Re: [CR]Grand Bois tires


Date: Tue, 7 Aug 2007 20:24:58 -0700
From: "Kurt Sperry" <haxixe@gmail.com>
To: "hersefan@comcast.net" <hersefan@comcast.net>
Subject: Re: [CR]Grand Bois tires
In-Reply-To: <080820070314.4149.46B93527000B40F9000010352200761064020E000A9C9D0A08@comcast.net>
References: <080820070314.4149.46B93527000B40F9000010352200761064020E000A9C9D0A08@comcast.net>
cc: Classic Rendezvous <classicrendezvous@bikelist.org>
cc: Classic Rendezvous

Someone hopefully will correct me if I'm mistaken but it is my understanding that rolling friction is more a function of inflation pressure than tire width. Two tires inflated to the same pressure, one with twice the cross sectional area of the other, the actual contact patch will be roughly equal (see physics of the behavior of confined gasses), but the "fatter" tire will need to deform its casing less to conform to the road at that equal pressure, thus less energy will be loss to hysteresis/heat and theoretically at least the wider tire should roll more efficiently. I think the quasi-myth that skinny tires are "faster" is based more on intuitive reasoning than science. Skinny tires LOOK faster though, that's for sure!

Kurt Sperry Bellingham WA USA

On 8/7/07, hersefan@comcast.net <hersefan@comcast.net> wrote:
>
> There actually are wonderful tires in the 25mm width - try the Vittoria
> opens or perhaps the Deda Giro De Italia (made by Challenge) that may be
> available as a Challange model and meassures around 24mm.
>
> But - a top quality 28mm (or 30mm) can be just about as fast as a narrower
> tire, but is lots more comfortable. The reason the Grand Bois tire is so
> exciting is that it isn't 25mm. In Bicycle Quarterly, it was shown, if my
> memory is right, that the Clement 28mm Del Mondos were FASTER with respect
> to rolling resistance than the Crit Setas. So the reason the Grand Bois is
> so great is because the size makes so much sense. The Thai Clement Paris
> Robaix tires in 24mm were actually slower than the 28mm Del Mondo
> counterparts! The reason is that the Paris Robaix had a heavier casing than
> the Crits - but only when a sufficiently wide casing is used, does the
> rolling resistance benefit of the wider tire outweigh the detrimental effect
> of the heavier casing.
>
> Mike Kone in Boulder CO
>
> -------------- Original message --------------
> From: "Daniel Artley" <dartley@baltimorecountymd.gov>
>
> > I've been riding the newer 700 x 28 Grand Bois 'Cerf' tires for a week
> or
> > so now, and really am pleased with how nice a tire it is. It's still a
> > bit larger than my ideal, but for it's size it feels lighter, rolls
> really
> > well and really sticks to the road. I believe Jan Heine compared the
> ride
> > to a Clement 'Campione del Mondo', I'm thinking more 'Paris Roubaix',
> but
> > that was a long time ago for me. The tread is razor straight while at
> > speed, really a nicely put together tire. Running 92 x 95 lb's. in the
> > fr./rr., they just about took out all the expansion cracks on my stiff
> RS
> > touring bike and my hefty heifer body, with just a couple more pounds
> for
> > my ideal feel. I've been looking for a nice gum walled daily rider now
> > for some time. This is as close a new one as I've found.
> >
> > Now if I can only convince Jan to try to get the Grand Bois' in a
> 25-25.5
> > mm tire for that 'criterium seta' ride!
> >
> > Happy trails,
> >
> > Dan Artley in Parkton, MD