Kapusta

What exactly do you think we are wrong about?

The leverage ratio (between the brake lever and caliper pads) is much higher in a disc brake system than a rim brake system. This means that the disc pads move less distance over the throw of the lever, but exert greater force on the rotor. This is a simple fact. Do you think I am wrong about that?

WHY do you think that is? Two reasons.

First, it NEEDS to be, because the disc itself has much less leverage over the wheel. The disc caliper MUST exert more force than the rim claliper in order to achieve the same stopping force. Do you disagree with that?

Second, it CAN be designed to have greater leverage over the pads. Take a look at how far your disc brake pads move when you pull your lever all the way. Maybe 0.5 mm? Maybe less? Now look how far your rim brake pads are from your rims. They are much farther away. If your rims brakes had the same leverage over the pads as your disc brakes, you would pull the lever all the way to the bar and never get the pads to hit the rim. Do you disagree with this?

What part exactly do you think I am wrong about?

Think about this: why don't they design rim brake calipers and levers so that the levers have MORE leverage over the pads than they do now? More leverage would make stopping easier, so what don't they do it? The answer to that is the very point I was making.

Flip Flop Rider

with ya on cantilevers being the worse

Koyote

@Kapusta , here is what I wrote. Your last post, above this one - which seems to be a reply - has absolutely nothing to do with the following.

Melvang

Those saying you can't modulate with hydraulic disc, I have never had a problem with mine. I have a Kona Roast with a Shimano XT brake lever, Hope caliper (believe 4 piston), no idea what the rotor is. Never had an issue with not having enough feel for modulation of the brakes. If they are two twitchy, they only using one finger. That's all I have ever used aside from a couple panic stops when riding in Jacksonville FL.

surak

Not that BF needs yet another discs vs rim debate, but the search for problems have looong ago come back with findings. They are rain, carbon rims, and as you said, tire size.

Kapusta

You are correct. As I keep repeating, we are not talking about the same thing. We are talking past each other. The difference is that I know we are, so I am not telling you that you are wrong.

You even said in your first response to Alo
I think that says it all.

And by the way, my last post was in response to you saying:
I was simply trying to understand WHAT exactly you think I am wrong about.

Koyote

I’ve explained why (I think) you are in error in post #15… But you don’t seem to have the reading comprehension for it. So I’m going off to bed.

Kapusta

You explained it in post #15? In my browser that is my own post.

matt92037

I saw this thread and wanted to weigh in, not with opinion, but more with my experience and curiosity. I am 200-205lbs been MTB'ing for 30+ years and riding discs for about 18 years. I have been roadbiking for only 4 years however and have never tried a bike with rim brakes (or mechancial shifting for that matter). My road bike has Shimano 9170 brakes and 160mm rotors front and rear.

My rides are typically straight up for 3 miles, then down for 3 miles, two to three times per ride. The decesnts hit grades of 14-17% frequently, lots of speeds in the low 40's. Some of the decents are smooth, no tight turns, etc so you can just open it up the entire way and brake hard at the bottom. Some decents find you in situations where you haul major ass, need to brake hard on a 15% grade (aweful concrete or tight turns in a narrow bike lane), then open it up, then need to dump speed quickly again, over and over. Before I can get to the bottom of those decents my front and rear rotors are nuclear reactor meltdown hot. I don't drag my brakes, I alternate front to back to give the opposing brake a break. There are many times I wish I had my XTR 4-pots and 200mm rotors on my road bike. Which leads me to the curiousity part:

How would a high end rim brake set-up work in this situation? For me I think I found the limits of a 200+ pound rider on tiny brake pads and tiny rotors. Going slower down the hills in question doesn't work to well either because when you are on grades that steep, to go slow you will be dragging you brakes. To reiterate i dont like using brakes going downhill but in some situations i have to, a lot, on really steep hill, for miles.

What do you guys think? My last rim brake setup on my MTB were ceramic coated Bontrager rims and they did really well for what they were.

Koyote

Thanks for reinforcing my point.

subgrade

I think I see where you got it wrong: in your own words, as long as it is impossible to pull the lever all the way to the handle bar, you can develop the same amount of force on the brake lever.
What Kapusta was saying is that the same amount of force applied to the brake lever translates to more force on the disc brake pads vs. rim brake pads, by way of greater mechanical advantage (any given amount of lever throw moves the pads of a disc brake a smaller distance compared to rim brakes).

Kapusta

So now you are just going to evade the subject?
Nice.

Koyote

I did not get anything wrong. I was never discussing disc brakes.

See above.

subgrade

So why were you posting it in this thread?

Koyote

You should read the thread.

alloo

When will bicycles get ABS?

Kapusta

Yes, as I said, we were not talking about the same thing.

Alo and I WERE talking about disc brakes, explaining the leverage differences between disc and rim calipers. And what I pointed out is completely accurate. It is a fact that the leverage ratios are different, and the reasons for this are the ones I stated.

Your response - which essentially points out that the leverage of a rim caliper does not change when you set the pads further away - is 100% accurate. But has no bearing on the point that Alo or I were making.

elcruxio

I'll assume you mean a bicycle front wheel cannot skid on clean dry tarmac type surfaces whilst riding forward?

This is one strange difference in people. I've been quite impressed lately by the control and modulation I get from my hydraulic disc brakes. Takes a bit of fiddling to get the one finger position setup properly but once that's done I'd wager the four piston hydraulic brakes I have on my fatbike are the most precise brake system I've ever ridden. I can do manuals with them, which hasn't ever been possible on any rim brake system or even mechanic disc brakes.

And then on the other side of the coin are vee brakes which are truly on/off with very little modulation in between. Very powerful yes, but also very dangerous as it's just way too easy to lock up the front wheel.

While that might be true the end result could end up being pretty darn bad in general. Steel rims are difficult to manufacture to the complex shapes aluminum rims are extruded to and the resulting rims would likely be less stiff than aluminum rims in all directions especially if one tried to get close to aluminum rim weights. Also I'm not sure steel rim walls would manage without flexing in such a system.

No it's not. Rotor truing is far easier and far less stressful than truing a properly tensioned and properly sealed wheel (sealed as in first lubricated and then thread locked with either a certain type of oil or with actual thread locker). Truing a wobble wheel is even more difficult if it hasn't been lubricated in the first place. Just had the pleasure of truing the machine built wheels of my new bike and it was horrible I tell you.

Probably depends on the brake. With modern calipers you need to set them up with a significant gap or the brake won't work as intended. With mini vees and road levers you need a tiny gap and you'll be adjusting it constantly. With cantilevers again you need a tiny gap to get any kind of power out and even then it's pretty abysmal what you can get. With actual vee brakes and mountain levers a decent gap is again ok. Just before midway is the best place for the brake to actually bite I find.

My BB7's bite at half pull and I get pretty nice performance from them. I've tried the instant bite too and didn't care for it as it A) makes the bike noisy (now I did say truing rotors is easier than truing wheels but I don't actually bother truing rotors all that often) and B) means I need to then adjust the lever travel as well and that's a hassle. I mean I could do it, but I'm not really sure where the adjuster screw is in my brifters if they even have one... In terms of when a mechanical disc brake bites there's no reason why you'd get any less power with a later bite point if the brake is otherwise setup properly. The most important factor of course is that with a single moving pad system the immobile pad is as close to the rotor as possible. With dual moving pads.. I dunno, I had such a bad time with the Spyre that I've temporarily given up with that.
I think most levers these days even compensate for travel so that's not a reason either.

I hear that a lot but I don't think it's entirely true in all situations. My townie bike has a modern version of the long arm caliper brake and what pushed me to get a townie bike with disc brakes was an incident where the old bike failed to stop with the front brake in a steep hill. Now mind you, the brake is setup properly with the adjustments which are available to that brake and it even has Kool Stop dual compound pads. Still failed to stop with a fistful of brake lever being grabbed. I've had the same thing happen with cantilevers which then pushed me to sell my cyclocross and get something else instead. And those too were properly adjusted. I know it's tempting to now indicate that clearly said brakes weren't properly adjusted but if I can't manage to adjust a set of brakes properly there's something deeply flawed in that system as it seems to require some arcane knowledge 15 years of wrenching my bikes does not provide. Sure it's possible that I can manage every other wrenching task without breaking a sweat whereas rim brakes are still a total mystery. I've only owned rim brake bikes for 10+ years but sure it's possible. But I think it's unlikely.

Come to think of it, I've never had a situation where I've been even in danger of going over the bars, but I think that's more to do with my weight. And having bikes with long wheelbases. Very rarely do I even lift the rear tire. But the only brakes I've lifted the rear tire with have been disc brakes. No rim brake has ever had the power available to achieve that. Then again, I've never owned an actual road bike with short travel calipers.

rydabent

There are a few reasons that disc brakes are superior. First of all they dont scab up your expensive rims. Disc brake bikes can take advantage of lighter stronger and more aero rims since they dont need a braking surface. Disc brakes are pretty much unaffected by water. Then too there is the fact that disc brakes dont heat up the rim and tire on long fast down hill runs. In a few cases it heats the rim and tire so much, the tire blows off the rim.

And lastly it pretty much makes no difference if you like them or not, it is what the mfg are putting on their bikes, due to economies of scale.

Kapusta

Let me see if this helps clear up anything:

No, you are not "wrong" in this post. As said in my last post, what you are saying is true, because when you set the pads farther away on a rim setup, you are in fact not changing the mechanical advantage.

However, what what I am failing to see is the relevance of this to the point Alo made is post 12, which (I believe) I clarified in post 15, and then which I once again broke down in post 26..... all of which you are insisting are "wrong".

I've given you ample opportunity to explain where exactly I was in error, but all you've done in response is blame my reading comprehension. Which is a little ironic considering this all started when you said.....
Well, I actually DID understand what it meant, and I tried to explain it to you.

Oh, well.

delbiker1 

AAARRGGHH! Time to stop looking at disc brake threads. The argument is tedious, unnecessary, and seemingly endless.

Flip Flop Rider

so what's the verdict, disc brakes good? Will I flip over the handle bars (endo)?

how about maintenance and adjustments. Fairly easy?

Kapusta

The sad thing is that the OP was not looking for a good/bad discussion, just an explanation, and some folks were trying to do just that. But no matter what, it always turns into a better/worse argument. Heck, I am so used to seeing these arguments that at first I did not realize the OP was sincere.

cyccommute 

No, I didn’t miss your point. Your and Alo’s point are wrong. I don’t need to set my rim brake pads as close to the wheel as a disc rotor pad needs to be set but the pads generally need to be set closer than most bike shops will set them up initially. The reason is that a rim brake takes less clamping force as you pointed out In

A rim is just a rotor. Bicycle can generate enough braking force with rubber pads and calipers that are set further away from the rotor than hub mounted discs can because of the size of that rotor. The maximum braking power is at the point where the bike is just about to rotate the rider around the center of gravity, i.e. doing an endo. Any front brake that is properly adjusted is capable of doing that. Detune a hub mounted disc to the point where it takes half lever travel to get to the point where the pads contact the rotor and see just how bad a hub mounted disc can be.

Kapusta

If rim brakes COULD be set up with a higher leverage ratio, they would be. Why do you think that they are NOT set up higher ratio than they are?

The reason is that higher leverage would reduce the pad travel too much. THis is why canti levers do not work well with v-brakes: too much leverage results in not enough pad travel.

This is exactly the reason that companies messed around with "servo" levers like the old XT v-brake levers. Low leverage in the beginning of the lever pull to close the distance to the rim, then significantly higher leverage at the end where you want it. Some of the Shimano hydro disc setups do the same. EDIT: I see below you point out that even regular levers increase leverage throughout the stroke. This is true, and I would ask: why did they design them that way? But the levers I am talking about do it much more so.

How close you personally set your pads is not the point. The point is that disc and rim brakes are design with vastly different amount of pad travel needed.


This is all true... but not relevant to the point I was making. You seem to think I am making some disc/rim power comparison.... I'm not.