downhill rims?

Ric tried to scribble ...

Quoted message said:

At the end of a longish descent on my road bike my brakes are fading badly and the rims are fairly
hot to the touch. It's not a huge problem, as I still have enough braking in reserve if I keep the
speed down. But I wondered if the pros use different rims and brakes for the mountain sections of
the big races?

Ceramic rims help ..

--
Digweed .... 😉

Quoted message said:

Ceramic rims help ..

...make things worse.

From J Brandt on rbt FAQ

"Ceramics are insulators, both electrical and thermal, so the braking energy converted to heat in
the brake pad cannot transfer to the aluminum rim where it can be dissipated. The result is rapid
pad wear and reduced brake effect."

Tony

Tony Raven tried to scribble ...

Quoted message said:

Quoted message said:

Ceramic rims help ..

...make things worse.

From J Brandt on rbt FAQ

"Ceramics are insulators, both electrical and thermal, so the braking energy converted to heat in
the brake pad cannot transfer to the aluminum rim where it can be dissipated. The result is rapid
pad wear and reduced brake effect."

In practice I find ceramic rims are most excellent, no matter what the severity or length of
downhill I ride .. I do ride off-road though, so maybe this doesn't translate to on-road ..

--
Digweed .... 😉

[email hidden] schreef ...

Quoted message said:

At the end of a longish descent on my road bike my brakes are fading badly and the rims are fairly
hot to the touch. It's not a huge problem, as I still have enough braking in reserve if I keep the
speed down. But I wondered if the pros use different rims and brakes for the mountain sections of
the big races?

A rather costly solution to your problems would be disk brakes that leave the rims cold but can
induce other problems.

A far cheaper solution are Magura HS-33 rim brakes. These (practically) don't fade. And if you
alternate the braking between front and back (or learn to brake less......) the rims won't
*over*heat.

--
Regards, Marten

"Ric" <[email hidden]> wrote in message "]news:[email hidden]...

Quoted message said:

At the end of a longish descent on my road bike my brakes are fading badly and the rims are fairly
hot to the touch. It's not a huge problem, as I still have enough braking in reserve if I keep the
speed down. But I wondered if the pros use different rims and brakes for the mountain

sections

Quoted message said:

of the big races?

Did you not see the TDF this year?
Mr. Beloki did have a huge problem :-(

Pete

Ric said:

At the end of a longish descent on my road bike my brakes are fading badly and the rims are fairly
hot to the touch. It's not a huge problem, as I still have enough braking in reserve if I keep the
speed down. But I wondered if the pros use different rims and brakes for the mountain sections of
the big races?

They will almost certainly use different wheels to most of us. They almost certainly brake less too.
I have not experienced your problem on long descents (8 miles), on the bike I am thinking of I have
MA3 rims, not anodised, Shimano 105 calipers and aztec blocks (I think, maybe fibrax). The rims get
hot but braking power does not seem to be diminished.

Ric said:

At the end of a longish descent on my road bike my brakes are fading badly and the rims are fairly
hot to the touch. It's not a huge problem, as I still have enough braking in reserve if I keep the
speed down. But I wondered if the pros use different rims and brakes for the mountain sections of
the big races?

It's impossible to "burn up" the brakes on a solo bike [1]
- see John Forester's website for more details. If the tyres are already at their maximum pressure,
it is possible to blow them off the rims though. The pressure could rise by about 30% with
constant braking on a mountain descent.

The pros are more concerned about heat softening their tubular cement, so if they still ride tubs,
they will alternate between front and back brakes to allow the rims to cool.

[1] a tandem has the same size rims but twice the weight, so normally a third drag brake is fitted
to get rid of some of the heat at the hub.

Tony Raven said:

Quoted message said:

Ceramic rims help ..

...make things worse.

From J Brandt on rbt FAQ

"Ceramics are insulators, both electrical and thermal, so the braking energy converted to heat in
the brake pad cannot transfer to the aluminum rim where it can be dissipated. The result is rapid
pad wear and reduced brake effect."

Tony

I have not noticed this in practice with my rims/brakes combo on alpine descents.

Quoted message said:

They will almost certainly use different wheels to most of us. They almost certainly brake less
too. I have not experienced your problem on long descents (8 miles), on the bike I am thinking of
I have MA3 rims, not anodised, Shimano 105 calipers and aztec blocks (I think, maybe fibrax).

The

Quoted message said:

rims get hot but braking power does not seem to be diminished.

Probably fair to say I am bigger and heavier than most pro-cyclists (1.95m and 95kg) so their is a
lot more kinetic energy to convert to heat. Also, I live in a hot climate (south of France). I don't
know the exact spec of my bike - but it is a Giant OCR with good quality rims and brakes. The brake
fade never becomes dangerous and I don't need to change anything on my typical rides. However, I do
wonder how it will stand up to the descent of Ventous which I want to do next week.

Ric said:

Quoted message said:

They will almost certainly use different wheels to most of us. They almost certainly brake less
too. I have not experienced your problem on long descents (8 miles), on the bike I am thinking of
I have MA3 rims, not anodised, Shimano 105 calipers and aztec blocks (I think, maybe fibrax). The
rims get hot but braking power does not seem to be diminished.

Probably fair to say I am bigger and heavier than most pro-cyclists
(1.95m and 95kg) so their is a lot more kinetic energy to convert to heat. Also, I live in a hot
climate (south of France). I don't know the exact spec of my bike - but it is a Giant OCR with
good quality rims and brakes. The brake fade never becomes dangerous and I don't need to change
anything on my typical rides. However, I do wonder how it will stand up to the descent of
Ventous which I want to do next week.

I try not to keep the brakes on constantly, brake, release, brake, release, thats what I do. Have
faith in your tyres to keep their grip at high speeds, ride around the melted tarmac and loose
chippings. I wouldn't worry about Mont Ventoux, I crossed the Pyrenees in the beginning of August
this year, remember how hot it was ?, my brakes were good enough.

Ric <[email hidden]> wrote in message "]news:[email hidden]...

Quoted message said:

Quoted message said:

They will almost certainly use different wheels to most of us. They

almost

Quoted message said:

Quoted message said:

certainly brake less too. I have not experienced your problem on long descents (8 miles), on the
bike I am thinking of I have MA3 rims, not anodised, Shimano 105 calipers and aztec blocks (I
think, maybe fibrax). The rims get hot but braking power does not seem to be diminished.

Probably fair to say I am bigger and heavier than most pro-cyclists (1.95m and 95kg) so their is a
lot more kinetic energy to convert to heat. Also,

I

Quoted message said:

live in a hot climate (south of France). I don't know the exact spec of my bike - but it is a
Giant OCR with good quality rims and brakes. The brake fade never becomes dangerous and I don't
need to change anything on my typical rides. However, I do wonder how it will stand up to the
descent of Ventous which I want to do next week.

Pros rims & brakes aren't significantly different to what we'd be using - I'b put it down to
riding style.

If you just brake for the corners, you put a lot less heat into the rims (and give them time to cool
before next braking) than you do if you brake continually to keep a moderate speed. You have to
trust your brakes though.

Andrew