Carbon Tubular Versus Carbon Clincher Braking for sustained mountain descents

[mcteague]

Originally Posted by flying

I also love the look of both the Bora's & the WTO's

While I have done no real tests, and lots of hills but no mts nearby, I swear the Bora WTO 33s I got recently stop even better than any alloy I have owned. Today I did a wet ride, not full on rain, just heavy fog and mist. Everything got pretty wet and still they stopped just fine. As with metal rims I tend to drag them slightly to rub off the layer of water but they still worked great.

Tim

[flying]

Originally Posted by mcteague

While I have done no real tests, and lots of hills but no mts nearby, I swear the Bora WTO 33s I got recently stop even better than any alloy I have owned. Today I did a wet ride, not full on rain, just heavy fog and mist. Everything got pretty wet and still they stopped just fine. As with metal rims I tend to drag them slightly to rub off the layer of water but they still worked great.

Tim

I have always heard Campagnolo's AC3 Carbon brake tracks were excellent

But truthfully it is not just braking for me...
I like the added confidence as I bomb down some mountains around here with terrible pave in sections due to tree roots etc under the pave & some pot holes.
Of course I never intend to be hard on a wheel etc but these things of course hide in the shade of the trees that caused them

So for instance..........two weeks ago coming down I hit a pot hole sharp edge so hard I pinch flatted & lost a water bottle out of an otherwise tight cage

Fixed the flat & checked my Zondas...no prob not even a bit out of true
With carbon I would not feel able to really know the result of such an incident quickly out on the road

[poff]

Here is my 2c - I once got stuck in traffic descending Passo Stelvio to Bormio, with bumper-to-bumper both uphill and downhill, so it was impossible to pass cars going down. My aluminum rims were toast at the bottom. Think about what would've happened with carbon rims.

[Kirk007]

Originally Posted by poff

Here is my 2c - I once got stuck in traffic descending Passo Stelvio to Bormio, with bumper-to-bumper both uphill and downhill, so it was impossible to pass cars going down. My aluminum rims were toast at the bottom. Think about what would've happened with carbon rims.

What a miserable way to descend the Stelvio, yuck!

I descended the other side two years ago in semi heavy traffic - very aggravating as a few drivers would come to almost a complete stop on the switchbacks then accelerate inbetween, closing out passing opportunities without risking a head on with approaching traffice. My coated alloy rims were fine at the end though and I'm sure carbon would've been too as braking was short bursts entering switchbacks with a little steady pressure to keep from rear ending the cars but there was plenty of off time in between.

[fogrider]

I have 4 pairs of tubular carbon rims all Reynolds. 1 pair of 32s, 3 pairs of 44s. all have been rock solid. I've hit potholes all full speed and no issues. I've broken spokes, but that's been fixable. Braking has been fine with Reynolds blue pads..and I avoid the riding them in rain...I mean who does that when there are disc brakes?

I've been riding tubulars for more than 25 years in San Francisco Bay Area mountains. Mt Tam and Diablo are technical descents in that there are steep and tight off camber turns. To the south are fast but sweeping turns. I've ridden tubulars up and down everything here including Hamilton which is 20 miles of descending. Sure the rims get warm to hot, but most of the time, I'm on the pedals and tucked looking for speed. When I go for the brakes, I'm looking bleed some speed, not stop. That said, I'm very familiar with these roads and adjust my speed to the road conditions and yeah, I've slowed down over the years. I know the roads in Colorado are long with lots of elevation change, but are they steep? are there tight turns?

[nmrt]

Oh yeah! There are tight turns.
Many hill climbs in Boulder (Superflag, SuperJames) where I ride are twisty and steep.

Originally Posted by fogrider

I have 4 pairs of tubular carbon rims all Reynolds. 1 pair of 32s, 3 pairs of 44s. all have been rock solid. I've hit potholes all full speed and no issues. I've broken spokes, but that's been fixable. Braking has been fine with Reynolds blue pads..and I avoid the riding them in rain...I mean who does that when there are disc brakes?

I've been riding tubulars for more than 25 years in San Francisco Bay Area mountains. Mt Tam and Diablo are technical descents in that there are steep and tight off camber turns. To the south are fast but sweeping turns. I've ridden tubulars up and down everything here including Hamilton which is 20 miles of descending. Sure the rims get warm to hot, but most of the time, I'm on the pedals and tucked looking for speed. When I go for the brakes, I'm looking bleed some speed, not stop. That said, I'm very familiar with these roads and adjust my speed to the road conditions and yeah, I've slowed down over the years. I know the roads in Colorado are long with lots of elevation change, but are they steep? are there tight turns?

[Viewer]

Originally Posted by nmrt

...I need to choose between rim braking tubular wheels and rim braking clincher wheels (tubes/tubeless)...

Sorry, but pointless question. Tubular rules that roost.

Always has. Always will.

[alexandrumarian]

Originally Posted by chrisroph

I had a tubular shift on an alloy rim on a sustained steep descent (yerba buena in the santa monica mtns) once years ago. The red clement cement became somewhat liquified from heat and braking forces caused a shift of the tire. The valve stem was centered before the descent but was cocked at an angle at the bottom.

Happened to me too. Steep descent, narrow road, vegetation blinding corners, potholes, sand, dung, 210lbs...had to drag the brakes a fair bit. At the bottom I stopped to feel front rim temperature like I usually do after this sort of descent. It has hot but didn't leave my skin on it. Noticed tire looks a bit weird - noticeable hump for about 10cm. Pushed a bit on it, lifted easily as the glue was melted, and i think the same for the basetape glue. Then it reset like that and I had to limp back to the car with a wobble.

This was Bora 35s with Corsa 2.0 28mm. I think a smaller (23 or 25) tub might be a bit safer as it falls a bit deeper in the groove. Also higher pressure makes it harder to be pushed off the rim once the glue is liquid.

I did some experiments at home, baked pieces of wood glued together with both mastik and conti carbon. After 10 mins at 110 Celsius they both open up with ease. Clamped the pieces back, waited to cool, tried to break - it repairs by itself pretty decently. But that time when the glue is hot can be very dangerous....

[chrisroph]

Originally Posted by cgolvin

I'm sure it didn't help that the road surface at that time was an absolute nightmare. OT, but once as I was shattering my bones descending Yerba I got passed like I was standing still by a guy on a full squish MTB, who was enjoying himself a hell of a lot more than I was. Fortunately, that road is now probably the nicest descent in the Santa Monica mountains.

It was probably in the mid-1970's as I left Socal in 76 and haven't ridden Yerba since leaving. I do remember it as an insane and bumpy descent.

[Pastashop]

Originally Posted by alexandrumarian

Happened to me too. Steep descent, narrow road, vegetation blinding corners, potholes, sand, dung, 210lbs...had to drag the brakes a fair bit. At the bottom I stopped to feel front rim temperature like I usually do after this sort of descent. It has hot but didn't leave my skin on it. Noticed tire looks a bit weird - noticeable hump for about 10cm. Pushed a bit on it, lifted easily as the glue was melted, and i think the same for the basetape glue. Then it reset like that and I had to limp back to the car with a wobble.

This was Bora 35s with Corsa 2.0 28mm. I think a smaller (23 or 25) tub might be a bit safer as it falls a bit deeper in the groove. Also higher pressure makes it harder to be pushed off the rim once the glue is liquid.

I did some experiments at home, baked pieces of wood glued together with both mastik and conti carbon. After 10 mins at 110 Celsius they both open up with ease. Clamped the pieces back, waited to cool, tried to break - it repairs by itself pretty decently. But that time when the glue is hot can be very dangerous....

The heat build-up on steep descents is not a new issue, and impacts tubulars and clinchers, though somewhat differently. Both technologies have been around long enough for there to be some sound physics-based understanding of the mechanisms at play, and how they can be mitigated.

Regarding the pressure — it depends, and likely the opposite may need to be done, at least with clinchers.

Quoth:

“ This is a serious problem both for tubulars and clinchers because most
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.”

https://yarchive.net/bike/rim_heat.html

... if you read further on the matter, Jobst Brandt specifies a set-up for minimizing heat transfer from the rim and at the same time arresting tubular tire creep when the glue liquefies.

[Ozz]

Originally Posted by alexandrumarian

....After 10 mins at 110 Celsius they both open up with ease. Clamped the pieces back, waited to cool, tried to break - it repairs by itself pretty decently. But that time when the glue is hot can be very dangerous....

Jeez....must be a long steep hill where I would be applying the brakes for 10 minutes!

I am usually on my brakes for 1-3 seconds at time...scrub speed, get thru corner and onto the next turn.

[alexandrumarian]

Originally Posted by Ozz

Jeez....must be a long steep hill where I would be applying the brakes for 10 minutes!

I am usually on my brakes for 1-3 seconds at time...scrub speed, get thru corner and onto the next turn.

I think it goes sour when the factors pile up: long and steep, hot road, carbon...even if you don't drag the brakes, the heat accumulates and carbon has a slow transfer compared to alu.

it also matters a lot on how heavy and how skilled the rider is. For example on a normal road (say from 6 to 9% and decent surface) I am fairly confident and get pretty good strava times but as soon as it goes over 10%, I crap my pants and need to brake a lot. At over 200 pounds I guess I should just switch to discs....

[Ozz]

Originally Posted by alexandrumarian

I think it goes sour when the factors pile up: long and steep, hot road, carbon...even if you don't drag the brakes, the heat accumulates and carbon has a slow transfer compared to alu.

it also matters a lot on how heavy and how skilled the rider is. For example on a normal road (say from 6 to 9% and decent surface) I am fairly confident and get pretty good strava times but as soon as it goes over 10%, I crap my pants and need to brake a lot. At over 200 pounds I guess I should just switch to discs....

I know....just giving you a hard time (in fun) about the homemade experiment....

Cheers!

[alexandrumarian]

Originally Posted by Ozz

I know....just giving you a hard time (in fun) about the homemade experiment....

Cheers!

Main reason for that was to test Continental's claim that it has superior heat resistance. My day job is to build wood stuff using glues so i am a bit obsessive about doing destructive glue and procedure tests. My test showed the conti is no better than mastik, at least at 100 deg C. Conti carbon is "interesting". No matter how well (or elaborate) you do your glue job, it has low adhesion strength. When you rip an old tub it is not much harder than undoing a strong velcro. Mastik can be quite a pita to remove. I would want the Conti carbon if I ever had to replace a tub on the road. Another advantage of Conti is easier cleaning from the rim, in case you want to start the job from the fresh. In general, I think they overdid this strength reduction. You'd need pretty low quality carbon for chunks to break off....

[Mark McM]

Originally Posted by Pastashop

The heat build-up on steep descents is not a new issue, and impacts tubulars and clinchers, though somewhat differently. Both technologies have been around long enough for there to be some sound physics-based understanding of the mechanisms at play, and how they can be mitigated.

Regarding the pressure — it depends, and likely the opposite may need to be done, at least with clinchers.

Quoth:

“ This is a serious problem both for tubulars and clinchers because most
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.”

https://yarchive.net/bike/rim_heat.html

... if you read further on the matter, Jobst Brandt specifies a set-up for minimizing heat transfer from the rim and at the same time arresting tubular tire creep when the glue liquefies.

These are earlier writings from Brandt, and echo the conventional wisodom that tires blowing off during braking was due to excessive pressure build-up. But in later writings after a closer examination Brandt espoused a different theory. Essentially, it was shown through testing that although pressure does increase from brake heat, it is still usually well below the tire's static blow-off pressure. Instead, it is now believed that tire blow off is due to heat softening up the tire bead and also decreasing the friction between tire and rim. That, combined with the cyclic compression (from weight) and tangential tugging (from braking torque) at the ground affected zone, is what cause the bead to squirm and seat from the rim. The upshot of this is that reducing tire pressure before a descent may not be as effective as once thought.

Here's some more information on this:

http://pardo.net/bike/pic/fail-037/000.html