Spare tire smaller than the tires on the truck?

[Capital E]

Looking for the collective wisdom of the internet about not running a spare that matches the tire size on the truck. I'm considering just running the stock spare and if I get a flat I can run the stock spare on the front of the truck. If you aren't in 4 wheel drive and you have different size front tires (from side to side) what damage can happen? I've had so few flats in my life and am really never that far from civilization (unfortunately). It would only be for a few miles (<100) to a tire shop to get the flat fixed. What are the risks?

 

[deserteagle56]

Need more information? What are you driving - what kind of front axle? With my Fords, with hubs unlocked different size tires in the front don't matter. Is there a front axle disconnect in your truck?

 

[carnut1969]

I think the risks would be mostly instability and the truck wanting to pull one direction. That assuming an open differential. 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. But.. if you have a limited slip or post-traction differential, it can be a problem. These have clutch packs that balance the power transfer between the axles and they are not intended for continuous use, they will probably heat up and possibly burn the clutches out.

 

[ttengineer]

As long as you don’t have locked diffs, it’s fine for an emergency.

I wouldn’t do 60 on the highway with it either, but a back road at 35mph would be fine.

If you have free spin hubs, or an axle disconnect even better.


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[Capital E]

Need more information? What are you driving - what kind of front axle? With my Fords, with hubs unlocked different size tires in the front don't matter. Is there a front axle disconnect in your truck?

It's a 2019 RAM 3500. It has automatic hubs so no manual disconnect.

 

[badm0t0rfinger]

No way I'd be at all confident on a donut, whether on a trail or on the highway. Plus if you have the space for a donut, you should reasonably have room for a full sized. 100 miles is too far for me on a donut, and to not have the flexibility and have my trip potentially ruined by that would be heartbreaking. I sometimes carry 2 spares on the trail.

 

[Capital E]

No way I'd be at all confident on a donut, whether on a trail or on the highway. Plus if you have the space for a donut, you should reasonably have room for a full sized. 100 miles is too far for me on a donut, and to not have the flexibility and have my trip potentially ruined by that would be heartbreaking. I sometimes carry 2 spares on the trail.

I should clarify-definitely not a donut. I mean just using the stock full size spare versus buying another aftermarket wheel with a 37" tire to match the size of the tires on the truck. Keeping the stock spare in the location under the bed where a 37" won't fit.

I edited the thread title so it made more sense. I wouldn't drive anywhere on a donut.

 

[Buddha.]

I’d try to fit a 37 or close to it. If you’re on a road trip and have to drive around on a 32” while looking for a 37” is gonna ruin your plans.

 

[billiebob]

I'm betting there will be a DOT regulation banning unmatched tire sizes.

But if you have an autolocker or limited slip it'll be more costly repairing the dif than buying a matching tire. All the needs to match is the diameter. I ran 33x12.50 KOs and my spare was a 33x9.50KO.

And as mentioned, the handling will be positively dangerous.

 

[IdaSHO]

I refuse to not run a full size spare.
I even go as far as a matching full size spare on matching wheel, to do a 5-tire rotation.

I would encourage you to at least run a similar diameter spare.
If you don't have the space or want the added weight of a legit matching full size spare, look to a narrower tire with a decent load rating.

Or learn how to mount/dismount tires on the trail, and run a spare tire without the wheel.

Also, are you sure a 37" wont fit the stock location, if you deflate it first?
It will take some doin' to get it in there, but it might fit.

I know the frames are different, but I have a 35 in the stock location on my 2011 superduty, with room to spare.
Enough that I bet a 37" would fit...

 

[ttengineer]

A 37 will not fit in the spare location on a Ram.

It’s really not dangerous to run a different tire.

Like I said I wouldn’t do it for long or at high speed, but differentials are literally designed to spin axle shafts at different speeds. Why do you think your tires don’t chirp around corners? The inside tire will always spin at a slower speed than the outside tire.

The number of people that don’t get that is astounding.

Don’t run it on the rear, or in 4 wheel drive and you’ll be fine.


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[Regcabguy]

The front's diff's open. it won't hurt anything if you've got a tire store in your area or somewhere on the road reasonably close by. A half worn 35 fits under the 3rd gen rams. I guess you 37 guys have to take up a bunch of floor space in your bed. I've got hubs. I never used to get flats but my karma's ended. I seem to get one every year anymore.

 

[alanymarce]

A short distance is not going to be a big deal, although the bigger the difference between the "big" and the "standard" the more I would be concerned. We always have a spare the same size as the tyres we're running on the vehicle (often two spares).

As long as the flat tyre hasn't been destroyed you would presumably repair it instead of putting on the spare?

 

[badm0t0rfinger]

I should clarify-definitely not a donut. I mean just using the stock full size spare versus buying another aftermarket wheel with a 37" tire to match the size of the tires on the truck. Keeping the stock spare in the location under the bed where a 37" won't fit.

I edited the thread title so it made more sense. I wouldn't drive anywhere on a donut.

Okay that makes a fair bit more sense. I understand it sucks, but I wouldn't be willing to do it. I'm okay with using a different tire, a used tire, anything really thats the same size... but hell if you have to a 35 inch tire is better than nothing.

My question would then be where are you going to put the old tire if you got a flat if you don't have room to include a full sized spare now? I know that sometimes a flat 37 can fit into the spare area underneath a pickups bed, but not always.

As long as you keep the same sized tires on the drive axle, I dont think it would be problematic.

 

[warrpath4x4]

Does this imply some people dont already know how ?
Very odd...

some people dont even know how to change a tire