Different Size Spare?

barrypt5 · 06-27-05, 02:11 PM

Does anyone have any thoughts either way about having the spare tire be a different size than the other 4? I have 285/75 R16’s on my Cruiser and I assume the standard spare up underneath. If I only plan to use the spare in emergency situations and may never be more that say 75 miles from somewhere to get the 285’s back on is this ok/no? Any thoughts? Anyone do this right now?

Thanks

Barrypt5

Scamper · 06-27-05, 03:37 PM

I wouldn't worry about it. Most car mfgs now put the little doughnut tires in as spares which are relatively much smaller than what you're talking about. And you see a lot of people driving on them at 75mph too!

NorCalDoug · 06-27-05, 04:40 PM

Search and ye shall find...

landtank · 06-27-05, 05:36 PM

As a "data point" let us now how long the VC lasts once the spare is mounted.

stlcruiser · 06-27-05, 06:03 PM

You'll probably end up purchasing another 285 tire to replace the damaged one. Why not have the correct one as a spare and only have to change it once?

Steve
94'

tarbe · 06-27-05, 07:26 PM

I run 295/75 and have a 255/85 for a spare. Essentially the same diameter, skinnier so it sits up higher when stored, and about $70 less than the 295.

If I trash a 295, the 255 will just be on long enough to get me to a Discount Tire. But I won't have to worry about trashing my VC.

Rusty Phillips · 06-29-05, 01:58 PM

I would go to one of those used tire places and buy a used 285/75/16 or see if one of your buddies has an old one around somewhere.

should be able to get a fairly decent one for $25 or less and get it mounted for another $5 to $10

of course theres a lot of treadless baldies out there that someone might try to sell you, but as long as it holds air even a bald 285/75-16 is a better spare tire than the 275/70-16 under there now

ps - somewhere in hers's a spare tire lift (IIRC a couple washers and a longer bolt) that you might want to do, my ass is sagging pretty low to begin with, the spare tire hanging down doesnt help matters

parabola · 06-29-05, 04:32 PM

Sorry I'm new.

What does VC mean?

landtank · 06-29-05, 04:43 PM

Viscous Coupler. There is one in the t-case. When there is a difference in the rate that the 2 driveshaft spin it begins to lock to compensate for what it thinks is wheel spin. Now with an odd ball tire on the truck the driveshafts will rotate at different speeds which will lock up the VC, however there is NO wheel spin, it is a high traction situation which can be damaging to the drive train.

Darwood · 06-29-05, 04:49 PM

I could be pulling this out of my who who hole, but I beleive at least one auto manufacturer has had a recall since they had an undersized spare on a full time system like the US 80. The recall was due to the undersize spare creating too much heat and ruining the center diff if the spare was used. (I'm probably wrong about the recall but I'm sure their have been warnings issued by auto manufacturers to that effect)

As a mater of a fact I think my subaru has a full sized mini spare for the same reason. The spare is skinny but just as tall as the normal tires.

Land Speeder · 06-29-05, 04:56 PM

real world experience, not theory, you can use a different size tire for a spare, but do not lock your difs!

Darwood · 06-29-05, 05:03 PM

Quote:

Originally Posted by Land Speeder

real world experience, not theory, you can use a different size tire for a spare, but do not lock your difs!

How long have you been driving around like this? Also where not wondering if you can drive around with different sized tires, but rather whether it's a good idea.

Just let us know how it goes and how many miles you've driven like this. As Doug said we need some data points.

Darwood · 06-29-05, 05:04 PM

Also forgot to point out that 91-92s don't have a VC so you don't count

Land Speeder · 06-29-05, 05:35 PM

Quote:

Originally Posted by barrypt5

If I only plan to use the spare in emergency situations and may never be more that say 75 miles from somewhere to get the 285’s back on is this ok/no? Any thoughts? Anyone do this right now?

I was answering the above question. That's my data point, not tryng to argue the point, because I know what I know.
"Nothing is right or wrong, but thinking makes it so"
I drove like this about 5 or so miles down the road and flexed it in an empty lot. for about 15 minutes then back. And because I've seen this topic come time and again, I decided to do tight turns in circles to see for myself, and had no problems.
I'm not saying the setup is ideal, I am just saying, by experience, it is possible.
So if I don't have a VC, and doing this messes up a VC, and someone has a VC, then they should not do this.

dieseldog · 06-29-05, 05:57 PM

I'll make the blanket statement that you should never run different diameter tires on any axle to which power is being delivered. If you follow this advice, you'll never regret it. To do otherwise invites more problems than you already have. Hey, you've already got a flat, why trash your drivetrain too? Differentiation (be it side to side or front to back) is made far more perilous when you run different diameters--not to mention it fawks up your handling and braking characteristics.

Doc · 06-29-05, 07:42 PM

Diesel's advice is good- for full time 4wd vehicles.

You can run different sized tires on a regular 4wd vehicle with open differentials. Example: my FJ60. You can run different sized tires on the rear (powered) axle as long as you still have an open diff. If you have an automatic locker (aussie, lock right, etc...) don't try it.

Land Speeder · 06-29-05, 07:51 PM

I figured that when I install my Aussie this weekend I would no longer be able to use a different size.
But since now, what have I been damaging (no sarcasm, genuinely want to knwo)? If the reason is because of a VC, and I don't have one, what else would I be damaging. When I did the real world testing, I felt no binding at all.
What happens to all the people who never check thier tire pressure and allow it to be waaaay off?
And per the VC description given earlier, what's the difference between a VC and a locked center diff? They both appear to be doing similiar things.

Doc · 06-29-05, 07:54 PM

Land Speeder, your truck (if it is indeed minus a VC) is like my FJ60 example, a traditional 4wd. Running a smaller size spare will hurt nothing, even on a powered axle.

I thought though, that 91-92's were still full time 4wd? If this is the case, do they not use a VC? Do they use some other method?

Doc · 06-29-05, 07:56 PM

Also, a VC acts like a limited slip differential in ways. It allows a certain amount of slipping between two ends of the power 'chain' before it locks up. A traditional 4wd center diff is an 'open' differential in 2wd mode, and LOCKED in 4wd mode.

In 2wd it allows as much spinning and slipping as you want to take. In 4wd, it allows zero slipping and I bet if you put your rig in 4wd and drove on pavement in circles that rear tire would chirp.

Rich · 06-29-05, 08:01 PM

Just to clarify, part time 4wd trucks have no center differential.