Hi guys

I hope I'm posting in the right forum here.

Having ridden mountain bike trials for over 12 years I've just got my first moto trials bike - 2012 Gas Gas TXT 280 Pro Racing.

Absolutely loving it so far - real challenge but so much fun.

My question is regarding the rear brake. I'm used to hydraulic rim brakes with a grind on my mtb trials bike which are insanely powerful and then hydraulic discs on my downhill bike which are equally powerful but obviously not as grabby.

The front brake on my Gas Gas is really sweet, I can easily stoppie or lock up for nice endos etc really happy with it. However the back brake compared to what I'm used to is pretty weak.

If I really step on it the rear wheel will lock, but I cant see it holding on gaps, rear wheel hops or correcting a wheelie that's been overcooked! Is this typical of rear trials brake? Lever feel is OK its not really spongy or anything like that. I appreciate the disc is very small so I assumed power would be fairly limited.

Watching some of the top guys they fully commit to huge gaps landing back wheel first pretty much vertical - as you would on a mountain bike trials bike. I assume their brakes must be pretty powerful otherwise they'd just loop out?

If this isn't typical if anyone could share any tips for improving rear brake performance?

Are there uprated pads I can buy to get more bite / power?

Any help / advice would be greatly appreciated.

Cheers

James

Sounds like you have bad pads or some other issue. You could also just try the water trick. Get the pads and rotor really hot and pour water on them.

Edited November 6, 201411 yr by lineaway

Rears are usually fairly toutchey! Do as he said, get a bottle water, run up the gears and a 2-3 good hard stop tries usually heats them. Douse with water immidiatly. Repeat then let dry.

Thanks for the info I'll give that a try. Glad that it isn't the norm!

If I am to replace the pads - any recommendations?

Galfer pads are good.

Just a quick update:

New Galfer pads fitted, bit of a caliper clean up and a bleed and its spot on. Really nice lever feel and loads of power.

Back wheel stuff making a lot more sense now

Cheers for the help.

Anyone explain how the water thing helps?

If you take steel and heat it then quench it rapidly it increases hardness

One would think that increased hardness would adversely effect friction

I'm not gettin why this does anything at all

Ours is not to wonder why, but to do and die.

No serious, I don't know either, but it works.

Maybe it boils the gunk out of the pads?

I agree whole hardly with 0007 on this matter. I have spoken several times in the past about the in insane practice of pouring cold water on a hot brake rotor. It is a bad and dangerous practice.

Here is what I wrote a while back:

Some one posted: "I usually perform 2-3 good hard stops from a good high speed run in 5th gear to warm them, then let them cool and resume normal operation. Do this 2-3 times to thermocycle them, then on a final trip do the same to get them and the disk good and hot and douse them with a water bottle to steam off."

I wrote: Warning to the wise on getting your disk hot and then dosing it in cold water!

I have witnessed this resulting in the disk cracking and or warping due to the aneling effect that the radical drop in temperature causes.

I was present when a friend of mine tried this and and then went over the bars after the brake disk shattered after it hit a rock and he broke his collar bone.

Edited November 30, 201411 yr by billyt

I do the opposite... to bed the pads in from new! I spray cold brakes with water then ride and heat them up... let cool and spray again and ride a bit more. You can see even sweep area of pad on disc when done. I one end at a time.

You have to bed discs and pads in by bringing up to temp gradually. Some of the better car disc makers have temperature markers... warm, hot, very hot and you bring the disc up to these marked temps gradually. It "sets" the new pad and gives best rotor/pad grip.

It sure goes against the grain for me to pour cold water on very hot brakes...

Mags

Edited November 29, 201411 yr by mags

The first time I saw the water trick was Tommi Avilla start a brand new bike out of the crate. Once started he did the water trick on the brakes. He did a trials school for the weekend. That was all he did to the bike. It ran like **** since he never jetted it, but he rode rocks we only dreamed could be ridden. Been a believer in the water trick ever since. Good enough for a world champ, and it has always worked for me.

It is just to steam them off. The brakes on Billy's car hit water on occasion I would guess, time to trade it!

Mark

The rotors on a car disc is much thicker than what we have on our bikes.

On a trials bike If it does not crack the disc it will eventually warp it if done many times and done really hot.

I guess it is all relative to how hot you get the disk.

The heat draws out the oil and grease from the pad and disc. Best way I saw a guy clean his brakes

was he got them hot and then sprayed the crap out of disc and pad using brake cleaner and then poured corn starch all over them and let them sit for a while. The corn starch drew out oil grease and crap.

Edited November 30, 201411 yr by billyt

I have it on good authority (someone who was there and saw it) at the last round of the worlds here in Australia... Dynamite and Fujigas brakes were cleaned between runs. The pads were out each time and the pads washed with a brush and dried.

I had the rear wheel out of the monty recently so pulled the pads out and washed them dishwashing liquid soap and a tooth brush then dried in slow oven. Cleaned disc with spray can brake cleaner. To be honest they were not that dirty or contaminated but would do it after a day of fun in the mud.

I give the brakes a good spray with the hose when washing the bikes after each outing. I then run the bike and warm up engine and dry brakes out.

The Beta has about 65 hrs or so now and still original pads so far.

Mags

Well I'm a believer of decontaminating brake pads with brake clean and pressure washin the pad faces out of the bike but I think I will refrain from bake and douse

If had something scientific like specific temperature to heat and time to quench from a brake disc manufacturer I might pay more heed

I am a hobbyist knife maker and that tought me about different properties of different types of steel and the temperatures involved to harden and temper, you never quench in water, oil or heated salt solutions are used

In this case I doubt you could get the metal warm enough to do anything more than take hardness out of the steel, but to do that you want to cool it as slow as possible, not quench at all, in fact you wrap it in insulation to slow the cooling process

So it sounds odd