Interesting Encounters

[flecc]

That's true Ian, and it certainly is for lightweight me against some of those athletic hulks!

I also think we can get less tired at times on our e-bikes which even gives a relative cycling advantage against the athletic types when the going is tough.

I only ever used the restrictor for the first 300 yards tryout of the bike, then about turned, came back and disconnected it. I couldn't stand the way it worked, preferring the natural behaviour of the motor.
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[Ian]

I couldn't stand the way it worked, preferring the natural behaviour of the motor.
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I know what you mean Flecc, it just gets into it's stride and then fades away. I doubt I'd have managed todays 28 miles on one battery in de-restricted mode though.

 

[flecc]

True again! Mine's better since conversion to T bike as it's lighter and rolls much easier, but still only around 20 miles since I don't make an effort to do better as I enjoy the performance too much. Now the radical battery has settled down fully the bike's surge of acceleration from 20 to 24 mph when the throttle is snapped open is addictive.

But that range is good enough since I'm happy to take a spare battery with me.
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[coops]

Hi all sorry to arrive late to the discussion - an interesting encounter indeed Ian! Like flecc, I'd be surprised to see another ebike at all, and happily astonished to see one identical to mine (changes aside), even another ezee bike (there must be quite a few out there?...) would be a pleasant surprise .

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.

Didn't think you had steep hills where you are, Ian .

I didn't read your last post thoroughly flecc, so you may have already said some of this, ditto for all the other posts.

Newton, (I'll blame him!)... he say that the bike & rider accelerate downhill until the total force acting on the bike in the direction of motion (downhill component of the "weight", or gravitational force and, uphill, the air & rolling resistance forces) is zero i.e. they cancel each other out, after which point the bike travels at a constant velocity i.e. like a "terminal velocity" - for so long as the total force acting in the direction of motion remains zero.

So the "weight" or component of gravitational force acting on the bike & rider can increase the downhill speed, so long as the total retarding forces of air & rolling resistance do not equal or exceed it.

Flecc's T-bike illustrates that: the reduced force of air & rolling resistance means the bike's terminal velocity is still higher than his Torq was before, despite less "forward"/downhill force due to the lower weight of the T-bike (i.e. the reduction of retarding forces (air, rolling resistance) is greater than the reduction of "accelerating" force, or weight, hence total forward/downhill force is higher overall ).

The opposite is a heavily laden tourer, heavy but not aero-efficient, which has a lower terminal velocity for the gradient due to high air resistance - the main factor slowing all bikes at these sorts of speeds.

Thats the (sort of) "standard" answer, though I'd be surprised if that alone explains your observation Ian, since as you say the weight difference is not so great and the Torq not so "aero" as many road bikes, so many of the other factors mentioned probably come into play.

The energy sistuation is rather more complicated, I started to describe it in another thread, and not strictly necessary to help explain what's going on.

Phew!

Stuart.

 

[flecc]

Yes that's similar to what I posted Stuart, except that as Newton didn't know what a bike was, he wasn't aware of the particular factors other than air resistance which slowed it's downhill acceleration, and I've highlighted those in the term "stiction".

My stating that a gain due to additional weight is an initial one is also consistent with Newton, and those conclusions of mine were reached without an apple in sight.
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[coops]

Yes, I prefer to enjoy eating my apples rather than have them give me a headache, and same with my cycling too now . I like the term "stiction"

I was going to add I didn't think Newton had a bike, but I'll still blame him for my post .

 

[coops]

Good results all round for your T-bike then, flecc, by the sounds of it: 20 miles derestricted and with steep hills (I assume!) is not to be sniffed at, especially if its high speed (that battery mod is very appealing! 24mph is a bit more than before, isn't it! Might get 22mph for me ) and easy pedalling as you suggest.

The aero improvement & lower weight alone increase uphill & downhill speed too!! So that's.... er .... faster & more efficient in all circumstances then! .

I'm planning to hold off a tyre change till I get padded grips for the bars (with throttle mod ), to see how much they "soften" the ride and how high I can tolerably run front tyre pressure, so that I can then choose tyre width accordingly.

Does that make sense do you think, in terms of making upgrades while at the same time reducing the aero & rolling resistance?

 

[flecc]

Yes, that makes sense, but I don't think you'll get very much reduction. Given the "throw" of the front motor weight and rigid forks, the tyre width reduction will be very limited. The widest Marathon Plus is 38 mm, less than the standard 1.75" Kenda which is roughly 44.5 mm, so that could be the limit.

Below that there's 35 mm, 30 mm, and 28 mm MPs, but the last two would be impossible with the motor.

However, any of them at any Schwalbe approved pressure rolls much easier than the Kenda.
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[ITSPETEINIT]

Great Science

Well! Is there another interesting encounter?
Peter

 

[coops]

Sorry for the skip further off topic Pete .

Thanks flecc: that'll do for me I'll probably end up choosing between the 35 & 38mm then.

On topic, sort of, its interesting how surprising it is to meet a fellow Torq owner on local roads, yet on pedelecs here we have many members daily discussing changes/mods to our bikes, many of which are not only identical makes, but have very similar modifications too! (T-bike is unique though ) Like gears, bar grip, throttle & tyre changes for instance.

It feels very strange - like a niche within a niche community!

I've never even seen another ebike on the roads, so no encounters of that kind, but I often meet walkers and cyclists very interested in my bike which is pleasant and their enthusiasm contributes to my continued "buzz" from riding it .

I'll have to catch up on the rest of the thread in detail tomorrow now I think.

 

[Ian]

I've never even seen another ebike on the roads, so no encounters of that kind,

Flecc and others have also commented how few they see. I perhaps see more than most but still it's a very small number. These figures suggest that possibly half a million have been sold over the last 3 years, I doubt that Ford have sold that many cars but I know which I see most of!

 

[ITSPETEINIT]

A bit over the top!

prState: they might be going as fast as they dare but I doubt they'd pass up an oportunity to accelerate faster between bends.

Richard. Its sounds feasible that you would begin a descent at a higher speed than a conventional cyclist. Most descents are preceded by an accent that would tire many cyclists, they would probably crest the hill almost at a standstill and then let gravity alone take over. By contrast you would perhaps crest the hill at 9 mph and quickly accelerate to 15mph before gravity took you to terminal velocity

I think one would have to be in the mind of the T. de F. rider to understand the 'limitations' he experiences on the descent. I expect, in the main, they are natural, like 'fear', knowing his capability: factors like gravity, bends (of all angles), roadside safety furniture and the efficiency of their brakes combined with rim heating all impact on outright speed. That's what concerns them: "Terminal" velocity!
As for the speed at which a conventional cyclist crests the brow of a hill: he must be travelling fast enough to maintain balance; fast enough to maintain momentum. Slackening off at that point will bring him to a standstill with a few torturous feet remaining. Who would deny him the revel in the downward swoop to recharge his 'battery' ? He has no back-up (unless he's read a few of these postings)
I used to go over the top of hills at 10 mph before electric bikes became a viable means of travelling up hill - but that was in another life. The good old days? More exhausting but more rewarding in some respects than the cycling of today. Imagine riding around England for 10 days or so and hardly meeting a motor car. Is this Utopia I see before me?

Peter

 

[flecc]

Imagine riding around England for 10 days or so and hardly meeting a motor car. Is this Utopia I see before me?

Peter

English roads post World War 2 were quite clear until the end of the 1950s due to nearly all cars having been requisitioned by the authorities during the war and variously destroyed in the war effort.

At the start of the 1950s I could sometimes ride a motor bike the 25 miles from Bournemouth to Southampton during the day and not see a single car or other motor vehicle until reaching the other end. Today it would be virtually impossible to find a point where a car wasn't in view!
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[Beeping-Sleauty]

aahhh,...sundays.

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 ..........

i had the good fortune to 'chase' a very fit & pretty Lady cyclist from Goldhanger to Colchester ( about 15 miles) yesterday in the sunshine.

it was my return journey, so there was not a lot of 'Poke' left in my SLA, but we overtook each other a couple of times, on one pass i noticed she had stopped and dis-mounted and was bent over hands on knees, she could pull away from me on the flat, but paid on the hills, up & down and arrived no more than a hundred seconds in front of me.

i think we both enjoyed the race, she waved as we parted, there was some considerable incentive to try and stay up with her, as she had a most attractive rear view and was wriggling around and working hard at staying in front, nice hand-built bike too.

wish all sundays were like that....
beeps

 

[Ian]

Now that was an interesting encounter Beeps.
Isn't it funny how certain things can bring out reserves of energy you never knew you had

 

[lum]

Hi guys,

As there has been a lot of attempts to explain this phenomenon involving non-equivalent variables (kinetic energy, force, acceleration, pressure etc.) I have to jump in here in support of Rooel's post. Rooel quotes a post from another forum:

"....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."

OK it is badly worded, it doesn't state whether by “component of gravity” it means force or acceleration but its implication is correct – that drag force is approximately constant between the two riders but the force due to the gravitational acceleration increases with rider mass.

Note it is *acceleration* due to gravity that is the constant. Force increases linearly with rider mass. Force due to gravity (Fg)

Fg = mass * gravitational_acceleration

Therefore gravity exerts approximately 1000N force on a 100kg rider or 50N force on a 50kg rider (although only a proportion of this force accelerates the rider due to the slope of the hill, he isn’t free-falling). In the absence of frictional forces and wind resistance both riders accelerate at the same rate and obtain the same speed at the bottom of the hill.

It is wind resistance that can explain why the heavier rider can go down a hill faster. The force due to drag (Fd) is:

Fd = ½ * density * frontal_area * drag_coefficient * square_of_velocity

The reason why the heavier rider goes down the hill faster is due to that fact that frontal area increases less rapidly than rider mass (you can prove this to yourself using the equations for volume and surface area of a sphere for example – volume increases with the cube of radius while area increases with the square of radius). Therefore Fg, the accelerative force, increases more rapidly with rider mass than Fd, the decelerative force. Therefore the terminal velocity is higher for the heavier rider.

This is why a brick beats the feather when it is chucked out of the tower.

 

[flecc]

I agree Lum.

As I posted earlier, and in agreement with the force versus resistance here and your mention of friction, the initial acceleration gain over seconds is due to weight versus the drag components (rolling resistance, friction etc) which I grouped under the term "stiction", air resistance being negligible initially. I think this has relatively more importance on a low speed vehicle like a bike, only a few riders exceeding 25/30 mph downhill before braking a bit, many long before reaching those speeds.

As speed rises of course, air resistance increasingly takes over and eventually becomes the only component worth considering as you've posted.
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[rooel]

Thanks to all those who have provided mathematical solutions. I think I understand them as I read them - slowly - but would hesitate to pass them on to someone else in my own words. However it does appear, if I understand most of what has been posted, that my original simple suggestion was correct: the heavier rider/bike managed to keep up downhill with the furiously pedalling sports cyclist thanks to the greater weight of the former.

This is heartening as it corresponds with what I have seen and experienced.

Rainfilled buckets of water to be slung on the handlebars at the top a hill and jetisoned at the bottom, therefore, sounds like a good idea, and certainly much more sensible than my suggestion of picking up, and throwing off, bricks.

 

[flecc]

In short, yes, and yes!
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[Ian]

Note it is *acceleration* due to gravity that is the constant. Force increases linearly with rider mass. Force due to gravity (Fg)

Fg = mass * gravitational_acceleration

Sorry to throw a spanner(or an apple) in the works but according to Newtons first law of motion inertia has to be considered as a force opposing that causing acceleration and I see no mention of it here.

The result is that while the force exerted on an object due to gravity increases in proportion to the objects mass so does the force required to accelerate it in exactly the same proportion. hence the heavier object will not accelerate faster, as shown with the battery rolling experiment.

Air resistance is of course a factor but all other things being equal it will affect and slow the larger rider to a greater extent.