Kayak on roof rack upside down or not, best for fuel economy

[danyeates]

Hello,

Just a quick one for you!

I have a long journey tomorrow, about 4.5 hours and I plan to take my kayak on the roof of our little Civic. I have the proper Thule aero bars, but no kayak rack or holder, I just lay it on the bars. It sits on the bars perfectly either the correct way up or upside down. So what would be best? It’s a big kayak, over 4m long and weighs about 25kg, so will create quite a lot of drag, therefore using quite a lot more fuel over a long distance.

So, does it matter which way up I have the kayak? The correct way up, or upside down? It fits more snugly upside down, but I can support the hull with a tube so that it doesn’t rock when it’s the correct way up. Physicists, please help!

Thanks,

Dan

[Snowboy]

Obviously make sure the hole is covered to make it less of a wind trap.
Apart from that I doubt it will make much difference.

[Stevemr]

I think, upside down is best. Not sure why, just looks right!
Also if its open, and starts to fill with rain, it will get very heavy!!!!

[davepoth]

I'd guess upside down - the airflow will be disturbed by the hole where you sit otherwise. With the hole sat in the already disturbed air between the bars it should be less of an issue.

[BadRotorFinger]

Mine was always upside down, better fit to bars. I think fuel consuption is negligible strapped either way.

[madbadger]

Stevemr said:

I think, upside down is best. Not sure why, just looks right!
Also if its open, and starts to fill with rain, it will get very heavy!!!!

A canoe full of water will weigh more than your car and will squish it into a tiny mess.

[Snowboy]

madbadger said:

Stevemr said:

I think, upside down is best. Not sure why, just looks right!
Also if its open, and starts to fill with rain, it will get very heavy!!!!

A canoe full of water will weigh more than your car and will squish it into a tiny mess.

A canoe half full of water would make braking and handing quite interesting too I should imagine.

Especially if you brake hard and all the water rushes to the front.

[anonymous-user]

Definately upside down!

[hairykrishna]

Next to no difference is my guess. I'd just go with the one that seemed the most secure.

Check it experimentally - brim the tank and drive one way with the right way up, brim the tank at the other end and do the return journey with it the other way up. That way you'll know next time you have a long drive!

[cornet]

Top tip - make sure windows & doors on your car are closed before you put the kayak on the roof after using it. I've seen a few people make this mistake

[GroundEffect]

The biggest problem will be the bars themselves. Wont make much difference up or down.

[Snowboy]

cornet said:

Top tip - make sure windows & doors on your car are closed before you put the kayak on the roof after using it. I've seen a few people make this mistake

Why?
Because of water spillage?

[danyeates]

Wow, lots of replies! Thanks!

BTW, this is the kayak, it's open, so has now hole. Lots of drain holes too!



I've transported it many times, but only to the local coast, less than a mile away. Not done any long runs with it.

My thoughts were whether lift or downforce would have any noticeable different to economy and/or handling?

[AndyNetwork]

had a similar kayak on mine last year, and to be honest, I put it upside down. As others have said, the indents etc on the top will then be in the already disturbed air, rather than adding drag. Also the smooth base on the kayak will aid aerodynamics slightly.

One of the other guys finds putting his kayak upside down on his Range Rover improves the aerodynamics.

[Captain Muppet]

hairykrishna said:

Check it experimentally - brim the tank and drive one way with the right way up, brim the tank at the other end and do the return journey with it the other way up. That way you'll know next time you have a long drive!

This.

Turn your ignorance into knowledge.

[danyeates]

AndyNetwork said:

had a similar kayak on mine last year, and to be honest, I put it upside down. As others have said, the indents etc on the top will then be in the already disturbed air, rather than adding drag. Also the smooth base on the kayak will aid aerodynamics slightly.

One of the other guys finds putting his kayak upside down on his Range Rover improves the aerodynamics.

Yep, good point, makes sense. Thanks.

[danyeates]

Snowboy said:

madbadger said:

Stevemr said:

I think, upside down is best. Not sure why, just looks right!
Also if its open, and starts to fill with rain, it will get very heavy!!!!

A canoe full of water will weigh more than your car and will squish it into a tiny mess.

A canoe half full of water would make braking and handing quite interesting too I should imagine.

Especially if you brake hard and all the water rushes to the front.

Bye bye kayak!

[danyeates]

Captain Muppet said:

hairykrishna said:

Check it experimentally - brim the tank and drive one way with the right way up, brim the tank at the other end and do the return journey with it the other way up. That way you'll know next time you have a long drive!

This.

Turn your ignorance into knowledge.

Interesting. Could do.

[HustleRussell]

danyeates said:

My thoughts were whether lift or downforce would have any noticeable different to economy and/or handling?

I'm pretty sure a Civic with a kayak on the roof has enough downforce to fully invert in tunnels and drive along the ceiling.

I reckon the kayak will add about 25kgs of downforce

[S10 GTA]

Captain Muppet said:

This.

Turn your ignorance into knowledge.