What determines wheel zippiness?

[Chriull]

51 minutes ago, mrelwood said:

Me and @Mike Sacristan seem to disagree. Pedals tilting forward makes the natural no-effort stance (ankles at 90•) tilt forward as well. 

Seems like everyone has his own preferences. I can't stand downward tilted pedals. They give me the feeling of somethings wrong...

51 minutes ago, mrelwood said:

Three times?! By moving the CoG just from 8.5cm to 10.5cm before the axle? Sounds incredible.

No.

By the riders torque created by putting the weight on the oedal tips. At an 20° incline.

51 minutes ago, mrelwood said:

Less lean? This I don’t understand either. The center point, the no-acceleration position of the CoG is still the same, directly above the axle.

Not at an incline.

[Chriull]

2 hours ago, mrelwood said:

Less lean? This I don’t understand either. The center point, the no-acceleration position of the CoG is still the same, directly above the axle. For the effectively longer pedal, to reach the tip of the pedal, doesn’t it require a lean that moves the CoG (or point of force contact) further from the center?

For positive accelerations on an incline one needs a certain minimum moment arm ("displacement") which is not dependend on the pedal tilt. So the minimum lean, cog shift, force of attack point offset is the same distance from the axle for all pedal tilts. Just with an upward tilt its a bit further away from the pedal center as with a downward tilt.

So "further" from the center is relative - depending on how one measures

Btw: my statements refer to the setting described in 

with clarifications in the following posts.

2 hours ago, mrelwood said:

Just like longer pedals allow for a further lean, but still require the same amount of lean for the same displacement?

Here the graphs for an 20° incline and resulting acceleration vs. "Forca attack point on pedal measured in m from pedal center". One time for +5° pedal tilt (backwards tilt, pedal facing upwards) and one time for -5° pedal tilt (forward tilt, pedal facing downwards)

So with +5° one gets positive accelerations starting from ~7.5 cm from pedal center, with -5° starting from ~9.5 cm from pedal center. That should be (imo as explained by @RockyTop) the same displacement/moment arm for both cases. Equals about the ~2cm difference in distance from the pedal center, as linked below)

And with the +5° version the max acceleration of ~0.4 m/s² of the -5° version is already reached at ~8,5 cm from pedal center vs the max 10.5 cm for the -5° version...

But however - these numbers show great benefits for quite extreme inclines like this 20°, quite at the border of what's doable with this wheels geometry. The less the incline, the less the difference gets. So the max incline reachable with this wheels geometry would be 24.9° with horizontal pedals (22,2° with -5° tilt and 27.3° with +5° tilt...)

Ps.: Just to have the numbers again - the difference in maximum moment arm/displacement between +5° and -5° is about 2 cm:

 

 

[Mono]

6 hours ago, mrelwood said:

Three times?! By moving the CoG just from 8.5cm to 10.5cm before the axle? Sounds incredible.

Yes, it's because we started with a very small thrust, because we remove the negative thrust coming from the incline from the denominator:

   Each 1cm forward displacement of the CoG gives roughly 4.3kg = 90kg x 1cm / 21 cm of additional thrust.

At 8.5cm forward displacement of the support point we have 90kg x 8.5cm / 21cm = 36.4 kg forward thrust, minus sin(20º) x 90kg = 30.8 kg backward thrust at 20º road incline, = 5.6 kg. Now we add from a 2cm shift 2x4.3kg and get (5.6 + 2x4.3) / 5.6 = 254%. If we consider the original thrust generated at 8.5cm, it is only (36.4 + 8.6) / 36.4 = 124%, so it becomes 24% additional thrust instead of a factor of three (generously rounded).

Edited December 18, 2019 by Mono

[Mono]

4 hours ago, mrelwood said:

Less lean? This I don’t understand either.

I think what was meant was a less extreme position on the pedal, as "lean" is not part of the model. This is really trivial: if we are on the pedal tip and move the pedal tip forward (by tilting the pedal back) we don't need to stay on the pedal tip to get the same acceleration, hence "less lean".

__
There are two fundamentally different EUCing cultures populating this globe. One for which 40km/h is not exactly speeding and the other for which surpassing 25km/h is simply off limits. Always good to keep this in mind 

Edited December 18, 2019 by Mono

[Chriull]

4 hours ago, mrelwood said:

 

Less lean? This I don’t understand either. 

 

38 minutes ago, Mono said:

I think what was meant was a less extreme position on the pedal, as "lean" is not part of the model. 

Yes. And my original formulation was

"Or otherwise - with 5° upward tilt less lean/"bringing the cog forward" is needed for the same acceleration."

So "less lean" is just one of the possibilities to bring "the force attack point" nearer to the pedal center.

As you state lean is not part of the model, or a position of the cog, just a "force attack point"(?is this a proper english expression?) And the force vector. But these are of course determined by the stance, position of the cog and the "lean"

[Mono]

I also feel often to be in an awkwardly dorsiflexed position with my ankle, whereas a forward tilt usually bothers me less (thought it may happen that my toes threaten to catch the ground surface, higher pedals would help to prevent this). I wondered how much that depends on the rider height, as a tall rider needs less lean to move the CoG and usually has taller feet. The lean effect seems to be small though: assuming the CoG at 1/2 of the rider height, a 170cm vs 200cm rider need to lean 3.4º vs 2.9º to move their CoG by 5cm forward without changing foot position (if I got the numbers right). Still:

A smaller rider on a larger wheel needs to dorsiflex more and hence may prefer some pedal dip.

A bigger footed rider with a smaller wheel and lower pedals may fear catching the ground with a toe or feel that sliding on the pedal is more detrimental because they have less forefoot pedal support to begin with and hence may be opposed to pedal dip.

__
There are two fundamentally different EUCing cultures populating this globe. One for which 40km/h is not exactly speeding and the other for which surpassing 25km/h is simply off limits. Always good to keep this in mind 

Edited December 18, 2019 by Mono

[mrelwood]

Thank you guys for being patient enough to explain the results to a bit slower functioning brain...  I finally got it!

3 hours ago, Mono said:

A smaller rider on a larger wheel needs to dorsiflex more and hence may prefer some pedal dip.

Well, I’m 193cm tall and have a EU 46-47 shoe... But otherwise the theory does sound sound.

[Mono]

15 minutes ago, mrelwood said:

Thank you guys for being patient enough to explain the results to a bit slower functioning brain...  I finally got it!

Well, I’m 193cm tall and have a EU 46-47 shoe... But otherwise the theory does sound sound.

I thought the theory would predict that you are somewhat less happy with pedal tilt on the KS-16S than on the MSX. But then I realized that I actually do not know the ground clearance of the KS-16S  I just assumed that it is rather low.

Edited December 18, 2019 by Mono

[mrelwood]

2 hours ago, Mono said:

I thought the theory would predict that you are somewhat less happy with pedal tilt on the KS-16S than on the MSX. But then I realized that I actually do not know the ground clearance of the KS-16S  I just assumed that it is rather low.

It’s not very low actually, I think it was one of the highest when it came out.

Anyway, my bigfoot pedal extension plates reach 4cm on the 16S and 6cm on the MSX to the front of the original pedal edge. But since the DIY plate is on top of the original pedal, I stand a bit higher, and maybe more importantly my shoes can’t bend like they would on the original pedals, since there is no real overhang. So my toes may actually stay further from the ground due to the extensions.

The extensions may also be why I prefer a slight forward tilt even for steep inclines, as the footing length I can use for balancing doesn’t get anyway near as short as it would without them.

[Chriull]

56 minutes ago, mrelwood said:

Anyway, my bigfoot pedal extension plates reach 4cm on the 16S and 6cm on the MSX to the front of the original pedal edge.

Wow - 14.5 instead of 10.5 cm should be quite a game changer... Even if not used to the full extend!

58 minutes ago, mrelwood said:

I stand a bit higher, and maybe more importantly my shoes can’t bend like they would on the original pedals, since there is no real overhang.

I ride normally with shoes with a very flexible sole - so my overhanging toes grabbing around the pedal tip are mostly endangered on off road inclines with roots/stones... So thats (maybe) the main reason why i detest forward (downward) pedal tips - a reason you don't seem to know/have with your extension!

[RockyTop]

When angled back 5 degrees you have shifted the weight of the EUC behind the CoG. So you will have to make up for that before gaining the advantage of the extra 2cm. ( I turned my MSX pedals around and gained almost 2 cm.) 

correction, you have moved the CoG behind the center of the wheel. 

Edited December 19, 2019 by RockyTop

[Mono]

5 hours ago, RockyTop said:

When angled back 5 degrees you have shifted the weight of the EUC behind the CoG.

My V8 has around 7kg head weight at its circumference at 22 cm. Angling this head weight by 5º shifts in effect 7kg by sin(5º) x 22cm ≈ 1.9cm and generates 0.6kg ≈ 7kg x 1.9cm / 22cm thrust which is canceled by shifting 80 kg rider weight by 0.17cm ≈ 1.9cm x 7kg / 80kg in the opposite direction.

Edited December 19, 2019 by Mono

[RockyTop]

7 hours ago, Mono said:

My V8 has around 7kg head weight at its circumference at 22 cm. Angling this head weight by 5º shifts in effect 7kg by sin(5º) x 22cm ≈ 1.9cm and generates 0.6kg ≈ 7kg x 1.9cm / 22cm thrust which is canceled by shifting 80 kg rider weight by 0.17cm ≈ 1.9cm x 7kg / 80kg in the opposite direction.

Hold up!! I get another 5 degrees to the positive. It is 5 degrees each way.     .... I am going to have to borrow my wife’s fingers and toes for this math.......  that’s ...  0.34cm.  ... And that is on a tiny little V8.  Think about the ridiculously shaped 18s. 

Has anyone bought up the inertia of disportioncate weight above the axle that opposes acceleration and braking? 

As much as I enjoyed reading this post I prefer stability to zippiness.

Given @mrelwood‘s and my size I am not sure that our experience on a larger wheel is actually all that less zippy compared to a smaller person proportionally on a smaller wheel. Small wheels are just too hyper or “zippy” to me. 

After gaining riding skills, I have no complaints about acceleration or steep hills. I no longer notice effort for either. 

@Mono would you want your V8 to be more zippy? 

Edited December 20, 2019 by RockyTop

[Mono]

13 hours ago, RockyTop said:

@Mono would you want your V8 to be more zippy? 

I guess so, but I also don't see zippiness to be the opposite of stability.

[mrelwood]

2 hours ago, Mono said:

I guess so, but I also don't see zippiness to be the opposite of stability.

V8F?

[RockyTop]

3 hours ago, Mono said:

I guess so, but I also don't see zippiness to be the opposite of stability.

Stability caused by inertia. ( acceleration. Braking and turning) On a smaller wheel, (KS16s ) If I hit a bump, or a burst of wind, or have to shift my feet the wheel can jumps out from under me with an unintentional bust of speed or redirection. I have to be much more precise in my movements. I feel like I am working on a Swiss watch with a ball pean hammer. The bigger wheels require a commitment of energy to alter speed or direction. As I said,  I suspect that rider size makes a difference in wheel response. I believe that my 18XL might be as zippy to me at 100kg+ as a 16s is to someone at about 70kg. As a result the 16s is much more responsive, hyper, zippy to me than someone smaller. Speed is also a factor. When you increase size and weight the relevant speed for the same response would also increase.

ie. Rider’s inertia compared to wheel’s inertia. 

Disclaimer: I love my KS16s. I really do. I just would not use it blindly hitting bumps in the dark at high speed like I do on my MSX....... .  Disclaimer 2:  don’t ride blindly at night at high speed. That would be stupid. 

[mrelwood]

 

2 hours ago, RockyTop said:

As I said,  I suspect that rider size makes a difference in wheel response.

 

2 hours ago, RockyTop said:

Disclaimer: I love my KS16s. I really do. I just would not use it blindly hitting bumps in the dark at high speed like I do on my MSX....... .  Disclaimer 2:  don’t ride blindly at night at high speed. That would be stupid. 

So, you and me weigh and heigh the same, and we both own the 16S and the MSX. We also share our opinions on behaviour of different sized wheels. So I think you are absolutely correct! 

Ps. I don’t ride blindly in the dark at high speed either, most times...  If I momentarily lapse concentration though, no better wheel to do it with than the MSX.

[Mono]

20 hours ago, RockyTop said:

Has anyone bought up the inertia of disportioncate weight above the axle that opposes acceleration and braking? 

First, it looks like a ≈2% effect: the rider weight above the axle is ≈5–15 times larger and 3–8 times further away than the head weight of the wheel. So I guess that means if the wheel stays upright the rider has to lean in ≈1/10/5=2% more. Second, one should feel also this more pressure pushing up under the sole. I can imagine that this is perceivable for very top heavy wheels. Third, it is factored in when we consider the overall weight that needs to be accelerated, where the weight distribution does not matter. I don't see how weight distribution of the wheel could be otherwise relevant, but I am not absolutely positive either.

[RockyTop]

6 hours ago, Mono said:

First, it looks like a ≈2% effect: the rider weight above the axle is ≈5–15 times larger and 3–8 times further away than the head weight of the wheel. So I guess that means if the wheel stays upright the rider has to lean in ≈1/10/5=2% more. Second, one should feel also this more pressure pushing up under the sole. I can imagine that this is perceivable for very top heavy wheels. Third, it is factored in when we consider the overall weight that needs to be accelerated, where the weight distribution does not matter. I don't see how weight distribution of the wheel could be otherwise relevant, but I am not absolutely positive either.

Picture a KS18s.  Just to see the problem more easily imagine that 90% of the weight is in the top 2 cm. Now bolt the tire of the wheel standing upright to the back of a flat bed truck. Imagine that the EUC bolted to the truck is traveling down the road at 50km/h. Now slam on the brakes in the truck. The top of the wheel will continue forward. The back of the pedal will lift. The back of the pedal lifting is the opposite of braking. When you brake or accelerate the EUC’s pivotal weigh is fighting you. 

The weight above the axle has leverage on your control lever. ( pedal)

Edited December 21, 2019 by RockyTop

[Mono]

1 hour ago, RockyTop said:

The weight above the axle has leverage on you control lever. ( pedal)

Yes, and I computed the effect size of the leverage. Compared to the effect by the rider on the pedal it is 2–5%, if I was not mistaken. The (relative) effect of the wheel weight itself is around 4 times larger, because its effect is not reduced by being closer to the axle than the rider is. So it seems 4-5 times more important to be concerned with wheel weight itself than with the distribution of the wheel weight.

Edited December 21, 2019 by Mono

[RockyTop]

1 hour ago, Mono said:

Yes, and I computed the effect size of the leverage. Compared to the effect by the rider on the pedal it is 2–5%, if I was not mistaken. 

 Sound right. 

1 hour ago, Mono said:

The (relative) effect of the wheel weight itself is around 4 times larger, because its effect is not reduced by being closer to the axle than the rider is. 

Ok.  But every bit counts. If that weight were below the axle it would help rather than hurt. ..... 

I came to the party late. The big three were already spoken for. 

1) wheel size 

2) pedal size 

2.005) hanger length and pedal angle. 

3) delayed response software 

I am left with weight distribution. 

[Mono]

Nothing wrong with exploring all possibilities. That's the whole point, actually...