gearing question

Plus a set of gears with a ratio of 4:10 will spin much faster than a set of 3:55's will at the same speed.

 

I think I get the jist of it. I know basicly how it works but the only way to vary the speed would be to change the angle of (pinion?) Teeth and have more teeth on (ring gear?) Therefore creating shallower space where they mesh ...

The question is what is the average difference in useful life over say 2.64 to 3.08 to 3.55 to 3.90? For say a 90% interstate 80k 5 axle setup

 

The angle of the pinion does NOT vary the speed. Ring and Pinions are always matched... What you may be confusing this with is possibly the "pitch" (angle of the gears as they mesh, always 45" deg in a perpendicular rear), or number of teeth per rotation, or shimming the rear end for proper clearance. (not related to angle)

I don't have numbers on any rear's useful life? My guess, the tires will still make the same amount of turns, and the only difference you'll find is in the gear wear, input shaft and thrust bearing...thus making the the higher ratio 3.90 last longer... but anyone needing that high of gear must be hauling heavy and should not be included because of the abuse. What a conundrum this is!

Wish you both luck finding those answers!

 

What exact model of transmission do you have now? The formula is the same as the road speed calculator. Just substitute the overdrive gear for the low gears and figure out the same miles an hour for the start off speed.

 

18918B is a transmission model, not an 18 speed. I need exact specks to get you exact numbers.

 

Um...18918B is an 18 speed:

RTLO-18918B - 1850 torque - Splitter 17%, 33.1" long, 716 lbs., PTO speed is 79% of engine speed
Reverse low direct: 15.06:1
Reverse low over: 12.85:1
Reverse high direct: 4.03:1
Reverse high over: 3.43:1
Low low: 14.40
Low high: 12.29
1st low: 8.56:1
1st high: 7.30:1
2nd low: 6.05:1
2nd high: 5.16:1
3rd low: 4.38:1
3rd high: 3.74:1
4th low: 3.20:1
4th high: 2.73:1
5th low: 2.29:1
5th high: 1.95:1
6th low: 1.62:1
6th high: 1.38:1
7th low: 1.17:1
7th high: 1.00:1 (direct)
8th low: .86:1 (over)
8th high: .73:1 (double over)
Some other 18 speeds (RTOF 15618 like mine for example) have only one overdrive @ .85:1