Speedo That Far Off?

[DizzleGT]

yeah, so i put 17' Voxx with 215 40r 17 on my car. now, there was a link in someones thread to a speedometer calc thing. anyway, its saying at (for instance) 60 mph, i'll be showing 63. is that true with all the speeds? or just up higher? and also what about braking? will it be okay? i've had to get on them before, but never at highway speeds. oh well, they look so damn good! lol. if anyone has some insight, get back me. thanks!!

[SWortham]

No, it shouldn't be that far off. 215/40-17 is actually really close to the stock overall diameter. Did you put in 195/60-15 for the tires you're comparing it to?

[Gearcat]

I have the stock tires on my car and when I pass the photo radar it tells me I am usually indicating about 3 MPH higher than my actual speed. This adds up quickly, unfortunately. An extra 3,000 miles on the odometer over a 100,000 mile span is a lot. Did you guys know that our cars also log our mileage in reverse? Hyundai is leaving nothing out here ... they want us to rack up as many miles as possible to get that warranty out of the way.

With the larger tires (215 instead of 205) you should be closer than stock size as far as equalling out the difference in indicated and actual speed/distance.

[BobMs_wht2k2]

I know that with 215/45/17 my speedo is 100% correct. I showed about 2% slower with the OE 195/60/15 tires.

[DizzleGT]

okay, doh! i must of put something wrong in. it says now i'm like 1.3 percent off. or i mph. not too shabby. so that meansthe 215 40r 17 combo actually makes it smaller? i swear it uses more gas. i took a trip to indy not too long ago and used a whole tank down and back. normally it is like a half take or so on how fast i go. i dunno, well thats cool. i feel better now.

[SWortham]

Yep, it's smaller. 205/45-17 would be closer to stock. Or my favorite, 215/45-17 is a little oversized but works really well.

As for the gas mileage, it's probably been affected by the increased rotational mass. I don't know how heavy your 17's are but it's a pretty safe assumption that you've at least increased rotational mass over stock by distributing more weight to the outer rim. So it's going to take more power to get the wheels spinning.

[redgum]

Fortunately all tires are not create equal. One thing all the calculators i've seen are is a manual input for the overall diameter. Some tires will be on or off target depending on brand/model.

For example this is the official size stock by calculator:
(195 * 60%) x 2 + 381 = 615mm or 24.23"

Kuhmo hp4 which came with my car have these specs:
P195/60R15 87H BSW 5.5 - 7.0 24.1 7.8 on 6.0 360/A/A 19lbs

Michelin energy (2005 GLS):
195/60R15 88H RRBL 5.5 - 7.0 24.2 7.5 on 5.5

Interestingly enough the 2002 GLS has different tires selected on the michelin.com website. For the 2002 they list the following:

P195/60R15 87H RRBL 5.5 - 7.0 24.1 7.8 on 6

Which tires do you have now and which ones are the old ones, this is what you will need to determine your actuall mileage difference. The calculators do give you a good estimate but its better to check the tire specs.

[elantraNJ]

i put on 17 rev II's and my spedo is off by 5mph and my odometer is off!

[BobMs_wht2k2]

i put on 17 rev II's and my spedo is off by 5mph and my odometer is off!


Ummm . . .it's not the wheel size, it's the tire size.

[elantraNJ]

yea sorry i put 205 40 r17

[SWortham]

205/40-17's are too small. A lot of people have them though because they come with a lot of the tire & wheel specials from online stores. 205/45-17 are closest to the stock diameter.