Backspacing/ tire size - The 1947 - Present Chevrolet & GMC Truck Message Board Network

David67 · 05-23-2010, 02:55 PM

Hey guys,

I'm hoping to be able to order my wheels/tires today so I can install the 5 lug axles that will be coming in this week. I'm trying to finalize the measurements so that I can be sure that everything will fit.

I've decided on the American Racing TTII's, 18x9.5 in the rear and 17x8 in the front. Between the hub and the bed (stepside), there is 6 in. of clearance. Between the hub and the outmost part of the fender, there is 7.25 in. with 6.5 to the inmost part of the fender lip.

The two main backspacing options that I'm looking at for this rear size wheel are 4.31 and 4.54. The main thing I am concerned about is the tire clearance. Does anyone know how much further a 275 or 285 tire would stick out on each side of the wheel?

Also, can anyone help with determining the tire height or what they think would look the best (with a 4/6 drop)? For instance, if a tire is 275/50/18, how is the 50 determined?

Thanks!

David67 · 05-23-2010, 04:22 PM

Alright I've figured out that the aspect ratio(the 50) is a percentage of the tire width. What I'm set on right now just happens to be 275/50/18...it was pretty much a guess to begin with but that's what I ended up calculating. The overall height of the wheel/tire will be the same if not slightly more than what you can see in my "Rear almost finished" thread, which might show up just above this one

stevencvn72 · 05-23-2010, 05:00 PM

Not too sure what you're asking here but the first set of numbers ie: 275 is the distance from bead to bead or where the tire touches the rim on the outside of the wheel to where the tire touches the rim on the inside of the wheel. The second set of numbers ie: 50 is what percentage of the first number is sidewall. In this case 50%. Anyways, ultimately I would think you want the overall tire diameter to be equal in the front and back. A good tool is this:
http://www.miata.net/garage/tirecalc.html

It's java run and I've used it a lot...and no. I don't nor would I ever drive a miata. Good luck!

David67 · 05-23-2010, 05:07 PM

Stevencvn72

Thanks a lot, that'll be a big help!

05-23-2010, 02:55 PM	#1
David67 Registered User Join Date: Mar 2010 Location: Spring, TX Posts: 886	Backspacing/ tire size Hey guys, I'm hoping to be able to order my wheels/tires today so I can install the 5 lug axles that will be coming in this week. I'm trying to finalize the measurements so that I can be sure that everything will fit. I've decided on the American Racing TTII's, 18x9.5 in the rear and 17x8 in the front. Between the hub and the bed (stepside), there is 6 in. of clearance. Between the hub and the outmost part of the fender, there is 7.25 in. with 6.5 to the inmost part of the fender lip. The two main backspacing options that I'm looking at for this rear size wheel are 4.31 and 4.54. The main thing I am concerned about is the tire clearance. Does anyone know how much further a 275 or 285 tire would stick out on each side of the wheel? Also, can anyone help with determining the tire height or what they think would look the best (with a 4/6 drop)? For instance, if a tire is 275/50/18, how is the 50 determined? Thanks!

05-23-2010, 04:22 PM	#2
David67 Registered User Join Date: Mar 2010 Location: Spring, TX Posts: 886	Re: Backspacing/ tire size Alright I've figured out that the aspect ratio(the 50) is a percentage of the tire width. What I'm set on right now just happens to be 275/50/18...it was pretty much a guess to begin with but that's what I ended up calculating. The overall height of the wheel/tire will be the same if not slightly more than what you can see in my "Rear almost finished" thread, which might show up just above this one Last edited by David67; 05-23-2010 at 04:23 PM.

05-23-2010, 05:00 PM	#3
stevencvn72 Kill Bill...et Join Date: Aug 2008 Location: Winchestertonfieldville, Wa Posts: 366	Re: Backspacing/ tire size Not too sure what you're asking here but the first set of numbers ie: 275 is the distance from bead to bead or where the tire touches the rim on the outside of the wheel to where the tire touches the rim on the inside of the wheel. The second set of numbers ie: 50 is what percentage of the first number is sidewall. In this case 50%. Anyways, ultimately I would think you want the overall tire diameter to be equal in the front and back. A good tool is this: http://www.miata.net/garage/tirecalc.html It's java run and I've used it a lot...and no. I don't nor would I ever drive a miata. Good luck! __________________ -Steve I ♥ Grease '67 Chev stepper http://youtu.be/38p_2Iu2fd0

05-23-2010, 05:07 PM	#4
David67 Registered User Join Date: Mar 2010 Location: Spring, TX Posts: 886	Re: Backspacing/ tire size Stevencvn72 Thanks a lot, that'll be a big help!



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