Tested: Does a shorter, lighter tire always equal more speed?

I missed this the first time that it ran. I've been debating the change to the 17" rim for next season to give clearance for bigger brakes. It looks like it makes a lot of sense along with the conversion to 294MM brakes. 

Great info as always Andy. 

codrus (Forum Supporter) said:

Unfortunately the Haney book is out of print, there's no e-book version, and used copies are going for crazy prices online.  I borrowed a copy from a friend to read and it had a lot of interesting things to say, so it's definitely something to keep your eyes open for.

Sounds like a good reason to buy Dad said the F word! and just scribble in the spare pages. 

In reply to codrus (Forum Supporter) :

https://archive.org/details/insideracingtech0000paul/mode/2up

tealchief said:

In reply to codrus (Forum Supporter) :

https://archive.org/details/insideracingtech0000paul/mode/2up

Different book, the one I was talking about is this one:

https://www.amazon.com/Racing-High-Performance-Tire-Using-Balance/dp/0768012414

(and yes, a 3rd party seller on Amazon is asking $2500 for a used copy).

In reply to Andy Hollis :

https://grassrootsmotorsports.com/articles/wheel-width-is-wider-always-better/

At the end of this article you dropped a full second going from a 25" 225/45R17 to a 23.2" 205/45R15, and chalked it up to the diameter. In hindsight, do you think the improvement was more from the sidewall support (with the 225 being pinched onto a 7" wheel) and the weight reduction (6lb per corner)? 
 

Thanks! 

Lindenwood said:

In reply to Andy Hollis :

https://grassrootsmotorsports.com/articles/wheel-width-is-wider-always-better/

At the end of this article you dropped a full second going from a 25" 225/45R17 to a 23.2" 205/45R15, and chalked it up to the diameter. In hindsight, do you think the improvement was more from the sidewall support (with the 225 being pinched onto a 7" wheel) and the weight reduction (6lb per corner)? 
 

Thanks! 

Essentially, yes.

A 225 on a 7 isn't getting any benefit from it's additional width over a 205.  So the gearing and weight benefits of the 205 combo prevail.  Note that those SSR's are exceptionally light.

Put the 225 on a proper 9, and the 205 on a proper 8...and it would be a different story.

In reply to Andy Hollis :

Thank you for the response! Your data collection and analysis is amazing so I'm happy to support the effort! 

While this testing may contradict some of your prior testing, doesn't it reenforce your longstanding findings that wider is better (in almost every case)?

These types of explorations are always of great interest.  Keep up the deep diving!

edmknapp said:

While this testing may contradict some of your prior testing, doesn't it reenforce your longstanding findings that wider is better (in almost every case)?

It reinforces the concept that wider *and* taller are both usually better, all other things being equal.  But taller almost always has side effects that may take quite a bit of effort to minimize/accomodate.

More importantly, it reinforces the idea that only testing will tell the whole story.

I've got another one of these tests planned for 2025, now that Nankang is coming out with a 275/35-15 CRS.  And then there's P1 in 285-15 & 305-15...but also 285/30-17.  That last one could be a real show stopper.  I've been running 225/40-17 R7's on the front of my CRX for local TT, so this is a similar idea but in a 200tw.