Can I alter my 2002 Ford Ranger's wheels and/or gearing for better fuel economy when cruising?

I own a 2002 Ford Ranger pick-up and use it for work and pleasure. I have noticed that on a motorway run, at 70mph it is running at just over 3,000rpm. I realise that it is a 4x4 and is therefore lower geared for better off-road performance, but I was wondering if I could do anything to lower the engine speed? I tow a 2-tonne trailer for work so was thinking that changing the gear ratios might not be a good idea. I was thinking about the possibility of doing something to the wheels. At the moment it is on 15-inch wheels with a 75-profile tyre and I wonder what difference it will make if I go up one or two inches and keep the 75 profiles? The main reason for doing this is to reduce engine speed and hopefully the fuel consumption too.

Asked on 22 October 2010 by OW, Gainsborough

Answered by Honest John
Don't do it. The vehicle is optimised to run at that final drive ratio. Driving at 60 instead of 70 would have a much more beneficial effect anyway. My own car is about 15 per cent more fuel-efficient at 60 than it is at 70.
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