225/45/17 vs 245/40/17 Same Compound and Wheel, which is faster

[ZDan]

Originally Posted by RT-BRZ

All very interesting data. The only thing that's tough to get past is that the 225 tire at the same aspect ratio is taller than the 215 tire.

What would have been GREAT would be if they also tested 235/45-17 (and maybe 235/40-17 as well).

The 225 results appear to overachieve relative to 215 and 245 rather than just interpolating between them. Could be due to "better" gearing for this particular course? Seeing results for 235/45 and 235/40 could help clear that issue up.

[MacSpeed]

The TR test are better than nothing but still need to be taken with a grain of salt.

They do not adjust tire pressures for one. They run what the door says for psi. once that is changed and FSB is added to the mix like street class autox plus bump stop tuning and shocks, these results get thrown on their head.

Don't get me wrong, this is all cool data but I would be careful pulling hard absolutes from it.

[jflogerzi]

Originally Posted by MacSpeed

The TR test are better than nothing but still need to be taken with a grain of salt.



They do not adjust tire pressures for one. They run what the door says for psi. once that is changed and FSB is added to the mix like street class autox plus bump stop tuning and shocks, these results get thrown on their head.



Don't get me wrong, this is all cool data but I would be careful pulling hard absolutes from it.

I don't think anyone is putting it as be it 100% Truth. And I agree tire pressure is going to have more impact.

Sent from my Pixel 6 using Tapatalk

[MX-5RACER]

Originally Posted by cmiovino

Speaking in terms of autocross only, it's common that everyone is putting as wide of a tire on as possible. All our second gen guys (and there's a lot of them) are running 245's and even 255's on a 7.5".

Everything goes out the window when speaking in terms of autocross. I can still remember the days of people putting 275 Hoosiers on 6" wide rims on DS Type R Integras back in the day.

As with anything else, test as much as you can. Keep in mind that for some of us, $/run or lap weighs heavily on the tire and width choice.

A friend of mine once said that the RA-1's suck compared to a Hoosier, but they suck for a LONG time.

[GrandSport]

edit: doh, wrong thread!

[Scargod]

What I'm curious about, and don't see much about, is what horsepower does to our tire selection. I can only assume that people are stock unless they say otherwise.
Then you start gutting, lowering, adding aero. All that is not clear unless stated, which it seldom is, or perhaps you go digging for the poster's info.

I've seen people talk about running 255's on road courses. I think some (most?) have turbo's.

I get 230 HP from my 2022 BRZ. I've no rear interior, but I have a wing and splitter. I'd guess I'm under 2,800 with light 17" wheels, rotors, coilovers, lighter exhaust.
I'm very happy with the performance of my 245 F1 Supercar's. Good lap times.
So, could there be an advantage for me on tighter, shorter courses with 255's? If it's only 50-75°F will there be an issue getting them up to temp?
Goodyear doesn't make an F1 Supercar tire in 255 though there are tires like Falken's and Kumho's, but is their lesser traction performance outweighed by their larger surface area? I'm not going to go to Hoosiers or similar that cost a lot for the laps.

[RedReplicant]

I have never had issues getting a 245 on a 10 or 255 on a 9, 9.5, or 10 to temp even in a car that weighed 2400lb with me in it and made 220whp (and I still don't with my current car at 2850 min / 205 avg whp). I'm more worried about the drop-off from heat after 1-3 laps depending on tire.

Assuming you're talking SC3R there isn't much faster other than going Hoosier. GRM did tests a while ago with a more narrow A052 vs another couple wider super 200tw tires, if you dig around though.

[timurrrr]

I love data.

[RedReplicant]

Andy also wrote another semi related article a few days ago too

https://grassrootsmotorsports.com/ar...ize-comparison

[GrandSport]

Originally Posted by Scargod

What I'm curious about, and don't see much about, is what horsepower does to our tire selection. I can only assume that people are stock unless they say otherwise.
Then you start gutting, lowering, adding aero. All that is not clear unless stated, which it seldom is, or perhaps you go digging for the poster's info.

I've seen people talk about running 255's on road courses. I think some (most?) have turbo's.

I get 230 HP from my 2022 BRZ. I've no rear interior, but I have a wing and splitter. I'd guess I'm under 2,800 with light 17" wheels, rotors, coilovers, lighter exhaust.
I'm very happy with the performance of my 245 F1 Supercar's. Good lap times.
So, could there be an advantage for me on tighter, shorter courses with 255's? If it's only 50-75°F will there be an issue getting them up to temp?
Goodyear doesn't make an F1 Supercar tire in 255 though there are tires like Falken's and Kumho's, but is their lesser traction performance outweighed by their larger surface area? I'm not going to go to Hoosiers or similar that cost a lot for the laps.

I think that a variable not given adequate consideration is alignment.
If you can't get enough negative camber to get the tire flat, it really doesn't mattter how much tire is not touching the ground (or doesn't have significant load).

So yeah, when you're only riding on the outside inch of tire around turns because these tires are so grippy these days, regardless of the tire width, the tire that is 10% lighter will be faster.

[ZDan]

Originally Posted by GrandSport

If you can't get enough negative camber to get the tire flat, it really doesn't mattter how much tire is not touching the ground (or doesn't have significant load).

So yeah, when you're only riding on the outside inch of tire around turns because these tires are so grippy these days, regardless of the tire width, the tire that is 10% lighter will be faster.

IMO opposite should be more generally true. If you don't have enough camber, a wider tire should roll over onto the sidewall less.