It has been the longest fall I’ve ever experienced with very little snow here in the valley and warmish temperatures. This has really not done the skiing any favors but it’s been great winter riding weather and perfect for product testing. This soft and friendly weather has allowed me to move ahead on the testing of disc brakes on my road bike that I hadn’t planned on doing until spring.
So – I took the plunge and had the good guys at Joe Young Wheels build me up a set of wheels using DT rims and DT 6 bolt hubs – the rear being spaced at 135 mm. I then got to work and made some custom disc brake tabs to work with my frame and fork design. The designing of the tabs was the time consuming part as there are many considerations in getting it right – they need to be stiff enough both laterally and rotationally, they need to be light, they need to distribute the braking load well and they need to be attractive. After cutting them from steel plate I dove in and ruined an otherwise perfect paint job (sorry Joe Bell) and fillet brazed them in place. I didn’t bother doing any finish work or polishing as I just wanted to see how the set up worked and thought I may just end up removing them anyway.
Now I can hear the mix or reactions out there right now and imagine they range from “very cool!” to “no one needs disc brakes on a road bike!” and for what it’s worth I was thinking both of these things myself at first. Disc brakes have been around in the larger world for a very long time. They were first made popular by Dunlap on the Jaguar C Type of 1953 after having been proven on aircraft. Discs have been in common use on mountain bikes for a solid 15 years now and the bugs have been worked out of the system. So when the UCI approved discs for use on cross bikes recently I could very easily see a further cross over to road bikes.
What advantages does a disc brake have over a traditional rim brake and what are the disadvantages? I’ll jump right to the disadvantages -
* disc brakes add weight – how much depends on what type of brakes you are replacing. The disc caliper is a bit heavier than most rim brake calipers and there is a disc rotor for the caliper to grab that you otherwise don’t need. It’s not a lot of weight but there is some.
* disc brakes require ‘bedding in’ – when you first set up a disc brake in the work stand they seem to work well and then take it out for a test ride and to be frank they dont’ work very well…….at least at first. Disc brakes require heat to bed the pads to the rotors and until this occurs the braking power is just not there. It takes just a little bit to bed them in and I did it on my bike by going down a hill near my house dragging the brakes until they got really hot. Once this happens the braking is sublime.
* disc brakes require different skills to set up – when you think about it a rim brake is really a big disc brake with the rim doubling as the braking rotor. A disc brake works the same way but the braking force is applied to a small rotor bolted to the hub – you squeeze the lever and the disc pads clamp the rotor and the bike stops. The real difference in setting the two type of brakes up boils down to how one sets up the disc caliper on the frame/fork. This technique will be specific to the brand of brake used but with the Avid BB-7′s I’m using right now it could literally not be easier. You leave the two main caliper bolts a bit loose, squeeze the brake lever to align the caliper to the rotor and tighten the bolts and you are now 95% of the way there. All that’s left is to spin the two dials to set the pads the right distance from the rotor and you are done. I see this as less of a disadvantage and more of something new to learn. Once you learn it I think it’s as easy and quick as dealing with a rim brake.
* disc brakes are safer on long fast descents – The issue with rim brakes with long downhills is that they heat up the rim and this in turn heats up the air in the tire and increases the air pressure. Not a big deal on regular hills but a very big deal when riding in the high mountains. This increased air pressure can lead to the tire blowing off the rim or in the case of carbon rims can cause the rim to fail. This is rare frankly but it does happen. You can also have your rim glue holding on your tubular tires soften allowing the tire to roll off. We saw this a number of years ago in the Tour when Beloki hit a patch of goo on the road on a fast downhill that had lots of braking. His bike slid in the warm tar and when it hit the grippy stuff his tire rolled off and it effectively ended his career. Again – this is very rare but it’s something that those of us that ride in the mountains now have to keep in mind and manage.
* disc brakes work in all weather conditions – the issue with rims brakes in the wet is well known. The problem is that the braking surface is right down next to the wet road constantly being doused with water. Add road grit and oils and the braking can be downright bad. Discs on the other hand are up and out of the road slime and since they get hot almost instantly they burn the water off the rotor within a single rotation of the wheel and you get the same braking you get in the dry. Think of how well your car brakes work in the rain. Hit the pedal and stop. Bike discs are the same way, even in the wet.
* disc brakes don’t wear out your expensive rims – normal rim brakes grab the rims with pads and grind what ever dirt and grit on them into the rims. This in time wears the brake track of the rims and can actually wear the rims out. This doesn’t happen often with aluminum rims but it’s all too common on carbon rims.
* disc brakes don’t care what size tire you run or if you want to use fenders – A rim brake has packaging issue around the tire. You can only run a tire so large under a short reach caliper brake and fenders can be difficult to fit unless the bike is designed for a long reach brake. A disc brake doesn’t care what size tire you use. If the tire fits in the frame/fork it will work. You also have the added benefit that you don’t need to quick release the brake to remove the wheel – just undo the skewer and the wheel drops out.
* disc brakes don’t care if your wheel is true – with a rim brake a broken spoke can be a minor pain or make for a long walk as the rim won’t spin between the pads. With a disc brake the wheel will turn as long at it clears the frame.
* disc rims can be lighter – this is an as yet unrealized advantage. Rims designed and made without the need to have brake tracks will end up being lighter. The rim brake type rim needs to have a flat surface for the pads, needs to be able to deal with the compressive force the brakes apply to them and needs to act as a heat sink. A rim designed to just hold the tire will be lighter and the word on the street is that we will see rims weights drop soon for disc wheels.
* disc brakes have the best modulation – this is the BIG one IMO and more than enough reason on its own to consider discs. Most types of brakes, rim or disc, will provide enough power to lock the wheel when dry but a disc brake will provide much better modulation. This may not seem to be a big deal until you try it for yourself. With a rim set up you can have a hard time feeling what the tire’s contact patch is don’t on the ground and how close it is to locking up. With a disc you get much better feedback and consistent braking power and this allows you to carry more speed deeper into a corner and then brake later and harder. This means you’ve got a longer distance at a higher speed and in the end you will get to the bottom of the hill sooner than you would have with rim brakes. Cars and motorcycles have been working on brakes for a very long time in order to carry more speed deeper into a turn but it’s rarely talked about on a bicycle. I think we will see that change as road discs become more common. One thing I can’t over-stress here is just how much fun it is to do this – barrel into a corner and then drop anchor to get to your corner speed instead of feathering your rim brakes to keep speed in check all of the time. There are very few things that can actually make you faster on downhills and discs are one of them.
According to my word counter I’ve put down 1539 words so far and that seems like enough but I have a few things to add. I don’t think you are going to die in a great flaming crash using rims brakes the next time you go down a hill and I don’t think discs are for everyone. If you live in a place without steep long hills and you only ride in the dry then I doubt you would see much advantage to having discs. I spoke to a friend the other day who said he only needs enough brake to not his his garage door when he gets home from a ride and I understand that. But if you ride in the wet and/or in the mountains I think you would enjoy the advantage disc brakes give. I’ve been riding mine for a few months now and abusing them big time and I’m very pleased and can’t picture going back to rim brakes on either my road or cross bike. One thing I feel confident in saying is that Pro Tour guys will all be riding discs in the next few years. The advantages will so outweigh the downsides for them that it will be a done deal and we will see safer descending in the hight mountains of the grand tours. The strong rumors have it that both Shimano and Sram will be offering a high end disc set up that will be lighter and more simple this next model year. We should also see a move toward hydraulic actuation soon from both these guys and the already great modulation will only get better without cable stretch.
I will be offering disc brakes builds on road and cross bikes as soon as I can. It will no doubt be a few months down the road at least but I will offer them as an option as soon as I can. At this point I don’t know how it will affect the pricing but I expect it will be a slight upcharge. As soon as I know more I’ll pass it on.
1994 words – wow, that might be a record. Thanks for sticking with me.