Road bikes with discs

meanredspider

airbag wrote:

Where's a general purpose road bike, with carbon loveliness, near enough racing geometry, but practical nods like guard mounts, bigger tire clearance and brakes that don't eat rims or suck in poor conditions?

I bring you http://volagi.com/bikes

Or any version of the Liscio

meanredspider

Ouija wrote:

supersonic wrote:

They'll be putting suspension forks on next ;-)

Mmmmmm........
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dhope

airbag wrote:

Walk into a ferrari dealership and you can't buy a race car, you buy a racing-style car with everyday practical touches.

And most of the things on today's racing-style Ferrari came from yesterday's racing Ferrari. Disc brakes are evidently at the tipping point if the pro peloton are considering them. Then they'll filter down to high end road bikes and eventually the rest. Whether you or I will actually appreciate the benefits they give is the same as asking whether we'll drive a racing-style Ferrari at its limit or whether we'll just floor it in a straight line on the M1 occasionally and smile at the pretty noises the engine makes.

pdw

Less fettling to keep everything working at 100%: so I've been told

I've got discs on my commuter, and I'm not convinced by that one. Certainly with BB7s I've found it's a compromise between getting the pads close enough to work, and not being so close that they rub, and I find that every time I remove and replace a wheel the brakes will need a tweak to stop them rubbing. Bring on decent hydraulics...

meanredspider

pdw wrote:

Certainly with BB7s I've found it's a compromise between getting the pads close enough to work, and not being so close that they rub, and I find that every time I remove and replace a wheel the brakes will need a tweak to stop them rubbing. Bring on decent hydraulics...

There's something not quite right there...

pdw

Initialised wrote:

Haven't we missed something here, with rim brakes you can't safely brake under heavy cornering due to judder and the lateral forces deforming the wheel making braking uneven and prone to locking the rear wheel

Huh? I think you need to get your brakes looked at, but with any brakes you can't safely brake under heavy cornering because you're using the available grip to corner.

tgotb

Initialised wrote:

Haven't we missed something here, with rim brakes you can't safely brake under heavy cornering due to judder and the lateral forces deforming the wheel making braking uneven and prone to locking the rear wheel, with disc brakes the rotor doesn't deform while cornering like a rim does allowing the rider to brake through the corner rather than before the corner thus allowing higher cornering speed and the option of adjusting the line through the corner with less risk of locking the wheel. Hence MRS' confidence on descents.

I thought you couldn't brake hard on tight corners anyway, because of the risk that the tyres, already highly loaded by the cornering, will let go completely. Hence, you should break just before cornering. That said, I haven't tried it; maybe MRS can comment, as I also thought the same principle applied in cars.

To the Ferrari analogy - I should imagine a lot more people are racing bikes than cars in the UK. I also imagine that a lot of people would buy race-spec cars if they were road-legal and they could afford them, even if they had no intention of racing them. I think the real difference is that race bikes are relatively affordable, and you can ride them on the road, whereas a race-spec Ferrari is not road legal and presumably costs silly money...

pdw

meanredspider wrote:

There's something not quite right there...

Agreed - there's got to be some tiny imperfection - maybe just dirt - in the dropouts or axle that means that it doesn't seat in exactly the same place. The issue is that the pad/disc clearances are so tight that even a tiny misalignment will cause a bit of rubbing.

meanredspider

Actually it is a technique in car racing to "trail brake" or continue to brake as you corner. Part of the principle is that, by braking, you increase the load on the front tyres through weight transfer and, by doing so, increase the available grip. It's basically the same principle as the rear tyre going "light" under braking and locking easily. "lift-off oversteer", especially in fwd cars, is the same mechanism.

The principle should be the same for bikes only more pronounced because road bike frames are so stiff the weight transfer is rapid and extreme (an engineering principle being that "the stiffer the member, the greater load it carries" )

The trick, as ever, is not to exceed the load-carrying capacity of the tyre. If you're supersonic, that's easy

meanredspider

pdw wrote:

meanredspider wrote:

There's something not quite right there...

Agreed - there's got to be some tiny imperfection - maybe just dirt - in the dropouts or axle that means that it doesn't seat in exactly the same place. The issue is that the pad/disc clearances are so tight that even a tiny misalignment will cause a bit of rubbing.

Yup - I don't find I need to run the pads that tight. Is the disc true? Are they the "road" version of BB7s? Have you adjusted the arms so they are off the stops? Or is it that you just like really "immediate" levers?

asprilla

meanredspider wrote:

pdw wrote:

Certainly with BB7s I've found it's a compromise between getting the pads close enough to work, and not being so close that they rub, and I find that every time I remove and replace a wheel the brakes will need a tweak to stop them rubbing. Bring on decent hydraulics...

There's something not quite right there...

I have the same issue with mine. I've never been impressed with them.

Performance has either been on par with rim brakes or they rub.

I'd certainly never recommend anyone buy them. That's why I'm quite excited about TRP Spyres; mechanical discs with pistons on both sides.

pdw

meanredspider wrote:

Is the disc true?

True enough. They're not perfect, but when they rub they rub pretty evenly.

Are they the "road" version of BB7s?

Yep.

Have you adjusted the arms so they are off the stops?

Yep.

Or is it that you just like really "immediate" levers?

Yep.

Do you have old or new STI levers? I've got the old ones but I suspect that they'd be less fussy with the higher cable pull of the newer Shimano levers.

They're not bad brakes, but I reckon there's much better to come. I reckon roadies will be a lot more sensitive to slight disc rubbing than MTBers so I wouldn't be surprised if once we start getting dedicated road calipers (rather than just MTB ones with a different cable ratio) we'll see non-linear response to get the pads properly clear of the disc or similar.

All the other advantages of discs still stand, but I spend more time fiddling with BB7s than I do with the rim brakes on my other bikes.

supersonic

Cornering flex is very noticable in the MTB world, even with discs. Load the bike hard into corners and often the brake will start to rub and squark a bit. Does vary on the hub/build/fork/axle/skewer of course.

Non linear response though is the cornerstone of the Shimano Servowave disc brake system. The set up starts with large pad clearance and fast engagement, followed by a gradual ramp up of leverage. Does work well, but I find the initial part of the travel can feel a bit notchy.

Servowave levers can be got for flat bar systems too - hence you can run the levers with cable disc brakes. I use Avid Speed Dial 7 which have adjustable leverage and lever reach, combined with all the angle set up combos of the pads and cantis.

Initialised

TGOTB wrote:

Initialised wrote:

Haven't we missed something here, with rim brakes you can't safely brake under heavy cornering due to judder and the lateral forces deforming the wheel making braking uneven and prone to locking the rear wheel, with disc brakes the rotor doesn't deform while cornering like a rim does allowing the rider to brake through the corner rather than before the corner thus allowing higher cornering speed and the option of adjusting the line through the corner with less risk of locking the wheel. Hence MRS' confidence on descents.

I thought you couldn't brake hard on tight corners anyway, because of the risk that the tyres, already highly loaded by the cornering, will let go completely. Hence, you should break just before cornering. That said, I haven't tried it; maybe MRS can comment, as I also thought the same principle applied in cars.

You can't brake hard enough to lock the wheel, but with discs the rotor isn't laterally loaded (deformation of the wheel) so you can brake harder, later and with more control than you can with rim brakes. In a car the centrifugal force acting on the vehicle is typically around 90 degrees to the wheel as cars don't bank for corners, deformation happens in the tyres not the wheel on a two wheeler some of the centrifugal force is acting on the tyre increasing grip as the banking angle increases toward 45 degrees by pushing the tyre into the road meaning that braking through the turn is feasible.

supersonic

You can't brake hard enough to lock the wheel, but with discs the rotor isn't laterally loaded (deformation of the wheel) so you can brake harder, later and with more control than you can with rim brakes

Can you expand on this? Not sure what you mean by "can't brake hard enough to lock the wheel" and why any deformation results in less control (or even where this deformation is!).

EKE_38BPM

Maybe my google-fu is weak or maybe what I want doesn't exist, but does anyone know where I can get a 700c 1" steel disc fork?

meanredspider

pdw wrote:

Or is it that you just like really "immediate" levers?

Yep.

Do you have old or new STI levers? I've got the old ones but I suspect that they'd be less fussy with the higher cable pull of the newer Shimano levers.

They're not bad brakes, but I reckon there's much better to come. I reckon roadies will be a lot more sensitive to slight disc rubbing than MTBers so I wouldn't be surprised if once we start getting dedicated road calipers (rather than just MTB ones with a different cable ratio) we'll see non-linear response to get the pads properly clear of the disc or similar.

I suspect the answer I've quoted is the cause of your woes. I'm happy with a bit of initial travel - especially as I ride mostly on the hoods. I use Ultegra Di2 brifters and Gore Ride-On Pro cable on the front.

Yes - I think there will be much better to come. At the moment it's a compromise - deflecting the disc. Personally, I'm looking forward to the HY-RD calipers. My bike has internal brake cable routing so I don't think hydraulics will be very neat

tgotb

EKE_38BPM wrote:

Maybe my google-fu is weak or maybe what I want doesn't exist, but does anyone know where I can get a 700c 1" steel disc fork?

Can you get a beefy fork and then get a framebuilder to braze on the disc attachment?

Initialised

supersonic wrote:

You can't brake hard enough to lock the wheel, but with discs the rotor isn't laterally loaded (deformation of the wheel) so you can brake harder, later and with more control than you can with rim brakes

Can you expand on this? Not sure what you mean by "can't brake hard enough to lock the wheel" and why any deformation results in less control (or even where this deformation is!).

Brake hard enough to to lock up and you'll skid and go over, with discs you can get closer to the limit with more control. Deformation of the wheel turns it from rectangle to parallelogram and makes rim brakes un evenly load one side compared to the other making braking at the limit while cornering unpredictable.

supersonic

Ah I see what you mean. But not a problem I have had with my brakes, I have the modulation and control. In fact more than on some disc brakes, which can be too grabby, robbing you of fine control.

Fat-Boy-Roubaix

I have always thought my brakes are shite in the wet, and then when an emergency crops up in the wet I am reminded that they are still able to lock everything up pretty rapidly when you throw them on using the "I must stop to survive" technique

meanredspider

supersonic wrote:

Ah I see what you mean. But not a problem I have had with my brakes, I have the modulation and control. In fact more than on some disc brakes, which can be too grabby, robbing you of fine control.

I'd love to know what system of rim brakes and what system of road discs you use - what you report is the complete reverse of my experience (and generally that which I read related to the comparison of brake types too). I'm not sure it makes engineering sense either. But I'm sure it's right so what's the secret?

meanredspider

Fat-Boy-Roubaix wrote:

I have always thought my brakes are shite in the wet, and then when an emergency crops up in the wet I am reminded that they are still able to lock everything up pretty rapidly when you throw them on using the "I must stop to survive" technique

The first car crash I ever had was in the wet. A lorry stopped suddenly in front of me with no brake lights. I hit the brakes and not a lot happened. Eventually, with my foot through the floor and the wheel up under my nose, the brakes locked. I skidded into the back of the truck. To cut a long story short, I had been sold completely the wrong brake pads for the car by the dealer.

The purpose of this story is to try to get across a point I've made over-and-over: locking brakes is a terrible measure of brake effectiveness. A locked brake is useless and the same result can be achieved by a stick in the spokes. Powerful, progressive and predictable - you need all three.

jds_1981

meanredspider wrote:

I'd love to know what system of rim brakes and what system of road discs you use - what you report is the complete reverse of my experience (and generally that which I read related to the comparison of brake types too). I'm not sure it makes engineering sense either. But I'm sure it's right so what's the secret?

I'm fully with you http://xkcd.com/8/
I can accept that a well maintained road bike with good road bike brakes will provide acceptable performance, especially in the dry.
In my experience though, I've found neither of my road bikes braking to be particularly satisfactory in the wet, especially if I hadn't cleaned both the rims and brakes for a week or so (something which is quite common in winter.)
There's the initial few rotations while the rim clears, and then not much bite.
My mtb disk brake just worked when I used it for a winter. Didn't have to clean it or change the pads once.
Also the squeezing force required is very different. From the hoods I managed to tweak something in my forearm once through panicked braking in the rain as I had to squeeze so hard. My mtb just needs one or two fingers.

These are my mtb brakes http://www.chainreactioncycles.com/Mode ... elID=22185 . £30 each.
You can get some 105s for £35 http://www.wiggle.co.uk/shimano-105-570 ... e-caliper/

I just have a very different experience to several in this thread. http://www.youtube.com/watch?v=ZLXZ5wgX8iI

supersonic

I think that the comment of 'locking the brakes' has been misinterpreted. I mentioned it previously in regards to the fact that, should I want to lock the brakes, I can, and that in wet conditions, locking happens with less effort. And also mentioned I can do this with control, and up to the point of locking. I am certainly not saying that locking brakes is a prerequisite of a good system; to me it is all about control. Saying that, if the brakes lack power to lock the wheels then I doubt you can get to the point of maxiumum decelleration, or be able to control it.

As for brakes used, I have used dozens of systems, if not owned quite as many ;-). With rim brakes, as with discs, leverage and feel does vary, but the key to me is well maintained rim surface and good pads. On my flat bar road bike I am using Avid Speed Dial 7 levers with Avid Arch Rival calipers and Kool Stop Eagle Claw 2 pads. I have had no problem wit many drop bar rim brake systems either, but as above, careful pad choice, rim care (and set up is key). Tektro systems have I have been rather fond of, a good budget option.

Bad brakes are bad brakes regardless. Many cable disc brakes are absolutely dire (as many rim brakes are), the BB5 and BB7 being the better ones, but still not many are used by MTBers off road. My criteria for an off road brake differs from that of an on road brake.

PS I find the majority of Shimano rim brake pads to be awful. The BB7 is the best of the cable disc brakes.

In the end it is what works for you, and if you can try systems then it is really worth it. Many do focus on outright power though, and I feel that this can reduce fine control feedback. Power and control - and think we all agree on that ;-). Or maybe I just don't ride fast enough ;-). But catch me if you can offroad lol.

Daz555

I have to say I love disc brakes. I have them on my MTB but not on my commuter or road bike. If I was to replace my commuter it would be discs all the way. My road bike is brand new however and had there been a disc equipped bike in my price range I'd have bought one without question.

I love the discs because of their excessive power (don't care if it is needed or not - but I'm 90kg), the modulation, and that they work instantly in the wet - there is no buildup of braking power as water is cleared from braking surfaces - which is always noticeable on rim brakes. Some combinations of pad/rim are better of course but it is still there regardless.

meanredspider

supersonic wrote:

. On my flat bar road bike I am using Avid Speed Dial 7 levers with Avid Arch Rival calipers and Kool Stop Eagle Claw 2 pads. I have had no problem wit many drop bar rim brake systems either, but as above, careful pad choice, rim care (and set up is key). Tektro systems have I have been rather fond of, a good budget option.

Ah - this begins to make some sense. You aren't talking about drops but flat bar brakes. That's not really an apples-to-apples comparison. V-brakes are far more effective than "road" calipers and the actuating lengths are different allowing for more power and control. I'm betting you couldn't match the performance of your flat-bar set up with drops for rims. I know I certainly couldn't.

I'm not arguing for all mechanical disc systems just the principle of disc brakes. I've only used the BB7s and a brief brush with BB5. I like the BB7 but I will be upgrading to some form of hydraulic caliper as they become available.

supersonic

The main benefit off road for me is in the mud - rim brakes can become quickly clogged up when riding through deep clag. In drier weather though I am happy to use V brakes off road

Hydro discs have come of age now for MTBs. Very few are poor - certainly not like a few years ago when lots were plagued with problems which obliterated any of the physical advantages and principles. I am hoping that the new found reliablity of say Shimano systems find their way to road bikes and that teething problems are few. Avid on the other hand are still playing catch up, their hydraulic brakes are pretty much universally criticised. A stark contrast to the cable brakes.

I forgot to mention fork strength earlier - some road forks will have to be beefed up to cope with disc brake stresses. The left leg sees quite a strong rearward force under braking, and you also have a downwards reaction force at the axle. So much so that the left leg can bend backwards noticably, twisting the wheel with skinny forks. I imagine the ultralight road racing forks will go up in weight a little. MTB forks are starting to use assymetrical designs now.

Initialised

supersonic wrote:

Ah I see what you mean. But not a problem I have had with my brakes, I have the modulation and control. In fact more than on some disc brakes, which can be too grabby, robbing you of fine control.

I found my XTR V Brakes to be more all or nothing than any discs I've used. Riding a road bike with discs is a nice talking point while they're still niche. Also I like being able to emergency stop on a blind corner from 20+ without risking a slide. Using BB5s, had noise at first but after the first service they were redone and are now quiet most of the time. Drag and weight may rule them out of so events but it'd be nice if more high end frames were compatible.

supersonic

This is where my Avid Speed Dial 7 levers come in - I have a large range of leverage adjustment:



The red dial shuttles the cradle up and down, so you can dial in leverage and alter modulation. XTR pads were dire though, first things I would have binned!