This might seem like a dumb question

I have the stock 15" rims on my mystique, I wanted to get 17" rims to enhance the looks of my car. My parents say that my speedometer will be off because of the difference in the sizes. Is this true and if so how can I fix that problem?

Yes it will be off and you can go to a shop to have it recalibrated.

Check this link to see how far you will be off.

http://www.miata.net/garage/tirecalc.html

It is not a dumb question but your parents are right ! It's a simple physics problem. For a given rpm, a 17" wheel will roll in one hour over a larger distance than a 15" wheel. Your speedometer would then give you a false reading. It must be recalibrated.;)

Go to www.blackrobotics.com they make a yellowbox that will allow you to correct the problem if you want.There under $100. bucks and you can buy a cheap GPS receiver to calibrate it yourself.

It is not the rim size but the overall rolling diameter of the tires. Plus sizing is when you go from a 205/60/15 to a 205/50/16. The rolling diameter is similar due to the shorter sidewall of the tire. I have 225/45/17's on mine and the speedo is only 5% off as the rolling diameter is only SLIGHTLY taller than the stock combo.

Originally posted by andy v:
It is not the rim size but the overall rolling diameter of the tires. Plus sizing is when you go from a 205/60/15 to a 205/50/16. The rolling diameter is similar due to the shorter sidewall of the tire. I have 225/45/17's on mine and the speedo is only 5% off as the rolling diameter is only SLIGHTLY taller than the stock combo.

That's right. The 5% increase (because of the bigger diameter of the rims/tires) means that if your speedometer indicates 100mph, you are actually rolling at 105mph and that is why the speedometer has to be recalibrated. Same applies to the odometer.

Ok so if I get it recalibrated how much would that run me and can any car place help me out with it?

Frankly, I would not do this (costly) mod because, besides the recalibration of the speedometer, rubbing of the tires would be the big issue. You are going from 15" to 17" wheels so be sure before deciding to go ahead. Also, the 17" wheels will require low profile tires and these are less comfy than the standard ones and are usually associated with a specially tuned suspension. Just my opinion ...

As long as you stay close enough to the stock rolling diameter, you will be fine. Use the Miata wheel diameter link that someone posted earlier to find out what size you need. But I can tell you off hand that for 17's , Contours should ride on 225/45R17 tires.

Recalibrating your speedo is unecessary IMHO. Who really gives a flying fugg if the tacho says 50mph and your doing 52.5mph?

Save the money and spend it elsewhere!

As for the comment about rubbing and comfiness - that's also BS!

If you get the correct offset wheels (42mm for a 7" wide wheel, for the Contour)rubbing will be minimal, and nothing a rubber mallet and 30 minutes of your time can't fix.

I have 18's and the ride is still good. You'll just have to learn to be more alert while driving, so as to avoid potholes. And being more alert when driving can only be good!

The forums are refreshed and BS is already flying - ahh you gotta love the internet!

Thanks for your very stylish response!

I am not the kind of guy who would fix a problem with a rubber mallet... And even a "minimal" rubbing is unacceptable to me! As for the necessity of the speedometer recalibration, I agree with you but I was merely answering to a question.

Good luck with your slalom driving.

God forbid you haver to use a rubber mallet on a car - that's just unheard of!

Those panel-beaters/smash repairers are just barbaric! GIVE ME A BREAK!

Your opinion of what is an acceptable modification to a car is flawed due to the fact that you won't make necessary adjustments as required, then maybe you should leave the helpful suggestions to those who have done it.

If we all though like you we would all be driving stock vehicles - how exciting is that?!

Ok thanks for all the help guys. One last thing before I go ahead and buy these new rims. These rims are the rims I want to get. Go down to the gunmetal concept pro wheels. I am getting the 17" ones, I just want to make sure that these wheels will be alright on my car. Thanks!

As long as they are 42mm offset and a 4x108mm bolt pattern they should be ok. So call and find out. The only thing is make sure you get the right size tire (225/45R17), and not the ones they are selling in the package deal in the link you posted.

Captain Bart, Mine have no rubbing whatsoever. I looked very hard and found the correct offset for the wheels and no body mods were needed. BTW, 5% is very close to the factory specs for a speedo(+or- 2%). Any more than 5% and you can have computer probs as well.

You can run other tire sizes beyond 225/45/17

Most on the site run 215/45/17 because it will leave you rub free near 100% of the time.
225/45/17 will rub on cars with the pre98.5 wheel liners.

I have seen SVT's on 215/40/17 and that looks fine too. Less sidewall means greater probability of damage to your wheel if you hit sumin.

225/40/17 is a rare size but is very doable. Check Nitto tires for this size.

Its your choice...........ALL are acceptable

Thanks Andy.

The problem with departing from the OEM tires is that it seems no two Contours are made the same. Some poeple have installed for example 225/50/16 instead of the original 215/50/16 on their SVTs with no problem at all. Others had serious rubbing problems with the same tires installed on the same model/year car. The old forums were full of stories on this subject. I myself have to get rid soon of my noisy KDW tires and I really don't know what size/brand to choose. Some CEGers advice to actually put the tires on the car and see if they fit correctly. Anyway, whatever the tires one chooses to replace these KDW tires, one would never get the exact rolling diameter, and thus an error of +-2% in the speedometer is inevitable. I find that an error of 5% or more would not be without an impact on the electronics and the controls of the car.

Originally posted by 96mystiquezetec:
Ok so if I get it recalibrated how much would that run me and can any car place help me out with it?

Go to www.blackrobotics.com they make a yellowbox that will allow you to correct the problem if you want.There under $100. BUCKS and you can buy a cheap GPS receiver to calibrate it yourself.

I'm running 225/40/18's with no rubbing after bending very little metal and readjusting the liners up all the way.Less than a half hours work.

Yeah, those rims would look great. My rims are very similar...Axis NE-0s, except that mine aren't gunmetal. They're polished with white accents. The deep polished dip on the rims that you're looking at will look really good, especially while you're driving. As for your earlier tire discussion, you can calculate it yourself at http://www.superford.org/garage/calculators/index.php

I'm runnin 215/40/17 and they don't rub at all. My speedo is a little less than 5% off (overall rim/tire diameter of my new tires are 5% smaller than stock) according to the calculations from the above calculator.

Hope this helps

Originally posted by 96mystiquezetec:
Ok thanks for all the help guys. One last thing before I go ahead and buy these new rims. These rims are the rims I want to get. Go down to the gunmetal concept pro wheels. I am getting the 17" ones, I just want to make sure that these wheels will be alright on my car. Thanks!

Well, this certainly cheered me up on that link:

LOL

Who cares if it is even 5%. So if your speedo reads 50, you'll be going 52.5? Wow....be careful not to speed. LOL. If you want to be anal, recalibrate the speedo.

You should be fine... it will just vary between 1-2 mi (speed). But will vary about 100-200 miles on your odometer I think (over time)

Don't go larger than 17" otherwise you will need to get it recalibrated.... which involes opening up the transmission and playing on one of the gears.

just my advice

I am running 17" Cougar rims with 215 / 50 -17 tires. The only time I heard it rub was when I hit a Michigan pothole.

As a former Furd Parts Techie, mod'd 'tour owner, and dedicated gadfly:

the "electronics" could give a damn less -- ECU just assumes you like running @ higher revs all the time!

Rubber mallet: presume Stazi is ref-ing banging in the lip on fender; works, but your local tire shop probably has a tool to actually roll the lip under, which is infinitely aesthetically more pleasing.

worried about rub? == a. measure your existing clearance w/wheels neutral (straight ahead), full right AND full left. Be sure to check inside [duh, back side of tires when looking at 'em from shiny side of car] as well as outside clearances. b. in each postion, also have cousin Bubba {250 pounds, no teeth & IQ to match wheel diameter} depress the suspension (gently sit on the corner) so's ya kin check when suspension deflected -- if'n ur real brave, have him bounce a bit while you have the tape measure in there. NOW: if using same rims, you can kinda fairly accurately judge what your new clearance will be if you check your new tire's section thickness (NOT just tread width); if you're plus sizing, make sure you have all your figures checked carefully for offset, as well as tread width & section width. Almost all manufacturers provide both measurements in their real spec sheets.

"oh it's too hard and uncomfy"

-- refuse to comment. Go borrow your Uncle egbert's 1967 MG Midget or Bugeye and take a ten mile ride on most representative interstates: if the expansion joints don't knock your hemorrhoids off and change your pitch an octave, then come back & whine about a hard ride -- handling often has it's own price. Also -- put GOOD struts & springs on when doing a tire aspect-ratio change -- I personally can recommend Terry Haines "Koni ST200 kit".

Firm but a five hundred mile stint still leaves the kidneys & gonads where they began.

If wide tread for nominal size is important & snow don't fly often, I also can't recommend Bridgestone S03's enough, unless tire wear is a major concern -- then go see Manny & rest of the pep boys for your 80000 miles bowling balls on rims.

My $0.02