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Setup tips - How to improve tire contact and minimeze Uneven tire wear

Motorsport Wheel Alignment Fundamentals

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Hello

I have a M3 F80 and would like some tips in what can improve my alignment set up and tire pressure to get better tire contact patch and consequently minimeze uneven tire wear in my track days events.

Car Setup is almost stock except :

> front Millway camber plates and Fall-Line Ajustable rear toe link kit

> square slick tires Pirelli DMA 305/660 r18 , with front 10 inch wheels and rear 11 inch wheels.

Alingment is maxed negative camber in front (-3,44 Left and -3,51 Rigth) and rear maxed negative camber ( -2,1 Left and -2,11 Rigth ) , toe -1.0mm front left and rigt and rear toe +0,6mm left and +0,8mm rigth.

Hot tire pressure 32 psi

My review about car handling , it has very low understeer but i have to be very smooth in gas pedal to control oversteer.

The tire wear is excessive in the 4 tires outer side , what you guess that i need to change in the alignment setup or tire pressure to maximize tire contact path and consequently be able to be fast in corner ?

Mostly track days that i run has more left turn like Interlagos Speedway ( Brazil) , running more pressure in the rigth tires is a better solution ?

Thank you

Attached Files

Wow, that's some uneven wear!

You don't seem to have mentioned any spring and/or anti-roll bar changes from stock? Reducing the body/chassis roll is an intergral part of controlling the tyre camber as there's a direct relationship with each degree of chassis roll giving a degree more positive camber. If you're using a basically stock car with slicks this body roll can be rather significant.

Another factor is whether you're using the OEM suspension components, particularly the bushings/rubbers, as under the higher loading you can apply with slicks there may be a little bit more compliance.

My suggestion - and I strongly recommend you get as many suggestions/comments/advice as you can, as I may be erroneous - would be to increase the roll resistance with aftermarket ARBs and, maybe, try dropping the tyre PSI to 30, or even 28, to give a little more compliance and reduce the 'running on the sidewall' affect from a stiff carcass?

Hi Gord, thanks!

The only mods in suspension is the front camber plates and the adjustable rear toe link. I know it is to soft but i will run in the next weeks 2 track days and tryng to do and learn some changes to get better performance, upgrading more parts in the suspension is my future plans.

So will be dificult to get better tire contact changing toe out (front) and toe in (rear) ? For example change in the front/rear to ZERO toe ?

Dropping the tire pressure to 28 will force to aply more contact in the outter size rigth ? On your experience this type of slick can run lower than 28 psi if i notice some improvement ? ( car weight is around 1600kg)

The tires are really wear more in the outter side of the rigth side of the car (f/r) , almost all the curves , and fast curve are to the left side , running different tire pressure is a good idea ? If so more or less tire pressure in the size that suffer more load ?

Not sure why you think a toe change is going to do anything other than the most minor change to the wear issue - especially as there seems to be no tyre scub?

I'd suggest saving the entry fee, and other associated costs, and putting that towards, at a minimum, up-rated ARBs. There is only so much rubber on the tread area and you're quite likely to wear it to the point of a blow-out if you do another track day.

At the moment, the camber is set max negative, so Toe and tire pressure is the things can change in the setup. I am searching uprated links and a Coilover, thanks

I'd suggest reversing the tyrees on the rims, in the mean-time, to get a bit more life out of them?

Hi Eduardo. Thanks for providing some good info with your question. I'm finding it difficult to see much detail in the picture of the tyre wear, it would be helpful to have a close-up picture of each tyre and with the treadwear holes in view if possible.

Assuming that the outer edge is very worn (which is what it looks like might be happening in that photo) then what Gord is saying is correct. The amount of body roll in a road car, when driven on a race track is always excessive. It's like that to help make it more comfortable and compliant when commuting on the road. When you go and fit higher grip tyres like you have, you make it even worse. It seems to me you are just getting too much roll, which is causing the outside of each tyre to roll over which causes the outer edge to wear.

Your static wheel alignment settings seem like a sensible starting point to me.

My recommendation is to invest in a set of uprated springs plus uprated anti-roll bars. There are plenty of suppliers out there making good quality uprated suspension components for your model of car. You'll just have to make a choice based on what your intended us is - track only? Or track and road? Using firmer springs and anti-roll bars. If the car is more track focussed, then upgraded to some aftermarket dampers at the same time is a good idea.

As for the hot tyre pressure, your tyre supplier is best to advise you on that depending on which construction you are using. 28 psi does sound on the high side, but again, the internal pressure requirements are very dependent on the construction of your tyre. Pirelli slicks do tend to need higher hot pressure than some other brands like Michelin or Goodyear for example.

Let us know how you get on

Hello,

greetings from europe!

I am also in a similair case. This a european subaru GC8, with STI GC8 front alloy arm. It has coilovers, and 22/22 arbs.

Front end geometry it 3° camber, probably 7° caster (at least that's the angle the strut is at with a protractor), and parallel toe

Rear end geometry is 2.1° Camber and minimal toe in (0.04")

Rear tyre wear is ok, front ones are still very used up on the outside.

From the attached picture and going by the size of the number plate, (110mm high, 550 wide), I measure between 3 and 3.5° roll (anyone can confirm?)

My question for you would be, what are the typical value of roll you usually see on track car? I felt the value of3° was ok/in control, but then tyre wear still isn't great?

What would be your input on that?

thanks

Attached Files

I like the G-sensor hanging on the rear view mirror!

If you want to minimize tire wear then slow down. If you want to make the tire wear even, you will need to work on dampers, and suspension geometry (such as getting camber curves that match the body roll). If you can't change the suspension to create more camber in roll, then it's best to limit the roll with stiffer springs or anti-roll bars.

Body roll is entirely dependent on center of gravity, cornering force, track width and spring + ARB rates. For a street car some tracks 5 deg might be OK, for purpose built cars, we see 1deg.

This car is like drive to the track and back, but no other road driving. So it's still registered but pretty much a track car.

No cage yet.

I indeed mean to even the tyre wear and not reduce it :D

With the suspension design, Mc pherson, I already fitted a "roll center kit" that help a slight bit in that matter, but its only like 8mm correction.

Modifying the geometry isn't really an option I guess?

Lowering CG would screw me even more in camber loss department. Trackwidth that's all that fit under stock fenders.

I guess its a stiffer spring and arb I must be looking at.

Can you raise the spindles relative to the A-arms on your Mcpherson struts? That's one way to lower the car while keeping the camber. Custom A-arms are another possibility to increase the track and camber. Are you limited to stock fenders?

Consider trying some front toe-out, get that inside tire working more!

The only thing I can do is lower the LCA ball joint to the spindle. which was already done with a so called rollcenter kit.

To my knowledge there is no way to "raise the spindle" relative to the strut. Or this would be an aftermarket dropknuckle?

I am lurking on some subaru STI newage LCA which are about 10-15mm longer, but that must be paired with longer Axles (awd obliged) which I don't have.

I would say the limit is what I set it to :D

It is no racing, just trackday fun, but still looking for some performance ;)

But yeah, I'm not ready yet to roll/pull/cut the fenders yet. It feels like to me if I bandaid the "not optimal grip" with wider track/wider wheels, then I am hiding the issue and I could even be better performing than that! Basically wanting to extract the best of the current combo before going one step further.

I did try some minor toe out on the front but the car back end would be very unstable on turn in. like the front end would throw the rear end to the outside. I have not tried yet to put a bit more toe in in the back and go back to toe out on the front.

Thank you for your valuable input :)

I'm not up on Sub' models, etc, but this is the sort of thing David was referring to -

https://www.wisefab.com/subaru-impreza-1992-2014-front-drop-knuckle-kit

And maybe for the rear

https://www.wisefab.com/subaru-impreza-1992-2007-rear-drop-knuckle-kit

Have a look around https://www.wisefab.com/ and there will be other suppliers.

I see.

I had a look at these and other suppliers. Wisefab is by far the cheapest.

The thing is, with such kind of drop knuckle, would you gain more performance by slamming the car 50mm more, or keep the car a tad higher?

I guess this is always the compromise CG / RC / Camber curver isn't it?

Hey,

Any input on that drop knuckle question?

Let's say the drop knuckle has a 50mm RC correction (vlaue annouced by wisefab, equivalent to 35mm ball joint lowering according to my measurement on the wisefab kit)

Would it be more beneficial to drop the car 35mm more and get to the same point geometrically wise, or have a 20mm drop a get a 15mm suspension geometry correction?

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