Road Shifters and Mech Disc Brake

[Jupestar]

I’m sure this has been asked / debated before. But searching has not found anything obvious.

I’ve a groupset of 2012 SRAM Red 10s Mech. Thought I would try and run mechanical discs off the shifters. Road calipers (TRP Spyre). They are ok, but really just about ok. Not in the same league as the original SRAM Red rim calipers, and nothing compared to my TRP Hylex SS.

The set up seems fine, in that the calipers starts to move as soon as the brake is touched and they release clean.

But they just don’t grab tight. The levers are short pull, but I thought they would work with TRP spyre Road mech discs.

Is there likely a compatibility issue? Or do I need to just try and improve the set up further?

[mattsccm]

The calipers are often seen as good as they get as far as cable go. Some of us prefer Avid BB7's in the raod spec which of course are SRAM by another name. Maybe they match ?
I bet it's set up assuming the pads are borken in etc. Possibly they are a touch too tightly set and the lever isn't at its optimum pull position.
Hard to tell (by me anyway) without playing a bit.

[Eyebrox]

Are both pads adjusted (via hex key) so that each is 0.5 mm away from the rotor? Are the sprung arms fully released (ie no pre-load)? Are cables compressionless and running with no sharp bends? Are you using organic or sintered pads? You don't need much lever pull to get the Spyres to lock the wheel. SRAM should be fine. I go through a lot of organic pads but I have the pistons pushing the pads fiercely against the discs. They wear quickly but the bike stops abruptly with minimal pressure on the levers. My front brake always worked well but the rear only came up to scratch when I straightened the cable run and removed the gaps between pads and rotor.

[NickJP]

Paul Klampers calipers come in a choice of length arms to suit levers with different amounts of cable pull. They're pretty expensive, though.

[Jupestar]

Thanks for the response, Seems a set up problem rather than a compatibility issue.

I set it up as follows.

1) compressionless outers (full length)
2) left the caliper fairly loose and tightened each pad bit by bit till it grabbed the disc centered.
3) tightened caliper to frame.
4) backed off each pad slightly to allow wheel to spin freely.
5) pulled cable through tightly and set in bolt. (No pre load). I’m not concerned I need pre-load Movement and release of the arm looks good.

They came off an old bike, with the same discs… And they worked fine before but different shifters. Shimano tiagra I think. I’ve taken them apart and serviced them.

Guess next up is to try new pads…

Previously they were run with only part outers, than might make a difference.

[mcshroom]

They don't tend to tell us exactly, but we've discussed on here before that the TRP brakes might be optimised to the Shimano NSSLR brake pull, which pulls a bit more cable than SRAM levers.

Hopefully you can adjust out the difference, especially if you can remove any lost compression in the system. Otherwise, it might be that Avid BB7 Roads would match better with your levers.

[Jupestar]

They don't tend to tell us exactly, but we've discussed on here before that the TRP brakes might be optimised to the Shimano NSSLR brake pull, which pulls a bit more cable than SRAM levers.

This is the sort of thing I was worried about,
If the 2012 version and quite enough cable pull.

In terms of tight bends in the housing I actually have them under the handle bar tape in normal brake housing. Then switching to compressionless just after the bar tape via a inline cable adjuster. Possibly the bend it to tight here, or I should try compressionless. But feels like would achieve a marginal gain. As currently the lever starts pulling the brake arm immediately.

I’ll have a play around, new pads, on the shortest cable run I can do to test. After that I’m done. Mech disc on my MTB are great,I was hoping for something similar.

The TRP hylex on the commuter are also great. Fitted them straight out the box about 4 years ago and never touched them. New pads once. Simple swap job done. That’s does so many miles!

I’m sure the Spyres are also great, in fact I know them are as these came off my mate Cube which had great stopping power…. (Till he crashed it). Just maybe not 100% compatable to the shifters.

[iandriver]

Did you use compressionless brake outer? I find it makes a big difference myself to the overall feel.

[Jupestar]

Did you use compressionless brake outer? I find it makes a big difference myself to the overall feel.

After the bar tape: yes. Around the bars: No.

[biketips666]

They don't tend to tell us exactly, but we've discussed on here before that the TRP brakes might be optimised to the Shimano NSSLR brake pull, which pulls a bit more cable than SRAM levers.

Hopefully you can adjust out the difference, especially if you can remove any lost compression in the system. Otherwise, it might be that Avid BB7 Roads would match better with your levers.

The levers-to-disc-callipers subject has been discussed quite a bit. It would be nice if there were just two cable pulls - mountain and road. It turns out not. There's three - mountain, new road, old road. Except that even that doesn't seem to be true. It's not as though there's some central body laying down specifications for all this. Some kind soul in another forum tried to gather all the information together:

https://www.bikeforums.net/bicycle-mech ... atios.html

See what I mean? Not exactly consistent is it?

Though it does confirm my experience. With BB7s and Sora R3000 (NSSLR) levers the braking was underwhelming. When I changed the levers to Ultegra 6510s it improved dramatically.

When I still had the Sora STIs on, I fitted a pair, well just one, R317 calliper. I mean, they're part of the same groupset, they should work perfectly together, yes? No. They were appalling. I daresay I could have spent time fiddling, but they were so awkward to set up (compared to the BB7s) and so horribly cheaply made, I just wanted out. PM me if you want to make me an offer, rear completely unused, front less than 5 miles. There are more expensive Shimano cable disc callipers, they might not be as nasty. Though I don't suppose Shimano are committed to cable road discs.

Yes, as mentioned above, TRP Spyres are reckoned to be a match for modern Shimano levers. Except that TRP are a bit coy about saying that explicitly.

I realise that doesn't really help you, except to reiterate the point that lever to caliper matching is fraught. I daresay careful adjustment and careful installation of compressionless cable might help, a little or a lot. But it still seems to me that if the mechanical advantages aren't compatible, anything you try to compensate is a bit of a silk purse-sow's ear scenario.

[biketips666]

Paul Klampers calipers come in a choice of length arms to suit levers with different amounts of cable pull. They're pretty expensive, though.

I considered Klampers and in fact they would have been cheaper than what I did. Which was buy a pair of ST-6510s, to match the BB7s. Then, given that ST-6510s are old, I thought I should buy backups. Which I did, including a pair of NOS ones (you can imagine what they cost!).

The Klampers also seem to be made of out unobtanium. I rang Paul (the factory) and they acknowledged production was a problem, but they're in the process of building bigger manufacturing facilities. What they did say was that the "short pull" option for the Klampers is meant for "current Shimano or SRAM, that kind of stuff".

There's now a considerable gap between EU prices and GB prices. And yes, I mean GB - one site, Bike24, actually lists Northern Ireland as a destination, but not the UK (or England, Scotland, Wales). At current price differences, it's probably almost cheaper to have a weekend break in The Netherlands and bring a pair across.

[Jupestar]

anything you try to compensate is a bit of a silk purse-sow's ear scenario.

This is exactly what i'm concerned about engineered to a mm precison then something goes wrong on the road.

I stuck clean pads in, and jigged up a 400mm straight compressionless cable run to the shifters, i couldn't ride it but a couldn't see much of an improvement on the stand - i could pull the wheel through by hand with the lever pulled right down. It rideable but i wouldn't want to be coming down a mountain on them.

Either the shifter/caliper combo is incompatable, or the set up is too finicky its not worth it.

Thanks for the input, Need to consider my options,

1) Try a different caliper - AVID BB7.
2) New frame and wheelset (for Rim). To enjoy the full groupset.
3) Swap the brifters, for TRP Hylex and Bar end.
4) Sell the Red Groupset, its totally unnessescary for me, but it does feel really nice.

Ironlically it will probably be 2) eventually. This groupset has fallen in my lap, it rides nice (even with no proper brakes) and i really fancy using it all.

[biketips666]

I stuck clean pads in, and jigged up a 400mm straight compressionless cable run to the shifters, i couldn't ride it but a couldn't see much of an improvement on the stand - i could pull the wheel through by hand with the lever pulled right down.

That's doesn't sound right. Even if you're an olympic powerlifter you shouldn't be able to shift the wheel with the brake applied hard, on a stand. The force you're applying with your arm surely can't be anything like as much as the force of bike, rider and luggage (?) going down a steep hill at 30 mph. Though physics isn't my strong point, so feel free to correct.

In fact it's one of the frequently quoted errors isn't it, to mistake braking performance on a bike stand with "real world" brake performance?

It rideable but i wouldn't want to be coming down a mountain on them.

I wouldn't ride to the end of the drive on a bike like that.

Either the shifter/caliper combo is incompatable, or the set up is too finicky its not worth it.

Thanks for the input, Need to consider my options,

1) Try a different caliper - AVID BB7.
2) New frame and wheelset (for Rim). To enjoy the full groupset.
3) Swap the brifters, for TRP Hylex and Bar end.
4) Sell the Red Groupset, its totally unnessescary for me, but it does feel really nice.

Ironlically it will probably be 2) eventually. This groupset has fallen in my lap, it rides nice (even with no proper brakes) and i really fancy using it all.

It's a pain, isn't it?

I'd maybe try 1). See if you can pick up a pair of BB7s on eBay. If they don't improve things you should be able to turn them around for not much less than you paid for them.

[Jupestar]

I'd maybe try 1). See if you can pick up a pair of BB7s on eBay. If they don't improve things you should be able to turn them around for not much less than you paid for them.

I've 'sort of' taken your advice. BB7 roads secondhand are pretty hard to come by, so i've got some BB5's Road on the cheap. I know the set up is going to be a bit finicky, but if i can get them to work then at least i know its the throw from the levers which is the problem. Doubt i'll get to fit them till Sept now, if it fails will probably chuck the whole thing in the skip and walk away.

[biketips666]

I'd maybe try 1). See if you can pick up a pair of BB7s on eBay. If they don't improve things you should be able to turn them around for not much less than you paid for them.

I've 'sort of' taken your advice. BB7 roads secondhand are pretty hard to come by, so i've got some BB5's Road on the cheap. I know the set up is going to be a bit finicky, but if i can get them to work then at least i know its the throw from the levers which is the problem. Doubt i'll get to fit them till Sept now, if it fails will probably chuck the whole thing in the skip and walk away.

I've never used BB5s, though I seem to remember that the general opinion was that BB7s were a lot better for some reason. Let me just google...

https://www.mtbr.com/threads/avid-bb5-v ... cs.759626/

...mmm.

You might not get an accurate impression of what BB7s would be like. Anyway, good luck with that, I hope you gain something useful from it. As I said, I came up with a combination I'm very happy with, but only by committing myself to 15 year old levers. Though that isn't really a problem.