Aerodynamic drag and why a coupe is better

Pooltee · Post by **Pooltee** » Thu Sep 10, 2020 12:44 pm

If on the rare occasion I use my car for work, I tend to drive it exactly the same, regardless of roof up or roof down. Not heavy driving, but not dithering about either.

Same round trip with the roof up, just under 1/4 of a tank,
Roof down, just over 1/4 of a tank

It works about at just under 2 Litres of burn difference across the two comparisons over 150 mile round trip.

It might also be worth noting that if I don’t have the roof down, it’s usually because it is a lot cooler, or raining, and both of those factors will only make a petrol engine run better, so not entirely down to drag in my case.

Post by **srhutch** » Thu Sep 10, 2020 1:31 pm

I bought a roadster because I could put the roof down, not so worry about how much fuel I'm using.

You can't put a price on a nice summers night drive with the roof down. An experience a coupe driver can only dream of.

Mr Tidy · Post by **Mr Tidy** » Thu Sep 10, 2020 7:50 pm

srhutch wrote: ↑Thu Sep 10, 2020 1:31 pm I bought a roadster because I could put the roof down, not so worry about how much fuel I'm using.

You can't put a price on a nice summers night drive with the roof down. An experience a coupe driver can only dream of.

Well now I know another reason to stick to Coupes! Must be why my MC is currently showing 26.9mpg average, although that may be more to do with being gentle with it for now as the bearing shells have only just been replaced.

As for driving with no roof the only sort of dream that conjures up for me is a nightmare.

Stevo1987 · Post by **Stevo1987** » Thu Sep 10, 2020 8:20 pm

I don't make a point of monitoring my fuel consumption. It is not the reason I bought the car. Average is maybe 25 mpg. I did notice a few weeks ago that on a trip down south to my brothers new gaff I went through half a tank which worked out to roughly 37 mpg. I think for most of the tie the roof was down. Now, the caveat is Mrs Stevo was accompanying me and she adopts the brace position whenever I change down a gear so I was being extremely gentle. Suffice to say on to returning to the homestead I made an excuse to pop to the shop for something medicinal and blew the snot out of it.

BMWZ4MC · Post by **BMWZ4MC** » Fri Sep 11, 2020 7:14 am

Mr Tidy wrote: ↑Thu Sep 10, 2020 7:50 pm
srhutch wrote: ↑Thu Sep 10, 2020 1:31 pm I bought a roadster because I could put the roof down, not so worry about how much fuel I'm using.

You can't put a price on a nice summers night drive with the roof down. An experience a coupe driver can only dream of.
Well now I know another reason to stick to Coupes! Must be why my MC is currently showing 26.9mpg average, although that may be more to do with being gentle with it for now as the bearing shells have only just been replaced.

As for driving with no roof the only sort of dream that conjures up for me is a nightmare.

Mine is showing an average of 18 mpg

Thanks for the interesting article Pbondar

Pbondar · Post by **Pbondar** » Fri Sep 11, 2020 9:14 am

BMWZ4MC wrote: ↑Fri Sep 11, 2020 7:14 am
Mr Tidy wrote: ↑Thu Sep 10, 2020 7:50 pm
srhutch wrote: ↑Thu Sep 10, 2020 1:31 pm I bought a roadster because I could put the roof down, not so worry about how much fuel I'm using.

You can't put a price on a nice summers night drive with the roof down. An experience a coupe driver can only dream of.
Well now I know another reason to stick to Coupes! Must be why my MC is currently showing 26.9mpg average, although that may be more to do with being gentle with it for now as the bearing shells have only just been replaced.

As for driving with no roof the only sort of dream that conjures up for me is a nightmare.
Mine is showing an average of 18 mpg

Thanks for the interesting article Pbondar

Your welcome..the original point if the article was not to justify or not the extra cost of roof down motoring simply to rationalise in part differing fuel consumptions...plus the confirmation that wind deflectors and some spoilers have a benefit for top down motoring

flybobbie · Post by **flybobbie** » Fri Sep 11, 2020 11:03 pm

It was said the Princess was more aerodynamically efficient going back wards, at least until the steering ball joint broke off!

R_P_M_ · Post by **R_P_M_** » Sat Sep 12, 2020 1:30 am

This is what you get when you spend the first 1000 miles of ownership warming her up and driving your favourite b roads

: Screenshot_20200912-011007.png (599.65 KiB) Viewed 412 times

Busterboo · Post by **Busterboo** » Sat Sep 12, 2020 9:33 am

R_P_M_ wrote: ↑Sat Sep 12, 2020 1:30 am This is what you get when you spend the first 1000 miles of ownership warming her up on the way to your favourite b roads Screenshot_20200912-011007.png

Why is this figure so bad?

R_P_M_ · Post by **R_P_M_** » Sat Sep 12, 2020 9:54 am

Busterboo wrote: ↑Sat Sep 12, 2020 9:33 am Why is this figure so bad?

that's what you get using the car as intended on b roads.

Lazza · Post by **Lazza** » Sat Sep 12, 2020 11:01 am

: 3A06AD1C-F330-41C5-8D75-C5E9EF148E49.jpeg (96.71 KiB) Viewed 357 times

This was from last weekend in my 35i. I drove from Wokingham, Berks up to Norwich, Norfolk for the weekend. I was in no rush so just cruised it both ways.

It’s about as high as I get. Normally it’s mid to low 20s.

Busterboo · Post by **Busterboo** » Sat Sep 12, 2020 4:41 pm

R_P_M_ wrote: ↑Sat Sep 12, 2020 9:54 am
Busterboo wrote: ↑Sat Sep 12, 2020 9:33 am Why is this figure so bad?
that's what you get using the car as intended on b roads.

Yes, your 17.5 mpg is at an average of 34.9 mph, which in reality is quite quick on B roads over the given 53 miles. That said, my global figure is 26.4 mpg at an average of 30.1 mph.

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