You would think that flying up a steep hill with a shift-kitted motorized bike would be a piece of cake.....but it's NOT.
Firstly, the correct engine with good torque (not just horsepower) needs to be chosen. Hillclimbing and headwinds sap a lot of power out of motorized bikes. Once the struggling engine drops rpm and starts lugging, mph drops quickly. When the MB begins to slow down when climbing a hill, it is EXTREMELY difficult for the engine to catch its "second wind". Lugging is where any engine starts to literally beat itself up. The MB rider must pull over to the curb lane's edge. He must pedal-assist, maybe to the point of resting his engine and pedal furiously. With no engine assist, the MB slows down to the speed of a slow-moving bicycle. There will be no powerful engine-assist.....until the bike crests the hill!
Why is that? There are at least two reasons. Firstly, the engine does not have the extra low speed torque needed to push thru the headwind OR climb a steep hill. Orrrr, the bike is not geared correctly to keep the engine in its rpm power band. Orrrr, the clutch springs are too soft and engage right off-idle. At this point, the engine has a fraction of the power it needs to climb uphill. With its OEM 8,000rpm clutch springs, I'm pretty sure my GP460 engine would have no problems climbing the steepest hills. With 3,000rpm springs, it cannot. However, with 8,000rpm springs, the 460 engine would be EXTREMELY difficult to manage in street traffic. Engagement would be brutal and the engine would be VERY loud. I HAVE tried 4,000rpm clutch springs. The bike behaved EXACTLY like a LOUD modified moped. It also had absolutely no clutch engagement below 10-15mph. This made the engine very impractical and useless, so I switched back to 2700rpm clutch springs.
It would seem that the simplest way to overcome the engine's weakness would be to install a shift kit. Sounds logical, correct? Just install super-low gearing and your troubles would be over, yes?
Wrong.
Is it just me, or is everyone having the same pedal-assisting issue?
By choosing the correct combination of sprockets, one can create an MB with a super-low granny gear(first gear). On flat ground, it's good for a quick start, Orrrr, the MB rider can start off in second gear from a standing stop. On a steep hill, the super-low first gear gets the bike moving quickly from a stop. Second gear is also stiff, so there is still some hillclimbing ability. The BIGGEST problem is on a narrow two-lane road up a very steep hill in congested traffic. Once the cars ahead of you slow down to a stop.....you're dead on a hill. Even if you're blessed with a granny gear, that can only work well for you IF THE DARN CARS DON'T STOP EVERY FEW FEET IN FRONT OF YOU ON THAT STEEP HILL!!!
Why is it difficult to climb steep hills on a shift-kitted bike?
I believe the problem lies in the fact that you cannot EFFECTIVELY pedal-assist on an MB with a shift kit. You and the engine share the same chain and driven sprocket. The optimum gear ratio for the engine is the WORST gear ratio to pedal or pedal-assist. The best gear ratio for pedal-assisting is the WORST gear ratio for engine-assist!
When the engine is pushing the bike @ 25 mph, there is no effective pedal-assist. It even feels like you're pedalling with a missing bicycle chain. And by the same token, if you're in 7th or eighth gear, you can pedal, but those gears are the engine's highway gears, so the engine can't help pull you up the hill without lugging and hurting itself!
Solutions?
If the engine was front-mounted with shift kit connected to a front wheel cassette, pedal-assist on the rear cassette would be VERY effective with proper gearing.
If engine and shift kit was rear-mounted, and you had a front-mounted chainring w/cassette gears where you pedal with your arms, that would be effective.
If you installed a torquey engine, that might help push your bike uphill.
If you installed a second engine on the front wheel, the extra torque would work.
If you installed a second engine on the rear mount, that might work.
If you installed clutch springs which engaged @ a higher rpm, that might work, but low end would be nonexistent.
I already installed granny gear ratios. First gear is 46:32:1. The cheapest and simplest solution would be to find and install a stiffer engagement spring for my single-spring clutch.
I just got an epiphany!!!!
With a Happy Time engine, what you COULD do is make use of your weak manual clutch!
When climbing a steep hill, when the engine rpm starts to drop, disengage the clutch. Raise the engine rpm for a second or two, then pop the clutch. The engine will be at a higher rpm and have more power to pick up a bit more speed/rpm. Of course, this is just theory. I don't have a HT engine w/manual clutch, so I can't prove that. It MIGHT work for the HT engine, tho.
Sorry for the rant. This is one problem I'll try to work on. I just have two short hills on my commute that I worry about, so it's not REALLY a big issue.
combination.
