August 2013 Tire Test

In the Aug 2013 issue of Grassroots Motorsports Magazine, there was a tire test on the new Bridgestone RE-11 – compared to a Goodrich g-Force Rival. I am hoping to get comments from the author of the article Andy Hollis.

I note with interest that a prelude to the actual test was a skipdpad evaluation to determine the best inflation pressure for each tire. It started at 40 psi and dropped 4 psi until maxed out. This portion was not well documented and I have lots of questions concerning the procedure – particularly since it contradicts what many have been saying about the relationship of traction and inflation pressure (and I would not be one of those!)

Also of interest was that the 2 tires got different results – 32 psi for the BS and 27 psi for the BFG.

In reply to CapriRacer:

We've described the procedure in past articles, but still get asked a lot. So we recently just wrote it all up so we can link it.

http://www.facebook.com/notes/hollis-racing/how-to-do-skid-pad-testing/417124891704816

Hope that explains it.

As to your preconceived notions on pressure versus grip, here's the deal: there is an optimal range of pressures where a tire develops max lateral grip. Anything either above or below that range will be slower. So we start above the optimal, drop into the optimal, and keep dropping until it gets to be suboptimal again. Then we go back to optimal to verify.

Optimal pressure depends on all kinds of things, though tire design and wheel width are the most important. Alignment settings, body roll, vehicle weight, etc, all contribute.

Thanks Andy for the link to the info

Ditto that. Thanks for quick reply Andy!

Andy,

Thanks for the reply.

That makes me feel a bit better - particularly since the results fit my preconceived perceptions - and NOT those with whom I have been arguing. In particular, that the max grip occurs in the normal range of inflation pressures and NOT near the max pressure written on the sidewall (or worse, above).

But more importantly, your write up indicates you aren't just willy-nilly picking a pressure or following a procedure that has a built in flaw. You are following a procedure that will get you to the answer.

But I also know that folks will wonder if there is a significant difference in the normal range of pressures. In other words, in spite of the fact that optimal grip occurs at X pressure, operating a tire at Y pressure is nearly the same.

Can you fill in that gap?

BTW, you may want to visit my website:

www.BarrysTireTech.com

That should explain why I get involved in these types of conversations.

CapriRacer wrote: But I also know that folks will wonder if there is a significant difference in the normal range of pressures. In other words, in spite of the fact that optimal grip occurs at X pressure, operating a tire at Y pressure is nearly the same. Can you fill in that gap?

Not sure exactly what you are asking here, so I'll answer with this:

The optimal pressure curve for any given tire is typically bell shaped. There is a range where the same grip (as measured by skid pad lap times) is delivered. And it tapers off as you move away from this range. The breadth of that peak depends on the tire model, the car's setup, and especially the wheel/tire width matchup. Change the car, the setup, the wheel...and you change the curve, even if the tire stays the same. And different tires certainly generate different curves.

BTW, if you use any of this on your site, please attribute. Bugs me when I see my write-ups on the web unattributed. Thanks.