Can I use a smaller tire as a spare? (1 Viewer)

Joined
Sep 24, 2012
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Seattle
After getting stuck in foot-deep snow this weekend (thank god for my More Power Puller), I’ve decided it’s time for a rubber lift. My truck is currently on 30x9.5 BFG K02s, and I’ll probably go to a 33x10.5 of the same type for an extra 1.5”. I have a stock-ish suspension, so thats likely the max.

Is it ok to keep a 30x9.5 spare and buy just 4 new tires? Plenty of meat left on the existing tires. I’ve got the the stock open differentials, so if my mechanical understanding is right, having a smaller tire on one side for a while shouldnt damage anything - or am I wrong? If I had to use the smaller spare, better in front or back?
 

3_puppies

SILVER Star
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Dec 2, 2002
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Helena MT
short distance to get home is fine, I wouldn't drive it across country like that.
better if on the front axle

going 33's over 30's will net a 1 1/2" gain in height
 
Joined
May 28, 2020
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101
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Pennsylvania
After getting stuck in foot-deep snow this weekend (thank god for my More Power Puller), I’ve decided it’s time for a rubber lift. My truck is currently on 30x9.5 BFG K02s, and I’ll probably go to a 33x10.5 of the same type for an extra 1.5”. I have a stock-ish suspension, so thats likely the max.

Is it ok to keep a 30x9.5 spare and buy just 4 new tires? Plenty of meat left on the existing tires. I’ve got the the stock open differentials, so if my mechanical understanding is right, having a smaller tire on one side for a while shouldnt damage anything - or am I wrong? If I had to use the smaller spare, better in front or back?



Thanks a lot I am now $400 lighter in the bank account.... Had to see what a More Power Puller is... I own one now ! :beer::beer::beer:
 
Joined
Sep 24, 2012
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Seattle
Thanks a lot I am now $400 lighter in the bank account.... Had to see what a More Power Puller is... I own one now ! :beer::beer::beer:

When you’re stuck on a mountain road at 4000’ with darkness approaching, you do not want to be relying on a Harbor Freight comealong built out of butter-grade sheet metal. That MPP dragged the whole truck sideways out of a snow rut without breaking a sweat. 13k lbs test on the synthetic line, I believe.

Don’t think of it as $400 spent, think of it as $1000 saved on a winch :)
 

60Works

60 Series Iron Works
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Fine in 2wd for 5 miles. Would be very hard on your spider gears to go 500.

Front in 2wd saves your diff but will cause differential braking and handling issues.

Odd size tire in 4wd could seriously damage things unless you're continuously in mud or deep snow.

I run a small spare on my DD but have a full size for the trail.
 
Joined
Apr 14, 2008
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North of LA California
Chains on all 4 tires would probably work better than bigger tires for snow.

Wider tires will help as you're stepping up from 10.5 to 11.5.
My wrangler duratracs were amazing in snow compared to people struggling in KO2s'. Tire brand and tread does a lot.
 
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Vancouver, Canada
I never understood the problem with different size tires in an open diff. Yes the diff gears will spin but they do that everytime you turn your steering wheel anyways. They are built to spin. Of course in 4wd it will wreck your transfer case on any hard surface.
 

60Works

60 Series Iron Works
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I never understood the problem with different size tires in an open diff. Yes the diff gears will spin but they do that every time you turn your steering wheel anyways. They are built to spin. Of course in 4wd it will wreck your transfer case on any hard surface.

Yes, the spiders are made to spin. But not a lot, not fast, and not continuously. Most of a vehicle's mileage is from driving on the highway in a straight line. The spiders get very minimal wear driving straight. When a vehicle is turning the spiders spin is at a much slower speed; though the pressure is much higher. These are very different conditions. The rotational bearing is steel on steel (meaning there is no bearing). There are bronze thrust bearings between the spiders and the cage. They can handle extreme pressure very well but aren't as good with speed. If your diff oil is low they will overheat and gaul in very short order.

Engineers design for expected life span in expected conditions. In college I remember calculating the expected cycles of a reverse gear with a specific metalurgy, diameter, tooth dimensions, torque, and compound angle of cut. It is that specific. Most reverse gears are 100k cycle parts. Modern vehicles are designed so most of the parts fail within the same mileage range. It's a disposable mindset.
 
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Joined
Dec 28, 2010
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Moscow, ID
1.) Thanks for the reminder about the MPP. I'm interested in getting one so I have a portable emergency winch for my Impreza (which is *dangerously* good at taking me places in the snow where mistakes mean getting too stuck for my discount maxtrax) and a handy side/rear pull option for wheeling in the cruiser...and any time somebody else is stuck in a spot I can't winch from, or I need to move a log that's down in a gully, or whatever.

2.) If it's a question of saving money, do it, but try to buy that 5th matching tire before it's time to rotate it in with the other four. If it's a question of space...I run 33x10.5 and keep my spare in the stock spot and have no regrets. I'm going to be happy for the extra clearance when I finally get or build a tire carrier, but a KO2 will barely hang past your shackles in back, and I promise it won't hurt your tire if you lightly drag it over some rocks. If you're dragging it, you're wheeling hard enough that you're scuffing the sidewalls of the other four, basically. I had a lot of fun using my old Super Swamper spare as a cushion for hard landings before I got my lift (and tires that weren't so bald they hydroplaned in sunny weather).
 
Joined
Sep 24, 2012
Messages
470
Location
Seattle
1.) Thanks for the reminder about the MPP. I'm interested in getting one so I have a portable emergency winch for my Impreza (which is *dangerously* good at taking me places in the snow where mistakes mean getting too stuck for my discount maxtrax) and a handy side/rear pull option for wheeling in the cruiser...and any time somebody else is stuck in a spot I can't winch from, or I need to move a log that's down in a gully, or whatever.

2.) If it's a question of saving money, do it, but try to buy that 5th matching tire before it's time to rotate it in with the other four. If it's a question of space...I run 33x10.5 and keep my spare in the stock spot and have no regrets. I'm going to be happy for the extra clearance when I finally get or build a tire carrier, but a KO2 will barely hang past your shackles in back, and I promise it won't hurt your tire if you lightly drag it over some rocks. If you're dragging it, you're wheeling hard enough that you're scuffing the sidewalls of the other four, basically. I had a lot of fun using my old Super Swamper spare as a cushion for hard landings before I got my lift (and tires that weren't so bald they hydroplaned in sunny weather).
I was actually also wondering whether a 33x10.5 would even fit in the spare tire well, thanks for the input.
 
Joined
Dec 28, 2010
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Moscow, ID
It's close, but I think you could even fit a 34" tire if you were a little patient. In terms of width, I wouldn't personally go wider than 10.5, but if you had some weird combo of 33x12.5 tires and a big honking lift, I guess it wouldn't cause problems.
 
Joined
Sep 24, 2012
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Seattle
I’m assuming 33s will fit on all 4 corners with a stock-ish suspension without rubbing at full turn/flex? I installed a new OME “near-stock” suspension a couple of years ago, and I think the body sits about 1” higher than factory.
 

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