[rhop101]

Hi Everyone,

This video and article came out from a review TireRack did a year ago.

I’ve thought about posting it as a response to a few threads so instead I decided to post it once as its own topic and I reviewing all the posts over the past year in the Tracking/AX sub forum and here I’ve haven't seen this video discussed on the forum. Since it’s related to wheel sizes I decided to post it here.

Video:

Article: https://www.tirerack.com/tires/tests...&affiliate=HP5

They took their fleet of BRZs and tried out 3 tire sizes:

- 215/45
- 225/45
- 245/40

On 3 different 17” wheel widths:

- 17x7”
- 17x8”
- 17x9”

The interesting result was that 225s on a 9” wheel were the fastest average speed tire over 245s on a 9” wheel by about 0.3% on that day, in that car on their comparison track.

225s on a 9” rim were about 1% faster than 245s on an 8” rim (same disclaimer)

Brief Analysis
As I’m getting ready to buy dedicated wheels and tires for my car for AX competition after running on the stock wheels for the last 2 seasons, this article gives me some interesting thoughts.

Our cars are obviously heavier with slightly worse weight distribution, but have more torque. So with this in mind here we go.

1. More wheel width = better for run times.
2. Wide tires without wheel support “may” be money down the drain.
3. If money is no object going 18” to get the the 9.5” wheel options and shorter sidewalks maybe better for support.
4. Other suspension tweaks are likely required to get the most out of wider tires.
5. I’m way overthinking this for a car that isn’t SCCA Solo competitive on a National level.

I wish TireRack would do another video comparing diameter sizes to answer that. Although our cars are like 19s on the 3/4 series because we have the shorter sidewall.

Anyways just want people to be informed so they can make the best decision for themselves since the result of this is a bit surprising.

[M3SQRD]

Another wheel width and tire width comparison (there are plenty more articles and videos on this topic) that includes a 720s which applies to wider tires and wider wheels. Similar findings and conclusions.

Why do you find the results surprising? If you aren’t fully utilizing the width of the tire then less/loss of performance is expected.

https://grassrootsmotorsports.com/ar...always-better/

[dradernh]

Hoosier recommends a tread width +/- 1" of the wheel width. So if the tread width of a 245/40-17 R7 you'll mount on an 8.5" wheel is 9.7", for example, you'll have a tire whose tread is crowned or rounded once mounted on the too-narrow wheel. It may look flat or close to flat to the eye. If you place a framing square up against the sidewall and the tread, however, you'll see the effect. It's especially clear when doing this side-by-side with a tire whose tread width is a better match to the wheel's width.

A framing square demonstration was the process by which I was strongly encouraged not to run too-wide BFG R1 255 tires on the sets of 9" wheels I had, even though I had no trouble bringing those tires up to their recommended temperature range on the track. Instead, R1 245s were a better fit for the wheels and for my lap times, the latter of which made a difference to me when competing in two different clubs' TT events.

One of the many added values offered by Tire Rack are its data points. These include the tread widths of the tires they sell, as explained here: https://www.tirerack.com/upgrade-gar...re-tread-width.

That site is where I learned that the 245/35-18 Michelin PSS tires that came on my M240i have a significantly wider tread width than do the 255/35-18 Michelin PS4S tires that came along later. Who knew, right.