Breaking force

[Spen]

Today it's wet and horrible and my mind has wandered to the question of whether anyone has seen a comparison of the actual braking force achieved by rim, v and disk brakes? Just to be clear this is not a x is better than y question, just a question about numbers.

[flat tyre]

I don't have any empirical data to answer your question, but I do have both rim brake and disc brake bikes. In my experience your question is largely academic as I have found in practice that the limiting factor governing braking performance in the wet has been the available friction between the tyre and the road! Both types of brake will easily lock the wheel in the wet if one is a bit heavy handed on the brake lever, so I suppose that the amount of braking force available from either type of brake must be that same in this instance.

[chris_suffolk]

Today it's wet and horrible and my mind has wandered to the question of whether anyone has seen a comparison of the actual braking force achieved by rim, v and disk brakes? Just to be clear this is not a x is better than y question, just a question about numbers.

Not sure what you are asking:

Are you trying to break your brakes?

[Jdsk]

I recommend starting with "Bicycling Science":
https://mitpress.mit.edu/books/bicyclin ... th-edition

Jonathan

[gregoryoftours]

I've never seen a comparison of relative braking force achieved by different types of cycle brake but I can't really see how an objective one would be possible.

But purely in terms of power a 'good' hydro disc brake set up properly will require less effort at the lever to produce the same amount of braking power than any other brake type commonly used, and the braking force of disc brakes in general is less adversely affected by wet conditions than rim brakes. (Not drum brakes obvs). Even though powerful a good hydro disc will also modulate very well. Of course loads of disadvantages and advantages too. I'm not going to get involved in that.

You could look at cycles where braking power for minimal effort at the lever is a high priority like downhill bikes - they're mostly using 4 pot hydro discs.

It's so hard to average out the countless factors to arrive at any kind of a meaningful objective comparison of braking force; so many models of each type of brake, they won't all fit the same bike so can't be tested exactly the same realistically, differing brake pad compounds within each category, conditions affecting each type differently, how they're set up, other parts of the bike affecting the braking performance eg frame/fork flex, etc etc.

[rogerzilla]

Your body position has a big influence. If you hang right off the back of the saddle in an emergency stop, you can use almost as much front brake as you like. I have locked up a front wheel on several occasions, twice on a dry road.

[gregoryoftours]

This looks like some approximation of an attempted objective study into braking performance but not braking force related to effort at the lever. It was a real world test to the extent that tyre traction was a factor, so a more realistic test but not a raw braking force test. I think you might have to pay to read the full study, I could be wrong though. Maybe it's available somewhere else.

https://saemobilus.sae.org/content/2020-01-0876/

[Mick F]

Some time back, when I bought my Moulton ........ it had Tektro calliper brakes.
Twice - or was it three times? - descending a steep and long Cornish hill, the front rim overheated and burnt out the inner tube. Inner tubes were scrap after that.

The issue was that the Tektro callipers were too bendy and not giving enough of a powerful grip and therefore dragging.
Changed to Shimano 105 callipers, and even though I've REALY tried through experimentation, the rims don't overheat at all and braking is much much improved.

[rogerzilla]

People (me included) have tried using electrical insulating tape on Moulton rims when they can't find 20" rim tape. It doesn't take much heat to soften the glue, then everything starts wriggling around in there and your valve stem gets torn off. Or the tape actually melts.

[Mick F]

With mine, the rim was so hot, I had to give it ten minutes to cool off before I could even hold the wheel.
The front tube had a huge hole in the area next to the hot rim. Only option was to replace the tube ........... of which I always carry two.

Rim tapes are, and were, Schwalbe.
https://www.sjscycles.co.uk/rims-tape/s ... -rim-tape/

[Tompsk]

There is high mechanical advantage with discs from the lever to the pads but this is reduced by a factor of about 4 as a 160mm disc is about 1/4 the diameter of a 700c or 29" wheel. So with disc brakes the force at the surface of the tyre can be about 25% of the force at the disc. With rim brakes the force at the surface of the tyre is about 95% of that at the rim (both for 700c wheels and 30mm ish tyres). Try (carefully!) stopping a slowly turning wheel by touching the rim and disc and you will get a sense of the forces and heat involved. Overall the mechanical advantage from the lever to the road is better with disc brakes.

Correctly set up (modern) rim and disc brakes can easily lock up a wheel even in the dry so both are equaly capable in that sense. If the rider has weaker hands then discs may be better.

For smaller wheeled bikes there is less rim to soak up the heat so they will get hotter, discs will gain there and as a 160mm disc is a better size ratio to the smaller wheel you should get 50%(?) of the brake force delivered to the surface of the tyre

(Correction to avoid implying locking a wheel is a good thing)

[Spen]

What I was really wondering is if we perceive braking forces to be different rather than experience different braking forces. Personally I find rim brakes on a drop bar bike terrifying, they never seem to "pull" properly, despite being able to lock the back wheel. With flat bars and v brakes there is a noticeable increase in "pull" and again the back wheel will lock, same thing with discs on flat bars. Obviously hydraulic disc can exert a higher force on the rotor than a rim brake does on the rim, although there are several examples of hydraulic rim brakes available, but as braking force is greater the further it's applied from the hub, do these things cancel each other out?

I've seen many videos on youtube comparing different brake types but the only difference appears to be in the wet, which is often attributes to rim brakes having to dry the rim, but is this due to the pad material in discs being more abrasive as it's easier and cheaper to change a rotor than a rim?

[Jdsk]

Personally I find rim brakes on a drop bar bike terrifying, they never seem to "pull" properly, despite being able to lock the back wheel.

The ultimate limit to deceleration lies elsewhere, as above.

But those aspects of feel, progression, play, consistency, mechanical advantage, front to rear balance etc are very important.

When I'm fettling other people's bikes I'm staggered what they'll tolerate.

Jonathan

PS: The most memorable "feel" that I can recall is the first time that I applied the Magura hydraulics on my KingCycle.

[Mick F]

........Personally I find rim brakes on a drop bar bike terrifying, they never seem to "pull" properly ...........

I would suggest, therefore, you haven't ridden a dropped bar bike with the correct levers and rim brakes.
Mercian is Campag and is perfect. Moulton has Tektro levers and Shimano 105 rim brakes. Both bikes have dropped bars and the braking on both bikes is perfect.

Going back to my previous post, the Tektro rim brakes I had on Moulton were terrible even though they were as original on the bike when new. I reckon the bike was dangerous descending at speed. As soon as I realised what the problem was and swapped to Shimano 105 the problem disappeared.

[Mike Sales]

PS: The most memorable "feel" that I can recall is the first time that I applied the Magura hydraulics on my KingCycle.

I once had a KingCycle with Maguras. I remember the braking but also the flexing of the frame. (Not under braking but when pushing hard.)