xc brake advice for heavy rider... £160 new kit

wolfsbane2k

Hi guys and gals.

I've finally got back on my bike (Kona Hoss 2007) after about 12 months off due to weather/new baby, and the first thing that's happened is my Hayes soles brakes have given up the ghost on the front.
Inspecting the front caliper showed a rusted ram which appears to be leaking fluid now.

I've always wanted to replace them due to them being single caliper, so my front wheel has always twisted when I brake which scares the hell out of me when cornering as well.

So now I'm looking for a new full kit for front and back , have approx £160 total. Looking at a new shimano xt785 , which I was looking at last year.

Are these still "reasonable" for the price?
PS, I'm still running the original discs, is it worth replacing these as well?

Thanks in advance.

Wolfsbane2k

cooldad

Yes, or SLX or Deore.
If the rotors are ok leave them.

wolfsbane2k

Thanks. I Looking at the forum and other posts, i think i'll go the SLX (M675) and save up to replace the rotors - they have been straightened about 4 times already, so new ones would be nice in the not to distant future.

(Edited - Correct P/N to M675 rather than M765)

njee20

I've always wanted to replace them due to them being single caliper, so my front wheel has always twisted when I brake which scares the hell out of me when cornering as well.

Whilst you're right to replace the Soles, and anything that says Shimano is a great choice, if your wheel is twisted that's nothing to do with the brakes. The rotor will be distorted very slightly to 'meet' the static pad with a single piston brake, but that won't affect the wheel.

lostboysaint

cooldad wrote:

Yes, or SLX or Deore.
If the rotors are ok leave them.

That. I've run Deore on my 26" hardtail and now my 29er hardtail for ages now with no issues whatsoever. Weigh 98kg.

wolfsbane2k

njee20 wrote:

I've always wanted to replace them due to them being single caliper, so my front wheel has always twisted when I brake which scares the hell out of me when cornering as well.

Whilst you're right to replace the Soles, and anything that says Shimano is a great choice, if your wheel is twisted that's nothing to do with the brakes. The rotor will be distorted very slightly to 'meet' the static pad with a single piston brake, but that won't affect the wheel.

The Twisting is somethign that i've previously been told is a mixture of single piston brakes that is exacerbated by a quick release axle, as the whole wheel can be seen to twist when braking - at all other times it's perfectly in line - it's just exacerbated when i brake going into a corner that the wheel twists off center, then the cornering forces make it twist a little more. Those are the words from 3 LBS's and Kona as well, so i "accepted" it.. it's a stonking bike in all other ways now it's got an XTR front and rear mech...

supersonic

The 3 LBS and Kona are wrong - single or dual piston make no difference to how much the wheel will twist under braking.

Fork and wheel flex yes, disc brake type, no. Your wheel is still going to twist the same with new brakes. Maybe even more so if you can brake harder.

njee20

The 3 LBS and Kona are wrong - single or dual piston make no difference to how much the wheel will twist under braking.

Fork and wheel flex yes, disc brake type, no. Your wheel is still going to twist the same with new brakes. Maybe even more so if you can brake harder.

This, that's total bobbins, how on earth would having one working piston cause your entire wheel to flex? As per my original point!

The Rookie

+2......basic physics, brake type isn't relevant at all.....

wolfsbane2k

njee20 wrote:

The 3 LBS and Kona are wrong - single or dual piston make no difference to how much the wheel will twist under braking.

Fork and wheel flex yes, disc brake type, no. Your wheel is still going to twist the same with new brakes. Maybe even more so if you can brake harder.

This, that's total bobbins, how on earth would having one working piston cause your entire wheel to flex? As per my original point!

Thanks for the feedback.

I can see it being because the majority of the braking force only being applied on one side of the rotor, pushing it into the static brake pad which is approx 2 mm away from it, so it causes the rotor to push away from the stanchion, and a small required twist in the centre equates to a visible, almost 1 cm shift at the top of the wheel away from straight.

Well, that's what I tell myself at the moment anyway.

I definatley don't want it to get worse... so perhaps I need more than a qr axle.

cooldad

You have a 9mm axle - the QR just replaces a nut.

wolfsbane2k

Yes, sorry, qr and 9mm go hand in hand in my head.

The Rookie

The static pad should never be 2mm away anyway, rather a fail on maintenance regime there!

That sideways force is tiny compared to the vertical reaction force from the braking slowing the circa 90Kg of bike rider and kit at over 1/2G braking, like probably 0.1% of it at most.

If the wheel rim is moving that much the bearings are shot or the axle is not mounted in the dropouts properly or the forks are fubarred.

wolfsbane2k

The Beginner wrote:

The static pad should never be 2mm away anyway, rather a fail on maintenance regime there!

That sideways force is tiny compared to the vertical reaction force from the braking slowing the circa 90Kg of bike rider and kit at over 1/2G braking, like probably 0.1% of it at most.

If the wheel rim is moving that much the bearings are shot or the axle is not mounted in the dropouts properly or the forks are fubarred.

2mm, that was a rough estimate. I find that with the crud that I ride through, unless i leave it at about this it gets too rammed with grit, so leaving it between 1 and 2 mm means an easier, more effective braking as the crud goes through, rather than destroying the rotors. I'll try with less.

90kg of rider + bike? I wish.... more like 150kg.. ( i am 6ft 7 but that's no excuse)
Forks are one of my concerns, and i do want to upgrade these - I was looking at rebas etc.

I'll take a video of it happening and post it on here.

njee20

Sounds like a flexy fork/wheel, just don't expect it to change because you've changed your brakes, they're having a minescule effect.

The Rookie

Try minimal clearence to stop crud getting in the gap in the first place, dual piston hydraulics have no visible gap and the slightest rub as does your one moving piston, so copy that!

150Kg, so at 1/2g braking (brisk but not anchored up) 75kg force, say 50Kg (pessimistic) on the front, 180mm disc is circa 1/5 the radius of the tyre so that is a brake reaction force at the dropout of 250kg....how much force do you thing the sideways force on the discs is?

wolfsbane2k

The Beginner wrote:

Try minimal clearence to stop crud getting in the gap in the first place, dual piston hydraulics have no visible gap and the slightest rub as does your one moving piston, so copy that!

150Kg, so at 1/2g braking (brisk but not anchored up) 75kg force, say 50Kg (pessimistic) on the front, 180mm disc is circa 1/5 the radius of the tyre so that is a brake reaction force at the dropout of 250kg....how much force do you thing the sideways force on the discs is?

Put like that.. when you add the centripetal force if the inertia change.. yep, flexible forks.

Ah well. Better make sure the brakes are upward compatable!