Hi folks, an off-topic question about a three-wheeled mode of transport, in case anyone who knows about disc brakes can help.
I try not to do anything too stupid on a unicycle because at other times I am wheelchair-pusher for my wife. We have an off-road wheelchair, a MountainTrike, which is awesome - it uses bespoke and quality mountain bike parts, with two gnarly 24" front wheels with disc brakes and shock absorbers and a single small free floating rear wheel. Ours is the MT Push which is attendant operated and braked, their main product has hand levers and chain drive for the chair occupant to propel and brake themselves.
The problem Iām looking to solve is that at times when Iām relying on the brakes going down a steep slope, if I were to slip and let go of the handles (and therefore brakes) Rachel would go sailing off at great speed to an uncertain future with no way to stop herself. We donāt have any push rims on the wheels and anyway Rachel wouldnāt have the strength to stop herself that way, and there is only one set of brake levers which are on the pusherās handlebar (one for each wheel, meaning they always have to be used in sync or else the chair will spin around - only useful when intentional!).
The cheap and cheerful solution suggested on a MountainTrike online group was to attach the chair to my waist with a hip belt and bungee line (I can do that - I used to use one to unicycle with the dog), so that if I slipped I would at least act as a drag anchor!
My initial thought for a more engineered solution was to see if a second pair of brake levers could be added inline with the current set, so then either Rachel or I could apply the brakes at any point. However in an emergency run-away situation they would still need to be applied equally and carefully, and with some force, in order to avoid the chair spinning and tipping over.
My most recent thought was inspired by a Flymo lawn mower (!) where I have to keep a lever pressed all the time in order to keep the motor going. I started wondering if the chair could be set up so that the brake was always on until the ābrakeā lever was squeezed to release it (I would have to get used to pushing whilst always squeezing the lever). This way if I were to let go of the chair it would just stop, without Rachel having to do anything.
So, does anyone familiar with disc brakes know:
Is there a way to add a second brake lever to an existing hydraulic disc brake setup?
Is there a hydraulic brake lever that works in reverse, so that you squeeze it to release the disc brake, rather than to engage it?
I couldnāt immediately find anything online, and thought people more familiar with the technology than me might be able to point me in the right direction.
Thanks for any ideas anyone can offer,
John
P.S. I was re-reading the above and thought āWhy do we even do this? It sounds so unsafeā - but then I realised the same might apply to unicyclingā¦
I know there are two lever brakes out there - which might allow for both wheels to get a second handle at Rachelās disposal. Alternatively perhaps you can find a tough elastomer loop. That when looped on / hooked over the brakes as they are - close it, apply the braking force. Youād then need to find a basic brake level - probably some old bike part for wire pull type brake - and attach it near to the actual brake lever. In effect this new lever would be used to release the closing effect of the elastomer.
Bit like how bus/lorry brakes work (from my basic understanding) where theyāre in fact ON - applied by default and a large spring applying the force. Their hydrologic system is active in removing this force, and when you brake you decrease this which lets the spring do its thing. This would mean any lorry where their hydrologic power failed the brakes will just apply.
Hope my description of my basic idea makes senseā¦
Thanks Felix - a less destructive version than looking for new (probably non-existent) āreverseā brake levers - Iāll have a look at the space available on the handlebars and think about that
Yes itās called the shimano grx sub lever. As far as I know that is the only solution for an in-line brake lever enabling two brake levers for the same caliber. I have no experience with it. The lever is quite short so you will probably need more finger power for the same braking force than a regular (longer) lever.
Shimano do a āsub leverā for their GRX gravel groupsets, probably just on the top-end group I think. It is a secondary level which is inlined into the brake line. I have a set of these on my gravel bike along with the drop-bar levers/shifters. You can probably make them work okay with a decent mineral-oil based mountain bike lever ā I think that is what Maxence has done (as referred above).
I wouldnāt worry too much about them braking the wheels independently ā the brakes on my recumbent trike brake separately on the front ā they are drums and the centre-of-gravity is lower, but it doesnāt actually pull all that badly ā it isnāt like standing on one brake on a tractorā¦ but I can see your concern.
As far as I remember Hope do/used-to-do a single lever which did two callipers ā but this probably wouldnāt solve your problem either.
For a solution that has the brakes work āthe other wayāā¦ ā well a crude hack would be to wrap some elastic round the lever and handlebar to keep them on, and then figure out how to essentially work the lever āin reverseā to āpullā the brakes off ā for example, tape or cable-tie an extension to the lever which goes 'backwards" over the lever pivot so that when you press on it it pulls the lever out against the elastic, releasing the brake. If you get something like this working you can make it somewhat less Heath-Robinson once youāve figured out what you need. In the first instance you could probably just pull the levers out but Iād imagine your hands/fingers would get tired pretty quickly.
[Standard disclaimers etc on actually doing any of this stuff etcā¦]
Edit ā I see Hammer has replied regarding the GRX levers while I was typing the above.
The simple and likely the most common natural reaction would be to never let go of the handles. If you happen to stumble, slip or fall the natural reaction would be to hold on tight rather then letting go. Just like a person using a walker assist device, the natural reaction is to hold on tight.
I donāt like my suggestion, but I saw it on TV as emergency brake for trucks: fix one end of a durable friction mat in front of the rear wheel. For emergency stop drop the other end of the mat in front of the rear wheel. The mat will be between tire and street. An irreversible straight foreward steering brake.
Thanks for this idea, and no worries re the old post, Iāve not solved the (theoretical) problem yet. The thought that something could stop the back wheel turning is interesting - itās the only wheel that has any kind of āforkā (the large front wheels have no obstructions around their circumference).
So I think it might be possible to have a smaller roll of friction matting or similar that would be placed so that if ever it isnāt being held away from the wheel it would drop into the fork in the direction of travel and then effectively wedge/ block the wheel from turning. Then the trick is to ensure that while pushing the wheelchair the matting/ wedge is held away from the wheel, eg by attaching a long enough piece of string to it so that I can secure the other end of the string under my hands while pushing, but if ever I let go the loosened string allows the rear wheel to be wedged by the friction matting. Iāll have a bit more of a think - this could probably be done without it all getting too messy or complicated.
I think that solution could work to some degree, but the center of gravity is nearer to the front wheels than the rear wheel. Plus the physics imposing that front brakes are more efficient than rear brakes when moving forward, I have some doubts that this would be enough to brake the wheel chair sufficiently. @holyroller , does Rachel have normal strength in her hands? If so, a set of additional brake levers would probably be the best solution. In sketchy situations she could even help braking, so she would be kinda ready if things went south.
Itās true that even braking action is required left and right for the wheel chair not to spin and tip over*. That said, tipping over at comparatively low speed is potentially still less harmful than what could happen if the wheelchair gained speed.
*The comparison to a trike is a bit misleading, since the trike has a fixed rear wheel and a longer wheelbase, which both work against it pulling to one side if the brakes arenāt actuated synchronously. Unbalanced braking on the pictured wheelchair should in my opinion have a much stronger effect than on a recumbent trike.
About 34 years ago I built a small but totally functional bicycle. The break mount consists of 2 metal sheets and 4 screws. This could be clamped to your rear wheel.
The two black plates of the picture above are just clamped in place by the 4 screws. It never got loose. @holyroller you could clamp these two plates above the rear wheel. The drawback is that it is not braking automatically.
That is one very unusual machine!
I hadnāt thought that I might be able to mount a calliper brake on the rear āforkā as itās such an odd shape, but Iāll have a think about it (I happen to have some spare Maguras, but I think that would be way too complicated!). As @Wheelou suggests having some kind of āemergencyā braking available for my wife to use would seem good, and my initial thoughts were around adding further brake levers inline with the current ones (but I think that would mess with pressures as there would then be 2 fluid reservoirs per brake line?), or adding a second pair of brakes to the existing discs (but that would need a whole new mounting point on each side, when the existing mounts are complex enough as it is, since left and right brakes have to be mounted in opposite directions).
Soā¦ While agreeing with @Wheelou that the rear wheel is not getting anything like as much weight on it as the front wheels, so is less than ideal, it still seems to me that there would be some benefit to fitting a simple calliper brake to it, with the lever fitted somewhere in the seat area where Rachel can reach it. That way if some gradual movement starts (like when I forget to secure the brakes on when walking away to open a gate, etc - not unheard of!) she has some control for those situations, which wonāt then get out of control. If we do any extreme wheelchairing near steep cliffs then I think the idea of a tether between me and the wheelchair is probably still the best option - at least we could both make our final descent together
This is the direct approach, in case you can flush out the air.
Sure, @Wheelou is right about weak rear wheel brakes. I ride my bicycle like a unicycle, so the main weight is above the rear wheel.
Primarily you can test the rear wheel braking force by blocking it i.e. with a stick, hopefully without bending the spokes.
