Modifications required to run 18" Wheels and Tires??????

Just plug your tire size into the calculations, go to tire wrack and insert your present size and it will show you tire sizes for 17" and 18" wheels which will have the correct diameter, and wheel off-set, so you will end up running wheels very close in diameter but with more width so you'll have more stability, yes there may be a 1 or 1.5 mpg loss, but safety first...

 

There will be a mpg loss and is usually around 4 mpg or more depending on your wheels and tire choice. Now modifications required. Just choose your tire carefully. A 225/40/18 would be very close to your OEM 195/65/15.

The UK tried to claim the 17" wheel upgrade on the Prius v only suffered a 1-1.5 mpg loss but I think it is hogwash. Everyone that upsizes and carefully monitors their mpg report much higher loss. My Genii goes from 55mpg with the 15s to 46.5 mpg with lightweight wheels and LRR tires. Then Geniii doesn't usually drop as much but it is still a larger hit than just 1mpg.

 

i heard 225 is about the widest you can go with the 18's... honestly, i wouldn't install anything over 215's... that's what i ran and i noticed on my genII that things get funny any bigger.. the genIII has bigger wheel wells and i've heard people running that size perfectly...

on a genII the widest you can go is 215 unless you really change the offsets... at 225 on a genII they will rub on big bumps.

you'll get more feedback from people who run 18's and larger. (not too sure how many are larger than 18's... but there are several people on here.. a few are located near me in los angeles)

honestly though... if i was you.. i would do it... id throw 18's on my genII but i know they wouldn't fit right. since so many have ran 18's on a genIII, i wouldn't hesitate too much.

from what i've seen though.. the smaller the sidewall.. the more the car can get twitchy at high speeds. (since the steering requires constant correction anyway since it has no dead space at center)... when i was running 225 all around it was funky... when i ran 225 in back and 215 in front it was simply scary to drive at high speeds (people shouldn't mix match anyway).... and i did a few trips cross country like that...

 

btw... for speedometer and such... i noticed it was less accurate with stock.. and with my current setup it is only 1.5 mph off at 80mph (timed with highway markers and clocked with multiple gps units.) stock was off by a few more mph... (done on purpose to keep people from speeding as much?)

 

Thanks, v8cobrakid

The215/40/18 will also work but is a little small than oem size so speedometer may be off by even more than stock 1-2 mph to fast. Because the tire's section width and frontal area is smaller than the 225 you should get better fuel efficiency if all else is equal. Once my computer is working again I will update my LRR tire thread with that size.

 

In a 225/45 17 tire the 225 is the sidewall height, the 45 is the tire width and the 17 is the rim size.

 

I can't imagine Toyota claiming a 1.5 mpg loss with 17" wheels to be unfounded, if you drop 10mpg there must be ulterior motives to much funn...

Speaking for myself, the difference between the stock 15's and 205/45 17's is 1.5mpg or less.

 

I'd like to know how you are measuring your mpg because you seem to be defying the laws of physics or you had terrible tires on the 15 wheels.

My experience is based on 4+years of swapping back and forth between 17s and 15s which includes the use of 5 different models of tire. Each time the drop was between 4-6mpg except in the case of my brand new 17" tires which dropped even more in the beginning but are also nearly an inch larger in diameter which will give a falsely low mpg reading compared to the 15s which give a falsely high mpg reading. Averaged out it's still approx. 4-6mpg.

As I stated above, the MPG drop seems to be less on the GenIII but I still read reports of 4mpg loss when switching to 18s.

If you are truelely experiencing only a 1mpg loss then my hats off to ya. That is pretty awesome. Great mpg, looks AND handling!

Ohh and I don't think it was Toyota who did the testing or made the claim in the UK. I could be wrong though.

 

i hope you don't work in a shop or anywhere around tires...

225 is the width.. in mm to be exact... 45 is a ratio that determines the sidewall hight... 45% of 225mm = 101mm or roughly 4 inches (tad wider than a business card)... and the part you have right... 17 is rim size...