So I recently went from my stock 15in rims to 17in rims and now my speedometer is off by 4 mph. I know I can get a tune to fix this but since I am putting my 15in stockers back on for the winter months I don't wanna have to get another tune everytime I switch my rims. So my question is, is their anything I can do so that my speedometer will be correct when I have both sets of rims on? Besides getting retuned each time I switch my rims.

 

Yes, the next time you get tires for your new 17" rims you can find a set of properly sized tires so that the overall diameter of your tire (from tread to tread) is the same as what was on your 15" rims. There's tons of tire size calculators on the internet, just google that and you should be able to figure out what side wall ratio you really need.

 

I never even thought about that. Thanks for the info

 

If you don't mind me asking, what was the original tire size on your 15's, and what size do you now have on your 17's? I doubt you will be able to size it perfectly, but this way it might end up being only 1 mph off at 60 mph or something like that.

 

the dealer should be able to do this for you on the house. they did last time i chenged sizes on my f350.

 

honestly I am not sure. All i know is that now my speedometer is 4 mph slower then the speed i am actually going at
well i didnt get it done at a dealer and my car has been out of warrenty for years but the main problem is, that since I am putting my stock 15in for the winter I would need to keep going back to the dealer for a retune everytime i switch tires

 

you know its off by 4mph, adjust your driving??? if you know and its a hassle why try to fix it when you already know how fast youre going.

 

i dont wanna have to keep thinking about "o i am actually going 4 mph faster then what my speedometer tells me" becuz im gonna forget one night while i am at college and im gonna be going a little over the speed limit and then a cop is gonna give my ass a ticket becuz im actually going 4 mph more then what i tjought i was doing.

 

stock 15” tire is 195/60

 

If that's the case, and if he is still running 195's on his 17's, then his sidewall ratio needs to be either 45 or 50. Of course that changes if he's running wider than 195. If he's running 205's or 215's, he needs a sidewall ratio of 45, and if he's running 225's he needs a sidewall ratio of 40.