Tyre wear analysis needed Toyo R888s on our race car

[TWSTD]

I am getting some odd tyre wear in the front of our EVO-powered charade race car. See the images below.

These R888s have worn very quickly and there is an odd wear patch in the centre of the tyre. Its easier to see in the flesh, but you can feel the dip in the centre when you run your hand across the width of the tyre. Before you ask, no they have not been run over-inflated. We run about 28-9psi hot. The car has suffered some bad understeer - im wondering if thats to blame? Any thoughts / suggestions on this wear?

http://www.drivenperformance.co.nz/imag ... ft2sml.jpg
http://www.drivenperformance.co.nz/imag ... ht2sml.jpg
http://www.drivenperformance.co.nz/imag ... ht1sml.jpg
http://www.drivenperformance.co.nz/imag ... ht3sml.jpg

[85AW20v]

I would still be thinking over-inflation when hot. It could be that the pressures are too low to start with, which means the tyres are flexing more, heating the tyre and resulting in over-pressure. A pound or two either way can make a big difference to the wear characteristics.

It doesn't look like you're using the edges of the tyres at all so to me, something isn't right with your pressures. I can't remember if it's the Honda Cup guys or RX7 class that run Toyo's but they would be the guys to talk to.

[evil_si]

You using air or nitrgen in those?
Definately looks like overinflation when hot

[TWSTD]

Using air. And i know does look like overinflation but IIRC Toyo suggested 30-32 psi and we are running well below that.

[evil_si]

Im not a tyre wear expert but certainly looks like over inflation, what are the rears doing?
what does pete think?
Id be Trying nitrogen in the next tyres to rule out the heat effecting the pressure

[strx7]

what pressure are they cold to achieve 28-29 hot?

[mjrstar]

What width rim? Could be a tad skinney for the rubber?

888's tend to be destroyed if you continue to beat down on them once they start go off. I have seen someone destroy a near new front left at pukekohe in about 12 laps...Whereas an 02 or 03G Dunlop seems to hold up better to the punishment.

[Makaveli]

Tyre pressure normally goes up by about 5 to 6psi when they get hot if I am correct. Also some racing tyres are only designed for a few laps and that's it. They are not the same as road tyres.

[TWSTD]

Its a 15x7 rim so yes slightly less than optimum width for a 225 tyre. We do see 4-5psi increase when hot, so often start about 24psi on a warm day.

[fxgt race]

I was wearing out tyres in two meetings, Why yes understeer, my car suffered badly from this , I now Have tuned the suspension to a tee and it is so gentle on the tyres now. One of the biggest things is castor, im up around 6 to 7 degs and with the added adjustible swaybar its handling sweet.

My tyres would wear the same as you a suggesting with understeer.

You say its evo powered, what is the weight difference , car setup is the answer, took me 4 years to get it wright.

[mjrstar]

Its a 15x7 rim for a 225 tyre..

I don't like the sound of this, i run my 205 race rubber on a 8 inch rim...

[strx7]

Its a 15x7 rim so yes slightly less than optimum width for a 225 tyre. We do see 4-5psi increase when hot, so often start about 24psi on a warm day.

i would imagine its weight balance and charasteristics are similar to the ae104. i used to start with 21psi in the fronts to see 29-30psi after 5 laps. and that was with nitrogen in them.
I think its a combination of things.
a) rim width not ideal for the tyre
b) tyre pressure
c) understeer/torque steer - that is probably the biggest factor

i had 205 R881s on 15x7's on the ae104 and ate them just like you have eaten your fronts.

[DVSMOTORSPORT]

Do you take tyre temps during the day? Tyre temps are an excellent way of diagnosing whats going on.

As a reference, in a 600kg RWD car I commonly started at around 16psi and went from there. Taking tyre temps and adjusting pressures straight off the track.

[TWSTD]

I did take tyre temps at the last 2 testing days yes. Will have to dig those stats out.

I do still need to work on eliminating understeer though. More -ve camber up front has helped. I need to get some advice on sway bars etc - we dont have one up front yet. Im wondering if we need one and slightly softer springs?

[pc]

What suspension settings are you running toe, camber, caster front & rear?

Rim width looks to be 1 inch too small.

[RomanV]

I doubt rim width is the issue, given that the R888 documents state that the 225/50/15 is designed for / fit for use on 6, 7, and 8 inch wide rims.

edit:

Unless it's a 225/45/15, in which case it's 7" minimum, either of which is fine obviously.

[matt dunn]

I doubt rim width is the issue, given that the R888 documents state that the 225/50/15 is designed for / fit for use on 6, 7, and 8 inch wide rims.

Promotional paperwork designed to sell tyres.

A 225 on a 6 inch rim will fit yet, work properly no.
I used to run 205's on a 6 inch rim and they were borderline

[TWSTD]

Front: We started with about 1 1/4 degrees -ve camber at the front and have worked up to 3 degrees to try an eliminate the understeer. Zero toe and 2 3/4 degrees caster.

Rear: 2 degrees -ve camber and i think zero toe as well.

[CAMB01]

The first time i ran my R888 at the track i was running too high pressures and understeering through every corner. Cold pressures were 24psi, and was getting up to 32 - 34 psi hot. The guy i bought them off said 29psi would be the absolute maximum hot pressure. Havnt been back to the track with those tyres yet to try a lower pressure. I run 205/50/15 on a 6.5" rim. Cutting it fine on those rims.

Biggest improvement i found was running 3.2 degrees negative camber on the front with 1.2mm toe out each side. This improved turn in substantially, and reduced understeer. On the rear i was running 2 degrees of negative camber with a zero toe setting. But as my car is alot heavier than yours not sure it would help as it may hinder it more.

Just food for thought.

[pc]

I figure that a 205 tyre on a 7" rim is about right, so you probably want a 8" rim. If still wearing in the middle after using wider rims, just keep lowering tyre pressures until it stops.

The understeer wont be as bad once the tyre wear is fixed, then look at a little bit of toe out in the front.