TIRE GURUS - max rim width in 19" for SS Camaro

[Zombie killer]

I need some expertise from my fellow Camaro brethren related to tire fitment in an somewhat urgent time by tomorrow morning. It seems the newly released pending tire allowance for the STP class in SCCA rules is being changed to allow a max rim size of 11' and a max tire size of 315s (was 10" rims size and 285s on the tire). I already ordered a new set of 19" rims during the Black Friday sales but I am considering a quick change to 19x11" rims if the rims will fit a SS Camaro fitted with 305/30/19s. The 305 size is currently the widest tire size that the RE71s come in for the 19 rims.

My question is has anybody actually run (or really knows for sure) the Forgestar F14s in 19x11 and run a 305 or wider tire without fitment issues? I was getting the et30 square setup for the 19x10 but might have to change the et for the 305s. Any suggestions? I am currently running 1" lowering springs and camber plates up top on stock SS OEM struts. I plan to switch over to the 1LE strut package later this month but I don't think it would change anything related to tire fitment.

Any advice on the 19x11 with 305s is appreciated.

[Norm Peterson]

You should probably investigate the Z/28 wheel specs, as I think they're 19x11 up front (but I don't offhand know what the offset is). Hope it's not too late.


Norm

[G701LE]

I am interested in this also. But I want 18's and am not lowered

[Zombie killer]

Originally Posted by Norm Peterson

You should probably investigate the Z/28 wheel specs, as I think they're 19x11 up front (but I don't offhand know what the offset is). Hope it's not too late.


Norm

I researched c5 quite a bit it before I posted but couldn't find much on the 19x11 on an SS. The Z28 fronts are 19x11 et 11 but they do poke out. They run 305s so that's perfect but I am not keen on the offset. Was hoping to find someone who has run the 19x11 with more tuck like an et 25 offset. My retailer put in a hold request to the manufacturer this weekend so maybe I can buy a few days and talk with Forgestar directly and see what they say.

[Norm Peterson]

11" is three whole inches wider than what came on the front of your car stock, and you can only push so much of that to the back side. Once the wheel's inboard flange gets within maybe 3mm of the strut, whatever is left from that 3" increase has to go on the outside. But the tire sidewall bulge may require more than 3mm wheel clearance, or you may become limited on tire size to something less than 305/xx.

If you make enough careful measurements for the wheels and tires that you do have, it is possible to get a pretty good idea how much more width can be added on the inside. Outside is simpler. When dropping down in wheel diameter, give yourself a little extra room, because the struts slope outward as they drop down closer to the axle. A 15° strut angle "steals" a little over 1/8" from your measured strut clearance at the wheel, going from 20" wheels down to 19's. Eighth-inches matter.

Ultimately it comes down to how serious you're going to be about things like steering response and precision vs the currently popular "flushness" look. My own personal take on a little 'poke' is that those who know what transient handling is and that you're chasing it will understand, and that the opinions of those who don't shouldn't matter. You yourself know from the get-go that it's all about function and performance.


Over the years, all of the cars that I seriously modified eventually ended up with front wheels at least 2.5" wider than what they came with stock, and at least 1.5" wider than the widest option ever factory-fitted to the same basic chassis. At this point, I think if I limited my choices for the really serious driving to no wider than "flush", I'd be leaving too much on the table. Note that this didn't rub . . . 18x11 with 285/35 MPSS.






Every last bit of inside room is being used (about 0.043" clearances)






Norm

[Norm Peterson]

Originally Posted by G701LE

I am interested in this also. But I want 18's and am not lowered

18's will have ~1/8" less strut side clearance than 19's at any given offset. Meaning you'd need offset that's 3 or 4 mm more positive than the minimum offset that ends up working with 19x11's.


Norm

[Zombie killer]

Well I did look closely at what I have now on my current setup. I can run a pencil between the tire and strut so that's about 1/4" gap I suppose. With the negative camber I am running , I could live with another 1" of run out to the outside and not be wider than the top of my fenders. I might could live with a little bit more poke as these rims would just be weekend autoX tires but not my preferred look. I would run flares but it seems that SCCA rules feel that it would give an unfair aero advantage to me. Smh on that one.

[JusticePete]

We have run 11.5 up front with 3 degrees of negative camber which tucks the top in nicely.

[Zombie killer]

Thanks Pete. Do you happen to recollect what the offset you ran was?

I can have my new rims made to a custom offset and I was leaning towards a rim setup that I can rotate. I am ok with ditching the front spacers if I can get the proper offset and still rotate my tires. Measuring my tracking width with toe plates... my front and rear widths are exact, but with good grip up front and the oversteer effects I experience, maybe a slightly narrow tracking width up front wouldnt hurt... and maybe help the oversteer? Or do you think the 1" difference in front to rear tracking width is too small to even make a noticeable difference.

FYI- My current rim with the 35 et requires a 5 mm front spacer because the tire would rub slightly during deflection from best I could tell. I was leaning towards a 30 et in the 19x11 rim and then having the option of using the 5 mm spacer up front (or not) to see how both options would work on the course.

[JusticePete]

Originally Posted by Zombie killer

Thanks Pete. Do you happen to recollect what the offset you ran was?

I can have my new rims made to a custom offset and I was leaning towards a rim setup that I can rotate. I am ok with ditching the front spacers if I can get the proper offset and still rotate my tires. Measuring my tracking width with toe plates... my front and rear widths are exact, but with good grip up front and the oversteer effects I experience, maybe a slightly narrow tracking width up front wouldnt hurt... and maybe help the oversteer? Or do you think the 1" difference in front to rear tracking width is too small to even make a noticeable difference.

FYI- My current rim with the 35 et requires a 5 mm front spacer because the tire would rub slightly during deflection from best I could tell. I was leaning towards a 30 et in the 19x11 rim and then having the option of using the 5 mm spacer up front (or not) to see how both options would work on the course.

My offsets are with Forgeline and different size barrels. I would need to know the barrel sizes you are using to convert the offsets.