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Brake stopping power

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I have the Rekluse left hand rear brake (LHRB) for my '06 450. It feels as firm as the front brake, not spongy at all, but while the front brake will lock up the tire at about 50% of the travel distance to the bar, the LHRB needs to be pulled about 90% of the travel distance to the bar. It gets very firm at about 50% of the travel and you think it will lock up the brake but it needs to be pulled in almost the rest of the way to the bar to skid the tire. I think this might be normal because the spinning mass is greater than the front tire, plus a couple of other reasons that I don't know about. I was wondering if getting a bigger brake line so that it holds more brake fluid would decrease the amount of pull on the lever until the wheel locks up.

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Barring anything incorrect about your assembly, to increase the stopping force you have to improve your leverage. This can be done in any of these ways:

> Increase the leverage of the force applied by the hand lever (modify or change the lever itself)

> Increase the hydraulic leverage of the master cylinder/caliper combo (smaller diameter master and/or larger diameter caliper piston)

> Increase the leverage of the brake at the wheel (larger diameter rotor and/or change from stainless steel to a carbon steel rotor)

A larger brake line will only speed up the flow of fluid. It will have no effect on pressure delivered, or stopping power unless you replace a "springy" hose with a stiffer braided steel one, or vice versa.

The problem is likely related to the fact that the hydraulic components were designed to have pressure applied by a lever driven by your foot, which is obviously much greater than what most people can do with their hands. I'm not familiar with this arrangement first hand, so it may be normal, or it may be there's something wrong.

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...replace a "springy" hose with a stiffer braided steel one...

Do the MXers come stock with springy brake lines? I thought it was just trail bikes that came with them to meet road law requirements. I need to get a braided front line if my '06 hasn't already got one!

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No. They all come with flexible hoses, of course, because the suspension has to move. There's no reason for there to be any law requiring a spongy hose, since any such thing would degrade braking performance. All brake hoses are built to resist any increase in their inside diameter when pressure is applied, but premium hoses resist it better than most OEM hoses do to begin with, and the "rubber" hoses do slowly degrade over time, becoming gradually less resistant to such swelling under pressure. Puffing up the brake hose is a simple waste of effort; some of your applied force goes toward doing that before going to applying the brakes. Standard road bikes and trail bikes may come with less stiff (diametrically) hoses simply because it's less critical in those applications, and probably less expensive.

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The Rekluse brake line is braided steel with a plastic covering. Now lets say for the sake of argument that everything is set up correctly and working right. What would be your best bang for the buck for improving performance of the brake.

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Puffing up the brake hose is a simple waste of effort; some of your applied force goes toward doing that before going to applying the brakes. Standard road bikes and trail bikes may come with less stiff (diametrically) hoses simply because it's less critical in those applications, and probably less expensive.

When I had a KLX250 the front brake was very spongy. I was told by the dealer that road going bikes come with spongy lines so that the rider doesn't accidently grab too much front brake and lose traction. It sounds like one of those weird government laws, he also said that having a vacuum carb on it was another "road safety" requirement (It doesn't seem to be the case anymore, but they do usually come heavily restricted if they have pumper carbies). I actually found that the spongy front brake felt worse on the road because it didn't have enough stopping power for the higher speeds (and dangerous driver guided missiles). I fitted a CR style braided line to it and it was so much better.

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Your dealer was making up BS to make something that was done to save money sound like something that was done for some higher purpose.

"Pumper" carbs are those with no float bowl, such as are found on two-stroke gas powered trimmers, etc. The flow of fuel is controlled by a diaphragm that senses the intake pulses in the engine.

Carbs with vacuum throttle valves are intended to eliminate stumbling on throttle opening. There are actually two throttle valves, one a butterfly type, like a car would commonly have, opened manually by the twist grip, and the other a slide valve opened by the air flowing in through the carb. The faster the airflow, the more the throttle opens. When done right, the throttle will open as fast as the engine needs it, but no faster.

This type of carb will not necessarily hinder engine performance at all, and Solex and SU racing carbs were made this way for many years.

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By saying "pumper carby", I meant a carby with an accelerator pump and cable actuated slide. The carby on the KLX was a vacuum actuated slide carby, it seemed to do the job ok. Yeah, vacuum carbies are probably more of a cost cutter.

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.. vacuum carbies are probably more of a cost cutter.
Not really. You can, of course, cut corners with any design, but the vacuum slide carbs aren't necessarily any less expensive to manufacture than carbs with accelerator pumps. It's just a different approach to the same issue.

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Stupid question...LHRB, I'm assuming that means moving the foot brake to the clutch lever position. Is that correct? Where do you move the clutch lever and why would you do this? What gains are there? :thumbsup:

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