This may be a dumb question but...Does changing the stock tire size impact the speedometer in any way? Guy at my job said that this should be taken into consideration when changing tire size. I didn't know...thought I'd ask the experts....

 

Yes, unless you keep the total diameter the same. For example, you bump up to 18's, you need to bump the sidewall down to like a 40 or so. There are certain calculators around, even on this forum if I'm correct?

 

yes it does

 

http://www.miata.net/garage/tirecalc.html

 

Yeah, and when you're looking up tire specs it should have a revolutions/mile number to go with each tire size to compare to stock

 

Yes it does. All tires have a RPM(revs per mile) in there specs. section. Easy to change with a tuner,ie X/cal2,diablo predator to name two. Ford dealer can do it too.

 

Another good site...
http://www.bigcustomwheels.com/info_specs.jsp

 

Absolutely...get a hold of one of those tire calculators and it should tell you exactly how much off it is...

 

In general for approx every 1/2 inch difference in tire height your speedo is effected by 1 mph and the odometer by 1.6 % which may not seem like much but in 10000 miles the odometer will also be off about 160 miles. when going to a different profile tire you should stay within the recommended replacement height to maintain the proper tire load specs and service description