I believe one of the advanced driver people said that drag (?) doubles from 60-70mph and doubles again from 70-85mph' date=' which means that they will be quite a big difference in economy between those speeds. However it can't be that important to them as I've never met an advanced driver who drives at 60mph where it is safe (and legal) to travel faster

Chris[/quote']

That can't be right! Surely drag increases quicker as speed builds (ie. doubles from 40 - 60, then from 60-75 and then again from 75-85ish, and so on...). I think you'll find the most efficient speed is somewhere between 50 and 60mph.

That can't be right! Surely drag increases quicker as speed builds (ie. doubles from 40 - 60, then from 60-75 and then again from 75-85ish, and so on...). I think you'll find the most efficient speed is somewhere between 50 and 60mph.

Quite possibly, but the point he was making was that if you travel at 70mph it'll be noticeablymore economical than driving at 85mph.

Chris

Yep agreed.

Yep agreed.

But you will arrive everywhere late!

Chris

That can't be right! Surely drag increases quicker as speed builds (ie. doubles from 40 - 60, then from 60-75 and then again from 75-85ish, and so on...). I think you'll find the most efficient speed is somewhere between 50 and 60mph.

I wouldnt have thought the increase in drag would be truely exponential as you suggest. Aerodynamic effects can make sudden changes in drag at given speeds - look at the problems Audi had with early TT's loosing it suddenly as the air flow changed over the rear of the car. The area behind the cra can accomodate a certain ammount of turbulence before it has any effect on drag.

I doubt that the Fabia spent a lot of time in the wind tunnel when Skoda's engineers were developing it, the aero features ar emor elikely there to reduce wind noise and/or make the thing look sporty.

Frontal wind resistance is a big factor too.

i worried as well irf but im still getting what you get after 14.5k. Not a noticeable difference between 70 and 85 on the 315 to cranwell, like 4mpg.

on way home from work though i average 22mpg. thats cos theres a small gap of time between me finishing work in one pub and the pub at home closing

oh dear me. im a jakey in the making

Re The air con having an effect on MPG I'm sure I read on here that the compressor for the aircon runs all the time in the fabia? I read that after I sold mine - but I seem to remember that it did not make any impression on speed as turning aircon on can do in some cars.

When I turn the air-con on, you can feel the effect it has on the acceleration when moving off in 1st. Through the gears it seems to have a slight effect too. I thought this was normal?

Yeah, the compressor might or might not be running but something electrical kicks in for sure - watch the rev counter on idle as you turn on the a/c - the engine speed momentarily drops as the load increases.

The compressor is always running, however, it's only running at full pelt when the air con is on. FWIW, I don't really notice a big drop in mpg (1-2mpg at most) when the air con is on and I'd rather be cool and comfortable than economical in this weather

Chris

There is a safety issue when using very tall gears for the speed in that there is no engine responsiveness if you need to avoid a potentially dangerous situation.

In my 5sp I use 4th at 30mph, 4th at 40mph and 5th from about 45mph upwards.

I can get very high mpg figures at 65mph on the motorway, but get about 45mpg around town with the a/c on at the moment, about 55mpg out and about in the country lanes. Would be higher on A-roads but I rarely use them for my job as it's usually obscure places at the end of 20 mile single track roads I have to visit lol.

If the Fabia vRS had spent ANY time in the windtunnel they would have noticed it is shaped like a brick

Depending on how well I stick to NSL (aircon always on, FMIC, propane & hybrid turbo with a mild remap at the moment) I get fuel economy between 30mpg (crazy driving) and 55 mpg (granny driving). Mostly it's 40+ mpg quite comfortably though.

I find Air-con makes a BIG difference to my economy, around town sometimes drop as low as 35. About 45 round town with it off.

You need to remember the wildly optimistic computer on some cars.

Did 550 miles each way last week to Scotland. It was cool on way up and scorching on the way down ( 8 hrs of aircon).

Economy was 51 - 52 MPG both ways (I filled up 4 different times reseting oddometer each time).

Journey MPG never dropped below 60 MPG.

I think economy is OK for a diesel........ but great when you consider the performance. Any petrol car with 220 lb/ft of torque would struggle to do 30 mpg similar driving. I know look at my Sig.

There is a safety issue when using very tall gears for the speed in that there is no engine responsiveness if you need to avoid a potentially dangerous situation.

Then surely you're driving in the wrong gear Try 3rd for 30mph

Chris