Grabby Disc Brakes in the Rain

prawny

Anyone else experienced this? Or is it particular to my crappy brakes?

Riding in the rain, occasionally when I first apply my brakes they will grab really really hard and it's worrying me that if it happened at the same time as I pulled the brakes on hard I would be on the floor before I knew it. Once it's happened once they go back to normal untill I've ridden 5-10 minutes without braking.

Does anyone know a way to stop it?

I never thought I'd be on here complaining my brakes work too well in the wet :roll:

ugo.santalucia

you are overthinking it... just brake when you need to and don't worry about the rest

prawny

I had for a bit, but I nearly came off last night when I tried to scrub a bit of speed off near a junction and nearly went over the bars, I'm not kidding.

The force it grabs with is more powerful than any rim brakes I've had on a road bike, even in the dry. It's scary.

roger_merriman

that doesn't sound right to be honest, the lower end Tektro Auriga Pros on my old hardtail that I use for commuting/pottering aren't in the least grabby, braking performance is unchanged.

prawny

Mine are Tektro Mira cable discs, the lowest of the low. I was planning on changing them eventually anyway, might get a new front sooner rather than later. It's a shame really, other than this they've been surprisingly decent.

ugo.santalucia

Brakes don't improve in the wet, stop drinking at work... :-)

prawny

NEVER! It's the only way to get through the day

Snakebite the 2nd

That's a really odd problem you have!

Sorry, not much help I know, but at least it's unique.

roger_merriman

prawny wrote:

Mine are Tektro Mira cable discs, the lowest of the low. I was planning on changing them eventually anyway, might get a new front sooner rather than later. It's a shame really, other than this they've been surprisingly decent.

Maybe new cables?

The Rookie

Something isn't right for sure, none of the many disc brakes I've had have ever done that, I wonder if the leading edge of the pad is falling into the holes in the braking surface causing it to catch.

rjsterry

The Rookie wrote:

Something isn't right for sure, none of the many disc brakes I've had have ever done that, I wonder if the leading edge of the pad is falling into the holes in the braking surface causing it to catch.

Was thinking the same. I was once borrowed a hybrid with very grabby Vee brakes. Turned out one of the pads was worn right down to the metal core - steel pads would be very effective, albeit they would chew through your rims in a matter of days.

veronese68

The Rookie wrote:

Something isn't right for sure, none of the many disc brakes I've had have ever done that, I wonder if the leading edge of the pad is falling into the holes in the braking surface causing it to catch.

I agree that something isn't right, but why would the leading edge catch more in the rain? But the only thing I can compare it to is that I once had an old Bonneville with drum brakes that used to be quite grabby. I improved things by filing a chamfer on the leading edge of the shoes. I know why this works on drum brakes, but I have no idea if it would work on discs. Thinking about it some car brake pads have a chamfer on them so there may be some advantage.

dhope

Possible that because the discs are wet then the first bit of the braking isn't as great, then when it does catch and scrubs the water then it feels like the brakes are grabby because you've missed the more gradual phase at the beginning?

I dunno. Mine screech a bit when it's drizzling but still stop fine.

prawny

The effect make the rookies theory the most plausible, it's the instant the pads touch the rim, I found a thread on another forum where someone had the same problem, there's an accompanying 'bang' too it's very strange. The other guy also had tektro brakes but didn't say what model, it's possible the discs are the same, they do have quite large holes in.

roger_merriman

prawny wrote:

The effect make the rookies theory the most plausible, it's the instant the pads touch the rim, I found a thread on another forum where someone had the same problem, there's an accompanying 'bang' too it's very strange. The other guy also had tektro brakes but didn't say what model, it's possible the discs are the same, they do have quite large holes in.

Try a new rota? It's a fairly cheap easy test.

ugo.santalucia

prawny wrote:

it's possible the discs are the same, they do have quite large holes in.

Of course, the Gruyere effect, why did I not think about it?

prawny

I think they might have done it in the dry tonight, possibly it's harder to tell because there's less difference between the initial bite and the grab in the dry. I'm going to try a different rotor and see what difference that makes.

ugo.santalucia

I can't believe this thread is still live... :-)

The Rookie

Veronese68 wrote:

I improved things by filing a chamfer on the leading edge of the shoes. I know why this works on drum brakes, but I have no idea if it would work on discs. Thinking about it some car brake pads have a chamfer on them so there may be some advantage.

It reduces a phenomena known as the leading edge effect......those who had old Mini's will know they have twin leading shoe drums on the front and a single leading shoe on the rear, the reason was to use the leading edge effect to create more braking where you wanted it at the front, the chamfer modifies the effect.