Gruber testing

[trickletreat]

As some of you know we had a gruber assist fitted to my wife's Trekwsd6300 by Steve at Electricmountainbikes.com.

In order to condition the battery, it is advised to flatten and recharge several times. I flattened it on Friday and recharged ready to do a few laps of our local 1km cycle track. The battery has five lights, 20%,40%,60%,80% and100%...the battery now cuts out with just the 20% light showing, so further conditioning may increase the available capacity. The battery details are RKB-Li-ion Akku 29,6V 6,75Ah.

The track is 1km in a figure 8, with a longer uphill and downhill section and shorter up and down sections. The longer bits are exposed to the wind and the shorter sections are sheltered. This Sunday I experienced quite a headwind on the longer downhill section. I am 79kgs and the bike/motor/battery/rack etc is 17kgs.

I cycled to the track without assistance to warm up, once there I did a timed unassisted lap with moderate effort, leaving me slightly out of breath...time was 2min 15 sec...approx 16.6mph.

The next lap I used the Gruber assist, and by using the gears kept the assist at max assist...I was breathing normally at the end...time was 1min 40sec...approx 22.4mph.

I then continued at max assist and constant low effort from me to test the range of the battery.

I did 32km/20miles in 53mins....22.6mph

The battery at this stage had lost two lights, the 100% and 80%.

I continued at the same level..

The battery cut out at 43km 26.7miles in 1hr 13mins...21.9mph.

I was still breathing without breathlessness. I rode a final unassisted lap with moderate effort, it took me 2min 20 sec.

As I stated, I constantly changed gear to use max assist from the motor. I was very impressed with the range under these conditions, coupled with the use we gave it in the Alps, I believe this battery would last all day, if used only when a bit of help was needed.

Nigel

 

[daniel.weck]

Impressive ! Do you have photos of the battery ? What chemistry is it ? (Li Po ?)
Cheers, Dan

 

[trickletreat]

Hi Dan, It is Li-ion.

nigel

 

[OTH]

...I constantly changed gear to use max assist from the motor. ....

Nigel

Can you explain this, please? How does the assistance vary depending on what gear you are in?

 

[trickletreat]

Can you explain this, please? How does the assistance vary depending on what gear you are in?

I will try

When setting the cadence rpm, you have to hold the red on button and pedal at the desired cadence between 60 and 90 rpm. This then acts as the default setting when the assist button is pressed.

While pedalling at a comfortable rate press the button, now if you are in too low a gear, the motor does not kick in; so select a higher gear{harder to pedal} and the motor starts to help. Select a yet harder gear, more assist.

There is a spread of about 5 gears [rear cassette] where the motor operates, the sound of the motor changes from a squeal, in too low a gear, to a hum, in the highest gear.

So as in normal cycling, you change up or down depending on the terrain,using the gear shifter as a power selector.

In effect, when pedalling, you find a comfortable cadence, without to much pressure on the pedals.

As there is no restriction on this setup[ unless requested] it allows you to get assistance in your highest gear, riding down hill.

An onlooker [cyclist], was surprised at the speed I passed him downhill, at such a low cadence, if that makes sense.

If you look back to my timed laps, unassisted and assisted, the difference to me was two fold. Unassisted, I was on the middle front chainring, high cadence, so as to reduce pedal pressure, but breathing harder at the end of the lap. While assisted, the chain was on the large front ring and a higher gear on the cassette. But with the same pedal pressure, resulting in a lower cadence, me not out of breath, and travelling much faster.

Nigel

 

[OTH]

Many thanks.

I'm still not sure if this would suit me. I don't necessarily want to go faster, but I do want to achieve high assistance when going uphill. Presumably, an increasing gradient acts in the same way as changing up a gear - to increase assistance.

 

[trickletreat]

Many thanks.

I'm still not sure if this would suit me. I don't necessarily want to go faster, but I do want to achieve high assistance when going uphill. Presumably, an increasing gradient acts in the same way as changing up a gear - to increase assistance.

Yes I understand. I used this in the Alps recently, on some steep and long gradients, thinking I could quickly flatten the battery for conditioning. I did not cycle fast and was at the opposite end of the gear range to the test I did at the track i.e small front ring at the front and the largest two at the rear. I found that I was cycling just fast enough to keep balance, but again with light pedal pressure and low rpm, hence I was not out of breath after doing it for an hour.

It's not about going faster, just the speed you would 'normally' ride at, but with a lot less effort..also then extends the battery life. The track test was the opposite in a way, as I exceeded my riding speed by constantly using the assist by changing up a few gears. You should give one a mornings test, where are you based, I am in Solihull.

 

[daniel.weck]

Oh I see. The website says Lithium Manganese (30V 6.75Ah, 1kg battery pack)

Gruber Antrieb - Gruber Assist - Fahrradantriebe » technology

 

[OTH]

Thanks again.

... cycling just fast enough to keep balance, but again with light pedal pressure and low rpm, hence I was not out of breath ...

Just what I need for the hills here - near Exeter. Unfortunately, rather far for a quick trip to Solihull.

I'm very tempted, as the system is so light and neat. But not cheap.

More medical tests due in two weeks. The results may influence my choice, so will continue weighing up the options until then.