"Brake Drag" what's the big deal?

[Jeff Mulvihill Jr]

Some people love them because they work, some people think the "drag" is going to slow them down. What's the big deal about the tiny amount of brake "drag" that Brembos have? Motorcycles went through the same issues years ago, car brakes "drag"... With the horsepower to weight ratio that karts have... has anyone done a test to see if the benefits of having vs. not having them is worth it? Or has anyone tested speeds at the end of the straightaway? I think I know the answer, but some confirmation and discussion would be interesting.

[fatoldman7]

I think the issues with brake drag might have more to do with what’s happening in the corners than what’s happening going down the straights. If you think about how much a chassis flexes in the turns, and how well the caliper stays aligned with the disk, there is more potential for brake drag being a problem in a long sweeper, or turning hard into a corner, than going down a straight. I know my Engenetic brakes dragged quite a bit in the corners on my enduro kart until I redesigned the caliper mount….just some thoughts….

[james fuchs]

this is a vary good point,we ran a cage cart for a season,i noted one night that the brakes were very hot ,seamed that the more the kart leaned in to turn the more the brakes where on. we made a mount that used two bearings hanging off axel with a torke arm two chassis ,worked good.jim fuchs

[Jeff Mulvihill Jr]

are you guys saying that the brakes were "dragging" enough to actually apply brake and slow the kart down or just that they were touching... My question is, if car and bike brakes "drag" under normal operating, what is the big deal in a karting application? Has someone shown that they actually slow you down with this "drag"?

[Erik Frank]

Jeff,

There is a fine line between a brake pad that is touching and one that is dragging.

To me, the big issue with a lightly dragging brake is not nescessarily the losses from the dragging, but the excess heat that can be generated. It doesn't take much to really get the brake pads and rotor hot when you have pads that are constantly dragging. If your brakes get hot, their performance drops, and your lap times go up! It can also be a safety issue (no brakes!) Best not to have them dragging...


-erik

[Dave Malloy]

Basic physics - The heat at the brake is a direct result of the energy taken from the forward motion of the kart through brake drag. More heat = more drag. Much of the heat gets dissipated into the airstream which is all lost speed. No fine line, really, any touching will produce heat. The more touching, the more heat and the slower the kart.

[Jeff Mulvihill Jr]

so kart brakes, unlike bikes and cars do not work as well "hot" therefore they are designed to pull the pads away from the rotor? Did anyone tell Brembo that? I'm not understanding. Are you guys talking in physics too far above my head or am I looking at cars and bikes and not understanding why they can have self adjusting brakes that "touch" or "drag" but my kart "shouldn't"? Quite frankly, the brakes on my kart work a lot better hot... maybe I haven't really cooked them, but I'm pretty hard on them... didn't the motorcycle industry go through this some time ago, like 20 years ago or so... all the same "thoughts" were there, but the fact of the matter was that self adjusting brakes were the way to go...?

[fatoldman7]

The big difference between car/bike brakes and kart brakes is how there mounted. Car and bike brake mounts are very ridged and do not flex. Kart calipers are mounted away from the bearing cassette , and if the bearing cassette is doing it's job, is allowing the axle to change angles as the chassis flexes.I remember coming into the pits after being out on a track that was easy on brakes and the brakes would be pinging away and way to warm for the amount of use I was giving them. I thought I was riding the brakes, until I would go out and do some laps as hot as I could without my foot on the brake pedal....same problem. This was true with both sprint and enduro karts.I know pay a lot of attention to how my calipers are adjusted, and how there mounted.

[Dave Malloy]

Generally, street vehicles are not concerned with the small amount of drag that brake pad touching produces. Touching is desirable to accomplish the self-adjusting feature that is required since they get less frequent maintenance than race vehicles. The pads are pushed away from the disc by its run-out so they usually are not touching. There is rarely any touching a moment after brake usage so there isn't any significant heat build-up. This small amount of touching and associated heat & drag can be avoided by the use of spring return pads with the added requirement that the brakes be adjusted. It's striving for that small benefit that pullback brakes are used. Drum brakes don't have the problem of dragging unless they are adjusted too close. They need to be adjusted routinely unless self-adjusters are included but they also need to be actuated. Most cars equipped with rear drum brakes need to have the emergency brake utilized in order to actuate the adjusters. Many drivers don't use their emergency brakes and end up with low brake pedals.

[Jeff Welch]

Jeff,

While I don't know much about performance/safety/etc. with dragging brakes, I can tell you how we fixed the problem.

On the DFM, which comes with Brembos, there is a brake fluid resovior usually mounted on the driver's fairing with a tube running down to the master cylinder. What happens is the pressure that the fluid creates via gravity prevents the pads from releasing all the way, thus causing a little drag. We put a one-way check valve in to allow fluid to go up but not down, taking the pressure off the pads. Then we made a small loop bypassing the valve and placed a valve with a lever to open and close the line in the loop. You close it when you drive, and in between sessions you open it up to refill the master cylinder. We've had no drag by doing this. You don't have to have the bypass with the valve if you don't want, but always check to make sure you have fluid.

Hope this helps.

Jeff Welch
Weltek Racing Online

[Jeff Mulvihill Jr]

Guys, I want to know what's the big deal WITH drag? If the Brembos work "better"... and they "drag" is this a karting "Myth" that brake drag is BAD or is there something that I'm missing?

[Dave Malloy]

Brake drag is bad! You're not missing anything. What do you mean that Brembos work? Are you saying that other brakes don't? Your question tends to make me wonder if you have brakes that aren't properly set-up.

I think the best answer to your question, if I understand it, is "it depends". As is said before, there's only a little drag for a short time. This little bit of drag will probably slow the kart unnoticeably. Some people think it's a big deal, some don't. Some people think that Brembos provide enough of an advantage in braking that they outweigh any disadvantage the drag creates. This decision may hinge on factors such as track type or driving style.

I have no experience with Brembos but I think the issues you want answers to are similar to many others made by racers. "What is better, A or B?" If there was one answer that was clearly accepted then everyone would use it. Obviously not everyone uses Brembos. All that anyone can do is look at the factors objectively and make their own decisions. I don't think the drag accounts for enough speed loss to make a difference. Of course I would want to make sure the drag is minimized with proper set-up.

My kart has Freeline pullback calipers which means I have to adjust them occassionally. I like the idea that they don't drag and I'm not going to pay to change them especially since they seem to work fine (once I figured out how to bleed and adjust them).