Tires; not your usual questions

[michaelh712]

I need some expert advice please. I have an unusual situation re; TIRES FOR MY 712. I have "recentered" H-1 rims, 8.25" x 16.5" with standard offset. I have 35X12.50X16.5 on the rear now with no rubbing problems, but these are too tall/wide for the front. I either need to install different tires in the front or change them all out. A limitation is fewer choices in 16.5" size.

Can I run wider and or taller tires in the rear and slightly narrower or smaller diameter in the front?

A trusted mechanic told me that different diameter tires back/front was OK, but that the OD height had to be within 1/4 ", or there may be damage to front differential when in 6 wheel drive.

Expert opinions anyone?
thanks, Michael

[ScottishPinz]

When in 6x6 or 4x4 the Pinz has no central differential so any difference in rolling circumference of front and back axles will wind up the transmission. As a vehicle corners there will also be a difference but off road this is scrubbed off by tyre slip. So no you shouldn’t run different tyres front to back.

[Erik712m]

Michael, I wouldn't go smaller tire's on the front. I wound think it would put unwanted pressure on the middle axle. Possibly a narrower tire's on the front, also look at the front springs. After going to wider tire I had to get stiffer springs from Mark. Raised the front about two and a half inches. You may want to consider just getting new tires all around.

[Jim LaGuardia]

All tires must be the same outside diameter, unmatched tires can result in damage to the front driveline and or other components.

[michaelh712]

Thanks to all our experts for their timely and sound advice. This confirms what I thought, but added the WHY. I did eventually find some good info on the net, mostly warnings about the sensitivity of AWD vehicles and the coupling that transfers power front to back. One source, TIRE RACK, even commented about how new tires of the same type/size vary measurably, and how just changing out one axle of tires could create a serious mismatch front/back from worn tires (smaller) on one axle vs. new, larger tires on the other. They offered a service to "shave" tires to a common diameter.

As for 4x4 (or 6x6) it appears that a more accurate indicator of match may be published revolutions per mile(rpm). For example, I found two suitable tires of the same make, but different "sizes" or diameters (34 " and 35") and widths. However, published sizes seem rather arbitrary, as the 34 and 35 are actually 1/4" diameter difference, and only 6 rpm difference. This seems insignificant on the road with front axle not engaged, and off road, tire slip would easily make up this small difference (less than 1% difference). Does this logic make sense?

[Jimm391730]

tire slip would easily make up this small difference (less than 1% difference). Does this logic make sense?

I did some study years ago and found that with "normal" tires ("normal" being a decent amount of tread, not new, but not bald, either) I got about 1% of tire slip on the drive wheels from just cruising 60mph down the highway; obviously, this is considered normal, and the drive train has to put enough torque to do this for all of your highway miles.

I've decided (and had it proven out over years of driving) that up to 2% difference should not be a problem for the drive train, but obviously you should take steps to minimize the difference if possible.

Jim M.
712W and 710M

[ka]

which is better?

trxus (33x12.50R18LT)
or
bfg mudder km2 (LT305/60R18E2)?


comparing both in ~ 33" outside dia. considering i want only one tire for all types of driving.