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Discussion Starter #1
Bought a 2007 Classic Duramax a few months ago and really like the truck. It has fairly new Falken 265-R70-16 tires on it with about 10,000 miles on them. I recently checked and found out the truck came with 245's so that explained why the speedometer seemed to be off. I crawled underneath and looked at the spare and it turned out to be an old 245 size so my question is would it be a big problem to run that 245 for a few miles with the 265's if I should have a flat out on the road and be unable to find a replacement Falken right away? I'm planning to hit the road with my 5th wheel camper this spring and was wondering if maybe it would be a good idea to pick up a size 265 tire to take along just in case of a disaster.
 

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Your spare is probably 245/75R16 and the ones you are running are 265/70R16 - these are extremely close in overall diameter - I wouldn't worry about the spare. I don't think your speedo should be off much at all either.
 

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Discussion Starter #3
Your spare is probably 245/75R16 and the ones you are running are 265/70R16 - these are extremely close in overall diameter - I wouldn't worry about the spare. I don't think your speedo should be off much at all either.
According to a chart I found online the 265's are a little over 8% bigger around than the 245's which seems pretty close to the figures I get when I check the odometer against posted mileage signs. It sure makes a noticeable difference in miles per gallon. I was a little disappointed with my initial mileage but when I adjusted for the tire size it was more acceptable.
 

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Ponyroper - are you sure? That doesn't seem right - 8% WIDER yes, but 0.3% taller

Like I posted though - I am assuming the spares tire size at 245/75R16 vs on truck 265/70R16

Tire Size Comparison Calculator I used says

Diameter - +0.3%
Width - +8.3%
Sidewall - +1.4%
Circum - +0.3%
Revs/Mile -3
 

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Discussion Starter #5
Sorry Stroodle I gave you the wrong tire size. Falkens are 265/75R16 not 70's. According to the site I was on that means tire circumference is 95.69 compared to 99.4. That's 3.877% not 8%. My Alzheimers really kicked in there. Should have looked it up before posting. You guys are way too sharp to let something like that by.
 
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