Running smaller tire diameter and negative effects on suspension and drivetrain internals

John T.

Newbie
Original poster
Dec 26, 2020
8
USA
Hello. I am trying to figure out if running a half inch smaller than stock tire diameter will create problems with things (like drive train internals) spinning too fast. I am trying to put on 255/60 18's and someone said it was a bad thing to run smaller than stock. First thing I thought of was y'all. Thank you for any help.
 

TollKeeper

Guru
Dec 3, 2011
6,886
Brighton, CO
As long as all 4 tires are the same size, no problems. However, your speedometer will be off a bit
 
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Mooseman

Master Blaster
Moderator
Dec 4, 2011
22,550
Ottawa, ON
If going to a smaller diameter tire, I don't think it would cause extra wear or anything like that, however, it will increase fuel consumption if you do mostly highway driving. It may help a little with city driving. Basically you are doing the same as changing to a higher numerically gear (i.e. from 3.42 to 3.73 gears).

But, the size you are proposing is actually LARGER than stock. The stock size is 245/65-17, which is 29.5" and the 255/60-18 is 30". So going to a larger tire will decrease RPM. When going 60 MPH on the speedo, you will actually be going 61 MPH.
Reference:

If you want to go to an 18" without changing effective gearing and speedo reading, you could go to a 245/60-18 which is almost the same size (29.6") as the original tire. That is also the size on GMT360's that came with 18" tires.
 
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John T.

Newbie
Original poster
Dec 26, 2020
8
USA
I deeply appreciate that blazing fast response. I did quote the wrong tire size originally (was trying to put on 255/55 18) but I still got the needed info. Thank you so very much. Hope everyone's day is great!
 
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John T.

Newbie
Original poster
Dec 26, 2020
8
USA
Uhhh....I started reading some of the other tire info posts and see now that I probably should have stated I was running one inch thick adapters that change it to the full size wheel pattern. I also have a Belltech lowering kit that drops it quite a bit from stock. I have NOT swapped/flipped the upper control arms yet as I am waiting to afford a brand new one for driver side since I just replaced the worn out pass. side. The wheels on it now are 20" aftermarket that came off a Yukon. Rubber is 275/45 Proxes ST's. that are severely worn on front inside shoulders. Wheels I want to put on are 18x9 with 52 mm positive offset for the adapters. My purpose in going down in wheel size is to try and recapture some of the original ride quality by adding sidewall but admittedly, I have very limited knowledge and budget. Most sincere apologies if this was crucial info as I'm not used to asking questions on a forum. Thanks once again for the help though. Please let me know if I should add more info. I'm going to do the thing where I describe my truck and mods in my profile later today. Thanks again!!
 

John T.

Newbie
Original poster
Dec 26, 2020
8
USA
I guess I won't be describing anything in a profile after all. Sorry, I assumed there would be something like that. Thank you.

EDIT: I put info I could remember in my signature.
 
Last edited:

Mooseman

Master Blaster
Moderator
Dec 4, 2011
22,550
Ottawa, ON
I'm not up on full size wheel swaps so I can't help you there. You might have to go through the whole wheel and tire section to find info.

 
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John T.

Newbie
Original poster
Dec 26, 2020
8
USA
Moose...just you being here is a great help. I'll get it figured out. Thanks again sir!
 

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