Bike Racks

[Domestiquehated]

But seriously folks - I had an interesting one recently: I have the Thule towbar mounted rack and had 3 bikes on the back on a long drive.  We heard a muffled bang on the drive and on getting home saw that the exhaust fumes had burnt through the tyre.  Moral, check proximity to tail pipe and remove wheel if necessary...

 

[jmaccelari]

 

Where is that thread about which system has the most wind resistance?

 

It should be easy to figure out: it's a factor of the total area exposed to the wind with

some sort of polynomial dependency on velocity (if I remember correctly from my

'varsity days). So assuming a constant velocity, it's a simple function of exposed

surface area.

 

Looking at the vehicle from the front (where hopefully most of the wind comes from*):

- bike in car has least;

- bike behind car on towbar rack has more;

- bike on "strap-on" rack higher up has more (assuming rack is higher in this case);

- bike on car roof has most.

 

*Unless you're in trouble, but that's another thread.

[AndreZA]

But seriously folks - I had an interesting one recently: I have the Thule towbar mounted rack and had 3 bikes on the back on a long drive.  We heard a muffled bang on the drive and on getting home saw that the exhaust fumes had burnt through the tyre.  Moral' date=' check proximity to tail pipe and remove wheel if necessary...

 

[/quote']

 

 

age old problem.

[Marius]

what is the link to Thule's SA site please, I'm looking for one of those "boxes" you fix to your roof so pack sh*t, thx!

[Domestiquehated]

 

Age young cyclist!  Age old person!  Old dog and all that...

[Minion]

 

Where is that thread about which system has the most wind resistance?

 

It should be easy to figure out: it's a factor of the total area exposed to the wind with some sort of polynomial dependency on velocity.

Almost right, but if only it were that easy.

 

Drag is a function of the shape of the vehicle, frontal area and square of the velocity. The first two are easy to calculate and are essentially constant across vehicles of the same type - think about it: the extra frontal area of a roofrack and bike is a very small percentage of the total frontal area.

 

The shape function, or drag coefficient, is then the critical factor here and this is much harder to calculate. In fact, it is heavily dependent on how the airflow separates from the vehicle i.e. what happens at the back of your car. This is right where you want to put a bike rack and bike.

 

Personally, I wouldn't base my purchasing decision on drag: it depends too much on your exact car, rack and bicycle configuration. If you can find test data that matches this then, yes, use it in the decision process. If not, the results are otherwise too variable.