kfmcmahon

So, I had the dealership do an alignment to increase negative camber front and rear on my GT3 to reduce understeer and get more even tire wear, after cording the outside of the left front and semi cording the left rear at Mosport (clockwise track) last fall.

Went back to Mosport last month....the car felt great and set some PB times -- probably 250 hot laps (20 heat cycles) over 3 days in SOLO/instructor group.

when switching the wheels from Hoosier R7's back to street MPSC2's, we noticed that the INSIDE shoulder of all 4 tires were corded-- the rest of the "tread" on the R7's looked to be evenly worn and the outside shoulder looked good still.

does anyone have an explanation?

dealer thinks the alignment ( now -2.7F and -2.3 R ) was too aggressive and that's why the inside corded?

what about too much or too little toe angle or possibly rubbing the inside tire edge on something in the wheel well (brake duct, etc) or too low of a ride-height now?


pics below ....all the cord you see is INSIDE EDGE

kfmcmahon

They only used shims (despite me mentioning guys on here used thrust arms or camber plates) to get the camber from -1.6 to -2.7 so the caster is off by a bit (went from 8 to 10 degrees)

could this also also be a factor ?

or is it just too much hard driving and this was the end of the lifespan for these once new-sticker tires. Underinflation? (best times were at 35F/36R hot temps)

if it is end of useful life I would expect there to be no visible "channels" in the tread like you can see in the pictures above

they weren't quite heat cycled out (times were consistent til the end) but were getting less grippy and gripped for fewer laps towards the final sessions

MileHigh911

where did you ave sway bars set? What was toe f/r?

TRAKCAR

20 heat cycles they are slow anyway.

19"?

250 laps, a bit too much camber and it's normal, I think?

major dad

I agree, 6 heat cycles is the limit for grip, it can drop off after that. Camber looks good to me.

Seth Thomas

Where are the toe settings?

C.J. Ichiban

20 heat cycles and they would be roasted anyway.

Hoosiers need as close to 3* negative camber or more as you can get on the front.

If your caster increased that significantly then you are probably getting a little inside tire drag on cornering but this is always a moving target. Despite popular opinion Hoosiers are not magic, they're still just tires.

kfmcmahon

sway bars med-med

here is alignment sheet.

kfmcmahon

yes, Forgeline GA1R's 19x9F, 19x12R
Hoosier R7's 265/35F, 325,30R


yeah, they were hard/fast laps too (for a street car)...just wondering because it is the opposite wear pattern from last event I did there (same 250 laps over 3 days)...maybe camber should be backed off a bit, but I see a lot of guys on here running more without issues??

kfmcmahon

Right CJ, that's why I was perplexed by the INSIDE tire wear at only -2.6/-2.7....thought with lower ride height and the fact that shimming (only-not thrust arms or camber plates) brings the TOP of the tire inwards and up toward the top of the wheel arch that it may be from rubbing??

I know the Hoosier's are not magic, but my PB lap times reflect 2 seconds gained per 1 minute lap (so 4 seconds at the Glen and 3 seconds at Mosport per lap) and they FEEL so much better than MPSC2's.... more confidence inspiring to push harder, get on throttle earlier, brake later, etc...

I can afford these tires, but nearly $2k for a 3 day event is painful!
I may just swap to RE-71r's and be done with Hoosiers?



My GT4 is currently at a different race shop getting Tarett race camber plates and TPC toe links to get it to -2.5F/-2.2 R with APPROPRIATE caster and toe, and will try R7 235 (I know!) and 295R and see how that compares to the GT3

sasportas

-2.7F with zero toe

-2.2R with 0.14 toe each side

Castor plates upfront to correct back to 8.5

R7

No inside cording at all. Very even wear.

I'm guessing that the excessive castor upfront and the limited toe setting in the rear is a good place to start making changes.

MileHigh911

SAS is on the right track!

kfmcmahon

I am an alignment noob, so can you explain why the excess castor up front is causing this? and how does more toe in the back correct it?

thanks,
KFM

C.J. Ichiban

The increased castor just keeps the tire loaded way longer than it needs to be, and slows down the rotation. Think about those super long front end Harley's. They cannot corner because of wonky castor.

It's hard to imagine that the combo of too much castor (you should be at 6-8 max?) and some increased negative camber would create rubbing issues- usually you rub the outside edge on the fender liners from ride height/not enough camber.

H82BL8

how can there be a track width difference be 3.5"?

camber looks good
toe looks good
caster should not exceed the factory......no need to