Wheel Maladies.....

[Ricky]

Hi all,

This sort of follows on from my previous thread, which I have discovered since is the wheel bearing (phew, still cost me £25 for the part though!). While we checked this, we thought it would be a good time to put on the set of cross spoke alloys (5.5J) that I had a new tyre put on during the week. That's where the problems started. They looked great, but now the car insists on drifting left when I let go of the wheel, and the steering feels a bit "funny". I took it for the tracking to be done at our local National tyre and exhaust centre, and they informed me the only way I could fix it was to put the old 13 inch wheels back on because the gearing is all wrong for the 15 inch wheels.....?

Does this sound plausible? Or is he talking absolute bo :censored: :censored: ocks (which I suspect he is)?

[Simon]

The wider wheels may make the steering feel a little odd especially reacting to road camber a little more than the standard issue wheels, but surely the handling will be better. The tyre fitter is presumably talking out of the back of his head because gearing has no relation to wheel alignment. Sure, the gearing will be altered because of the number of revolutions per mile that the alloy wheels do will be a little different to the number for the steel wheels but this will make the speedo over-read a little (well it does on my cross-spoked (6J) bog standard 1.6 Maestro anyway-I'm doing 27 true MPH when the speedo reads 30). Maestro's tracking is parallell, in other words 0 degrees, and that doesn't matter whether its got skinny standard wheels or chunky fat alloys. They made a special edition 1.6 Maestro called an Advantage, basic running gear, admittedly with MG suspension with the cross spoked alloys.

I've fitted brand new front suspension on the front and rear. When I'd finished I had to get the wheel alignment checked since I'd fitted two new steering ball joints. It was a mile out, but when the tyre fitter adjusted the tracking the car now runs (and pulls up) dead straight, "hands off".

[Ricky]

As I suspected, I'll have to take it elsewhere because the tyre that was originally on the passenger side front has worn quite a lot on the inside, but hopefully it can wait until the MOT in three weeks or so, unlike the wheel bearing which needs doing pretty soon, I'm just hoping it can make it through this week so that it can be done next weekend.....

Hopefully then it will go and stop straight, which it doesnt at the moment, it doesn't pull but as soon as I let go it seems to want to meet the kerb! It does seem to want to follow camber a bit more, which I dont mind, it is just the annoynace that I have to hold it in a straight line, rather than let it do it itself and just guide it there (you know what I mean!)

Won't be going back to National, however, they tried to blind the wrong person with science this time, even if the tracking service is cheap.....!

Ricky.

[G51 NAV]

Sure, the gearing will be altered because of the number of revolutions per mile that the alloy wheels do will be a little different to the number for the steel wheels but this will make the speedo over-read a little (well it does on my cross-spoked (6J) bog standard 1.6 Maestro anyway-I'm doing 27 true MPH when the speedo reads 30)
Surely a wheel and tyre-combination with a greater circumference than the original will cause a speedometer to under-read, as one revolution of the wheel will take the car fractionally further than it did on the old wheel and tyre. For example, at any given speed the wheels of a big lorry are turning round much slower than those of a Mini.

[mgdavid]

Have you fitted a pair of wheels and matching brand new tyres, as it wasn't clear from your first post. Are you sure all the wheels are the same and you haven't got a mix of Maestro 5.5" and Monty 6" ? If new tyres, are they assymetric, and are they fitted the correct way round on the rims?

[e692wtt]

Try swapping the tyres front to rear, or from left to right. There's a problem called Conicity where the bands inside the affected tyre aren't quite centralised as they should be. This can cause exactly the effect you are experiencing if the faulty tyre is able to affect the steering (ie on most cars if it is on the front axle) by trying to roll in a large circle and not a straight line, causing the car to pull to one side.

It's a minor manufacturing defect, but can cause major problems like this. It can also occur in tyres of any price and brand. If the defective tyre is on the front axle, then moving it to the rear axle should stop the tyre affecting the handling of the car.

It's also rare, but you can try this repair for free. :)


Re the change in gearing, fitting the larger wheels will (as said above) cause the engine to run at slightly lower revs for the same road speed in any given gear. Better for cruising but on a smaller engine the acceleration will be marginally reduced. Go for it!!! :)

[D87 SMW]

Surely a wheel and tyre-combination with a greater circumference than the original will cause a speedometer to under-read, as one revolution of the wheel will take the car fractionally further than it did on the old wheel and tyre. For example, at any given speed the wheels of a big lorry are turning round much slower than those of a Mini.

The speedo's are inaccurate in all MM's, looking in a magazine of road tests I have, the speedo's seem to over-read quite a lot.

For example, a true mph. of 50 shows as 55 mph. on the clocks, and 60 mph. - 66 mph. respectively.

So to work this one out, imagine two cars both doing a true speed of 50 mph. One being say a 1.6 with standard 13" wheels, and another 1.6 with 15" wheels.

The car with 13" wheels will read 55 mph. on the speedo, as the wheels would be turning fairly fast to achieve the speed of 50 mph.

The car with 15" wheels will read slightly less, as the wheels would not have to turn as fast as the smaller ones to achieve the speed of 50 mph.

Hope this is clear enough. :worried: :laugh: :rolleyes:

[skipweasel]

The speedo's are inaccurate in all MM's, looking in a magazine of road tests I have, the speedo's seem to over-read quite a lot.

For example, a true mph. of 50 shows as 55 mph. on the clocks, and 60 mph. - 66 mph. respectively.

Certainly when I'm doing an indicated 90 in my TD estate people are still overtaking me!

[E_T_V]

Re speedos overreading and wheel size changes, remember that the rolling radius, i.e the circumbference of the tyre is what alters the speedo. If you fit 15 inch wheels the tyres are a lower aspect ratio to keep the rolling radiuus nominally the same..

The problem comes to when you try to fit my alloys on my van and the speedo will be 20% out :0 20% under infact!

Try swapping the tyres about as suggested but you might find it is something like a worn bush or more likely that dodgy wheel bearing you sare talking about. Mine does exactly the same and I reckon it will be worn wishbone bushes and knackered CV joints... At 201k miles I can't really blame it for wandering a little!

[Ricky]

Crikey, so much to reply to!!

There was only one new tyre, and it currently is sitting on the back of the car, the front left tyre is actually by far the worst tyre on the car, it also contains a nail, so the theory is that I wear the last of it out and then need a new tyre in a couple of weeks or so, which brings us nicely to MOT time!! Concern has also been expressed about the wheel bearing affecting it at this end too, I think really I'll just have to get it done and see how it is afterwards! It didnt seem too bad driving it to work and back today, it wasn't unbearable but it will need doing.....! Following camber doesn't seem an accurate enough description! As for the 5.5/6J thing, I am sure I checked them all (I have 9 of them!), and I'm sure theyre all 5.5J (they were fairly cheap, too!)

I have just noticed you all saying about speedo gearing: I don't think this is what he was referring to, I think he was talking about steering rack gearing, hence why i'm pretty sure he was using his posterior to communicate!

Apologies for any spelling mistakes, I'm on the third (!!) computer, and it has by far the oldest and worst keyboard.....!

Thanks,

Ricky.

[Simon]

Sure, the gearing will be altered because of the number of revolutions per mile that the alloy wheels do will be a little different to the number for the steel wheels but this will make the speedo over-read a little (well it does on my cross-spoked (6J) bog standard 1.6 Maestro anyway-I'm doing 27 true MPH when the speedo reads 30).

...Granted I mistakenly typed "Wheels". My mistake. One would be foolish to attempt to drive on wheels that are not shod with tyres. Mine are, as are most peoples, so let's have a look at some tyre sizes to clarify.

Assume Maestro 1.3LX, steel wheels with 155 x 13 Tyres. (Rolling radius: 289.1mm; circumference: 1816.7mm). Now, if you assume cross spoked alloy wheels, 5.5J x 15 (NAM9191 MMV) shod with the manufacturer's recommended 185/55 x 15 tyres (Rolling radius: 292.25mm; circumference:1836.26mm) difference in circumference is +19.79mm, that's a percentage of +1.09% so when the speedo reads 70 MPH the true speed is 70.6 MPH and I'm as wrong as wrong can be and I should therefore be banned from posting on technical forums. (Hangs head in shame, pass the gun :giveup: ).

...However in my case I quoted earlier (A Maestro 1600 based on personal experience) let's have a look at the same story. Replace standard wheels shod with standard 165 x 13 sized tyres (Rolling radius:297.1mm; circumference:1866.73mm) with 6J x 15 cross spoked alloy wheels (NAM9073 MMP) shod, naughtily enough, with 195/50 x 15 (Easier to get hold of/more popular size/cheaper, rolling radius: 288mm; circumference: 1809.56mm) difference in circumference is this time -57.17mm, that's a percentage of -3.06% so in theory when the speedo reads 70MPH I should be doing a true speed of 67.86MPH therefore the speedo under-reads. My poor 16 year old speedo tells more lies than I do, and in actual fact it underreads more than this, for example when my speedo says 30MPH I'm doing 27MPH (unless those Police road signs are liars too), and I'm sure the error is more at 70MPH.

All that because I typed wheels and not tyres, but at least now you know how things can vary a bit. Use plenty of coppaslip to prevent alloys corroding to hubs.