29er braking performance

[Wannabe]

Simple solution. CHUCK THEM AND GET AVIDS!!

 

PROBLEM SOLVED....... :devil:

[Robrider]

Just from a science point of view..

 

Its about the application of force. Rotor pad apllies a force at a certain distance away from the hub. This creates a stopping moment (or torque if you would prefer) applied at the hub. The equation is M = Fxd. (d is the rotor radius)

 

That same moment is then applied to the stopping power of the bike, using the same formula, except now the stopping force F is applied to the ground and the distance d is the radius of the wheel.

 

if the rotor size and braking force are the same (ie one finger same pressure), then the increase in wheel size will decrease the stopping force

Edited September 4, 2014 by Robrider

[rouxtjie]

Cancel that....what beats a dragon rotor....kaalgat tjerrie...that is what

 

http://www.amazon.com/Dirty-Dog-Ace-rotor-6-bolt/dp/B0068S1AJS/ref=sr_1_10?s=sporting-goods&ie=UTF8&qid=1409823700&sr=1-10

[ChUkKy]

Simple solution. CHUCK THEM AND GET AVIDS!!

 

PROBLEM SOLVED....... :devil:

 

Eager beaver we have here... not even Friday and the first bit of *** has been flung

[DJ84]

Simple way of looking at it,

Most guys have upgraded their cars mags if you come from the golf 1 era.

 

same car, same motor, same brakes, bigger wheels.

Accelerated slower, had a higher top end in each gear as well as final drive and stopped quicker(marginally) grip dependent.

 

A larger contact area(tyre and earth) should assist in slowing down quicker not the other way around.

A larger disc helps disperse heat better and only aids more once the heat becomes too hot for the pads to work on the surface correctly.

 

Those are simple facts and it applies to bicycles as well.

[rouxtjie]

Simple way of looking at it,

Most guys have upgraded their cars mags if you come from the golf 1 era.

 

same car, same motor, same brakes, bigger wheels.

Accelerated slower, had a higher top end in each gear as well as final drive and stopped quicker(marginally) grip dependent.

 

A larger contact area(tyre and earth) should assist in slowing down quicker not the other way around.

A larger disc helps disperse heat better and only aids more once the heat becomes too hot for the pads to work on the surface correctly.

 

Those are simple facts and it applies to bicycles as well.

ja but what does your speedo read now

[zaslinger]

I had a similar issue with my SLX rear brake. The front was awesome, but the rear would bite, but then was a bit spongy and with more fingers & force, the lever would pull all the way to the handlebar. before locking up the rear wheel. Prior to lockup, braking wasn't how I wanted it.

 

Long story short, I replaced pads, changed the oil, bled the brakes numerous times, myself & twice at LBS - nothing helped.

 

Then I noticed that the brake hoses were not standard (I bought them 2nd hand off the hub)

So I got Shimano XTR brake hose and replaced the old one - BANG!!

Rear brake worked like a demon.

Instant bite 1 finger braking.

No sponginess

modulation was perfect with no excessive travel.

 

My casual observation - the other brake hose was expanding minutely under pressure, reducing the effectiveness.

Not a big issue on the front as the hose is short.

But over the length of the rear hose, this expansion was enough to degrade performance.

Edited September 4, 2014 by zaslinger

[LazyTrailRider]

I'm surprised that no one has used the word "moment" yet...

[Robrider]

I'm surprised that no one has used the word "moment" yet...

 

Er... I did

[JI Fourie]

I have SLX Breaks on my 29er and 160mm Alligator rotors front and rear with resin break pads. They work great I would not buy any other breaks as these are superb and does a relay good job.

[Vangar]

I have SLX Breaks on my 29er and 160mm Alligator rotors front and rear with resin break pads. They work great I would not buy any other breaks as these are superb and does a relay good job.

 

It's brakes....if they break thats wrong sir. Sorry pet peeve along with loosing.

[Headshot]

Robriders science makes sense to me. That' s why 29ers should all use rim brakes. I ride with a 203 mm front and 180 rear on my 2.35" 26er tyred bike. Beat that brake force niner people...:-)

[JXV]

Running 203 front and 180 rears on latest XT calipers on my SC LTc 29er. The brakes are savagely good. Better than older XT 180F / 160R on my old 26er.

 

I liked the post about the poor quality brake hose.. The hoses are a component we don't often consider. Any hose expansion under presure could dramatically reduce braking force at the caliper. Had this on a 4x4 once.....

[zaslinger]

 

Any hose expansion under presure could dramatically reduce braking force at the caliper. Had this on a 4x4 once.....

 

Strangely, the "non-standard" hose was fatter than shimano hoses, couldn't fit the shimano ferrule over the hose.

That's what tipped me off. Hose also had no markings? (Chinese fake? ;-))

[droo]

Your physics is flawed.

It is force that needs to be slowed down.

 

All things equal, all things will be equal no matter the wheel size.

velocity does not get changed by wheel size.

 

So please show me how this applies in a practical manner.

 

This. Same kinetic energy = same braking force required.

 

This only falls down because 29er wheels are heavier than 26, so E_k is greater, as is angular momentum.

 

Well, more stubs its toe than falls down. The differences are small enough to be negligible.

[L'Bie]

 

 

The rotor size definitely makes a difference,

but i fail to understand how the wheel size would make you need to upgrade the rotor size.

If both tires have the same amount of grip and the brakes have the same amount of grip,

you will need to apply the same amount of pressure to lock the wheels.

Archimedes said he could move the earth had he a long enough lever.

Different wheel sizes apply different lever ratios. The pivot is the axle with the one lever making the distance between the pivot and the effective brakepad average. The other lever is the distance between the tire surface where it is in contact with mother earth. Should you use the same rotor sizes on the 26er and the 29er, you will notice the 26er has a ratio closer to 1:1 than the 29er. If you want the same power, you have to get a bigger rotor. That's is assuming all other factors like dirt, air, alignemt etc. is sorted.