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Abarth 500 tire wear problem

Motorsport Wheel Alignment Fundamentals

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Hi!

I got problem with excessive side of tires wear.

It's whether I use slick or road tires.

I got BC coilovers. Made -3 degrees camber and i've put polyurethane control arm bushes - and it still occures.

I tried several tire pressure settings...

I got my wheel aligment (toe) set to toe in.

Should I set it to "toe out"?

How to set caster in this exact car? As I understood - If I add caster I'll add dynamic camber. But how to do it in Abarth 500? :)

Hi Mike,

If you can give me a little bit of background I'm happy to help out.

Can you please upload some photos of the tyres, what sort of competition and driving you're doing and what tyre pressures you're tried?

Thanks,

Tim

It would also help if you could give some information on the actual vehicle - the early Abarth 500 is a VERY much different vehicle from the latest version.

It's 2013 Abarth500 US version.Now it's -3' camber, Polyurethane control arm bushes, BC Racing coilovers, 205/40/17 Toyo Proxes TR1, and Michelin 20/61-17.

On Toyo i tried (all pressure was measured on warmed up tires) 1.8bar (26.1psi) , 2.0bar (29psi), even 2.5 bar ( 36 psi). On Michelin I only tried 1.8 -2.0 bar (26-29psi).

I usually go on trackdays. It occurs MOSTLY (but not only) on fast tracks with fast and long turns.

Here is link to a video from track. (before polyurethane bushings and -3' camber) :)

https://youtu.be/cD_IgTwxNa8

Attached Files

Hi Mike,

This is a lot more extreme than I was expecting! 😅 When you said side wear, I was thinking you were talking about still being on the tread, rather than the sidewall!

My first thoughts after seeing your pictures and video (great angle of the video by the way) is that either tyre pressure, rim width, body roll or camber settings are a long way out of the window.

It's a little hard to tell from this angle how much the actual chassis is rolling. It loos to me that when the tyre is really turning to the left hard, that you are loosing a lot of front right camber, but it's hard to be sure from this angle. This could be from compliance in the suspension (even polyurethane bushes flex a lot), too much body roll. As a result you may need to look at running more static camber, or possibly more caster to get more dynamic negative camber.

A couple more questions for you, more specific on the Michelin as this is a tyre I'm familiar with:

-Can you please send me pictures of the Michelin tyre wear?

-I assume this is an S9M compound and construction?

-What rim width do you run?

When you say these are the "hot" pressures. I wonder whether a lot of this wear could be happening when the tyre is cold, before it comes up to pressure- unless you are using tyre blankets or an oven, so they are hot when you go on track?

OK, Tim is going to be of most help, but some observations.

At the start there's a lot of rubber build up to the inner edges of the blocks, with badly torn outer edges, this would suggest the tread is being overheated and dragged to the inner side, usually as a result of excessive understeer, which is re-inforced by the wear pattern.

As Tim also noted, it appears you're using a lot of 'stretch' with the rim being too wide for the tyre used, or it's under tyred. This forces the tyre sideawlls to be in greater tension and will cause the tread to distort and 'pull under' under lateral loadings, actually riding up on the sidewall.

Some vehicles will need to be 'toed in', some 'toed out', the biggest factors ares the scrub radius and the suspension/steering deflection - you've apparently increased the former and reduced the latter, so I would be expecting lass toe in, or even toe out - either way, toe in will increase the tendency to load the outer edges of the tyres.

I would also suspect the vehicle has been lowered at some point, this may further compromise the OEM steering geometry which may be biased towards understeer in roll. More to the point, the roll centre will be compromised and this will lead to a reduction in roll resistance and increase in chassis roll and camber gain.

A further factor may be simple over-driving, a little slower on the entry will reduce the loadings and potentially be faster overall. If you can increase the rear roll resistance (assuming it isn't already lifting the inner rear) you may find some benefit. It may seem a little counter intuitive, but stiffening up the front to reduce roll may also help, the reduction in camber cain in roll may give better gains than the loss fron the greater tyre load.

You don't mention the rear of the car, especially the tyre wear patterns - you may find lower pressures there allow a little more tyre deflection and a reduction in understeer.

I couldn't find that specific tyre size for that version of the tyre, but comparing other Toyo tyres would suggest the spec'/optimum is a 7-7.5" rim, an 8" rim would be on the wide side, and anything wider would be looking for a problem - exactly what do you have them mounted on?

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