Trip Computer

[Guest j_mchattie]

Its in my interest to drive efficiently, and im looking to install a trip computer.

However, the mondeo fuel gauge is pretty erratic - is there an upgrade for it?

 

Or better still, are there figure from ford mph by mph? We are all told that 56mph is best speed - but then again, the printed figures only cover 56 and 75mph!

 

There is of course a best speed to drive at, but i cant seem to find it anywhere.

 

Any help please?

 

Thanks

 

James

[Guest vitrocmax]

As far as I understand the figures, the 56 and 75 relate to equivalents of 90 and 120 KPH, and are used to show the effect that speed has: it makes your mpg worse! :lol:

 

The best speed for efficiency is supposed to be the speed that comes with maximum torque, so if you do 25 mph/1000 rpm and the peak torque is at 3000 rpm, then maximum mpg should be somewhere around 75 mph. So the theory bit doesn't fit. :rolleyes:

 

Anyone else got some ideas?

[Guest j_mchattie]

I too have read that somewhere else, and it seems that this theory would be correct if trying to accelerate with best efficiancy, as this is when the engine gives out the most power as a trade off against fuel usage.

 

However, once at the most efficiant speed, maximum torque will not be the 'maintenance' engine output - it will keep accelerating the car past the speed limit.

 

So the max torque thing may be the best way to accelerate, but not to cruise at.

 

Im emailed ford, i want figures!

 

Thanks for your help

[johnb80]

But surely even when cruising the max torque RPM means that even at reduced levels i.e. throttled back the engine is producing most power with least fuel and thus at the optimum mpg point?

[Guest j_mchattie]

Im still waiting for figures from ford, i doubt if ill ever get them.

 

But once at crusing speed, its unessacery to have the engine turning over at max torque speed. If for instance 2000 rpm is enough output, then using 4000 will only double fuel consumption as the engine is kicking over twice as often. Sure, it wont actually be double, but it will be more.

 

Accelerating at max torqure surely means hard acceleration (as the revs are so high). But the AA say that gentle acceleration and reading to road ahead to keep a constant speed give best fuel economy, not sudden speed changes.

 

I cant see how having high revs and pushing the engine to run hard and fast to accelerate can save fuel (or tyres!). The AA think not.

 

I may fit a Trip Computer to my LX and make a graph......

 

Thanks for your comments

 

James

[johnb80]

I didn't explain my point very well and for my sins I drive a TDi Galaxy which produces it's maximum torque (330Nm) at only 1800 rpm so I get to use it regularly! The engine itself is going to be at it's peak efficiency at around it's maximum torque figure BUT aerodynamics also come into play to a greater extent as the speed increases which will cloud the issue somewhat. It's very noticeable on the Galaxy that if you devioate either side of 1800 rpm that fuel consumption suffers, I did a recent trip to Sandown Racecourse from Gainsborough, Lincs. In one direction steady 70 on the motorway, cruise set and used to accelerate back to 70 after roundabouts gave a fuel consumption of 44.9mpg On the return journey staying at a very boring 55 mph (1800 rpm) gave an incredible 54.7 mpg.

 

Regards - JB

[Guest j_mchattie]

I see. I often do a 125 mile drive from Coventry to South London, and at 56mph it can use around

[johnb80]

Don't walk, get civilised, get a diesel !!!