Vivax Assist versus Bosch 45kmh drive

[MEJ]

Hello,
My current e-bike is a self build having purchased just the frame only with its 200watt motor factory fitted into the seat tube providing a direct drive to the bottom bracket. Powered by a 30 volt 5.5Ah lithium Ion battery. The system is the derestricted version for off road use.
The system is called The Vivax Assist made by Gruber in Austria.

The system is built into a standard road bike frame made by Steinbach and I've built it up to be a light weight hybrid.

For the last 3 months i've been riding the bike with a power meter to measure my own pedal power input.
My standard commute to work is 20 miles hilly and with assistance from the motor I can average 22mph which requires a demanding effort from myself - actually my own average power output is 260watts in order to achieve this average speed.

This system is outstanding and i'm very impressed but is there another system out there that would give me a higher average speed for the same rider input on the pedals?
I want to reduce my commuting time but still want a challenging ride to maintain fitness.
I live in the quiet area of Pembrokeshire and my commute times are outside of peak traffic times and down quiet country lanes.

I was looking at a Bosch crank drive 350watt / 45km/hr version - like the Haibike Trekking S.

Any thought would be gratefully appreciated.

 

[Drunkskunk]

I haven't had a chance to ride either of those bikes, but on paper, the Bosch system is better. However, based on what you describe I'd suspect there is an issue with your bike, and it may perform better once that is addressed.

If you are supplying 260 watts at 22mph, i suspect you have achieved a speed where the motor is no longer giving any assistance. A normal road bike will need around ~250 watts at 22mph from the rider. Do you know how much power you use at 22 without the motor's assist?

Is it possible you have a dragging brake? perhaps a drive line issue? Really baggy clothing into a hard headwind? Is it possible you are pedaling in a non optimum cadence for the motor? Too slow or too fast of a cadence will be out of the motor's optimum range and it will give less assist.

 

[Willow]

...nice little left-hander in the background. What temp. is the water??

 

[MEJ]

Hi Drunkskunk

Yes you are correct there, riding on the flat without power assist then my own power is approx. 250watts @ 22mph.
I only use the power assist on the hills with a low gear selected. ( compact chainset 50/34T with Ultegra 12/27T cassette)
The power assist works by me setting a cadence level and if I dip below this value then the motor will assist to maintain the set point cadence up to a point of its maximum power output.
The assist seems to work best at approx. 80rpm in a low gear. The maximum cadence set point is 90rpm so when i'm climbing and my own cadence dwindles then the motor assists up to a point when my cadence is back at 90RPM in the same gear. If the hill steepens then I change to lower gear and the process repeats. When i'm going up a really steep hill and i'm in my lowest gear of 34T X 27T and i'm totally fatigued so cannot even maintain 60rpm with the motor on then the assist is not as effective in that range.

The system seems to assist better in low gear combinations of 80-90 RPM i.e using the small chainring and half the upper block on the rear.
On the flat doing about 22MPH using the big ring and the lower block sprockets then the assist doesn't feel as effective even though my cadence is just under 90RPM.

Regarding chainline, the chainset was factory fitted by Gruber and I've got a Mavic Ksyrium rear with Ultegra cassette. Rear drop out spacing is 130mm and I also maintain a good chainline when selecting my gears.
My handicaps on the bike would be my own weight - 180pounds, the fact I have to carry a loaded rucksack to work i.e lunchbox, puncture repair kit, pump and helmet light battery. I wear close fitting clothe i.e bib tights and cycling jersey.

cheers