Forgot I was counter-pointing in this thread, heh.
Interesting - could you expand on that?
Unless I'm totally mis-understanding something... the advantage of a shift kit is a variable gear ratio, so that you climb hills better and not redline on flat streets. From reading what others have posted and visually looking at my Q-matic, it evidently functions like the other transmissions out there except with far superior build quality and the clutch is located in the rear. This means that it still has a static gear ratio, and a bigger/smaller rear sprocket would be the only way of changing that... right?
My goal here is to be able to make it up the two decent-sized hills between home and work (and any other reasonable hills I might encounter), and then not strain my engine when I'm cruising along on flat terrain. I don't need to go over 30mph, but I'd like to get to that speed without my engine sounding like it's going to blow up.
Compared to a HS+4G, the HS+Q-Matic is lousy on hills:
4G has more reduction and less clutch slippage. It's available in 4:1 or 5:1. This allows much easier gearing for hills with a shift kit and being able to retain usable pedal cadence ratio - that is, being able to pedal while the engine is in it's powerband.
A Q-Matic has much less reduction and a much higher clutch slip rate. It's reduction is somewhere in the area of 3:1. This means you lose the ability to pedal+engine power your way under load unless you engineer a heckuva lot more reduction into the jackshaft and/or crank. The clutch doesn't fully lock until higher RPMs. This means accelerated clutch wear under heavy load and lower RPM. The Q-Matic also has a second area of potential slippage: the belt.
A Huasheng itself doesn't have much hillclimbing prowess, only ~2 ft/lbs of torque. When you're climbing a hill, a 4G's clutch will stay locked all the way until the engine bogs out. Not a Q-Matic, it'll burn up the clutch before the engine stalls. If you lack the ability to effectively pedal assist the engine at it's torque peak, you're losing out on a lot of additional torque. Chevrolegs make more torque than a Huasheng. Also, a Q-Matic clutch is likely slipping at a Huasheng's torque peak (4500 RPM engine, much less RPM at clutch).
If you're climbing a hill and your engine is at 5K RPM and falling, it's up to your legs to try to help. With a shift kit, everything goes through the pedal chain. Therefore, your jackshaft gearing and rear gear ratios become the most important thing to effective power delivery. What good is leg power to assist when at 5K engine RPM your pedal cadence is 160+? Example: with a 3:1 transmission and standard SBP 4-stroke shift kit jackshaft gearing, your reduction to pedal crank is 22.25:1. That means 45 pedal RPM for every 1000 engine RPM. Hence, you'd be unable to pedal assist over 3000 engine RPM.
My previous setup (Hoot transmission with jackshaft kit) could do that fairly well - it had some issues early on with the carb and a replacement carb fixed things right up, but I had all of a day and a half to explore that new carb's limits before the Hoot bit the big one. Still, I could putt up hills no problem and when cruising the engine was nowhere near redline.
If you already have the shift kit and engine and bicycle, why not just bolt a 4G up to that? Order a 4G and ask em if the 11T freewheel will work with the current model. If it does, order that too. Bolt it all up and you're back on the road. It's more compact and more responsive than a Q-matic.
Am I missing something obvious here? Say I had a hypothetical perfect bike frame that fit the engine, jackshaft kit, and Q-matic perfectly - does the QM work well to the point where the added gear ratios just wouldn't help much? Should I just go with a 60t or 62t sprocket in the back, and be mindful of the RPM on flats?
IMHO, that would be a better route than shift kitting a Q-Matic. By having the pedal and engine drivetrains separate, you're in a better position to add your pedal torque when you need it. The Q-Matic is an excellent straight-line transmission, but with a small engine like a Huasheng, you need all the help you can get sometimes.
Here are some pictures of a bike I helped a customer build, but he did way more than he needed to do and included a spring loaded chain tensioner and a few other unnecessary parts.
It is a Qmatic with a shifter kit, rear wheel has a Sturmey Archer 8 speed, custom exaust I built for him and a Honda GXH with a custom cam, High performance Carb and Filters, can you say ZOOM!
Looks like it has a horrible cadence:engine RPM ratio. That's almost unavoidable when one uses a S/A 8-speed in a shift kit. 1st gear is 1:1.
I doubt it's geared very well, care to share the gears used?
I my self I have a SBP 4 stroke shifter kit and I am going to do the shifter kit with my Huasheng 144F ID generator engine on my Felt MP, for towing and climbing hills and keeping the rpms down on the flats, all negative the talk in world will not change my mind.
Because I know exactly what I will end up with, a I bike that will be able to do what it is I need it to do and a stock qmatic will not do it.
Terry
Actually, you don't know that yet. It's not done. I hope you DO get it done tho, I'd like to see how silly a 144F looks in a nice Felt frame. RHS pics.
