I still haven't got round to testing the idea - the chain I have just keeps on going - but I did find the reply from RichLees that gave me the idea in the first place. I might do a bit of further research into this.

Originally posted by RichLees:
"a guy in the tuning department at Rover once told me that you get the best mpg by operating at the revs that would give peak torque on full throttle. so, gearing to run at lower rpm means less efficiency from slower turning engine and, hence, potentially worse mpg. ie I don't agree with gearing up for lower fuel burn and I agree it can put more load and hence wear on the chain. my xrl chugs at below 100kmh in top and so I usually change down to cruise at 90kmh. even then, I only get 62mpg and I used to get 65mpg when being gentle with my ZX9"

I've conducted a few long term 'experiments' with my AT on standard gearing, and these confirm that a) throttle opening has a major affect on fuel economy; b) riding in fourth rather than fifth gear at a constant low throttle opening has a greater affect on fuel economy than throttle opening in fifth alone; c) head winds (around 5-10 mph, sometimes oblique rather than directly head on)decrease economy by around 10% with a constant throttle opening. It's possible that Iain is right about set throttle/variable speed versus set speed/variable throttle are equal, but my data are not detailed enough to be able to tell (piss poor for a scientist, but there you are!).

Riding in fourth rather than fifth (only for a third of my morning journey) suggested that the economy drop would be greater than 10%, but fourth is a lot lower than fifth (much more than the minor gearing revision I have in mind), and the distance I tested this along with the relative lack of wind (and hills) on the day I tried it mean these data are inconclusive.

In reality I suspect the change with only a single tooth added to the back will not make enough of a difference, and it's all probably down to individual preferences. I just like to fiddle....

Stig

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