Gears...what are they for?

[t-rex grrr]

Hi Guys,

So what's the main reason for upgrading gears when you put on larger tires? With stock gears and 33's, is there a loss of power? Will running stock gears with 33's cause any permanent damage in the long run?

Thanks!

[Greg@RME]

The main reason you re-gear is to get the engine back to the optimal RPM operating range that it was in with stock sized tires. With 33's you've decreased the mechanical leverage that the engine had with stock tires. Your mileage and power suffer with the bigger tires and the speedometer will be off.

If you re-gear you can make up for the larger diameter tire & heavier weight, more rolling resistance, increased wind resistance due to the vehicle being taller, etc. Even with a re-gear your mileage still won't be as good as it was stock, but the engine won't be working as hard.

I don't think there's any real damage that can be done with 33's and stock gearing right away. An automatic transmission will more than likely run hotter when towing and heat kills autos. If you're towing often, especially lots of weight, I'd consider re-gearing as soon as you can.

Seems like 4.56's or even 4.88's are the most common ratios with 33-35" tires. If you're running 35's, towing or not doing a ton of freeway driving then 4.88's would probably be good. Otherwise 4.56's should work well.

Any questions?

[Crozhawk]

pretty good explanation here:

http://www.mrt-wheels.com/gear%20ratio%20chartl.html

[t-rex grrr]

The main reason you re-gear is to get the engine back to the optimal RPM operating range that it was in with stock sized tires. With 33's you've decreased the mechanical leverage that the engine had with stock tires. Your mileage and power suffer with the bigger tires and the speedometer will be off.

If you re-gear you can make up for the larger diameter tire & heavier weight, more rolling resistance, increased wind resistance due to the vehicle being taller, etc. Even with a re-gear your mileage still won't be as good as it was stock, but the engine won't be working as hard.

I don't think there's any real damage that can be done with 33's and stock gearing right away. An automatic transmission will more than likely run hotter when towing and heat kills autos. If you're towing often, especially lots of weight, I'd consider re-gearing as soon as you can.

Seems like 4.56's or even 4.88's are the most common ratios with 33-35" tires. If you're running 35's, towing or not doing a ton of freeway driving then 4.88's would probably be good. Otherwise 4.56's should work well.

Any questions?

Nope, thanks for the detailed answer!

[Erich]

So does this mean if I want to run 285's on a 16" wheel I need to regear?

[expat]

So does this mean if I want to run 285's on a 16" wheel I need to regear?

You would be fine leaving the gearing as is.

[4Runner_Russ]

Where do we buy gears for our trucks? I assume the install has to be done by a transmission pro?

doh:

http://www.toyota120.com/forum/showthread.php?t=419