Rotor size/lever leverage/stopping distance discussion

[RJUK]

Going to spend a few days in the alps bike park from next Friday. I will see if I can give some color to this 220 mm disc . The 200km until now as been done 100% on the bike park next to my house. But it’s short 200 meter D-

Good luck!

 

[steve_sordy]

Oof, that sucks, but it's good that you're still out riding and haven't let it stop you.

Have you tried more compliant handlebars or grips to see if that helps? I guess the vibration exacerbates things?

Thanks for your concern, but I am content with the set up I have right now. Thanks.

 

[Alexbn921]

I just did 12000 feet of elevation yesterday. My hands are thrashed and I couldn't have done it with smaller rotors.

 

[Planemo]

In the case of downsizing.... I'd probably not bother. IMO, it's better to be over-braked than under-braked. Whilst you might not be using your brakes to the fullest on your normal trails, if you go to a bike park or away on a biking holiday you don't want to find yourself cooking the brakes and in a world of bother half way down a long descent.

Agreed. There also seem to be some who are a little too worried about not getting their brakes hot enough (cue'd from the Hope literature) but for what we are using I really don't think this is something we should be worried about.

Race spec carbon brakes deffo need to be hot to work right but our pissy MTB stuff isn't quite of the same calibre. Maybe, just maybe if you are using full metal/sintered pads then it could be a consideration but for most pads, especially resin, we don't need to be worried about changing the hue of our discs. I've never had any issues with 220's/resin glazing put it that way.

 

[RJUK]

Agreed. Just bed them in with a series of back-to-back emergency stops to evenly distribute pad material across the discs surface and then just use the normally.

When you're bedding them in, keep rolling after each hard stop and go for a casual ride around after the last one to cool everything down. You don't want to leave them hot with the pad in contact with the rotor. Or at least, that's how you do it with car brakes, so probably advisable to do the same here just to be safe.

 

[irie]

... for most pads, especially resin, we don't need to be worried about changing the hue of our discs ...

I had to stop a bit quick from this speed today because a dog was in the way. Unfortunately I didn't get off and check the colour of my 220mm rotors, sorry

Edit: I use Shimano D03S resin pads in my Shimano M6120 calipers. Very boring I know.

 

[Planemo]

Unfortunately I didn't get off and check the colour of my 220mm rotors, sorry

If you'd had blued the rotors they would still be blue now, so go have a look

 

[irie]

If you'd had blued the rotors they would still be blue now, so go have a look

I really can't be arsed to see if the rotors are blued.

 

[Robstyle]

Re bedding in pads, the best way I've found:
Take new pads and rub the faces together under a running tap until water is running clear.
Put them in, still wet is actually better. Take some time to get the alignment right.
Choosing a low gear and one brake at a time ride your bike with the brake pulled in. You can run it pretty firmly pulled in.
It will probably start howling haha, this is good. Once you can't pedal or your front wheel locks they're bedded in.

It will only take 100m of riding if that.
I wouldn't do it any other way now, perfect brakes every time

 

[Zimmerframe]

I think @RJUK has to be commended on being patient and consistent through this thread.

We have the usual semantics about feel and everyone will like different things for various different reasons.

Everyone rides in their own way and on their own trails and many of us probably brake wayyyy too much !

Ultimately, most of our bikes have brakes which are very effective at what they're supposed to be doing and we're all influenced by the marketing of bigger is better (unless you're dating and then it becomes very subjective).

Ironically (based on @irie's post ..) I'm out from a huge off after OTBing at 45kph trying to avoid a dog which ran in front of me and managed to get enough brake force to do that rather than hit the dog on 200mm Shimano XT's - it was sh1t riding, but in the 0.1 seconds that existed at that point, options were limited and better choices could have been made.

I don't think you can really work just speed into rotor size either, on it's own, it's just another variable.

On a quick test ride the day before on a different bike with 200mm xt's, I never had any thoughts about braking.

 

[RJUK]

I think @RJUK has to be commended on being patient and consistent through this thread.

We have the usual semantics about feel and everyone will like different things for various different reasons.

Everyone rides in their own way and on their own trails and many of us probably brake wayyyy too much !

Ultimately, most of our bikes have brakes which are very effective at what they're supposed to be doing and we're all influenced by the marketing of bigger is better (unless you're dating and then it becomes very subjective).

Ironically (based on @irie's post ..) I'm out from a huge off after OTBing at 45kph trying to avoid a dog which ran in front of me and managed to get enough brake force to do that rather than hit the dog on 200mm Shimano XT's - it was sh1t riding, but in the 0.1 seconds that existed at that point, options were limited and better choices could have been made.

I don't think you can really work just speed into rotor size either, on it's own, it's just another variable.

On a quick test ride the day before on a different bike with 200mm xt's, I never had any thoughts about braking.

View attachment 120356

Thanks, I appreciate it. And I hope you didn't come off too bad from the dog incident.

 

[hansfrans]

Yeah, I'm not reading all that nonsense. Just Google it. Believe what you want, but larger rotors don't stop you faster. It's a common misconception because everyone thinks bigger=better and can't be bothered to look into the actual physics of it.

If you still don't get that after all I've said already then you're never gonna get it.

FWIW, I've never said that larger rotors are inferior and I have large brakes on both my car and bike. But I bought them knowing why - that they offer better heat dissipation under repeated braking, not because I think bigger brakes will stop me in a shorter distance, because I know that's not physically possible.

Just like you won’t get it that it’s not about locked wheels or that modulation is worse with smaller discs when going serious downhill? That’s while you ignore any argument and keep repeating that larger discs don’t shorten your braking distance.
In fact they do, since the moment of locking the wheel comes earlier.
Very theoretical but you ignore any real life facts anyway.

 

[RJUK]

Just like you won’t get it that it’s not about locked wheels or that modulation is worse with smaller discs when going serious downhill? That’s while you ignore any argument and keep repeating that larger discs don’t shorten your braking distance.
In fact they do, since the moment of locking the wheel comes earlier.
Very theoretical but you ignore any real life facts anyway.

What are you talking about? You're just spewing complete nonsense now.

Honestly, physics and facts don't care about your opinions. Believe what you want, but larger discs don't stop you faster, period.

You need to increase grip to stop in a shorter distance, so it's about tyres and suspension, not the size of part of the braking system.

 

[RJUK]

Since you won't listen to me, pick one of these and pay attention.

 

[Bummers]

Since you won't listen to me, pick one of these and pay attention.

I think the standard response to this is for people to state a different argument from the one you're making and then prove it wrong... Despite that not being what is discussed

 

[RJUK]

I think the standard response to this is for people to state a different argument from the one you're making and then prove it wrong... Despite that not being what is discussed

I know, right!

Other than repeating myself more I just don't know how better to make the point. But I guess some people just want to believe one thing and won't be swayed by logic and reason.

I get that it's an intrenched misconception though, and sometimes it can be difficult to change from a viewpoint that's etched into your brain... But this is a subject that can be easily Googled to confirm what I'm saying.

And logically, if the brakes can already lock the wheel... How can adding more "power" possibly slow the vehicle any more? The wheel can already be completely locked...

 

[irie]

I know, right!

Other than repeating myself more I just don't know how better to make the point. But I guess some people just want to believe one thing and won't be swayed by logic and reason.

I get that it's an intrenched misconception though, and sometimes it can be difficult to change from a viewpoint that's etched into your brain... But this is a subject that can be easily Googled to confirm what I'm saying.

And logically, if the brakes can already lock the wheel... How can adding more "power" possibly slow the vehicle any more? The wheel can already be completely locked...

The issue is not about being able to lock the wheel but rather about control of braking up to the point of locking the wheel.

 

[RJUK]

The issue is not about being able to lock the wheel but rather about control of braking up to the point of locking the wheel.

No it's not. The issue being argued is solely about braking distances. Not control, nor heat dissipation, or anything else.

 

[irie]

No it's not. The issue being argued is solely about braking distances. Not control, nor heat dissipation, or anything else.

Braking distance depends, given other factors, upon control.

 

[RiderOnTheStorm]

You're right about the big brakes stopping you quicker for the same amount of force applied to the lever though, then who is out there riding that isn't able to just pull the lever a bit harder?

I agree with your previous comments. In general I think people who fit larger rotors on their ebikes are expecting more braking power for a given force applied to the lever, and this extra braking power that they gained would then translate into stopping them quicker. So it's all relative

 

[RJUK]

Braking distance depends, given other factors, upon control.

Again, that's not what's being argued. Throwing lots of variables into the equation is just trying to distract from the core argument.

 

[RJUK]

I agree with your previous comments. In general I think people who fit larger rotors on their ebikes are expecting more braking power for a given force applied to the lever, and this extra braking power that they gained would then translate into stopping them quicker. So it's all relative

Agreed, they may be, but again that's still not the point. If those people buy larger rotors to stop in a shorter distance, they'll be disappointed.

As I've said before. There are benefits to larger rotors... Additional leverage being one, better heat dissipation being another. Neither have any affect whatsoever on stopping distance.

 

[irie]

Again, that's not what's being argued. Throwing lots of variables into the equation is just trying to distract from the core argument.

"Rotor size/lever leverage/stopping distance discussion"

To the contrary, it is perfectly valid to argue that fitting a larger rotor may increase control thereby reducing stopping distance, which is what the core argument is about.

 

[mtbbiker]

Agreed, they may be, but again that's still not the point. If those people buy larger rotors to stop in a shorter distance, they'll be disappointed.

As I've said before. There are benefits to larger rotors... Additional leverage being one, better heat dissipation being another. Neither have any affect whatsoever on stopping distance.

I haven’t read every post so please excuse me if I missed some of your points. I think people here agree with you that if you can lock up your brakes than putting bigger rotors on will not help you stop any faster.

The problem is, while your statement is true under most regular braking, but will fall short under extreme repeated braking of any decent descent. Those small rotors will begin to fade, requiring more hand pressure and longer stopping distance until the brake system cools off. If you are a lighter rider, or not aggressive rider, you may not experience this fading concern.. I think this is what people are disagreeing with you about.

 

[militantmandy]

My own (worthless) opinion. It's about effort.

Bigger disc=less effort
Less effort=more control/less fatigue

That's what matters to me anyway on long and steep descents.

 

[Planemo]

excuse me if I missed some of your points.

You did. The rest of your post has already been discussed.

 

[Planemo]

To the contrary, it is perfectly valid to argue that fitting a larger rotor may increase control thereby reducing stopping distance, which is what the core argument is about.

In theory you're right. In reality, very, very few people have difficulty modulating their brakes at around the lock point. You would have to have a severely badly designed system (totally incorrect master cylinder size being the main one) to have any real issues with modulation.

Another example would be someone with a low grip strength beyond a certain point. Or likewise, someone who has a grip like an ape.

Brake systems just aren't that badly designed for modulation near lock point to be a problem and haven't been for many years.

 

[RJUK]

"Rotor size/lever leverage/stopping distance discussion"

To the contrary, it is perfectly valid to argue that fitting a larger rotor may increase control thereby reducing stopping distance, which is what the core argument is about.

No it isn't. This thread split off from another thread where the argument started. I didn't name the new thread, but the whole argument was purely about stopping distances. Nothing else.

Also, I disagree with the premise that a larger rotor would increase control. Adding power to the system will make the brakes feel more like an on/off switch and make it easier to accidentally lock the wheel and lose control. Lever design may mitigate this to some degree, but better modulation will be seen with a weaker setup, not a stronger one. (Think trying to fill a coke bottle without spilling any liquid and choosing between a jug and a fire hose. The smaller amount of "power" will always be easier to control.)

What the additional leverage will help with, is hand fatigue, which could enable you to control the brakes better, in the event that you find your hands getting fatigued by using your existing brakes. However that's a very specific set of circumstances and again, is irrelevant to the initial point.

As others have said, people are now just finding every variable they can think of to prove the contrary, whilst missing the point.

 

[irie]

No it isn't.

Unsurprisingly I disagree and will leave it at that.

Rotor size/lever leverage/stopping distance discussion"

To the contrary, it is perfectly valid to argue that fitting a larger rotor may increase control thereby reducing stopping distance, which is what the core argument is about.

 

[Planemo]

Head, wall and bang. I'm out.