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-   -   Switched from 17's to 18's. Spare tire question (http://www.jeepgarage.org/f109/switched-from-17s-to-18s-spare-tire-question-32322.html)

JDrew 12-09-2011 05:11 PM

Switched from 17's to 18's. Spare tire question
 
I switched from 17's to the 18's (OEM swap). My question is, do I need to change my spare too? I feel silly for asking this question, but I don't know 100% in my mind if I'm right.

I don't have the "full size" spare I don't think. Its a base black wheel with a typical donut style tire.

I didn't change the OEM tire size on the 18's..

Would it matter greatly to use in an emergency or do you think there's enough tolerance within the AWD system to accommodate the difference, if any?

67rally 12-09-2011 10:21 PM

Re: Switched from 17's to 18's. Spare tire question
 
If the diameter of the tire is the same, the wheel size won't make a difference for a spare.

JDrew 12-10-2011 03:50 AM

Re: Switched from 17's to 18's. Spare tire question
 
Quote:

Originally Posted by 67rally (Post 531236)
If the diameter of the tire is the same, the wheel size won't make a difference for a spare.

Right, what i'm getting at is does anyone know if they're the same?

Mmartin 12-10-2011 11:07 AM

Re: Switched from 17's to 18's. Spare tire question
 
the stock 17's are 245/70-17's and the stock 18's are 265/60-18's. the circumference of the 17's are 95.8 inches and the 18's 95.9 inches. So you are fine. Also just as a note the stock 20's are 265/50-20's which is a circumference of 95.6 inches. If you want to look up more sizes go to google or you favorite search engine and search for "tire size comparison" and put in the sizes. In conclusion any of the 2 stock sizes could use the same spare.

67rally 12-10-2011 12:07 PM

Re: Switched from 17's to 18's. Spare tire question
 
Quote:

Originally Posted by Mmartin (Post 531474)
the stock 17's are 245/70-17's and the stock 18's are 265/60-18's. the circumference of the 17's are 95.8 inches and the 18's 95.9 inches. So you are fine. Also just as a note the stock 20's are 265/50-20's which is a circumference of 95.6 inches. If you want to look up more sizes go to google or you favorite search engine and search for "tire size comparison" and put in the sizes. In conclusion any of the 2 stock sizes could use the same spare.

Exactly. I swapped out my 245/40/17's for a set of 265/65/17's which are identical in diameter (and circumference)

This is a great calculator for comparing wheel and tire setups: http://www.rimsntires.com/specs.jsp

Mmartin 12-10-2011 03:08 PM

Re: Switched from 17's to 18's. Spare tire question
 
Yes, and just so you understand the numbers because I know I didn't till a few years ago the first number the 245 part is the width in millimeters the next number 40 is the ratio to the width, and then the last is the rim size. So in a 245/40-17 the sidewall is 40% of the tire width.

67rally 12-11-2011 01:23 PM

Re: Switched from 17's to 18's. Spare tire question
 
Quote:

Originally Posted by Mmartin (Post 531561)
Yes, and just so you understand the numbers because I know I didn't till a few years ago the first number the 245 part is the width in millimeters the next number 40 is the ratio to the width, and then the last is the rim size. So in a 245/40-17 the sidewall is 40% of the tire width.

Yes, I knew that, but someone will learn from it. Also, I mistakenly said 245/40/17, but the actual size is 245/70/17.

For those that don't understand the reason why the 245/70 and 265/65 are the same diameter...70% of 245mm is 171.5mm, and 65% of 265mm is 172.25mm. If a 285 would fit, you would have to drop down the sidewall to a 60 series (285x.6=171) in order to keep the diameter the same.

The last helpful tip is that, in general, if you increase the actual wheel size by one inch, like going from a 17" to an 18" wheel, while keeping the width of the tire the same, you will need to drop the sidewall by 5%. So a 265/65/17 is similar in diameter to a 265/60/18, 265/55/19 or 265/50/20.

JDrew 12-11-2011 02:08 PM

Re: Switched from 17's to 18's. Spare tire question
 
Thanks guys!! :)


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