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

I am in the market for some new 200TW tires to be used during PB Weather and Short stints going for a fast lap. Will contiune to use SX2's or maybe some RS4's for lapping sessions. I was reading some Tire Rack Comparisons and in some of there testing the 225 wide tire on a 9 inch rim was slightly faster than the 245 wide tire on the same rim. Is there any truth to this? They did mention they though the 245 wide tire on a 10 inch wide rim would probably be the fastest. I am thinking it allows for a wider part of the tire to contact the road/Track Surface with 9 by 225 combo? Also I would not complain saving some money too as 225's are cheaper.

This is down the path of holy war stuff on the internet, but if you search around for posts by Andy Hollis you'll find some interesting nuggets with respect to tire section width vs wheel width, optimizing a given tire, and how traditional street tires vs hoosiers work given wheel width.

The short of it is, for a street tire (non-hoosier / non-dot slick), a wider tire is not faster without a wider wheel.

Interesting enough weight is pretty damn close despite being a wider tire due to the 245 being a 40 vs the 225 being a 45 inch tall tire

Worth noting tirerack does not adjust pressures or alignment for their tests, you’re getting a bone stock car set to 35psi cold and run on their asphalt skidpad/autox course. It’s not bad data, but there’s a grain of salt there that when the results are very close odds are there’s more time to be found in each setup that they don’t have the resources to fully test. That’s where Hollis and GRM have an advantage.

Personally, if you’ve only got budget for one set of tires, be a lemming and follow the crowd (225 for an 8, 245 for a 9), otherwise I find myself putting a question mark next to my results and wondering if the standard is better. If you have the budget to test, or the willpower to go through the effort of testing and selling the scrubbed sets you don’t like, that’s when you start tinkering. Way too many variables and personal preference will absolutely play a role unless you’re a driving machine.

Tirerack test for anyone who missed it, sorry for the mobile link.
https://m.tirerack.com/tires/tests/t...y.jsp?ttid=296

I decided to give the 225/45/17 a try on my Current wheels which are 17x9 sized Apex.
I will be sure to post my thoughts. I won't have a way to compare times but I am interested in feedback, Steering feel etc...

225 will likely overheat slightly faster than 245 when pushing due to smaller surface area and less mass.
So even if 225 and 245 give you the same time at autox, 245 will likely be faster over a 5-mile lap at Thunderhill.

My knowledge and recommendations come mostly from autocross specific applications. With that said, 245/40/17 is going to be quicker than 225/45/17 in that setting every time, all other things considered equal. This even goes for cramming the widest tire on a small wheel. Even with stock suspensions and only about a degree of camber, again wider is better. Even the added grip seems to easily outperform any weight negatives.

Track driving, eh - it can depend, but I still think 245 has the edge. Other things start coming to play like how quickly you can warm up the tires in that session, what other suspension mods you have, etc. Other things need to be considered like replacement costs as you're hammering through tires more frequently too. And also the goal - just lapping days, vs time trial/attack type stuff.

If I'd have to pick though, the 245's are likely going to come out on top for times in most cases, even in the track world.

I don't have experience with different size tires on same width wheel but same car, same day, same driver, same tire compound a 255 on 9 inch wheel was about 2 seconds faster than 225 on an 8 on a roughly 2 minute lap track

:lol:

why laughing? I just always find it funny :)

I think he's laughing because the 40 and 45 refer to the aspect ratio of the tire - I.E. the height of the sidewall expressed as a percentage of the width, and you wrote (presumably just typo'd) it as a "45 inch tall tire".

On the 225/45R17, the sidewall is 45% of 225mm = 101.25 mm

On the 245/40R17, the sidewall is 40% of 245mm = 98 mm

I am a moron [emoji23]

Sent from my Pixel 6 using Tapatalk

Nah, you just learned a thing!

FWIW 225/45-17 is ~25" tall and 245/40-17 is ~24.7" tall.

I fricking LOVE the madness in how tire sizes are designated. Three different numbers, first one is in mm, next one is a percentage (unitless), and the third is in inches. Hilarious!

Unloaded 225/45-17 tire diameter in mm = (2x225mm*45/100) + (17in. * 25.4mm/in) = 634mm.
634mm/(25.4mm/in) = 25.0"

Curious what you'll think about steering feel. The best steering feel I've felt on these cars (gen 1 or 2) has been on 17x9 with a 200tw 235/40/17 tire. 225/45 is even more stretch, albeit with more sidewall too.