I have noticed that since I added a few ponies to my ITR that the inside front tire is wearing quite a bit on the inside (towards the center of the car). I can hear the poor inside front tire churning and working as I come off the corners. I am driving a little more aggressively as well. Camber is at -2.5 degrees with 1/16 toe at the front, zero toe at the rear and about the same camber. Tire pressures and camber were set with pyrometer across tread, and temps are fairly even, as are hot pressures. Front camber is perhaps not quite enough for optimum cornering, but I am wondering about this uneven tire wear. Is it due to camber or my driving style or is it normal. Power is less than 190 whp, so it is not a monster, but that front tire is just getting worked harder this year. Tires are Michelin Sport Cup, and will soon have to be replaced, as I rotate that inside front around the car and I run out of corners. Opinions?

 

Claude,

I've occassionally worn out the inside of the inside front first too, and so has at least one other guy that I'm aware of.

I think that's been mitigated on my car with the greater lockup from the Mugen diff. I could get detectable inside spin with the stock ITR diff in a few 3rd gear corners.

The alternative is to be more sensitive and use less throttle as you're coming off the corner - but that's a poor bargain.

Scott, who say's it's "Simple Really"...more $$$$...

 

I've done same, especially on the uphill corner at Watkins Glen...on a stock diff, which allows a fair amount of inside wheelspin.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by descartesfool &raquo;</TD></TR><TR><TD CLASS="quote"> Is it due to camber or my driving style or is it normal. Opinions?</TD></TR></TABLE>

The inside of your tire wearing fast is completely normal. The only way to reduce or even eliminate the wear would be to dial out camber, which is something you don't want to do! It's one of those things you have to compromise...... tire wear vs. turn-in and grip.

reducing that wheelspin could help. But I don't think you would want to extend the time you get back on the gas......

 

Well gents, that is all very helpful advice. I am going to consider being more sensitive. That will surely work. I will also wait before stomping on the throttle, and be more gentle. Smooth and slow. I also promise not to be on anyone's behind coming off the corner and make them think they should surely let me pass! I noticed while looking at my g-circle map that I am using the tire envelope more this year than last, and cornering more while braking and accelerating. Maybe that is promoting my new-found inside tire wear.

As for a different LSD like the Mugen, does it actually reduce inside tire wear and promote more equal grip between the fronts when exiting the corners? Any other diffs have similar benefits, and what about drawbacks?

 

Claude,

Reduce inside tire wear? I don't know if I'd say that exactly.

I do think that spinning the inside front on it's inboard edge would tend to increase tire wear, so not spinning it (as much) would be an improvement.

Promote more equal grip? I don't know that I'd say that like that.

You'll be able to put down more power because you're able to send more of it to the loaded wheel. LSD's lock-up the inside wheel TO the outside wheel by a percentage that varies as the design of the diff.

Quaiffe, Mugen, ITR, whatever - it all comes down to the lockup ratio and the transition/engagement. As to how to compare one to another in terms of lockup there's no easy way, we're stuck weighing testimonials. WRT transition/engagement the Torsen T2 (Quaiffe / ITR) is hard to beat for smoothness, but the Mugen's operation isn't noticeable on track.

I bought my Mugen because Scott Z told me that they ran one in their Motorola Cup / Grand Am ITR for several years without any maintenance or trouble, and the lockup with the optional rings was higher than on a Quaiffe. So far I got no complaint.

Drawbacks? Other than diminished personal wealth, there's probably nothing to make you regret a Quaiffe. The rattling and shaking at low speed with the steering wheel turned on the Mugen (or any typical clutchpack) might trouble some, but it comes with the bargain.

Scott, who thinks a better diff is a good thing on an ITR...

 

Hmm... I think Nate (solo-x) said something about this on the Subaru forum... maybe he'll post it here. Something about toe out increasing Ackerman effect and thus tire scrub on corner entry, didn't read it close enough to understand it, but it sounded really good.

 

Are your tire temps telling you that you really need that much negative camber? Sometimes I think we overdo it just because we can...

K

 

Reducing front camber was going to be my next experiment. Camber settings I am using were mostly determined by outside temp profile, as the inside tire is cooler when I come into the pits, and not as heavily loaded. It is a free experiment in any case, and leaves room for a different LSD in the future. As for Ackerman as a function of toe, this is a possible avenue of interest. If the wheels are turned a lot, then the inside tire might not be at its optimum angle for traction and extra slippage and wear could occur. It is just hard to know on what corners the actual wear is occurring. It is easy to notice the tire working on low speed corners where you come off with ore torque at the wheel, say in second gear. But I also noticed that in a 3 rd gear right hand sweeper (turn 3 at Mosport), it was easy to be hard on the tire's limit for quite a long time (i.e. not a scary corner so you can push real hard unlike some of the other corners at Mosport) and this is perhaps where most of the inside tire wear is occurring. setup might have to be adjusted for length of time running on the track. I ran a 1.5 hour enduro, and for that type of event, a different alignment might be a good idea. Hard to say about these alignment mysteries, turn-in, stability under braking, max grip, oversteer/understeer balance. There should be a formula or something!

 

What Nate said...

"toe-out could be considered "dynamic" ackerman. lets say you are using 1 degree of toe out on both front tires for 2 degrees total toe out(you never would use that much, but it works for the example). now you have to turn the wheel a bit more to get the same 7 degrees on the outside front. all that extra toe will result in the inside front being turned more then 14 degrees. (the 12 degrees from before, plus the combined toe out, which was an obscene 2 degrees total toe out, plus the ackerman effect on that additional degree you had to turn the wheel to get the outside front to the same place).

nate

*edit* i forgot to mention. the numbers i used are just random numbers plucked from thin air. they have no accuracy beyond illustration."

Extrapolating from that a bit, can you ditch the toe out in the front end of your car? That might stop the scrub on entry and make your tires live a little longer, if you can afford to give up a bit of turn-in response.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by descartesfool &raquo;</TD></TR><TR><TD CLASS="quote">Reducing front camber was going to be my next experiment. ...</TD></TR></TABLE>

I have an open diff and OE springs so the variables are DIFFerent - hah - but at VIR I have ended up with -2.5* on the outside (left) and -.5* on the inside. I first saw what you describe at Roebling and reduced it some. I kept an eye on it over three visits to Virginia and went even further.

K

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by descartesfool &raquo;</TD></TR><TR><TD CLASS="quote">...There should be a formula or something!</TD></TR></TABLE>

&lt;Will Ferrell On&gt; "gg.....gg......ggi.........Ack!"

Scott, who found that to be one of the most entertaining sentences he's read in a while...