Motoring: With a battery made for one: Rosemary Harbert tries out the Zeta, a power pack that fits on to pedal cycles

I give Sinclair Research eight and a half out of 10 for its Zeta, the battery- powered pack that drives the rear wheel of a bicycle.

A weak ankle prevents me from walking any great distance and I rely on my bicycle for shopping and rides around the countryside. Under my own power I can travel miles until I come to a hill. Then, if I dismount and push, my ankle causes problems. The Zeta appeared to offer the answer.

It arrived on the day promised. Fitting it on my bike presented some difficulty when I tried to line it up to get the drive wheel and belt to run on the centre of the tyre. There were no adjustments on the Zeta's bracket to aid alignment, and eventually I had to fix the bracket to my cycle frame a bit lower on one side.

I then went out and enjoyed the delights of power-assisted cycling, with a motor that can be switched on and off from the handlebar. On the flat, you don't need to pedal - the Zeta will take you along at about 15mph. On hills you need to pedal, but with the Zeta I took them in my stride. Riding downhill, however, presented a bit of a quandary. If I released the Zeta switch, the motor whirred alarmingly. The alternative was to leave the Zeta on and apply the brakes, which seemed a waste of power. After a few joyful trips I began suffering from a sore thumb caused by holding down the Zeta switch. My solution was to reposition the switch so that it could be operated with the ball of my hand.

More excursions have followed. I accept that the Zeta is an aid to cycling and have continued to provide input through the pedals. I sail up an average hill with a regal air, but long, steep hills have me puffing and blowing as I endeavour to prevent the motor from stalling. One solution is to stop every 100 yards and admire the view. The problem then arises as to how to remount elegantly and pull away without putting undue strain on the unit and my gammy ankle. The alternative is to walk, with the cycle on Zeta power. But to keep up with the contraption I have to run up all the steep gradients, and I arrive at the top puffing as much as if I had cycled.

There are several features I would like to see on the Zeta. On flat journeys I usually raise the Zeta off the rear tyre (using the a strap clipped to the saddle) and proceed under my own steam. However, when the riding gets difficult it is tiresome to have to dismount to release the strap. I want to be able to re-engage on the hoof. And when cycling with the Zeta turned off, it would be useful to have the battery lower on the cycle. There should also be an indicator to show the charge state of the battery. If I use then Zeta for 30 minutes, then I recharge for eight times that period (ie, for four hours). Only time will tell if this is correct. Just as automatic kettles switch off when water boils, so I want a battery charger that switches off when the battery is fully charged.

Zeta has improved my life. I now cycle where I would not have gone before. And I will know in about 12 months if the unit has stood the test of time and was a sound investment.

The Zeta costs pounds 144.95 (incl p & p) from Vector Services Ltd, 13 Denington Road, Wellingborough, Northamptonshire NN8 2RL (0933 279300).

(Photograph omitted)