nipples only have four flats.
Picked up the new spokes a few days later. Not quite as shiny as the sample I had from them originally, but a few minutes with some Solvol Autosol soon cured that for the one spoke I needed to fit right now.
Inserting the new spoke you soon discover that one of the long spokes has to be undone and swung out of the way, as when the thicker butt of the new spoke reaches the hole in the hub it fouls and can't be pushed in any further. Be careful not to damage the protective tape over the nipples in the well of the rim or it is likely to cause subsequent punctures.
With the adjacent long spoke out of the way you then find that the new spoke can't be pushed directly to its nipple waiting in the rim as it fouls the short spoke on the other side! However inserting the new spoke nearly all the way on the wrong side of the adjacent short spoke, then swinging it past it, is the way to go.
Then it's just a matter of screwing the nipples onto the two spokes and tensioning them. I just tightened until they 'pinged' at about the same pitch as the spokes around them.
One problem I found with the stainless nipples is that they are quite a bit softer than the chrome and distorted as I tightened them. This made the jaws of the spanner loose on the one pair of flats, but the other pair of flats had bulged out so I couldn't get the spanner on them to tighten it any further. As the thread seems to be identical and the chrome nipples are in good condition I reused that instead of the new stainless. A different design of spoke spanner that fits round three or three and a bit sides of the nipple would probably be better, but I've never seen one. I've never seen what my wheel repairer uses as he keeps his trade secrets by making me wait outside while he does them.

Finally I tested the wheel for roundness and run-out by spinning it on a front hub, it had no more than 1mm of run-out and no out of roundness I could detect so that was good enough for me. I ran at various speeds up to 70mph (OK, a bit over) and no detectable wobble or vibration anywhere. Time will tell if this repair holds up, at under an hour and £1.50 per spoke it is certainly cheaper and easier than driving to a wheel place and getting the tyre taken off the wheel, then driving to the wheel place and waiting while they change the spoke(s), then driving back to the tyre place to have the tyre refitted, plus cost at each place.

Update May/June 2009. After the May Yorvik run found one spoke broken, which is the first in twelve months or so, so replaced that prior to the New Forest. On the return from that plus a few extra days in Dorset one more broken in 640 miles, so no big deal, but this is in the wheel that I had completely replaced with stainless just two years ago, which rather gives the lie to the claim that it is the chroming process that makes those spokes brittle, as I went several years before I got my first chromed failure.

Last but not least, the rebuilder I have used is Ray Phillips & Son at Unit 3, Seven Stars Road, Oldbury, West Midlands, 0121 544 9060 just a couple of minutes from J2 of the M5. On the left (as you look at this map) just about where the green arrow is on this map i.e. between the canal bridge and the A457, even though that is shown as Park Lane and not Seven Stars Road. They've always replaced mine (individual spokes) while I wait and are very reasonable in price compared to the one or two other rebuilders I have found much further away. But ring before you start out to make sure they are there, don't just turn up (even if arranged in advance) as they come and go as they please.

Cleaning: The best results with the least damage take the longest - 4-5 hours for the four wheels. They get the following full treatment a couple of times a year, the rest of the time they have to make do with a hose brush and cold water on the car. The full treatment is time-consuming and painstaking, but the results are absolutely superb against the Black Tulip paintwork in the sun. This picture was taken in May 2008, the wheels are now 19 years old and have done around 45k miles. When I was doing them prior to the Broadlands Heritage Run two neighbours stopped to admire them, the one saying they looked like diamonds sparkling in the sun as she walked past the end of the drive.

Off the car, hose-brush and cold water in a bucket to get rid of the dirt from the bits you can reach front and rear, MkI digit in a chamois leather to clean and dry off the bits that the brush doesn't reach (maybe I should try Heineken ...). Spray-on wax polish (same as for the body and all other chrome - Turtle Wax) to the back and front of the rims and spokes, hub from the front only, but not too thickly or it takes ages to get rid of. MkI digit in a stockinette cloth to apply polish to all parts of rim, hub and spokes, rubbing at any stuck-on black bits. MkI digit in a clean duster to polish off all parts of rim, hub and spokes. BT miniature 'bottle brush' (about 1/4" in diameter) wrapped in several turns of the corner of the duster to poke in the small 'triangles' where two spokes join the rim and hub (Michael Beswick reports that disposable eyelash mascara brushes work well as an alternative, another dodgy request at the Boot's counter to go with the hypodermic syringe bodies for injecting hydraulic fluid to dampers and grease to bearings!).

The fronts can take longer, brake dust that has got wet then baked on can be difficult to shift, but it does vary according to disc pad manufacturer I have found. I did buy the 'wire-wheel brush' advertised in certain places when I first had the wheels but I think the bristles are too harsh for chrome. I did try wrapping that in a duster for a while to clean the spokes but find my digits are more effective. I only ever use a so-called chrome cleaner (actually an abrasive) like Solvol Autosol to shift baked-on brake dust from the spokes if I have been unable to shift it with wax polish, stockinette and digit.

Can make the fingers a little sore after four wheels, but you get lovely shiny nails...

Dunlop vs Dayton Added January 2010: There are usually quite a lot of disparaging remarks about Dunlop, not least because they are made in India. I've had mine 20 years/50k miles and apart from one or two rust specks on a couple of hubs which appeared some time ago but don't seem to be getting any worse mine still polish up beautifully, as I say above. I do spray them with WD40 at the start of winter, which I think help keeps the damp off them when garaged, I don't use the car in winter unless dry and salt-free. The usual recommendation is to go for Dayton, which I'd always imagined would be quite a bit dearer. However this British Wire Wheel (USA) price list shows that Dayton standard chrome wires are less than 10% dearer than Dunlop. Dayton's balancing instructions state that from 1990 their wheels have a fully machined hub that allows them to be mounted correctly on tyre balancing machines using standard cones. Before that, and quite possibly still the case for Dunlops, they have to be mounted using special inner and outer cones of the correct angles, which very few if any conventional tyre places have, or they will never balance correctly. On that basis alone it would be worth paying the extra for the Daytons. On the question of spokes British Wire Wheel states that both types have stainless, although Dunlops are chrome-plated. That certainly isn't the case with my 20 year-old Dunlops, which are ferrous. British Wire Wheel also says that if you want a high polish on their Dayton spokes it's another $40 per wheel, which is quite a lot! You would need to see just how dull the standard finish is before splashing out on that, I suggest, except for an all-out show car. There is also some confusion over truing. Dayton say theirs don't need truing. Victoria Britsh say their Dunlops have been shipped 8000 miles and although trued in the factory will need truing before fitting, and again 'after a period of time'. Moss US says to check for loose spokes and run-out when new, and again after a couple of hundred miles, truing is only mentioned in respect of 'old' wheels. No mention in Moss Europe I have found, both reputedly supply Dunlop wheels. The bottom line is that I've never had my wheels trued - when new or since, and when I was having spokes replaced by Phillips I know they checked for concentricity and run-out afterwards and never found any problems. And Dayton don't seem to be available in the UK anway. There are a number of specialist UK manufacturers/suppliers/repairers which seem aimed at vintage/veteran/exotica (P J Hallewell, SAS, Borrani, Richards) but only one specifically mentioning MGB wheels - MWS. They don't say where their wheels are made, but their logo looks very like one on the inside of my Dunlops from memory, and several sites indicate MWS and Dunlop are one and the same.