2019 ditch your rear disc brake ?

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cheapcookie   100 W

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Re: 2019 ditch your rear disc brake ?

Post by cheapcookie » Jun 01 2019 10:51am

I respect your opinion, I want to add a few things..

This is irrelevant but bmx old MTB bikes have the shittiest brakes cantiliver, v brake.

We have come a long way with hydro brakes.

I currently have standard rotors with mech disc brakes on my 29er SS not electrified, I ride it every morning one handed to bring donuts to the shop... uphill downhill stop signs yields redlights idiots... no problemo sombrero ...

I love wheelies, can't voice wheelieing on regen yet, BUT, I bet we could any day of the year.

Again my point isn't whatever your setup is ditch your rear brake, my point is plan for strong regen and stop freewheeling everything.

Ditch your rear brakes really means : keep on paying lots of attention to the front brakes, upgrades, maintenance...

In motorcycle class, they told us to plan ahead to be better prepared for peds with earbuds... If you haven't taken a moto class or riden a moto, I highly recommend doing it

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Re: 2019 ditch your rear disc brake ?

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Re: 2019 ditch your rear disc brake ?

Post by billvon » Jun 01 2019 12:56pm

cheapcookie wrote:
May 30 2019 1:07pm
I doubt the usefulness of a rear disc brake (lightweight human) because of powerful front brakes and regen braking
You can live without it with 99% of the safety of a mechanical rear brake. I've never gone without one just because they are so cheap, light and easy to use.
--bill von

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ferret   1 kW

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Re: 2019 ditch your rear disc brake ?

Post by ferret » Jun 01 2019 2:13pm

cheapcookie wrote:
Jun 01 2019 10:40am
Hey ferret, could you find the ditch your rear brake thread, and leave your opinion, especially tell us how pedaling is better with freewheel.

Thanks, Cookie.
Hi Cookie,
all the ebikes I've built or rode had a freewheel incorporated, so I don't know how hard is it to turn the motor while pedaling. I guess it would depend a lot on the specific motor and reduction ratio. Pedaling a heavy bike without power is hard enough for me without having to expand energy spinning the motor.
I seem to remember builds that employ an "electric freewheel" that automatically give enough throttle so that the motor spins at the pedaling speed, but that's not much better since you you'll still have to spin the motor if the battery runs out or an electrical gremlin surfaces.

As for the rear brake, I don't have the guts to ride a steep singletrail without a conventional disk brake. What will happen to my regen brake if a wire gets disconnected in the middle of a steep technical/fast downhill :shock: ?
Maybe variable regen can can have the power and modulation of a conventional brake, but even then I don't see the benefit. As mentioned before it is a massive complication for full suspension bikes because of chain growth issues. Full suspension usually requires a spring loaded tensioner, and that won't work with regen.

To sum things up, for my kind of off road riding I never seriously considered regen, but in a different application, such as a road going hardtail, it may have some merit.

Avner.
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dustNbone   10 kW

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Re: 2019 ditch your rear disc brake ?

Post by dustNbone » Jun 01 2019 2:40pm

If it extends my emergency stopping distance by more than 1 inch then no. I'm pretty sure real brakes still win.

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Chalo   100 GW

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Re: 2019 ditch your rear disc brake ?

Post by Chalo » Jun 02 2019 1:36am

dustNbone wrote:
Jun 01 2019 2:40pm
If it extends my emergency stopping distance by more than 1 inch then no. I'm pretty sure real brakes still win.
Using the rear brake extends your stopping distance. The hardest you can stop is with the rear wheel just above the ground.
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DanGT86   10 kW

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Re: 2019 ditch your rear disc brake ?

Post by DanGT86 » Jun 02 2019 10:04am

Chalo wrote:
Jun 02 2019 1:36am
Using the rear brake extends your stopping distance. The hardest you can stop is with the rear wheel just above the ground.
Not challenging that statement but am genuinely curious about your source material. Do have any links or articles explaining it?

Seems totally reasonable that the max braking force would cause maximum possible weight transfer towards the front on flat ground while traveling in a straight line.

Pertaining to modulation from regen, im most concerned about braking hard down hill while standing with my butt almost touching the rear tire. Throw in some mud or wet leaves and I would prefer to have maximum modulation on the rear brake to the point of full lock.

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Re: 2019 ditch your rear disc brake ?

Post by Grantmac » Jun 02 2019 12:19pm

Chain systems can be designed to take massive loads both directions with good result. Look how engine braking is used to slide a supermoto with control. When you aren't worried about sprockets that are designed to shift then chain tension isn't so critical.

What we need is a good means of modulating regen from a brake handle. Possibly a hydraulic pressure sensor hooked to a regular master cylinder? Anyone know the pressures they run?

As for failure modes with regen I think things like a shorted phase causing a lock up are more concerning. Mechanical brakes are after all not exactly failure mode free.

I would likely design any system with a removable link or other means of removing the chain so that you can limp home if you completely run out of power/suffer failure. At that point you know you're running front brake only and would plan accordingly.

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DanGT86   10 kW

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Re: 2019 ditch your rear disc brake ?

Post by DanGT86 » Jun 02 2019 1:53pm

I agree that chain retention is easier with non shifting standard teeth and singlespeed chain. The issue I keep bringing up about tensioners and chain management is based on the design of full suspension mountain bikes. Many common frames are not single pivot.

On the above mentioned supermoto application the motor sprocket is placed very close to the single pivot location of the swing arm. During suspension travel the chain growth can be less than a single link of chain so it cant come off. You build in a small amount of slack so it doesnt bind and you are good to go.

On a mountain bike with a horst link 4 bar type suspension there isnt a common pivot point. So the chain must grow and shrink during the travel. A derailleur can handle this on the slack side of the chain because it has tons of travel. When you regen the slack side becomes the working side and the full kinetic energy of speeding bike will instantly pull the derailleur/tensioner straight likely destroying it and the top side of the chain will have all the slack which could be several inches. This will throw the chain for sure. No rear freewheel means a thrown chain can still dump energy into the frame as it locks the wheel up or pulls you in by your pants leg.

Non freewheeling chains are serious business. Depending on the suspension geometry it might be possible to design idlers to get the chain growth to under the minimum length required to retain it. But most of the time if you are talking regen and suspension its going to be swing arm mounted final drive or a pivot point centric drive.

If someone did manage to design super heavy spring loaded tensioners similar to a derailleur that could handle regen forces, the braking wouldnt start until the tensioner had stroked to its limit so it would likely feel really sloppy and not have good modulation during the windup.

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Re: 2019 ditch your rear disc brake ?

Post by Grantmac » Jun 02 2019 2:09pm

Oh I definitely think that suspension configuration will need to be carefully selected to make it all work. A lot of the complexities of MTB suspension become far less critical with the smooth power of a motor providing assistance.
Possibly high single pivot bikes will prove ideal with a 1st stage reduction to the pivot then second stage to the wheel.

A completely purpose built design can probably use a totally novel way of combining both power systems.

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Chalo   100 GW

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Re: 2019 ditch your rear disc brake ?

Post by Chalo » Jun 02 2019 4:29pm

DanGT86 wrote:
Jun 02 2019 10:04am
Chalo wrote:
Jun 02 2019 1:36am
Using the rear brake extends your stopping distance. The hardest you can stop is with the rear wheel just above the ground.
Not challenging that statement but am genuinely curious about your source material. Do have any links or articles explaining it?

Seems totally reasonable that the max braking force would cause maximum possible weight transfer towards the front on flat ground while traveling in a straight line.
It's the result of the geometric physical constraints on braking when other factors such as the braking mechanism or tire adhesion don't impose a lower limit. The harder you decelerate, the more weight is shifted to the front wheel, until there's no more weight on the back wheel. Beyond that, the rear wheel lifts up and braking is progressively limited by the rising center of mass's angle above the bike's point of contact.

The point along this continuum where there is no weight at all on the rear tire, but it has not lifted off the surface enough to raise the bike's center of mass, is the point of maximum braking deceleration.

https://www.sheldonbrown.com/brakturn.html#panicstop

When other factors intervene sooner-- like compromised surface traction, braking force being limited by the brake itself, or the front fork's structural integrity-- then rear braking has a role in minimizing stopping distance.
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Re: 2019 ditch your rear disc brake ?

Post by Aquakitty » Jun 02 2019 6:27pm

Chalo wrote:
May 30 2019 1:14pm
Why keep the pedals?
Why do non-motorized bikes have pedals when we could just put a motor on them! Gee maybe because it's good exercise. Fat is the most efficient and environmentally friendly fuel in the end. Literally.
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Chalo   100 GW

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Re: 2019 ditch your rear disc brake ?

Post by Chalo » Jun 02 2019 6:34pm

Aquakitty wrote:
Jun 02 2019 6:27pm
Chalo wrote:
May 30 2019 1:14pm
Why keep the pedals?
Why do non-motorized bikes have pedals when we could just put a motor on them! Gee maybe because it's good exercise. Fat is the most efficient and environmentally friendly fuel in the end. Literally.
OP said
I [doubt] the usefulness of speeds, derailleur and cassette. Because of powerful top end and low end, added complexity
I was following his suggestion of what I consider a bad idea to its logical conclusion.

Personally I don't think any motorized bikes with dramatically higher than human speed should be equipped with pedals. Usually those are used as a disguise so that motorcyclists feel more comfortable usurping cyclists' rights-of-way and shirking their legal responsibilities as motorcyclists.
This is to express my gratitude to Justin of Grin Technologies for his extraordinary measures to save this forum for the benefit of all.

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Re: 2019 ditch your rear disc brake ?

Post by cheapcookie » Jun 03 2019 1:23pm

Chalo wrote:
Jun 02 2019 6:34pm
I [doubt] the usefulness of speeds, derailleur and cassette. Because of powerful top end and low end, added complexity
I was following his suggestion of what I consider a bad idea to its logical conclusion.

Personally I don't think any motorized bikes with dramatically higher than human speed should be equipped with pedals. Usually those are used as a disguise so that motorcyclists feel more comfortable usurping cyclists' rights-of-way and shirking their legal responsibilities as motorcyclists.
Cool assumptions

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Re: 2019 ditch your rear disc brake ?

Post by Chalo » Jun 03 2019 1:34pm

cheapcookie wrote:
Jun 03 2019 1:23pm
Chalo wrote:
Jun 02 2019 6:34pm
I [doubt] the usefulness of speeds, derailleur and cassette. Because of powerful top end and low end, added complexity
I was following his suggestion of what I consider a bad idea to its logical conclusion.

Personally I don't think any motorized bikes with dramatically higher than human speed should be equipped with pedals. Usually those are used as a disguise so that motorcyclists feel more comfortable usurping cyclists' rights-of-way and shirking their legal responsibilities as motorcyclists.
Cool assumptions
Safe assumptions.
This is to express my gratitude to Justin of Grin Technologies for his extraordinary measures to save this forum for the benefit of all.

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Skaiwerd   100 W

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Re: 2019 ditch your rear disc brake ?

Post by Skaiwerd » Jun 03 2019 2:27pm

Pedals help you go anywhere!
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