Unscientific brake tests..........

rolf_f

Now, a few days ago, in this thread the subject of braking performance came up - between discs and rim brakes and between braking off hoods of various ages and on the drops and I said I'd try some experiments. So I did!

First thing is - in no way can any conclusive conclusions be drawn from the results. Exact braking point would be slightly variable and speed at the point of braking varied too. The most useful conclusions are drawn between tests on the same bike but the numbers between bikes are interesting too.

The Bikes
1) Orange P7 hardtail mtb. Probably near 30lbs in weight in current trim. Running slicks and avid juicy 3 disc brakes in decent shape with sintered pads.
2) Raleigh Record Ace circa 1980. Probably about 24 lbs in weight (guessing a bit) - brakes are Weinmann 605 calipers. One side of the caliper isn't retracting properly so there is more clearance than there should be so there'll be a slight delay in brake application. Pads probably the same age as the bike and a bit hard.
3) Peugeot Triathlon racer circa 1989. Probably low 20 something lbs. Brakes are Shimano 105 calipers with concealed cables.
4) Dawes Horizon 1990. Weight about 28 lbs. Weinmann cantilever brakes. Original pads but in good condition.
5) Look 585 Optimum 2010. Weight 16 lbs. Campagnolo Centaur brakes – barely used.

The Test
Each bike was started from rest without pedal input. The bikes were allowed to roll down a hill. Drop was 52 feet in 228 metres with gradient fairly constant. Top speed was recorded for the Orange and the Dawes – 22 and 24.1 mph respectively (the only bikes with computers on them). In the case of all but the flat barred Orange, the test was repeated twice with one run braking on the drops and the other from the hoods. During the descent, for both tests, I steered on the hoods to avoid speed differences. Only the front brake was applied.

The image below shows the (slightly surprising) results.



Non scientific conclusions are:

Disc brakes are most effective.

Modern calipers are nearly as good (on my first run on the Look, I nearly went over the handlebars).

Disc brakes not as big an advantage as you might think but bike weight could be a significant factor here. On the other hand, the Look would have probably been going faster than the Orange at the braking point.

There is virtually no difference in the performance of the older drop bar setups. Surprising as there are significant weight differences and the condition of the bikes is a bit varied too. Most odd was the relatively good performance of the Raleigh on the hoods. This is maybe because the slack in the setup allows the lever to get much closer to the bar itself and therefore closer to the palm of my hand.

Braking on the hoods is less effective than braking from the drops. However, modern technology does reduce this substantially. Even so, I was over 4.5 metres later stopping on the hoods of the Look compared to the Orange. That could matter in traffic. On the old bikes, the difference was about the width of a road junction so the benefits of braking on the drops are obvious.

As I said, this isn’t science and I’d need to repeat quite a few times for it to approach that. However, it is at least data which is better than opinion!

supersonic

How hard did you pull the levers? If I pulled them fully I wouldn't stop, I'd be over the bars lol.

I think the tyres are the limiting factor here.

Radioactiveman

Next time you are bored and have nothing to do you can pop round and cut my grass if you like :P

rolf_f

supersonic wrote:

How hard did you pull the levers? If I pulled them fully I wouldn't stop, I'd be over the bars lol.

I think the tyres are the limiting factor here.

Levers pulled as hard as possible in each case as to brake safely to a stop. As I said, not exactly scientific. I did nearly go over the bars of the Look but the others I think were pretty much full force. Tyres not that much of an influence otherwise - the Dawes and Peugeot both have newish tyres - Schwalbe Delta Cruiser 28s on the Dawes and Michelin Dynamic 20mm on the Peugeot. The Raleigh has some ancient 32mm largely unused but hard and cracked tyres that may kill me. The old bikes really do seem surprisingly consistent. Look has Schwalbe Durano 25s.

Radioactiveman wrote:

Next time you are bored and have nothing to do you can pop round and cut my grass if you like :P

What do you think I was trying to avoid doing?

gert_lush

..any excuse for a pretty table of stats!

lost_in_thought

Ooooooh I like it! I don't have hills round 'ere but could do a very scientific braking performance from whatever speed I can get my brother's something-pot-hydraulic-disc-brake'd MTB to...

Added to to-do list...

FrankM

My guess is that the biggest difference in performance would come in the wet, and specifically in wet London streets where there's so much **** on the road.

roger_merriman

wet is where disks come into there own, and to a lesser degree high speed braking i.e. 40+ mph.

at a dry 20mph i'd expect it to be even, and differences to be tires.

whyamihere

Are the top and drop figures in the table backwards? You've shown it being consistently better to brake from the top (I assume this is the hoods) than the drop, which disagrees with both your analysis and common sense...

rolf_f

gert_lush wrote:

..any excuse for a pretty table of stats!

Do you like it? I colour coded and font'd it to match the bikes

whyamihere wrote:

Are the top and drop figures in the table backwards? You've shown it being consistently better to brake from the top (I assume this is the hoods) than the drop, which disagrees with both your analysis and common sense...

D'oh - I blame it on my cold. I'll correct it this evening - obviously you are right! I wrote the spreadsheet first and then did the tests and just always ran the drop test first and didn't think to check the headings :oops:

As for the wet test - I'll do that one when the weather allows - probably only on the Dawes and the Orange though.

wgwarburton

Rolf F wrote:

gert_lush wrote:

..any excuse for a pretty table of stats!

Do you like it? I colour coded and font'd it to match the bikes

whyamihere wrote:

Are the top and drop figures in the table backwards? You've shown it being consistently better to brake from the top (I assume this is the hoods) than the drop, which disagrees with both your analysis and common sense...

D'oh - I blame it on my cold. I'll correct it this evening - obviously you are right! I wrote the spreadsheet first and then did the tests and just always ran the drop test first and didn't think to check the headings :oops:

As for the wet test - I'll do that one when the weather allows - probably only on the Dawes and the Orange though.

Good info, Rolf.

So, given our previous discussions, does this change your position, at all? Clearly, braking from the hoods is less effective than braking from the drops, as expected, and that difference could be significant in an emergency.... however, it's also clearly "good enough" in the majority of situations (ie controlling speed, rather than emergency stops)... hence the reason so many people ride that way.

Incidentally, how easy do you find it to switch hand positions? I know that I can move from hoods to drops while braking steadily (ie slowing down, not panic-braking!), so if the situation looks like it might need to get more stoppy then I'll do that in anticipation.
Not much use in an emergency, I guess, though it's an automatic move and slicker than you might imagine. I presume this is no harder on modern levers than on the traditional ones?

Cheers,
W.

rolf_f

WGWarburton wrote:

So, given our previous discussions, does this change your position, at all? Clearly, braking from the hoods is less effective than braking from the drops, as expected, and that difference could be significant in an emergency.... however, it's also clearly "good enough" in the majority of situations (ie controlling speed, rather than emergency stops)... hence the reason so many people ride that way.

Incidentally, how easy do you find it to switch hand positions? I know that I can move from hoods to drops while braking steadily (ie slowing down, not panic-braking!), so if the situation looks like it might need to get more stoppy then I'll do that in anticipation.
Not much use in an emergency, I guess, though it's an automatic move and slicker than you might imagine. I presume this is no harder on modern levers than on the traditional ones?

Cheers,
W.

What I was most surprised about was that the Peugeot 105 setup was no better than the Weinmanns in terms of relative efficiency. I terms of speed control on the hoods I'd say that the Peugeot and particularly the Look feel better than the Weinmanns even if the Peugeot isn't really better. I wonder if the advantage the Look has is the dual pivot front brakes. Would be useful to repeat the test with a modern bike with single pivot brakes,

I don't have any problem moving rapidly to the drops but do tend to default to them if I feel I might need to brake in a hurry. I do use the drops a lot though anyway - hilly country encourages it!

One variable I forgot to mention is that the Dawes and Look are left front brake and the Raleigh, Peugeot and Orange right front brake. I don't think that has made much difference but it needs to be said! It could be argued that brake control might be worse for the Look and Dawes but the results don't imply it.

wgwarburton

Rolf F wrote:

...One variable I forgot to mention is that the Dawes and Look are left front brake and the Raleigh, Peugeot and Orange right front brake. I don't think that has made much difference but it needs to be said! ....

That's interesting. Now that I think about it I'd be a lot less comfortable braking from the hoods with the front brake under my left hand instead of my right... which suggests that I need my stronger hand to get enough power (or maybe control..?).

Cheers,
W.

lost_in_thought

WGWarburton wrote:

Rolf F wrote:

...One variable I forgot to mention is that the Dawes and Look are left front brake and the Raleigh, Peugeot and Orange right front brake. I don't think that has made much difference but it needs to be said! ....

That's interesting. Now that I think about it I'd be a lot less comfortable braking from the hoods with the front brake under my left hand instead of my right... which suggests that I need my stronger hand to get enough power (or maybe control..?).

Cheers,
W.

I had the same reaction on reading that, but is it not also possible that it's a psychological thing - braking with the front brake is more effective, so you use it more, thereby making it your 'default' brake, so the idea of shifting it to your 'non-default' side is troubling?

Using those grip test thingies (in all their ultra-scientific glory :P) my left hand is physically stronger...

rolf_f

For what it is worth, I've also in the past owned left and right hand drive cars; like most things that are a bit confusing at first, you soon get used to it.

A good thing about bikes with the cables running out of the top of the hoods is that it takes a few seconds to swap the cables over to find out (no need to remove the bar tape) - I did this with the Dawes to see if I would be happy left front braking before the Look was built.

il_principe

Surely tire size is too much of a factor to ignore?

The Rookie

Tyre size is irrelevant to braking grip unless (unlikley in this case) you excees te deigntemperature limit, friction=coeficientXmass, so halving the width, doubles the mass per unit area nd you have the same grip, if you overheat (or get no heat into) a tyre (the smaller tyre will overheat more readily) then the coeficient may change a bit, otherwise, its not relevant.

Excelent info, although my mate contends that rim brakes are natures ABS, wet tyre road interface, so you want wet rims to balance it up, me I'll stick with pulling the lever less hard on my discs.

Simon

supersonic

The amount of tyre in contact with the road is dependant on pressure, not size. Halve the width and you still have the same amount in contact if the pressure is the same.

This assumption does break down at very low pressures and certain grip profiles. But for a slick, is pretty accurate.

amnezia

Tyre material has a big effect on stopping power though.

The conti GP4000's i used to have on the commuter had phenomenal grip, never manage to lock them up once.

supersonic

it does indeed, those cheapo plastic things on budget bikes are horrific.

UndercoverElephant

OK, now if I've understood the physics correctly, and there's no guarantee of that, it's been a while.

The Orange was travelling at 9.8 m/s and stopped in 9 meters, assuming constant deceleration, it took 1.8 seconds to stop.

If we assume the same rate of deceleration ( 5.4 m/s/s ), but plug in the speed from the Dawes (10.8 m/s), the Orange bike would have taken 2 seconds to stop, and would have travelled 10.8 meters.

Given that we have no speed data for the Look, other than, "Probably faster than the Dawes", we can't be sure, but even if it was only as-fast as the Dawes, and it managed to stop in 10.5 m, we can conclude:

Road bike brakes are better than disc brakes!

I'm so happy. Well done Rolf!

UndercoverElephant

** Hoof **

PBo

UndercoverElephant wrote:

OK, now if I've understood the physics correctly, and there's no guarantee of that, it's been a while.

The Orange was travelling at 9.8 m/s and stopped in 9 meters, assuming constant deceleration, it took 1.8 seconds to stop.

If we assume the same rate of deceleration ( 5.4 m/s/s ), but plug in the speed from the Dawes (10.8 m/s), the Orange bike would have taken 2 seconds to stop, and would have travelled 10.8 meters.

Given that we have no speed data for the Look, other than, "Probably faster than the Dawes", we can't be sure, but even if it was only as-fast as the Dawes, and it managed to stop in 10.5 m, we can conclude:

Road bike brakes are better than disc brakes!

I'm so happy. Well done Rolf!

Physics fail!
Nothing too wrong with your numbers, however, interpretation is wrong!

In both cases, the bakes provide a force F to a bike mass m, to cause the acceleration. a
F= ma
The look decelerated marginally faster, so a slight difference in a.

HOWEVER given that m is almost twice as much for the Orange than the look, hence requiring almost twice the force, this more than trumps your small difference in a!

we can conclude:

Disc brakes are almost twice as good as road bike brakes!


btw rolf, not unscientific at all - just the opposite!

You've created a hypothesis, come up with a method to test that, included all the assumptions, caveats and problems with your method, and then published the results and interpretation for peer review!!! (maybe could have done with more of each sample, to average out, but hey )

Even if people come and rip your method and results to shreds, this too is all part of the scientific method......

Bravo!

UndercoverElephant

PBo wrote:

UndercoverElephant wrote:

OK, now if I've understood the physics correctly, and there's no guarantee of that, it's been a while.

The Orange was travelling at 9.8 m/s and stopped in 9 meters, assuming constant deceleration, it took 1.8 seconds to stop.

If we assume the same rate of deceleration ( 5.4 m/s/s ), but plug in the speed from the Dawes (10.8 m/s), the Orange bike would have taken 2 seconds to stop, and would have travelled 10.8 meters.

Given that we have no speed data for the Look, other than, "Probably faster than the Dawes", we can't be sure, but even if it was only as-fast as the Dawes, and it managed to stop in 10.5 m, we can conclude:

Road bike brakes are better than disc brakes!

I'm so happy. Well done Rolf!

Physics fail!
Nothing too wrong with your numbers, however, interpretation is wrong!

In both cases, the bakes provide a force F to a bike mass m, to cause the acceleration. a
F= ma
The look decelerated marginally faster, so a slight difference in a.

HOWEVER given that m is almost twice as much for the Orange than the look, hence requiring almost twice the force, this more than trumps your small difference in a!

we can conclude:

Disc brakes are almost twice as good as road bike brakes!


btw rolf, not unscientific at all - just the opposite!

You've created a hypothesis, come up with a method to test that, included all the assumptions, caveats and problems with your method, and then published the results and interpretation for peer review!!! (maybe could have done with more of each sample, to average out, but hey )

Even if people come and rip your method and results to shreds, this too is all part of the scientific method......

Bravo!

Double physics fail. Rolf was on the bike, I bet he doesn't weigh zero.

PBo

UndercoverElephant wrote:

PBo wrote:

UndercoverElephant wrote:

Road bike brakes are better than disc brakes!

I'm so happy. Well done Rolf!

Physics fail!
Nothing too wrong with your numbers, however, interpretation is wrong!

In both cases, the bakes provide a force F to a bike mass m, to cause the acceleration. a
F= ma
The look decelerated marginally faster, so a slight difference in a.

HOWEVER given that m is almost twice as much for the Orange than the look, hence requiring almost twice the force, this more than trumps your small difference in a!

we can conclude:

Disc brakes are almost twice as good as road bike brakes!

Double physics fail. Rolf was on the bike, I bet he doesn't weigh zero.

This is, as they say, a good point very well made!!

Assuming rolf is a healthy 80kg, then the orange/rolf combo is about 8% heavier. Look could have been going sufficiently faster to allow the value of a to have been 8% higher - not out of the question, and would give similar braking performance.

So in conclusion, we can definitely say:
Road bike brakes might be better than disc brakes! Or road bike brakes might be worse than disc brakes! Or they might be the same!
:?

rolf_f

UndercoverElephant wrote:

Double physics fail. Rolf was on the bike, I bet he doesn't weigh zero.

Not far off - less than 10 stone

As for conclusions re disc and road brakes, I think the best you can conclude is that modern calipers on a lightweight bike are near enough as effective as discs on a heavier bike assuming dry conditions. That doesn't imply in itself that a heavier bike with calipers or a lighter bike with discs will behave significantly differently (in this case significant probably means failing to stop before the side turning!).

What we need to test now is decent modern calipers on a heavier bike and a disc fitted road bike neither of which I have.

PBo

Rolf F wrote:

UndercoverElephant wrote:

Double physics fail. Rolf was on the bike, I bet he doesn't weigh zero.

Not far off - less than 10 stone

As for conclusions re disc and road brakes, I think the best you can conclude is that modern calipers on a lightweight bike are near enough as effective as discs on a heavier bike assuming dry conditions. That doesn't imply in itself that a heavier bike with calipers or a lighter bike with discs will behave significantly differently (in this case significant probably means failing to stop before the side turning!).

What we need to test now is decent modern calipers on a heavier bike and a disc fitted road bike neither of which I have.

this pushes things further in favour of the discs - difference due to mass is now around 17%, less likely that look decelerated 17% more quickly

UndercoverElephant

Actually what it's saying is that lightweight road brakes are fine for lightweight road bikes, whereas heavier discs are probably better for heavier mountain bikes.

Either way, given the same speed, Rolf would have stopped in a shorter distance on the road bike, ergo....

Road bike brakes on a road bike would probably stop you in a shorter distance than disc brakes on a mountain bike, assuming that Rolf doesn't actually go really slow on his fancy new bike.

rolf_f

UndercoverElephant wrote:

Road bike brakes on a road bike would probably stop you in a shorter distance than disc brakes on a mountain bike, assuming that Rolf doesn't actually go really slow on his fancy new bike.

Not quite - my P7 is fairly heavy for a hardtail MTB - it is steel and built to last. Most hardtail alloy framed MTBs are a good bit lighter.

As for my new bike - I go like the wind on it; however, in this test gravity was the sole propulsion unit! Probably means that a) I need to get some scales to weigh the bikes properly and that b) I need to add mgh and half mv squared to the spreadsheet A long time ago was A level physics.........

il_principe

supersonic wrote:

The amount of tyre in contact with the road is dependant on pressure, not size. Halve the width and you still have the same amount in contact if the pressure is the same.

This assumption does break down at very low pressures and certain grip profiles. But for a slick, is pretty accurate.

Sorry, I was referring to contact patch size rather than tyre size. I imagine discs on a 700/23 at 120 psi would just be massive overkill. You'd lock up. I've locked the rear wheel of my road bike when descending in Wales - Brun and I narrowly avoided stacking it straight into a car... no need for discs (on a roadie).

UndercoverElephant

Rolf F wrote:

UndercoverElephant wrote:

Road bike brakes on a road bike would probably stop you in a shorter distance than disc brakes on a mountain bike, assuming that Rolf doesn't actually go really slow on his fancy new bike.

Not quite - my P7 is fairly heavy for a hardtail MTB - it is steel and built to last. Most hardtail alloy framed MTBs are a good bit lighter.

As for my new bike - I go like the wind on it; however, in this test gravity was the sole propulsion unit! Probably means that a) I need to get some scales to weigh the bikes properly and that b) I need to add mgh and half mv squared to the spreadsheet A long time ago was A level physics.........

True, gravity was the sole propulsion, but the main drag factor will have been the wind resistance. I noticed only one speed reading for the Dawes, was this in drops or on hoods? I would have thought that a nice, well-fitted road bike in drops would have accelerated to a much higher speed than in hoods, which in turn would have been faster than the MTB over the same run. As such the speeds could be even more skewed.