Interesting Encounters

[Ian]

I've been out on the Torq today making the the most of the sunshine. This morning a lycra clad cyclist on a racing bike emerged from a golf club entrance a hundered meters or so ahead of me and on the gently rising slope began to pull further ahead until I lost sight of him. Further on where the gradient had become about 8% I caught up with him and then managed to stay with him for the next perfectly level mile without using power, clearly the climb had exhausted him. Then came a steep downhill run of about 1/2 mile, we both pedaled like the clappers and speed quickly reached about 30 mph, I was gaining on him so stopped pedaling, he continued to pedal furiously, head down in the classic racing position whilst I was merely coasting siting upright and still gaining on him, I didn't and still don't know how that could be. I can only assume there was a problem with his bike creating excessive drag.
Eventually the road turned uphill again and his speed fell off very quickly before he turned off. he was probably totally demoralised at his inability to get away from a very ordinary looking middle aged cyclist .

Later in the day I met another Torq rider, the first I've encountered. As we were heading in the same direction we rode together for a while, two middle aged cyclists maintaining what to any onlookers must have looked liked an impossible pace

 

[flecc]

Great stuff Ian, and how good to see another Torq owner out in today's glorious weather. I'd be pleased just to see another e-bike of any sort once in a while.

Still, I also enjoy the confusion my T bike brings to sports cyclists, and now they can't even see a motor when I approach them coming from the opposite direction either.
.

 

[nigel]

Nigel

That is a strange one Ian perhaps he was going through the motions without any effort i wonder if he new you were on a electric bike they normally find a few extra mph. That was good luck finding another torq rider had he added any extras to his torq. PS what distance did you travel today i did 21 miles. NIGEL.

 

[Ian]

I did 28 miles Nigel , but am very glad you managed any miles after this mornings post.

The lycra clad rider only knew I was there from occasional glances over his shoulder, I doubt he saw enough of of my bike to know for sure it was electric. it could well be that his downhill pedalling was just show with the bike freewheeling, he really had put some effort into the earlier climb and was probably still exhausted. I'd still expect a thin tyred racer with the rider in a low position to coast faster though.

The other Torq was still standard apart from additional lights and panniers, the owner saying he'd only had it a couple of months and had only started to really use it since the weather began to improve.

 

[DBCohen]

Since I started using my Cadence this week for my commute to work, I have particularly noticed a few incredulous looks as I overtake people on the mile-long hilly section that I use to get home.

They are clearly all thinking "how can that fat bloke be traveling up this hill so fast?"

 

[rooel]

Was that downhill ride not faster for the Torq rider thanks to gravity? The Torq with a middle aged rider probably had a huge weight advantage (for downhill at any rate) over the sports cyclist on his lightweight racer.

I have sometimes pondered the idea that the highway authorities should provide a pile of bricks at the top of every hill a few of which non-electric cyclists could load to speed the journey to the bottom where the ballast would be jetisoned (to be later returned to the top by the roadmen).

 

[Ian]

It's a popular missconception that weight has anything to do with acceleration downhill, acceleration due purely to gravity is 10 meters per second per second and and that is as true for a ton of bricks as is it is for a feather. The mythbusters TV program on discovery channel proved that a toy car weighing a few grams and a real car weighing over a ton will accelerate at a similar rate when allowed to role down the same slope, the limiting factor being the inability of the toy car to stay on the track at higher speeds. In actual fact the initial acceleration of the toy car was faster due to its lower rolling resistance.

Weight would have an advantange overcoming air resistance, but that would be offset by the greater frontal area of the heavier rider.

And anyway, I'm not that heavy.

 

[rooel]

My experience is not particularly scientifically measured but I have found that freewheeling down hill I seem to go faster than other lighter members of the family on similar bikes. And although I am not fat (or broad) I do incur slightly more air resistance than the others who are smaller. Is momentum of any relevance? I would rather be hit by a feather travelling at 10mph than a lorry at the same speed.

 

[Ian]

Momentum is only of relavence when you try to stop, or hit something, in which case kinetic energy is converted into pain!

Seriously though, the question of accelerative forces versus retarding forces is complex, although the ease at which I was catching the sporty rider does suggest there was more at play. Perhaps he had recently ridden through floods and damaged his wheel bearings

 

[ITSPETEINIT]

Uplight: down-heavy

Was that downhill ride not faster for the Torq rider thanks to gravity? The Torq with a middle aged rider probably had a huge weight advantage (for downhill at any rate) over the sports cyclist on his lightweight racer).

I have sometimes pondered the idea that the highway authorities should provide a pile of bricks at the top of every hill a few of which non-electric cyclists could load to speed the journey to the bottom where the ballast would be jetisoned (to be later returned to the top by the roadmen).

Lets be fair here. The 'ballast' would be returned to the top of the hill by e-bikers. That would even things out a bit in both directions. It would not take many pounds of ballast to bring the uphill operating speed of a Torq down to a 'grovel'. It would also serve to keep taxes down.
I recall on a quite steep, long hill in Manche, France, (the Departement, not the English Channel) we (wife and Me) had taken a good run at this hill on our gas powered cycles. We had to pedal like the clappers to maintain the minimum speed for motor assistance. I guess we were travelling at about 18 mph when an unassisted 'sportif' appeared on my wheel. He had no trouble drafting us to the top of this hill and bade us a cheery 'mercie et bon jour' at the top when he sped on his way.
Nice folks cyclists of all persuasions.
Peter

 

[Ian]

One thing that does sadden me on Sunday morning rides in fine summer weather is the amount of "ballast" in the form of bottles and cans that has been jettisoned from cars the previous night. The culprits should be made to gather it and take it to the top of the hill.

 

[prState]

What you need is rain collectors at the tops of your hills. You grab a bucket of water at the top, use it for ballast and dump it at the bottom so it doesn't restrict your next upward trip. Rinse & repeat on next hill.

Or you could just take a cool rinse off.

 

[Ian]

Now water is something we're not short of, although if this fine weather keeps up for more than a few days the water companies will declare a drought.

 

[rooel]

Having raised this hare, while others were composing their intriguing replies, I have found this:

http://www.bikeforums.net/showthread.php?t=31567

Here's a quote from one of the posts.

"....the heavy rider has approximately the same frontal area as the lighter rider (actually the heavier rider usually does have a little more frontal area), so the force due to aerodynamic friction (drag) is approximately equal. However, the horizontal component of gravity with respect to the road surface (the part of gravity that pulls you forward) is greater with the heavier rider than with the lighter rider - this is assuming that both riders are applying the same amount of power to the pedals.

To put it simply:

10 - 2 = 8 is greater than 8 - 2 = 6 [this is a reference to the gravity acceleration formula]

In order to match the heavier rider on the descent, the lighter rider would need to apply enough additional power at the pedals to overcome the deficit between their two gravitational forces...."

I think all of this is of particular relevance for electrically assisted cyclists, given the heavier weight of most electric bikes, and the fact that we are assisted to the top of hills by the energy stored in our batteries. Once at the top I see our weight as energy stored in a different way which is released as we descend.

 

[ITSPETEINIT]

How fast? How far !

Momentum is only of relavence when you try to stop, or hit something, in which case kinetic energy is converted into pain!

Seriously though, the question of accelerative forces versus retarding forces is complex, although the ease at which I was catching the sporty rider does suggest there was more at play. Perhaps he had recently ridden through floods and damaged his wheel bearings

Perhaps he was beginning a lovely day out (like I vaguely recall of my youth) when I travelled one hundred miles, over hill and dale, on just a packet of sandwiches and a bottle of orange squash.
"No battery came, no pylon stirred:
Nor throttle, nor hub motor heard.
A 'sporty' has no friend!".
apol. to Thomas Gray: http://www.englishverse.com/poems/on_a_favourite_cat

Two-Sprint-owner 'Geriatric' Pete.

 

[flecc]

Having raised this hare, while others were composing their intriguing replies, I have found this:

http://www.bikeforums.net/showthread.php?t=31567

Here's a quote from one of the posts.

"....the heavy rider has approximately the same frontal area as the lighter rider (actually the heavier rider usually does have a little more frontal area), so the force due to aerodynamic friction (drag) is approximately equal. However, the horizontal component of gravity with respect to the road surface (the part of gravity that pulls you forward) is greater with the heavier rider than with the lighter rider - this is assuming that both riders are applying the same amount of power to the pedals.

To put it simply:

10 - 2 = 8 is greater than 8 - 2 = 6 [this is a reference to the gravity acceleration formula]

In order to match the heavier rider on the descent, the lighter rider would need to apply enough additional power at the pedals to overcome the deficit between their two gravitational forces...."

I think all of this is of particular relevance for electrically assisted cyclists, given the heavier weight of most electric bikes, and the fact that we are assisted to the top of hills by the energy stored in our batteries. Once at the top I see our weight as energy stored in a different way which is released as we descend.

I'm afraid this isn't so Rooel, whatever component of gravity is used, it's always a constant, which I express in the old fashioned way as 32' per second/per second. The weight has no influence, and there is no deficit between riders of differing weights as Ian has posted. Despite Galileo's demonstration at Pisa so long ago, this remains very widely misunderstood, as Ian has also remarked.
.

 

[rooel]

Here is another one which seems relevant:

Cycling: Uphill and Downhill

and this is the conclusion paragraph:

"The primary forces a cyclist must overcome are air resistance and gravity. Air resistance increases exponentially with speed. In the transition from cycling on a flat road to climbing a hill, the decreased speed reduces air resistance to the point where drafting other riders provides little benefit. At this point, riders with superior aerobic power to weight ratios will be able to breakaway from the peloton. Due to scaling considerations, this favors smaller riders. Climbing ability can be enhanced by minimizing weight, and also by pedaling at a consistently high cadence. Large cyclists can achieve greater downhill speeds, but overall performance still favors smaller cyclists on hilly courses. Overall performance is enhanced by using a variable power strategy: increasing effort slightly on uphills and compensating with decreased effort on downhills. On extremely steep descents, it is necessary to pedal only at the start and when coming out of turns, in order to quickly achieve terminal velocity."

All of us here know of course that there are better ways to get up a hill fast than being lighter. And it does look like the majority opinion (based sometimes on mathematics and other times on simple observation) is that the greater weight provided by those batteries sends us (or drags us?) down hill faster than the lightweights. Our variable "power strategy" is to use the greater weight (of the battery) to climb the hills and then use it again to descend them faster.

 

[flecc]

Your post slipped in just after my above response Rooel.

The energy required to raise a weight is available as a counterbalance force according to gravitational laws, that's what the counterbalance weights on lifts do. However, that weight does not accelerate anything faster than a lighter weight would, acceleration as we've pointed out being a constant, whether at an angle or direct.

What these posters are all doing is confusing the two, when they are different issues. The energy expended in getting weight up a hill is lost in doing that, it is not stored in any way, it's just spent in opposing gravity. If it were stored, the bicycle would have to be heavier at the top of the hill after a climb!
.

 

[Ian]

Rooel, as I said peviously the forces are complex but here's a couple of easy experiments that prove that acceleration due to gravity is constant.

Take 2 objects of a similar shape and density but a very different size, I just tried it with a 6mm steel nut weighing 2g and a 16mm steel nut weighing 30g. Raise them high in the air and drop them, they will fall at the same rate and hit the ground together.

Take 2 objects that will roll, again of similar densities but different sizes (as are cyclists). I tried it with batteries an AA at 26g and a D at 157g, allow them to roll down a slope. They will accelerate at the same rate and reach the bottom together. I just tried it using a 1m long plastic board as the slope, with various inclines. The steeper the slope the faster the batteries roll, but they always roll together despite their vastly different weights.

OK, so the above experiments don't really have any air resistance to speak of, but air resistance is hugely variable in cycling anyway, and it's certain that the sport cyclist had a much lower resistance than me and yet I was rolling faster. The above experiments prove that weight is not a factor therefore other unknown factors must have been at work.

 

[rooel]

Agreed, flecc, the bike is not heavier at the top than is at the bottom. It no more gains weight on the way up than it loses it on the way down. However, having got all that weight to the top of the hill it is available for launching oneself over the other side.

And despite the mathematics it does seem to be a matter of observation that heavier cyclists/bikes freewheel faster downhill than lighter combinations.

Someone will have to do a test using two exactly similar bikes with the same make of tyres, wheel diameter, etc, and, if possible, with twins as riders, but one bike will have a large Sealed lead acid battery attached to the rear rack.

Such a test may prove that electic bikes "flatten" the hills not only by the assistance they provide on the way up but also by the faster speeds their weight provides on the way down.

Therefore, other things being equal, in hilly areas heavier electric bikes may be better than lighter ones (of interest to Powabyke owners perhaps) with quite the opposite being true of non-assisted bikes as they receive no help on the way up.