Odd car thing happened today

DiscoStu

Put roof bars on my car today for the first time.
My car usually does around 50mpg but with the bars on I've been getting nearly 70mpg!?! That's not how it's supposed to work, is it?
Pleasantly surprised.

skunkwerx

What bars are they?! Im getting meself some!

ICBM

Was there about a 30mph tailwind? That's about the only thing I can think of which might give that result...

duotone

Not driving your usual route I assume?

RaymondLin

Did you hit your head when installing it?

roundthebend

Maybe they gave you some lift which reduced the drag between tyres and tarmac?

DiscoStu

Thule WingBars, on a Mazda 3 2.2D.
I do about 250 miles a week with work and this was a normal day on familiar roads, and I drove in my usual fashion.
I've had the bars for months but have never needed them until now. I put them on this morning in prep for a job I'm doing on Friday, so they had no load on them today when I was driving around. I peaked at 69.3mpg, and my highest ever before today was 59.6mpg but that was long distance down the A9. Most days I'm between 48-54mpg and I've never managed to hit 60mpg before so if this keeps up I'm gonna leave them on and get another 100 miles out of my tank!

RaymondLin

May be it increased downforce and more traction and you have more grip and getting more power down…..

DiscoStu

RaymondLin said:

May be it increased downforce and more traction and you have more grip and getting more power down…..

So like two rooftop spoilers?

skunkwerx

Its the rooftop bars happy hour. 

Thats all it is. 

notanon

I would put another set on PDQ.

ThePrettyDamned

RaymondLin said:

Did you hit your head when installing it?

Proper laughed out loud. 

axisus

I am don't believe U

CHRISB50

Do they have small rockets in the back of them?

FX_Munkee

tone1

Are you sure it's definitely your car you fitted them to?

mart

You must have fitted them back to front. Cos if you'd fitted them the right way round, they would increase your fuel consumption.

chillidoggy

You are siraxeman and I claim my £10.

ESBlonde

I'd be more inclined to think the physics are right you can't disrupt the airflow and improve fuel efficiency. Those on board computors are not best trusted IME. The only way you know for sure is to neck the tank every time and write down the mileage/fuel. Over a period that gives the more likely answer (subject to the tyres meing properly inflated.

DiscoStu

I keep a regular eye on my mpg and my mileage as I'm self employed. My car's mpg computer has been accurate enough over the past year so quite a coincidence if it decided to play up the very day I make a physical change to the car's exterior.
I've mostly been town driving this morning and it's dropped to 62mpg but I have a lot of A road miles this afternoon so curious to see if it picks up again. I've got 3/4 of a tank in the car and will monitor it until it's empty.

I really hope I've made my car more Thule efficient!

http://i.imgur.com/Q0alHOE.jpg

Cirrus

ESBlonde said:

I'd be more inclined to think the physics are right you can't disrupt the airflow and improve fuel efficiency. 

You're making the assumption that the airflow is disrupted more by the addition of something to the roof. Sometimes adding something can reduce aerodynamic drag, of course...