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Lightsaber · 01-28-2015, 09:46 PM

Let's start the discussion on Z/28's aftermarket summer/winter wheel size

I'm not sure what jokes are the best to tell before we talk about size, so let's just get straight down to business.

A. Understanding the OEM size

6th generation Camaro Z/28's stock size:

Wheels:
Front - 19x11 5x120 +11mm
Rear - 19x11.5 5x120 +26mm

Tyres:
Front - 305/30ZR19
Rear - 305/30ZR19 (same as front)

These wide rubbers are obviously to help Z/28 corner, brake, and put down power better on a race track. Now, do you know why the Camaro Team chooses wheels of different width front and back? Here is a clue:

This slide is taken from the Z/28's Tech Background presentation (source: Z/28 Reviews). Mark Stielow, the programme's performance manager who presented that part, claimed that the "wheels are staggered [...] to improve rear tire handling at the limit." We know that when we use a narrower tyre for a wheel to have it installed in a stretched fashion, the sidewalls tend to feel as if they are stiffer. I guess that's what Stielow meant.

There are two slight problems associated with this (visually indistinguishable front and rear wheels with different width and offset):
1) A clueless owner/mechanic may put the front wheels on the rear, or the rear wheels on the front;
2) We can no longer equalize front and rear tyre wear by an easy tyre rotation.

For (1), an ad hoc solution can be simply marking the front and rear wheels with the word "front" and "rear." For (2), we will either have to change rear tyres more often than front ones, or take the hassle to dismount the tyres, cross-rotated them, mount them to correspondent wheels, and have them re-balanced.

Nevertheless, do ya wonder why didn't the Camaro Team simply use 19x11.5 +26mm wheels front and back, and put a pair of 15mm wheel spacers on the front? Wouldn't that also improve front tyre "handling at the limit?"

So there must be hidden or non-existent reasons that answer the following question:
a) Does narrowing the front wheels by 0.5 inches really save some significant weight?
b) If it has to be 19x11 on the front, why no 295/30ZR19 instead of 305/30ZR19 tyres?
c) Why use different offset front and rear wheels, instead of modifying front wheels hub or installing wheel spacers?

For now, I'd like just to assume that the Camaro Team was originally using ZL1 rear wheel and tyre combo (11" wheels and 305 tyres) front and back, then the test driver didn't like the rear sidewalls being soft, so they came up with some quick and dirty fix. That fix was to increase the rear wheel width by 0.5 inches. Hence this is where the nonsensical wheel sizes come from.

B. Coming up with aftermarket summer wheel size

Based on what we understand from the above discussion, I think we can simply order the following size for the summer:

Front - 19x11.5 5x120 +26mm; 15mm wheel spacers
Rear - 19x11.5 5x120 +26mm (same as front)

while retaining the OEM 305/30ZR19 size for the tyres. This is a good size still and all. You can find quite a range of choices to accommodate track, autocross, and street use. Example: Tire Search Result: Camaro Z/28

By having the same wheels, we can rotate the tyres easily and order a set of four tyres once a while, instead of ordering a set of two frequently.

C. Coming up with aftermarket winter wheel size

Aside from the less-enlightened drivers who drive to endanger during the snow days, driving a well-engineered rear wheel drive vehicle in the snow is plenty of fun! The rule of thumb for performance winter tyres is that 9" width for the wheels is about the limit. Tyre manufacturers usually don't make any winter tyres wider than that.

I think we can start like:

Front - 19x9 5x120 +26mm; 15mm wheel spacers
Rear - 19x9 5x120 +26mm (same as front)

These wheels go with 265/35R19 tyres, which make it possible for you to shop for winter tyres (example: Tire Search Result: Camaro Z/28, winter). At this size, you will have +0.4% diameter comparing to 305/30ZR19. You can also go for 275/35R19 size if winter tyres of such size is available and you like the beefy fashion. Regarding whether to go for 35 sidewalls and 30 sidewalls, here is a list of diameter change according to my calculation:

305/30ZR19: 0.00% (Stock)
265/35R19: +0.4% (35 sidewall is preferred for 265 width)
265/30R19: -3.4%
275/35R19: +1.5% (35 sidewall is preferred for 275 width)
275/30R19: -2.7%

Instead of 15mm wheel spacers on the front, you can also get 30mm spacers on the front and 15mm spacers on the rear if you don't like the "tucked-in" look of winter wheels. Nevertheless, be mindful to get (aluminium, no plastic!) hubcentric rings or spacers with the hubcentric collar that fits Camaro. I believe the factory hub size is 67mm. Example:

Front - 19x9 5x120 +26mm; 30mm wheel spacers
Rear - 19x9 5x120 +26mm; 15mm wheel spacers (same as front)

or:

Front - 19x9 5x120 +11mm; 15mm wheel spacers
Rear - 19x9 5x120 +11mm (same as front)

D. Your thoughts

Have you been thinking about getting aftermarket wheels? Rotating the tyres on your Z/28? Do the above discussion make any sense to you? Tell us your thoughts!

Cheers!

01-28-2015, 09:46 PM	#1
Lightsaber Drives: conscientiously Join Date: Jan 2015 Location: Canada Posts: 61 View My Garage	Let's start the discussion on Z/28's aftermarket summer/winter wheel size Let's start the discussion on Z/28's aftermarket summer/winter wheel size I'm not sure what jokes are the best to tell before we talk about size, so let's just get straight down to business. A. Understanding the OEM size 6th generation Camaro Z/28's stock size: Wheels: Front - 19x11 5x120 +11mm Rear - 19x11.5 5x120 +26mm Tyres: Front - 305/30ZR19 Rear - 305/30ZR19 (same as front) These wide rubbers are obviously to help Z/28 corner, brake, and put down power better on a race track. Now, do you know why the Camaro Team chooses wheels of different width front and back? Here is a clue: This slide is taken from the Z/28's Tech Background presentation (source: Z/28 Reviews). Mark Stielow, the programme's performance manager who presented that part, claimed that the "wheels are staggered [...] to improve rear tire handling at the limit." We know that when we use a narrower tyre for a wheel to have it installed in a stretched fashion, the sidewalls tend to feel as if they are stiffer. I guess that's what Stielow meant. There are two slight problems associated with this (visually indistinguishable front and rear wheels with different width and offset): 1) A clueless owner/mechanic may put the front wheels on the rear, or the rear wheels on the front; 2) We can no longer equalize front and rear tyre wear by an easy tyre rotation. For (1), an ad hoc solution can be simply marking the front and rear wheels with the word "front" and "rear." For (2), we will either have to change rear tyres more often than front ones, or take the hassle to dismount the tyres, cross-rotated them, mount them to correspondent wheels, and have them re-balanced. Nevertheless, do ya wonder why didn't the Camaro Team simply use 19x11.5 +26mm wheels front and back, and put a pair of 15mm wheel spacers on the front? Wouldn't that also improve front tyre "handling at the limit?" So there must be hidden or non-existent reasons that answer the following question: a) Does narrowing the front wheels by 0.5 inches really save some significant weight? b) If it has to be 19x11 on the front, why no 295/30ZR19 instead of 305/30ZR19 tyres? c) Why use different offset front and rear wheels, instead of modifying front wheels hub or installing wheel spacers? For now, I'd like just to assume that the Camaro Team was originally using ZL1 rear wheel and tyre combo (11" wheels and 305 tyres) front and back, then the test driver didn't like the rear sidewalls being soft, so they came up with some quick and dirty fix. That fix was to increase the rear wheel width by 0.5 inches. Hence this is where the nonsensical wheel sizes come from. B. Coming up with aftermarket summer wheel size Based on what we understand from the above discussion, I think we can simply order the following size for the summer: Front - 19x11.5 5x120 +26mm; 15mm wheel spacers Rear - 19x11.5 5x120 +26mm (same as front) while retaining the OEM 305/30ZR19 size for the tyres. This is a good size still and all. You can find quite a range of choices to accommodate track, autocross, and street use. Example: Tire Search Result: Camaro Z/28 By having the same wheels, we can rotate the tyres easily and order a set of four tyres once a while, instead of ordering a set of two frequently. C. Coming up with aftermarket winter wheel size Aside from the less-enlightened drivers who drive to endanger during the snow days, driving a well-engineered rear wheel drive vehicle in the snow is plenty of fun! The rule of thumb for performance winter tyres is that 9" width for the wheels is about the limit. Tyre manufacturers usually don't make any winter tyres wider than that. I think we can start like: Front - 19x9 5x120 +26mm; 15mm wheel spacers Rear - 19x9 5x120 +26mm (same as front) These wheels go with 265/35R19 tyres, which make it possible for you to shop for winter tyres (example: Tire Search Result: Camaro Z/28, winter). At this size, you will have +0.4% diameter comparing to 305/30ZR19. You can also go for 275/35R19 size if winter tyres of such size is available and you like the beefy fashion. Regarding whether to go for 35 sidewalls and 30 sidewalls, here is a list of diameter change according to my calculation: 305/30ZR19: 0.00% (Stock) 265/35R19: +0.4% (35 sidewall is preferred for 265 width) 265/30R19: -3.4% 275/35R19: +1.5% (35 sidewall is preferred for 275 width) 275/30R19: -2.7% Instead of 15mm wheel spacers on the front, you can also get 30mm spacers on the front and 15mm spacers on the rear if you don't like the "tucked-in" look of winter wheels. Nevertheless, be mindful to get (aluminium, no plastic!) hubcentric rings or spacers with the hubcentric collar that fits Camaro. I believe the factory hub size is 67mm. Example: Front - 19x9 5x120 +26mm; 30mm wheel spacers Rear - 19x9 5x120 +26mm; 15mm wheel spacers (same as front) or: Front - 19x9 5x120 +11mm; 15mm wheel spacers Rear - 19x9 5x120 +11mm (same as front) D. Your thoughts Have you been thinking about getting aftermarket wheels? Rotating the tyres on your Z/28? Do the above discussion make any sense to you? Tell us your thoughts! Cheers!