# Increasing in bycicle mass

1. Sep 30, 2014

### iustin.ouatu

Hello! Yesyerday I saw a bycicle which had attached to its back a box on wheels. Supposing that the coeficient of friction is the same as the coeficient of friction at the surface between bike`s wheels and ground, what of the 2 following cases is worser for the cycler ( he has to make more effort) :
1. The box is 6 kg mass.
2. There is no box and the cycler is heavier than initial with 6 kg.
Thanks you!!

2. Sep 30, 2014

### HallsofIvy

I don't see any reason why there should be any difference at all.

3. Sep 30, 2014

### gsal

and/or how the coefficient of friction between wheels and ground comes makes a different...assuming all wheels rotate and non slip...

4. Oct 1, 2014

### CWatters

Ok so are we assuming that the total weight in each case is the same but in 1) it's spread over 4 wheels and in 2) it's spread over 2 wheels?

I thought that twice the load on half the number of wheels might give the same rolling resistance... However wikipedia suggests that even if you change tyre pressures rolling resistance isn't directly proportional to load so there might be a small difference.

5. Oct 1, 2014

### gsal

I see, so, you are getting real...I was thinking classical physics with rigid bodies (disc wheels) ;-)

6. Oct 3, 2014

### Staff: Mentor

One advantage of carrying the load in a trailer is that you can arrange for it to be lower to the ground. When you transport extra weight above the rear wheel it makes the bicycle less stable, and with the higher centre of gravity the cyclist has to work harder to keep the bike balanced. You could have higher pressure in the trailer tyres, reducing losses, because you aren't concerned with a comfortable ride for the trailer. When you carry extra weight on the bike the tyre flattens and makes peddling more difficult. To restore a rounder tyre you can pump it harder, but then your ride becomes harsh and uncomfortable (even if the tyre can take the high pressure).