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Old 07-10-2016, 11:11 AM   #1 (permalink)
SDMCF
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Speed limiter helps fuel economy?

I have had a couple of Mercedes where the cruise control can be used as a speed limiter, so that you drive normally, controlling speed as you require, but the car will not exceed whatever speed you have pre-set. I rarely used that feature but just recently I started using it consistently and was surprised to find that it seemed to help with fuel economy. Possibly without it I inadvertently exceed the maximum speed at which I wish to travel, but I wouldn't have thought I do that often. The only other explanation I can think of is that driving a little faster down hills, which I often do, actually uses more fuel rather than (as I would expect) saving fuel by using gravity to my advantage. I would find that surprising if it were true, partly because of the logic and partly because I don't encounter large hills in my area.

I should perhaps point out that this was in a car with an automatic transmission in which I was not happy using EOC so my technique was more DWL rather than P&G.

Has anyone else noticed this? Or indeed tried a speed limiter without seeing this effect?

Unfortunately I have just changed cars and the replacement does not have a speed limiter so I am unable to perform tests to verify/quantify the effect.

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