Ugh…can’t believe I’m throwing out a tire diameter issue

[1nutcase]

First off,love the platform. 2021 GT2 AWD. 19” staggered. Have found myself with tires that are .2165 difference in diameter. Should I just try and sell two of them

 

[Snicklefritz]

Continentals? Because @7Andrei7 had issues with tires differing OD, causing the TSC to cut turbo power, except in Sport mode. Further investigation revealed a fault in tire construction.

 

[1nutcase]

Bridgestone potenza sports. Great deal but not if you can’t use them.

 

[Thomby]

Maybe I'm reading this incorrectly, because I don't know how you'd measure a diameter difference out to the third & fourth decimal (the variation in the tire itself would be more than that, not to mention wear would constantly change it), but if it's 0.2" difference in diameter, that's pretty minimal. Stock staggered wheels/tires have a 0.1" difference.

 

[D.J.]

First off,love the platform. 2021 GT2 AWD. 19” staggered. Have found myself with tires that are .2165 difference in diameter. Should I just try and sell two of them

Inches?

0.2165" sounds extremely close.

What are the tire sizes? What's the % difference.

 

[1nutcase]

Inches?

0.2165" sounds extremely close.

What are the tire sizes? What's the % difference.

Maybe I'm reading this incorrectly, because I don't know how you'd measure a diameter difference out to the third & fourth decimal (the variation in the tire itself would be more than that, not to mention wear would constantly change it), but if it's 0.2" difference in diameter, that's pretty minimal. Stock staggered wheels/tires have a 0.1" difference.

Yeah the decimal is splitting fine hairs. It was the difference in the two tires when I plugged the number into the calculator. .2 was also the difference on Bridgestone site.What got me started was a post I read concerning Differential light on shortly after installing tires at a .5 difference. Was advised to quit driving,have it towed. Remove AWD fuse etc..So now I’m freaking out a bit. At what point above the .1 factory spec do you start worrying about eventually taking out the differential. A great deal on tires won’t constitute toasting the diff.Tire sizes are 265/35R19 and 225/40R19. Stock rims for now. Looking for an aftermarket wheel replacement which brings an other set of issues. Geez I thought wheels and tires would still be a relatively easy issue. Not

 

[JSolo]

^^You're running staggered on a awd car?

Using a tire calculator based on tire size is erroneous. You need to look at mfg specs for said tires which will generally have actual tire diameters (for a given wheel diameter/width).

What interesting, given the mfg spec, for say the tire in my sig, ps as4, 245/40/18;

overall diameter = 25.9"
revs/mile = 803
measured rim width = 8.5"

1 mile = 5280 ft

Circumference = 2πR

So, 5280 ft/ 803 revs/mile *12 inches/ft / π = 25.12" inches for a diameter. This is different than their spec of 25.9". So which diameter is correct¿?

To keep confusion to a minimum, running the same size on all corners and call it a day.

 

[D.J.]

Yeah the decimal is splitting fine hairs. It was the difference in the two tires when I plugged the number into the calculator. .2 was also the difference on Bridgestone site.What got me started was a post I read concerning Differential light on shortly after installing tires at a .5 difference. Was advised to quit driving,have it towed. Remove AWD fuse etc..So now I’m freaking out a bit. At what point above the .1 factory spec do you start worrying about eventually taking out the differential. A great deal on tires won’t constitute toasting the diff.Tire sizes are 265/35R19 and 225/40R19. Stock rims for now. Looking for an aftermarket wheel replacement which brings an other set of issues. Geez I thought wheels and tires would still be a relatively easy issue. Not

Surely by "differential" you mean transfer case clutch. (I sometimes call it a center diff, but it's not)

But also, for the vast minority of the time, while driving, the transfer case clutch is not engaged (disconnected, operating in rear wheel drive only)

The clutch only engages during acceleration, and 0.2165" dia. difference is insignificant...


To elaborate on how insignificant this diameter difference is.
Imaging a square setup, as a real world example, say your front tires were 9/32" tread depth, and your rear tires were 5/32" (4/32" depth difference, (8/32" diameter difference))

8/32" is 0.2500" diameter difference (larger difference than 0.2165")

Would you be concerned for your transfer case clutches with minor wear differences between front and rear tires?

I would be comfortable with such an insignificant diameter difference.

Assuming your diameter difference measurement is correct.

 

[1nutcase]

^^You're running staggered on a awd car?

Using a tire calculator based on tire size is erroneous. You need to look at mfg specs for said tires which will generally have actual tire diameters (for a given wheel diameter/width).

What interesting, given the mfg spec, for say the tire in my sig, ps as4, 245/40/18;

overall diameter = 25.9"
revs/mile = 803
measured rim width = 8.5"

1 mile = 5280 ft

Circumference = 2πR

So, 5280 ft/ 803 revs/mile *12 inches/ft / π = 25.12" inches for a diameter. This is different than their spec of 25.9". So which diameter is correct¿?

To keep confusion to a minimum, running the same size on all corners and call it a day.

I’m not running a staggered setup on this car KIA is. The diameter was acquired through a general calculator found on line with plugged in tire sizes. Manufacturer varies. Checked against the manufacturer it was the same .2. In hind site should have bought all four the same size with different rim widths and called it a day. I’ll post these tires on facebook and move on.

 

[Snicklefritz]

...should have bought all four the same size with different rim widths and called it a day.

What width would that be? If you ran 225 square, wouldn't the narrower tires in the rear make them wear out even faster than OEM staggered 255 do?

 

[vipeboy2000]

I’m not running a staggered setup on this car KIA is. The diameter was acquired through a general calculator found on line with plugged in tire sizes. Manufacturer varies. Checked against the manufacturer it was the same .2. In hind site should have bought all four the same size with different rim widths and called it a day. I’ll post these tires on facebook and move on.

the factory staggered should be 225-40r19 front and 255-35r19 rear... i'm running 235-40r19 and 265-35r19 on rear on factory wheels now for about 40k miles now with no issues. of course if there are individual brand tire size discrepancies that sucks...

 

[D.J.]

In hind site should have bought all four the same size with different rim widths and called it a day.

No, NOBODY does that.

 

[ElChanclo]

No, NOBODY does that.

Hmmm, why not? I'm planning to do exactly that with the OEM rims and 235/45r19 snow tires next winter.
The tires are brand new and the OEM rims are 8.0 and 8.5, so I'm betting the .5" stretch/squeeze doesn't throw the OD out enough to trigger an AWD fault.

 

[D.J.]

Hmmm, why not? I'm planning to do exactly that with the OEM rims and 235/45r19 snow tires next winter.
The tires are brand new and the OEM rims are 8.0 and 8.5, so I'm betting the .5" stretch/squeeze doesn't throw the OD out enough to trigger an AWD fault.

Since you are not able to rotate your wheels, there really is no point to using square tires on staggered rims..

Square setup, works well, when you can rotate your wheels for even wear.

 

[ElChanclo]

Since you are not able to rotate your wheels, there really is no point to using square tires on staggered rims..

Square setup, works well, when you can rotate your wheels for even wear.

Gotcha, my winter driving is pretty sparse, the tires will probably expire before they wear out. I drive an 18" square all season setup the rest of the year for my rotations.

 

[Thomby]

Gotcha, my winter driving is pretty sparse, the tires will probably expire before they wear out. I drive an 18" square all season setup the rest of the year for my rotations.

You should trade me your 8.5" rears for my 8" fronts, and then you can have a nice square winter setup that can be rotated...

 

[Volfy]

Hmmm, why not? I'm planning to do exactly that with the OEM rims and 235/45r19 snow tires next winter.
The tires are brand new and the OEM rims are 8.0 and 8.5, so I'm betting the .5" stretch/squeeze doesn't throw the OD out enough to trigger an AWD fault.

It's more than just the ability to rotate wheels/tires.

8" and 8.5" rims will support that 235 tire differently. Up front, the steering wheels need to support their tires well for sharper handling and quicker turn-in. The rear driving wheels OTOH need good tire compliance, especially over rough pavement, so as to stay in contact with the road surface and to optimize grip.

Doing what you're planning achieves the exact opposite. Will the tires look okay? Sure, especially to the untrained eye. Will the car daily-drive just fine? Probably. Will you notice the issue mentioned above? Not unless you push you car hard, pull some good lateral G's, or spend a day on particularly rough track chasing you best lap time.

If I am Daryl Dixon (Walking Dead) stumbling upon a Kia Stinger with a full tank of gas but with this tire setup... F-yeah, let's roll.

Otherwise, there are better ways to spend your $$ on a proper square setup.

 

[Submarines]

Official guidance from KIA is that the front/rear circumference should be with 10cm of each other to prevent AWD issues. TSB10242913

 

[vipeboy2000]

Official guidance from KIA is that the front/rear circumference should be with 10cm of each other to prevent AWD issues. TSB10242913

View attachment 85935

ah.. so the factory size staggered is about a 5mm circumference difference (front 5mm larger circumference than rear) my set at 235/40r19 265/35r19 is about 8mm larger front to rear difference. So i could see possible issues if the rears are worn and fronts are new at that size... hmm.

 

[D.J.]

ah.. so the factory size staggered is about a 5mm circumference difference (front 5mm larger circumference than rear) my set at 235/40r19 265/35r19 is about 8mm larger front to rear difference. So i could see possible issues if the rears are worn and fronts are new at that size... hmm.

Must be a hell of a lot of rounding going on on sites like Tire Size Comparison if Pi is still 3.14159265359.

Cause- if these diameters are correct - to the MM -from (Tire Size Comparison)
Looks like they rounded their circumference to the nearest 5mm

If the diameter measurements provided are correct - would be 9.425mm Dia. difference for OEM staggered tires - with the front being larger by nearly 10mm circumference.

Kinda feels like using a micrometer on a 2 x 4 .​

Dia (mm) - Circ. (mm)
663 - 2082.875929
660 - 2073.451151
Difference - 9.424777961