How do you adjust the speedometer when installing larger diameter wheels and tires?

 

why bother? if you were going for 22's if they fit maybe... but at 18-20" it's not too much of a difference.

 

Why would you need to? When moving to larger diameter wheels, you can use a lower aspect ratio tire, such that the overall rolling diameter is the same as stock. Done that way, the speedometer is still accurate with the larger wheel/tire package.

 

Am I still the same if I went from:

17" OEM rims w/ 225/45/17

to

19" Enkei RS7 rims w/ 215/35/19

???

 

if I understand it correctly., straight and simple answer is yes.

1 step up in rim size, i size down in aspect ration.
you are 2 steps in rims 17-19's, and down 2 steps, 45's to 35's in aspect ratio.

If i am wrong PLEASE correct me, as this is the rule of thumb i have been going with for years..

 

I'd say you're ok;
215/45/17 (stock tC) = 24.62"
225/45/17 (your 17) = 24.97"
215/35/19 (you now) = 24.70"
All close enough that most peeps need not be concerned.

 

That's the general rule that most people use, but you have to pay attention to the tire width, since that combined with the aspect ratio determines the sidewall height. The rule usually works when you increase wheel diameter, but don't increase tire section width, which is why TongMan's 19's work, because he used a 215 width tire. If he had also increased tire width, then the equation changes, such that you shouldn't follow the rule, but do the math to see how far you'll be deviating from stock.

 

So the 19" rims w/ 215/35 tires are actually smaller than the 17" rims w/ 225/17 tires?

Also what if I get wider tires for the 19" rims like 225 width? What will that do?

 

make it worse..

stock is 215/45/17 so you need to base it off that.

 

Yes, diameter of your 19's is slightly smaller.
225/35/19 = 25.2"
What would happen? Your car would be a bit slower in acceleration, and have slightly higher top-end (unless the limiter stops it). The handling might remain the same, because of the added sidewall height conflicting the the improvement brought by the wider contact patch. The larger tires would also weigh more, and I'll bet your 19's already weigh more than stock anyway.

 

you guys are making this too complicated. The link below is a tire size calculator. Input your present tire size and then after that input what tire size you are going to. It will tell you how far off your speedo will be.

http://www.1010tires.com/TireSizeCalculator.asp

 

how about lets answer the first question..

NO.. YOU CAN'T?

:D