Ring and Pinion Strength with 40" Tires

[Sputnik40]

Can anyone explain in laymans terms how running larger tires effects ring and pinion strength. I'm in the process of swapping 38.5" TSL/SX's for 40" Good Year MTR's, running a FI/HEI 2F, SM420, a 2.31 transition year case (with a saver), and in the process of upgrading my course spline 4.11's to fine spline. I've got 30 spline longs up front and a pair of Poly rear axles - and am trying to engineer the u-joints to be the weak point.

A few friends were discussing that running 4.11's puts too much stress on the pinion....they're suggesting I go up to 4.88's minimum. Now I did break 2 course spline 4.11 pinions last year - but assumed it was from axle wrap due to soft springs and a centered track bar (not a ladder).

The question is - sitting around the garage using levers as an example, it's clear that larger tires are gonna stress the drivetrain, hence the pinions - but I'm wondering how much of a diff. 4.88's are going to make. Building up 3 diffs. with new RP's is not in my budget this year - but I'm definitely tired of swapping em on the trail.

I'd appreciate some posts on this .

 

[Pin_Head]

It's pretty simple: larger tires are a longer lever and it takes more torque to turn them. Going to 4.88s from 4.11 reduces the torque on the pinion by 18%. The 4.88 pinion is also fine spline, which is stronger than coarse spline 4.11 pinions.

 

[Sputnik40]

Understand the whole lever and torque concept . I simple number like 18% starts to help me to better understand the difference - Thanks!!!

It's pretty simple: larger tires are a longer lever and it takes more torque to turn them. Going to 4.88s from 4.11 reduces the torque on the pinion by 18%. The 4.88 pinion is also fine spline, which is stronger than coarse spline 4.11 pinions.

 

[Pin_Head]

5.29s would be 29% less torque on the pinion, but some folks think that the pinion gear teeth may be a the weak link. I don't have any personal experience with it.

 

[Tankota]

IMO 40" MTRs would be equivalent to 38.5 SXs. Considering they are probably the same height when aired down (SXs don't bulge hardly at all) and the weight is probably the same. I wouldn't be surprised if the MTRs are lighter.
The fine spline will be quite a bit stronger than the coarse. Probably shouldn't be running a cruiser rear pumpkin with that size of tire though (I may have a dana 60 rear but the front is still cruiser with longs in it ). The traction bar should help with the breakage. Most (definitely not all) of the pinions I've seen broken were from spring wrap.

 

[Poser]

Any driveline that binds up from spring wrap will destroy any pinion, coarse or fine spline, every time, without fail.

 

[Sputnik40]

I've got all my brackets and parts fabbed up for the traction/ladder bar, just been holding off on welding due to fiddling with spring packs and ride height.

I really like the gearing range I have with my SM420 and the 4.11's (at least for the east coast) - just don't want to spend the time and money switching over to 4.11 fine splines (have an FJ80 set in the mail) when it would be best to go 4.88's.

That being said - does anyone have an opinion on what gear sets are the best bang for the buck, OR are there any questions one can ask the vendors when discussing what they offer??? I'll do a search on that ques. as well...

 

[Trollhole]

Would sending them up to Bobby Long and have them treated help them any?

What size tires and gearing does Mike have on his? Does he break his stuff?

 

[Sputnik40]

From what I'm gathering the benefits or cryo'ing em would be about the same as swapping up to 4.88's - once I've got em out I might as well upgrade (heck wish I could do both). The new bar is going to help the most - just plain don't want to be swapping out diffs anymore or breaking rear axles, and with the poly rears it's either gonna be the wheel studs, the pinion, the u-joints or the t-case...

I fairly certain Mike's running 4.88's - but he's also got 4" lift springs that are a heck of a lot stiffer than the stock springs I want to stick with.

Would sending them up to Bobby Long and have them treated help them any?

What size tires and gearing does Mike have on his? Does he break his stuff?

 

[fj40charles]

I'd run 4.88. I think going any deeper and you're looking at broken ring gear teeth.

Also, if you're running a Toyota 4 speed ujoint, it will be difficult to make it a weak link since they are so durable.

I think the weak link may be your transfer case.

 

[Sputnik40]

Don't I have your old SM420? I just changed the lube on it last week and it was spotless - best buy I've ever made...

I'm sold on going 4.88 at this point - just starting to shop around.

You're right about the u-joints. I carry a spare t-case on the trailer just in case... Nothing I can do about that - except maybe go orion someday soon.

Frustrating, for the few times a year I really get to wheel, I'm spending too much time and money on this thing - but that's half the fun. If I lived closer to better wheeling spots, I'd shelf the surf trips and go 1-ton, and something different for tranny/t-case.

I'd run 4.88. I think going any deeper and you're looking at broken ring gear teeth.

Also, if you're running a Toyota 4 speed ujoint, it will be difficult to make it a weak link since they are so durable.

I think the weak link may be your transfer case.

 

[truehi9]

I would say that a bigger tire doesn't affect ring & pinion strength but it does affect ring & pinion stress.

I believe if the wheel is bound it doesn't matter what the tire size.

I believe a larger tire is harder to turn because the ring & pinion has less of a mechanical advantage over the tire making the larger tire bind/hook more often than a smaller tire causing more bound up opportunities for breakage.

In other words the smaller tire will spin more often, hook less often, since it is easier to turn.

I could be wrong though. Just my thoughts.

 

[Trollhole]

Call bobby and see what he says. I thought the dipping precess was pretty cheap.

When we go to the powertrax plant next month I will ask if they will give us a special club price break.

 

[Letsgomoreplaces]

coarse spline is weak

The course spline pinions are weak for one, but the axle wrap is whats breaking them

 

[Sputnik40]

If I havn't already stated - axle wrap was the culprit - I'm taking care of that - I just don't want to go thru that hassle again for any reason - hence either fine spline 4.11's or 4.88's.

Ringpinion.biz - got your quote Thanks - I got a better price on the Yukon's lined up with Timkin install kits at $135. I liked the price on the "house" brand but just don't know enough about this stuff yet to feel confident.

Anyone here, yourself included, want to do a gear manufacturer comment - for what it's worth? I have been told for years that there are only a few manufacturers - but do they do things differently or are they all really the same?

The course spline pinions are weak for one, but the axle wrap is whats breaking them