So, a 120 round trip. Each journey 45 miles M25, 12 miles A road, 3 miles B road.

Going there – bike in the boot, roof rack on cruise at 70 mph on the M25 – 55 MPG – nothing unusual there, about 3mpg I’d get with the rack.

Coming back, muddy bike on the roof, some slower traffic on the M25 for about 15 miles at 50mph then back to 70 – 57.6 MPG.

all via the ‘puter.

That can be right can it? I mean don’t get me wrong I’d be pleased if its real but blimey…!

Anyone else get this with a modern BM?

70 vs 55 is more important than the bike on the roof rack.

You mean speed & less drag?

When I’m watching F1 the commentators say that speed is the square root of drag or something like that. Sounds like speed means a lot anyway…

No, probably drugs and cross dressing were still involved.

It’s a different journey going back…elevation, wind, needing a poo and stuff like that.

EDIT: I feel dirty even replying to this.

wind, needing a poo

Those two being cause and effect of course.

I just get it in my head that the aero was seemingly not dented at all with a sodding great thing on the roof. I might be tempted to keep the bike out of the car nore now.

IT WAS A DIFFERENT ******* JOURNEY!!

AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAARRRRRRRRRRRRRRRRRRRRRGGGGGGGGGGGHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHH!!!!!!!!!

That can be right can it? I mean don’t get me wrong I’d be pleased if its real but blimey…!

Anyone else get this with a modern BM?

Yes (320d touring x-drive) but don’t believe the computer – mine lies to me by a good couple of MPG over every tankful.

Plus eco-pro is fine in the cruise, but I’m beginning to hate it for driving in traffic as the auto box becomes too laggy.

Try driving at 55 vs 70 with bike on the roof and off the roof.

70 with bike will be worse
70 without bike will be next
55 with bike will be next
55 without bike will be best.

It’s not rocket science…

Loads of things affect fuel economy, and that speed difference would account for a lot, but also if your destination was higher than the start point, then you’ll get worse fuel economy going to the destination, and better fuel economy coming back from it.

You probably had a 30mph tailwind on the way back.
70mph into a 30 mph wind =100mph ish of drag
50 mph with a 30mph tailwind = 20 mph ish of drag
et voila!
There was a strong westerly in the SE today.

Speed makes a huge difference. Long 50mph sections really boost the average.

Are you sure it’s not Rocket Science

Maybe I didn’t explain myself properly. I usually get 56-58 mpg out of the car in similar journeys (in normal or “comfort” mode btw, and I agree geoffj with your sentiment re Eco pro).

I was expecting with a rack, and then with a bike on the rack it would reduce much more of a differential than it did. Fwiw I’ve done the same journey with our Kuga and the difference is 35mpg vs 43 mpg without, with the 159 39mpg with 44 without.

We’re saying it’s the 50mph that has made the difference, along with the wind. So whilst you would have seen lower mpg as you expect, the slow section and the wind have more than compensated for it.

You’re doing better than me, and I never have a bike on the roof of mine (120d).

I drive everywhere in sport mode, but I assume that makes no difference to fuel consumption.

I ran an F30 320ED for 35,000 miles and regularly acchied over 60mpg, average was 58mpg and worst I ever achieved eas 50mpg.

This was mpg calculated by fuel in and the odometer too.Typically this was on the region of 10% less than the computer.

I now have a Merc A200 CDI and that averages 52 mpg under the same driving conditions and is less powerful too.

I was always impressed by the economy ,more so that it never felt short changed for power.

i think this is just his way of telling us he needs new sunglasses that dont look italian(to go with his italian heritage bland diesel motor) to go with his german………………*

*insert the blank

I drive everywhere in sport mode, but I assume that makes no difference to fuel consumption.

I’d be surprised if it didn’t.

Bike on a rack makes a massive difference to fuel efficiency.

Look how actually aero modern BMWs are, and then think about sticking a big thing on top full of many many elements.

Bike on a rack makes a massive difference to fuel efficiency.

Yet it didn’t, which was kind of my point. Its not the difference between journey A&B I’m talking about, its the difference between me using the car without a rack on everyday – 56-58mpg for a very similar journey and the difference on Sunday with a rack/bike on the roof 120 miles averaging 56mpg.

I would have expected a much lower average MPG with a rack & bike on the roof.

Me? My comment is more related to how you did in the bike race than what mpg you got. 😆

It wasn’t a race, just a ride.

If you had reasonable following wind a roof rack is going to make less of an impact:
Going 70mph into a 20mph wind = 90mph wind for drag purposes
Going 50mph with a 20mph following wind = 30mph wind for drag purposes

Big difference.

Having anything on the roof really messes with the MPG, even something low profile like a surfboard, although I do wonder if it’d be better to just stick it on the rack without the bag and wax it when I got there. Cost of wax + meths Vs a few MPG?

My focus will do 52mpg according to the EU tests, and it will beat that (on the computer at least) if you get stuck in enough 50mph sections on the motorway (or have to fit the space saver).

Bike on a rack makes a massive difference to fuel efficiency.

Yet it didn’t,

Yes it did – it improved it. Only marginally but imagine the money you’d save over a lifetime if you left a bike up there all the time 🙂

My head hurts.

So, because my journeys were first clockface 12 to 7 without the bike on the roof, then 7 to 12 WITH the bike on the roof with a SW wind and 25% of my journey was 20% slower, the bike & car acted as a sail to improve the efficiency?

Frankly though – don’t trust the computer.

Using the fuel gauge I’ve estimated the use of 2.3 gallons, which supports the reported MPG – 5% roughly.

My head hurts.

So, because my journeys were first clockface 12 to 7 without the bike on the roof, then 7 to 12 WITH the bike on the roof with a SW wind and 25% of my journey was 20% slower, the bike & car acted as a sail to improve the efficiency?

no -you just weren’t being blown along from behind you just weren’t pushing as hard against the air,

When I used to drive big over-sized lutons for a art handling company the non-turbo vans could only really manage about 50 to 55 mph – foot flat to the floor – because they were so tall and flat-fronted (unless we managed to slipstream a coach). Wind resistance was such an issue with them that we had to quote different prices and ETAs (as we charged by the hour) for journeys depending on whether we were travelling east or west as the prevailing wind really had a tangible effect on our journeys.

The best illustration of that is if you compare the effort different cars need to make to achieve their top speeds and the kind of power increase thats required for a car that has a 200mph top speed over one that can reach 100mph. All that effort is about pushing through the air – but if you look at the size of effort it takes to go 10 mph faster – and thats all pretty much just pushing air – then a 10mph headwind followed by a 10mph tail wind really makes a sizeable difference.

If yesterday – headwind vs. tailwind.

You’re comparing three different events all of which have too many differing variables to make an accurate comparison. Headwind, tailwind, 70mph, 50mph, no rack, a rack, a rack+bike. Too much! 🙂

You’re comparing three different events all of which have too many differing variables to make an accurate comparison. Headwind, tailwind, 70mph, 50mph, no rack, a rack, a rack+bike. Too much

You haven’t even stated the other variables like what BPM the music you were listening to was, or how much the phone-in on Jeremy Vine made your blood boil.

You haven’t even stated the other variables like what BPM the music you were listening to was, or how much the phone-in on Jeremy Vine made your blood boil.

Absolute Radio 90’s

My 320d will do 60mpg on a long run at 70mph. It’s never reported less than 50mpg even chugging around town…

And mine’s got the previous generation engine too (last of the E91’s )

I can’t believe the fun i’m missing out on by not owning a diesel

I can’t believe the fun i’m missing out on by not owning a diesel

0-60 7.1 secs, 380nm torque, RWD, all wrapped up in a bike friendly shape with comfy cruise ability, £30 tax.

Whats not to like?

Whats not to like?

The monthly rental cost.

0-60 7.1 secs, 380nm torque, RWD, all wrapped up in a bike friendly shape with comfy cruise ability, £30 tax.

Whats not to like?

The following:-

0-60 7.1 secs
narrow rev range
clattery idle
soft throttle response

I’ll take a good petrol engine and suffer the low MPG, and higher road tax anyday.

narrow rev range – driver skill nullifies this
clattery idle – can’t hear it inside, its not a concern to me
soft throttle response – sport mode & 2 turbos takes that away
The monthly rental cost – everyone pays for a car somehow, and I’m happy with £1500 a year.

My 320d ED will do about 80mpg at 50mph. Unfortunately I dont have any stats for 70mph but I imagine it would be high 60’s mpg.

Trip to Northumberland over the last few days. Going up averaged 63mpg, coming back 53 mpg. The difference was wind, lots of it coming back down south.

0-60 7.1 secs

Is that too slow?

narrow rev range

Nope not in mine. Pulls from about 750-4000rpm.

clattery idle

when do cars idle? Mine switches off when I stop

soft throttle response

Not sure what you mean there. BM’s have a button that allows you to change throttle response sensitivity to save fuel.

I must admit though even a BMW suffers from slow throttle response has the turbo spools up. Even my wifes Aygo has a quicker throttle reponse.

sport mode & 2 turbos takes that away

sorry, no they dont. All the sport mode does is shorten the amount of pedal travel that is needed to squirt fuel in to the cylinder, nothing more. The twin turbo takes away the narrow rev range.

If you turn off all traction you cant even put it in to sport mode, it reverts to comfort the cars standard throttle sensitivity.

and I’m happy with £1500 a year.

you even said yourself you didnt pay that much. It was about £300 per month when factoring in deposit etc.