Tires & Sprag Transfer

[comdiver]

How much difference in tire height between the front and rear tires can my sprag deuce handle? At what point will the transfer engage? What if you had new tires on one axle and used on the other, let's say 1/2" difference?

 

[gringeltaube]

1/2" difference in diam is normal, even new there are variations btw. different brands. (9.00-20 Denman almost 41" vs. Cooper 40.5")
The resulting 1% speed difference means nothing for your sprag TC: Rear tires combined have to slip 7% before front axle starts pulling too. In other words for every one complete revolution of the rear axles the front does only .93 while engaged. So to equal speeds while going straight your front tires had to be diam. of the rears divided by .93 larger. If the rears were worn 9.00-20s at 40" the front would have to be 43" !Doing a turn the fronts have to rotate faster so that even increases the allowed difference.
Clear enough?

 

[comdiver]

I new I had seen the % of slip somewhere, thank you. Two more questions. If you loose your middle drive shaft, to the rears, will the transfer engage the front and be drivable? Does anyone have a set of drive flanges/hubs that I could despline?

 

[Recovry4x4]

If you lose that shaft, the overrrunning clutch will engage. Desplined hubs on a sprag truck will be of no benefit unless you remove the front driveshaft. If you install the desplined hubs, the overrunning will engage and keep everything turning.

 

[comdiver]

I was thinking that if I had a "summer" trip dropping the front drive shaft would be worth while if I had a set of hubs made up.