Z51 wheel offset questions

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Aug 17, 2019 | 09:11 PM

stephen1254

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Z51 wheel offset questions

I understand the stock wheel offsets are 56 MM front, and 79 mm rear. Am I correct to assume a smaller offset number pushes the wheel further out towards the fender? A 50 MM offset front would be a 6 MM wider track on both sides?

Second question. Assuming stock tire sizes, how far can that offset number be reduced before running into issues with interference from the fenders?

Aug 18, 2019 | 11:13 PM

Kracka

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From: Fulshear, TX

Stock wheels are a negative offset design. Less negative offset would mean they stick out further.

Aug 19, 2019 | 03:32 AM

X25

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From: Sammamish, WA

Quote:

Originally Posted by stephen1254

Yep, +50 offset would mean wheels would be pushed out by 6mm on both sides, so 12mm wider track up front. Back when I had a Z51, my aggressive track wheels were set at 18x10.5" +51. So 5mm pushed out, but 25.4mm (1") wider on each side of the wheel (2" wider total), so 20mm closer to inside. At that level, at full lock, it would rub on the brake ducting, etc. For roadcourse track use, I'd recommend it. For street, I'd keep it at least 5mm "less" aggressive, which would mean 10" wide max for comfortable fit up front.

Quote:

Originally Posted by Kracka

Stock wheels are a negative offset design. Less negative offset would mean they stick out further.

They're not negative.

Last edited by X25; Aug 19, 2019 at 03:34 AM.

Aug 19, 2019 | 12:18 PM

subieworx

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Keep in mind that much of tire clearance to the fender comes down to tire diameter. The larger you go with tires the less room you will have to push the tires out towards the fender. I run 19x9.5 +56 with a 265 35 19 in the front and a 20x11 +76 in the rear with a 305 30 20. Both of these tires are a bit taller than stock which leaves me less room to make them fit. I had to trim my fenders and run about -2* of camber in the rear to get them to clear with the factory bolts lowered all the way.

Aug 19, 2019 | 12:22 PM

subieworx

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[QUOTE=X25;1599997095]Yep, +50 offset would mean wheels would be pushed out by 6mm on both sides, so 12mm wider track up front. Back when I had a Z51, my aggressive track wheels were set at 18x10.5" +51.
/QUOTE]

What size tires did you run on these?

Aug 19, 2019 | 12:26 PM

stephen1254

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Thanks for the responses. I'm looking at stock wheel and tire sizes, just slightly different offset. I've read a little about the effect of the different offset on scrub radius, but nothing definitive on how it would affect this car.

Aug 19, 2019 | 12:29 PM

X25

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From: Sammamish, WA

I initially ran 275/35/18 front tires, but later realized that there's so much more traction available with 315/30/18 tires. I had various sets (18/18, 18/19, etc). I've run them with 335/30/18 or 325/30/19 rear tires. Please note, these sizes add so much more traction that you'd need at least a good set of sway bars to run them, or else the car starts feeling like a boat : )

Last edited by X25; Aug 19, 2019 at 12:30 PM.