Tire Size with 18X9 Rims

Igors92 · Jul 12, 2007

I just purchased some 18X9 rims for the rear of my 03 GT and was wondering what size tire I would need to keep the speedo correct. I've got an auto and I was thinking 275/35/18 would that be correct?

lvmustanggt · Jul 12, 2007

275/35/18 is the best fit,

WydOpn · Jul 12, 2007

Stock tires on an 01 GT are 245/45/17, correct? If so, the overall diameter of the wheel+tire is:

(245mm*0.45 = 110.25mm) + 17" (or 431.8mm) = 542.05mm = 21.34"

and for the 275/35/18:

(275mm*0.35 = 96.25mm) + 18" (or 457.2mm) = 553.45mm = 21.79"

Pretty close, but ideally you should get it properly calibrated - does Dallas Mustang make a tuner for you automatic guys? Or do you have to go the Xcali route??

isjoining · Jul 12, 2007

your calculations are wrong

275/35/18 overall diameter is 25.578"

245/45/17 overall diamater is 25.681"

BennyBlown2v · Jul 12, 2007

Don't get too into calculating out the sizes... Stock tires at "26 inch" tires, so are 275/35 tires, BUT different brands are going to be slightly different anyway.

CobraRed_96_GT · Jul 12, 2007

WydOpn said:
Stock tires on an 01 GT are 245/45/17, correct? If so, the overall diameter of the wheel+tire is:

(245mm*0.45 = 110.25mm) + 17" (or 431.8mm) = 542.05mm = 21.34"

and for the 275/35/18:

(275mm*0.35 = 96.25mm) + 18" (or 457.2mm) = 553.45mm = 21.79"

Pretty close, but ideally you should get it properly calibrated - does Dallas Mustang make a tuner for you automatic guys? Or do you have to go the Xcali route??

WTF? Why are you multiplying 245 and 275? Width has nothing to do w/ the height of the tire our how many times it needs to spin in a mile. And both of those measurments are in mm, not just the width. Either way different tires's side walls act different ways and fluctuate.

isjoining · Jul 12, 2007

the tire's profile number is a ratio (percentage) that is why it gets multiplied with the tire's width to get the sidewall height...

BennyBlown2v · Jul 12, 2007

WydOpn said:
Stock tires on an 01 GT are 245/45/17, correct? If so, the overall diameter of the wheel+tire is:

(245mm*0.45 = 110.25mm) + 17" (or 431.8mm) = 542.05mm = 21.34"

and for the 275/35/18:

(275mm*0.35 = 96.25mm) + 18" (or 457.2mm) = 553.45mm = 21.79"

Pretty close, but ideally you should get it properly calibrated - does Dallas Mustang make a tuner for you automatic guys? Or do you have to go the Xcali route??

Even though it doesn't matter at all.... You messed up with your math, it would be like (245*.45*2)+431.8=652.3 (there are two sidewall sections measured if doing diameter).

Anyway, no you won't need to recal your speedo - it should be fine.

HoustonGT · Jul 13, 2007

Good god even i'm confused after reading all that mumbo jumbo. Just get some 275/35/18's and be done with it.

CRZYHRSGT · Jul 13, 2007

HoustonGT said:
Good god even i'm confused after reading all that mumbo jumbo. Just get some 275/35/18's and be done with it.

If you want to get specific, go to Tire Rack and select a couple different tires then click on the "Specs" tab...it will show you everything you need to know about every size and brand in order to put this puppy to rest...

Skidawg · Jul 13, 2007

A tire size calculator is here:
http://www.miata.net/garage/tirecalc.html

I got 265/35's when I went to 18's. The difference was 1.5%, so no calibration was needed (IMO).

WydOpn · Jul 13, 2007

isjoining said:
your calculations are wrong

275/35/18 overall diameter is 25.578"

245/45/17 overall diamater is 25.681"

haha - yeah, it would probably help if I included 2 sidewall sections huh?

CobraRed_96_GT said:
WTF? Why are you multiplying 245 and 275? Width has nothing to do w/ the height of the tire our how many times it needs to spin in a mile. And both of those measurments are in mm, not just the width. Either way different tires's side walls act different ways and fluctuate.

OF COURSE THE WIDTH HAS SOMETHING TO DO WITH THE HEIGHT OF THE TIRE!! Thats the way you calculate sidewall height: the width x aspect ratio. And No, the aspect ratio is not measured in mm - its the ratio sidewall height/width. And last time I checked, if the diameter of something is different, so is the circumference - which obviously changes the number of times it rotates in a mile.

And yes, different tires have different sidewall stiffness, but the guy's looking for the difference in height between his stock tires and his new ones - and there IS a difference. It just depends on how accurate you want your speedo to be - if 1.5% doesn't bother you, then throw the 275/35/18's on there and go with it.

Igors92 · Jul 13, 2007

Tire Size

I guess I could go with either the 245/40/18 or the 275/35/18 both tires would be really close to the correct speed reading.

Q: What tire would look better on the car and fill in the wheel well the best?

isjoining · Jul 13, 2007

275/35 would look best on a 9" wide rim, 245 wide tires would look stretched.

blckstng96 · Jul 13, 2007

get a 275/35,no less than a 265/35 and be done with it.

Tire Size with 18X9 Rims

Igors92

Member

lvmustanggt

New Member

WydOpn

New Member

isjoining

New Member

BennyBlown2v

New Member

CobraRed_96_GT

Active Member

isjoining

New Member

BennyBlown2v

New Member

HoustonGT

Gilded Gelding

CRZYHRSGT

New Member

Skidawg

Member

WydOpn

New Member

Igors92

Member

isjoining

New Member

blckstng96

Member

Similar threads

Tire Size with 18X9 Rims

Member

New Member

New Member

New Member

New Member

Active Member

New Member

New Member

Gilded Gelding

New Member

Member

New Member

Member

New Member

Member

Similar threads

Privacy & Transparency

Privacy & Transparency