Disc brake performance

dinyull

meanredspider wrote:

Dinyull wrote:

Considering the rears don't get used too heavily I'm shocked at how badly glazed they were,

They get glazed BECAUSE they are not used heavily. Disc brakes benefit from heavy use and I suspect many of the poor braking issues we see on here are because people drag brakes or simply don't bed them in properly to begin with.

Something I didn't know.

Are there a certain type of pads that are less prone to glazing? Seems like a bit of a design fault that you have to use heavy braking to avoid them glazing, especially commuting where scrubbing off a little bit of speed here and there is fairly common.

pinno

Late to this one and it may have been covered:

Are the pads contaminated? GT85 will penetrate the pad for example. Even some Diesel off the road could do the same.
There's no cure for that if they are. Bin them.

meanredspider

Dinyull wrote:

meanredspider wrote:

Dinyull wrote:

Considering the rears don't get used too heavily I'm shocked at how badly glazed they were,

They get glazed BECAUSE they are not used heavily. Disc brakes benefit from heavy use and I suspect many of the poor braking issues we see on here are because people drag brakes or simply don't bed them in properly to begin with.

Something I didn't know.

Are there a certain type of pads that are less prone to glazing? Seems like a bit of a design fault that you have to use heavy braking to avoid them glazing, especially commuting where scrubbing off a little bit of speed here and there is fairly common.

I think organic pads are the best all-round pad. There's a lot of hype around semi-metallic etc The faster a pad wears, the less prone to glazing it is and the less prone to contamination. Equally, you wear the pad not the disc. When I tried to buy some semi-metallics in Bourg d'Oisons (sp?) nowhere sold them because the local MTBers want to wear their pads not their discs.

The thing is I almost never use my rear brake. For starters, weight transfer means it is of limited capability anyway - especially on a road bike which is ultra-stiff (compared to an MTB) and where the weight is forward anyway. In using just my front brake, it gets a proper work-out which keeps it in good order. Applied progressively, the front tyre is loaded up progressively and can carry a huge amount of braking force. On the Volagi, I still run a BB7 rear (HyRd front - which will, again, cause our OCD friends much angst) because it doesn't get much use and it doesn't need to be very good when it is called on.

BTW - you'd soon glaze the brakes on your road car if you just dragged them.

meanredspider

Another point worth making about cable disc brakes is to focus on really good quality compressionless cable systems. By contrast to rim brakes that are full of flex throughout the entire system, disc brakes benefit from being ultra stiff. A lesson I learned when I converted my original Boardman CX from SRAM Apex to Shimano 105 (apart from a much sweeter gear change) was that the Shimano levers are much stiffer and really improved the braking. Flex in the system is akin to a spongy brake pedal on your car - it inspires very little confidence. Fit the best cables/outers that you can. The Volagi benefits from an internal cable run down the fork which seems to help stiffness in the system. I'm sure this is one of the reasons why hydraulic brakes feel better.

cycleclinic

I find my rear brake very effective but that maybe due to the heavy panniers. In fact on my MTB's the rear brake is very effective. There should be about a 30:70 weight distribution. So the rear should be effective.

Grippy tyres make disc brakes far more useful as you can use all the braking force that can be applied.

The overbraked comment acouple of pages ago makes me laugh. only with bike do people want inferior brakes. Imagine going to buy a car and speccing quite deliberatley drum brakes or tiny discs on a BMW M3 for example because as you tell the sales man that all I need I am over braked otherwise.

I do wonder where all the bicycle faulty logic comes from. The same people regain sanity when buying a car.

Jagwire compressionless casing is what use as like MSR I have full length outers for the front and rear brake. Without special casings the brakes would be spongy. They are firm instead.

dinyull

Yeah, I'm using 105 shifters with Jagwire compression-less outers.

Still, even at the best I've experienced in the dry, rim brakes pi$$ all over them. But not so much in the wet, which is why I use them.

Would love to give hydro a go, but there is no way I'm shelling out what they cost at the minute.

cycleclinic

that the thing my spyres stop me as well as my rim brakes. Rim brake lock my wheel up and want to throw me over the bars. My disc brake dont lock wheels and dont throw me over the bars. I stop just as quickly in the dry though.

This is what people get confused by. They confuse the feeling of the bike riding up with good braking. good braking is where your wheels dont lock and you just stop.

Faulty logic again. One of the issues disc brake have on road bikes is the lever. It is long and fixed. On an MTB I can move my lever out or in to adjust for reach and this also prevents the lever coming any where near to the bars. This improves feel. So part of the issue is road lever design and not being able to put enough force on the lever when on the hoods. I get onto the drops on a decent so I grab the levers more forcefully if I have too.

veronese68

Dinyull wrote:

Would love to give hydro a go, but there is no way I'm shelling out what they cost at the minute.

I get that. I have an ex-demo Parabox converter I bought. I reckon that or the Hope Vtwin are the best of the hybrid types as there is only a very short cable run and then hydraulic from stem to brake. Unfortunately they look a bit weird and they didn't catch on at all, hence the HyRd type options. After initial faffing due to buying a used set up that had been removed by a poorly trained chimp using mole grips they have been good as gold.
My next everyday bike will have full hydraulics, but at the moment there is no reason to change what I have.

meanredspider

thecycleclinic wrote:

I find my rear brake very effective but that maybe due to the heavy panniers. In fact on my MTB's the rear brake is very effective. There should be about a 30:70 weight distribution. So the rear should be effective.

Yeah - it's really the dynamic loading that matters under braking. The instant the the brakes are applied, a moment is generated that transfers weight to the front (even if the rear brake only is applied but far more so if the front is applied) - this loads up the front tyre. It can most clearly be experience on an MTB - brake hard and the forks compress. This actually helps maintain load on the rear MTB tyre. On a road bike, there's no such compression so the weight transfer is greater and more instantaneous. You can use this to your advantage by progressively braking and building load on the front tyre which gives it even more grip. It's only where the surface can't sustain heavy braking loads (wet road, gravel, mud) that braking is better distributed across the tyres. Hence MTBs and gravel bikes having big rear discs. Motorcyclists know that the front brakes are what do the work and performance bikes have pairs of huge discs at the front and piddling little discs at the rear. Same with my race car - huge 6-pot calipers at the front and tiny rear brakes. In the wet, I wind the braking bias to the rear because the fronts can't sustain the same load so the rears can do more work without locking.

The weight transfer is also why I don't think disc brakes are as useful for lighter riders. The weight transfer is a lot less and braking altogether less critical.

cycleclinic

I ride rigid MTB's though. I dont bother with that silly suspension nonsence. Also If I brake hard I push my self back just like you do when going downhill. easier to do on an MTB though.

Also my tendancy to decend on the drop may also keep more weight on the rear and keep the back brake useful. On the hoods you put more weight on the front.

Weight transfer though is quite real. Long rear stays probably help also. short stays and short wheel bases probably suffer more from weight transfer.

So it is not disc brakes that are the problem but bike design. As always though people blame the tech.

apreading

Dont shift too much weight to the rear on descents though. I realised a while ago that one of the reasons I got scared going fast on descents was because I was moving too far back, behind the saddle, to counteract for the downhill but the front end felt sketchy because I had little or no weight on it...! I now make sure to press down a little on the front to avoid this and feel much happier.

kajjal

apreading wrote:

Dont shift too much weight to the rear on descents though. I realised a while ago that one of the reasons I got scared going fast on descents was because I was moving too far back, behind the saddle, to counteract for the downhill but the front end felt sketchy because I had little or no weight on it...! I now make sure to press down a little on the front to avoid this and feel much happier.

I did that when I hit 50mph downhill on road by accident. It really unweighted the front wheel.

kingstonian

I really like disc brakes - have them on both my best bike and my commuter.

On the commuter (CAADX with Shimano hydro brakes) I'm finding that both the front and occasionally the rear brakes drag. The discs are properly aligned to the pads, so I'm wondering if for some reason the pistons aren't fully retracting after the brake lever is released. Whatever the reason, it is bloody annoying, especially as I've never had that problem on my best bike.

cycleclinic

I have never had weight distribution problems probably because I ride off road. you learn very quickly how to balance the bike and use your weight to keep control of the thing.

the rotor might be bent kingstonian. Even new rotors can be bent.

kajjal

There may also be too much fluid in the brakes stopping the pads fully retracting. If you undo the bleed port on the shifter, gently and slowly push the pads back and then while still holding the pads back tighten the bleed port back up. You will need a tissue to catch any fluid as it escapes. I had this on my diverges rear brake.

First.Aspect

Kajjal wrote:

There may also be too much fluid in the brakes stopping the pads fully retracting. If you undo the bleed port on the shifter, gently and slowly push the pads back and then while still holding the pads back tighten the bleed port back up. You will need a tissue to catch any fluid as it escapes. I had this on my diverges rear brake.

That's one I've not come across before. How could that happen? Bleeding the brakes with the slave cylinders fully deployed?

apreading

Its something that seemed to affect Avid's back in the day - mainly Elixirs. Seems that if you bleed them when cool, then it gets really hot, the fluid expands and can bind the brakes on. You dont even need to do as much as Kajjal says - with the wheels still on the bike, just loosen the screw in the bleed port of the lever, squeeze the lever just enough to let out a tiny dribble, hold the lever and tighten the screw (so that it doesnt suck air back in). Job done. Just be careful not to let too much out - better to err on the side of too little and need to repeat the process than let to much out and have to bleed properly again.

viewtopic.php?t=13065569

pilot_pete

thecycleclinic wrote:

One of the issues disc brake have on road bikes is the lever. It is long and fixed. On an MTB I can move my lever out or in to adjust for reach and this also prevents the lever coming any where near to the bars. This improves feel. So part of the issue is road lever design and not being able to put enough force on the lever when on the hoods. I get onto the drops on a decent so I grab the levers more forcefully if I have too.

It does depend on which levers/ system you have on your road bike though. I have Shimano RS785 levers which have reach and free stroke adjustment. This allows me to set them up so both front and rear feel the same and have the same amount of 'lever pull' to operate. It also means that I can adjust the lever further or closer to the bars as the 'starting point' to allow for hand size/ finger length.

I have found them to be absolutely superb in every way. They simply are vastly superior to any rim brake that I have used, especially in the wet. What I really like is that I can brake from the hoods, using one finger only and get plenty of force to brake really hard, something I couldn't do with rim brakes. The feel is superb both wet and dry. Maintenance is a doddle and changing the fluid every-so-often is all I have had to do with the levers. The calipers require a bit more as pads wear quite quickly, but as has been said before wearing out pads more quickly is better than rotors.

These levers were in effect a development leading to the new Dura Ace hydraulic di2 lever design. Shimano did not consider them worthy of the Dura Ace name (I suspect because they are a little chunky and needed further refinement), so I can only surmise how good the new DA levers are, although even I baulk at the price of them...

So I think it is important to compare apples with apples. In my experience my Shimano hydraulic discs are significantly better than the cable pull Avid BB5s that my winter bike came with, which are fiddly to set up but work satisfactorily if maintained properly, and they were a step up in wet weather braking over my previous Campagnolo Record rim brakes, which were perfectly adequate in the dry on allow rims, but lost a disproportionate amount of braking ability in the wet. The comparison could keep going down to cheap, unbranded cantilever brakes on my kids cheap knock about mountain bike from Halfords, which were truly useless!

My point is there are differing performance levels of product in the rim braked world just as there is in the disc braked world. Compare similar performance level components in each to make a proper comparison of the differing characteristics.

For me, the benefits of carbon rims coupled to hydraulic disc brakes with all those lever adjustments and differing characteristics of feel and modulation in both wet and dry conditions mean that they tick the most boxes on my braking wish list.

meanredspider

@PP ^^^

For what reason have you been changing the brake fluid? I'm always surprised when I see people talk of changing fluid or bleeding brakes. Unless something has gone wrong, there should be hardly any need to do this on a bike.

Agree, though. The better Shimano hydro brakes are utterly brilliant.

fat daddy

ARRRRGH ... right I have reached breaking point. and my honking effing brakes.

sanded the disks, replaced the pads .... 1 journey 3.1 miles, back to the honking noise and smears of black crap over the disc ???

The lever also feels slightly spongy with a long throw ..... I am thinking these things are leaking ... when I changed the pad there was a wet spot on the back of the pads.

So decision time

(1) convert bike to rim brakes ... need, brake levers, calipers, new forks, new wheels and welding on the rear triangle
(2) convert the bike to drops and buy mech disc brakes
(3) buy a new set of brakes, rotors, pads, levers, calipers
(4) throw the bike through a Halfords shop window (I didn't buy it from there but that would make the rant epic)

meanredspider

What model of brakes are they? Is it flat bar? Definitely sounds like something is wrong.

fat daddy

yeah flat bar

Shimano BR-M447 Hydraulic Disc - 160mm

might swap for sram db3's ??? .... or something else

pilot_pete

Hi Fat Daddy

Sounds like a simple leak to me...which contaminates your pads and prevents them from working. Could be caliper, brake line/ banjo joint, caliper seals etc etc. Just clean it all up, bleed it and then check/ inspect closely to find out where the leak is. It may be a single component needs replacement (as Shimano tend to be throw away rather than repair if it is a caliper) and obviously a new set of pads if those fitted have been contaminated. Probably a fairly simple fix which will restore your brakes to top performance. It may be frustrating, but chucking everything away and starting again with another brand seems a little extreme to me...

PP

pilot_pete

meanredspider wrote:

@PP ^^^

For what reason have you been changing the brake fluid? I'm always surprised when I see people talk of changing fluid or bleeding brakes. Unless something has gone wrong, there should be hardly any need to do this on a bike.

Agree, though. The better Shimano hydro brakes are utterly brilliant.

Shimano recommend changing the fluid when it becomes 'significantly discoloured in the reservoir'. Being a road bike I can't see the reservoir, so I replaced it after 18months and there was some discolouration in what came out. Nothing significant and I am sure it could have stayed in situ longer with no adverse effects, but for the minimal cost on such an expensive bike I was happy to change it.

PP

meanredspider

Pilot Pete wrote:

meanredspider wrote:

@PP ^^^

For what reason have you been changing the brake fluid? I'm always surprised when I see people talk of changing fluid or bleeding brakes. Unless something has gone wrong, there should be hardly any need to do this on a bike.

Agree, though. The better Shimano hydro brakes are utterly brilliant.

Shimano recommend changing the fluid when it becomes 'significantly discoloured in the reservoir'. Being a road bike I can't see the reservoir, so I replaced it after 18months and there was some discolouration in what came out. Nothing significant and I am sure it could have stayed in situ longer with no adverse effects, but for the minimal cost on such an expensive bike I was happy to change it.

PP

Makes sense. I've never bothered on my MTB though the brake systems are significantly cheaper on those. I'm just not sure what mechanism there is for the fluid to deteriorate unless you're doing lots of alpine descents regularly. Even then, mineral oil should cope for a long time. I'm definitely in the camp that believes there is such a thing as over-maintaining (or "If it ain't broke...")

pilot_pete

I can see where you are coming from.

I have read a Shimano tech's comments saying that it should be changed when it discolours (which is in the Shimano dealer manual) and he commented that this is about once a year for someone who rides one bike year round. He was referring to a MTB I think, but I thought I'd check after 18 months.

The thing is changing the fluid is just bleeding the system, not taking anything apart, so nothing to really suffer from disassembly/ re-assembly.

I do enjoy very fast descending, so would rather err on the side of caution when it comes to brakes. This is also the reason why I change pads before they reach the wear limit. Twenty odd quid is a small price to pay for piece of mind to me...

PP

meanredspider

Nothing wrong with that. I change the brake fluid in my race car after pretty much every race (no point after Thruxton as you only use the brakes once a lap in reality). It's only because bleeding bike brakes can be fiddlier and messier and, whilst I really enjoy last of the late brakers, I don't think I generate so much heat on UK rides to warrant worrying about fluid breakdown or boiling. If I were planning to do the AD6 malarkey again and hammer my brakes for a day, I'd definitely freshen the oil up before and after.

pinno

Yeah - option 4 FD - through the window of Halfrauds. Pics please.

kajjal

First Aspect wrote:

Kajjal wrote:

There may also be too much fluid in the brakes stopping the pads fully retracting. If you undo the bleed port on the shifter, gently and slowly push the pads back and then while still holding the pads back tighten the bleed port back up. You will need a tissue to catch any fluid as it escapes. I had this on my diverges rear brake.

That's one I've not come across before. How could that happen? Bleeding the brakes with the slave cylinders fully deployed?

I have seen it twice now on new bikes but only on one wheel each time. I am guessing they must have an incorrect sized bleed block or are just not paying attention. It took me a while to work out why it was so hard to align the calliper properly and once sorted it was easy enough.

vrsmatt

ugo.santalucia wrote:

apreading wrote:

That said, when I had a 2004 Stumpjumper with V brakes it was much much lighter than the equivalent with discs that came out the following year and I never felt short of brakes

New to this topic and clearly the OP has an issue with disc/pad contamination, judging by the fact he thinks its ok to clean the pads with baby wipes leads me to think a competent mechanic/owner would sort it in no time with new pads and proper disc cleaner followed by a proper bedding in.

However the comment above about never feeling under-braked on your v-braked mtb means that frankly you ride like a 5 year old girl, and/or exclusively in the dry.

i have MTB'd for over 25 years and ridden road bikes for 15 years, it is 100% fact that even budget properly maintained discs are better than rim brakes in the wet and back in the day in the 90's when I was riding rigid high end mtbs I reckon we ran out of braking power at least a few times per ride, or ALL RIDE LONG if it was wet, even when XTR V-Brakes came along, they were much better than canti's, but still cack in the wet, you cant argue with physics.