Bendy Dual Pivots

[Mick F]

The Tektro R539 dual pivot callipers on my Moulton are ok, but a bit flexible ............. bendy.
http://www.tektro.com/products.php?p=44

Squeeze the brake levers reasonably firmly, and the operating arms of the callipers bend maybe five or six millimetres - maybe even eight millimetres.
Compare that to my Campag brakes on Mercian for the same pressure, and they hardly bend or flex at all.

The Moulton brakes are acceptable, so no real major complaints, but it does show me that there are callipers - and there a callipers.
Something less "vague" would be nice.

What are my options?
What's out there?

[pwa]

Do you think that the flexing is due to the arms being longer?

[tatanab]

Like you I prefer Campag, but on my touring bike I need a deeper drop so have Shimano R650. If they are a bit pricey there is the cheaper R450.

If you can find them, and if they are deep enough, 2006 (I think) Campag Centaur have a 52mm drop.

[Mick F]

Do you think that the flexing is due to the arms being longer?

The flexing/bending is throughout, and if I compare the front Tektro R539 to my front Campag Athena, they seem exactly the same geometry.

Difficult to photograph one in front of the other.

[Brucey]

it could be the arms themselves but it could also be the brake blocks being differently squishy or (more likely IMHO) that the tektro brakes have more/thicker plastic bushings in the pivots. Most of the less expensive DP brakes have much less well engineered pivots than the more expensive ones.

cheers

[TrevA]

Ive previously had issues with bendy Tektro's calipers in 47-57mm size. Fitting Shimano pads improved things a bit, but In the end, I swapped the calipers out for some Shimano ones.

[peetee]

You can get a big improvement in brake feel and power by paying close attention to the cables. There is no substitute for quality and, although I rate Clarks cables for middle of the road braking systems, even standard Shimano cables have better feel. The trick is to properly finish the cuts you make to the outer casing. Even expensive cable cutters can make a mess of the coil so make sure it is not partially unwound and at the same time file the end square so the winding tapers away gradually and the whole outer cable sits flat.

[Samuel D]

Do not get the Shimano BR-R650 callipers expecting them not to flex. They flex plenty (as do the pads, etc., but I have observed this closely and the arms themselves flex too).

It makes me wonder how these aluminium alloy things don’t fail from fatigue.

The BR-R650s brake well despite this flex. Flex in the arms shouldn’t reduce force, merely increase lever travel.

[Roadster]

It's a wonder Tektro DPs work at all, and yet they do!

[Mick F]

Hi guys, and good morning.
More info:
Bear with me.

Over 2,000miles ago, I sold the Tiagra STIs and bought Tektro levers matched to the callipers, and that improved the feel and braking efficiency.

I removed the Tektro pads nearly 1,000miles ago and fitted new Campag Record ones. (I have spares)
This transformed the braking from "only ok" to "quite good". On new rims now, and the brake efficiency seems the same.

I first stated looking at this issue when I realised that the rear brake wasn't very good. I re-routed the cable, and that improved it quite a bit. What gets to me, is that if I really pull hard on the rear brake lever, the rear wheel doesn't lock up ever.

The front brake is very good ........... but front braking is always very good on bikes despite the callipers or pads or cable compared to the same on the rear.

It is normal for the longer run to the rear brake to have more stretch, but when I squeeze either lever, the callipers flex alarmingly, and that is the issue IMHO with the braking system. No matter how hard you pull, much of the effort is lost in calliper flex.

It's not the drop to the pads that flexes ........... though it does a bit ............ it's the arms, especially the long one clamped to the brake inner, that flexes alarmingly. I'm waiting for the alu forging to fatigue and snap.

What do folk recommend?
Must be silver.
I'll measure up the actual drops later.

-------------------------

PS:
55mm front and rear.

[deliquium]

I noticed for the first time yesterday that I can get the rear wheel to lock up on my TSR with DP calipers - after a change of colour re-cabling. Maybe brown cables are magical

Using Tektro R539 (silver natch) 47-57mm drop calipers, Clarke Elite pads and BLB brake levers. The latter were determined by 23.8mm North Road handlebars and although 'interupter' levers they're remarkably ergonomic and do the biz as stand alone units.

[Brucey]

the arms may well see enough stress that they flex alarmingly. Will they fatigue? Maybe, eventually.... but you need to do an awful lot of braking before the number of cycles is large number. One presumes that the brake manufacturers test their products and ensure that they have an adequate life...

If the arms bending is most of what you want to reduce, changing brakes isn't going to achieve much, unless the new brake arms are built differently or much thicker and/or heavier; the reason for this is that whilst the strength of different aluminium alloys varies appreciably, the stiffness doesn't.

BTW if the front brake has adequate power and modulation but the (otherwise similar e.g. in reach etc) rear brake doesn't, there is really only one culprit; the cables. IIRC the rear brake cable run on a Moulton TSR is pretty dismal; it has several extra bends and joints in it that it needn't have had, and they are scientifically arranged so that the rearmost length of cable housing can fill with water.... so an easy test is to replace the rear brake cable run with

a) a better quality cable and/or
b) a simpler full housing run with fewer bends

and see if that makes much difference. I think it should do because Bowden cables are known to become incredibly inefficient once they have lots of bends in them; you could easily be losing over half your effort to friction in the cables on a bad cable run.

cheers

[Mick F]

I noticed for the first time yesterday that I can get the rear wheel to lock up on my TSR with DP calipers

Are you saying that before you fitted new cables and pads, you couldn't lock the rear wheel?

I was thinking earlier, that if I discount the flexing of the callipers and the stretch of the cables, what I actually need is more friction per brake lever movement. Campag Record pads are wonderful, but maybe there's something even more grippy?

Meanwhile, I have a spare 2006 Campag Chorus rear brake, and from what I can see, it could fit the rear on the Moulton.
This brake calliper is rigid. Very rigid and full Campag quality.
I may try it out .......... if it fits.

[pwa]

Hi guys, and good morning.
More info:
Bear with me.

Over 2,000miles ago, I sold the Tiagra STIs and bought Tektro levers matched to the callipers, and that improved the feel and braking efficiency.

I removed the Tektro pads nearly 1,000miles ago and fitted new Campag Record ones. (I have spares)
This transformed the braking from "only ok" to "quite good". On new rims now, and the brake efficiency seems the same.

I first stated looking at this issue when I realised that the rear brake wasn't very good. I re-routed the cable, and that improved it quite a bit. What gets to me, is that if I really pull hard on the rear brake lever, the rear wheel doesn't lock up ever.

The front brake is very good ........... but front braking is always very good on bikes despite the callipers or pads or cable compared to the same on the rear.

It is normal for the longer run to the rear brake to have more stretch, but when I squeeze either lever, the callipers flex alarmingly, and that is the issue IMHO with the braking system. No matter how hard you pull, much of the effort is lost in calliper flex.

It's not the drop to the pads that flexes ........... though it does a bit ............ it's the arms, especially the long one clamped to the brake inner, that flexes alarmingly. I'm waiting for the alu forging to fatigue and snap.

What do folk recommend?
Must be silver.
I'll measure up the actual drops later.

-------------------------

PS:
55mm front and rear.

It's got to be the best Shimano you can get, which I assume is BR650.

Slightly weak rear brake is not such a big problem in practice because, as you know, it is easy to lose grip with the rear wheel on a descent if you brake hard, and that does not help you stop. Also, new rims give poorer braking, so you may be about to see some improvement there anyway.

[steady eddy]

What about the Tektro Quartz r737 long drop brakes I have these on my new Pilgrim audax bike - they look good - are robust and stop well.