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Discussion Starter · #1 ·
Rather than lowering the car I was thinking about putting 17 inch wheels on to fill in the excess space of the 15 inch that I have on the car now. I know if I change the overall diameter of the wheels larger it will affect the speedometer, what would be the appropriate wheel, tire make up for 17 inch wheels filling in some of the space that the 15 inch give me?

I know about aspect wheel, tire ratio, but what I need is a bigger diameter wheel, tire combo.
 

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iirc I thought miata.net had some sort of online program to help?
 

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I do not know what tire sizes you need. But I do have some other input.

If you do not adjust the ride height then running larger diameter tires will not only fill the gap but it will also lift your car off the ground. You'll have a lifted Spyder.

Also, running larger diameter tires will do more than just make your speedometer run lower, it will also make your odometer clock miles slower, understating the actual mileage of your car. If you plan to keep it forever and ever then no problem! If you plan to sell it, then it complicates things as you explain why your car is higher mileage than reported. Not disclosing it is illegal.
 

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Rather than lowering the car I was thinking about putting 17 inch wheels on to fill in the excess space of the 15 inch that I have on the car now. I know if I change the overall diameter of the wheels larger it will affect the speedometer, what would be the appropriate wheel, tire make up for 17 inch wheels filling in some of the space that the 15 inch give me?

I know about aspect wheel, tire ratio, but what I need is a bigger diameter wheel, tire combo.
A larger tire-wheel combo should affect acceleration also. Stock overall tire dia is about 23 inches. If you go to tirerack and select the tire of interest and select specs you will see overall dia column. You can then find which 15", 16", 17" tires with a 23" overall dia. Yokohama lists many different tire-wheel sizes with overall tire dia of 23"
 

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A larger tire-wheel combo should affect acceleration also. Stock overall tire dia is about 23 inches. If you go to tirerack and select the tire of interest and select specs you will see overall dia column. You can then find which 15", 16", 17" tires with a 23" overall dia. Yokohama lists many different tire-wheel sizes with overall tire dia of 23"
As long as the overall diameter is near 23", the speedometer & odometer will not be significantly affected. You must choose tires that meet this requirement. That may not be so easy.
Appropriate tires to fit 16" wheels are very rare. 17" wheels are easier to accomodate.

Handling, Steering Response, Acceleration, etc, etc, may also be of concern, depending upon how you use your car. Lower profile tires (which you'll need) are less tolerant of pot-holes, and produce a harsher ride.


Edit:
If you maintain the 23" diameter, you will not "fill in" the wheel openings, but the visual impact will be altered. If you opt for a larger over-all diameter, you can "fill in" the gap at the expense of performance.
 

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NOTE: I am lowered with the Sportivo set up, but it's less than an inch lower than stock.



205/40r16 front 225/45/r16 rear



205/40/r17 all around (these are my "show" wheels, with all seasons, NOT my autox set)
 

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Rather than lowering the car I was thinking about putting 17 inch wheels on to fill in the excess space of the 15 inch that I have on the car now. I know if I change the overall diameter of the wheels larger it will affect the speedometer, what would be the appropriate wheel, tire make up for 17 inch wheels filling in some of the space that the 15 inch give me?

I know about aspect wheel, tire ratio, but what I need is a bigger diameter wheel, tire combo.
I think this is what you are looking for - saves a lot of time.

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

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Discussion Starter · #8 ·
NOTE: I am lowered with the Sportivo set up, but it's less than an inch lower than stock.



205/40r16 front 225/45/r16 rear



205/40/r17 all around (these are my "show" wheels, with all seasons, NOT my autox set)
Still the same overall diameter of stock wheels? Just lower profile?
 

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But as others have stated it will mess with the speedo, and slow the car down.
It does mess with the speedo, I am off about 4 mph at 70. However, I do not agree with it slowing the car down. If it does, it so minor that you can not tell it. I do not have a side pic my 16/17 combo, but will take one here in bit and post it with my tire sizes. I do have H&R springs on mine and like the tire fill on the rear but not the front.
 

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Running 225/45-17 in rear and 205/45-16 in front. The rears are 25" tall and the fronts are 23.3" tall. I have no rub on the rears and some slight rub on the right front when I hit a dip with a passenger or take an extremely hard banked left turn when in the car myself. Not quite sure why this is as the front left has never rubbed. I must have a little difference on camber from one side to the other as the rub so slight it has not left any marks on the tire and only a "cleaned" spot in the fender liner just as it meets the fender.





 

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Running 225/45-17 in rear and 205/45-16 in front. The rears are 25" tall and the fronts are 23.3" tall. I have no rub on the rears and some slight rub on the right front when I hit a dip with a passenger or take an extremely hard banked left turn when in the car myself.
That is why on my 16" set up I have 205/40 up front. I had rubbing when I had 205/45 up front.

I have zero rubbing with the 17's btw
 

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If anyone is interested in figuring wheel height the formula is really simply

Example, 185/55/15

185 x .55 x 2 / 25.4 + 15 = 23.01

Got it? Width multiplied by the aspect ratio in a percent, multiplied by 2 (for each sideall), divided by 25.4 (converting it to inches) then add the diameter of the wheel and there you have it

And IMO large wheels look funny on small cars, just look at any stock bodied spyder on 18s
 

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My speedo is fine btw. My car is far from stock, so I don't notice any power difference from my 16's to my 17's.... Maybe if you tried donking..... I know they did a test on a miata that 16's were slower than 15's, but it wasn't much. I doubt you would notice it under normal driving conditions
 

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This is the most terrible idea I've heard of. :lol:

Upsizing without the appropriate tires will just look horrid. Afterwards you'll worry less about the fender gap and more about the height gap between your car and the road. :lol: That is why lowering ride height is even more important on bigger wheels.

But live and learn, please try it and report back ...:lol:
 

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it doesnt just depend on rim diameter but also the tires size. im on 245/40/17 on the rear tires and my speedo shows %7.389 slower than what im actually going. i kind of notice it too when im driving any stock car. look around my threads for pics.
 

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I think this is what you are looking for - saves a lot of time.

http://www.1010tires.com/tiresizecalculator.asp
Great Link. Thanks!

In my opinion, taller tire/wheel combo does lower the RPM on highway speeds. It also cover's the gap in the wheel well. It also raises the ride height which is great for people who have this car as Daily Drive. ALL this works great for me.

You do end up sacrificing looks of a "tall" sports car and the speedometer is lying to ya... nothing that could not be manageable.

What is the maximum diameter that the wheel well on the rear will accept?
 
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