[2SS Capt]

Originally Posted by 2SS Capt

That's why if you run 275/35/20 on the fronts you should run 315/30/20's on the rear (non-1LE SS)... That math, math's out just fine...

245/40/20 --> 275/35/20 (98.0 vs. 96.25)
275/35/20 --> 315/30/20 (96.25 vs. 94.50)

1.82% F-R difference stock
1.85% F-R difference alternate sizing

About as close as you can get...

Originally Posted by Msquared

I fixed your statement for you. You arranged your math backwards: the stock SS or SS 1LE has a shorter front tire than rear. Your proposed replacement has taller front tire than rear. It's nowhere near "as close as you can get" regarding tire heights: it's a about a 3.6% swing in the opposite direction! And to add insult to injury, you've now decreased front section width 10mm and increased rear width 10mm. Why would anyone do this intentionally to their car?

What I know from direct experience is that having a 2.6% taller front tire than rear will make the ABS computer unhappy. You can get a flashing traction control light, the car may not allow you to use cruise control, and the ABS will more easily invoke ice mode. Will a 1.85% taller front do the same? I don't know, but I know there's no good reason to try it.

Originally Posted by 2SS Capt

I am talking from stock SS (non-1LE) sizing to the alternate sizing, my math is correct, both are slightly shorter sidewall than the stock SS (NON-1LE) and the traction control will be fine as the ratio stays very close to the stock ratio...

Originally Posted by Msquared

You guys are right: I completely forgot that stock non-1LE SS cars have slightly taller front tires. So yeah, for that car a slightly taller fitment would probably be fine. And since that's the kind of car the OP has, then this applies to him. I think the 1LE version has differently calibrated ABS and traction control, and I would not say it's a wise fitment for that car. But that doesn't apply to the OP's case.

Sorry for my mistake!

No worries! All good!

[FlukeSS]

FYI 285/35 fits on the non 1LE fronts, and 305/35 fit on the back as long as you don't do any aggressive driving like track/strip. If you do then you'll want to move the wireharness.

And the F-R difference is closer to 1% as opposed to 315's on the back.

285 x 2 x .35 = 199.5 or 7.85" + 20" = 27.85"

305 x 2 x .35 = 213.5 or 8.40" + 20" = 28.40"

27.85 / 28.4 = 0.980 or 1.2% difference front to back which is the same setup I have at the moment.



Just read OP's post as well: 285/35 on the fronts is the best you can do and is better for 305/30's on the back if you have them.

305/30 = 305 x 2 x .3 = 183 or 7.20" + 20" = 27.20 back with 27.85" on front again less than 1% difference.

The problem with 275/30/35 fronts is that depending on the Rep wheel the lip of the rim sits out past the tire where 285 fronts the tire lip sits out past the rim lip.

Which is what happened to my car on 275/30's with a 20x10 ET20 ZL1 front rep wheel and on Advan V105 front tires which are 11.2" wide. My current front tires are Atturo AZ850's which are 285/35R20 and are 11.4" wide. That 0.2" makes all the difference on 285's.

[arpad_m]

Originally Posted by FlukeSS

FYI 285/35 fits on the non 1LE fronts, and 305/35 fit on the back as long as you don't do any aggressive driving like track/strip. If you do then you'll want to move the wireharness.

And the F-R difference is closer to 1% as opposed to 315's on the back.

285 x 2 x .35 = 199.5 or 7.85" + 20" = 27.85"

305 x 2 x .35 = 213.5 or 8.40" + 20" = 28.40"

27.85 / 28.4 = 0.980 or 1.2% difference front to back which is the same setup I have at the moment.



Just read OP's post as well: 285/35 on the fronts is the best you can do and is better for 305/30's on the back if you have them.

305/30 = 305 x 2 x .3 = 183 or 7.20" + 20" = 27.20 back with 27.85" on front again less than 1% difference.

The problem with 275/30/35 fronts is that depending on the Rep wheel the lip of the rim sits out past the tire where 285 fronts the tire lip sits out past the rim lip.

Which is what happened to my car on 275/30's with a 20x10 ET20 ZL1 front rep wheel and on Advan V105 front tires which are 11.2" wide. My current front tires are Atturo AZ850's which are 285/35R20 and are 11.4" wide. That 0.2" makes all the difference on 285's.

1. First off, let's establish that 275/30 in the front is a no go for a 10" wheel, 275/35 is the practical minimum that works fine with OEM 1LE wheels and reproductions such as the MRR M017. That said, tire dimensions and profiles vary between manufacturers even in the same sizes, so it's possible even 275/35 is too small with some tires; not being a tire expert, I obviously don't know them all.

2. 285/35 in the front is manageable, but OP needs to know that it will rub against the driver side wheel well liner at full left lock because of a bracket that pushes against the liner from its other side.

This is mostly okay for street work and definitely a no-no for track duties IMO. However, pairing this front tire size with 305/30s in the rear is not ideal, see point 3 as to why.

3. Front:rear ratios themselves don't matter, because the tune can be set up for any specific ratio, which btw is different between the SS and the SS 1LE and can also be adjusted. What does matter is how much one deviates from the stock ratio set up in ECM (if tire circumferences aren't adjusted in the tune).

Here are some examples with their aggregate F:R ratio deviations from stock (so this isn't F:R ratio but the deviation thereof from the stock ratio). Anything above ~3% here is another no-go, because it will cause ABS and Stabilitrak issues due to wheel speed variances to a degree the tune isn't expecting.

Reference (stock SS)
F 245/40/20 --> 27.7" diameter
R 275/35/20 --> 27.6" diameter

Alternative setup A (mine)
F 275/35/20 --> 27.6" diameter, deviation from stock: -0.4%
R 315/30/20 --> 27.4" diameter, deviation from stock: -0.7%
Overall deviation from stock front to rear = -0.4 - (-0.7) = +0.3%

Alternative setup B
F 285/35/20 --> 27.9" diameter, deviation from stock: +0.7%
R 315/30/20 --> 27.4" diameter, deviation from stock: -0.7%
Overall deviation from stock front to rear = +0.7 - (-0.7) = +1.4% ==> OK (although not ideal because it increases the rake from 0.1" to 0.5")

Alternative setup C (your suggestion)
F 285/35/20 --> 27.9" diameter, deviation from stock: +0.7%
R 305/30/20 --> 27.2" diameter, deviation from stock: -1.4%
Overall deviation from stock front to rear = +0.7 - (-1.4) = +2.1% ==> OK (although even less ideal because it increases the rake from 0.1" to 0.7")

Alternative setup D
F 275/30/20 --> 26.5" diameter, deviation from stock: -4.3%
R 305/30/20 --> 27.2" diameter, deviation from stock: -1.4%
Overall deviation from stock front to rear = -4.3 - (-1.4) = -2.9% ==> dodgy, it inverts and magnifies the rake from 0.1" to -0.7", but mostly because it's dangerously close to 3%, prone to intermittent CELs

and so on. Again, overall deviations around and above 3% introduce the risk of ABS and Stabilitrak malfunctions and unwanted check engine light appearances.

This is just my simplified method of calculating tire fitment with given wheel sizes (10" front, 11" rear). There are many other factors and I'm sure the ECM uses a more complex calculation, but the ~3% threshold was validated with several setups here in the forums, and I tried a bunch of combinations myself before arriving at setup A.

[SSShark]

Excellent post arpad_m! I appreciate the time that went into it. I see now that my suggestion for the 295/30 tire for the fronts would poke out too far from the rim itself. I see why GM went with the 285/30's. For me, the best setup looks like the one that I currently running since my car is now lowered. I've actually measured all four corners from the top lip of the fender to the top edge of the rim and all four measure exactly 4-1/4". I can't ask for anything more than that. Thanks to everyone for the well thought out input

[Msquared]

Originally Posted by arpad_m

1. First off, let's establish that 275/30 in the front is a no go for a 10" wheel, 275/35 is the practical minimum that works fine with OEM 1LE wheels and reproductions such as the MRR M017. That said, tire dimensions and profiles vary between manufacturers even in the same sizes, so it's possible even 275/35 is too small with some tires; not being a tire expert, I obviously don't know them all.

I may (once again) be missing something, but I don't see how this is established at all. I am many other ran 275/30/19 on 19x10 front wheels for autocross use, and I've seen plenty of 275s stretched onto 11" wheels. There are differences between different models of tires, but in general a 275/30 will fit a 10" rim width just fine. Also in may case, that was paired with a 305/30/19 rear, so the rears were 2.75% taller than the fronts. There were no issues with ABS calibration or anything like that.

[arpad_m]

Originally Posted by Msquared

I may (once again) be missing something, but I don't see how this is established at all. I am many other ran 275/30/19 on 19x10 front wheels for autocross use, and I've seen plenty of 275s stretched onto 11" wheels. There are differences between different models of tires, but in general a 275/30 will fit a 10" rim width just fine. Also in may case, that was paired with a 305/30/19 rear, so the rears were 2.75% taller than the fronts. There were no issues with ABS calibration or anything like that.

My post wasn't clear about that, sorry, I had setup D from my post in mind when I wrote it. It isn't that the tire won't fit or the car won't run, but it's suboptimal when someone wants meaty rear tires (and yes, there are so many combinations and purposes, nobody can enumerate them all...).

Also, it has 18% less sidewall than stock, even less than a 1LE with its 285/30 fronts, yet you're on a non-1LE SS, I just find it hard to like on a normal SS.

[SSShark]

We got a little side tracked here My original question was whether or not the 295/30's for the fronts, would be feasible with my current setup. Anyway, here is a better angle pic of my car. As I mentioned a couple of posts back, the 285/30's with the 305/30's seem to be the best way to go since my car is lowered almost an inch. It wouldn't make any sense for me to go with a taller front tire. I was overthinking it a little. Thanks for all the input guys

[FlukeSS]

Guess I'm going to post this again.

IF you stick to 1LE sizes on a non 1LE you have nothing to worry about. 295's should fit on a 20x10 unless you don't have a 20x10 front wheel and with the correct offsets. Now rather or not it rubs at 295 depends on offset, aspect and wheel diameter, and/or spacers. But, as an example the ZL1's have the same exact wheel and tire setup as the 1LE, except the ZL1 1LE has a wider wheel and tire size while the diameter is 19" as opposed to 20".



Now this is the ZL1 1LE and non 1LE ZL1 wheel and tire setup stock:



The difference between a ZLE vs a non 1LE SS is suspension, and brakes. If the tire size works on a ZL1 1LE then it should work on an SS 1LE without little to no modification rather small or large and it SHOULD work on an SS non 1LE just the same because there are less parts used to build the SS unlike the 1LE's. That is the rule of thumb, anything that deviates beyond those specs is where you can run into problems, may require modification, spacers, etc.


Alternative E setup (my Setup) - People say you don't have to move the wire harness on the back with 305/35, but I chose to move it regardless. The issue is the squat that is involved with the car at the drag strip on my Drag Radials. If you don't strip or track the car then feel free to take their advice and don't move the wire harness. I also have the option of going 315's now without having to worry about the wire harness. And I also can go balls deep at the strip with 305/45R17 with some hoosiers, and pray my rear end doesn't have a caniption fit. But no rubbing to worry about on the back.

285/35R20 - 20x10 ET20
305/35R20 - 20x11 ET43

1.2% deviation.

[Msquared]

Originally Posted by FlukeSS

IF you stick to 1LE sizes on a non 1LE you have nothing to worry about. 295's should fit on a 20x10 unless you don't have a 20x10 front wheel and with the correct offsets.

This is all true.

But, as an example the ZL1's have the same exact wheel and tire setup as the 1LE, except the ZL1 1LE has a wider wheel and tire size while the diameter is 19" as opposed to 20"....
The difference between a ZLE vs a non 1LE SS is suspension, and brakes. If the tire size works on a ZL1 1LE then it should work on an SS 1LE without little to no modification rather small or large and it SHOULD work on an SS non 1LE just the same because there are less parts used to build the SS unlike the 1LE's.

The ZL1 1LE (ZLE) has different fender width than the regular ZL1, SS 1LE, or SS; and it also has small black flares. These are specifically done to accommodate the 11" wheel and 305mm front rolling stock with legal fender coverage. The ZLE also has smaller-diameter front coil springs/seats and smaller strut bodies than the SS 1LE or ZL1. It is not accurate to say that anything that fits on a ZLE will also fit on a regular SS or even an SS 1LE.

[FlukeSS]

Originally Posted by Msquared

This is all true.


The ZL1 1LE (ZLE) has different fender width than the regular ZL1, SS 1LE, or SS; and it also has small black flares. These are specifically done to accommodate the 11" wheel and 305mm front rolling stock with legal fender coverage. The ZLE also has smaller-diameter front coil springs/seats and smaller strut bodies than the SS 1LE or ZL1. It is not accurate to say that anything that fits on a ZLE will also fit on a regular SS or even an SS 1LE.

Hence, 19" Wheel 325 width requires spacers, moving wire harness among other things.

I thought I read on here that people have put 305's on the front in the standard SS though. Unless I miss read it.

https://www.camaro6.com/forums/showthread.php?t=606379

https://www.camaro6.com/forums/showthread.php?t=549974

Yep even APEX confirmed it will work. But I guess negative camber is required as well. Appears my statement still holds true though.