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Tires And Gear Ratio

kurt1993

By kurt1993
in Tires, Wheels & TPMS

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kurt1993 Enthusiast

kurt1993

Posted
Posted

I have an 01 Gmc Sierra 2500HD 8.1L with the allison automatic 5 speed i think and 3.73s and i upgraded from 245s to 265s does this mean my active gear ratio is lower now and i would have to get new gears to get back to the 3.73s now that i have larger tires? I think id like to upgrade again to 285s if i do that should i get 4.10s to keep acceleration and towing capability? gime some info please

 

thanks,

 

-Kurt

oldscsc Enthusiast

oldscsc

Posted
Posted

The first number (265 in this case) is the tire's width in millimeters. Changing the width doesn't affect your gear ratio. The wider the tire the heavier, though, which will also make it feel doggy. Changing height (the second number, say 65 for example) is what changes your gear ratio. The second number is an aspect ratio. i.e. A 265/70 tire is 70% as tall as it is wide (265 millimeters). The taller the tire, the more it effectively lowers (numerically) your gear ratio.

mhenshaw Senior Enthusiast

mhenshaw

Posted
Posted

You really don't need to worry about regearing unless you get 35s or bigger. You will not even tell a difference with the big block you have going up to a 285.

 

Plus unless you install it yourself it will cost $1000-1500 to regear the front and back.

kurt1993 Enthusiast

kurt1993

Posted
  • Author
Posted
The first number (265 in this case) is the tire's width in millimeters. Changing the width doesn't affect your gear ratio. The wider the tire the heavier, though, which will also make it feel doggy. Changing height (the second number, say 65 for example) is what changes your gear ratio. The second number is an aspect ratio. i.e. A 265/70 tire is 70% as tall as it is wide (265 millimeters). The taller the tire, the more it effectively lowers (numerically) your gear ratio.

 

Oh thanks sorry i ment to say 245/75/16s to the new 265/75/16 so the tire went from a 30.5" to a 31.5" and i want to end up with a 33" tire so should i think about changing my gears to 4.56 or 4.88s

Stevens03 Senior Enthusiast

Stevens03

Posted
Posted

Good lord no. You shouldn't even have to consider a gear swap till you upgrade to 35" tires, especially with the 8.1L. Gears aren't a cheap or easy mod and should be left to someone with experience. If you heavy tow, then maybe... but I doubt you hardly feel the difference in tire size. Gears for a 4x4 will cost you about $1400 for the gears, master rebuild and installation.

 

If you truly felt a power loss and you wanted it back, then 4.10's would be fine for 33" tires, 4.56's for 35" tires. If you go to a larger tire then 35", then 4.88's could be considered, but you'd want to match the gear with the tire size.

 

Jumping from 3.73's to 4.10's wouldn't be worth the cost. Just not enough difference. If you wanted more power off the line, I'd jump straight to 4.56's with 33" tires but thats alot of gear for that size of tire.

kurt1993 Enthusiast

kurt1993

Posted
  • Author
Posted
Good lord no. You shouldn't even have to consider a gear swap till you upgrade to 35" tires, especially with the 8.1L. Gears aren't a cheap or easy mod and should be left to someone with experience. If you heavy tow, then maybe... but I doubt you hardly feel the difference in tire size. Gears for a 4x4 will cost you about $1400 for the gears, master rebuild and installation.

 

If you truly felt a power loss and you wanted it back, then 4.10's would be fine for 33" tires, 4.56's for 35" tires. If you go to a larger tire then 35", then 4.88's could be considered, but you'd want to match the gear with the tire size.

 

Jumping from 3.73's to 4.10's wouldn't be worth the cost. Just not enough difference. If you wanted more power off the line, I'd jump straight to 4.56's with 33" tires but thats alot of gear for that size of tire.

 

Yeah id like some more grunt right off the line.... could i say change the gears in the rear diff and leave the fronts the same? or would that totally mess with the 4x4 when its engaged? I really want the feeling that the 245/75/16s useto provide with the more badass look of a 33" 285/75/16 or 35" 315/75/16

kurt1993 Enthusiast

kurt1993

Posted
  • Author
Posted
Good lord no. You shouldn't even have to consider a gear swap till you upgrade to 35" tires, especially with the 8.1L. Gears aren't a cheap or easy mod and should be left to someone with experience. If you heavy tow, then maybe... but I doubt you hardly feel the difference in tire size. Gears for a 4x4 will cost you about $1400 for the gears, master rebuild and installation.

 

If you truly felt a power loss and you wanted it back, then 4.10's would be fine for 33" tires, 4.56's for 35" tires. If you go to a larger tire then 35", then 4.88's could be considered, but you'd want to match the gear with the tire size.

 

Jumping from 3.73's to 4.10's wouldn't be worth the cost. Just not enough difference. If you wanted more power off the line, I'd jump straight to 4.56's with 33" tires but thats alot of gear for that size of tire.

 

 

also the 8.1L isnt really all that powerful for its size i mean HP wise and i think its 330hp and 420 ft lbs but thats with an aluminum block and 4.10s i think so mine is only like 330 hp still but only like 380 torques so id probably be better off with a 6.0 idk i dont even know what those numbers are im more concerned with RWHP/RWTQ and if the tire sizing affects those numbers

Stevens03 Senior Enthusiast

Stevens03

Posted
Posted

ok, well You do NOT want to have different gear ratios in the front/rear Unless you pull the front drive shaft so there's no way of engaging it. If you have the money to burn, then I'd vote for the 4.56's for the extra grunt. :cheers:

ybsane Enthusiast

ybsane

Posted
Posted
Good lord no. You shouldn't even have to consider a gear swap till you upgrade to 35" tires, especially with the 8.1L. Gears aren't a cheap or easy mod and should be left to someone with experience. If you heavy tow, then maybe... but I doubt you hardly feel the difference in tire size. Gears for a 4x4 will cost you about $1400 for the gears, master rebuild and installation.

 

If you truly felt a power loss and you wanted it back, then 4.10's would be fine for 33" tires, 4.56's for 35" tires. If you go to a larger tire then 35", then 4.88's could be considered, but you'd want to match the gear with the tire size.

 

Jumping from 3.73's to 4.10's wouldn't be worth the cost. Just not enough difference. If you wanted more power off the line, I'd jump straight to 4.56's with 33" tires but thats alot of gear for that size of tire.

 

Yeah id like some more grunt right off the line.... could i say change the gears in the rear diff and leave the fronts the same? or would that totally mess with the 4x4 when its engaged? I really want the feeling that the 245/75/16s useto provide with the more badass look of a 33" 285/75/16 or 35" 315/75/16

 

 

 

I would check with Justin at Black Bear first and see what he can do for a tune on the motor first, not sure what he can do for the Allison but I sure since the after market can for Diesels that he should be able to also.

 

Rob

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