I know this will stir up controversy but I really am curious and want to learn. I have done some research and to my understanding, in a manual transmission car, the transmission (put simply) has synchros and gears. When you shift from one gear to another, the transmission uses the synchros to match the transmission rpm to the drive shaft's rpm so that the gears mesh well and don't grind. The normal process of shift gears goes clutch in --> shift --> rev match --> clutch out and the clutchless process is let throttle out --> slip out of gear --> rev match --> slip into gear. The normal process takes the engine out of the equation while mating the transmission to the drive shaft but the clutchless shifting process keeps it in the process. My thought process is that in a theoretical situation you can clutchless shift absolutely perfectly and very little wear will be applied to the synchros and to the clutch. This could also be achieved by shifting normally. Technically the only thing different between the two methods is that one has an engine and one does not and if both methods were completed perfectly then they would achieve the same thing and minimal wear. The only reason that clutchless shifting would wear more than traditional shifting is that the synchros have to synchronize the engine and transmission with the driveshaft while the traditional method would only synchronize the free spinning transmission and the driveshaft. I would assume that clutchless shifting would wear less if done within a very small rpm range around the exact rpm but if done outside of that would then wear more. Is that range so small that clutchless shifting is pointless and you'll never get it in that range most of the time? If so then I pose another question. What are the differences between a bike transmission and car transmission that would make (from my research around online) the bike transmission capable of clutchless shifting while the car transmission not capable? I have heard from multiple people that clutchless shift on their bikes daily and have done it for a while and had no transmission problems. Thanks!

 

Motorcycles have dog engagement - much more robust an engagement system.

If you do what you are suggesting, the synchro will see all of the rotational inertia from the motor/clutch/flywheel/pressure plate coupled to the input shaft and the transmission/half shafts and wheels/tires put through them coupled to the counter shaft...they are brass and don't like to be put under that kind of load. Get a gear in your hand with the synchro on it and you will see that the synchro rotates around the gear slightly to all the input shaft/counter shaft speeds to match up - without the inertia as described.

 

My bike has helical gears 1-4.

You are just going to damage synchros and probably eventually bend shift forks with your 'clutch less shifting'.

Motorcycles have sequential transmissions with quickshifters that actually cut the throttle to allow those shifts to happen.

Of you really want clutchless, there are a few sequentials out there for Honda applications.

https://www.youtube.com/watch?v=qRI8-w6DJO4

 

I shift my car without using the clutch and love it, shaved 3 tenths off my quarter mile time by doing this.

 

First I'll say I know how to do this and other than for the novelty, there's not a lot of point. If you're racing you don't do it, its something to do while in traffic.

First remember you will grind it a few times while learning. The way to learn is to go drive your car and take note of RPMs verse certain speeds. Say your car is doing 30mph in 2nd gear and its going 4000rpm. and that same car, at 30mph in 3rd gear is doing 2800rpm. If you were going on a slight decline (to where in neutral your not going faster or slower), the goal is to ease off the throttle and slide the shifter out of 2nd gear (at 4000rpm.) Then you'll want to slide the shifter into 3rd gear while revving at 2800rpm. If you're off by more than a hundred RPM or so, you're gonna grind. The larger the RPM difference, the more it'll grind. The first time ya try it, you'll back off the throttle and slide out of 2nd gear and let off the throttle, your RPMs will fall. Then you rev the engine slowly and when its at about 2800rpm, slide into 3rd gear. This whole time you're not pushing the clutch pedal of course, clutch-less shifting.
Now when doing this, as I said, on a slight decline it'll be easier, but if you do this on a straight road, as soon as you're out of gear the car is going to decelerate some, so you're gonna have to adjust what RPM you wanna shift at. When you learn your car, you can push a little on the shifter and when you get the RPMs like within a hundred, you'll sort of 'feel' it and be able to get into gear without grinding.

P.S. Do NOT use gm synchromesh to make this easier, the viscosity is WRONG for Honda transmissions and it will wear your bearings in a matter of months. Always and only use Honda MTF, ask around, this is the best fluid to use, there are no cheap upgrades for this.

P.S. again: Again I advise against doing this for the purpose of racing, and also remember that everytime ya grind you are wearing your synchro ****. In general I suggest against clutchless shifting period. In the time it takes you to learn to rev match and slide in and out of gear, its almost always faster to just use the clutch. I suggest practicing on a bad tranny you don't care about. But if this is your daily driver and you don't wanna wear your shifts out, shift the regular way...thats what synchronizers were invented for.