Gear ratio: What's Best?

[albi1cnobi1]

Hey Everyone,

I have a 99 Mountaineer with the 3.55 gear ratio.(axle code 45) I want to install 33's and was looking for some advice. Do you think the 3.55 will be o.k. or do you think I will need to re-gear. If so what's the best ratio to go with. I may have a line on some 4.10 axles, is that too much? Anybody chime in and let me know what you think. Thanks

 

[Maniak]

You change your gearing to keep the rpm range around the same as it is now. Assuming 235x75.r15 tires with 3.55 gears now, and a 32.5" tall 33" tire, you would need about 4.10 gears to keep the rpms about the same as they are now.

The way I look at it is.. your going to increase the tire size by about 12%. That means you need to numerically increase the gear ratio by 12% or so. If your between gears, go numerically up to the next gear ratio since you are not only turning taller tires, but wider/heavier too.

~Mark

 

[albi1cnobi1]

My brain hurts from the speed at which you ran those numbers. I can trouble shoot electronics and tackle almost any thing mechanical on my rig, but for some reason gear ratios always confuse me. Thanks Mark for that quick response.

 

[albi1cnobi1]

Almost forgot. If, as you're saying my RPM's will be roughly the same after the 4.10's than is it safe to say the speedo should be close?

 

[Maniak]

It will be close, but not exact...

3.55 to 4.10 is a 15.4% change
235x75.r15 (29" tire) to 32.5" (33" tire) is a 12% change. So, your speed will be off by 3% (read fast by 3%).

~Mark

 

[albi1cnobi1]

That's too close to worry about. Besides, I can check the GPS and correct from there. Thanks again, Mark

 

[unclemeat]

My 04 Ranger has stock 4.10 axles with 31s. It does not get great gas mileage, but it is fun to drive. My 91 X has 4.56 axles with 33s.

If you use the vehicle as a daily driver, the 4.10s and 33s will be a good choice.

If it is a trail rig weekend warrier, 4.56 with 33s is realy a better choice.

 

[albi1cnobi1]

Yeah it's my daily driver. So I guess it's looking like 4.10's.