Low speed hub ?

stevenatleven

Pedelecer
Apr 18, 2011
212
140
Fife
Hi I have done about 4000 miles in the last 18 months, mainly hilly touring and hilly day rides on my 2 e bikes. One has a Dapu 250w motor and the other an Oxydrive 350w motor. Range is fine on both bikes if I keep the power assist low but i usually end up climbing hills at 6/7 mph.The motors whine and feel laboured and I know they are not very efficient at this speed. I can crank up the level and ride at 10/11 mph but this shortens the range to much for the 110+ kilo load. So I am thinking of building a Xiongda 2 speed set up with a 18Ah battery that will give me the range and low speed grunt,but before I do thought I would ask advice here. Any motors out there that achieve max efficiency at low speeds or is there a better 2 speed alternative to the Xiongda ?
 
D

Deleted member 4366

Guest
Using a higher level of power doesn't mean you use more battery. It can mean that you use a lot less. You have to consider efficiency and speed. The Oxydrive would be about 60% efficient at 12 mph 50% at 9 mph and 30% at 6 mph. That means that you're wasting 2/3 of your power at 6 mph. Also, you spend less time using the higher power on the hill when you go faster.

The Xiongda avoids all those problems, so would be the perfect solution apart from its one drawback. It's quite wide, so it takes a bit of practical nouse to install and get the rim central.

The low speed motors are also better gor climbing. The 48v 201 rpm Q128H is very good if you're happy with the 25km/h limit. It'll just about reach 19 mph with a fully charged battery, which will drop to 15 mph as the battery empties.
 

stevenatleven

Pedelecer
Apr 18, 2011
212
140
Fife
Hi Dave Thanks for the Q128H suggestion, I will look into it. I get what your saying about using more power to get up the hills quicker but unfortunately even at the highest setting keeping the bike at 12 mph on steep hills finds my fitness wanting. Last week on a tour of the 68 Pennine cycleway I found the constant hills very tiring. The Xiondga hub would be the central part of the build so I could tweak the frame and dish the wheel to suit overcoming the width/centre problems.
 
D

Deleted member 4366

Guest
If you have rim brakes, you can stretch the frame a bit more and add a spacer (washers) on the left side, so that you don't have to dish the wheel. You can do the same with a disc brake, but you then need to space the caliper adapter by a similar amount. I did that on my Rocky Mountain. In this photo, you can see the washers on the caliper bolt, just under the axle. It was about 7 on the back bolt and 5 on the front one because the widened frame is no longer parallel. Small dishes are OK, but the difference in spoke tension from one side to the other rises rapidly the further you go. I'd say that a 10mm dish is the practical limit.

The Q128H motor gives a lot of torque. It's happy at about 6 mph, where you'll get about 500 watts of output power with a 20 amp controller. The Xiongda can only do 15A at 48v. It's better efficiency at low speed means that you get the same 500w of output power at 6 mph. That compares with about 250 watts from your present bike, so both options will give you double the power.

The winch mode on the Xiongda is like no other electric bike. It's very useful when you're hampered while carrying 20 kg of shopping, but for normal riding, including steep hills, the simplicity of the Q128H gives it an advantage.
 
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