Crazy tire info

[Catmonkey]

So yesterday, I mounted the TF Competitions on my car I purchased from Cotten waiting on some wider hoops from TF. I will be mounting the 325/30-20s I had on 11" wide OEM STVPP wheels in what will end up being 11.5" wide TFs. Reason for the wider hoop is to get to the same offset I was running with spacers on the widened stockers.

I wanted to compare the sidewall of 295/35-20s MPSS' mounted on the Comps to the 325/30-20 MSC2s mounted on my widened wheels. What??? The cross section width is the same. This just demonstrates how wide the MPSS is with the rim protector feature and how much wheel width influences actual cross section. These measure roughly 12.6" at the cross section. The widest wheel Michelin recommends for the 295 is 11.5", while an 11" rim width is the narrowest rim Michelin recommends for the 325. The 295 would be a bit more forgiving on offset, as the outer edge is narrower.



Food for thought for anyone shopping wheels and tires.

 

[Poisonous West]

Hi Catmonkey, I am a little confused. The picture you posted, are both tires (MPSS 293/35/20 & MPC2 325/30/20) mounted on 11” width wheel?

 

[Catmonkey]

Yes, both wheels are 20x11. 295 is on the left.

 

[RedVenom48]

Welcome friends, to the wonderful world of non standardized tire sizing and ratings!

 

[Poisonous West]

Yes, both wheels are 20x11. 295 is on the left.

Thanks for the clarification.

I also have MPSS 295/35/20 (the K1) on my car with aftermarket wheels (20X11 for rear).

The MPSS is good tire but I just don’t have any traction in 1st and 2nd gear at my power level on street. Also, I have that wobbling issue.

Have you try both tires (MPSS and the Cup 2) and how much more grip you got from the Cup 2 tire (325/30/20)?

 

[Robert M]

Welcome friends, to the wonderful world of non standardized tire sizing and ratings!

Yep, it all matters where the specific tire manufacturer starts the measurement of the tread. Do they measure their tread from the point where it ends (well over on the sidewall)? OR do they measure the tread width at the point where it breaks over the sidewall? <<Those two different different measurement points change everything for height and width and can make two tires of the exact same numerical size wayyy different in reality size when compared side-by-side. Or two tires that would from all indications (295 vs. 325) seem to be far apart suddenly very close in side-by-side comparison.



R

 

[Catmonkey]

I was running MPSS 315/35-20s on that 11" rim before the 325 switch. My cars been out of commission since I got the SC2s pending completion of a gaggle of upgrades. I'm sure it will help some, but I'm not overly optimistic.

 

[Steve@TF]

replied to your email OP

i was wondering what the 295 mpss would look like on an 11.5" wheel. i know it will work but i think it would look a bit too stretched. like how vette guys run them. that doesnt really look right on these cars imo. what do you think? would it be too stretched?

 

[Catmonkey]

Yep, it all matters where the specific tire manufacturer starts the measurement of the tread. Do they measure their tread from the point where it ends (well over on the sidewall)? OR do they measure the tread width at the point where it breaks over the sidewall? <<Those two different different measurement points change everything for height and width and can make two tires of the exact same numerical size wayyy different in reality size when compared side-by-side. Or two tires that would from all indications (295 vs. 325) seem to be far apart suddenly very close in side-by-side comparison.

I've never seen a manufacturer publish a tread width on a radial tire. Tire Rack uses some method they explain on their website for thread width, that doesn't make a lot of sense from my perspective, but these are not coming from the manufacturer. You'll also notice that tire manufacturer's publish the actual rim width used in their cross section measurement. For instance, Michelin states the 325 is 13" when measured on a 12" rim. It loses close to 1/2 in girth mounted on an 11" rim in my circumstance, so wheel size is also relative to tire width too. Remember the inside of the wheel well to the outer fender is only 13.5" wide. You need some room for the wheel/tire to articulate.

 

[Catmonkey]

replied to your email OP

i was wondering what the 295 mpss would look like on an 11.5" wheel. i know it will work but i think it would look a bit too stretched. like how vette guys run them. that doesnt really look right on these cars imo. what do you think? would it be too stretched?

In the process of responding back to your e-mail.

I think the 295 looks a bit too stretched for the 11", so yeah, I think it would look pretty bulbous with another 1/2" of rim width. I had looked up the wheels that Michelin developed the 295s for, and if I'm not mistaken all of them were mounted on 11" widths for the specific production application. I think they would look better on a 10.5" rim.

 

[Robert M]

I've never seen a manufacturer publish a tread width on a radial tire. Tire Rack uses some method they explain on their website for thread width, that doesn't make a lot of sense from my perspective, but these are not coming from the manufacturer. You'll also notice that tire manufacturer's publish the actual rim width used in their cross section measurement. For instance, Michelin states the 325 is 13" when measured on a 12" rim. It loses close to 1/2 in girth mounted on an 11" rim in my circumstance, so wheel size is also relative to tire width too. Remember the inside of the wheel well to the outer fender is only 13.5" wide. You need some room for the wheel/tire to articulate.

A few years ago I read some information related to variations in tire width in at a tire store in a tire journal magazine, but here is a link that sums up what I read a few years ago, the third and forth paragraphs sum it up.............

https://www.tirerack.com/tires/tiretech/techpage.jsp?techid=201


^^^^It all depends upon where that original 295mm or 325mm is measured to start with, is it the "whole tread" all the way to the end on the sidewall? or is it just the tread contact surface that is the mm for the tread width? It makes a big difference and contributes to tires "running on the narrower side" and tires "running on wider side" when comparing two identical different brand tires.

We know that 295mm is 295mm and 325mm is 325mm, but where that is measured on each tire when spec'ed by the manufacturer is the unknown. The measurement method can be figured out with some measuring, but it is not standardized across the tire industry, thus the width and height differences with "same size" tires, and 295's equaling 325's...........or very close on same size rims.


R

 

[Catmonkey]

Like I posted previously. The manufacturer's data indicates what size tire the cross section measurement was made with. Tire Rack's technical discussions on tire width indicate that you can figure an increase or decrease from the cross section measurement of .2" for every .5" increase or decrease from the measurement wheel width, respectively. While not exact, it will probably get you in the ballpark for all intents and purposes. I think the shorter the aspect ratio, the closer it will be to half of the change in wheel width, possibly more. It will be interesting to see how the cross section of the 325/30-20 will change when it's mounted on a 11.5" wheel. Likewise, that 295 could probably make better use of 10" or 10.5" wheel and not take up as much real estate within the wheel well.

 

[Booky]

I took this picture to show how much the wheel width will affect the contact patch of the tire.

Wheel on left is 20x9.5, wheel on right is 20x11, both are wrapped in the exact same tire, 305/35/20 Nitto 555R.

 

[Dinosgt]

I took this picture to show how much the wheel width will affect the contact patch of the tire.

Wheel on left is 20x9.5, wheel on right is 20x11, both are wrapped in the exact same tire, 305/35/20 Nitto 555R.

That picture is utterly amazing. Thanks for posting it.

I just went through the 'find a 305 tire that tucks in the rear' nightmare for six months and found exactly what catmonkey and others have been talking about - There is little rhyme or reason to this stuff. I had custom offsets done, along with assurances from the wheel package guys that my combination would work - but only to find it didnt - mostly because Michelin makes some crazy wide rubber for given 'size'

I called engineers at Michelin, tire reps, tuners, wheel makers etc and couldn't get a read on what will work. Turns out, had I gone with a different OE in the same width, it would have been fine. But I already owned 2k worth of rubber and wanted a good fit.

Ended up with a 11 rim with a 58 mm offset for a MPSS cup 2 that properly 'fit' on the car, mostly thanks to the help of members on this site.

Thanks to all for sharing this stuff. It's eye opening.


Sent from my iPhone using the svtperformance.com mobile app

 

[Robert M]

When I had my 1995 Cobra R I had the original BFG Comp T/A in the original 255/45/17. During that time I installed an exact same size 255/45 Goodyear GS-C (standard on the 1994/95 SVT Cobra) on a spare set of same 1995 Cobra R wheels, the Goodyear was about .75 shorter and had a flat sidewall while the original same size BFG had a sidewall bulge and was taller. That is when I started the tire research and why two exact same size tires (different brands BFG vs. Goodyear), mounted on two identical rims had so much difference once they were mounted. <<Like I said, these where labeled as same size 255/45/ZR17, brand new with tread labels/stickers and installed on the same exact 17X9 rims, there was no mm comparing/calculating to do, it was a real head scratcher until I did some tire research and realized that where Goodyear measures their tires for 255 and where BFG measures their tires for 255 were not the same, and then the difference in the 45% sidewall follows the same differences.



R