Rotor size/lever leverage/stopping distance discussion

[RJUK]

Moderator Edit : Moved from Canyon Strive Thread to this thread.

Ah good to know, thanks.

What's the performance gains? better heat tolerance I guess?

Exactly that. Same as having a physically larger rotor. More mass = better resistance to brake fade.

Having a larger diameter rotor just helps spread the heat, it doesn't make the brakes stop you faster. If you can already lock the wheels (which you should be able to!) then the only way to stop faster is to fit grippier tyres. Installing bigger rotors will just help resist fade better, whether the diameter is bigger or whether the disc is thicker.

That's why they tend to fit smaller rotors on the rear - the rest brake doesn't tend to do as much of the braking as the front, so doesn't need to dissipate as much heat. Also, with a larger diameter rotor there's more of a levering force, so you probably get a bit more power, which doesn't really translate to stopping you faster, but can make it more likely that you'll lock the rear wheel when you didn't intend to. "Snapper" brakes, I guess. That's why it can be better to have a bigger brake on the front than the rear. Cars do the same.

 

[Mars2]

Exactly that. Same as having a physically larger rotor. More mass = better resistance to brake fade.

Having a larger diameter rotor just helps spread the heat, it doesn't make the brakes stop you faster. If you can already lock the wheels (which you should be able to!) then the only way to stop faster is to fit grippier tyres. Installing bigger rotors will just help resist fade better, whether the diameter is bigger or whether the disc is thicker.

That's why they tend to fit smaller rotors on the rear - the rest brake doesn't tend to do as much of the braking as the front, so doesn't need to dissipate as much heat. Also, with a larger diameter rotor there's more of a levering force, so you probably get a bit more power, which doesn't really translate to stopping you faster, but can make it more likely that you'll lock the rear wheel when you didn't intend to. "Snapper" brakes, I guess. That's why it can be better to have a bigger brake on the front than the rear. Cars do the same.

Finaly A guy that don't think bigger is better
. So tired of the guy's on car, bike... that fit bigger brake because they want to stop faster when it's the tire that make you stop faster and the brake that dissipate the energy.

That is why rally car have big brake on tarmac and small brake on dirt or snow. More energy to dissipate on tarmac because of sticky tire sticky and more contact surface) on a sticky surface.

 

[Mars2]

I had the Hayes dominion 4 on my previous bike, amazing brake. Specialy on the long downhill bike park in the alps. Never got any fading with 200mm rotor.

It's couple week I think I want to down grade the front brake of my CFR from to 220 to 200mm.
It's to sensitive for me and I end up often blocking the front wheel. too much leverage compare to grip of my front tyre on super dry surface of summer.

 

[wessobert3000]

I had the Hayes dominion 4 on my previous bike, amazing brake. Specialy on the long downhill bike park in the alps. Never got any fading with 200mm rotor.

It's couple week I think I want to down grade the front brake of my CFR from to 220 to 200mm.
It's to sensitive for me and I end up often blocking the front wheel. too much leverage compare to grip of my front tyre on super dry surface of summer.

The Hayes Dominion A4 are hands down the best brakes I ever used. And I tried it all: shimano Saint, xt, magura, shigura, sram…

 

[Mars2]

same for me. Only one I did not try are TRP, Trickstuff ( I had trickstuff pads on my code R) and Hope.
I only get bad report from friend on hope so no interest their.

Shigura was second best after Hayes

 

[hansfrans]

Finaly A guy that don't think bigger is better
. So tired of the guy's on car, bike... that fit bigger brake because they want to stop faster when it's the tire that make you stop faster and the brake that dissipate the energy.

That is why rally car have big brake on tarmac and small brake on dirt or snow. More energy to dissipate on tarmac because of sticky tire sticky and more contact surface) on a sticky surface.

Never heard this before. Sure the tires matter but a larger diameter should result in better leverage.
It takes less force to stop a spinning bike wheel when gripping the tire compared to gripping the brake disc.

 

[RJUK]

Never heard this before. Sure the tires matter but a larger diameter should result in better leverage.
It takes less force to stop a spinning bike wheel when gripping the tire compared to gripping the brake disc.

Sure, but the brakes can only slow the bike so much before the tyre breaks traction. You could have a 4 inch disc or a 24 inch disc, but as long as they are both capable of locking the wheels the bigger one won't stop the bike any faster. It will, however, resist fade better due to the increased size of the disc. To stop faster you need to increase the traction of the tyres.

As such, tyres are the most important factor in stopping distances, not brakes... Unless the brakes are so weedy that they can't even lock a wheel up. (In which case they should be classed as faulty.)

 

[RJUK]

Ok sure any break is capable of locking the wheels, but with smaller discs you will need much more manual force which is then harder to dose. So the larger disc needs less manual force for locking the wheel and that means the necessary level of force is reached faster, so the larger disc can be said to stop the bike faster (at the same level of manual force)

It's actually the opposite. A smaller disc is easier to modulate as you'll need more force through the lever to stop the bike. If you have too much force through the brake then they feel "grabby" or like they're very on/off. That's also why you want a smaller brake on the rear than the front.

Downhill your weight is over the front wheel more, plus the bike is moving forwards, so when you brake the weight transfers forwards over the front wheel and off of the back wheel. As you have more braking being done by the front wheel you want a bigger disc to dissipate the extra heat and because all the weight is at the front you're less likely to lock up the wheel and it's nicer to have more power. At the rear there is less weight and so having a really powerful brake is likely to cause the wheel to lock up, also, there's less heat being generated at this end of the bike because all the weight moves forward under braking. As such, a smaller brake is better, as it allows for lower weight, better modulation and you don't generally need the additional heat dissipation.

Of course, if you're hammering really long descents on a hot day and overheating your brakes then sure, a larger/thicker rotor will help. I suspect very few people with 200mm rear rotors are overheating them though. Also, you can probably remedy it easier with different pads.

You're right about the big brakes stopping you quicker for the same amount of force applied to the lever though, but then who is out there riding that isn't able to just pull the lever a bit harder? I'd guess that we all "learn" how hard we can pull the brakes before they lock up the wheel and brake up to that point, regardless of how hard that means squeezing the lever. A small brake is just as capable of stopping a bike in the same distance as a large brake, it's just that with the large brake you will probably need to apply less force. However, the smaller brake will be easier to modulate, as you'll have to squeeze the lever harder to lock up the wheel, which means you're less likely to do so accidentally.

Unless you're regularly overheating your brakes or getting very tired braking fingers then the smaller option is probably better, for that additional modulation and reduced weight. (Otherwise bike manufacturers would just be throwing motorbike brakes on our bikes.)

 

[Jdog]

I don't agree with some of this rotor size talk and think you guys need to do some further research on this.

If you get an identical bike on the same surface at the same speed, one with 220mm and the other with 200mm rotors you'll have more stopping power on the 220mm rotors, 10% more to be precise and better heat dissipation which will give more consistency. Yes there is the possibility of less modulation due to the increased stopping power needing less movement required at the lever but the power will be more readily usable and result in less arm fatigue so for me (and many others) the pros outweigh the cons. And lets be honest any disc brake can lock a wheel.

I'm not factoring in the traction of the tyres or surface as it'll be identical I am just talking about the basic mathematical equation of leverage ratio of a bigger rotor and increased surface area for better heat dissipation both of which would result in better brake performance.

An interesting article on this - Are 220mm Rotors Worth it? Why Bigger Brakes Are (Almost) Always Better
Below is a good shortened example.

I think if we want to go into this further it would be better suited in it's own thread as we're off topic from the incredible Canyon Strive On.

 

[RJUK]

I don't agree with some of this rotor size talk and think you guys need to do some further research on this.

If you get an identical bike on the same surface at the same speed, one with 220mm and the other with 200mm rotors you'll have more stopping power on the 220mm rotors, 10% more to be precise and better heat dissipation which will give more consistency. Yes there is the possibility of less modulation due to the increased stopping power needing less movement required at the lever but the power will be more readily usable and result in less arm fatigue so for me (and many others) the pros outweigh the cons. And lets be honest any disc brake can lock a wheel.

I'm not factoring in the traction of the tyres or surface as it'll be identical I am just talking about the basic mathematical equation of leverage ratio of a bigger rotor and increased surface area for better heat dissipation both of which would result in better brake performance.

An interesting article on this - Are 220mm Rotors Worth it? Why Bigger Brakes Are (Almost) Always Better
Below is a good shortened example.
View attachment 119435

I think if we want to go into this further it would be better suited in it's own thread as we're off topic from the incredible Canyon Strive On.

Sure, I don't think anyone is disagreeing that bigger rotors equal better heat dissipation, but bigger rotors will not give you shorter stopping distances or stop you any quicker. That's down to the tyres. Bigger rotors will likely require less force on the lever to provide the same power, so may give the feeling of being more powerful, but you can achieve that in other way as well - for example in lever design (longer lever = more leverage etc.)

But if the benefits are better heat dissipation and you're not over heating the brakes in the first place, then you're just carrying around extra weight for nothing.

 

[yorkshire89]

Downhill your weight is over the front wheel more, plus the bike is moving forwards, so when you brake the weight transfers forwards over the front wheel and off of the back wheel. As you have more braking being done by the front wheel you want a bigger disc to dissipate the extra heat and because all the weight is at the front you're less likely to lock up the wheel and it's nicer to have more power. At the rear there is less weight and so having a really powerful brake is likely to cause the wheel to lock up, also, there's less heat being generated at this end of the bike because all the weight moves forward under braking. As such, a smaller brake is better, as it allows for lower weight, better modulation and you don't generally need the additional heat dissipation.

Of course, if you're hammering really long descents on a hot day and overheating your brakes then sure, a larger/thicker rotor will help. I suspect very few people with 200mm rear rotors are overheating them though.

Your right about more braking force through the front when you are hard braking (in a straight line).
I don't agree about less heat being generated at the rear over the course of a long descent. You are much more likely to cook a rear brake due to the amount of time you can actually use it (not just by poor technique).

It's fairly common to go through 3-4 pairs of rear pads for every front pair.

 

[Rob Rides EMTB]

Sure, I don't think anyone is disagreeing that bigger rotors equal better heat dissipation, but bigger rotors will not give you shorter stopping distances or stop you any quicker.

Of course larger rotors can lead to shorter stopping distances, unless you're just riding flat pavements?!

Larger rotors = better heat dissipation, which is important going downhill. Therefore, will will result in better braking performance and shorter stopping distances when brakes reach a certain temperature.

But its not just heat dissipation. Mechanical leverage also comes into play..

Larger rotors have increased leverage - its a bigger lever to stop motion (more rotor contact area / longer circumference area) for the pads A larger lever means a better mechanical advantage in stopping rotation.

The rotor speed at the pad is also changed with larger rotors.

 

[Jdog]

Sure, I don't think anyone is disagreeing that bigger rotors equal better heat dissipation, but bigger rotors will not give you shorter stopping distances or stop you any quicker. That's down to the tyres. Bigger rotors will likely require less force on the lever to provide the same power, so may give the feeling of being more powerful, but you can achieve that in other way as well - for example in lever design (longer lever = more leverage etc.)

But if the benefits are better heat dissipation and you're not over heating the brakes in the first place, then you're just carrying around extra weight for nothing.

I hear what you're saying but it's not correct. In real world testing bigger rotors will stop you in a shorter distance and quicker, whether that be due to it being easier to obtain the optimal stopping power due to increased leverage ratio or better heat dissipation it will factually result in reduced stopping times and distances, otherwise why aren't we all on 160mm rotors? I don't dispute better tyres would also help stopping times and distances but to say bigger rotors don't result in better stopping times simply isn't true.

Example videos of this:
GMBN - MTB PHD -

 

[RJUK]

Of course larger rotors can lead to shorter stopping distances, unless you're just riding flat pavements?!

Larger rotors = better heat dissipation, which is important going downhill. Therefore, will will result in better braking performance and shorter stopping distances when brakes reach a certain temperature.

But its not just heat dissipation. Mechanical leverage also comes into play..

Larger rotors have increased leverage - its a bigger lever to stop motion (more rotor contact area / longer circumference area) for the pads A larger lever means a better mechanical advantage in stopping rotation.

The rotor speed at the pad is also changed with larger rotors.

Not quite. If you're getting the brakes hot enough that it affects performance, then sure - but again that falls under heat dissipation, which I've already said is better with a larger brake.

But on cold brakes, same bike, same tyres, same bit of track/pavement, a bigger rotor won't stop the bike any faster. Even taking leverage into account. Both brakes have enough power to lock the wheels up, so how does having a bigger rotor stop the bike faster? Both brakes can stop the wheel dead. As such, braking distances come down to the tyres.

Of course, once they heat up the larger rotor resists fade better and stopping distances will be better for the larger rotor, which is what I've said from the start. Bigger brakes resist fade better.

 

[Jdog]

Not quite. If you're getting the brakes hot enough that it affects performance, then sure - but again that falls under heat dissipation, which I've already said is better with a larger brake.

But on cold brakes, same bike, same tyres, same bit of track/pavement, a bigger rotor won't stop the bike any faster. Even taking leverage into account. Both brakes have enough power to lock the wheels up, so how does having a bigger rotor stop the bike faster? Both brakes can stop the wheel dead. As such, braking distances come down to the tyres.

Of course, once they heat up the larger rotor resists fade better and stopping distances will be better for the larger rotor, which is what I've said from the start. Bigger brakes resist fade better.

If you're locking your brake you're doing something fundamentally wrong, certainly in terms of braking performance.

The whole principle of modulation, leverage ratio and disc temperature is to achieve optimal braking which you'll need the disc to be rotating for, hence the idea behind ABS. Yamming on your brakes to the point of lock up will take all of this out of the equation and then it will be solely on tyre traction but that that point you might as well just throw an anchor off your bike and hope it gets traction in the dirt.

 

[Rob Rides EMTB]

But on cold brakes, same bike, same tyres, same bit of track/pavement, a bigger rotor won't stop the bike any faster. Even taking leverage into account. Both brakes have enough power to lock the wheels up, so how does having a bigger rotor stop the bike faster?

If we're talking about locking wheels then the variable is also tyre grip.

My understanding:

Given this scenario identical bike, other than rotor size, the bike with smaller rotor would require more hand lever force to lock the wheels.

Another way to look at it - if two idential bikes were riding side by side, identical rider, identical braking forces, that are gradually then increased to lock the rear wheel, the bike with the larger rotor will lock the wheel in a shorter time period (and distance) and therefore stop faster.

I think we're getting into semantics really now though

 

[RJUK]

I hear what you're saying but it's not correct. In real world testing bigger rotors will stop you in a shorter distance and quicker, whether that be due to it being easier to obtain the optimal stopping power due to increased leverage ratio or better heat dissipation it will factually result in reduced stopping times and distances, otherwise why aren't we all on 160mm rotors? I don't dispute better tyres would also help stopping times and distances but to say bigger rotors don't result in better stopping times simply isn't true.

Example videos of this:
GMBN - MTB PHD -

No, but factually speaking, it's not the size of the disc that determines the stopping distanxe it's a common misconception because everyone always thinks bigger brakes = stop faster. That's simply not true, providing everything else is the same and both brakes can lock the wheel up. If both brakes can lock the wheelbup# how do you suppose that having more power will help? Hold that already locked wheel even tighter?

Bigger brakes only combat brake fade, which when the brakes get hot will mens they perform better. So yes, they're better for sustained descents assuming you're reaching the limits of the brakes you already have. You're more likely to reach those limits on a heavier bike, doing more downhill etc. That's why XC bikes and regular road bikes have smaller rotors. Else if bigger brakes always meant better stopping power anyone without a downhill rig would be crashing at the end of every road. They don't, because the lightweight bike and less hilly terrain means they're not overheating the brakes so the performance remains fine.

If everyone is exceeding the limits of their brakes on this bike it does rather beg the question of why Canyon fitted them.

 

[RJUK]

If you're locking your brake you're doing something fundamentally wrong, certainly in terms of braking performance.

The whole principle of modulation, leverage ratio and disc temperature is to achieve optimal braking which you'll need the disc to be rotating for, hence the idea behind ABS. Yamming on your brakes to the point of lock up will take all of this out of the equation and then it will be solely on tyre traction but that that point you might as well just throw an anchor off your bike and hope it gets traction in the dirt.

Agreed. Nowhere have I said that locking your brakes is desirable.

 

[Rob Rides EMTB]

No, but factually speaking, it's not the size of the disc that determines the stopping distanxe it's a common misconception because everyone always thinks bigger brakes = stop faster. That's simply not true, providing everything else is the same and both brakes can lock the wheel up. If both brakes can lock the wheelbup# how do you suppose that having more power will help? Hold that already locked wheel even tighter?

Found a white paper. For a given hand force, brake force in Nm is higher with a larger disc diameter.

https://www.sensorprod.com/news/white-papers/2010-03_ctb/wp_ctb-2010-03.pdf

 

[RJUK]

If we're talking about locking wheels then the variable is also tyre grip.

My understanding:

Given this scenario identical bike, other than rotor size, the bike with smaller rotor would require more hand lever force to lock the wheels.

Another way to look at it - if two idential bikes were riding side by side, identical rider, identical braking forces, that are gradually then increased to lock the rear wheel, the bike with the larger rotor will lock the wheel in a shorter time period (and distance) and therefore stop faster.

I think we're getting into semantics really now though

Agreed. I'm not arguing this point, either. But assuming both brakes are capable of locking the wheel, then adding power beyond that will not help. The tyres are the part that reduces stopping distances, not the brakes. Barring if you overheat the brakes, as that clearly will degrade performance - this is when larger rotors are better, if you find yourself over heating the brakes.

If you never overheat the brakes then chucking larger rotor on there will not stop you faster. The additional leverage from the larger rotor will mean that you have to exert less force on the lever - agreed. But that doesn't make you stop faster, it just will likely reduce fatigue in your braking fingers. The downside of this is that it will be easier to lock the wheel up as well.

If you have a brake that can apply 110% of the braking force required to lock the wheel and another that can apply 500% of the force needed to lock the wheel, then you're more likely to accidentally lock the wheel with the more powerful brake. It's a balancing act between power and modulation. That's why the manufacturers have special cams in their levers that allow a powerful initial bite, but then reduce leverage further in the stroke to give better modulation and prevent you accidentally locking the wheels. Trick levers like this allow the fitting of larger discs, but assuming the same lever, the smaller disc will always be easier to modulate, whereas the larger disc will require less pressure on the lever for the same slowing force at the hub.

 

[RJUK]

View attachment 119449

Found a white paper. For a given hand force, brake force in Nm is higher with a larger disc diameter.

https://www.sensorprod.com/news/white-papers/2010-03_ctb/wp_ctb-2010-03.pdf

Again, not disagreeing with that. A larger disc has a greater leverage force on the hub. However, that won't cause you to stop in a shorter distance. It just means you need to squeeze less hard for the same braking force (Which could even cause you to lock the wheel accidentally, in the extreme.)

I've had this very debate before with people far smarter than me on car forums. All the boy racers think bigger brakes = faster stopping, then go and chuck some awful Nankang tyres on to save £50.

The old guard of mechanics, and boffins with far more knowledge will tell you that bigger brakes do not equal shorter stopping distances. They do however resist fade better - that's why sporty cars have bigger brakes. Not because your average person doesn't need to be able to stop fast when a kid runs out in the street, but because sporty cars are intended for track use or expected to be used at high speed on the autobahn where regular brakes can very quickly experience fade.

 

[Jdog]

View attachment 119449

Found a white paper. For a given hand force, brake force in Nm is higher with a larger disc diameter.

https://www.sensorprod.com/news/white-papers/2010-03_ctb/wp_ctb-2010-03.pdf

A perfect graph to depict leverage ratio.

It's not that it feels like you're applying less pressure to get the same force it's that you're factually applying less pressure to get the same force. If you applied the same force on the leaver of 200mm and then 220mm you'd get more stopping power from 220mm and thus better braking performance.
Another way to look at this, imagine trying to undo a wheel nut with a 10 inch bar and 50nm of force then doing the same with a 50in bar, it's 5x the leverage ratio which basic maths will tell you more leverage equals more force output.

 

[RJUK]

A perfect graph to depict leverage ratio.

It's not that it feels like you're applying less pressure to get the same force it's that you're factually applying less pressure to get the same force. If you applied the same force on the leaver of 200mm and then 220mm you'd get more stopping power from 220mm and thus better braking performance.
Another way to look at this, imagine trying to undo a wheel nut with a 10 inch bar and 50nm of force then doing the same with a 50in bar, it's 5x the leverage ratio which basic maths will tell you more leverage equals more force output.

View attachment 119455

Again, not disagreeing with this. But applying less force at the lever does not mean you'll stop faster. For the same amount of force at the lever you will stop faster, but threshold braking with either brake will stop you just as quickly. The only way to stop faster is to increase the threshold before grip is lost... Which means gripper tyres.

If you're out there regularly overheating your brakes then absolutely you should get bigger/thicker rotors. You can also change the pads for ones that resist heat better or find a solution to cool them better.

If you're regularly getting sore hands from braking, then absolutely try larger diameter rotors as this will increase the leverage on the hub and reduce the effort required by your hands.

If you find you're overshooting corners or just want to stop in a shorter distance for whatever reason, then upgrade your tyres.

 

[Mario Antony]

On big rotors:
You'll have higher leverage (bigger diameter) - less pulling force at lever require to desacellarate the EB
Bigger area in each rotation - less heat in the disk for same length you're braking

Would love to try HOPE V4 with vented disks - although I'm really happy (and surprised) with stock brakes on the Underdog.

On this "brakegate", think in terms of cars:
Bigger is always "more better"
4 pistons better than 1 or 2 piston. (6 or more pistons, increases weight, but gives better modulation!).
Vented disks over solid.
Grooved to remove pad glazing.


Ps: Completly agree that maximum braking is limited by tire grip! But even this will vary according to incline (more incline DH, more weight over the front = more reaction = better grip).

 

[RJUK]

On big rotors:
You'll have higher leverage (bigger diameter) - less pulling force at lever require to desacellarate the EB
Bigger area in each rotation - less heat in the disk for same length you're braking

Would love to try HOPE V4 with vented disks - although I'm really happy (and surprised) with stock brakes on the Underdog.

On this "brakegate", think in terms of cars:
Bigger is always "more better"
4 pistons better than 1 or 2 piston. (6 or more pistons, increases weight, but gives better modulation!).
Vented disks over solid.
Grooved to remove pad glazing.


Ps: Completly agree that maximum braking is limited by tire grip! But even this will vary according to incline (more incline DH, more weight over the front = more reaction = better grip).

That's kind of the point though. Performance cars always have bigger brakes, not because they need to stop faster in a straight line (a child could run out in front of any car) but because they're designed to be used on track days or autobahn blasts, so they need brakes that can resist fade better.

As such, everyone's assumption is that bigger brakes = faster stopping, which is completely false. If both sets of brakes have enough power to lock up the wheels then it's tyre traction that is limiting the braking distance.

Are bigger brakes "better" than smaller ones... It's not as easy as just saying yes.

Do they resist fade better? Yes.

Do they require less force on the lever/brake pedal for the same amount of slowing? Yes.

Do they stop the vehicle in a shorter distance (not taking brake fade into account, as we already addressed that)? No.

Do they add unsprung weight to the vehicle? Yes. Is that good? No.

So it's a case of choosing the appropriate brake for your use. You could get out the welder and adapt your bike to take a motorcycle brake. The disc is bigger and thicker and the caliper and pads are much larger. But you'd likely take longer to stop than a 160mm MTB brake because of all the additional weight and additional rotating mass. The suspension feel would also be awful because of all that unsprung weight.

Sure, that's a crazy extreme, but the point is that bigger is not always better, which is why not all bikes have 220mm rotors all around by default. If you're not overheating your brakes then getting bigger rotors because you believe they will stop you faster is going to lead to disappointment and no real gain.

If you want bigger rotors to ensure that you never get brake fade even if you go on bike park days in summer or on a trip to the mountains then by all means. Just don't expect them to shorten your braking distances under normal use.

And this is coming from someone with big red Brembos on all four corners of his car, so I'm well aware of the benefits, but I know my car wouldn't stop any quicker than an identical car with the smaller brakes from a lower model. On a track day the car with the smaller brakes would likely cook them in a lap or two though and I'd still be OK.

 

[Jdog]

So do they fit on the back without modifications? Cause I'm confused while those Hope rotors are laying in my shopping basket
Btw, have you tried 200 or 203mm at the back?

They do fit yes but the Hope rotor rivets rub on Shimano brake a known issue for years. Excuse my dutty bike but the photo shows it actually hits the calliper where it mounts to the adapter:

I did 220mm front and 203mm rear as direct replacements for OEM then you don't need new adapters as comes with Shimano 203mm on the rear.

 

[Mario Antony]

That's kind of the point though. Performance cars always have bigger brakes, not because they need to stop faster in a straight line (a child could run out in front of any car) but because they're designed to be used on track days or autobahn blasts, so they need brakes that can resist fade better.

As such, everyone's assumption is that bigger brakes = faster stopping, which is completely false. If both sets of brakes have enough power to lock up the wheels then it's tyre traction that is limiting the braking distance.

Are bigger brakes "better" than smaller ones... It's not as easy as just saying yes.

Do they resist fade better? Yes.

Do they require less force on the lever/brake pedal for the same amount of slowing? Yes.

Do they stop the vehicle in a shorter distance (not taking brake fade into account, as we already addressed that)? No.

Do they add unsprung weight to the vehicle? Yes. Is that good? No.

So it's a case of choosing the appropriate brake for your use. You could get out the welder and adapt your bike to take a motorcycle brake. The disc is bigger and thicker and the caliper and pads are much larger. But you'd likely take longer to stop than a 160mm MTB brake because of all the additional weight and additional rotating mass. The suspension feel would also be awful because of all that unsprung weight.

Sure, that's a crazy extreme, but the point is that bigger is not always better, which is why not all bikes have 220mm rotors all around by default. If you're not overheating your brakes then getting bigger rotors because you believe they will stop you faster is going to lead to disappointment and no real gain.

If you want bigger rotors to ensure that you never get brake fade even if you go on bike park days in summer or on a trip to the mountains then by all means. Just don't expect them to shorten your braking distances under normal use.

And this is coming from someone with big red Brembos on all four corners of his car, so I'm well aware of the benefits, but I know my car wouldn't stop any quicker than an identical car with the smaller brakes from a lower model. On a track day the car with the smaller brakes would likely cook them in a lap or two though and I'd still be OK.

The limiting factor will always be tire grip. Although there are ways to have better grip with the same tire. ex: better suspension tune / design. Nevertheless at the end of the day, its tire grip that will be the limitinh factor.

On rotor sizes, I believe that by using less lever force on bigger rotors, riders are lead to think it brakes better.
Like braided hoses, that expand much less, and will require less force, because the hidraulic pressure is efficiently use to push the piston, and not expanding the hose.

In terms os sizing, you have MX or Enduro Moto, with "small" diameter compared with SM/Road bikes, and that is to limit brake skid/lock.
On dirt you won't use the full power of dual brakes, or evem 320mm disks.

What is required on Dirt is power and control.

Saying this would a 240mm disk brake be excessive? I don't think so, but presently I'm ok with 220/200! Like I was with 200/180... and back in time 180/160!

 

[RJUK]

The limiting factor will always be tire grip. Although there are ways to have better grip with the same tire. ex: better suspension tune / design. Nevertheless at the end of the day, its tire grip that will be the limitinh factor.

On rotor sizes, I believe that by using less lever force on bigger rotors, riders are lead to think it brakes better.
Like braided hoses, that expand much less, and will require less force, because the hidraulic pressure is efficiently use to push the piston, and not expanding the hose.

In terms os sizing, you have MX or Enduro Moto, with "small" diameter compared with SM/Road bikes, and that is to limit brake skid/lock.
On dirt you won't use the full power of dual brakes, or evem 320mm disks.

What is required on Dirt is power and control.

Saying this would a 240mm disk brake be excessive? I don't think so, but presently I'm ok with 220/200! Like I was with 200/180... and back in time 180/160!

Exactly. If a tyre had infinite grip and never slipped, then a larger rotor would stop you faster due to the extra leverage, but in reality that's never the case and all brakes can lock the bike's wheel up. Adding power won't stop it any faster, it'll just lock the wheel with less force and that's not a positive thing! If you fitted 160mm rotors to a Strive:On and rode it next to a Strive:On with 220mm rotors at the same speed and with the same tyres, then both jammed on the brakes at the same time, right up to the threshold of grip, they would both stop at exactly the same time. Maybe the 160mm bike would stop a barely measurable fraction sooner due to reduced weight, but you'd need perfect lab conditions to notice it due to how small the weight difference is.

Sure, after numerous back-to-back stopping the 160mm rotors would start to suffer from heat induced brake fade, and if you kept going long enough the 220mm rotors would eventually suffer also, but I said from the start that the benefit of larger rotors was increased resistance to brake fade.

It's the equivalent of having a bolt torqued up to 2Nm and easily undoing it with a 9 inch long wrench. Buying a 10 inch long wrench will mean you can use less force to undo that same bolt, but it won't undo it any quicker.

That said, all of this sounds like I'm saying bigger brakes are worse, which isn't the case at all. These ebikes are fairly heavy so will introduce more heat into the brakes to stop. They also tend to travel faster, which again means reigning them in from higher speeds which also puts more heat into the brakes.

My point was just that they won't stop you more quickly. If you're looking to stop more quickly, get softer compound tyres or reduce your tyre pressures to increase your braking grip.

I'm surprised that people go through rear pads several times faster than front pads though. With the weight of the bike shifting forwards on deceleration I'd have expected front pads to wear out first as they do on cars. The bike manufacturers seem to think the same way, as they often tend to fit larger brakes up front, as with our bikes.

Aaaanyway, I'm sure this has dragged on plenty long enough now. Enjoy your bikes, whatever brakes you decide to fit.

 

[Jdog]

This brake chat is beyond boring now. Start a separate thread ffs

 

[Mario Antony]

Exactly. If a tyre had infinite grip and never slipped, then a larger rotor would stop you faster due to the extra leverage, but in reality that's never the case and all brakes can lock the bike's wheel up. Adding power won't stop it any faster, it'll just lock the wheel with less force and that's not a positive thing! If you fitted 160mm rotors to a Strive:On and rode it next to a Strive:On with 220mm rotors at the same speed and with the same tyres, then both jammed on the brakes at the same time, right up to the threshold of grip, they would both stop at exactly the same time. Maybe the 160mm bike would stop a barely measurable fraction sooner due to reduced weight, but you'd need perfect lab conditions to notice it due to how small the weight difference is.

Sure, after numerous back-to-back stopping the 160mm rotors would start to suffer from heat induced brake fade, and if you kept going long enough the 220mm rotors would eventually suffer also, but I said from the start that the benefit of larger rotors was increased resistance to brake fade.

It's the equivalent of having a bolt torqued up to 2Nm and easily undoing it with a 9 inch long wrench. Buying a 10 inch long wrench will mean you can use less force to undo that same bolt, but it won't undo it any quicker.

That said, all of this sounds like I'm saying bigger brakes are worse, which isn't the case at all. These ebikes are fairly heavy so will introduce more heat into the brakes to stop. They also tend to travel faster, which again means reigning them in from higher speeds which also puts more heat into the brakes.

My point was just that they won't stop you more quickly. If you're looking to stop more quickly, get softer compound tyres or reduce your tyre pressures to increase your braking grip.

I'm surprised that people go through rear pads several times faster than front pads though. With the weight of the bike shifting forwards on deceleration I'd have expected front pads to wear out first as they do on cars. The bike manufacturers seem to think the same way, as they often tend to fit larger brakes up front, as with our bikes.

Aaaanyway, I'm sure this has dragged on plenty long enough now. Enjoy your bikes, whatever brakes you decide to fit.

People drag their brakes (rear brakes) [aka: trail braiking] on anything other than going straight!