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Hi all,

I have purchased some 15" alloy wheels previously fitted to an M*T* shod with 205/50R15 tyres . My car now seems to steer itself on non perfect surfaces. I will be driving along okay then suddenly the car seems to veer slightly off course needing a determined correction to bring it back on line. this does not happen on good smooth surfaces but is non the less very disconcerting when it does. Is this the start of wear in the rack, track rod ends or something else which only manifests itself at present on bad surfaces. Any thoughts?

Cheers

Phil

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You could try swapping wheels side to side, and checking that either of the front brakes, or to a lesser extent the rears are not sticking slightly. But before this, check that the pressures are even on both sides. Are the tyre types the same on both sides? The road surfaces are now so bad that they can cause a problem despite the condition of the car.

 

It may be suspension/ steering wear but less likely than above.

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Proper wheel alignment check for starters, and check all tyres for condition and pressure.

 

Inspect the suspension front and rear - the local MoT man and his shaker plates might be a good starting point.

 

One prime suspect for this sort of behaviour might be the rear trailing arm mountings, for example, the problem isn't necessarily at the front end.

 

Cheers

 

Alec

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Many low profile tyres on wide tyres will "track" on road surfaces even a little less than perfect, causing almost constant correction to be required.

Think about it, the tyre patch is considerably larger on the 15" wheels and with a wider tyre magnifying any surface imperfections the steering input back to you is considerable. Of course check all the steering items you mention but I'd bet it's the tyre and wheel equipment.

 

Mick Richards

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OK Mick,

 

without having experienced any steering problems thus far . . . . which must be 5 or 6 years now . . . . .

 

I did once, many years ago, experience a similar steering issue to that described with our road 7V8, 205/60x13 on 7" Weller Steels, which turned out to be the left trailing arm mount coming adrift, and the right wasn't far behind.

 

Need I add we discovered that only after checking everything at the front without success, having first rebalanced wheels and checked alignment . . . . ..

 

Cheers

 

Alec

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Hi Alec,

 

Certainly theTR7 rear trailing arm suspension system which is shared with the Dolomite is "orrible" . The trailing arm bushes when they go soft and under torque from the axle/acceleration/braking/cornering forces squirm all over the place with the car taking off in different attitudes under different circumstances. That's why I changed the rear axle location on my race car and changed it from trailing arm to leading arm with rose bushes.

As you say the trailing arm mounts are suspended on the rear of cockpit firewall which isn't really man enough for hard work, it was always our first place to check at the end of the season and weld up any cracks in the firewall. However Phil describes his handling as "I will be driving along okay then suddenly the car seems to veer slightly off course needing a determined correction to bring it back on line. this does not happen on good smooth surfaces but is non the less very disconcerting when it does." Normally the trailing arm bushes need an input of torque as described above to deform them which then cause understeer/oversteer hence that doesn't to me tie in with his description. Rather a car "tracking" problem with the tyres picking up surface irregularities and "tramlining" until over the surface change.

 

Mick Richards

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Don't discount the tyres themselves as a possible source of the problem. I once had a new E class Mercedes that suffered in the way described. Once I ditched the Continental tyres for Michelin Pilots the problem went away.

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WOW,

What a lot of info to digest. I can discount rear trailing arm bushes as I had them replaced along with front and rear shock absorbers together with anti roll bar bushes. I can't swap the front wheels as they have directional tyres on, but could swap front to back. I was running 28 psi on the front and 30 psi on the rear. would increasing the front pressures to 30 psi make a difference?

The tyres are the same across the axle Marshall Matrac FX 205/50R15 86V . I have never used these before so maybe it was a bad tyre choice that has caused this wandering. Just a bit of information this problem occurs on a steady throttle not under acceleration or braking.

Thanks to all who took the time and trouble to reply, I am sure the answer is in there !

Cheers

Phil

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I run with MGF wheels on my 7 with (until a couple of weeks ago) continental 205 on the rear and 185 on the front for about 35k miles. Tyre pressures usually 30/31 rear & 28ish front and no problems with tramlining on any surfaces. Its just been swapped to 185 continentals all round and after a 2000 mile bash around Europe including alpine passes and (legal) speeds >100mph no steering problems with 30psi front and rear.

 

Hope that helps

Edited by HowardB
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Hi Phil.

If your tyres are unidirectional, they can be the root cause of this as they wear/load up with camber etc.

A quick test is to run down a known/repeatable 'problem road', noting the problem.

 

Set all pressures accurately.

Switch the back tyres left to right so they are going the 'wrong' way (this is OK for a test, not for permanent use)

re drive the road, same conditions, noting results.

refit rears as original sides, and reverse fronts l-r.

try road test again.

 

this identifies/rules out tyres.

 

I have had 2 cars now where 'aging' unidirectional tyres on the back steer the car like a dodgy supermarket trolley!!

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Hi Phil,

 

I think you might well have answered your own question, as in tyre choice . . . . .

 

A tyre that works well on a modern car with front wheel drive isn't necessarily going to work as well on any rear wheel drive car, let alone a classic with a 40 year old suspension design.

 

Cheers

 

Alec

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I'll go with the tyres as suggested previously.

Just resolved an identical problem (also with MG wheel/tyre combo) where the car would not drive straight over about 60mph. Fortunately had different makes of tyre back to front. Swapped wheels front to rear and problem completely disappeared. This was after trying various spacers, wheel alignment, pressures, with no effect.

Jerry

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  • 3 weeks later...

We have all been spoilt by our modern cars with their easy road manners. Anyone else on here old enough to remember crossply tyres and how badly they used to follow any road markings? Certainly kept you awake trying to steer in a straight line!

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