Forum home Road cycling forum Road general

Braking on carbon rims. Advice please!

topcattimtopcattim Posts: 766
edited August 2018 in Road general
I’ve recently started riding on Mavic Cosmic Carbon rims which are lovely, but...

I’m currently in Annecy and have been doing some long climbs and descents in the heat. Today was a gravelly hairpin filled descent and I was on the brakes more than usual even for me as a cautious descender. But I burst the front tube from heating the rim too much on braking I guess. I really don’t think I’d been dragging the brakes (I’d been trying to pulse them) but clearly had overheated the rims: big bang, big rip in tube and trouble keeping bike upright. I think I need to learn to use the rear brake a bit more even though I know it is not as effective. I stopped several times on way down after the blowout and the front rim was often really hot to touch, rear not so much.

Any advice on how to improve and handle the carbon rims better? Perhaps it was just bad luck but I’m now a bit spooked for the rest of my week in the Alps.
«1

Posts

  • mangliermanglier Posts: 678
    Cadence (long pulse) braking.
    Swap out latex tubes for butyl ones.
    That's about it before going tubeless or disc.
  • n1ckstern1ckster Posts: 158
    Use appropriate brake blocks, don’t feather as this builds up heat unnecessarily, brake hard and fast not slow and long.

    If possible, modulate (fully release and reapplying) the lever pressure to allow heat to dissipate
  • topcattimtopcattim Posts: 766
    Thanks both. A mate of mine has also suggested lowering tyre pressure. I've got 25s, weigh 65kg and have been running at about 95. He's suggested lowering to 80. Worth a try?
  • orlokorlok Posts: 85
    topcattim wrote:
    Thanks both. A mate of mine has also suggested lowering tyre pressure. I've got 25s, weigh 65kg and have been running at about 95. He's suggested lowering to 80. Worth a try?
    Miles per hour.?? :roll:
    There will be always a moment of tailwind.
    Pinarello F10 - Ultegra 6800 - Carbonspeed C38 - Tubeless
  • topcattimtopcattim Posts: 766
    orlok wrote:
    topcattim wrote:
    Thanks both. A mate of mine has also suggested lowering tyre pressure. I've got 25s, weigh 65kg and have been running at about 95. He's suggested lowering to 80. Worth a try?
    Miles per hour.?? :roll:
    :D Yup. That's why I've been having trouble braking!
  • sungodsungod Posts: 12,681
    as above brake hard and late, if it's a long descent and you can't manage rim temperature just stop for a few minutes to let things cool a bit

    the rear brake won't stop you on a descent, and it'll be easy to lock up if you try (which may just shred the tyre), but you can pulse it to shave a bit of speed until you need the front

    sitting up increases drag which will also help control speed, but when you need to brake hard you want your weight way back

    this might help you with technique...

    http://www.flammerouge.je/factsheets/descend.htm
    my bike - faster than god's and twice as shiny
  • orlokorlok Posts: 85
    topcattim wrote:
    orlok wrote:
    topcattim wrote:
    Thanks both. A mate of mine has also suggested lowering tyre pressure. I've got 25s, weigh 65kg and have been running at about 95. He's suggested lowering to 80. Worth a try?
    Miles per hour.?? :roll:
    :D Yup. That's why I've been having trouble braking!
    You'll be better with discs.! :lol:
    There will be always a moment of tailwind.
    Pinarello F10 - Ultegra 6800 - Carbonspeed C38 - Tubeless
  • shirley_bassoshirley_basso Posts: 3,217
    75F80R should be plenty of pressure.

    I was descending recently in the Pyrenees and was considering whether my braking style would cause overheating on my carbon wheels which I chose to leave at home.

    I wouldn't go so far as to say your anecdote is a 'horror story' but I know I'm a censored descender and heavier than you at 75kg and glad I bought alu wheels for my first alpine trip.
  • Use your body position to aid the braking ( sit up when you start braking) the extra drag will help reduce the amount of wheel braking you need. It might unsettle you until you’re used to it. But it should help in the long run.
  • Using Carbon rims on routes with long fast descents is always going to be a less than great idea. But there’s plenty you can do to help with the tube exploding issue.
  • mercia_manmercia_man Posts: 1,368
    The last time I was at the top of Ventoux- a year ago - I walked around the bikes to see what wheels people were using. There were hundreds of bikes. I only spotted one carbon wheel. I think that says something.
  • n1ckstern1ckster Posts: 158
    Mercia Man wrote:
    The last time I was at the top of Ventoux- a year ago - I walked around the bikes to see what wheels people were using. There were hundreds of bikes. I only spotted one carbon wheel. I think that says something.
    I watched hundreds of cyclists racing round the alps and Pyrenees this July and there seemed to be plenty of carbon rims........
  • mercia_manmercia_man Posts: 1,368
    n1ckster wrote:
    Mercia Man wrote:
    The last time I was at the top of Ventoux- a year ago - I walked around the bikes to see what wheels people were using. There were hundreds of bikes. I only spotted one carbon wheel. I think that says something.
    I watched hundreds of cyclists racing round the alps and Pyrenees this July and there seemed to be plenty of carbon rims........


    Yes but those were pro racers on closed roads riding carbon tubs which don't suffer the well documented overheating and melting rim issues of carbon clinchers. In the real world of amateur riders on roads with traffic, my experience is that most cyclists still prefer the extra safety of alloy rims in the Alps and Pyrenees.
  • MatthewfalleMatthewfalle Posts: 17,571
    Mercia Man wrote:
    n1ckster wrote:
    Mercia Man wrote:
    The last time I was at the top of Ventoux- a year ago - I walked around the bikes to see what wheels people were using. There were hundreds of bikes. I only spotted one carbon wheel. I think that says something.
    I watched hundreds of cyclists racing round the alps and Pyrenees this July and there seemed to be plenty of carbon rims........


    Yes but those were pro racers on closed roads riding carbon tubs which don't suffer the well documented overheating and melting rim issues of carbon clinchers. In the real world of amateur riders on roads with traffic, my experience is that most cyclists still prefer the extra safety of alloy rims in the Alps and Pyrenees.

    Bizarrely there were lots of people using carbon clinchers at things like the Etape and the Marmotte and MF must agree with the sentiments of N1ckster.

    Perhaps MerciaMah and the OP should stop believing the scare stories and learn how to ride and brake in the Alps and similar

    #itsnotthatdifficult
    Postby team47b » Sun Jun 28, 2015 11:53 am

    De Sisti wrote:
    This is one of the silliest threads I've come across. :lol:

    Recognition at last Matthew, well done!, a justified honour :D
    smithy21 wrote:

    He's right you know.
  • mercia_manmercia_man Posts: 1,368
    Mercia Man wrote:
    n1ckster wrote:
    Mercia Man wrote:
    The last time I was at the top of Ventoux- a year ago - I walked around the bikes to see what wheels people were using. There were hundreds of bikes. I only spotted one carbon wheel. I think that says something.
    I watched hundreds of cyclists racing round the alps and Pyrenees this July and there seemed to be plenty of carbon rims........


    Yes but those were pro racers on closed roads riding carbon tubs which don't suffer the well documented overheating and melting rim issues of carbon clinchers. In the real world of amateur riders on roads with traffic, my experience is that most cyclists still prefer the extra safety of alloy rims in the Alps and Pyrenees.

    Bizarrely there were lots of people using carbon clinchers at things like the Etape and the Marmotte and MF must agree with the sentiments of N1ckster.

    Perhaps MerciaMah and the OP should stop believing the scare stories and learn how to ride and brake in the Alps and similar

    #itsnotthatdifficult

    Now, now. No need to disparage me, MF, when you know nothing of my riding experience in the Alps and similar. All I am saying is that I rarely see ordinary riders using carbon clinchers in the high mountains. The vast majority are on alloy rims.
  • shirley_bassoshirley_basso Posts: 3,217
    It's not really a scare story if it's actually happened to him, is it?

    Would you recommend that someone learn how to descend on carbon rims for their first trip to the mountains?

    In the Pyrenees there are some pretty steep, fast descents for which I definitely preferred having alu braking surfaces (Tourmalet, Ventoux) whereas Peyresourde & Aspin I didn't really brake much - and I am censored at descending.

    For my first alpine trip I was glad to ignore some of the comments on here who said to take my carbon wheels, and bought some alu wheels and swisstop blue pads which performed flawlessly.

    After a few more trips, I'll see how my descending goes and whether I want to take carbon wheels, but why bother when you get get pretty good, lightweight alu wheels for around £200. (I got barely used Zondas with brand new tyres for £200).
  • MatthewfalleMatthewfalle Posts: 17,571
    Mercia Man wrote:
    Mercia Man wrote:
    n1ckster wrote:
    Mercia Man wrote:
    The last time I was at the top of Ventoux- a year ago - I walked around the bikes to see what wheels people were using. There were hundreds of bikes. I only spotted one carbon wheel. I think that says something.
    I watched hundreds of cyclists racing round the alps and Pyrenees this July and there seemed to be plenty of carbon rims........


    Yes but those were pro racers on closed roads riding carbon tubs which don't suffer the well documented overheating and melting rim issues of carbon clinchers. In the real world of amateur riders on roads with traffic, my experience is that most cyclists still prefer the extra safety of alloy rims in the Alps and Pyrenees.

    Bizarrely there were lots of people using carbon clinchers at things like the Etape and the Marmotte and MF must agree with the sentiments of N1ckster.

    Perhaps MerciaMah and the OP should stop believing the scare stories and learn how to ride and brake in the Alps and similar

    #itsnotthatdifficult

    Now, now. No need to disparage me, MF, when you know nothing of my riding experience in the Alps and similar. All I am saying is that I rarely see ordinary riders using carbon clinchers in the high mountains. The vast majority are on alloy rims.

    Spoils MM if that came out wrong - no disparaging needed.

    However, every time one of the MFs has ridden in the Alps, Pyrenees, Abruzzo - all Giro/Tour standard climbs - he hasn’t seen anyone who is thinking about their braking, lines, riding - have any issues at all.

    The wheels aren’t to fault - there are no design problems otherwise they wouldn’t be allowed to sell them - it’s all down to technique and confidence.

    Again, apologies for any dissing

    #humblepie
    Postby team47b » Sun Jun 28, 2015 11:53 am

    De Sisti wrote:
    This is one of the silliest threads I've come across. :lol:

    Recognition at last Matthew, well done!, a justified honour :D
    smithy21 wrote:

    He's right you know.
  • MatthewfalleMatthewfalle Posts: 17,571
    It's not really a scare story if it's actually happened to him, is it?

    Would you recommend that someone learn how to descend on carbon rims for their first trip to the mountains?

    In the Pyrenees there are some pretty steep, fast descents for which I definitely preferred having alu braking surfaces (Tourmalet, Ventoux) whereas Peyresourde & Aspin I didn't really brake much - and I am censored at descending.

    For my first alpine trip I was glad to ignore some of the comments on here who said to take my carbon wheels, and bought some alu wheels and swisstop blue pads which performed flawlessly.

    After a few more trips, I'll see how my descending goes and whether I want to take carbon wheels, but why bother when you get get pretty good, lightweight alu wheels for around £200. (I got barely used Zondas with brand new tyres for £200).

    MF would suggest he go to some big hills and learn first.

    It’s not that difficult - it’s just about thinking. If he’s panicking and slamming the brakes on repeatedly it’s either because he can’t control his speed, has made bad decisions re technique/line/body position, has no confidence because he’s worried about stuff, etc. myriad of reasons.

    What’s the point in buying carbon wheels if you aren’t going to use them when it’s nicest - ie on holiday?

    #randompurchase
    Postby team47b » Sun Jun 28, 2015 11:53 am

    De Sisti wrote:
    This is one of the silliest threads I've come across. :lol:

    Recognition at last Matthew, well done!, a justified honour :D
    smithy21 wrote:

    He's right you know.
  • shirley_bassoshirley_basso Posts: 3,217
    "MF would suggest he go to some big hills and learn first"

    What if these don't exist where you live and your first encounter is in the mountains?
  • mercia_manmercia_man Posts: 1,368
    Mercia Man wrote:
    Mercia Man wrote:
    n1ckster wrote:
    Mercia Man wrote:
    The last time I was at the top of Ventoux- a year ago - I walked around the bikes to see what wheels people were using. There were hundreds of bikes. I only spotted one carbon wheel. I think that says something.
    I watched hundreds of cyclists racing round the alps and Pyrenees this July and there seemed to be plenty of carbon rims........


    Yes but those were pro racers on closed roads riding carbon tubs which don't suffer the well documented overheating and melting rim issues of carbon clinchers. In the real world of amateur riders on roads with traffic, my experience is that most cyclists still prefer the extra safety of alloy rims in the Alps and Pyrenees.

    Bizarrely there were lots of people using carbon clinchers at things like the Etape and the Marmotte and MF must agree with the sentiments of N1ckster.

    Perhaps MerciaMah and the OP should stop believing the scare stories and learn how to ride and brake in the Alps and similar

    #itsnotthatdifficult

    Now, now. No need to disparage me, MF, when you know nothing of my riding experience in the Alps and similar. All I am saying is that I rarely see ordinary riders using carbon clinchers in the high mountains. The vast majority are on alloy rims.

    Spoils MM if that came out wrong - no disparaging needed.

    However, every time one of the MFs has ridden in the Alps, Pyrenees, Abruzzo - all Giro/Tour standard climbs - he hasn’t seen anyone who is thinking about their braking, lines, riding - have any issues at all.

    The wheels aren’t to fault - there are no design problems otherwise they wouldn’t be allowed to sell them - it’s all down to technique and confidence.

    Again, apologies for any dissing

    #humblepie

    Thanks for that, MF. You are a gentleman. And I quite agree that technique and confidence play a major part in safe descending. I have found this is even more important when riding a touring bike loaded with camping gear down mountain passes. (I’m too old for that now). Descending on a lightweight road bike is a doddle in comparison.
  • topcattimtopcattim Posts: 766
    Thanks for everyone’s thoughts. I’ve done a fair bit of Alpine and Dolomite riding on alloys but this is my first time on carbon rims. I do think there’s room to improve my technique so this is a good prompt!
    Two specific questions though:
    1) if I drop the tyre pressure from previous 95psi on 25s to 80psi will that make tube bursting any less likely? (I weigh 65kg)
    2) I was using a tube for 19-23 tyres not a 25 and upwards tube. Lesson learned. But if I now use a 25+ tube will that stress it less and again make it less likely to burst?
  • mercia_manmercia_man Posts: 1,368
    I'm a lighter rider like you and believe lower tyre pressures than 95 on your 25s will be beneficial generally and may improve your safety on descents. Similarly, fitting tubes that are the right size for your tyres should also help.

    But as others have said, don't drag your brakes for long periods (I know this may be impossible if you are following slow riders or motor traffic), brake sharp and short when approaching bends, use both brakes and ride sensibly. I always try to follow the Highway Code advice to drive at such a speed that you can stop in the distance you can see to be clear - works with bicycles, too.

    And if you fear your rims are overheating, stop for a while to let them cool. That's a technique I've used a fair few times on mountain descents on a tourer with camping gear, on a tandem and a Bike Friday performance folder with 20 inch wheels towing a suitcase trailer. And if it's raining, I always apply the brakes gently and regularly to clear the rims of water.
  • Mercia Man wrote:
    The last time I was at the top of Ventoux- a year ago - I walked around the bikes to see what wheels people were using. There were hundreds of bikes. I only spotted one carbon wheel. I think that says something.

    It's just saying that on that day you saw more aluminium rims than carbon. The top of the Madeleine was full of carbon wheeled bikes when I revisited this summer (one solitary disc bike). I spent the week going up and down Cols in various weather conditions including blistering heat on a set of Ksyrium Pro Carbon SL wheels with no issues.

    OP, I wouldn't be too worried about it. You'll be fine. IMO the descents in that region are a lot more technical than other parts of the Alps and Pyrenees and they need a wee bit more effort to ride down. It's a great place to hone your descending skills. It's also easily the best place to take your bike in France and I'm very jealous. I'll be back again next year!

    (If it all goes t*ts up you can just pop into Mavic HQ just outside the town)
  • DeVlaeminckDeVlaeminck Posts: 6,020
    I think carbon braking has come on a lot in recent years. Personally I'd still probably play safe with alloy rims but that may be based on old technology. I've ridden latex tubes in the Alps with no problems and people say they are a risk too.
    AFC Mercia women - sign for us
  • svettysvetty Posts: 1,904
    Never really sold on the 'tyre burst' thing. The tube is constrained by the tyre and rim. If the rim gets very hot it's conceivable that the tube could undergo thermal stress rather than excess pressure. This is most likely where the tube is in direct contact with the rim (either side of the rim tape between the tape edge and the tyre bead). This could lead to localised melting/weakening if the temperature gets hot enough. It's this that leads to the tube failing not excess pressure aka bursting.
    FFS! Harden up and grow a pair :D
  • shirley_bassoshirley_basso Posts: 3,217
    Does it matter how? It still happened.

    While the obvious answer is to learn to descend better, a good set of alu wheels can cost just as much as a reasonable set of carbon wheels.

    If you know you aren't good at descending, why risk it?

    Buy alu wheels, get better at descending, then use carbon wheels if you want to.

    I was lucky one of my mates could basically ride alongside me giving out tips which was really handy. I'm still censored though as it mostly boils down to guys, which I don't have much of!
  • svetty wrote:
    Never really sold on the 'tyre burst' thing. The tube is constrained by the tyre and rim. If the rim gets very hot it's conceivable that the tube could undergo thermal stress rather than excess pressure. This is most likely where the tube is in direct contact with the rim (either side of the rim tape between the tape edge and the tyre bead). This could lead to localised melting/weakening if the temperature gets hot enough. It's this that leads to the tube failing not excess pressure aka bursting.

    It’s sometimes due to the point at which the clincher is hooked into the rim becoming softened, then the tyre ‘ripples’ under braking, the tube pops out / herniates and it contacts the road. Then you get a bang as the tube bursts / punctures and then the bit that popped out obviously retreats back under the tyre.
  • Mercia Man wrote:
    The last time I was at the top of Ventoux- a year ago - I walked around the bikes to see what wheels people were using. There were hundreds of bikes. I only spotted one carbon wheel. I think that says something.


    That’s generally been my experience as well.
  • When you brake there’s a noise that the brakes on the rim makes. The pitch / sound when the rim starts to overheat changes quite significantly. Listen for the change of pitch and then swap the lions share of the braking to the other wheel. And listen for the same effect, then swap the lions share of the braking back the other way. Repeat until stopped or no longer needing to brake.
  • BrakelessBrakeless Posts: 867
    Mercia Man wrote:
    The last time I was at the top of Ventoux- a year ago - I walked around the bikes to see what wheels people were using. There were hundreds of bikes. I only spotted one carbon wheel. I think that says something.


    That’s generally been my experience as well.

    Strava shows your biggest climb as 879ft. Did you drive up there?
Sign In or Register to comment.