Disk brakes and big steep hills
Discussion
No, you won't. 100kg vs 70 is FA to a disc. Look at the disc on a 125 cc motorbike. That stops 250kg of bike plus rider from 60mph, over and over again. It's not that much bigger than a pushbike disc.
Seriously, a disc brake will carry on working WAY beyond your capabilities as a rider. Do you imagine that the manufacturers haven't factored this in?
Seriously, a disc brake will carry on working WAY beyond your capabilities as a rider. Do you imagine that the manufacturers haven't factored this in?
HughG said:
Just out of curiousity are you a powerfully built company director or a lithe whippet of a cyclist? Or put another way, if I were doing similar on my Shimano 675s with 160 discs trying to stop my lardy near 100kg do you think I'd have a problem!
Fair question. I'm half-sized so do only weigh 64kg, though the bike with kit was another 20kg so total weight 84kg. I don't think another 20% weight would change anything, but there must be a point at which it would. However there were plenty of more powerfully built riders doing the same thing as me and no-one had a fade problem. I really do believe though that you would be more likely to have a problem through overheated rims on a conventionally-braked bike before you suffered fade on a disc-braked bike.
richardxjr said:
^ my mate on the same ride is over 120kgs inc bike & luggage, with the same brakes and again no problems. f
ker hit 92km/h in the run into Briancon.
Bloody hell, that's fast. I've hit 80kph but keeping your eyes free from tears is nearly impossible even with specs. You need proper eye protection to keep the wind out. It's hard to get high speeds in the Alps because the hairpins don't allow you to let it run for long enough to get over about 70kph. Not that 70k is exactly hanging about when you're in T shirt and shorts.ker hit 92km/h in the run into Briancon. ecs said:
I've done huge descents on my DH bike before in the past - the disks got so hot they were glowing and the mud on the disk side of the frame was caked on dry. No fade though.
I descended down the side of the shard once on a disk equipped unicycle. Break disc got so hot, it melted 3 of the windows on floor 19. No fade though.battered said:
Seriously, a disc brake will carry on working WAY beyond your capabilities as a rider. Do you imagine that the manufacturers haven't factored this in?
someone didn't get your memoThis article about brakes on Tandems was interesting reading...
Discs on the back, rims on the front:
http://santanatandems.com/Techno/UnderstandingBrak...
Discs on the back, rims on the front:
http://santanatandems.com/Techno/UnderstandingBrak...
Pachydermus said:
battered said:
Seriously, a disc brake will carry on working WAY beyond your capabilities as a rider. Do you imagine that the manufacturers haven't factored this in?
someone didn't get your memoMagura spout some rubbish...
"Hydraulic rim brakes are lighter than disc brakes if you look at the complete system"
"Rim brakes are more aerodynamic than disc brakes"
"With rim brakes you already have the biggest possible rotor on a wheel: the rim!"
"Rim brakes don’t suffer from heat build up/overheating on the hydraulic system, as the distance friction partners (rim/pad) is really far away from the hydraulic piston, so no expansion chamber is even neccessary."
battered said:
No it's not valid, and imo never was.
Discs are resistant to fade long after any rim brakes have melted and been destroyed.
I managed to cook a 160mm hayes to the point the disk warped and the pads were smoking coming down Brass Knocker in Bath... Some disk applications such as the hayes 160 L are IMO not up to the job ! That said, I've put on a 160 mm shimano disk and its coping much better ! Discs are resistant to fade long after any rim brakes have melted and been destroyed.
Edited by PorkRind on Monday 26th September 16:32
Kawasicki said:
Pachydermus said:
battered said:
Seriously, a disc brake will carry on working WAY beyond your capabilities as a rider. Do you imagine that the manufacturers haven't factored this in?
someone didn't get your memoMagura spout some rubbish...
"Hydraulic rim brakes are lighter than disc brakes if you look at the complete system"
"Rim brakes are more aerodynamic than disc brakes"
"With rim brakes you already have the biggest possible rotor on a wheel: the rim!"
"Rim brakes don’t suffer from heat build up/overheating on the hydraulic system, as the distance friction partners (rim/pad) is really far away from the hydraulic piston, so no expansion chamber is even neccessary."
I guess this is the first time that us MTB-only riders can at least feel a bit smug at being in front of Road riders for once in terms of development.
If you've ever ridden a MTB in the Alps, you know there's a certain technique to saving your brakes, although these days you can get away with murder, brake-dragging is the killer - noobs, when first encountering the sorts of steepness you get in the Alps drag their brakes to keep the speed between the corners more familiar and cause havoc - but if you let them off between the corners they don't build up heat and they don't give you any more gip than at home.
Compared to rim brakes though?! Can't comment on the needs of Roadies specifically, but when it comes to MTB I can think of no instance when I'd prefer to be in rim brakes, they're a total liability on a MTB.
Kell said:
This article about brakes on Tandems was interesting reading...
Discs on the back, rims on the front:
http://santanatandems.com/Techno/UnderstandingBrak...
In car brakes, theoretically drum brakes are more powerful than discs. Discs on the back, rims on the front:
http://santanatandems.com/Techno/UnderstandingBrak...
IN the real world the reason why discs are more powerful than drums is because the drum brake warps and flexes under powerful braking, whereas the disc doesn't
I have seen the same thing with Rim brakes- the rim itself can be folded inwards i you pull the brake hard- ie the rim is being pinched by the pads. This means you are utilitsing considerable energy just bending metal not stopping the bike.
On discs you only create friction which only creates stopping power (and heat of course) - there is no flex in the disc.
Does that make sense?
The other thing of course is that discs are less likely to be contaminated than rims whhich are by their nature close to the road surface.
I'm not sure you can just arbitarily say "x is better than y" without taking into account all parts of the system.
In that article, the levers went to the bar. That's boiled fluid.
This is a car with hot brakes. The fluid is fine. Is the fluid at a lower temperature here than on a disk braked road bike? I'd be interested to know, but I suspect not.
So was it the brakes to blame, or st fluid? A system is only as good as it's weakest link. For racing, anything lower than Castrol SRF would stop you running a 911 in a club meeting. For racing down an alp, it's likely that better fluid is needed than for racing down the shops.
IMO, it will always be the case that good rim brakes are better than st disks. As to whether good disks are better than good rim brakes, MTB implies that they probably are on balance, but there's certain aspects in the "for" column in each case, rather than an outright "better at everything".
In that article, the levers went to the bar. That's boiled fluid.
This is a car with hot brakes. The fluid is fine. Is the fluid at a lower temperature here than on a disk braked road bike? I'd be interested to know, but I suspect not.
So was it the brakes to blame, or s
t fluid? A system is only as good as it's weakest link. For racing, anything lower than Castrol SRF would stop you running a 911 in a club meeting. For racing down an alp, it's likely that better fluid is needed than for racing down the shops. IMO, it will always be the case that good rim brakes are better than s
t disks. As to whether good disks are better than good rim brakes, MTB implies that they probably are on balance, but there's certain aspects in the "for" column in each case, rather than an outright "better at everything".PugwasHDJ80 said:
In car brakes, theoretically drum brakes are more powerful than discs.
IN the real world the reason why discs are more powerful than drums is because the drum brake warps and flexes under powerful braking, whereas the disc doesn't
I have seen the same thing with Rim brakes- the rim itself can be folded inwards i you pull the brake hard- ie the rim is being pinched by the pads. This means you are utilitsing considerable energy just bending metal not stopping the bike.
On discs you only create friction which only creates stopping power (and heat of course) - there is no flex in the disc.
Does that make sense?
The other thing of course is that discs are less likely to be contaminated than rims whhich are by their nature close to the road surface.
I understand all the bits and bobs in the article, just interesting that metal forks are better than carbon for disapating heat, and that for real heavy loads (i.e. two people, one bike) they still recommend going with rim braking on the front.IN the real world the reason why discs are more powerful than drums is because the drum brake warps and flexes under powerful braking, whereas the disc doesn't
I have seen the same thing with Rim brakes- the rim itself can be folded inwards i you pull the brake hard- ie the rim is being pinched by the pads. This means you are utilitsing considerable energy just bending metal not stopping the bike.
On discs you only create friction which only creates stopping power (and heat of course) - there is no flex in the disc.
Does that make sense?
The other thing of course is that discs are less likely to be contaminated than rims whhich are by their nature close to the road surface.
That's not to say rim brakes aren't without problems, elsewhere it mentions that if the rims get hot enough they blow the tyres off the rim.
also, reading the article about the crash above, it does say that the guy specced and fitted his own brakes, without knowing the consequences of what he was doing.
Kawasicki said:
"Rim brakes don’t suffer from heat build up/overheating on the hydraulic system, as the distance friction partners (rim/pad) is really far away from the hydraulic piston, so no expansion chamber is even neccessary."
No instead they heat up the tyre and tube ultimately causing it to blow.Fluid heat issues aside, I've heard it is possible to glaze disc pads from constant dragging on a long descent which massively reduces the effectiveness of the brake, but this is symptomatic of poor technique and not necessarily a failing of brake design. Maybe some pad materiels are more prone to glazing?
BaronVonVaderham said:
Fluid heat issues aside, I've heard it is possible to glaze disc pads from constant dragging on a long descent which massively reduces the effectiveness of the brake, but this is symptomatic of poor technique and not necessarily a failing of brake design. Maybe some pad materiels are more prone to glazing?
Yep, everything is a compromise.Again race car analogy.. Paid blues are virtually unglazable. However, they wear quickly, and produce 4 metric tonnes of dust every race.
Paid orange are virtually unglazable, last quite a while, but squeal so much you're surprised that bats don't come.
Yellows seem like the happy medium, but are a bit cack when cold, and if you noob enough, you can get the pedal to go a bit wooden.
Pretty sure all brake systems have similar options - E.g swissstop make 4 pad compounds just for ally road wheels...
I've had a tyre blow with heat from rim brakes ion a mountain descent the side wall just split. I can't see that happening with discs.
I came down Mt Ventoux last week on rim brakes with no problems and that's 21 k of downhill. I don't think I've had any other mountain descent that did not include any level or gentle rise that did not give some respite from braking. Ventoux has some straights that you just let off and hope everything works at the next bend.
I have disks on mtb but the rims do get a lot more crap than a road bike so there's no grinding paste effect on the rims as with rim brakes.
I've just bought a new road bike, with rim brakes. I can't really decide one way or the other for the road but mtb definitely.
I came down Mt Ventoux last week on rim brakes with no problems and that's 21 k of downhill. I don't think I've had any other mountain descent that did not include any level or gentle rise that did not give some respite from braking. Ventoux has some straights that you just let off and hope everything works at the next bend.
I have disks on mtb but the rims do get a lot more crap than a road bike so there's no grinding paste effect on the rims as with rim brakes.
I've just bought a new road bike, with rim brakes. I can't really decide one way or the other for the road but mtb definitely.
battered said:
wobert said:
The diameter of the disc (or rather the radius) has a direct influence on the torque that can be reacted during braking.
With everything else being equal, a larger diameter disc will give greater stopping force than a smaller disc.
It will, for any given brake caliper effort. Given however that any hydraulic disc brake can lock either or both wheels under any conditions with a modest squeeze, it's academic. Once you can easily lock either wheel, "better" brakes just mean that you can lock the wheel with less brake lever effort. If the effort required is already very small, then it's no benefit.With everything else being equal, a larger diameter disc will give greater stopping force than a smaller disc.
I've recently come back from a trip to Tenerife where my prime goal was a 'quick' descent of Tiede. On a previous visits, with Ultegra rim brakes, braking became more difficult with it becoming more 'binary' the more I braked. Hydraulic discs in comparison were fantastic, consistent braking along with a goof feel meant it was far more enjoyable.
Interestingly, the 'car park' test suggested that the brakes are no more powerful that rim brakes, I certainly never felt in any danger of locking up.
I started this thread because a friend,whom rides 20000km a year, mostly in the Pyrenees, won't use disks because of the overheating and fading stories.Michel is nearley 70 years old and lives bikes.
My tandem has the best brakes ever,rims are Andra with css,Shimano deore v-brakes with Swiss stop blue blocks,rear is a drag brake.The main rear is the biggest disk and caliper Hope make.
I'm still undecided to be honest.
My tandem has the best brakes ever,rims are Andra with css,Shimano deore v-brakes with Swiss stop blue blocks,rear is a drag brake.The main rear is the biggest disk and caliper Hope make.
I'm still undecided to be honest.
I and ten others have recently got back from riding the entire length of the Pyrenees, all of us on conventional calliper brakes. With types pumped to their maximum every single morning, and some of us descending very very quickly indeed, between us over 7,000km of riding, not one single problem with overheating. Never ridden disk brakes so can't comment on them.
Gassing Station | Pedal Powered | Top of Page | What's New | My Stuff