Naked Science Forum

Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: Astronomer_FB on 04/03/2009 11:08:27

Title: Bike rider easily doing 45.
Post by: Astronomer_FB on 04/03/2009 11:08:27

My dad told me that if i were to ride my bike behind a car that was going say 45 mph that I would be "pullled" by the car to make me go faster and do 45 easily without much work is this true ( when i say pull i don't litteraly mean rope and knots.)

Title: Bike rider easily doing 45.
Post by: lightarrow on 04/03/2009 12:04:21

Quote from: Astronomer_FB on 04/03/2009 11:08:27

My dad told me that if i were to ride my bike behind a car that was going say 45 mph that I would be "pullled" by the car to make me go faster and do 45 easily without much work is this true ( when i say pull i don't litteraly mean rope and knots.)

It depends on the car and at which distance to it you are riding. It could be true, because behind a moving veichle there is a zone of lower air pressure. It's exploited in car races for overtakes.

Title: Bike rider easily doing 45.
Post by: syhprum on 04/03/2009 13:40:22

A lot better than 45MPH is possible

http://www.canosoarus.com/08LSRbicycle/LSR%20Bike01.htm

Title: Bike rider easily doing 45.
Post by: techmind on 04/03/2009 14:11:07

If the roads where you are are anything like the roads in my bit of Cambridge, you wouldn't want to be doing 45mph on them on a pedal-cycle -- especially if you can't see the ground more than a couple of metres in front of you owing to the car/truck.

Good idea in theory, but very dangerous in practice. Not to mention if the car/truck stops unexpectedly.

Title: Bike rider easily doing 45.
Post by: dentstudent on 04/03/2009 14:36:29

That's true - I can get up to about 40 mph reasonably easily on my bike, but it takes far longer to stop a bike from that speed than it does a car, especially if it is in the least bit damp.

Title: Bike rider easily doing 45.
Post by: Don_1 on 04/03/2009 14:48:02

I have seen many cyclists 'slip-streaming'. They tend to use large vans or lorries for the purpose. I have had cyclists slip-streaming me on many occasions. They can reach quite some speed.

On one occasion, whist driving a 7.5 ton truck, I was forced to break heavily when a child's ball rolled into the road ahead of me. Fortunately their parent was quick to act and grabbed the child, stopping him from running out in front of me. I released the brakes and continued on my way. A few hundred meters further on, I noticed the car behind me flashing his headlamps. The driver told me that a cyclist who had been slip-streaming me had run into the back of my truck when I hit the breaks.

Being unable to see what is directly behind a truck such as this and a 100 odd kilo cycle and rider hitting a fully loaded 7,500 kilo truck making no impression, I was totally oblivious to what had transpired.

Had that child's parent not been so alert, I would have come to a complete halt and the cyclist would have ended up under the truck. I might then have carried on, dragging the cyclist along the road, under my truck. This cyclist was very lucky. A few cuts and bruises, a dented bike and pride, and a caution from the police.

Others have not been so fortunate. Run over and/or dragged along between the rear wheels, the lucky ones die. The really unlucky ones' survive to sport their horrific injuries.

Please keep this to just theory, do not put it to the test.