Massive momentum ;-)

[Dave_h34]

Hi all, nice forum you have here.

So, all about me: reasonably keen cyclist, big bloke (100kg), reasonable fitness, lots of downhill and flat speed, struggle when it comes to the hills (Sheffield/Peaks). I presently commute to work twice a week, 15 miles each way, 250m of climbing on the way in, probably double that on the way back (safer route), takes me about an hour in and 1hr15 back on my slick shod 29er mountain bike (Pinnacle Ramin One with hydraulic disc brakes).

The plan? Well being an engineer I do love a good project and I wonder whether I could add an ebike conversion to get my commute time down a bit by filling in the 'speed dips'. I'm not looking to expend less energy on the commute, just reduce the time somewhat and also reduce the speed differential between myself and the traffic - more power, more speed!

Is a ebike going to do this for me?

I've had a bit of a poke about, read the basics and understand the legal stuff. I'd be looking at converting the Ramin, and the one thats really caught my eye is the Bafang BBS02 750W. I guess it'd have plenty of poke but is it expecting too much for it to haul up 110kg Sheffield's hills (mainly I'd say 5-7% grade but up to 20% in short bursts)? Will a 10-13Ah battery cope? Would a lower power unit be more sensible?

Thanks

 

[Kinninvie]

I think the BBS02 would be perfect for the job.
I have one and the hills here in Teesdale are similar to yours(but a lot nicer of course).
I currently have a 10Ah battery and get 30 miles range out of it and that includes quite a few hills and is fitted to an MTB with knobblies on so would suggest a 13Ah battery would be better for you as it will give you a bit of reserve for windy days etc.
I am 110Kg.
I have just got a pair of 16Ah LiPos for mine and will be testing the range with them in the next few days.

 

[RobF]

Your desire to increase speed rather than reduce effort could be a problem.

You are already averaging 15mph, and would need to up that by several mph to produce any worthwhile time saving.

Ebikes in general are not built for road speed.

Banging on a high power motor might give you the grunt you need, but does the bike have the gearing for 25/30mph?

At that speed you will slurping power like there's no tomorrow.

Twenty ah is a lot of battery weight, 10ah charged at both ends might make a better sprinter bike.

 

[Dave_h34]

Thanks for the thoughts and comments guys. Present bike has 32-11 top gear (very low for road but I like the single chainring simplicity) and I can punt it along at 23mph ish Max, I'm more worried about the gearing going low enough than high enough on the bbs02. I guess my average speed is OK but I can drop down to 10mph or even 5mph on the steep hills. If assist could pull me back to 15mph then I'd be very happy!

 

[Deleted member 4366]

The BBS02 should do it OK; however, that puts a lot of strain on the gears and chain. If you're going to commute every day on it, carry a spare chain.

IMHO a hub-motor is better for commuting, and crank drives are better for sporting stuff. You have to use the gears a lot more on a crank drive, which can be tedious when you have cold hands in the winter. A nice Bafang BPM or CST or an Ezee motor will waft you along effortlessly.

I used to commute 15 miles each way with a BPM motor. It wasn't too hilly except for one 2 mile 10% climb on the return. I used to use about 12ah on a bad day putting in a reasonable effort myself. As you already do it without power, your legs must be a lot stronger than mine, so I reckon you should be alright with a 13ah battery, which is about as high as the nice frame-mounted ones go.

If you want plug and play, the Oxydrive and Ezee kits are quite good. The Oxygen one is perhaps a bit more modern and faster. , but if you go too fast, you'll use up your battery more quickly. There's bigger battery options with the Ezee kits. There's also the Woosh BPM kit about the same speed as the Ezee, but a bit cheaper and limited battery options. Alternatively, you can mix and match all the stuff by buying it direct from China, which will give you whatever speed, power and range you want relatively cheaply, but with a bit more DIY involved.

 

[Artstu]

I'd also avoid your chosen crank-drive and go with a hub motor.
Don't worry about needing low gears either. Whilst not a direct comparison my 250w Bosch bike goes up hills at twice the speed I go up hills on a entry level racing bike, and time and again on this forum the Bosch motor for hub gears has been described as a poor hill climber.

 

[RobF]

The gearing on your bike sounds OK, and I'm sure you and one of the motors mentioned will be able to get up hills much faster.

A hub motor is probably best for the reasons outlined by d8 upthread.

They tend to be quieter, only downside can be wheel removal for a puncture, but you can engineer that when you build.

Installing the motor in the front gives better balance, handling, and all but eliminates the chances of a broken spoke.

The motor/controller will have to run in derestricted mode.

Going too fast on the flat invites unwanted attention.

On the same gearing you will still spin out at 23mph, which is no bad thing.

Time will be gained on the hills, accelerating up to speed, and doing that speed for longer stretches than you do at present.

 

[derf]

I'd also avoid your chosen crank-drive and go with a hub motor.
Don't worry about needing low gears either. Whilst not a direct comparison my 250w Bosch bike goes up hills at twice the speed I go up hills on a entry level racing bike, and time and again on this forum the Bosch motor for hub gears has been described as a poor hill climber.

I second that, I finished a bpm build a week ago and it is much more relaxing than crank drives (hard to describe, it has more in common with surfing than running would be one way to put it), also cheaper (bpm2 with controller from BMS around £200, if you add 2 16 Ah lipos from hobbyking another £160, really easy to build, even I could do it)

 

[Dave_h34]

Hmm, interesting points. The mid drive thinking was owing to comments about them being more suitable for hills. Good point about the speed/attention thing. I was thinking on my way back this evening that it might be better to limit top speed to save juice for hill assist. More research to be done! This is today's commute, plenty of time at higher speed but also a fair bit at low speed. Do you think the hills would be asking too much of an ebike?

 

[D8ve]

You should have no problems with the hill climb. On a legal restricted bike I road up the hills in bath when I would struggle to cycle them.
Join the electric bike group on strava to see others performance.
Ignore me though 100 kg 50+ on an unpowered recumbent.

 

[Dave_h34]

Do all pedal assists require a square taper bottom bracket? I haven't had one of those for years! That could be a show stopper for my hollowtech II equiped bike.

 

[trex]

no. If you convert with a BBS01, the motor replaces your bottom bracket. If you convert using a BPM, you can cut out the centre of the magnet ring and araldite it to the smallest ring.

Other solution:
stick magnets into the four ring bolts

ready made ring:

 

[Deleted member 4366]

Do all pedal assists require a square taper bottom bracket? I haven't had one of those for years! That could be a show stopper for my hollowtech II equiped bike.

No. Hollowtech are dead easy. Octalink can be done, but it'd not so straight forward.

 

[Dave_h34]

Ah, very good.
It's ages since I've been such a noob on a forum asking newbie questions! And no one has said 'do a search!' yet, very friendly!

 

[Spotty dog]

Have just fitted a BBS 01 to my bike I used an inward dished 42t chainring to improve chainline. I still think 1st and 2nd gear are not really usable due to chain angle add to that the power of a BBS 02 put thru chain and I can't see it or the cassette lasting very long so im going for hub gears instead.
I almost went for a BBS 02 but it is clearly stamped 750w on the underside of motor so did think if im stopped or involved in an accident as far as police are concerned it is a motobike.
I have the 250w unit it assists quite well on hills I struggled to get up, with moderate input from me it goes up at 10mph.
I,ve ordered a 350w controller for it will boost it from 15 to 18amps, when guarantee expires on motor it will be fitted.Will give a boost in power and I still have a motor with 250w stamped on the casing .

 

[Geebee]

Hmm, interesting points. The mid drive thinking was owing to comments about them being more suitable for hills. Good point about the speed/attention thing. I was thinking on my way back this evening that it might be better to limit top speed to save juice for hill assist. More research to be done! This is today's commute, plenty of time at higher speed but also a fair bit at low speed. Do you think the hills would be asking too much of an ebike?

I doubt the BBS02 would break a sweat climbing that hill it averages out to a bit under 10% grade, even a legal hub would help a lot on that.
The below is from endless shpere from a rider on my local mountain, he runs a BBS02 750w.

"Tom L wrote:I made it up the mountain no fuss. Started at about 450m and rode to 1271m over a distance of 11km. Trip time was 27 minutes.Just so you know: the record (starting from 96m) is 59mins

So 27mins is impressive!"

 

[Deleted member 4366]

The problem with those sort of results is that there's no context for them. How heavy was the rider? How hard was he pedalling? the only meaningful data is when somebody compares two different products like what Kinninvie showed. We need more like that.

 

[Artstu]

A better comparison would be with his unassisted time up the hill. I'd have thought some of these powerful bikes must be in excess of three times faster than unassisted.

 

[Geebee]

A bit more data.
"I was in 5th most of the way for the first half, then dropped back to 4th, 3rd and even 2nd for some of the steeper bits higher up. I was spinning about 80 RPM which I find comfortable. Yep this is the 750W kit from LC.

Edit: Regarding efficiency. I just calculated that it takes a theoretical 265Wh to raise my and my bike's combined weight that height (potential energy equation). I really dont think I was outputting more than 100W continuously, so for 27 minutes that's an extra 45Wh for a total of 295Wh used. Which works out at about 90% efficient. This drops to 80% if I was outputting 150W. Obviously with no way to measure my output this is only a very rough guess."

The ride starts at the bottom of the page, the one with the senic photo.
http://endless-sphere.com/forums/viewtopic.php?f=28&t=50104&hilit=mt+wellington&start=1000

 

[Deleted member 4366]

The motor itself is only 80% efficient. Add losses from the transmission and controller, and you'd be closer to 70% at that the back wheel. That's only achievable over a very narrow rpm range, which you're unlikely to be able to hold during real world pedalling. I'd estimate that most of us would achieve about 60 - 65% efficiency overall.

That cadence of 80 is very high. It's maybe typical of a sporting cyclist. Most of us non-sporting types have a cadence of about 60 to 65.