[ice_lt1]

Hello all. I am thinking about a staggered setup and am wondering if a 245/40/20 front and a 305/35/20 rear will cause any stabilitrak issues. Thank you!

[ChibbMD]

I don't know for sure, but that seems like a really big size difference. Why not run the staggered sizes that come stock on some of the other models (i.e. SS 1LE)?

[arpad_m]

It won't cause issues, but that's a weird combo... I have obviously never tried it, but it feels like a recipe for corner understeer. Why don't you want to go wider in the front for more grip?

Also FYI if you keep your fronts but go with 325/30/20 in the rear, your tire heights won't change at all, but you obviously need wider wheels and (depending on the wheel offset) possibly spacers as well.

[ice_lt1]

Originally Posted by arpad_m

It won't cause issues, but that's a weird combo... I have obviously never tried it, but it feels like a recipe for corner understeer. Why don't you want to go wider in the front for more grip?

Also FYI if you keep your fronts but go with 325/30/20 in the rear, your tire heights won't change at all, but you obviously need wider wheels and (depending on the wheel offset) possibly spacers as well.

The tires I wanted didn’t come in a 255/40/20 so I just went with what came in my LT1. My current setup is 275/35/20 and 305/35/20 and it’s fine. Was just wondering if the computer would get all wack.

[arpad_m]

Originally Posted by ice_lt1

The tires I wanted didn’t come in a 255/40/20 so I just went with what came in my LT1. My current setup is 275/35/20 and 305/35/20 and it’s fine. Was just wondering if the computer would get all wack.

Yeah, that's a valid setup, too. As long as the deviation from the stock front/rear ratio is less than ~3%, the computer will be happy. Wish I had definitive proof, but of course we don't have access to the actual software, so everything will necessarily be conjecture; however, there have been several examples of under and over threshold setups here in the forum, guys with the latter having stabilitrak / ABS issues.

I run 315/30/20 in the rear because it's a closer match and I have extra weight in the front.

[FlukeSS]

Originally Posted by arpad_m

Yeah, that's a valid setup, too. As long as the deviation from the stock front/rear ratio is less than ~3%, the computer will be happy. Wish I had definitive proof, but of course we don't have access to the actual software, so everything will necessarily be conjecture; however, there have been several examples of under and over threshold setups here in the forum, guys with the latter having stabilitrak / ABS issues.

I run 315/30/20 in the rear because it's a closer match and I have extra weight in the front.

I can tell you this much, at 6.8% my ABS and TC went apeshit, even at the drag strip. Braking didn't feel right, and ABS cut out completely until I had to change the front tire diameter and reset the tire size in my tune. This happened when I got the 555R2's on the back with 305/35R20. I was running 275/30R20's on the front when this happened. 26.49 front diameter vs 28.40 rear diameter.

Relative to the front wheel diameter that is a 3.5% difference from the tire size setting in the tune. While the back tire difference was at: 3.4% difference from the tire size setting in the tune.

[FlukeSS]

Originally Posted by ice_lt1

The tires I wanted didn’t come in a 255/40/20 so I just went with what came in my LT1. My current setup is 275/35/20 and 305/35/20 and it’s fine. Was just wondering if the computer would get all wack.

You'll want to check the tire size setting in the tune.

You should be using a tire size setting in the tune of 27.99. That puts your tire size difference at 1.5% relative to the front and back wheel diameter. But you have up to 3% difference before you start noticing things.

Also bare in mind if you swap wheels seasonally like I do, I use stock tire sizes for winter tires, which means I have to change my tire size in the tune to 27.65 for winter driving, and then back to 28.14 for summer driving with the bigger tires.

If you use the same tire size all year round, then you only need to set 27.99 in the tune, and you'll be good from that point on.

In the tire wizard in HP tuners you can set the tire size: Mine is set to 27.65 with stock wheel and tire diameters. But in your case you'll want to make sure that is set to 27.99. If you have an A10 like I do, then leave the gear ratio set to 2.77? or 2.72 whatever it is for the LT1. Either way keep the same gear ratio that the tune is already set to.

I believe tire shops have a way to set your speedo for you, which is the same thing as below except they do it with their equipment if I remember right.

[david_acm]

Interesting, I always wondered if I had to keep in mind the speedometer difference when using a different tire diameter. Thanks, super helpful!

[bandier]

I recently installed 285/35R20 in front and 305/35R20 in rear. They are working out fantastically. Arpad is a wealth of knowledge and experience in helping me comfortably come to this tire sizing decision. It was not his top pick but did reassure me it would work without computer issues. As a matter of fact, she's at the alignment shop right now. Not needed, but grants piece of mind.

[grampa_ss]

I run your exact setup and have for years. No Stabiltrack issues. Also, as FlukeSS stated, change your speedo to 27.99. I actually have mine at 28.0 and my speedo is spot on.

[KingLT1]

Originally Posted by ice_lt1

Hello all. I am thinking about a staggered setup and am wondering if a 245/40/20 front and a 305/35/20 rear will cause any stabilitrak issues. Thank you!

It works fine. I ran that size on stock SS wheels for 8yrs. Need to adjust tire height setting in tune or speedo will be off as already mentioned. I recently went 1" wider wheels both front and back, so I now run 275/35 front and 305/35 rear. While the 305 works on the stock 9.5 SS wheel the tire is bulged some and doesn't utilize all the tread pattern. I still was able to pull 3.0 0-60's(2.76 with 1ft roll out) on the street.

[FlukeSS]

Originally Posted by KingLT1

It works fine. I ran that size on stock SS wheels for 8yrs. Need to adjust tire height setting in tune or speedo will be off as already mentioned. I recently went 1" wider wheels both front and back, so I now run 275/35 front and 305/35 rear. While the 305 works on the stock 9.5 SS wheel the tire is bulged some and doesn't utilize all the tread pattern. I still was able to pull 3.0 0-60's(2.76 with 1ft roll out) on the street.

Stock SS wheels or stock SS 1LE wheels?

There's a difference.

You ain't fitting a 305 on a stock non 1LE wheel on the back, it won't work, and if I remember right people said 295 was the biggest you can do on a 9.5" wheel.

[KingLT1]

Originally Posted by FlukeSS

Stock SS wheels or stock SS 1LE wheels?

There's a difference.

You ain't fitting a 305 on a stock non 1LE wheel on the back, it won't work, and if I remember right people said 295 was the biggest you can do on a 9.5" wheel.

I have had 305/35/20 555r drag radials on my stock SS 20x9.5 wheels for 8yrs. You ought to try reading outside this general section. Plenty of info on it being done over the years.

https://www.camaro6.com/forums/showthread.php?t=486613

[Msquared]

Originally Posted by KingLT1

I have had 305/35/20 555r drag radials on my stock SS 20x9.5 wheels for 8yrs. You ought to try reading outside this general section. Plenty of info on it being done over the years.

https://www.camaro6.com/forums/showthread.php?t=486613

If all someone is doing is drag racing, that may work fine. If someone wants good handling and grip while cornering, it's not going to work well.