Mismatched spare issues?

really.....lol...

 

Not in a straight line...

 

I've read about 1:100 rule of thumb for mismatched tires on an open diff. So 200 miles with the spare would cause wear on the diff equivalent to 20,000 miles of normal driving. Basically no immediate harm to the diff.

 

I agree...no 4wd or traction control for now

 

In a straight line with 2 different sized tires one tire is going to be chewing... The smaller one..

the two tires are connect through the axle and planetary gears in the differential..

 

Interesting....I’m 400mi from home

Wonder if I should change the diff fluid when I get back?

 

Millions of new cars produced every year have extra small space saving spare tires(donuts) in the trunk.
They usually include instructions for maximum speed and distance to be traveled on those tiny tires.

If one never rotated the tires on their vehicle, the fronts would potentially be smaller in diameter after many thousands of miles.

 

I wouldn't be to worried bud..

Your size difference is minimal and think of the force on the ring and pinion... The oil give such great lubricity that nothing wears out... Your side and axle gears will be fine..

Its more so the tire that takes the beating...

Now if you were running 33-35" tires... You might wanna check it..

 

The owner's manual usually has a distance limit of 100 miles or so on the donut spare.

 

Yes. Would be good to change it anyway. Rear diff break-in occurs within the first 500 miles. (That's why the owner's manual says no towing for the first 500 miles.) Unlike the engine or tranny, there's no filter in the rear diff. Fluid change will flush out all the metal shavings from break-in.

 

I had one of my 255/85r16 STMaxx tires blow out on me on a remote trail once and only had a 32" spare in the bed....I put the smaller tire up front and made sure that the 2 rear tires matched. I spent most of the rest of the trip (3 days) in 4WD with no issues, and then had to drive 300 miles home on the highway. No issues. As long as when you're on the street/highway, your drive wheels (rear wheels) are matching, you'll be fine. Just made for some wonky steering and probably not good for the tires themselves.

 

The owners manual also says you are supposed to put the tire on a NON-drive wheel. If you have a flat on a front wheel drive car, that might mean first replacing a perfectly good rear tire with the donut, then installing that good tire in place of the front flat tire. I've seen sooooooooo many people not do that.

 

it will act as though it is always in a turn, should be totally fine to get back to civilization so you
can even them up later

https://www.youtube.com/watch?v=yYAw79386WI


but yeah sort all your tires out and put the odd one in front and keep 4wd off
the front open diff is coasting, not powered, for least possible wear

 

I don't think you understand...

 

NO, U

If it’s a simple open diff, meaning it’s just a set of gears in there (one wheel wonder we used to call it), then it won’t make any real difference, as if you were just driving around in a circle all day

 

lol...


Your signature really doesn't lie...


One tire is going to be spinning faster than the other causeing those planetary gears in the diff to want to turn..

Whichever tire has more traction is going to make the other one want to over rotate or under rotate..

Like I said... Most likely the smaller tire because its point of contact is closer to the hub than the larger tires..

The further a tire is away from its center axle, the harder it is to spin..

 

I decided to do maths...

turning radius of the longest tacoma is 22 feet, rear axle is about 5.5 feet wide, so outter radius being 22 feet, inner radius is 16.5, that means outer tire in a full circle does 138.5 ft, while the inner does 104. That's a difference of about 25%

Now with his 1" tire size difference, that equals about a 3.3% difference, or in the case of his 400 mile drive one tire would spin 8400 more revolutions than the other. 255,200 total vs 263,600.

I'm not saying one way or the other, just that in the grand scheme that seems like a minuscule difference. Do UPS trucks fry their differentials with their SOP being to turn right 90% of the time?

 

Generally a differential will tolerate tires with a difference of up to 2-3%, even in 4wd. You can use the tacomaworld tire calculator to determine what the differences are between the two tires. And I'd only run a spare for a very limited time.

That said, I run matching spares and do 5 tire rotations on all my rigs.

 

My concern is that I’ll do all 400mi all in one shot.....so it really is like making a left turn for 400mi

I’m not really concerned about the life of the spare since it’s a spare after all

The diff is what I’m almost concerned about......I think if this were a permanent solution then it would cause wear issues. It’s only this trip, so I think I’ll get away with it. Staying out of 4wd and turning traction control off is gonna be the ticket.

As for the WWIII part of this thread (looking at you @Pot_Lickr and @127.0.0.1 haha) I think you’re both correct and that you’re both getting at the same thing, you’re just looking at it from two different perspectives of duration.....yes, it makes sense the smaller tire will get the working share of the torque from the axel because it’s the easier tire to turn....and yes, the open diff is indeed able to allow the wheels to spin at different rates which means the inside bits of the diff are working away.....where I think you’re splitting hairs is the end game and at what point it starts to make a difference.....if this were to go on forever, the diff would wear out much faster than if the tires were the same size.....since it’s only 400mi, I think it’ll be just fine.

That said, I’ll let you know if I blow a diff somewhere in northwestern WI on Friday haha

 

Thanks everybody for your help.....I think I’m still going to stick with the 33” game plan in a couple weeks, and just live with a 33” spare in the winter while my 32” Blizzaks are on

If anybody knows of snow tires that come in 255/85/16 or 255/80/17 gimme a shout