Advice on building an electric bike for velodrome pacing

[George Holland]

Hello there

I hope someone can help with some advice. I ride on the velodrome and we use pacing motorbikes for training, called Dernys. I want to build a simple electric version so that I can pace my younger sister. It is strictly off road usage, completely flat and with little acceleration and deceleration required.

I need to be able to top out at 45mph and this could use some pedal assistance but this will only be for a max of 10 seconds.

Most of the time it will chug along at 20-30mph and would need to last about 1-2 hours at this pace.

I like the idea of a front wheel drive as I can keep the rear fixed single speed and pedal for some extra power. It will be mounted onto a rigid steel mountain bike frame circa early 1990s

Could someone recommend a reasonable quality kit for about £600 that would do this or is that just fantasy?

Would 500watts direct drive do this with pedal assist, 48v 10Ah battery and such like?

Cheers!

G

 

[Deleted member 4366]

20 to 30 mph is feasible, but not for one to two hours for £600. $5 mph for £600 is fantasy I'm afraid.

30 mph takes 1000w. At that speed, any help from you is insignificant. You'll be using, therefore, 1000wh per hour. A 1000wh battery costs about £600.

 

[clanky]

Hello there

I hope someone can help with some advice. I ride on the velodrome and we use pacing motorbikes for training, called Dernys. I want to build a simple electric version so that I can pace my younger sister. It is strictly off road usage, completely flat and with little acceleration and deceleration required.

I need to be able to top out at 45mph and this could use some pedal assistance but this will only be for a max of 10 seconds.

Most of the time it will chug along at 20-30mph and would need to last about 1-2 hours at this pace.

I like the idea of a front wheel drive as I can keep the rear fixed single speed and pedal for some extra power. It will be mounted onto a rigid steel mountain bike frame circa early 1990s

Could someone recommend a reasonable quality kit for about £600 that would do this or is that just fantasy?

Would 500watts direct drive do this with pedal assist, 48v 10Ah battery and such like?

Cheers!

G

Hi George,

The bike I built is not far off your spec and price range (1000W with a 15 amp hour battery), have a look at my post and you'll see some pictures. I think if I put slick & high pressure road tyres on my spec'd bike you could get around 40 mph with a fair bit of peddle assist (if you have the fitness). The big downside of a mountain bike frame is that the wind resistance is massive, when I ride off-road I really feel the difference when I put myself in low position. I went for a budget build using Chinese parts, it's holding up well so far after several trail rides but I can't imagine it will be as good as the higher end gear long term. As for front wheel drive, I don't think it will be a problem for you as you won't be worried about quick steering. Front wheel kits are cheaper too. I guess if you built it and didn't get on with it there would be plenty of people happy to buy the used parts. If you need a battery PM me and I let you now the supplier I used in China. Clanky

 

[trex]

George, the velodrome presents very little difficulty for the bike, I think you only need about 500W constant power for 30mph. Another thing you'll need is a high gear ratio, about 140 gear inches.
a BBS02 running at 48V will provide you with 500W-750W constant power, 700C wheel, Nexus 7/8/11 gear (the Nexus has 21T rear sprocket) and 72T chainring with BCD adapter will complete the kit.

 

[Deleted member 4366]

As for front wheel drive, I don't think it will be a problem for you as you won't be worried about quick steering.

Be careful what you say. Do you have any experience with front wheel installations? 350W is about the max that you can safely install in front forks, which will hardly get you past 20mph.

You need very strong steel forks for anything over 20mph. I'd be surprised if you could make a successful installation of any front motor that can do 40 mph.

 

[Kinninvie]

I have a 1000W Dillenger front wheel kit mounted on a cheapie Halfords Trax MTB and it runs happily at around 27mph.
With a 10Ah battery it will last for 11 miles on full throttle without pedalling on the flat on a calm day.
That means the battery is flat after 25 minutes!!

 

[clanky]

I have a 1000W Dillenger front wheel kit mounted on a cheapie Halfords Trax MTB and it runs happily at around 27mph.
With a 10Ah battery it will last for 11 miles on full throttle without pedalling on the flat on a calm day.
That means the battery is flat after 25 minutes!!

Hi Kinninvie, your experience is similar to mine, from 15 Ah I get an hour of trail riding with a bit of pedal input - the surface conditions make a big difference though. It was beautiful riding conditions in the woods first thing this morning! I guess for velodrome riding you could design a bike for a quick battery swap over. How do you find the steering on your bike? I considered getting a front drive like yours but worried it would affect the steering to much.