[WishfulSS]

I am autocrossing a 2024 1LE with 19 inch 10/11 fr/rr rims. I have a set of 285/35/19 at all four corners. I am considering adding trying some 305/30/19s on the rear. Has anyone tried this set up for autocrossing or track? Our cars come with taller rears and this is shorter rears but wider for a little more grip. Will this work?

[Nick S]

the 305/30R19 will be shorter overall diameter then the 283/35R19 front. From what I've seen and been told, the ABS and stability system will not like this because the rear tire will always look like it's rotating faster than the front tires.

[clyde]

There is someone running the 285/305 combo and having decent results. The diameter difference doesn't appear to cause issue when TC/ECS are disengaged. Not sure there's enough data yet to draw conclusions about whether it's faster (or slower for that matter) than 285s all around.

[WishfulSS]

Yes the original size tires are 285/30/20 and 305/30/20 with diameters of 26.8 front and 27.2 rear 3.7% difference. 286/35/19s are 26.9 inches f/r, so 0% difference. The 285 fr and 305/30/19 rear are 26.9 and 26.3 inches which is now a 3.4% difference but now about 7.1% difference front to rear from stock. What I have heard (read on this forum) is that most of the people at nationals run with all nannies off so no impact on tire diameter difference. Theoretically then, the larger 285/305 difference will not matter with nannies off but more rear traction should help. Still I appreciate any input and thoughts.
The Chevy engineers (from traction modes explained on this forum) said that Track/Race mode is the fastest with PTM on and everything else off. Will the 285/305 setup effect PTM?
I have tried Track/All off and Track/Race with no clear winner the one day I played around but I am still learning the car. Last weekend I was 25th and 18th in Pax out of about 120 people each day.

[pitrott1]

Originally Posted by Nick S

the 305/30R19 will be shorter overall diameter then the 283/35R19 front. From what I've seen and been told, the ABS and stability system will not like this because the rear tire will always look like it's rotating faster than the front tires.

Where did you get the 1LE door handles??

[eimarshall]

I ran 305s on a 19" x 10/11 setup with no issues.

[WishfulSS]

Originally Posted by eimarshall

I ran 305s on a 19" x 10/11 setup with no issues.

That is all around and were they 305/30/19s? Did the tire shop have issues putting the 305s on a 10 inch rim?

[Nick S]

Originally Posted by pitrott1

Where did you get the 1LE door handles??

I had made them myself. Used vinyl wrap and cutout 1LE letters using templates. Then wrapped over top of those letters around the entire handle to create the 3D look.

[dpevans]

Originally Posted by Nick S

I had made them myself. Used vinyl wrap and cutout 1LE letters using templates. Then wrapped over top of those letters around the entire handle to create the 3D look.

nice

[apexit53]

running this exact setup right now, only at autocross events and to and from the hotels lol.

I have had hard pedal once after the finish. other than that ive had full confidence in the brake and its surprised me. I expected more of an issue, with that said.... now ill probably have a ton of issues lol.

[clyde]

Originally Posted by WishfulSS

That is all around and were they 305/30/19s? Did the tire shop have issues putting the 305s on a 10 inch rim?

I had the old 305/30-19 RE71R on the 10" fronts. First set took us a few sessions of attempts. Second set went a lot easier because we knew what to do: heat, Murphy's Tire Lube (and lots of it), dangerous inflation pressure, patience and commitment to see it through.

[WishfulSS]

Originally Posted by apexit53

running this exact setup right now, only at autocross events and to and from the hotels lol.

I have had hard pedal once after the finish. other than that ive had full confidence in the brake and its surprised me. I expected more of an issue, with that said.... now ill probably have a ton of issues lol.

What tire pressures are you running? Currently running 33 front and 32 rear with the 285s all around.

[VR Baron]

Originally Posted by WishfulSS

What tire pressures are you running? Currently running 33 front and 32 rear with the 285s all around.

If it helps, I run the same sq setup. Been using 33-34/32 hot, so about same as you. Seems to be best for me so far. But still 1/8” above arrows as the sidewall is stiff on the 10.75” wheels, maxed out camber and hotchkiss front bar, so take that into account. I am trying 32/30 next time to see how it does.

[WishfulSS]

Originally Posted by VR Baron

If it helps, I run the same sq setup. Been using 33-34/32 hot, so about same as you. Seems to be best for me so far. But still 1/8” above arrows as the sidewall is stiff on the 10.75” wheels, maxed out camber and hotchkiss front bar, so take that into account. I am trying 32/30 next time to see how it does.

I spoke with a driver who goes to nationals at a national tour event and he said he was running 32/31 f/r. Next weekend I will post pyrometer temperature profiles at 33/32 and 32/31 after I get the 305/30/19s mounted on the rear. Running stock suspension with recommended Chevy of -2.0 frontand -1.5 rear camber with minimum toe.