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E-bike conversions: hub v bb?
I’m planning on adapting a road bike to either a rear wheel hub assist or bb assist. I read somewhere that the rear wheel e-hub can cause slippage on the road surface on steeper climbs and as I have a lot of steep hills around me, this is a key consideration. I also want to convert a full suss mtb, so interested to know whether anyone has real-world experience of these conversions.
How much difference is there between the two types of conversion? Is it the case that hub conversions are best for road and bb is better suited to off-road? What is the bet kit?
HUb motors are the easiest to fit. Fine for the flat and commuting. BB mount kits are better for hills because they run thru the bikes gears so they remain at more efficient speed when climbing
Front wheel motors can slip. Rear wheel motors are fine.
So your choice is between ease of fitment – Front wheel easiest, hub hardest V efficiency of use – BB mount is most efficientTurnerGuyFree Member
BB mount means pedalling always required, hub means you can take advantage of the loophole that lets you just use the throttle !
EWrrmm wrong. if its being fitted now you have to pedal. Older kits both BB and hub could have a throttle. NO distinction in law between hub or BBthisisnotaspoonFree Member
There’s an advantage that a hub motor shouldn’t burn out on steep hills when you run out of gears where it’s possible to overload a bb mounted one if your cadence drops too much and the controller tries to put too much current through the motor.
Having said that you could probably do the same to a hub given a steep enough climb, but it should be designed to have enough power to keep it moving and prevent that.
Kits vary from simple motors in hubs that just output 250w as long as you pedal (or press a button of illegality) to torque sensing ones that add to your pedaling proportionately, the features of any particular kit affect the feel of the assistance more than where it’s mounted.
Tempted to put a mid drive kit on my ofo to allow it to tow a trailer easily. Either that or I wondered if a motor hub would fit too the trailer which could have interesting consequences to the handling!
middrive, bottom bracket is better for hills. bafang being the obvious.
Problems you’ll get firstly are chainstay clearance, on the drive side of the the diameter of the bbs02 is about 110mm, so you need the space to fit that tight up against the frame, it curves into to about a 90mm diameter so there is a bit of wiggle room there.
But really you can’t convert every bike.
2nd consideration if you can fit that is your bb width, the bbs02’s are only really made of 68mm bottom brackets, so if you do put it into a 73mm bb, you’ll need to offset the no drive side, and extend your Q factor a bit. I like the width myself, you can get offset crank arms, or a 20mm pedal extender on that side works.
3rd consideration you’ll have is where you are going to put your battery. On a hardtail it’s easy just fire it on the down tube and make sure you’ve got space(I got the dimensions of the battery and made a cardboard cutout to check before I bought). On a full suss, generally it looks a complete pain. On my hardtail I drilled and extra 2 water bottle holes in the frame so I’ve 4 attachment points on it aswell. On a full sus, I guess you could mount it upside under the downtube, but tbh, I’d expect that eventually rip out of the frame with any kind of abuse, so don’t really fancy the idea. Obviously road bike should be fine. just check the battery will fit in the frame.
4th consideration on the mtb is where the motor will go, if you’ve a bendy join at the bb on the down tube the motor is going to point straight down. Obviously not good for clearance from rocks etc.
As for the wisdom of converting a road bike, I wouldn’t, you don’t really need it.
I basically separate my cycling these days, mtb is battery powered, road is self powered.
Guess if you are using it as a commuter, then maybe but for that I’d just convert a hardtail, more comfy than a road bike.
I bought my stuff from em3ev.com and would recommend them. Hand an issue with the motor when I first bought it, and they replaced the controller on it FOC. You’re buying from china, but they had a guy in london I just sent the motor to to fix the issue, which was decent.
ultimately the bafang stuff is decent, but if you have a go on a standard emtb these days, you can tell it is just a better system over all. But the bafang is decent.
DIY bolt on conversions are all shit
buy a mid motor complete bike with a good motor that senses torque, cadence and speed delivering smooth intuitive assistance.
for commuting, a shimano mid motor hardtail with slicks is ideal.
for actual road. buy the lightest mid motor Eroadbike you can afford.
Oh.. and derestrict them. 15.5mph is a stupid assist limit for the road. (it’s 28mph in the states… which makes a lot more sense)
DIY bolt on conversions are all shit
G overstates are per. 😆 They may not be as good, but if you’ve a bike kicking about, you can get a conversion happening a fair old whack cheaper. That is the main attraction.
(it’s 28mph in the states… which makes a lot more sense)
It’s variable state to state, most are 20mph, some go up to 30, some take the northern ireland approach.benp1Full Member
I’ve been considering this for a little while for my Big Dummy. Still undecided so currently on leg power
Hub mount feels like an easier solution, mid mount like a better solution. then faffing about with something with power like a BBSHD to something with a 250W limit like a BBS01. Not that fussed about going quick, just want assist to help with heavier loads like kids/shopping/cargo on inclines. It’s fine on the flat
YOu have riden all the different conversions Geex? I have ridden quite a few different conversions and and also most of the types of fully built bikes.
The best of the conversions ride 99% as well as a steps or bosch and better than some of the full builds I have ridden. A crap cheapo conversion is crap. the key thing is torque sensing. thats the key factor for ridability IMO
The torque sensing and the like will help no doubt if you are into techy up hills and the like, still get on fine with the bafang though, the 9 assist levels, mean I just do manually torque setting and adjust the power to suit as I go.. But really, 95% for the time, you are just winching yourself uphill to get to the top, how sophisticated does that winch need to be is a question to ask yourself.
Ultimate point is if you’ve a decent hardtail kicking about, you can(usually, assuming motor and battery fit) convert it for much cheaper. Full sus is doable but harder.
If don’t have bike, just go out a buy an ebike, don’t do a conversion.
The advantage of torque sensing is you do not need to adjust anything or adapt your riding style. I agree that you can manually do it via assistance levels. Mine is used as a utility bike – its just nicer to have the power the motor puts out proportional to the effort you put in.
No you haven’t TJ
The “best” conversions do NOT ever ride as well as a well designed mid motor complete bike/frame.
You are not someone I’d ever listen to on advice about bike handling. and neither should anyone else.
you know fine why.
You shuld have a wee shot of mine. Nowt to do with handling – all about how the motor responds.
I did not say “well designed mid motor mounting” I said fully built bikes. Not the same thing
Have you ridden all possible conversion kits? Obviously not thus you cannot know how they ride.
I really think yo would be suprised by a ride on mine. the motor power delivery is 99% as good as a bosch or steps.
You shuld have a wee shot of mine. Nowt to do with handling
Please stop dishing out poor idiotic advice.hols2Free Member
Ignoring Geex and to go back to the OP
the best setup is a fully built bike with steps / bosch or a similar BB motor. Next best is a bb mount kit with torque sensing. Next best is a bb mount kit with cadence sensing. HUb motors are a poor relation altho the best of them torque sense as well – but if it ( as one fully built not kit bike I rode)_ has multiple chainrings it thows the torque sensing out. as yoiu have more torque on the smaller chainring
Hub motors are much easier to fit. Front wheel motors are not as good as rear wheel motors but are easier to fit
Finally – on a road bike a legal ebike kit or full build only really helps on hills.
That’s not ignoring me TJ.
You’ve followed my advice to the letter.
thanks for your cooperation
There was an article in the recent CTC mag about electric road bikes. What surprised me was that both the bikes on test had rear hub motors. Not sure why. Guess I’ve just got used to eMTBs which all seem to be BB systems.
I can see that BB mounted makes more sense for an MTB as you want to maximise the ratio of sprung to unsprung mass, but I guess it’s less clear on a road bike. The (claimed) advantage of the hub mounted option seemed to be that it was lighter (both the bikes were “light weight” eRoadBikes) and I think there might have been something about less drag with the motor off as well. I know the reviewer said something about them feeling like normal bikes with the motor off.
Anyway, hope that’s some help. As you were.
Yeah. but rear wheel drive means weight distribution becomes really poor which affects handling massively. Most road/commuter Ebikes are sold to folk like TJ who don’t really understand how to handle a bike well in the first place. nevermind the extent moving a load of weight to one end negetively affects it’s handling. 😉
Quite a few current mid motors have no drag and a few mid mounted systems are now a lot lighter. (at the expense of torque/power and range tho)
I recently bought a Trek Conduit from Rutland Cycling for £1299 (1/2 price) – id looked at Bafang and Tongsheng (torque sensing) mid drive conversions but the motor+battery+import duty etc+value of the bike to convert meant the Trek was pretty much a similar price but I ended up with better integration and a legal* bike.
*I chipped/hacked the software after a week as the 15.5mph limit is unworkable
So not legal so that argument is null
So not legal so that argument is null
It was legal as bought and the same legality as any other 250w/15,5mph conversion or bike. I think I was saying that as good as a conversion can be I dont think they can beat the integration of a full off the shelf system/bike. Conversions win on price compared to a bike unless you can get a decent discount on an ebike.
BB mount motors have two main advantages in terms of power delivery. firstly as they work thru the bikes gears the motor is kept spinning in a better speed range at low speed so gives its power more efficiently ( grinding a motor at low revs high power draws a lot of amps and overheats)and secondly if torque sensing then the torque sensor is not confused by the gears as it is with a rear wheel sensor
Awaits Geex telling me I am talking shite again.
The kits cannot beat a full build BB mount – but the best of them are within a whisker of being as good.
I’ll only tell you you’re talking shite when you ARE.
the only thing you’ve got wrong about decent mid drive units is the torque sensor works WITH the speed and cadence sensors and uses software to deliver smooth torque/power curves. cutting in and out more subtly than your shitty bolt on things. 😉
your whiskers must be a lot thicker than mine
Have you ridden a high quality mid drive conversion? almost indistinguishable from a step or bosch.
Now’s when I’ll be telling you you’re talking shite.
It was nice while it lasted
I guess your e-bike back in for warrenty again .
So Geex – have you ridden a high quality torque sensing conversion?campgarethFree Member
Tj, not to be antagonistic like geex but what high quality torque sensing mid drive do you have in mind? All the bafang ones I know of are cadence sensing (bbs02, bbshd) except their higher end Max series that only comes on prebuilt bikes since it needs frame modifications.
Mine is a sunstar so3- but no longer made as it was too expensive compared to a bosch / steps bike.
Tongsheng do one I believe and I think there are others but as its several years now since I did the research I am not sure of the names. There is also some stand alone torque sensors that can be added to some kits even mid mount bafengs I believe
Its a fast moving area of development and my knowledge may be out of datethatscoldFree Member
In the STW recommend what you got yourself I’d go for this Here For the road bike. The controller is built into the battery case so it makes for a neat conversion. 350W so not legal, but equally not crazy powerful. It will happily assist up hills or to 21-22 mph on the flat if you change the speed settings. If you don’t fit the throttle you can get away with not changing your brake too.
I wouldn’t use this for a mtb though. As others say you need a mid drive for that.
it wasn’t even on a par controlability/assist wise with a yamaha mid motor. which are neither smooth nor intuitive compared to an E8000. I certainly wouldn’t ever consider one for an Emtb.
You’re recomending I try motors you yourself haven’t even tried and admit to having little to no knowledge of so what exactly is your point?
So you haven’t actually ridden a torque sensing mid drive kit such as the one I have- much as I thought.
Caampgareth – I forgot the pendix which is a high quality BB mount torque sensing system. Perhaps the best available now https://pendix.com/
Geex – yes a bafeng is simply controlled and therefore not nearly as good as the full build bb mount type. But they are not a “quality torque sensing kit”
A Torque senser is IMO essential but it is only one part of what makes for good control. The software and how it uses the torque, cadence and speed data to deliver assistance is what really matters.
I’d be incredibly surprised if your “no longer made” system is anywhere near as controlled as a regularly updated and tweaked current system as fitted to complete emtbs.
eg E8000 or Brose S mag.
Can we see your bike please?
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