Author Topic: Caliper brake power--what factors affect ?  (Read 2274 times)

Caliper brake power--what factors affect ?
« on: October 26, 2015, 07:03:38 am »
Notice considerable difference in brake power between my short drop Campag Veloce dual pivots ---set about halfway on pad arms, and my Shimano deep drop, set to their deepest position. Both being used with Campag levers.

So is the difference mostly down to inherent extra flex in  brake arms due to extra depth or is it mismatch of levers? Is it worth just trying different pads (currently Aztec on Shimanos, Campag supplied on Veloce) ?

thanks
....after the `tarte de pommes`, and  fortified by a couple of shots of limoncellos,  I flew up the Col de Bavella whilst thunderstorms rolled around the peaks above

T42

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Re: Caliper brake power--what factors affect ?
« Reply #1 on: October 26, 2015, 08:19:57 am »
Leverage is the major diff.  For equal forces applied to the cable and equal distances between the cable ends and the pivot, the pinching force exerted on the rim is proportional to the distance between the block and the pivot.  The deeper the drop the weaker the pinch.  Double pivots confuse the issue but the same rules apply - basic physics.
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Re: Caliper brake power--what factors affect ?
« Reply #2 on: October 26, 2015, 08:31:16 am »
Thanks T42---so effectively basic physics will prevent me from ever getting the deeper pivot brakes, set at near 57mm drop position anywhere near as powerful as the short reach which are probably running at 45mm drop ?
....after the `tarte de pommes`, and  fortified by a couple of shots of limoncellos,  I flew up the Col de Bavella whilst thunderstorms rolled around the peaks above

Samuel D

Re: Caliper brake power--what factors affect ?
« Reply #3 on: October 26, 2015, 08:35:52 am »
There is probably some difference in mechanical advantage, whether from the design of the callipers or the different slot heights of the respective brake pads. A clue is in the pad clearance at the rim, greater clearance suggesting weaker braking.

Flex in the brake arms should not affect braking force directly but would affect lever travel and feel.

Friction in the entire system from lever to calliper is important but friction in the calliper pivots especially so. When the brakes are applied the pads tend to be dragged around the rim. This creates a strong reaction load in the pivots, greatly increasing pivot friction compared to friction when the wheel is stopped (i.e. the friction you experience when you pump the brake lever, even hard, while stopped).

This pivot friction (stiction) ultimately limits the braking force you can apply. Its effect on braking varies greatly with pivot bearing quality (hence expensive callipers ‘mysteriously’ working better despite equal mechanical advantage) and also with the distance between the pivots and the rim (unequal in dual-pivot callipers and longer in long-reach callipers). It is also the secret of the V-brake’s stopping power: the short distance from pivot to rim reduces the effect of pivot stiction, converting more of your lever force to pad force while the wheel is turning.

I would try different pads, maybe Kool Stop. Then new cables and housings of known quality. Then, if braking is still bad, replace the long-drop calliper with a Shimano BR-R650 if it’s not already that or even Tektro/TRP’s best equivalent – I read somewhere it is even better than the BR-R650 but I forget the model name.

Re: Caliper brake power--what factors affect ?
« Reply #4 on: October 26, 2015, 08:52:40 am »

This pivot friction (stiction) ultimately limits the braking force you can apply. Its effect on braking varies greatly with pivot bearing quality (hence expensive callipers ‘mysteriously’ working better despite equal mechanical advantage) and also with the distance between the pivots and the rim (unequal in dual-pivot callipers and longer in long-reach callipers).

so is that why my old Campag Chorus brakes proudly advertised (on the front dual pivot) `ball bearing pivots` and the rear single pivot one was verging on nigh useless and  was far interior to a set of Veloce brakes, dual pivot no ball bearings?

I`m currently using BR650s, but I`d suppose that as they`re much used pivot smoothness my have reduced ? I also noted an improvement in brake power when changing the length outer from frame stop to caliper from Goodridge back to a more flexible Campag outer, the Goodridge outer was so stiff it seemed to inhibit smooth caliper movement !
....after the `tarte de pommes`, and  fortified by a couple of shots of limoncellos,  I flew up the Col de Bavella whilst thunderstorms rolled around the peaks above

Re: Caliper brake power--what factors affect ?
« Reply #5 on: October 26, 2015, 08:55:45 am »
Thanks T42---so effectively basic physics will prevent me from ever getting the deeper pivot brakes, set at near 57mm drop position anywhere near as powerful as the short reach which are probably running at 45mm drop ?

Not entirely - if the cable arms are also longer the leverage is maintained. It's as likely to be the amount of cable the Campag levers pull as the calipers, or the pads.

I've got/used Shimano 650, Shimano 451 and TRP 957 (I think that's the number). The TRP are outstanding, the Shimano very good, but you need decent pads. The TRP pads are excellent, the 650 pads OK and the 451 are fine, but are monoblocks.

On the Shimano brakes I'd swap pads for Koolstp Salmon or dual compound.

Mike

Samuel D

Re: Caliper brake power--what factors affect ?
« Reply #6 on: October 26, 2015, 09:05:25 am »
so is that why my old Campag Chorus brakes proudly advertised (on the front dual pivot) `ball bearing pivots` and the rear single pivot one was verging on nigh useless and  was far interior to a set of Veloce brakes, dual pivot no ball bearings?

Probably. At first glance, low-friction bushings or ball bearings may seem like gratuitous hardware in calliper pivots, since when pumping the brake lever of a stopped bicycle the tiny pivot friction of any brake is irrelevant. But the harder you brake while moving, the greater the reaction load and the greater the resulting pivot stiction. At some point the pivot stiction prevents you from increasing the braking force despite all your effort at the lever.

If you already have the BR-R650, take it apart and meticulously clean and lube it. Can’t hurt!

Re: Caliper brake power--what factors affect ?
« Reply #7 on: October 26, 2015, 10:04:24 am »
There are basically two places where mechanical advantage occurs.  Firstly at the levers: the more the lever moves for a given movement of the caliper the greater the advantage, and stopping power – until the lever hits the bar.  Second: the comparative length of the caliper arms above and below the pivots.  The shorter the lower part (with the brake block) in relation to the upper (attaching to the cable), the greater the advantage and the better the braking.

Of course you then have other variables such as type of block, cable friction, and mechanical wear.

Re: Caliper brake power--what factors affect ?
« Reply #8 on: October 26, 2015, 10:07:55 am »
so is that why my old Campag Chorus brakes proudly advertised (on the front dual pivot) `ball bearing pivots` and the rear single pivot one was verging on nigh useless and  was far interior to a set of Veloce brakes, dual pivot no ball bearings?

Dual pivot on the rear caused wheel lock problems as they were too good.  Hence the reason why Campag go for dual on the front and single on the back.  Overall, the brakes work very well.  Using only one brake will have limitations as they're designed to be used together.

Samuel D

Re: Caliper brake power--what factors affect ?
« Reply #9 on: October 26, 2015, 11:14:29 am »
Is the TRP RG957 designed for ‘Super SLR’ or ‘New Super SLR’ cable pull ratios or some other standard?

I ask because the BR-R650 is designed for the old ‘Super SLR’ levers. So if you use it with the latest Shimano STIs that pull more cable, braking power is reduced (though the combination is safe enough for Shimano to officially tolerate).

If you’re using ‘New Super SLR’ levers and the RG957 is designed for those, that alone would explain a significant improvement in braking power from the BR-R650.

I don’t know how much cable Campagnolo levers pull compared to the old and new Shimano standards.

Re: Caliper brake power--what factors affect ?
« Reply #10 on: October 26, 2015, 02:04:21 pm »
Is the TRP RG957 designed for ‘Super SLR’ or ‘New Super SLR’ cable pull ratios or some other standard?

I ask because the BR-R650 is designed for the old ‘Super SLR’ levers. So if you use it with the latest Shimano STIs that pull more cable, braking power is reduced (though the combination is safe enough for Shimano to officially tolerate).

If you’re using ‘New Super SLR’ levers and the RG957 is designed for those, that alone would explain a significant improvement in braking power from the BR-R650.

I don’t know how much cable Campagnolo levers pull compared to the old and new Shimano standards.

RG957 is for 2.5 ration levers, i.e. 'new super slr'. BR650, 450, 451 are for 2 ration levers, i.e. 'super slr'.

RG957 with 6800 levers is superb.

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Re: Caliper brake power--what factors affect ?
« Reply #11 on: October 26, 2015, 02:25:48 pm »
Differences in the condition (let alone the model) of pads and rim can dwarf everything else, so you can't be sure of a fair comparison when these factors are different.  Flex, in practice: I rate as less important than rim/pad condition and mechanical advantage (leverage).  Braking can be good even with drops as long as Alhonga's when everything else is good.
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Samuel D

Re: Caliper brake power--what factors affect ?
« Reply #12 on: October 26, 2015, 03:04:03 pm »
RG957 with 6800 levers is superb.

I bet, given what you said about the cable pull. Just a pity the RG957 is so expensive.

Re: Caliper brake power--what factors affect ?
« Reply #13 on: October 26, 2015, 04:10:45 pm »
Just took my BR 650 brakes apart---can see why stiction could affect performance, the pivot point was just a brass sleeve over a rather loose joint of a bolt; anyway greased and cleaned but with small degree wobble on pivot can imagine that it would bind up quiet easily under load; and oh yes a pity about TRP price  ::-)
....after the `tarte de pommes`, and  fortified by a couple of shots of limoncellos,  I flew up the Col de Bavella whilst thunderstorms rolled around the peaks above

Re: Caliper brake power--what factors affect ?
« Reply #14 on: October 27, 2015, 01:44:46 am »
I've got/used Shimano 650, Shimano 451 and TRP 957 (I think that's the number). The TRP are outstanding, the Shimano very good, but you need decent pads. The TRP pads are excellent, the 650 pads OK and the 451 are fine, but are monoblocks.

Hello Mike,

How would you compare the RG957 and BR650 for being able to get an SKS 35mm mudguard as far up and away from the tyre as possible?

I have BR650s, and the chunkiness of the brake arms and pivot bolt surround where the mudguard rests up against prevents raising it any further despite there being room in relation to the frame.  This means clearance to my 30mm Schwalbe Winter tyres is very small.

Looking at comparative front-on photos of the two brakes, the RG957s look more slender in the critical areas and appear to arc slightly higher, seemingly to offer more clearance for raising the mudguard - would you say that was the case, and if correct could you estimate how much additional clearance the RG957s might give over the BR650?

Thanks!

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Re: Caliper brake power--what factors affect ?
« Reply #15 on: October 27, 2015, 11:46:46 pm »
One thing to bear in mind about the bearings is that if they are warn and there is some play in them, that will affect braking performance, as it will make the brakes hard to adjust and they will also squeak a lot.  My old FSA calipers used to be good but I've recently retired them for this reason.

Re: Caliper brake power--what factors affect ?
« Reply #16 on: October 28, 2015, 12:42:26 am »
I've got/used Shimano 650, Shimano 451 and TRP 957 (I think that's the number). The TRP are outstanding, the Shimano very good, but you need decent pads. The TRP pads are excellent, the 650 pads OK and the 451 are fine, but are monoblocks.

Hello Mike,

How would you compare the RG957 and BR650 for being able to get an SKS 35mm mudguard as far up and away from the tyre as possible?

I have BR650s, and the chunkiness of the brake arms and pivot bolt surround where the mudguard rests up against prevents raising it any further despite there being room in relation to the frame.  This means clearance to my 30mm Schwalbe Winter tyres is very small.

Looking at comparative front-on photos of the two brakes, the RG957s look more slender in the critical areas and appear to arc slightly higher, seemingly to offer more clearance for raising the mudguard - would you say that was the case, and if correct could you estimate how much additional clearance the RG957s might give over the BR650?

Thanks!


My 957s are without guards, but I suspect you'd get one or two mm at most. On my frames, the frame is the issue rather than the brakes. Having said that, I just moved from 28 to 26 (26 on the rims I've built up) tyres to get a bit more clearance under my 451s (same forging as 650).

Mike

Re: Caliper brake power--what factors affect ?
« Reply #17 on: October 29, 2015, 02:18:52 pm »
You should try 1080 calipers with 100mm drop, used on cruiser bikes and Raleigh Twentys with the smaller 406mm BMX-sized wheels.  There is a general retarding effect rather than actual braking.

As well as the reduced mechanical advantage, a lot of lever travel is wasted because long brake arms aren't very stiff, and flex a lot when the brake is applied.  If the lever hits the handlebar due to this flex then this also limits the stopping force.
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Re: Caliper brake power--what factors affect ?
« Reply #18 on: October 31, 2015, 06:39:03 pm »
My 957s are without guards, but I suspect you'd get one or two mm at most. On my frames, the frame is the issue rather than the brakes. Having said that, I just moved from 28 to 26 (26 on the rims I've built up) tyres to get a bit more clearance under my 451s (same forging as 650).

Thanks for the information.

Perhaps surprisingly, a couple of mm may be all it takes. 

Getting the mudguard up as high as possible whilst at the same time limiting contact with the unnecessarily chunky bit of caliper is not easy.  The problem with contacting the caliper at that point is that it is off-centre and forces the mudguard out of alignment, which if not precisely positioned causes the edges at the end to touch the tyre whilst rest of the clearance is ok.  Having to subsequently tighten the mudguard bolt also plays havoc with getting the position right.  Only really a problem when using the 30mm studded Schwalbe Winter or '32mm' Continental Top Contacts though.....

2mm might just be enough to eradicate that alignment problem, but it would be an expensive experiment!

Re: Caliper brake power--what factors affect ?
« Reply #19 on: October 31, 2015, 07:57:13 pm »
How about carefully re-engineering mudguard sides around area where it contacts caliper, ie cut away a portion mudguard? Or change mudguard design as shapes may vary
....after the `tarte de pommes`, and  fortified by a couple of shots of limoncellos,  I flew up the Col de Bavella whilst thunderstorms rolled around the peaks above