My new 2005 Ram 3500 SRW has stock BFG Rugged Trail T/A LT265/70R17 tires. I'll be switching to Rickson 19.5" wheels and Hankook DH01 265/70R19.5 tires. I've only ordered a set of 4 wheels/tires - I'd like to keep the stock spare. However, the new tires have a diameter 3" larger than the stock tires (stock tire diameter = 31.5"; new 19.5" tire diameter = 34.5").

Question: If I ever have a flat tire and mount the stock spare either on the front or rear, do I risk damage to the drivetrain or suspension? I would definately keep my speed under 50-55mph in this event until reaching the nearest tire service shop.

TIA, Rob

 

Yes you do. If you have a locking diff in the rear it will imediatly try to lock and damage it and if you have 4wd the front side gears will not last long in non-4wd mode from the difference in tire diameter as something has to give. You need to carry an exact same diameter tire for a spare.

You could also set an ABS code for one wheel trying to spin faster (the smaller one) than the other wheels.

Get the same size spare as the others and then you can also do 5 tire rotations

 

You have a spare on either side of the rear axle At least until you can get a replacement tire.

 

Sorry, my truck's SRW

 

My bad..skipped right over that part in the thread.

 

Well you might as well have both opinions. Regardless of 4x4 or 4x2 you should be able to put the tire on the front without any worries (as long as you stay in 2wd). The only load on the front end in 2wd is to turn the front driveshaft - which the spider gears can easily handle at only a 10% speed difference. Older 2nd gens with a front axle disconnect split the RH side axle and had the spiders turning one fwd onebckwd ALL the time you are in 2wd and those live forever.

For the rear end - if your diff is open - I still think you are fine for light loads (although I would say just plan on swapping the flat rear with a good front and putting the odd size on the front). Again - this is only a 10% difference between L and R - that is why they call it a differential. At very high torque loads maybe you'd heat the spider washers - but thats like saying don't go around a curve with a heavy load? If you have a limited slip - then it'd probable not be recommended - although I think the 3rd gen torque biasing type would actually work fine as there is nothing that really "locks".

My $.02 anyway

Mathew

 

I'm with Mathew on this one. Just be sensible about your speeds and don't go to long and you should have no problems front or rear. JMHO

 

It looks like you have the money to get an identical spare, but will it fit underneath?
Mike

 

If the flat's in the rear, I would take off one of the front tires and mount it in the rear and use the spare tire up in front just to be safe. It'll be a pain in the rear, but worth it. I think this confirms what Matthew said.

 

ditto to the front to rear odd on front, keep it under 55 for less than 300 miles, change diff fluid etc...

 

Thanks for all the comments guys! Think I'll keep the stock 17" wheel/tire spare. Just doesn't seem worth the hassle and expense to dump the 17" spare and buy a new 19.5" wheel+tire spare. Also, I've decided to go with 245 tires rather than 265 so the tire diameter increase will only be 1.9" vs 3". Now, if I understand correctly, this is the procedure I should follow if or when I encounter a flat tire on the rear axle:

1. jack up front - remove 19.5" wheel - mount 17" spare
2. jack up rear - remove 19.5" flat - mount 19.5" front wheel

Correct? Of course, this assumes I only have one jack.