Tire pinch or stretch question

Related to my track day post, I have a question about wheels and tires. Who better than this crowd, right?

The Elantra N has an 8" wide wheel designed to run a 245 tire. Going wider realistically requires a wider wheel.  I found a set of 18 x 9.5 wheels in the right bolt pattern for a very good price so I snagged them. I am still limited with room in the wheel wells, so the question is this: will a 245 pinched onto an 8" wheel work better than a 245 stretched onto a 9.5" wheel?  Is the 9.5 wheel really of use if you are not running something bigger, like the class max 285? What if they fit up front and not out back, can I run wider fronts and channel my inner Randy Pobst? 

I feel like I will have to suck it up and buy the right thing; a 9" wide wheel with the ideal offset. Since these were cheap I thought I would play around and see. 

I have no data to back this up beyond seat of my pants. 

I always felt pinched setups were more forgiving than stretched setups. If you shocked the tire it had a better chance of grabbing the surface again. 

It may well be a figment of my imagination. 

A slight stretch typically provides a stiffer sidewall and better steering feel, the 949 guys found they were faster with the more predictable setups. 

I run 245/35 Conti ECS on 18x9.5 ET45 wheels on my BRZ. Once I get the nerve to shave the rear tab I'll step up to 255 maybe 265. 

Adding wheel width always makes the car faster than adding tire width.

245's belong on at least a 9" wheel, if not a 9.5 or 10. 

245 on an 8 is a waste of rubber width.

https://www.tirerack.com/tires/tests/videoDisplay.jsp?ttid=296

I was running 19x8.5 +35 AV20s on my Kona N with the stock 235/40-sized all-season tires. They were a little stretched and the ride was stiffer but I didn't worry about clearance issues. I also wasn't lowered, I was running the stock springs. I think the EN can get away with an 18x9.5 with a 255/35 or similar tire without clearance issues, at least at stock height. YMMV.

I briefly looked into the 18s for my KN but decided not to open that financial can of worms. I do know, however, that a few KN guys were switching to 18x9.5 +45s and ran the aforementioned 255/35s. Some brave souls tried 265s but I can't remember if any adjustments were needed.

Andy Hollis said:

Adding wheel width always makes the car faster than adding tire width.

245's belong on at least a 9" wheel, if not a 9.5 or 10. 

245 on an 8 is a waste of rubber width.

https://www.tirerack.com/tires/tests/videoDisplay.jsp?ttid=296

100% this is my experience.  245s on a 10.  205s on an 8.

It made the car WAY faster than a 245 on the 8s we were running.

Of course, this begs the question of why OE's pinch tires all the time.

Two reasons:

1) Ride quality.  Pinched tires provide a smooher ride

2) Load ratings.  Bigger tires provide higher load ratings, which some cars need - -maybe at only one end.

Top is a 255 on the 9.5, bottom is 245 on the 8". I think the stretch may also help with clearance. Sadly, the Indy 500s are worn to the cords, so I won't be able to use this awesome tire. (Ha!)

Keep in mind that these are 18s and not 15s, 245/40R18 is a theoretically ideal fit on an 18x8 wheel according to tire manufacturers (who prefer a squeezed setup as Andy pointed out), and looks pretty square, maybe slightly squeezed. Putting them on 18x9.5s will only be a mild stretch and will work even better than on an 18x8.

I view stretching and pinching as a way to control sidewall stiffness and thus steering response, sidewall flex and ride quality. 

These aren't the best pictures, just what's on my phone, I'll try to get some better ones once I've logged off for the day. 

This is what a 245/35/18 Conti ECS (the ECS 02 came out right after I got these on the car in late 2022), on an 18x9.5 wheel. 

Smaller width that you're considering, but here is some perspective.

245 / 40 on an 8in

245/40 on a 8.5in

Wheels are different offset, but I thought I'd include a pic for ref.

Note that not all 245's run the same tread width.  Those Contis run narrow-to-normal.  Most 200tw stuff runs normal-to-wide.

pinchvalve (Forum Supporter) said:

Top is a 255 on the 9.5, bottom is 245 on the 8". I think the stretch may also help with clearance. Sadly, the Indy 500s are worn to the cords, so I won't be able to use this awesome tire. (Ha!)

You're comparing two tires with vastly different sidewall structures and probably overall widths relative to nominal sizes which isn't really useful data. A052s have basically zero sidewall structure and will always look more pinched than just about any other tire as a result. And as a result they do generally want more wheel than other tires.

My analysis of the overall situation is similar to toyman's. For a given wheel width, pinching more tire on it if anything reduces ultimate pace slightly but makes that ultimate pace easier to accomplish by being more forgiving, at the expense of feel, response, and usually wear. Personally I like a little bit more than "optimal" but not as much as some people like to stuff on. My target is tread width slightly less than wheel width.

Andy Hollis said:

Of course, this begs the question of why OE's pinch tires all the time.

Two reasons:

1) Ride quality.  Pinched tires provide a smooher ride

2) Load ratings.  Bigger tires provide higher load ratings, which some cars need - -maybe at only one end.

I always assumed curb protection was a factor also.

I am wheel size limited on the racecar so I went pinched just to get more weight capacity. 235/50R16 on a 7x16 wheel. On the street I like 235s on an 8" wheel for a good combo of steering feel and curb protection.

Andy Hollis said:

Note that not all 245's run the same tread width.  Those Contis run narrow-to-normal.  Most 200tw stuff runs normal-to-wide.

Then there's the R7 where the 245 would be considered a 265 in any other tire. :)

One non-performance consideration if these wheels are also used on the street is that a tire with a normal or pinched fitment is somewhat forgiving of mild curbing and you'll just get a slightly scuffed sidewall.  A stretched tire is not providing any protection and any tap of the curb will cause cosmetic damage to the wheel.

TravisTheHuman said:

Andy Hollis said:

Of course, this begs the question of why OE's pinch tires all the time.

Two reasons:

1) Ride quality.  Pinched tires provide a smooher ride

2) Load ratings.  Bigger tires provide higher load ratings, which some cars need - -maybe at only one end.

I always assumed curb protection was a factor also.

Depends on the tire.  Many modern tires have quite large outboard rim protection beads.  

Others have almost zero -- "Talking 'bout you, A052"

Andy Hollis said:

Of course, this begs the question of why OE's pinch tires all the time.

Two reasons:

1) Ride quality.  Pinched tires provide a smooher ride

2) Load ratings.  Bigger tires provide higher load ratings, which some cars need - -maybe at only one end.

Tire pressures to get even wear when driving like a normal person are also a lot lower with a pinched setup.

A long long time ago, when 13" tires were still a common thing, I used to have to run 20psi for even wear on a 205/60 on a 5.5" wheel.

Another interesting thing is that pinched setups seem to be a lot more forgiving of camber.

I always have enough tire width to lay the wheel face down without it touching the garage floor. If I were autocrossing I might not follow that "rule" though.

Shew and here I am putting 275's on 10's or 14's.....

In stock or street autocross classes I tend to see a ton of pinched tires (at least the last time I saw ES Miatas). I guess if you can't increase wheel width it's still better to have more tire than not.

CyberEric said:

In stock or street autocross classes I tend to see a ton of pinched tires (at least the last time I saw ES Miatas). I guess if you can't increase wheel width it's still better to have more tire than not.

Even a 205 is pinched on a 6" wide wheel.  😉