Good brakes?

[Goat Herder]

So by your own findings motorcycles should all have rim brakes?

 

[Chalo]

The difference is hard to believe, but a friend who rides mountain bikes tells me hydraulic disc brakes are as much a change for the better as cable to hydraulic?

Nope. Pretty much any disc brake will be a step down in power from a Magura hydraulic rim brake. The lever feel and response is pretty similar.

Few people have enough experience with really good rim brakes to be able to make informed judgments about rim brakes versus discs.

Chalo

 

[Goat Herder]

I road many a mile with V brakes I don't like them any more since finding good disk brakes.

Why Disk Brakes Are Better Than V Brakes on a Mountain Bike

There's more..

 

[Goat Herder]

Should I Get Disc Brakes or Rim Brakes? - Do Disc Brakes Weigh More Than Rim Brakes?

 

[Chalo]

So by your own findings motorcycles should all have rim brakes?

No-- the energy levels are too high and the tires too fat to make rim brakes a good match.

But motorcycles DEFINITELY should not use bicycle disc brakes, since those are even less able to dissipate energy than rim brakes.

Chalo

 

[Chalo]

I road many a mile with V brakes I don't like them any more since finding good disk brakes.

Why Disk Brakes Are Better Than V Brakes on a Mountain Bike

The technical misconceptions and hogwash in that article are almost as impressive as your own. I'll critique yours when it's particularly detrimental for other readers here, but I'll just say that on the basis of that article, no technical opinion by that writer should be trusted.

Energy is proportional to velocity squared. It applies to vehicles and to brakes, too. You and the author of that article should try to figure out the implications.

Chalo

 

[Goat Herder]

The technical misconceptions and hogwash in that article are almost as impressive as your own. I'll critique yours when it's particularly detrimental for other readers here, but I'll just say that on the basis of that article, no technical opinion by that writer should be trusted.

Energy is proportional to velocity squared. It applies to vehicles and to brakes, too. You and the author of that article should try to figure out the implications.

Chalo

I have not ever argued that the proportionate leverage at the rim of a V brake was unworthy.


I have suggested that there are Disk brakes on the market that have exceptional properties. I have not once compared my brakes to any of my experiences to going down from say the crest of the Sandia's. At a point of such a decent I would stop to let any kind of brake cool off.


Sure I think we all no by now that proportionality a true motorcycle rim will not take the heat. Uh yeah bigger tires is a given.

One of the reasons I put the article there was so we can all learn. So good deal there. You found something

Uh impressive as my own? hold on there killer. I have only ever suggest two brake set ups that I was familiar with. I spoke for my driving habits and never strayed any different from my observations. I don't spend my day's screaming down from the crest of the Sandia's and never have or even suggested that I did.

I go through town and everything is flawless for that. It always has been.

At some point even a cars brakes have to be let to cool off.

For the record I still prefer disk brakes and yes I know my limitations.

I did leave links to suggest Disk brakes have improved though.

 

[Goat Herder]

Magura Gustav M discs (which performed best in the test but failed at 1100W dissipation) are still just about the stoutest available. At that time the used (I believe) 180mm rotors. An equally sturdy 203mm rotor would offer 13% more braking leverage and heat rejection with the same caliper. That means it fails at 1240W instead. It's not an overwhelming difference.
Chalo

Based on a data sheet that is going on 10 years old! Where you nonchalantly drummed up your own percentages?


Here is what you left out... A whole lot of technical advancements have taken place since 2001. We are in 2010 now. Brake calipers have greatly improved and so have the pads. The materials have greatly improved. Percentages based on here say to a ancient test 9 years ago does not totally wash. There are too many moot points I personally suspect there. Dunno?

Cars use a myriad of different compounds in there pads and there is always some advancements taking place. Disk brakes closely follows automotive philosophy and use many of the same materials.

As a auto mechanic I can say I have observed this hands on in just the last 9 years alone.

There are pad arrangements I suspect that make things run cooler now!! If not. There is much less fade.

CHRIS' TANDEM TIPS: Rim brakes, disks and overheating - hard data



Chalo

In my observation, 203mm rotors tend to be spindlier than the old Gustav M rotor, larger but with no more surface area. Magura now offers the Gustav M with a 210mm rotor.
Chalo

Sure this sounds like a great brake!

There is no substitute for heat capacity to dump energy into, and surface area to reject it from. A 203mm stainless steel rotor weighs about 180g and has a specific heat of .5 joule per gram per degree C. A Velocity B43 rim weighs about 770g and has a specific heat of .9 joule per gram per degree C. And the rim has much higher thermal conductivity, and it has many times the surface area, so it can absorb a lot more heat and reject it many times faster than a disc rotor.

That's why disc brakes can work so impressively at modest loadings, but fail long before rim brakes that seem unimpressive by comparison. They're perfectly adequate for normal size riders on normal weight bikes moving at normal bike speeds. Turn up the energy levels from there, and you can have problems.
Chalo

My experience with a disk brake that I suggested only go to what I have found that works. The two brakes that I mentioned and suggest are more than adequate for me and what I have demonstrated.

I find a 165mm rotor to be more than adequate for the rear brake on my mountain bike. I use a 9" (229mm) hard anodized aluminum rotor on the front. The thick aluminum rotor has more heat capacity, as well as more surface area to reject heat and more mechanical advantage at the caliper. But that's appropriate for a front brake that can apply at least three times as much braking as the rear.

Chalo

I would say this defiantly is true. However I like the ability to lock up the rear and gently dump a bike if I have to. I prefer a larger rear disk. Yes 80 % percent of the braking always gets done on the front. This is perhaps what you were trying to demonstrate here.

Because the physics are contrary to your experience, I chalked that up to peculiarities with your equipment. I already showed you how a good rim can soak up seven and a half times as much heat as a 203mm rotor, and pass that heat to the air several times faster. And I have shown you tests that demonstrate disc brakes fail at lower energy levels than rim brakes.

So I have to conclude that your rim braked wheels were simply not the equal of your disc braked wheels.
Chalo

Well lets see I told you that I had the pads hot enough to see obvious smoke vapors. At the time of my observations I had a Avid BB7 203mm in the front and a V brake in the rear. To make things perfectly clear I was doing panic stops from 30 miles an hour. Why one should know there limitations. Total of one test stop did it. I had no fade from ether brake at the time as it was a one time panic stop. Not multiple. To check them immediately again the rear had faded more than the front.

Now to make it perfectly clear this was an absolutely straight rim when I did it . The rear pads were absolutely to the letter of Adjusting Direct-pull Cantilever Bicycle Brakes ("V-Brakes ®").

So I observed a warped rim from this kind of stop. An aluminum rim on more than one occasion. With more than just one rim.

Now to make it perfectly clear I have yet to warp any of the two 203mm disk brake set ups that I have mentioned as being decent brakes for me. How ever I have got them them hot enough to fade on a much heavier bike the Morini. [Extreme ridiculous braking] They still complimented constant play full driving without any prob's for me and could easily do any panic stop in the city.

With cars I am drawing a clear picture here. On lighter cars especially if you tighten the lug nuts unevenly it only takes about two weeks to get a pulsation from a warped disk rotor or one good panic stop. That is why we are supposed to torque our lug nuts evenly. Think of a guy improperly using a impact wrench. Now a bicycle spoke rim never really has evenly torqued spokes. I said my wheels were perfectly straight remember.

Disc front wheels are dished, therefore weaker than equivalent symmetrical front wheels. Disc rear wheels have narrow flange spacing, therefore less stiffness than conventional rear wheels.
Chalo

This is a great thing to bring up but I think if more folks use thicker gauge spokes it is a bit of a moot point.

So if you and all the weight of the bike get trapped at the hub's say the rim brake is involved at the tire. Now all your weight and inertia is being transferred directly into the hubs and spokes.

So if you use a disk brake all of your weight and inertia goes to the same place

Those guys are not immune from getting things wrong. In this case, they were wrong. A disc braked wheel must be built with a stronger rim and/or more spokes to be equally as strong as a given non-disc wheel. Fortunately, most of them are built that way.

Chalo

You are not immune your self As well as I

No-- the energy levels are too high and the tires too fat to make rim brakes a good match.



Chalo

At which point I think a bicycle with a motor on it can enter this category. My Morini with straight wheels to this day.. has not been all that bad. While I would adment with any of these said brakes coming down off the crest of say the Sandia Mountains would be particularly foolish and does not fit my agenda for such riding. A 50cc motor can only take so much of a beating when perhaps it should be let to cool off as well.

You make some fair points. I think with some common since all these brakes do there job.

Yes a rim brake has more leverage, it still is not bullet proof non of this stuff really is.

While we were waiting for an ambulance the ride leader pulled the front wheel out and took the tire apart. The tube had begun to melt in several places.

Just saying anything can be used out of proportion.

 

[Kevlarr]

Lets not forget that it's not so much the ability to dissipate heat but it's the ability to dissipate the gases that form during braking. Brake fade is caused by gas buildup between the braking surfaces. Look at any car race that's run at night and you'll see the brake rotors glowing red hot during braking.

 

[reb1]

Wow that was interesting. I have 48 spokes in all wheels on my bicycles. When I purchased the tandem I weighed only 195. The wife was around that being pregnant and the two wheeled cart I built to haul all three tots including the one on the way weighed 50 lbs empty. We lived in a student town and the tandem was our station wagon. We needed good brakes. The self energizing brakes and the drum were adequate. I even had special brake pad holders that were heavy aluminum with fins on them to dump heat.
As I look at motorizing the tandem I dislike not having my drum brake. I am seriously considering a custom front hub to allow the use of the drum brake. The rim of the bicycle is a rather large disk. This is why I like the hydraulic rim brakes. 9 years and never any trouble with needing to replace a brake line or change fluid or adjust the position of the pads other than when replacing a rim. Changing the pads by hand is a real plus. I will stick with these for my purposes on my tandem. Rim brakes 2011: MAGURA - The Passion People!
I build my own wheels. After I build a wheel front or rear and check it after several hundred miles. I rarely need to true it. This is why 48 spokes on all wheels. Even with two riders weight exceeding 500 lbs and doing panic stops the wheels stay straight. If you are using wheels with only 32 spokes than expect to create a taco now and then.
The Magura Big is sold through there industrial division. Greenspeed sells these brakes as an option on there trikes. They can be ordered to operate of of one or two brake handles. They can be ordered for right and left for trikes or quads. You would need to contact Greenspeed or do a web search for the Magura Big and contact Magura or someone who sells other than Greenspeed. Greenspeed Recumbent Trikes - Magura BIG Disc Brake Option
You will need to contact Santana about there new disk brake. Here is a page from there site. Mechanical vs. Hydraulic

 

[Goat Herder]

Thanks for that incite Reb1 scaling up on the spokes speaks volumes. I only have used run of the mill wheels & aluminum rims. Got me thinking now.

Big trucks are way more forgiving about warping rotors than light cars. The right wheel for the right job!
I really always wanted heavier duty spoke wheels for the stuff I have been playing with. That is the route I will taking. I am considering 10 gauge spokes have to custom order them. Any body got links?

Yet when you consider a prolly needed flex in the picture and a more unified unibody structure so to speak 48 spoke prolly wins hands down. [with lighter gauge spokes] I am supposing.....

Good to hear from folks with hands on experience