The latest addition to the Eco Travel Network fleet is a specially commissioned ‘Rural Twizy’ whose name will be chosen via a competition at The Hay Festival next week. To cope with our rural environment and practical usage patterns, our rural prototype has the following modifications:
- Raised suspension
- Increased suspension travel
- Larger (external) diameter tyres with better grip for poor road and track surfaces
- Two heavy duty rear luggage racks
- Two fore-and-aft bike racks
These modifications were done by Red Castle Classics of Caerphilly, who specialise in classic car restoration.
The general consensus is that the Rural presents a much more “rugged” appearance than a normal Twizy, being significantly higher off the ground with much chunkier wheels. The modifications do not make much difference to driving. There is more tyre noise on smooth surfaces, but on rough ones the softer suspension reduces noise levels. The softer suspension allows it to lean slightly more but it still feels very “solid” and the low centre of gravity means that the Rural doesn’t roll any more than a regular Twizy.
The Twizy’s performance was not much affected by the modifications. Indeed, the Rural will actually go slightly faster flat out because the Twizy speed limiter has not been adjusted for the slightly larger diameter of the tyres. Acceleration from rest feels a little slower, as one would expect when more of the initial torque of moving from rest is taken up by the tyres. The Rural Twizy weighs 40 kilos more than a standard Twizy with doors, most of which is probably down to the tyres. As these are un-sprung weight and higher rotating mass, the additional energy will come at some cost in performance. The Twizy does not enjoy class-leading aerodynamics in standard form, so the additional air drag of the bike and luggage racks is unlikely to have a noticeable effect, and they certainly don’t add much to the wind noise, which is ever present in an open car. For the effect of the modifications on fuel consumption, see the separate section below.
The luggage racks are securely attached to the main Twizy chassis at 3 points either side of the vehicle, cross-braced to share the load and put it as far forward as possible. The bike rack feature is very impressive, enabling two bikes to be carried securely with their centres of gravity nearly level with the back axle, and within the narrow width of the car. These racks can be removed when not required.
Range and Fuel Consumption.
Since we can safely assume that the designers of the Twizy are competent, we expected the modifications to have a negative impact on range and fuel consumption. As far as we were able to measure, there is an overall loss of about 20% on projected range, but to put that in perspective we need to take into account what we normally achieve with a Twizy, and the tests we did, before judging what the effect would be in general use.
At this time of year when air temperatures are starting to move up to the optimum 20 degrees Celsius for a Twizy, we expect to achieve 50 to 53 miles on a full battery, though we very rarely travel that far without re-charging because we don’t have to. What we do normally, and did for these tests, is fully charge the battery, reset the “trip” odometer, do the trip, note the trip distance and estimated remaining range, then fully recharge the battery noting the watt-hours taken from the wall to do so. All consumption figures are therefore “wall to wheel”, rather than the usual (and obviously more favourable) “battery to wheel” figure that EV dashboards (though not, alas, the Twizy’s) typically display.
We did 4 runs in convoy with a regular door-ed ‘Urban Twizy’ – with similar miles “on the clock” as the Rural, following the same route at the same speed. We did 2 additional runs in the Rural Twizy with two people aboard, for which we have no comparable Urban Twizy figures on the same day, but one of these was identical to a previous convoy trip.
This is a very limited test, but the results were consistent and provide a guide to what anyone about what they might reasonably hope to achieve. Only one of the runs was conducted at maximum speed, because we don’t typically drive a Twizy at its maximum speed, and we don’t expect most of the Rural Twizy’s trips to done at top speed either.
Here is a summary of the results:
|Urban Twizy(1 person)||4||70||8040||115||52|
|Rural Twizy(1 person)||4||70||10160||146||42|
|Rural Twizy(2 people)||2||29||4570||158||41|
So the Rural Twizy’s range (for us) is about 80% of the range we would expect in an equivalent standard Urban Twizy, and he therefore uses about 25% more energy for the same distance. There are Twizy owners who choose, or are obliged, to drive their Twizys much faster than we do, who typically show the same consumption figures as the Rural does for us. We would expect that they, too, would see a 20% reduction in range, say from 40 miles to 32 miles, but we obviously haven’t done enough testing to know how speed sensitive the reduction in range is.
We also tried a couple of runs with 20kg of luggage (bike plus bags) loaded on the rear of the Rural Twizy. One of these runs involved a long steep climb. We found that the added luggage weight only made a small difference of about 3% in fuel consumption, which is probably less than the error in our somewhat crude measurement.
Only once during our 4 convoy trips was the Rural “ahead” of the Urban on its own estimate of remaining battery (though these are notoriously volatile!). This was after a lengthy sequence of ups and downs followed by a longer descent. It would be interesting to know whether the Rural Twizy’s softer tyres and greater weight are improving power regeneration. They explain its slightly slower acceleration from rest.