Tire size vs. crawl ratio

[DsrtJeeper]

I've been thinking about this and i'd like some educated feedback.

Why doesn't tire size equate into the final crawl ratio?

Larger tires will rotate slower but cover more ground per rotation than a smaller tire with equivalent gearing.

Smaller tires should be condusive of more power and torque with everything else remaining the same.

For a nice slow crawl; wouldn't smaller tires with a 100:1 crawl ratio crawl slower than a larger tire with same ratio?

In other words....small tire rotates faster but covers less ground and larger tire rotates slower but covers more ground. The smaller tire would actually be traversing ahead slower. No?

Tire size is taken into consideration when determining ideal gear ratio for a given rpm. Why isn't it considered in the final crawl ratio?

[blkTJ]

Originally posted by DsrtJeeper
Tire size is taken into consideration when determining ideal gear ratio for a given rpm. Why isn't it considered in the final crawl ratio?

who said it wasn't???

[Dukes69]

I think you may be taking it a little too literaly. Think of a transmission. Say you have a 3.14:1 first gear . . . but is that 3.14:1 with 28 inch tires, or 37 inch tires? So what is the actual ratio? Its still 3.14:1. I think anyway.

I guess you could start the "corrected" crawl ratio movement.

[blkTJ]

my axle gears work well for on road driving with the tires I'm running.

my transfer case gearing was based on the the maximum reduction I could get out of one box at the time I bought it.

with the ax-15 my final crawl ratio is somewhere near 90:1. This, with 35s mind you, is somewhat acceptable while playing in fairly large rocks.

if I were running 37s i doubt I would be happy with the on road characteristics of my axle gearing. if I lowered that, my final crawl ratio would follow.

in the end, your Jeep is either set up so it works or it isn't. you (or the people that watch you drive) are best qualified to make that decision.

[mnjeeper]

Originally posted by DsrtJeeper

For a nice slow crawl; wouldn't smaller tires with a 100:1 crawl ratio crawl slower than a larger tire with same ratio?

Yes. Same crawl ratio, different FPM speed.

[DsrtJeeper]

Originally posted by blkTJ
who said it wasn't???

In looking at the crawl ratio formula; no tire size is asked for. I guess the ratio is the ratio and poop on tire size.

[Kiwi]

This is what I use

http://www.tommyjeep.com/apps/ratio/index.asp

[Robert J. Yates]

Originally posted by mnjeeper
Yes. Same crawl ratio, different FPM speed.

*bingo*

[derf]

I put together a little tool of my own:

http://www.dfw-tx4wd.org/gears.html

I have a bunch more transmissions to add when I get around to it.

[dirtgrip]

Originally posted by derf
I put together a little tool of my own:

http://www.dfw-tx4wd.org/gears.html

I have a bunch more transmissions to add when I get around to it.

Don,t forget the 4:1 option for the 231 Tcase.

[Stu Olson]

There is crawl ratio.

There is crawl speed. This is the one where tire size is considered.

[DsrtJeeper]

Originally posted by Stu Olson
There is crawl ratio.

There is crawl speed. This is the one where tire size is considered.

Thank you; Stu. That is what I should have said.

[derf]

Originally posted by dirtgrip
Don,t forget the 4:1 option for the 231 Tcase.

It's already there. Second on the list: Custom 4.0 (Jeep/Toyota).

[dirtgrip]

Originally posted by derf
It's already there. Second on the list: Custom 4.0 (Jeep/Toyota).

Right you are-need to put my glasses on.

[dirtgrip]

Originally posted by derf
It's already there. Second on the list: Custom 4.0 (Jeep/Toyota).

Right you are-need to put my glasses on.

[dirtgrip]

Originally posted by derf
It's already there. Second on the list: Custom 4.0 (Jeep/Toyota).

Right you are-need to put my glasses on.