Brake confusion?

[Stephen Merritt]

Its a Evelo aries hub drive version... best warranty i could find with the least complaints about the company and they actually talked to me with in a couple of hours in detailed form instead of waiting a week to emailed back for some less than meaningful explanation for my questions about a particular bike. I was willing to pay a few hundred more that something somewhat equally specked from people that acted like they really wanted to sell their product...

 

[Nova Haibike]

I don't want to stop in 5 ' from 35 mph. Problably throw me chin first over the handlebar. Hydraulics are a mania. Total waste of money

Hydraulic actuated discs is not only about power. They have much better feel, much better modulation than mechanical discs. A hydraulic brake is not always more expensive either; for example a hydraulic Shimano Deore caliper is actually less expensive than the mechanical Avid BB7.

The only real drawback to Hydraulic brakes is when it comes time to bleed them. Some brands are a pain to work with. Even with the easy ones, it just takes much more time than replacing a cable on a mechanical system.

 

[dAz63]

Yes I prefer disc brakes over other types simply because you have more consistently in braking wet or dry, and I prefer hydraulic disc brakes over the mechanical discs because of more braking power and self adjusting, the pads wear evenly unlike mechanical which can wear diagonally if you forget to adjust them because only one side moves which flexes the disc over to the fixed inner pad, hydraulics move both pads evenly and self centre.

Fitting new pads on hydraulics is simply push the pistons back in, fit the pads, pump the brake lever and the pads are centred and adjusted.

12,000km on one bike no leakages or problems with the brakes

 

[justforfun]

35-40 mph hill close to home with stop at bottom. V-brakes work but hydraulic disc brakes are much sweeter with heavy ebike.

 

[erider_61]

Had my Voltbike Bravo almost a year..love the hydraulic brakes. The bike has amazing stopping power and just replaced the front pads with upgraded ceramic pads after 2,500 km.

 

[Sierratim]

Had my Voltbike Bravo almost a year..love the hydraulic brakes. The bike has amazing stopping power and just replaced the front pads with upgraded ceramic pads after 2,500 km.

Terrific mileage on those brake pads. We're in a very hilly small town. I got ~500 miles (sorry, no conversion math this evening) on the first set of Shimano organic pads. What type of terrain do you ride?

 

[dAz63]

I don't want to stop in 5 ' from 35 mph. Problably throw me chin first over the handlebar. Hydraulics are a mania. Total waste of money. BTW my hands are so fragile the thumb shifter has destroyed my r. thumb joint.

Yeah I have arthritis in both thumb joints, asked my doc about it, he said it's the most used joint in the body so don't use them, yeah like that's going to happen.

I really don't like click shifters for that reason, one of my bikes uses them and it can be a real effort to push the lever in, the other bike has a grip or twist shift, much faster to shift and no strain on my thumb joint.

 

[erider_61]

Terrific mileage on those brake pads. We're in a very hilly small town. I got ~500 miles (sorry, no conversion math this evening) on the first set of Shimano organic pads. What type of terrain do you ride?

So 500 miles is a little more than 800 km
I ride mainly flat terrain with 1 really steep hill down to the beach. I highly recommend the switch from metallic resin pads to ceramic pads. The only downside will be increased rotor wear but to me the trade off in increased stopping power is worth it...

 

[Sierratim]

So 500 miles is a little more than 800 km
I ride mainly flat terrain with 1 really steep hill down to the beach. I highly recommend the switch from metallic resin pads to ceramic pads. The only downside will be increased rotor wear but to me the trade off in increased stopping power is worth it...

What brand of ceramic pads are you using? Do they need to be bedded in like metallic pads?

I'm running finned Kool Stop semi-metallic pads now with better life, but no change in stopping power.

 

[justforfun]

Over 6K on oe pads, working just fine.

 

[Sierratim]

Yeah I have arthritis in both thumb joints, asked my doc about it, he said it's the most used joint in the body so don't use them, yeah like that's going to happen.

I really don't like click shifters for that reason, one of my bikes uses them and it can be a real effort to push the lever in, the other bike has a grip or twist shift, much faster to shift and no strain on my thumb joint.

My oldest son converted his click shifters to twist shifters to reduce pain. His LBS did it very reasonably, thought this was several years ago.

 

[Sierratim]

Over 6K on oe pads, working just fine.

What type of terrain do you ride?

 

[justforfun]

What type of terrain do you ride?

Mostly flat pavement with a few hills.

 

[erider_61]

What brand of ceramic pads are you using? Do they need to be bedded in like metallic pads?

I'm running finned Kool Stop semi-metallic pads now with better life, but no change in stopping power.

All brake pads need to be bedded in. I purchased the ASHIMA brand...reasonable price and I do notice a difference in how quick they bring me to a stop at full speed...

 

[Sierratim]

My 160 mm mechanicals will stop me & 60 lb groceries in 15' from 35 mph. Pull me right off the seat. How fast were you planning to go?
Use the switched handles from the conversion kit, they are 1" longer than the handles the bikes come with.
Every auto disk brake caliper I put new pads on has leaked unless I replaced the cylinder. Why would I want that problem on a bicycle where hydraulics are not required? Plus the fluids are non-standard and cost more than fine wine.

I can believe braking that hard would pull you off the seat. A quick 'back of the envelope' calc estimates that braking from 35mph to 0mph in 15 feet will generate 2.7Gs of deceleration. I don't know what the total weight is but assuming something like 300lbs for ebike+rider+cargo then each tire would be resisting 405lb, if they are loaded equally in braking. I'm not sure I could hold on at 2.7Gs, much less avoid skidding the tires, but I suppose it's possible.

This got me thinking, could I actually stop my ebike within 15 feet doing 35mph? It doesn't fit my experience well so I dug a little deeper. I found an online paper that has brake test results that seem useful here. The tests report a max braking force of 450N for a 160mm rotor. For two wheels this yields 900N of braking force. This test used hydraulic brakes, but if you pull the brake lever hard enough you might get to these figures with mechanical disc brakes.

Doing some 'back of the envelope' calcs and borrowing Newton's 2nd law F=ma (where 'm' is total weight & 'a' is the deceleration required to stop in 15 feet = 2.7Gs) we get F=2.7G*9.81m/s^2/G*136kg = 3,602N required braking force to stop within 15 feet from 35mph. Way over the available 900N that the lab tests reported as being available.

A few more calcs show that the available 900N braking force yields a deceleration of 0.67Gs which would stop the bike in ~60 feet. This ignores the tire rolling resistance, but is much more in line with my experience.

So what am I saying? I get up to 35mph+ going down the hill from my home. I'm saying In wouldn't be reasonable for me to plan on stopping within 15 feet, even with hydraulic brakes and 203mm rotors. I'd something more like 60 feet, which is just about the 'alert' distance I've used for some years now. If anything moves into my 'alert' distance, I hit the brakes, hard. Never hit anything yet, but I would have with a shorter 'alert' distance.

 

[PDoz]

I can believe braking that hard would pull you off the seat. A quick 'back of the envelope' calc estimates that braking from 35mph to 0mph in 15 feet will generate 2.7Gs of deceleration. I don't know what the total weight is but assuming something like 300lbs for ebike+rider+cargo then each tire would be resisting 405lb, if they are loaded equally in braking. I'm not sure I could hold on at 2.7Gs, much less avoid skidding the tires, but I suppose it's possible.

This got me thinking, could I actually stop my ebike within 15 feet doing 35mph? It doesn't fit my experience well so I dug a little deeper. I found an online paper that has brake test results that seem useful here. The tests report a max braking force of 450N for a 160mm rotor. For two wheels this yields 900N of braking force. This test used hydraulic brakes, but if you pull the brake lever hard enough you might get to these figures with mechanical disc brakes.

Doing some 'back of the envelope' calcs and borrowing Newton's 2nd law F=ma (where 'm' is total weight & 'a' is the deceleration required to stop in 15 feet = 2.7Gs) we get F=2.7G*9.81m/s^2/G*136kg = 3,602N required braking force to stop within 15 feet from 35mph. Way over the available 900N that the lab tests reported as being available.

A few more calcs show that the available 900N braking force yields a deceleration of 0.67Gs which would stop the bike in ~60 feet. This ignores the tire rolling resistance, but is much more in line with my experience.

So what am I saying? I get up to 35mph+ going down the hill from my home. I'm saying In wouldn't be reasonable for me to plan on stopping within 15 feet, even with hydraulic brakes and 203mm rotors. I'd something more like 60 feet, which is just about the 'alert' distance I've used for some years now. If anything moves into my 'alert' distance, I hit the brakes, hard. Never hit anything yet, but I would have with a shorter 'alert' distance.

I'm definitely not arguing about the bs factor, but do you have a reference for that article used for the 160 mm rotor calculation?

Just for personal interest based on seat of pants experience - vast differences in braking abilities between, say, my wifes 160 mm rotors with shimano mt200 calipers vs daughters mtb with mt520 - presumably this comes down to 4 pistons / bigger pads / different pad materials and different leverage ratios worthink through wider tyres with a longer contact patch and much stiffer frame / forks/ running gear ? Whilst I doubt it would be a factor of 4....I'd be interested to see how thorough the study was

 

[Sierratim]

I'm definitely not arguing about the bs factor, but do you have a reference for that article used for the 160 mm rotor calculation?

Just for personal interest based on seat of pants experience - vast differences in braking abilities between, say, my wifes 160 mm rotors with shimano mt200 calipers vs daughters mtb with mt520 - presumably this comes down to 4 pistons / bigger pads / different pad materials and different leverage ratios worthink through wider tyres with a longer contact patch and much stiffer frame / forks/ running gear ? Whilst I doubt it would be a factor of 4....I'd be interested to see how thorough the study was

The 160mm rotor results are from an internal test report by a bicycle component manufacturer. My youngest son is lead mech engineer for them and asked me not to link to their results. Seems like one of those "trust me, I'm an engineer" moments...

Braking results are highly variable and there aren't a lot of publicaly available results which leads to reports of "35-to-0 in 15 feet" which is just a disaster waiting to happen when someone buys into this.

Interestingly, there are braking distance calculators available such as San Francisco's Exploratorium at https://www.exploratorium.edu/cycling/brakes2.html . This calculator estimates braking on dry pavement to need no less than 46-1/2 feet. Not a bad correlation with the 'bank of envelope' calcs I poised in my first post.

 

[PDoz]

The 160mm rotor results are from an internal test report by a bicycle component manufacturer. My youngest son is lead mech engineer for them and asked me not to link to their results. Seems like one of those "trust me, I'm an engineer" moments...

Braking results are highly variable and there aren't a lot of publicaly available results which leads to reports of "35-to-0 in 15 feet" which is just a disaster waiting to happen when someone buys into this.

Interestingly, there are braking distance calculators available such as San Francisco's Exploratorium at https://www.exploratorium.edu/cycling/brakes2.html . This calculator estimates braking on dry pavement to need no less than 46-1/2 feet. Not a bad correlation with the 'bank of envelope' calcs I poised in my first post.

I'd love to watch video footage of your son reading this thread.....does he suffer repetitive strain injuries from shaking his head?

 

[Sierratim]

I'd love to watch video footage of your son reading this thread.....does he suffer repetitive strain injuries from shaking his head?

His twin brother is also a mech engineer and also a MTB enthusiast. I sent them both the "35 to 0 in 15 feet" poat and they went crazy, well, as crazy as engineers get I suppose!...

 

[Bruce Arnold]

The calculations of stopping power and distance are fascinating and I thank y'all for sharing them. Just thinking about my own experience without doing any testing or calculating, I can't imagine stopping from 35 within 15 feet on level ground, much less downhill.

There's another physics question that seems even more pertinent: center of gravity. Assume for a second that you can stop that fast at that speed. You're going to do a stoppie, and probably go ass-over-tea-kettle in the process.

Hit a railroad rail in the rain once. It caught my front wheel in the groove around the rail. Instant deceleration. The bike and I both did a forward flip. All I can say is, thank god for that brown belt in judo. Because I landed on my feet, unharmed. The bike was okay too. This story is not relevant to the topic. Just a random memory of a somewhat-similar scenario.