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...THEN your speedo will be inaccuratedriggity said:I'd choose 235/40 17s over 235/45 17s for a WRX if you want to put 235s on.

235/40 17s and 235/45 17s will be off by almost the exact same amount just in different directions. I'd rather make my gearing shorter than make it taller.RLsChMiDt said:...THEN your speedo will be inaccurate

What?driggity said:235/40 17s and 235/45 17s will be off by almost the exact same amount just in different directions. I'd rather make my gearing shorter than make it taller.

If you have a 17" wheel, and add 40 mm of tire sidewall, you're overall diameter of the wheel/tire is going to be 5 mm smaller than the stock wheel/tire diameter.

For example, my 225/40/18s side by side with stock rims/tires is the SAME EXACT diameter...thus no inaccuracies (sp?) in the speedometer reading.

Maybe I'm misunderstanding you...

Harsher!2point0 said:eh... I think I will just stick with 225/45/17's.

How harsh is the ride on 225/45/17 compared to the stock tires/wheels?

Let's put it this way, it feels like a well tuned sports car!!

Bumpy, but not too bad! I can live with it, so I'm sure you can too!

Stock WRX tire 205 55 16 Revs per mile 811

225 45 17 revs per mile 808

235 45 17 revs per mile 796

235 40 17 revs per mile 827

225 40 18 revs per mile 804

This is based on what the tire *should* be. As we all know each manufacturer measures differently.

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No, you're misunderstanding the numbers on the side of the tire. 40 does not mean 40mm of sidewall. To get sidewall height you use that as a percentage and multiply it by the width of the tire. This is why a 225/45 17 and a 215/45 17 are different diameters.RLsChMiDt said:What?

If you have a 17" wheel, and add 40 mm of tire sidewall, you're overall diameter of the wheel/tire is going to be 5 mm smaller than the stock wheel/tire diameter.

For example, my 225/40/18s side by side with stock rims/tires is the SAME EXACT diameter...thus no inaccuracies (sp?) in the speedometer reading.

Maybe I'm misunderstanding you...

Think about your setup. If you took 15 mm off of each sidewall compared to stock(55 to 40) you'd have 30mm less total sidewall. But you took off 2 inches of wheel diameter which is about 50.8mm. That would most definitely not be the diameter as the stock setup.

WOW! Now I understand why people use 45 on 225s for 17s...because stock is what, 55?driggity said:No, you're misunderstanding the numbers on the side of the tire. 40 does not mean 40mm of sidewall. To get sidewall height you use that as a percentage and multiply it by the width of the tire. This is why a 225/45 17 and a 215/45 17 are different diameters.

Think about your setup. If you took 15 mm off of each sidewall compared to stock(55 to 40) you'd have 30mm less total sidewall. But you took off 2 inches of wheel diameter which is about 50.8mm. That would most definitely not be the diameter as the stock setup.

I was like, the difference is so great it doesn't make sense!!

THANKS SO MUCH ! I just learned something!!!

Do 225's fill in the gap a little in the fender? NOT lateral, but horizontal. Like if you look at the car from behind, will the tire be closer to the outside of the car?

Like when you see those little probe's with HUGE tires sticking out beyond the car itself. I don't want that, I just want the tire to be pretty even with the outside of the car.

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Akiata,

Thanks for the fun Tire Calculator Site. Be havin' fun with it for the last 20 mins. He, he, he, boy I'm I easily amused.

But in general, 225's will look and drive fine.

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Yes.driggity said:you're misunderstanding the numbers on the side of the tire. 40 does not mean 40mm of sidewall. To get sidewall height you use that as a percentage and multiply it by the width of the tire. This is why a 225/45 17 and a 215/45 17 are different diameters.

For example, if you have a 225 x 45 / 17 tire, then the total sidewall height is 45% of 225 mm, ie 225 x 0.45 = 101.25 mm.

If you have a 215 x 45 / 17 tire, then the total sidewall height would be 215 x 0.45 = 96.75 mm.

Huh? You just said yourself that the aspect ratio is a % of the tire width. Going from 55 to 40 would therefore not necessarily equate to a 15 mm difference.driggity said:Think about your setup. If you took 15 mm off of each sidewall compared to stock(55 to 40)

The easiest to determine the speedometer variation would probably be to look at the difference in tire rolling circumference or to simply use a tire calculator...driggity said:But you took off 2 inches of wheel diameter which is about 50.8mm. That would most definitely not be the diameter as the stock setup.

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