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Old 01-02-2020, 07:47 AM   #6 (permalink)
EcoModding Lurker
Join Date: Dec 2019
Location: Switzerland
Posts: 53
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Hi everyone, and happy new year!

During the holidays, did some coastdown testings on a 750m long stretch road. Online DEM shows it flat (max 0.1m elevation difference).

First had to calibrate my speedometer with a GPS which showed it was 5% too optimistic.
Then coasted down two times each way from 80km/h to around 50km/h and filming the speedometer.
In order to have some comparisons, I did the same test again with the passenger mirror folded.

I think my biggest error would be in the weight estimation, otherwise I've had my air density values checked by a real engineer and corrected with local absolute pressure (QFE) and temperature.

I am getting the following values :
0.606m2 for CdA stock
0.587m2 with passenger mirror folded (which means I would save about 0.08l/100km at 120km/h (73mph))

0.0112 for tyre rolling resistance. Not that bad since they are winter tyres (Continental TS860) but the smallest size possible (195/65/15).

This seems quite good as I get only 2.3% difference between the stock experimentally determined value of 0.606m2 and the initially calculated value of 0.593m2.

Otherwise for the time being my fuel efficiency has been worse, about 5l/100km (47mpg us) but I haven't done any long trip (max 70km) and it has been mostly mountain driving to ski resorts, which can not be good with a 1300kg car.
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