[DaveC113]

Originally Posted by Msquared

I think that somewhat depends on the brand/model of tire. I believe the 315 Rivals are fine on 11" wheels (that's what I ran on my C4). But the Yoks and new Falkens seem to like wider wheels, and almost everyone is running the 315s on 12" wheels.

That was for 315/30/18 RT660s. Just his opinion... he tried mounting them on 12s and ended up going with 11s.

[DaveC113]

The Falken RT660 in 315/30/18 is specified for 10.5 - 11.5" rim widths.

I think people may be overcompensating by running 12s. I tend to go with the mfg'ers recs whenever possible.

https://www.tirerack.com/tires/tires...omCompare1=yes

EDIT: previously said ZLE runs 325s on 11s, that was wrong... 305 on 11s and 325s on 12s...

[Mountain]

Instead of words, I’ll let pictures talk: 315/30R19 (used) on 11” and 305/30R19 (new) 10.5”.

[94boosted]

Originally Posted by Mountain

I am at -2.6 and am right at the line between bad wear on the street and good wear on track. Right around -3 degrees, I think would be a nice to be at for the track, but I think those extra few tenths-of-a-degree will just destroy the inside shoulder of the tire on the street, even at 0-toe or slight positive toe.

Some anecdotal evidence here but I managed to achieve -2.8 front camber and was running a bit of toe out to boot and still managed to wear the outside edge of the Bridgestones more than the inside edge, this was after ~125 autox runs and maybe 2500 street driven miles. Not sure what the Falken wear is like compared to the Stones as I haven't put my Falkens on yet.

[VR Baron]

Here’s a most likely a unfair question. And real data out there as to if a wicker bill
Creates enough downforce during autocross? Some say those real tall ones do help. Not doing one of those though. The 1le has the small one of course, but don’t see how a wicker bill or taller helps in autocross with mostly low speeds and tight turns. Maybe on long 60mph plus straights
I was thinking on this for maybe possible help with the EDiff issues with exit snap oversteer with square tires.

[Msquared]

Originally Posted by VR Baron

Here’s a most likely a unfair question. And real data out there as to if a wicker bill
Creates enough downforce during autocross? Some say those real tall ones do help. Not doing one of those though. The 1le has the small one of course, but don’t see how a wicker bill or taller helps in autocross with mostly low speeds and tight turns. Maybe on long 60mph plus straights
I was thinking on this for maybe possible help with the EDiff issues with exit snap oversteer with square tires.

Depending on your class, you're probably allowed a 10"-chord spoiler that spans the entire width of the car. If you do it right and put at the very back of the decklid, it will create significant downforce and change the handling balance on faster corners of an autocross course. They work by damming up airflow, which creates a higher pressure over the rear deck, which pushes down on the car. They do this forward of the spoiler about twice the distance as the spoiler is tall. So a 10" spoiler set vertically will increase pressure over roughly 20" of deck surface across the width of the spoiler. If you lay the spoiler back at any angle, you are just decreasing its effectivness. The little stock spoilers and added wickerbills will not do enough to make a difference at autocross speeds.

I don't think this is the best solution for the snap-oversteer caused by the eLSD. That usually happens at pretty low speed as you exit a corner, whereas the spoiler works best at higher speeds. I see it as helping by allowing you set the car loose for low-speed turn-in at small-radius turns but adding some rear stability for the same setup in slaloms and higher-speed turns.

[VR Baron]

Originally Posted by Msquared

Depending on your class, you're probably allowed a 10"-chord spoiler that spans the entire width of the car. If you do it right and put at the very back of the decklid, it will create significant downforce and change the handling balance on faster corners of an autocross course. They work by damming up airflow, which creates a higher pressure over the rear deck, which pushes down on the car. They do this forward of the spoiler about twice the distance as the spoiler is tall. So a 10" spoiler set vertically will increase pressure over roughly 20" of deck surface across the width of the spoiler. If you lay the spoiler back at any angle, you are just decreasing its effectivness. The little stock spoilers and added wickerbills will not do enough to make a difference at autocross speeds.

I don't think this is the best solution for the snap-oversteer caused by the eLSD. That usually happens at pretty low speed as you exit a corner, whereas the spoiler works best at higher speeds. I see it as helping by allowing you set the car loose for low-speed turn-in at small-radius turns but adding some rear stability for the same setup in slaloms and higher-speed turns.

Thanks, and makes sense as to how they work. They appear to add understeer into corners, so set up loose to enter better but hopefully keep rear stable on those slow exits as you say.
I use a square setup, but a hotchkiss front bar set soft now. It makes the square setup behave more like a stock staggered setup, good turn in, almost neutral mid corner, just a touch of understeer, but on those 90 degree exit turns onto a straight the snap oversteer does happen, but is quick, mostly self correcting, or I can briefly counter steer and all good.
Think will leave as is for now and get more seat time as she is and go from there

[Scargoes]

Originally Posted by VR Baron

Thanks, and makes sense as to how they work. They appear to add understeer into corners, so set up loose to enter better but hopefully keep rear stable on those slow exits as you say.
I use a square setup, but a hotchkiss front bar set soft now. It makes the square setup behave more like a stock staggered setup, good turn in, almost neutral mid corner, just a touch of understeer, but on those 90 degree exit turns onto a straight the snap oversteer does happen, but is quick, mostly self correcting, or I can briefly counter steer and all good.
Think will leave as is for now and get more seat time as she is and go from there

What is your rear toe setting? It's possible to calm down the oversteer by adding a bit more rear toe in.

[VR Baron]

Originally Posted by Scargoes

What is your rear toe setting? It's possible to calm down the oversteer by adding a bit more rear toe in.

-.125 total in. Rear really only steps out with nannies off. Track race not a issue. But track race has its own issues and a bit slower

[Msquared]

Originally Posted by VR Baron

-.125 total in. Rear really only steps out with nannies off. Track race not a issue. But track race has its own issues and a bit slower

Agreed, and it is definitely the stock eLSD calibration causing this. The autocross reflash is supposed to fix it, but make sure it's legal for your class first (it isn't in Street class for SCCA). Also, IME tires that hook better than the stock GYs in a straight line help a lot. The Falken RT660 mitigates the oversteer to the point where I don't even notice it anymore.

[foshjowler]

Coned away every run, and lost a 1st in CAM because of it. Each run only had one cone and 3 of them I never knew I hit. Guess that means I was just clipping them with my rear wheel.

This was my first time at this site, and the pavement is way grippier than I was expecting. Took me a couple of runs to get to where I was really pushing it.

[VR Baron]

Originally Posted by Msquared

Agreed, and it is definitely the stock eLSD calibration causing this. The autocross reflash is supposed to fix it, but make sure it's legal for your class first (it isn't in Street class for SCCA). Also, IME tires that hook better than the stock GYs in a straight line help a lot. The Falken RT660 mitigates the oversteer to the point where I don't even notice it anymore.

Matt, totally agree on the EDiff cal. Here in SoCal no dealer will do it. Only one “ gm performance dealer” said yes, but never done one before, they didn’t care to look into it, and I have pn’s for them, nor even confirm a price. Just come on down and take your chances. Not a lot of confidence in them, and the service reviews are horrible.
As to class, I dont run scca but can. I do nmca west, been doing it for eight years. Cars are classed by type and all groups are basically Cam C...lol Tires I run are 305/30/19 Re71s, bought two sets from last batch tire rack at half price��
The hotchkiss front bar on soft does help to mitigate the step out with getting weight to the rear better. And a very low grip, old surface doesn’t help.
Next time out I may do a different combo, use track mode, nannies off, but suspension in sport, steering in tour. Our bad surface likes suspension in sport, track is a bit stiff, but maybe throttle in track will be more progressive and not so abrupt coming off corners to help calm the rear(?)

[DaveC113]

Originally Posted by VR Baron

Matt, totally agree on the EDiff cal. Here in SoCal no dealer will do it. Only one “ gm performance dealer” said yes, but never done one before, they didn’t care to look into it, and I have pn’s for them, nor even confirm a price. Just come on down and take your chances. Not a lot of confidence in them, and the service reviews are horrible.
As to class, I dont run scca but can. I do nmca west, been doing it for eight years. Cars are classed by type and all groups are basically Cam C...lol Tires I run are 305/30/19 Re71s, bought two sets from last batch tire rack at half price��
The hotchkiss front bar on soft does help to mitigate the step out with getting weight to the rear better. And a very low grip, old surface doesn’t help.
Next time out I may do a different combo, use track mode, nannies off, but suspension in sport, steering in tour. Our bad surface likes suspension in sport, track is a bit stiff, but maybe throttle in track will be more progressive and not so abrupt coming off corners to help calm the rear(?)

It's unbelievable these dealers won't sell you a GMPP reflash, as I said if you're in Denver make an appt with Stevinson Chevy. They have a service tech that knows all about this stuff.

I've got 2 events in with the new 305/30/19 RE71s on all 4, it's taking some time to learn how to drive the car again, how to handle heat and tire pressures, etc. They also seemed to get a good bit grippier after initial use so I keep on having to learn new limits and for the 1st time an instructor told me I wasn't being aggressive enough in some areas! I usually overdrive the SC3s...

The e-diff tune does make corner exit far more predictable, it reliably locks the diff and you can really rotate the car with the throttle in a controlled manner.

Despite being a beginner and just learning the new tires I managed 24th out of about 135 entries in the last 2 SCCA events. Our region is very competitive with most of the CAM-C cars arriving on trailers. Despite this at the last race I was less than .2s from 2nd place and less than .5s from 1st. And I know I have a lot of room for improvement. This car is just amazing, it's so much fun to drive!

[VR Baron]

Originally Posted by DaveC113

It's unbelievable these dealers won't sell you a GMPP reflash, as I said if you're in Denver make an appt with Stevinson Chevy. They have a service tech that knows all about this stuff.

I've got 2 events in with the new 305/30/19 RE71s on all 4, it's taking some time to learn how to drive the car again, how to handle heat and tire pressures, etc. They also seemed to get a good bit grippier after initial use so I keep on having to learn new limits and for the 1st time an instructor told me I wasn't being aggressive enough in some areas! I usually overdrive the SC3s...

The e-diff tune does make corner exit far more predictable, it reliably locks the diff and you can really rotate the car with the throttle in a controlled manner.

Despite being a beginner and just learning the new tires I managed 24th out of about 135 entries in the last 2 SCCA events. Our region is very competitive with most of the CAM-C cars arriving on trailers. Despite this at the last race I was less than .2s from 2nd place and less than .5s from 1st. And I know I have a lot of room for improvement. This car is just amazing, it's so much fun to drive!

Nice job Dave!

Yeah annoyed with Chevy on the EDiff. And unfortunately I live in so cal, so won’t be in Colorado anytime soon..lol
Here is of my thoughts and findings that may help you.
Been running re71s for years. Yes they take a few break in laps. They like precise driving, basically not a large slip angle. And yes more grip then the Goodyear’s I have read . I replace at about 100 laps. 115 laps they slide more it seems. 150 laps and a lot less steering response . Even at 70 lap range with hotchkiss front bar set in middle they responded. Not so at 100-113 laps. Had to set bar soft to get the car to turn without a lot of understeer on tight turns and plowing out. Now on new tires I leave bar soft though scca champs like it in the middle. On my no grip surface middle setting feels good and solid but understeered more then I like. It helps tame the exit EDiff problem , but slows me to much in tight turns.
Will deal with the slight, correctable exit oversteer with soft bar setting.

As to psi, I like to start at 31/28 . No more then 34/31 hot(warm per dic readout)
34/31 is after three 50 second laps. Other scca guys like that to. Our top guys in zle’s use same. At 30/28, front bar soft I roll to arrow tops is all though scuffing go’s past that.