Squizz

Stratman,

Same as you, I have the MY01 alloys and 215/45/17 tyres on an MY99. My tyres are Goodyear Eagle F1's though. I'm running 32psi all round. (Coz I'm lazy, and never could tell the difference).

There is a possibility that tyre deflection is causing the tyres to rub against the struts on the rear of the car. Take the wheels off and check for signs of rubbing on the strut and tyre.

I seem to remember there was only a problem with 45 profile tyres if the car was lowered from standard. (But this would only be the case if the strut length was different!). Clearance is VERY tight.

I'm strapped for cash, so will check mine out regularly and when I do need new tyres, I will probably go for 215/40/17s.

I have noticed a difference in the handling, but nothing dramatic. But along the same lines you mention...

[Edited by Squizz - 7/1/2002 1:24:31 PM]

stratman

I just have fitted a set of brand new 17"alloys to my MY99 turbo, with 215x45x17 Bidgestone Potenzas RE011 which came off a new shape Impreza turbo.

They look great but I am now experiencing what feels like an under-damped rebounding effect on bumpy or undulating surfaces, almost feels like the shockers are goosed but that cant be it cos the car has only done 23k miles. The car isnt bouncing just the wheels.

I have also now realised that the profile should be 215x40 therefore the rolling diameter is 24mm greater than it should be. Could this be the cause of the problem?

I did expect a harder ride with the 17's but not this bouncing wheel effect. Has anyone else experienced this and is there a remedy?

The Zohan

What tyre pressures are you running?

russell hayward

As Paul says, check the pressure, 33f 30 r or 32 r should do the trick.

According to http://www.miata.net/garage/tirecalc.html
your speedo will under-read by 1.5% with the 215/45 profile

stratman

Thanks for your comments.

I am presently running 33f/31r.

I have tried various pressure permutations but to no avail



[Edited by stratman - 6/23/2002 10:06:57 AM]

The Zohan

Stumped i'm afraid

rovo

The only other thing I can think of at the moment is that your new 17" wheels are relatively heavy.

SDB

i think rovo is onto it..

it sounds like you are experiencing the difference from the change in sprung / un-spung weight ratio.

If the wheels genuinely are bouncing but not the car, then it is indeed that is underdamped, but if the unsprung weight (remember there is less tyre than there was, so it's not as simple as saying the wheels are heavier or lighter) has increased the body of the car will move more than it did before.

So.. options are...

unsprung weight up, which means that the body of the car is moving more than it did (although it may feel like only the wheels)...

or

unsprung weight down and somehow your dampers are not coping with it.

I would bank on the first option though.

All the best

Simon

TonyBurns

iTrader: (3)

Your running the wrong size tyre for your car!
on 17's you should either be running 205/45/17 or 215/40/17, as your running 215/45/17 you will have speedo inaccuracies and probably not getting the best handling out of your car.
Would suggest that you change your tyre size to one of the 2 above!

Tony

stratman

My dealer ( Robinsons ) lent me the original 16" wheels for a week so I could make comparisons.

The ride was much improve with the 16" back on and as expected acceleration improved due to correct rolling diameter.

I weighed both wheels and to my surprise they were both 18Kg

So the problem is not the unsprung weight. Could it be the weight acting at a greater tyre diameter ? I wonder. Or is it just a symptom of the particular tyre ie RE 011?

Dealer has offered to swap tyres on 17s for 40 profiles but is this going to cure the problem.

Lots of ???

I suppose I should just keep the 16" wheels on, but the 17" look better



[Edited by stratman - 6/29/2002 8:39:54 AM]

[Edited by stratman - 6/29/2002 8:42:39 AM]

Brun

If the dealer offered to swap the tyres for 40's do it. Even if it doesn't sort the problem, you will have the correct rolling radius. I assume you mean they will swap em for free?

stratman

No...I would have to pay the difeerence between the part worn tyres and the new ones.

And I would have to return the the 16s.

Hoppy

I think it's tyres. Lower profile, harder ride, and different tyres, new or old, always feel different. Not necessarily worse, just different.

I take it your old wheels are OEM, ie 53mm off-set? But if they are 48 or something your new 55mm off-sets will feel strange.

Whatever, your tyres are defo sh1te so get some Toyo T1-S or Goodyear F1 rubber on there.

Cheers,

Richard.

rovo

Similar to what Simon de Banke wrote, the vertical spring stiffness of the tyre also is part of the equation of how the tyre and car body are damped. Could be that your 17" combination is sensitive to it.