Hey guys..just wondering in the event of a flat (knock on wood) can I use my 30inch spare even though I'm running 225/75/15's? Would this really screw up the diff. having one larger tire on, even though they are open diffs? It would only be in 2wd too...oh and don't have manual hubs just ol'ADD up front.

 

If you have manual hubs, put it up front.

But try and get a full size spare. I got mine for 20 bucks on a rim!

 

b-b-b-b-bump!

 

Yeah, but where do you put a full-size spare??

 

I tie my spare down with ratchet straps in the bed. This is a full size spare too...it's just a couple inches bigger than the stock size 225's (28") I'm running. So can I run this if need be without doing damage?

 

Let some air out of it. It should be fine if you are not driving very far, or very fast.

 

I'm running 31's all around but my spare is a worn out 32" MTR. I put them side by side and they're almost the same. I'd say let some air out of the 30" if you need to use it and do yourself a favor and install manual hubs.

 

Interesting, i've had smaller spairs but never bigger.

 

Obviously a matching spare is fine. But if you compare a "donut" spare on most sedans today vs. their full size, you'll see a difference there too. You can sit there and spin 1 tire doing a burnout for forever there's no damage to the diff. Lets see....

The Quick & dirty math:
30" spare has a circumference of ~95"
225s have a circumference of ~88"
95-88 = 7" difference between tire circumferences
88"/7 = 12.7
So ~ 13 rotations of the 225 tire will equal 12 rotations of the 30"

Now, the important part;
5280 feet in a mile (63,360")
So with 225's = 720 rotations per mile
With 30" tire = 667 rotations per mile
Difference of 53 rotations per mile
At 50 miles an hour, you're spiders will spin 2,650 every hour or .73 times every second.

3/4 rotation per second doesn't sound that bad. Like taking a turn.

 

Just put your spare on your truck at home, deflate it untill its around the same diameter as your 225. Note the PSI.

 

Thanks guys...ya the spare is from the PO when he had 30's all round. If it's okay for short distances than I'll just air down like some of you suggested. The 225's Dunlop Radial RoverXT's are great now with gas prices here at $1.22/L...I'm getting 500-550kms/tank, not too shabby. Although our '91 civic gets 700km/42L tank...Blah!....but I still love my Toyota truck!