Bike cover - any aerodynamicists on here?

[Ayjay]

I raised this issue a last year but it just seemed to turn into a debate about the pros and cons of covers but with only one response directly addressing MPG.

I know that we have one or two aircraft engineers amongst us who may or may not know anything about aerodynamics but can anybody take a guess (educated or otherwise!) of how much difference covering the bikes on my tow bar mounted bike rack will make in terms of drag and consequent diesel consumption. I ask as we will be doing a long trip over the next three weeks (1500 miles or so) and I’m weighing up keeping the bikes covered whilst on the move in what’s already a very large brick shaped thing. My preference is to keep the cover on as it gives some protection from bad weather and road crap and also adds another layer of security and having already used it on a long trip, I’m not worried about it flapping about and shredding itself or making a lot of extra noise. However. if the potential impact on MPG is reckoned to be dramatic………

Here’s some pictures of the rack with cover on. Unfortunately, I haven’t got one from front on but you can get the idea. Despite what it looks like from the two angled snaps, the covered bikes don’t actually stick out much at either side (a couple of inches if at all). Ignore the saggy 4rse - they were taken before getting the suspension sorted:


Cheers in advance.

 

[Bav]

I'm no expert, but if it's causing additional noise then I'd say it's causing additional drag. How much that drag affects mpg I have no idea, but I would reckon the other reasons you mentioned for having the cover would trump any efficiency loss.

Going anywhere nice?

 

[Ayjay]

@Bav. Cheers for that. There's no additional noise that either of us can hear (Mrs AJ has got very good hearing but mine in the right ear has unfortunately been almost destroyed by half a Iifetime of gunfire). I think I'll be sticking with the cover unless somebody comes up with anything dramatic!

 

[david173]

I would say, sat that close to the tailgate it would make no tangible difference to the MPG cover or no cover. The brick shape bus in front has just punched a big hole through the air for it all to pass through (in board terms)

 

[Johnboy57]

My view is that it won't make a huge difference because the air behind the van will be turbulent anyway. However a couple of other points to consider...

I recently did a long journey in winter and arrived home late. Unloaded the bikes in the dark, and stored them in our basement - then forgot about them. When I came to use them they had completely rusted due to all the salt thrown up from the road. When you see how quickly the rear window gets covered in the wet at speed then it is no wonder the bikes were completely covered..... obvious really!!

I read on the California forum about one owner who had 3 expensive bikes stolen off his carrier while parked at the service station. They cut through the security cable and loaded them into a van in no time.

In both cases above the cover you propose would be a benefit. In the case of theft, it is another cumbersome thing to remove and also hides what type of bikes you have.

 

[Bav]

@Bav. Cheers for that. There's no additional noise that either of us can hear (Mrs AJ has got very good hearing but mine in the right ear has unfortunately been almost destroyed by half a Iifetime of gunfire). I think I'll be sticking with the cover unless somebody comes up with anything dramatic!

I mis-read your original post - I thought you'd said it was making lots of extra noise. If no noise, then no additional drag... probably.

 

[Bav]

They cut through the security cable

Yeah, always best to use a decent U-lock - I use Abus Granite.

 

[Ayjay]

@Bav. Sorry, I didn't respond to your question - the plan is tunnel to Calais on Tuesday morning, on to Brittany and back via Normandy and maybe Belgium or The Netherlands depending on time / weather.

 

[Mike23864]

I raised this issue a last year but it just seemed to turn into a debate about the pros and cons of covers but with only one response directly addressing MPG.

I know that we have one or two aircraft engineers amongst us who may or may not know anything about aerodynamics but can anybody take a guess (educated or otherwise!) of how much difference covering the bikes on my tow bar mounted bike rack will make in terms of drag and consequent diesel consumption. I ask as we will be doing a long trip over the next three weeks (1500 miles or so) and I’m weighing up keeping the bikes covered whilst on the move in what’s already a very large brick shaped thing. My preference is to keep the cover on as it gives some protection from bad weather and road crap and also adds another layer of security and having already used it on a long trip, I’m not worried about it flapping about and shredding itself or making a lot of extra noise. However. if the potential impact on MPG is reckoned to be dramatic………

Here’s some pictures of the rack with cover on. Unfortunately, I haven’t got one from front on but you can get the idea. Despite what it looks like from the two angled snaps, the covered bikes don’t actually stick out much at either side (a couple of inches if at all). Ignore the saggy 4rse - they were taken before getting the suspension sorted:
View attachment 158946
View attachment 158947View attachment 158948
Cheers in advance.

Probably not much you can do apart from make sure your tyres are at the right pressure (van not bikes) strap down the bike cover so it doesn’t catch the wind and create a parachute effect and try and distribute the weight evenly as much as you can. If you’ve an onboard water tank empty it out to save weight etc

 

[Ayjay]

Thanks for all the comments which mostly agree with my own thoughts. I think I've got the security / lock business more or less covered with a combination of D Lock and chains / cables. I always work on the basis that if they really want it, they will take it but if you make it potentially a bit too difficult and slow for them, they will also prefer a softer target and go elsewhere.

 

[Bav]

@Bav. Sorry, I didn't respond to your question - the plan is tunnel to Calais on Tuesday morning, on to Brittany and back via Normandy and maybe Belgium or The Netherlands depending on time / weather.

Bon voyage!