When should a spare be temporary?
 

Morning folks! I hope your all doing well..

Ive heard you can damage the transmission of a FWD car by running different size wheels, but what happens to our trucks LS differentials when we do that for long periods? And how much do the circumference's need to be different, for the damage to occur? 5%? 1%? .5%?

I'm asking because I'm considering running 235/85/16 XPS Ribs on my tandem trailer and noticed the outside diameter is almost same as the 265/70/17's on the truck, meaning I could use the 8 lug trailer spare for both truck and trailer. One less thing..

Shown here, the 16" and 17" tires are very close to the same circumference of 99.6" and 99.2" or only .4% difference and 2 additional revolutions per mile.
Is that close enough to use this 16" trailer spare on the truck indefinitely, or no rush to change it back to the correct wheel?

Thanks!

This small difference should not pose any problems.
I do not think that "straight" roads are that straight.
I would be more concerned with offset and different tire characteristics on a loaded rig, so drive carefully.

Thanks Alpine.

Yeah LT tires on trailers is controversial, but plenty of people have had great luck with LT's under their travel trailers especially the XPS Rib compared to the ST "china bombs" that come from the dealer. All ST's are 'china bombs' with the exception of Goodyear Endurance and I ran LT bridgestone duravis r250's on my featherlite toy-hauler with good results myself..
ST tires are speed rated for 65 max so screw that, as keeping up with traffic is safer than staying under max redline of 65 mph..

The trailer rim will have 1/4" positive which will move the tire out 1" on the truck, so no worries about less back space..

Or are your talking about me wanting to run one 16" tire with three 17" tires on the truck and the effect on handling?

I'm talking about the difference in almost all aspects like sidewall flex between those 2 types of wheels.
You are used to the truck feeling symmetrical, so you do a left turn for example and the feedback from the vehicle tells you if you were close to too fast or not. (or that it's slippery)
With let's say one different wheel on one corner a left turn is different from a right turn . (More or less sidewall flex, more or less body roll ). On the front axle even a little bit of difference in the tire centerline can lead to brake pull.

I'm with you on tires that let you run with the flock without exceeding their design speed, especially in hot conditions.