Weird tire wear for track car

[Spetz]

Hi everyone,

I have a 2001 Mitsubishi Mirage 2dr that I use on a technical but smooth circuit.

I run 205/50/15 semi slick tires on it and the front is exhibiting odd wear pattern.

The tires are getting very little wear on the outside with most of the wear being in the middle.

I know this suggests that they are over inflated (I run 32psi hot) however if I start dropping the pressure from 32psi hot grip seems to suffer.

I am running -2.5 camber and +6 castor at the front with 1mm total toe out (-1.3 camber rear, 2mm toe out).
Springs are fairly stiff but there is enough roll (9kg/mm all round).

At the same time my front end grip is very limited with lots of understeer which I assume is due to not using all of the tire contact patch but I have no idea what to do.
I will be going softer front swaybar.

Is it possible that I am running too much camber/castor?

 

[clinebarger]

The tires may be "scrubbing" when making turns with that much Castor.....Along with the negative Camber. I'm guessing the factory suspension geometry doesn't support big changes?

 

[BrocLuno]

What do the rears look like?

Very little wear on the outside suggests that camber is not effective as set. Yes, you prolly want more wear mid/inside, but you should see some on the outside too. I would try -1.5* camber and see what happens ...

 

[RoadRaceJosh]

What tires specifically? How wide are the wheels?

 

[CapriRacer]

Have you considered that Ackermann might be the problem?

Ackermann (multiple spellings!) is where the steering links add toe out as the steering wheel is turned. Another way to put it is that the steering geometry forces the inside wheel to turn in further than the outside wheel. This compensates for the fact that the inside wheel travels a shorter distance in a turn.

- BUT -

Race cars, with their large slip angles, don't need as much Ackermann as street cars. To change the Ackermann, you have to reposition the steering arms. In some cases that means bending them. In some cases, it's just a matter of shims.

I notice that the alignment you are using includes toe out. I would think that would aggravate the Ackerman situation, so I would start with dialing some of that out (and even to the point where you have toe in!) - Keeping in mind that the feel of a car doesn't translate into speed. Sometimes a fast car doesn't feel very stable.

And doing this in my head, I think the set up you have is going to result in wear in the center of the tire- and the alternative is wear on the inside edge, which would indicate you need to redo the Ackermann.

 

[mightymousetech]

Guess you don't have a limited slip? You are spinning your front inside tire.

What are your tire temps? Can't really give any advice until you pull proper tire temps.

 

[Spetz]

Thanks everyone.

The tires are Nankang AR-1 205/50/15 mounted on 15X7 +30 rims.
The car does have a clutch type mechanical 1.5 way diff.

It runs MacPherson front struts and the way the castor has been added is the strut top camber plates have been swapped from left to right so there is castor gain along with camber gain when adjusted.

The weird thing is that temps are pretty even at around 120-130 deg F between inside, middle and outer part of the tire.

The car understeers quite heavily no matter what I seem to do

 

[mightymousetech]

Actually sounds like your front springs are just too stiff.

 

[dgunay]

-2.5 camber and +1 total toe is optimal for FWD on race track. No need to change that.

You should change the rear toe though, 2mm toe out is too much. Usually 0 toe is optimal in the rear for FWD but you have to stiffen up the rear.

I also think front springs are too stiff. You can try it by removing the front sway bar temporarily and see if the traction gets better. I'd also get an aftermarket rear sway bar to stiffen the rear.

Does it have LSD? If not, you should get one.

 

[thescreensavers]

Originally Posted By: Spetz

It runs MacPherson front struts and the way the castor has been added is the strut top camber plates have been swapped from left to right so there is castor gain along with camber gain when adjusted.



When you adjust the camber plates toe changes fyi

 

[Spetz]

The rear does have an aftermarket swaybar.

The springs don't feel too stiff and there is dive during braking however the front swaybar is from a Mitsubishi FTO and my next step is to revert back to stock.

It doesn't feel like the odd wear is from not enough body roll though

 

[IndyIan]

Maybe your diff isn't working anymore? Could be just the tires too. My snow tires are wearing in the middle on my Focus. Never had that happen with any other tire on the car and I'm running normal pressures its just the tires I guess.

 

[dgunay]

Originally Posted By: Spetz
The rear does have an aftermarket swaybar.

The springs don't feel too stiff and there is dive during braking however the front swaybar is from a Mitsubishi FTO and my next step is to revert back to stock.

It doesn't feel like the odd wear is from not enough body roll though


I was trying to address the understeering problem only in the previous post. Springs may not feel too stiff, but the problem is, front end must be softer than the rear. If they are equally stiff/soft, then it will always understeer, especially if you don't have limited slip diff.

In regards to the odd wear, it has nothing to do with the springs. I think that's because of excessive toe out on the front (excessive for daily driving). I think there is nothing that you can do, except going back to 0 toe, which is not optimal for the track.

 

[mightymousetech]

Originally Posted By: dgunay
-2.5 camber and +1 total toe is optimal for FWD on race track. No need to change that.

You should change the rear toe though, 2mm toe out is too much. Usually 0 toe is optimal in the rear for FWD but you have to stiffen up the rear.

I also think front springs are too stiff. You can try it by removing the front sway bar temporarily and see if the traction gets better. I'd also get an aftermarket rear sway bar to stiffen the rear.

Does it have LSD? If not, you should get one.


To add:

Can try just disconnecting one front sway bar end link and see how it helps. Running the same spring rate front and rear seems a bit strange, especially on a FWD strut car. My Civic racecar (not one listed) runs rear springs that are 500% stiffer than the front. It has nothing to do with "feels" stiff, or dive under braking. Who suggested using those spring rates?

 

[Spetz]

The coilovers are from MCA (www.mca.com.au) which have a really good reputation were used with 9kg springs after talking to them about my needs etc.

These cars generally run softer rear springs to front for street use as there isn't much weight over the rear.
Normal street kits from Tein or BC use 5-7kg front and about 4-6kg rear.

I will swap out the front swaybar to stock and hope that helps things.
I'd be surprised if the springs are too stiff but I can go softer, 8kg all round

 

[mightymousetech]

Originally Posted By: Spetz
The coilovers are from MCA (www.mca.com.au) which have a really good reputation were used with 9kg springs after talking to them about my needs etc.

These cars generally run softer rear springs to front for street use as there isn't much weight over the rear.
Normal street kits from Tein or BC use 5-7kg front and about 4-6kg rear.

I will swap out the front swaybar to stock and hope that helps things.
I'd be surprised if the springs are too stiff but I can go softer, 8kg all round


The amount of weight in the rear of the car really means nothing for this.

To increase grip at one end, you have to make that end softer. This is why street cars come from the factory with such soft rear springs, to decrease oversteer. On track, you want to increase oversteer, which means decreasing rear grip compared to the front, or increasing rear spring rate.

My Civic racecar came with much softer springs in the rear from the factory, about half the spring rate of the front. Set up for track use I was running 300# front, 1000# rear. Front was double wishbone suspension, so with the motion ratio, the front was closer to 200#. With front struts, there is no motion ratio. My car would NEVER understeer, cornering required almost full throttle to keep the car from oversteer.

Also, with an LSD with FWD, you HAVE to be on the gas while cornering. If you lift, the car will understeer. You have to be at least balanced throttle to pull the front end around the corner.

I wouldn't even bother swapping the front bar, just try without the front bar connected. Just remove one front end link.

You need to find somebody who knows how to set one of these up for actual track use.

 

[dgunay]

Originally Posted By: Spetz
The coilovers are from MCA (www.mca.com.au) which have a really good reputation were used with 9kg springs after talking to them about my needs etc.

These cars generally run softer rear springs to front for street use as there isn't much weight over the rear.
Normal street kits from Tein or BC use 5-7kg front and about 4-6kg rear.

I will swap out the front swaybar to stock and hope that helps things.
I'd be surprised if the springs are too stiff but I can go softer, 8kg all round


Again, fronts should be softer than the rears. I'd leave the rears alone and try to get the fronts softer as much as I could.

As a reference, my current setup is 230 lbs/in (F) and 275 lbs/in (R). Front sway bar is stock, but I upgraded rear sway bar from 11 mm to 20 mm ('15+ Civic SI sway bar). -1.7 front camber and -1.3 rear camber with 0 toe all around (for tire longevity). This is my daily driver and this setup is more than enough for twisty back roads and it is still able to offer relatively comfortable ride.

For race track, I'd probably get the fronts around 200-220 lbs/in with no sway bar, and I'd keep the rear springs 550+ lbs/in and try to get thickest rear sway bar possible. For an automatic daily driver, that's an overkill though. But I would have done this setup if I didn't sell my '08 SI.

For autocross, I'd probably go stiffer on the front, not stiffer than the rear, for better steering and overall turn-in response. Nothing crazy, but you can go with an aftermarket front sway bar in this case.

To sum up,

1) I were you, I wouldn't touch the rear suspension (except the alignment).

2) I would just get softer springs for the front side. Disconnect the front sway bar, and see if you get better traction. Your car doesn't have a limited slip. Without the LSD, you must keep the front inner tire on the ground when cornering. This is one of the reasons why you should try softer spring rates on the front for a FWD car. If the front end is stiff, inner tire will lose contact with the road when you are on the limit.

3) Your rear toe alignment is wrong.

4) Get a limited slip diff if it is a track car, you will thank us later.

 

[Spetz]

The car does have a 1.5 way LSD which when I drove on the street would make the car run wide depending on throttle application