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19x10.5 or 11 with 305/35/r19 on all 4

So I have spent hours reading and searching but haven't found definitive answers based off real experience. Does anyone know if I can fit 305/35/19s on all 4 with either 19x10.5 or 11 wheels and what offsets I would need? Trying to stay square for rotation. Found a screaming deal on bulk 305/35/19s and would like to make it work. 2011 gt. I would like to run the adjustable frpp track suspesion with camber plates. (Or what ever suspension combo i need to make it work) 80% track use and 20% daily drive. Thanks so much in advance for sharing your knowledge.
 
If these are for the track is there a reason you’re not using 18” wheels? Go 11” wide regardless of the diameter.
 

TymeSlayer

Tramps like us, Baby we were born to run...
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I thought the only real advantage to running 18s vs. 19s is the selection of tires you can run and some rotation mass weight. I can find rubber that suits my driving level so I've stuck with the 19s. I'm in the process of either going with some 19x11 inch Forgestar or possibly Apex wheels with 305/30/19 PS 4S tires but if there are other compelling reasons to switch to 18s, I'm all ears. These would be my third set of wheels and would be used for my HPDE track days.
 

Norm Peterson

Corner Barstool Sitter
939
709
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a few miles east of Philly
I thought the only real advantage to running 18s vs. 19s is the selection of tires you can run and some rotation mass weight. I can find rubber that suits my driving level so I've stuck with the 19s. I'm in the process of either going with some 19x11 inch Forgestar or possibly Apex wheels with 305/30/19 PS 4S tires but if there are other compelling reasons to switch to 18s, I'm all ears. These would be my third set of wheels and would be used for my HPDE track days.
For the same section width and profile tires, 18's will lower your car's CG (body, wheels, tires, axle, and all) by 1/2" . . . without adversely affecting front strut or axle roll steer geometry or materially affecting anti-squat. Small, but virtually all 'win'.

The only catch I see at this point is that the PS4S doesn't come 305 wide in 18" yet (per Tire Rack, Michelin has recently released quite a few more 18" sizes and even a few 17's in PS4S).


Out of 10.5's or 11's . . . go with 11's (FWIW, my sig picture is showing 285/35's on 18x11's).


Norm
 
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4,540
5,038
Well, kind of, depending on the aspect ratio, you should be able to find 19s as "short " as a lot of 18s, the 19s will have a bigger footprint..you need to really think it through. The big advantage to 18s is that there is virtually a metric crapload of used race tires in many sizes available, but..if ultimate performance is your goal, you may find something in the 19s, if you want to have fun then prolly 18s are a better choice.
 
I came across 5 sets of 305/35/19 pilot sport track tires all 75-80% tread for silly cheap. So I wanted to figure out a way yo make them work since that will last me a while.
 
They are gt350 take offs from a driving school. Manufacture dates of 2015 and 2016. Has anyone ran the 19x11 +50 SVE S350 wheels on the front with say, 18mm spacers?
 

JDee

Ancient Racer
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It's my understanding that you'd need more like a 22mm spacer and at that you'll have maybe 3-4mm strut clearance. Check the section width of those tires, they may actually be 315mm.

I just finished a 2 day intensive course on this issue and that was the concensus.

Right @RES_22?:D:p:)

BTW, I have the LMR SVE S350 10" and 11" wheels and LMR were very much against using the 11" wheel on the front when I went to buy a set of 4 X 11" wheels. Spacers aren't legal on the highway where I live so I'm sticking with the 10's and 11's since I still drive the car to the track.
 
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Norm Peterson

Corner Barstool Sitter
939
709
Exp. Type
HPDE
Exp. Level
5-10 Years
a few miles east of Philly
On the 11" wide measuring rims, 2.5 mm narrower (312.5 compared to 315) buys you about 1.25 mm more room. So, theoretically, the wheels could have 1.25 mm less offset and still work. But I don't know how much tolerance there is on that 312.5 mm section width, only that there must be some.

Every inch that a wheel is narrower than the 'measuring' width for any given tire size brings the section width of that size down by about 10 mm (5 mm per side). So a 312.5 mm wide tire on 11's ends up being about 302.5 mm wide on 10's. Tread width and load capacity @ inflation remain essentially unchanged.


LMR is no different than just about every other aftermarket wheel source - their recommendations (insistences?) are going to err on the side of caution for a number of reasons. In this case, caution nearly always means narrower.


Norm
 

JDee

Ancient Racer
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halfway between Mosport and Shannonville
So the calculation to get the distance from hub of wheel face to outside of tire sidewall is the section width/2 + the effective offset (which is offset minus spacer). So 312.5/2=156.25 + (50-18=32) = 188.25 distance . If you build in a safety factor and take the SW at 315 it's 189.5.

@RES_22 has 305/30/19 PSC2 setup with the N4S wheels +50 offset and a 22 mm spacer (28mm effective offset) and he has 4-5mm clearance at the strut with camber plates, aftermarket shocks/springs, bushings, bars, etc, hasn't had issues yet. His number using the above calculation is 186. On his car that 18mm spacer clearly would only give 2-3mm clearance.

I have 8mm measured clearance on my stock suspension 285/35/19 on 10" +40 S350 wheel. Based on my stock car and my measured clearance the maximum distance in there is 193mm but every car is going to be very different.

I am a newbie on this so I stand to be corrected, but that 18mm spacer seems tight to me!:)
 

JDee

Ancient Racer
1,465
1,446
Exp. Type
W2W Racing
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20+ Years
halfway between Mosport and Shannonville
Every inch that a wheel is narrower than the 'measuring' width for any given tire size brings the section width of that size down by about 10 mm (5 mm per side). So a 312.5 mm wide tire on 11's ends up being about 302.5 mm wide on 10's. Tread width and load capacity @ inflation remain essentially unchanged.

Norm

That's very interesting, I was under the impression from reading stuff on the weeb that it had the opposite effect due to sidewall bulge from the narrower rim. Good to know. Does any tire measurement go up in that scenario? Does the tread want to bulge or anything weird? Looking at running a 295/30/19 on a 10" wheel +35 offset wheel to replace a 285/35/19 on 10" +40 offset wheel, the measuring width for that tire is 10.5" SW is 11.9" or 302 mm. I'm expecting not to have clearance issues with no suspension changes but thought the bulge might cost a few mm of SW? I found a picture of that tire on a 10" and there was no sign of sidewall bulge at all which surprised me.
 

Norm Peterson

Corner Barstool Sitter
939
709
Exp. Type
HPDE
Exp. Level
5-10 Years
a few miles east of Philly
The sidewall bulge looks bigger on a narrower wheel because the wheel is getting narrower faster than the tire is, and the only reference you have when you "eyeball" the bulge is how far out past the wheel flange it goes. You don't see that the rim is narrower. If you want to get really picky, tire diameter does increase minutely on narrower than measuring-width wheels (by something like 5% of the difference between actual wheel width and measuring width for the tire size).

I doubt that contact patch width varies enough to matter, particularly if you find yourself adjusting inflation pressure downward to minimize center-tread wear. In any event, the actual tire contact pressure against the pavement is far from being uniform (like any of the weight divided by inflation pressure calculations assumes is the case). The very edges of the tread are going to be lightly loaded (because the shape of tire shoulders curves upward away from the pavement) even when the outermost rib is generally more heavily loaded than the average over the entire contact patch. Unit pressures against the pavement within the contact patch can easily vary from some minimum number to 50% higher. It might look something like this ↓↓↓

Tire Contact Patch Pressure Distribution.JPG

Wheel width is defined between the bead seats, which are inside the flanges of the wheel. Typically, wheel flanges run about half an inch, so (as a made-up example) a tire that is claimed to be 11.2" wide when mounted on a 10" wide wheel would only have 0.1" of apparent bulge (what you see) because the outside of the wheel is ~11" wide. But relative to the 10" wheel's bead seat width, it's still 0.6"/side.

You can see that on the narrower wheel, the tire is narrower. But its sidewall bulges out more past its rim and is more sharply curved. This is my own spreadsheet which uses an approximate curve-fit for the sidewall shape. It's not perfect, but it is more useful than any of the online-available plots that ignore section width variation with wheel width. 255/45-18 on 8" (min-recommended) and 9.5" (max-recommended) wheels, if the text in the picture is too small or too obtuse.

255-45-18 on 8 and 95 wide wheels web.jpg


Norm
 
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Just going to bring this back up.
Boss 302, P springs,305/30/19 PS4,ET 52 Apex 19x11.
I use a 20mm front spacer and no rear.
Front fits great, rear is a slight problem though as the rim protector
on the PS4 contacts the bump stop bracket at full droop.
Not extremely hard but touching.This is with the rear centered at ride ht.
 

Mad Hatter

Gotta go Faster
4,412
3,085
Santiago, Chile
320/650-18 tires on Apex 18x11 wheels... Fits fine with space to spare with 15mm spacer (cortex setup).. Friend has a S550 with LMR SVE 350S 19x11 wheels with square 305/30-19s but needed a 25mm spacer with Ford racing setup..
 

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