Spare tire questions

[BananaDan]

A few questions.  I just ordered my spare wheel, a 15" rallye (yes, I know these cars didn't come with Rallye spares).  I need to get a tire for it, BFG Radial T/A, but I am not sure what size to get.  I have 275 60-15's out back and 235 70-15's up front today.

1. I have heard that I should get a spare that is the same diameter as my rear tires, because putting a spare on that is a different diameter than the other rear tire/wheel could cause issues with the SureGrip rear end?  True or not?

2. I'm 95% sure a 275 60R15 can't fit in the trunk where the spare goes due to it's width.  I know that a PolyGlas F-60-15 will fit on a 15" Rallye with an extended tie-down rod (AMD sells them I believe) b/c that's what DodgeDon has.  If I don't need to match my rear wheel/tire diameter as mentioned above, what would the equivalent modern tire size to an F-60-15 be?  If I do have to match it, does anyone know what size tire would give me the same diameter as my current rears but would fit in the trunk?

Dan

[BananaDan]

 

Anyone have any help on this to offer?

[471_Magnum]

1. true
2. 235-70-15 and 275-60-15 are both 28" tires. 235-60-15 is pretty close to a F60-15.

235's will barely fit into the trunk of a gen 2. You may actually have to air down a bit.

[BananaDan]

I found a tire-size calculator online and have come up with this.  Can someone double-check my math?

The F60-15 (known to fit as a spare on a 15" rallye rim) is 9.2" in width and 25.9" in diameter.
A 235/70-15 is 9.25" in width and 28" in diameter.

Assuming the extra 1" will fit in the trunk against the back seat area I should be ok here.  (2" in diameter bigger, but only 1" is in the back, the other 1" would be in the open area of the trunk.)  This also gives me a spare that is identical to my front tire setup, and the same overall diameter as my rears if in fact that is a concern of having two different diameter tires on the rear.

Sound correct?

Dan

[471_Magnum]

The width is the problem, not the height. A 235-70-15 will fit, but it's tight... real tight. Air it down a bit and carry a compressor.

Here's a question you may want to ask yourself:
"Where am I going to put a 275-60-15 if I have to change a tire?"

[BananaDan]

True, good thought.  I just want to see what my options really are b/c once the tire is on the rim I can't return it.  I can't really try different sizes on for fit before I buy.

Dan

[twodko]

I have the same tire/wheel combo and the same dilemma. 

[471_Magnum]

You're strategy needs to be to carry a smaller spare, then if a rear tire goes flat, rotate one of the front tires to the rear. Then you can throw a spare on the front with no ill effects to the rear diff.

A 275 will fit into the trunk partially. You won't be able to shut it though. Bring a bungee cord.

[Just 6T9 CHGR]

...or a AAA card

[BananaDan]

You're strategy needs to be to carry a smaller spare, then if a rear tire goes flat, rotate one of the front tires to the rear. Then you can throw a spare on the front with no ill effects to the rear diff.

A 275 will fit into the trunk partially. You won't be able to shut it though. Bring a bungee cord.