From noted wheel author Jobst Brandt:
Subject: Re: Dark art of descending!
Date: 23 Aug 1999 22:03:22 GMT
Jeff Potter writes:
> Going down the top super steep half was like doing a pushup! I had to
> brake full-on on the straights not to go too fast for the curves.
> Tired hands. SUPERHOT RIMS! I had sewups on, so I stopped for a
> few minutes halfway down.
> How do you guys deal with superhot rim heating? Is there such
> a thing as too steep?
I don't know how you kept the tires from slipping on the hot glue and
piling up on the stem. This is the usual indicator that tubular tire
wheels are too hot. The next is that the tire lifts off in the
compressed area just ahead of the stem.
This is a serious problem both for tubulars and clinchers
clincher tires, given enough heating time on a hot rim will blow off
if inflated to the hardness that most racers like for criteriums
(hard). The faster you can go, the more power goes into wind drag and
the more air rushes over the rims. Slowing down does not help, unless
you reduce speed to a walking pace.
For steep descents where the rims stay hotter than you can bear to
touch for more than a minute, you should let some air out of the tires
to where you would normally want to re-inflate them after some disuse.
I don't mention a pressure because that depends on the tire size.
Small tires heat up faster than large ones but the blow-off pressure
is the same, it being dependent only on the opening of the rim width.
> I felt I was going too fast for the curves yet it was too steep to
> slow down enough! Well, that was when I was 'rawest,' I got a lot
> bolder at the halfway down point. It was fun to start throwing the
> body into the turn, to point the shoulders out to the exit of the
> turn, all over again. Kind of point the body, then pull the bike
All that "body English" is gratuitous gesture, much like the
motorcyclists who stick their butt out in curves while their bikes
never get down to 45 degrees (where hiking out becomes necessary to
keep hardware from dragging on the road). In fact, if you are taking a
bunch of ess bends rapidly, you'll have no time to change your
position. Just keep your weight on your (horizontally positioned)
feet, and unless the road is rough, keep light pressure on the saddle.
> The other good rule was: make half your turn by the halfway point!
I disagree, because you can slow down much faster than you can
accelerate. The trajectory is naturally asymmetric. And you can
brake all the way to the apex of the curve, but you cannot pedal at
that lean angle.
> The other good rule was: make half your turn by the halfway
> point!into the turn you're already throwing yourself down and to the
> inside and looking to the far straight, you twist your shoulders
> toward the center of the turn. It feels like you're getting yourself
> all oriented to the exit even before you've gone in!
That may look impressive but it doesn't have any positive effect on
the lean of the bicycle and its traction on the road, that being what
counts in order to corner at the limit.
> Does this at all relate to a correct way to handle switchback descents?
The term switchback refers to mountain railroading where at the end of
each traverse, a switch is turned to back up the next traverse, after
which another switch is turned to head up the next traverse. The
appropriate term is hairpin turn and these are the ones where
trajectory asymmetry is most conspicuous, because braking can be hard
enough to raise the rear wheel when entering but one cannot accelerate
similarly. Most riders often find themselves with extra unused road
on the exit of such turns. This exemplifies the difference between
entry and exit of turns.
> Does anyone descend the top half of Flagstaff without much braking?
I'm not familiar with that road but there are many that have gradients
that requiring stops to cool the rims. There is no way of descending
them continuously unless you have insulators between the tube and rim.
Insulating rim strips are no longer offered because they were an
artifact of dirt roads that required riders to descend so slowly that
all potential energy went into the brakes and almost none into wind
drag. These rim strips were cloth tubes filled with kapok, their
insulating purpose being a mystery to most riders when they were last
Jobst Brandt <email@example.com>