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Old 05-18-2019, 08:59 AM   #1
vtirocz

 
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Thoughts on this 285 square setup using stock SS wheels

I'm considering the following setup using stock SS rear wheels and SS 1LE front tires at all 4 corners. Anyone run something similar on track (road course) or autocross? How much would I be leaving on the table compared to just going with the SS 1LE wheel/tire combo front and rear (285/305)? I'm interested in feedback from folks running a square setup if the balance or handling was compromised. I like the stock SS split spoke machined face gray painted wheels, but just wanted a more aggressive setup (closer to SS 1LE).

Front/Rear:
  • SS rear wheels: 20X9.5; 39m offset
  • SS 1LE front tires: 285/30/20
  • 12mm hubcentric, wheel centric spacers (needed for rear SS wheel to fit in front): http://www.motorsport-tech.com

My main concerns would be the suspension tuned for the staggered setup and deviating from that. The other concern is the rev/mile difference (~3%) if there's no way to correct the speedometer.
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Old 05-18-2019, 01:00 PM   #2
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Switching to wider fronts like that will give the car a natural tenancy to oversteer rather than the nearly neutral characteristics it has with the OE tires and track alignment. There's a couple of ways to compensate for that with suspension component and/or alignment changes, though.

I wouldn't be concerned about the speedo that much. 3% is ~2 mph at highway speeds. There is a way to correct through a tune, but not worth going through that whole process for only a speedo change when it's not that far off IMO.

Lastly, with a front spacer that big, you're going to want longer wheel studs since the OE ones won't have enough thread engagement. I'd assume ARP makes some that are 12-ish mm longer, but I believe the wheel studs from the Silverado are also the same material grade as the camaro but longer.

Personally, if it's feasible for you, I'd recommend going with a separate set of 19" wheels and tires for track use and keep your current OE wheels with less aggressive tires for street and wet track use. 19" 305 square setup is pretty easily accomplished, you'll have a better selection of tires to choose from in that size for the track, and you don't have to make any sacrifices for driving on the street.
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Old 05-18-2019, 03:51 PM   #3
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If you can fit 285, why not. That's my daily setup.. going on 11,000+ miles.
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Old 05-19-2019, 09:57 AM   #4
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Quote:
Originally Posted by Alpha1BC View Post
Switching to wider fronts like that will give the car a natural tenancy to oversteer rather than the nearly neutral characteristics it has with the OE tires and track alignment. There's a couple of ways to compensate for that with suspension component and/or alignment changes, though.

I wouldn't be concerned about the speedo that much. 3% is ~2 mph at highway speeds. There is a way to correct through a tune, but not worth going through that whole process for only a speedo change when it's not that far off IMO.

Lastly, with a front spacer that big, you're going to want longer wheel studs since the OE ones won't have enough thread engagement. I'd assume ARP makes some that are 12-ish mm longer, but I believe the wheel studs from the Silverado are also the same material grade as the camaro but longer.

Personally, if it's feasible for you, I'd recommend going with a separate set of 19" wheels and tires for track use and keep your current OE wheels with less aggressive tires for street and wet track use. 19" 305 square setup is pretty easily accomplished, you'll have a better selection of tires to choose from in that size for the track, and you don't have to make any sacrifices for driving on the street.
Thanks for that feedback! One point I'd make is that the general consensus from review is that the SS (non-1LE) is set up to understeer (SS 1LE is probably closer to neutral). For instance, Randy Pobst gave it a 3.5 - 4 (on a scale of 10) for tendency to understeer. The square setup would directionally help with this, but not sure if it would go to far.

See 9:14 in this video for his comments:


Regarding the 12mm spacers, I'd definitely replace the studs and would plan to use them both front and rear in order to push all wheels out 12mm compared to the stock setup. It's only needed in the front though for clearance.

Thanks for the recommendation on a 19" setup. I will look into that.

Quote:
Originally Posted by Vtor_ZL1 View Post
If you can fit 285, why not. That's my daily setup.. going on 11,000+ miles.
Thanks. According to Goodyear, the 285s fit on a 9.5" wide wheel. Based on the table calculations above, they should fit within the window of current tire size offerings on the SS.
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Last edited by vtirocz; 05-19-2019 at 12:37 PM.
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Old 05-19-2019, 03:06 PM   #5
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Quote:
Originally Posted by vtirocz View Post
Thanks for that feedback! One point I'd make is that the general consensus from review is that the SS (non-1LE) is set up to understeer (SS 1LE is probably closer to neutral). For instance, Randy Pobst gave it a 3.5 - 4 (on a scale of 10) for tendency to understeer. The square setup would directionally help with this, but not sure if it would go to far.
Right, but keep in mind most publicized reviews are likely done with the factory alignment, not necessarily the track alignment. Both cars have an understeer tendency out of the box. The track alignment (which you'll definitely want to keep from destroying the outside shoulders of your tires on the track) makes the camber much more negative in the front resulting in a nearly neutral setup on both. Not that camber is the only factor, but it's definitely significant. Take that and throw more capable front tires on and you get more of an oversteer tendency if you don't change anything else. There's always more alignment or spring/roll bar mods that can be done to help balance it back out. Not trying to say you'll make the car undriveable or anything like that if you put a square setup on your car, just making the point that you can do some other stuff to get more out of the package if you're able to hold the car at its limit.

Quote:
Originally Posted by vtirocz View Post
Regarding the 12mm spacers, I'd definitely replace the studs and would plan to use them both front and rear in order to push all wheels out 12mm compared to the stock setup. It's only needed in the front though for clearance.
I wouldn't put the spacers in the rear. The spacers up front will make the rear wheels closer to the original offset of the front tires, and therefore keep the center of the contact patch (and front trackwidth) the same as it is OE. Spacers on the rear will slightly increase the rear trackwidth and will impact how the car handles. Will also change loading for your wheel bearings because the contact patch is moved further outboard, and compounded with stickier tires could cause bearings to wear faster.
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Old 05-20-2019, 04:02 AM   #6
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Quote:
Originally Posted by Alpha1BC View Post
Right, but keep in mind most publicized reviews are likely done with the factory alignment, not necessarily the track alignment. Both cars have an understeer tendency out of the box. The track alignment (which you'll definitely want to keep from destroying the outside shoulders of your tires on the track) makes the camber much more negative in the front resulting in a nearly neutral setup on both. Not that camber is the only factor, but it's definitely significant. Take that and throw more capable front tires on and you get more of an oversteer tendency if you don't change anything else. There's always more alignment or spring/roll bar mods that can be done to help balance it back out. Not trying to say you'll make the car undriveable or anything like that if you put a square setup on your car, just making the point that you can do some other stuff to get more out of the package if you're able to hold the car at its limit.
You have a good point with factory alignment vs track alignment. My car's 'before any adjustment' camber settings were -1.3º and -1.1º on front, and -1.2º and -1.1º on rear. Compare those to the track alignment specs (regular SS here) of -2.0º on front and -1.25º on rear, and you can see that just doing the track alignment alone will help reduce the tendency to understeer.
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Old 05-20-2019, 12:45 PM   #7
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I run a square set up for my autocross set up and my trackday set up and the car still favors oversteer even with the rear sway bar on the softest setting.

Current autocross set up
19x11 with 305 RE-71r's
19x12 with 305 RE-71r's

Current trackday set up
19x10 with 325's (cheap set of summer coopers)
19x11 with 325's
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Old 05-20-2019, 01:07 PM   #8
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I found the stock setup to be understeer biased. Went to 19x10 with 275s square and found the car to be neutral. Went through a set of rs3s, Star specs, and 595rsrr (terrible tire). Will continue with the square setup.

I also have MRC.

Last edited by TheMaGikDucK; 05-20-2019 at 01:08 PM. Reason: Autocorrect
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Old 05-20-2019, 07:37 PM   #9
vtirocz

 
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Quote:
Originally Posted by Alpha1BC View Post
Right, but keep in mind most publicized reviews are likely done with the factory alignment, not necessarily the track alignment. Both cars have an understeer tendency out of the box. The track alignment (which you'll definitely want to keep from destroying the outside shoulders of your tires on the track) makes the camber much more negative in the front resulting in a nearly neutral setup on both. Not that camber is the only factor, but it's definitely significant. Take that and throw more capable front tires on and you get more of an oversteer tendency if you don't change anything else. There's always more alignment or spring/roll bar mods that can be done to help balance it back out. Not trying to say you'll make the car undriveable or anything like that if you put a square setup on your car, just making the point that you can do some other stuff to get more out of the package if you're able to hold the car at its limit.



I wouldn't put the spacers in the rear. The spacers up front will make the rear wheels closer to the original offset of the front tires, and therefore keep the center of the contact patch (and front trackwidth) the same as it is OE. Spacers on the rear will slightly increase the rear trackwidth and will impact how the car handles. Will also change loading for your wheel bearings because the contact patch is moved further outboard, and compounded with stickier tires could cause bearings to wear faster.
Thanks for that feedback! I put higher importance on more closely matching the SS 1LE wheel outer edge's "distance outboard of hub" rather than centerline's "distance (inboard) of hub". Both calculations are shown in green in the table below. My assumption is the outer edge of the tire takes on most of the load so you'd want that to better match the more aggressive setup (SS 1LE in this case). It sounds like you disagree with that approach though.
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Old 05-20-2019, 07:38 PM   #10
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Quote:
Originally Posted by TheMaGikDucK View Post
I found the stock setup to be understeer biased. Went to 19x10 with 275s square and found the car to be neutral. Went through a set of rs3s, Star specs, and 595rsrr (terrible tire). Will continue with the square setup.

I also have MRC.
Thanks! Just to clarify, did you have the track alignment or street alignment?
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