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How much will a tire size change affect my speedometer?

3K views 6 replies 4 participants last post by  calgarymazda3 
#1 ·
I was just at a tire shop looking at new tires for my '10 Mazda3. The factory tire size is P205/50R17. The guy at the tire shop told me that I could easily put on P215/50R17 tires on the car (which I didn't really know was possible). How much would this affect my speedo and odometer, and is this generally a good or bad idea? I want to keep the stock wheels on the car, but the increased tire size has a much better selection to choose from as far as replacements go.
 
#2 ·
[quote author=Guitar Salad link=topic=209961.msg4228384#msg4228384 date=1336782969]
I was just at a tire shop looking at new tires for my '10 Mazda3. The factory tire size is P205/50R17. The guy at the tire shop told me that I could easily put on P215/50R17 tires on the car (which I didn't really know was possible). How much would this affect my speedo and odometer, and is this generally a good or bad idea? I want to keep the stock wheels on the car, but the increased tire size has a much better selection to choose from as far as replacements go.
[/quote]

you have some options without changing the diameter of the tire greatly or affecting the speedo too much.
Rather than tell you...here is a great calculator that will tell you the difference for various tire sizes.
lots of people go wider....
http://www.1010tires.com/tiresizecalculator.asp
 
#4 ·
[quote author=adumbrille link=topic=209961.msg4228392#msg4228392 date=1336784393]
They would read 1.6% higher speed
[/quote]

negative ghostrider
it will be bigger so....actual speed is higher, speedo reads lower
 
#6 ·
[quote author=adumbrille link=topic=209961.msg4228485#msg4228485 date=1336837062]
oops. That's what I meant. 1.6% higher speed. Hence the speed would read slightly lower
[/quote]

yup. speedo would read 59 when he is going 60mph.
 
#7 ·
[quote author=Guitar Salad link=topic=209961.msg4228384#msg4228384 date=1336782969]
I was just at a tire shop looking at new tires for my '10 Mazda3. The factory tire size is P205/50R17. The guy at the tire shop told me that I could easily put on P215/50R17 tires on the car (which I didn't really know was possible). How much would this affect my speedo and odometer, and is this generally a good or bad idea? I want to keep the stock wheels on the car, but the increased tire size has a much better selection to choose from as far as replacements go.
[/quote]


Once my 205/50R17's are worn out, I plan to install 215/50R17's. Like your tire guy said, much better tire selection plus the 205's look totally wimpy on our Mazda. The 215's would be slightly wider & just slightly taller, improving handling & performance.
 
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