We Built A Coast Shift Mountain Bike!

With this setup, you can change gear anytime you want without any pedaling. Why aren't we all shifting gear like this? To get this setup, I needed a couple of pieces of kit. Firstly, a crank with a freewheel setup on it and obviously a bottom bracket to match. Believe it or not, there's a couple of places out there that have this kind of technology. First is Trials Riders. Those bikes actually have a freewheel on the crank, but I find it very difficult to find the compatibility with a chainring that wasn't miniscule because as we know, Trials Riders have very little weak legs. I had to go looking at tandem bike technology. Having a freewheel on one set of cranks on a tandem gives you independent coasting. If the captain up front is super keen, chopping away at the pedals like mad, the stoker at the back can actually be freewheeling and chilling whilst he's not looking. As you might imagine, the tandem technology world isn't a hot bed for new stuff. Actually, the cranks I found are called Shun and they come only as a square taper bottom bracket option. Luckily, I did find a square taper bottom bracket to fit this frame, 73 mil, with a wide enough Q factor to make sure these cranks just about clear the chainstays, although they do look a little flexy. The Shun freewheel crank system is of questionable quality. There is some friction in that freewheel and a bit of wobble as well, but it works. All you then need is a flexible nylon fixation on the cassette and the Donoghue Racing Co-Shift system is complete. Well, we have the technology, so let's The bike is absolutely silent because the hub freewheel isn't doing anything and the freewheel on the cranks just doesn't make any noise, although it is spitting grease out of it a little bit. Actually, being able to shift all the time there works really well. I've always felt like I'm quite sensitive to what gear I'm in. I think maybe because of riding with flat pedals, you don't want to be spinning too fast, your feet come off. Just being able to always shift, I really like. Actually, the inspiration for this video came from my e-bike. You don't shout at me, but I've got a Propain E-Carno, which uses the SRAM powertrain motor. With that, it's got automatic shift, which is very clever, but also it's got a coast shift. When you hit the shifter, it actually spins up the chainring. I know e-bikes have freewheels actually on the crank anyway, but they've got two freewheels on there. That really is actually, apparently, I've looked into it, it's more for smooth transition for when it assists you, but also with that SRAM transmission, the only one that does it. Hang on, Shimano motors do it as well. Like I say, it will spin the chainring forward, which just pulls the chain, obviously, across the cassette, so you can shift whenever you want. That got me thinking, actually, you could do that with a mountain bike, and that's what I've done. So far, I'm really enjoying it, but I think I need to do a bit more riding. Actually, it's a fun day for it as well. I'm back for more. I'm going to do another run. This is fun, and I love the way the bike is silent and relearning how to shift. I guess we need to talk about potential disadvantages. So far, I've not felt any, but there's definitely risk involved because your chain is spinning all the time. Obviously, it's pulling through the mech. On the occasion when you might get a stick into your wheel or into your chain, normally, you could hear it and stop pedaling and potentially save anything from breaking, but with this, it's spinning all the time. If a stick goes in your rear wheel, there's a real chance that it could snap your mech off because you've just got too much going on. You've got tension the whole time. Obviously, I'm running the very fancy Eagle transmission, so they're pretty chunky, but they are really solid. The risk of snapping it is less, I would say, but there is definite risk. Also, there's more friction all the time. If the chain is spinning, chains are really, really efficient. We know that. They're used in all sorts of applications because they are so efficient, but it is running the whole time, so friction will be in the system, and it's going to wear out quicker. Yes, when you're not pedaling, there's not that much tension being pulled through it, but it's just going to be running the whole time, the chain movement and the suspension. You may be aware of a product called the O-chain. If you're not, it's basically a spider, a chainring spider. It actually detaches the cranks from the chainring a little bit. There can be some movement because when your suspension travel goes in, your rear axle moves away from the BB, and it stretches or puts tension on the chain. That tension on the chain can stop the rear wheel moving quite as freely. That's why loads and loads of pro downhillers and enduro racers put O-chains on their bike to make their rear suspension more active. Now, I've racked my brains as to how this might work with this system. If you're a mechanical engineer or you're into physics, please jump into the comments down below because, obviously, as the rear wheel is moving, my chain is moving, so there is some slack in there. As far as I can tell, that should take off some of that tension. Actually, this kind of freewheel has got an awful lot of movement. Actually, if I push on the chain there, can you see that chainring is revolving back to a point? It does lock out and then it pulls that back. If I can get this right, I think it is giving me some of those same advantages as an O-chain. Obviously, disadvantages is the engagement when I'm going to pedal, but please get involved if you have an answer to that. Also, a really interesting part of this is it works like gearboxes. We've talked about gearboxes on bikes for forever, 20 years probably. Lots of you may remember the Honda RN01 downhill bike where the chain moved all the time. There was none of this on the back, no rear mech, no cassette. Basically, they moved that stuff to the middle of the bike. Again, you could coast shift with that because the chain is always moving and there was some resistance. That's what you always heard. No one got to ride those bikes except for the pro team, but there was some resistance involved with those gearboxes. Even the modern-day gearboxes, with most of those, you can coast shift. Just change your gear whenever you want, even standing still, and it will move into the gear within the gearbox. I see advantages that way. Also, the unsprung mass, moving it from your rear wheel to put it on the sprung mass is going to make your suspension be able to move easier and work better as well. That's not necessarily the case with this system, but the argument for moving the gear is to the and how quiet it is. Obviously, I've just taken away the freewheel on this one, makes no noise. Although, it is a bit messy. There's grease coming out of it and not sure how long that shun freewheel would last. The one thing I was worried about that hasn't happened was my chain spinning so fast and potentially it dipping in the middle like it's not being pulled the other way fast enough. Particularly, I actually tried freewheeling with it in that 52 tooth downhill. Obviously, the chain is spinning around really fast there. I thought it might dip down behind there and once it gets stuck there, it would break. I was worried about that, but it has not happened. Should my chain get more dirty and a bit more friction in there, maybe it would, but it hasn't happened. I'm impressed. Engineers, get involved in the comments. I'd love to know your opinions and why aren't we all shifting like this, but also is this an alternative to the O-chain or even you could stick a neutral gear in there. I didn't want to do it because this is a one-piece, very expensive cassette. I've done it in the past where you replace one of the lowest sprockets with just a smooth spacer so your chain runs completely freely. You could do that with this because you could shift up and out of it as well. Maybe something for the future, but let me know your opinions down below. Get involved and give thumbs up if you like a bit of home engineering in the garage with some tandem parts.