10 pounds of weight lost adds 1mph to your speed?

[400bhp]

what did you study at Uni Colin?

 

[black'n'yellow]

As has been said above - weight mainly affects climbing speed.

weight affects any situation where the bike needs to be accelerated.

 

[ColinJ]

what did you study at Uni Colin?

Electronic Engineering.

weight affects any situation where the bike needs to be accelerated.

Well, strictly it is Mass, but there is a direct correlation between the two!

 

[ColinJ]

On a well-maintained bicycle, frictional losses in the transmission and rolling resistance of the tyres are small compared with the effect of wind resistance when riding at a reasonable speed. Frictional losses are increased by increased weight, but that is an increase in something small so we can pretty much ignore it. What really matters on the flat is how weight and wind resistance are related. Wind resistance is proportional to frontal area and weight to volume.

If you imagine a cube whose sides are 1 metre in length, then the area of one face is 1 sq.metre and its volume is 1 cubic metre. Now double the length of the sides. The area of one side is now 4 sq.metres but the volume is increased to 8 cubic metres i.e. volume increases much quicker than area with increasing size. Big cyclists don't suffer increases in wind resistance in proportion to their weight. Bigger cyclists tend to be more powerful than smaller ones, assuming that their size isn't entirely due to fat! For that reason, bigger cyclists tend to have an advantage over smaller cyclists on the flat, especially into headwinds.

In terms of climbing - on a steep hill, speed will be low so wind resistance will be low, and friction will still be low. Nearly all of the cyclist's energy is used in overcoming gravity so weight is very important - it has to be lugged up the hill. Now, a fit cyclist who is twice as heavy as a fit skinny cyclist is unlikely to have twice the power to compensate so skinny cyclists tend to make better climbers.

How about accelerating on the flat? Well, the power-to-weight ratio of a skinny climber tends to be better than that of a bigger rider so their 'jump' could be better, but once they get up to speed they might struggle to maintain it and be reeled back in by bigger, stronger riders.

As for descending ... A big rider with more power than a small rider has a natural advantage anyway, and their gravity-assistance increases much quicker than their wind resistance with increasing size so their 'terminal velocity' is higher. I have often freewheeled past smaller riders who are pedalling like mad downhill!

 

[philinmerthyr]

I weigh 21st want to get down to around 15st a loss of about 100lb. I currently average around 13 mph in a hilly area.

That means I'll be averaging 23 mph. I'll give sky a ring

 

[ColinJ]

I weigh 21st want to get down to around 15st a loss of about 100lb. I currently average around 13 mph in a hilly area.

That means I'll be averaging 23 mph. I'll give sky a ring

You certainly will get a lot faster, Phil! (Don't know about the 23 mph though ...)

When I was fit, I could average about 17 mph on hilly routes round here. When I got fat, I was doing barely half that speed. On the flat though, I could still do a reasonable speed.

 

[simmi]

In terms of climbing - on a steep hill, speed will be low so wind resistance will be low, and friction will still be low. Nearly all of the cyclist's energy is used in overcoming gravity so weight is very important - it has to be lugged up the hill. Now, a fit cyclist who is twice as heavy as a fit skinny cyclist is unlikely to have twice the power to compensate so skinny cyclists tend to make better climbers.

Makes a lot of sence.
I am getting better but still finding hills really hard.
Weight today 201lb so will find it hard and don't think my gearing is doing me any favours either with 12-23 and 39/52, still find myself reaching for a gear I haven't got.
Still 28th Aug was 227lb so better hill climbing may not be too far ahead.

 

[ColinJ]

.
I am getting better but still finding hills really hard.
Weight today 201lb so will find it hard and don't think my gearing is doing me any favours either with 12-23 and 39/52, still find myself reaching for a gear I haven't got.
Still 28th Aug was 227lb so better hill climbing may not be too far ahead.

Well done on the weight loss, but a 39/23 lowest gear really is not doing you any favours on the hills!

(There are some people who subscribe to the "What doesn't kill me, makes me stronger" philosophy but I'm not one of them! I think you will do more hard rides if they don't feel like they are half-killing you and you will naturally start using higher climbing gears as you get fitter and lighter. I'd be tempted to investigate lower gearing.)

 

[simmi]

Well done on the weight loss, but a 39/23 lowest gear really is not doing you any favours on the hills!

Out of a matter of interest what lowest gear ratios do people use.
Do you try to remain seated when climbing, have got a friend who says to remain seated as long as possible because standing uses way more energy.

 

[Sittingduck]

34/27 lowest gear, for me. I sit and stand but not at the same time.

 

[black'n'yellow]

Out of a matter of interest what lowest gear ratios do people use.
Do you try to remain seated when climbing, have got a friend who says to remain seated as long as possible because standing uses way more energy.

please don't go down the route of thinking that gearing is the key to getting up hills - it isn't. Fitness is.

 

[400bhp]

 

[simmi]

please don't go down the route of thinking that gearing is the key to getting up hills - it isn't. Fitness is.

Hi black'n'yellow so would you be able to get up most hills with a 23/39 or more importantly should I be able to when I get fitter.

 

[black'n'yellow]

Hi black'n'yellow so would you be able to get up most hills with a 23/39 or more importantly should I be able to when I get fitter.

sorry, that's a bit open ended, as I don't really know what you mean by 'most hills'..?

 

[User6179]

please don't go down the route of thinking that gearing is the key to getting up hills - it isn't. Fitness is.

You on a single speed then ?