replacement tires on stock 17" rims?

[sportscarguy]

looking to replace the bridgestones....

will 225/55/17 fit on the stock 17" rims? i read it will offset the odometer, but 225 is only increasing the width not the diameter......i don't get it

what about 235/50/17 on stock 17"rims? will these fit? i tried it on the tire size calulator http://www.miata.net/garage/tirecalc.html that 235/50/17 will be better for the odometer...but won't it look like the wheel is smaller than the stock tires since the radius is smaller now?

what size is our rim size 17x7 or 17x7.5? bolt pattern and offset?

[DocJohn]

looking to replace the bridgestones....

what size is our rim size 17x7 or 17x7.5? bolt pattern and offset?

The stock rims are 17 x 7 with a 5 x 114.3 mm bolt pattern and a +50 mm offset.

[jsie]

i read it will offset the odometer, but 225 is only increasing the width not the diameter......i don't get it

225/55/17: the 55 means the sidewall height is 55% of the width of the tire.

So, changing from 215/55/17 to 225/55/17 will increase about 11mm in dia. or 5.5mm in radius.

[stockae92]

seems like 235/50/17 does have some good choices out there.

this can be my ticket to stay with the stock 17"x7" rims

[theprodigy79]

You got it figured out bro. 235/50 17 would be a nearly exact diameter match, but depending on the tire cut may become an issue if you decide to lower your car (many 235s should work, but wider cuts will pose a clearance problem). 225/50 17 and 225/55 17 are both also well within reasonable range (1.7% fast and 1.6% slow respectively, however considering speedometers are never precise from the start that's not noticeable).

[PhreakdOut]

Check out the previous thread regarding 235/50R17 tires on the Gen2.

http://www.solaraguy.org/viewtopic.php?t=14480

I posted before and after pics. The clearance between tire and strut body is just fine on my lowered Gen2. (I did keep the OE wheels.) I have roughly 1" more width on the tread and the handling is much better (wet or dry). Also, there's still room between the tire and wheel well lip. (Not rolled yet.)

Research your tires on tirerack.com to get sectional widths and tread widths of most popular tires. You can use the Firehawk LH as a base number since we know that fits.

[theprodigy79]

Yup, Phreakd is the man of reference whenever I speak of "someone" having 235s on his lowered ride the Firestones must be a narrower cut than the Michelins... As I said, there are some 235s that can be used, but others that may be a wider cut and would potentially rub.

Phreakd, I can't tell from your pics, but would your tires still be able to fit up in your wells without rubbing on suspension or your fender lip?

It's kinda hard to tell from these shots (these are what I already had up on my site, I'll have to take some angled close-up shots and post) but you can kinda see how my Michelin Pilot Sport 225s sit. You can see they are almost flush with the outside of the car; and keep in mind, that fender lip sticks in around a quarter inch (maybe a bit more)...

[Mole]

225/55/17: the 55 means the sidewall height is 55% of the width of the tire.

never knew that... so having these calculations, a p275 35 18 would be a different height than p205 35 18 ? ?

perhaps i'm missing out on something or reading it wrong?

[theprodigy79]

That's correct Mole. A 275/35 would have 96mm walls (very low profile), while the 205/35 would only have 71mm walls (essentially riding on rubber)

[theprodigy79]

*WARNING, THE FOLLOWING CONTAINS SIMPLE MATH... BEWARE*

Just to make everything clear for those who don't understand about the tire size ratings (I'm not pointing anyone out here, this is for anyone who is interested or doesn't understand... it's just a good knowledge to have)... I'll take a generic tire size (my own current tire)...

Let's use 225/45ZR18

225 is the tire width in mm. 45 is the side wall aspect ratio in %. Z is the tire rating (not always listed in that particular spot, but sometimes placed there). R represents if the tire is a Radial or not (steel mesh belts wrapped around the tire). 18 is the wheel size the tire will fit on in inches (good ol American contrast with mm and inches on the product)

To find the size of the side wall in mm, multiply the tire width by the side wall aspect ratio (as a decimal, so for 45% it would be .45)

In this case, the side walls are 101.25mm (225x.45)

If you are sticking with one rim size, that's pretty much all you need to know... HOWEVER, many of you are upgrading rim sizes (if you haven't already... So it gets just a tad more complicated (not much though).

Besides possible clearance issues, the only other issue with changing your tire diameter is throwing off your speedometer (which you can easily have recalibrated at a place such as Precision Tune or the like). There are generally no other detrimental effects of switching tire sizes (keep in mind, smaller diameter tires will increase your accelleration and drop your top end speed, while larger diameters will lower your accelleration and increase your top end speed).

If you don't want to mess with recalibrating your speedometer, however, you need to keep your tire diameter within around 3% of it's original size (just a rule of thumb)... How do we figure out the overall diameter of the tire?

Let's go back to our 225/45R18s, shall we?

Okay, so we already determined the side walls are 101.25mm... We now need to include the overall diameter of the rim... But Americans are pretty stupid, and the rim is in INCHES!!! What now?!? Simple... One inch is equal to 25.4mm. So lets find this diameter! Also, we must remember that we have TWO side walls across one axis!!! Our general formula is as follows:

Tire width (mm) = W, Side wall aspect ratio (decimal) = S, Rim size (inches) = R

W x S x 2 + R x 25.4 = Overall Diameter (D)

To clean that up a bit (yay, algebra!):

2(W x S) + R x 25.4 = D

So our setup for this tire is:

225 x .45 x 2 + 18 x 25.4

Now, if you remember simple 4th grade mathematics, you will remember that multiplication comes before addition (unless brackets are involved!) So our OVERALL tire diameter here would be:

659.7mm TA DA!

18" turns out to be 457.2mm, so you add that to 2 of our 101.25mm side walls (202.5mm total) and BAM! (Emeril)

So you have 17" rims and you wanna upgrade to 18"??

My Solara Gen2 came with 17" wrapped with 215/55VR17s... I wanted to upgrade to 18"s... How?

Okay, I want to find the overall diameter of the factory tires:

(215 x 55%)(2) + 17"x25.4mm = 118.25mm x 2 + 431.8mm = 668.3mm

So we need to find a tire within around 3% of 668.3mm (I prefer somewhere in the 1%s, but that's just me)... So we can have + or - 20.05mm... meaning anywhere in the range of 648.25mm to 688.35mm and we'll be fine (no speedometer recalibrations here!)

Okay, now that we have that understanding... a simple way to remember it is, for every inch you add on a rim, you want to subtract 12.7mm (one half inch) from the side wall (and vice versa for going with 1" smaller rims). That way you don't have to keep on calculating overall diameter...

In my case (and all of you as well who have factory speedo calibrations), stepping up to 18" rims from 215/55R17s...

We determined above that these tires have an overall diameter of 668.3mm...

We can safely use anywhere in the range of 648.25mm to 688.35mm



For an 18" rim:

225/45R18 = 659.7mm = 1.3% difference
225/50R18 = 682.2mm = 2.1% difference

235/40R18 = 645.2mm = 3.5% difference (not within our 3% range, but many dealers will say it's fine... and in the big scheme of things, it probably is) (watch clearance)

235/45R18 = 668.7mm = .06% difference (not common high performance tire size) (watch clearance)
245/40R18 = 653.2mm = 2.3% difference (watch clearance)
245/45R18 = 677.7mm = 1.4% difference (watch clearance)

255/40R18 = 661.2mm = < 1.1% difference (*WARNING* This fits our car, but does NOT clear the fenders... If you are dropped, or you often have people in your car or drive on bumpy roads, I DO NOT ADVISE GETTING THIS TIRE!)


For 19" rims:

225/40R19 = 662.6mm = .9% difference
225/45R19 = 685.1mm = 2.5% difference
235/40R19 = 670.6mm = .3% difference (watch clearance)
245/35R19 = 654.1mm = 2.1% difference (watch clearance)
245/40R19 = 678.6mm = 1.5% difference (watch clearance)

For 20" rims:

225/35R20 = 665.5mm = .4% difference
225/40R20 = 688.0mm = 2.9% difference
235/30R20 = 649mm = 2.9% difference (watch clearance)
235/35R20 = 672.5mm = .6% difference (watch clearance)
245/30R20 = 655mm = 2% difference (watch clearance)
245/35R20 = 679.5mm = 1.7% difference (watch clearance)

For all practical reasoning, I'm not going to go above 20" rims on for our dear Solara...

Keep in mind, if the overall diameter is larger than factory, your speedometer will be slow (you will actually be exceeding the speed your speedometer shows). If the overall diameter is smaller than factory, your speedometer will be fast (you will be traveling slower than your speedometer reads).

Also keep in mind... Your speedometer is NOT 100% accurate (no matter how new your car is). There is always an undefined margin of error.


Anyways, I hope I've been of some help!

-James

[Lone Solara]

^^^ James, excellent writeup. I say make it a new topic, and let's make it a sticky.

The only other things I would add would be the offset (5x114.3) and the rim widths.

[PhreakdOut]

Holy Schnikes! Nice write up Prodigy!! Did it take you a case of Mountain Dew to get through all that? LOL

To respond to your previous question, I get about ½" clearance between the tire and strut body. No worry on the clearance since runout or variance due to underinflation always goes to the lower half of the tire.

The Firestone tread "shoulder" (the portion between the sidewall and the first row of treads) have a very squared off profile. More typical of an all season tire versus a summer tire with rounded shoulders. The sectional width was about as agressive as I could find. (Translation: I am very confident that most tires will fit fine with no problems.) Just in case, have the tire shop break down just one tire and try it on in both front and rear postions. This way you don't end up with a full set that they have to refit into another size.

Worst case scenario, if you're in a bind with clearance to the strut, there should be enough room between the tire and fender lip to add a 1/8" or 1/4" spacer. (I'm not fond of these since the lugs' contact with the studs is shortened by this amount. )

Have fun & post pics.

[theprodigy79]

^^^ James, excellent writeup. I say make it a new topic, and let's make it a sticky.

The only other things I would add would be the offset (5x114.3) and the rim widths.

Thank you, I appreciate the feedback! I already threw it into the tutorials for both Gen 1 and Gen 2 when I first wrote it; If the mods decide it should be a sticky that would be cool.

Rim width and offsets are a completely different subject that I really don't have enough confidence in my knowledge to get into. If someone else wants to step up in that arena, that would be pretty badass.

Holy Schnikes! Nice write up Prodigy!! Did it take you a case of Mountain Dew to get through all that? LOL

Haha actually all it took was one cup of coffee (black)... I came into work this morning in a bad mood cuz my GF was stressing me out over our beach trip next week (I won't be able to post or check out the site for a week )... so I turned to SolaraGuy for some mind relief, saw that there was still confusion going on about tires, and decided to go ahead and nail it closed.

The Firestone tread "shoulder" (the portion between the sidewall and the first row of treads) have a very squared off profile. More typical of an all season tire versus a summer tire with rounded shoulders. The sectional width was about as agressive as I could find. (Translation: I am very confident that most tires will fit fine with no problems.) Just in case, have the tire shop break down just one tire and try it on in both front and rear postions. This way you don't end up with a full set that they have to refit into another size.

That is very true about A/S vs Summer tires, and something I had actually not taken into consideration in my previous posts about tire clearance. I currently use 225/45 max performance summer Michelins on an 18" rim; I tried stepping up to the 255/40R18 Pilot Sport A/S, and it was pretty much a no way no how for a dropped Solara... don't get me wrong, it... "fit"... but if you hit a good bump, went over a speed bump, or had rear passengers / a trunk load it WILL rub (it actually overlaps the fender)... so I also tried on the 235/40 of the Pilot Sport A/S and it woulda rubbed... but just barely... Between that, and the fact that it woulda been 3.5% diff in diameter (see my above opinion) I decided to just stick with my Summer 225/45s... I'll deal with Winter when it comes I guess; last year I drove through 3-4" of snow in my dropped Solara with my summer tires... It wasn't fun, but it was somehow managable (even though my anti-lock breaks didn't like it)...

-James

[Lone Solara]

The only other things I would add would be the offset (5x114.3) and the rim widths.

Oops, just realized that's not the offset, it's the bolt pattern. Offset is about +40 on an 18".