Tire Stretch and Maximizing Performance

[DaveG99]

I know lots of the people here run an 8" wheel. Is there an optimal range (section width and tread width) that a tire should be for an 8" wheel to maximize performance?

 

[Zissou]

Paging Rick!

From my research, I've read that a 205 stretched onto a 8" wheel produces faster lap times.

I suppose we should clarify; what kind of performance are we trying to maximize? Lap times or drag racing?

 

[DaveG99]

Lap times. I'm just wondering if like a 7.1" tread width is much different than a 7.8" tread width on a 8" wheel. What's the optimal width?

 

[felopr]

performance wise, you would want a little stretch so it minimizes body roll by tire shoulders deforming under load, you get also a faster/predictable turn in. the bad thing if you stretch it alot it comprises comfort (if you track you dont really care lol) also it looks ricey as fuck imo lol.
It all depends on where are you running , track or street

 

[Plainrt]

Also tire tech on street tires has been changing a lot over the years. Sidewalls now are pretty stiff on the top street tires vs older tires where some of this info out there came from of which width is faster.

 

[DaveG99]

performance wise, you would want a little stretch so it minimizes body roll by tire shoulders deforming under load, you get also a faster/predictable turn in. the bad thing if you stretch it alot it comprises comfort (if you track you dont really care lol) also it looks ricey as fuck imo lol.
It all depends on where are you running , track or street

How much is "a little stretch" ?

 

[Meowoosh]

On my 1st gen turbo track miata, I run 15x8 with 205 rivals. I wouldnt run anything wider on that wheel size, for track day use without limitations on specs. Im about to go up to 15x9 and 225.

For the fiesta, im using a wider tire on a narrower rim just for the sake of meeting autox regulations for h street.

For 15x8, I only use 205. Even a 195 is too stretched. 205/50s are perfect.

 

[Meowoosh]

I also read an article on racing tires and wheels and from a physics perspective, any given tire will perform better on one wheel that is wider than another, as long as the tire is still able to mount safely and properly. Contact patch is what we are trying to visualize here.

 

[DaveG99]

On my 1st gen turbo track miata, I run 15x8 with 205 rivals. I wouldnt run anything wider on that wheel size, for track day use without limitations on specs. Im about to go up to 15x9 and 225.

For the fiesta, im using a wider tire on a narrower rim just for the sake of meeting autox regulations for h street.

For 15x8, I only use 205. Even a 195 is too stretched. 205/50s are perfect.

And tire rack leaves the tread width blank on those tires. But the section width is 8.4" which is super wide for a 205.

 

[DaveG99]

Im trying to decide on tires and how much stretch they will have on a 16x8 wheel.

The 215/45/16 bfg rivals and the AZENIS RT615K+ are both plenty wide at 8.4" SW / 7.5" TW for the rivals and 8.7"SW / 7.6" for the azenis. But I was wondering if a 205/45/16 would fit on the 16x8" wheel.

Id really like to put on some re-71r's 205/45/16 but their width is 8.1" SW / 7.1" TW which seams narrow but I could be wrong. Im just not a fan of the super stretch look but I do care more about performance over looks.

 

[TDavis]

I agree that 205s are perfect for a 8" wide wheel. Not too much stretch to look stupid nor is it square. Just right.

IMO its either between a 205 or 215 for 8" wheel.

 

[Meowoosh]

And tire rack leaves the tread width blank on those tires. But the section width is 8.4" which is super wide for a 205.

True! These BFG Rivals are the widest 205s I've ever seen! "Cheater tires"

To OP, ultimately it is your choice. A wider tire offers more grip. A wider wheel can utilize more of the tire. I think the trade-off here is precise handling vs. overall outright grip. Because the fiesta is a great handler, and doesn't have as much lateral grip as the FoST, I'd stick with what it's good at and go with the precise feel of the 205s. This will also communicate more information to you as the driver which might help with the numbness of the electronic rack

 

[OggiSiMangia]

I have a 16x8 wheel with Hankook RS4s at 205/45/16. They fit almost square with a tiny bit of stretch I think it’s perfect imo. These tires rip man. And I’ve been daily driving them for 5k miles so far and bring them to the mountains every weeekdn for hours and still have a bunch of grip/tread left.

 

[DaveG99]

I have a 16x8 wheel with Hankook RS4s at 205/45/16. They fit almost square with a tiny bit of stretch I think it’s perfect imo. These tires rip man. And I’ve been daily driving them for 5k miles so far and bring them to the mountains every weeekdn for hours and still have a bunch of grip/tread left.

Post a picture please

 

[OggiSiMangia]

Post a picture please

Idk how to be honest lol i can text you a few 😂

 

[Goingnowherefast]

There's benefits to running the widest wheel possible (with a correctly fitting tire) on a road course or AutoX. This is because by putting a tire on a wider wheel, you can artificially increase sidewall stiffness, which enables you to drop tire pressure without experiencing tire rollover. This drop in tire pressure increases the area of the contact patch, resulting in more grip.

This theory has been tried and tested and proven time and time again with 225's on an 8 vs. 9 inch wheel. In almost every scenario, a 225 will be faster on a 9 inch wheel than an 8 inch wheel on a road course. There is LOADs of information detailing this in the Miata/GRM world.

This is for the track obviously, for the street who cares.

 

[DaveG99]

Idk how to be honest lol i can text you a few ??????

Those pics looked great! Ill see if I can post a couple

 

[DaveG99]

 

[Plainrt]

What offset are those. Little more poke than I like but looks good yet.

 

[Goingnowherefast]

Sexy. I'm guessing they rub a bit in the rears though right?