Drop bars and disc brakes on a mountain bike – a primer
I get quite a few questions from customers buying Gryphons and Peregrines asking what needs to be considered when using drop handlebars and disc brakes on a mountain bike. There are a few things which need to be kept in mind, which are not always straightforward, so I will try to give a comprehensive run-down here.
I’m not talking here about stem clamp diameter (which nowadays has pretty much one option – 31.8mm) but the portion of the bar which you grip and to which brake levers are fitted. Traditional mountain bike flat bars have a diameter of 22.2mm (7/8″) and as such all brake levers designed for use with such bars have a corresponding clamp size. Most road bars however have a diameter of 23.8mm, and require levers designed for drop handlebars in order to fit. What this means for the disc brake user is that you can’t fit hydraulic brake levers designed for flat bars to your drops – not without some significant bodging (done entirely at your own risk) anyhow.
For off road use most riders prefer a bar designed with dirt use in mind – for reasons of position, control, comfort, and strength. Of course it is possible to use a standard road bar, but it won’t really give the best experience when riding technical terrain. Most opt for a much wider, shallower flared drop bar. Some good options are the Ragley Luxy (which I had a hand in designing and as such are my preference), the Salsa Woodchipper and On-One Midge. These bars are meant to be ridden primarily in the drops and the wider, flared hand position affords a much greater deal of control in rough terrain than a road bar. However if your use involves a significant amount of time on the road or gravel some find these too wide – certainly if it involves any navigating through traffic. As such there are some options available which offer a nice middle ground. The 52cmSalsa Cowbell has become a recent favourite on my Peregrine, and the Nitto RM-014 Dirt Drop or WTB Mountain Roads are also a good option.
As referenced above, off-road drops are designed to be ridden primarily in the hooks. As such the bars should be positioned to so as to place the hands when in the hooks in a similar position (relative to saddle and pedals) as what they would be when using a typical flat or riser bar. They do not need to mean that you have a lot lower or longer reach than you would on a typical mountain bike. A frame such as the Singular Gryphon which is designed with drop bar use in mind enables most to achieve this without resorting to overly high rise and short stems with large stacks of spacers.
Given that you are restricted to using levers designed for drop bars, which ones will work with cable actuated disc calipers? Essentially there are two routes to take; standard (road) pull levers, or long pull (mountain) levers. When we say pull, this is the amount of cable which gets pulled during lever actuation. When long arm side pull rim brakes were introduced (“V-brakes”) they required more cable to be pulled in order to move the brake arms far enough that there was sufficient pad clearance when not applied. This became the de-facto standard for all mountain brakes and as such the majority of cable actuated disc brake calipers are designed with the use of such a lever in mind. In order to provide compatibility with such disc calipers (or indeed V-brakes) some manufacturers (Dia-Compe and Tektro notably) produce drop bar levers which pull sufficient cable to operate them. If you already have mountain disc calipers then these provide the cheapest and simplest solution. However this essentially restricts you to either singlespeed or shifting with bar end shifters. A much more flexible option is to use disc brake calipers designed for use with standard road pull levers such as Avid BB7 Road, Tektro Lyra or Shimano BR-505 to name a few. This allows a much wider choice of brake lever and are compatible with integrated shift/brake levers such as Shimano STI. Mixing and matching of short pull levers and long pull calipers (and vice versa) is not advisable. In the former case there is insufficient clearance between pad and rotor and excess mechanical advantage of the lever over the caliper resulting in a mushy brake feel.
A further possibility is starting to take hold, in addition to bodging MTB hydros as mentioned above. Hydraulic disc brakes designed for use on drop bar equipped bikes. Most solutions to date (such as the TRP Parabox or Hope V-Twin) utilise a remote master cylinder which is then actuated by a cable operated by a standard road lever. These result in very powerful and consistent braking though are heavier than a full cable actuated system and require the somewhat aesthetically unpleasing master cylinder to be mounted under the stem. However if you must have hydros these are currently the best options available. Ideally we would see levers with master cylinders encased in the lever body, and indeed some such systems are in the early stages of development, such as those from Formula. These are designed for use with electronic shifting systems from Shimano and Campagnolo, as there is insufficient space in the lever body for both a mechanical shifter and master cylinder. While they are undoubtedly “the way of the future” these are still in their early days though I am sure we will see more refined solutions from the big S’s in the next year or two.
Forgetting any further ‘bodges’, shifting gears with drop bars requires use of road shifters. Within that you are primarily restricted to offerings from Shimano or SRAM – Campagnolo require their proprietary cassettes and freehub bodies which are generally not available on hubs with facility to accept a disc rotor. For road shifters you then have a choice between bar-end shifters, or integrated shift/brake levers. Fortuitously, for both 9 and 10 speed Shimano systems road shifters and rear derailleurs are cross compatible. So you can use 9 or 10 speed STI’s to shift across a mountain cassette with a mountain derailleur. For 10 speed it gets a little more complicated, especially if you want to use a triple chainset. Singular frames are primarily designed for use with a mountain chainset, the wider stance allowing room for larger tyres. With bar end shifters this is not a problem, the friction shifter will move a mountain front derailleur just fine. For STI’s it’s more complicated. Shimano (in their wisdom) use a different cable actuation ratio for road and mountain front derailleurs. So if you want to use a road shifter you need to use a road front derailleur. For a double this is not a problem. On a triple however you will need both a triple compatible shifter, and a triple front derailleur.
Other more esoteric possibilities include Alfine internally geared hubs with Versa or J-Tek shifters. Then Retroshift levers, Kelly Take-Offs or Paul Thumbies all give options for mounting down-tube/bar-end shifters on the bars. Or if you like Campagnolo shifters you can also go theShimergo route which has the added benefit (for a certain level of shifter) of discrete adjustment of the front derailluer and less compatibility concerns.
Well, that’s about everything I can think of regarding drop bar set up on a mountain bike, though as always, if you have any further questions, please just mail me.
This entry was posted on Monday, January 21st, 2013 at 10:39 am and is filed under Uncategorized. You can follow any responses to this entry through the RSS 2.0 feed. Responses are currently closed, but you can trackback from your own site.