Shimano braking performance on 29" with 160mm rotors and a stuck lockring

as a full grown 80kg adult, i only run 160mm rears on my bikes, 29er, 27.5, might be 140 on the road/gravel bike.. more than enough braking performance for me with a 4 pot shimano.

Something isn't right

Is this unsatisfactory braking performance typical of Deore M-6x00 brakes and non-ice-tech rotors?

Nope, functionally all Shimano 2 pots are the same and should have the same amount of power, and nothing its noticeably different between 29er and 26er wheels. 

Given in your initial description of the issue I would hazard a guess that the rotors were contaminated, to which you appear to have used with new pads in the new callipers, that may well have subsequently contaminated the pads. The rotors then changed so everything is now contaminated, try new pads and a nice clean set of rotors.

I guess the original installation of the stock Specialized hub and brakes required the rotor being installed with the axle bolt removed

I doubt that very much, is the lock ring splined to the inside or outside, there are deeper internal spline lock-ring tools available, like THIS ONE

I find most 160mm brakes won't lock up on tarmac (why would they really need to, that'd be way more power than needed on a trail).  29'ers just made that worse as the brakes are effectively working against a bigger lever.  Bear in mind also that a lighter rider will lock up for less effort.  

Having made those excuses, deore and below don't get servo wave so they feel OK initially by lack ultimate power. I've got the trekking version which half makes up for that by having longer 3-finger levers which allows you to run them father inboard for 1 finger power.  Longer term I want to swap the levers for proper XT ones.

As for the front CL, I'm guessing they used a thinner walled tool?  Is yours aluminum of steel?

Posted by: steve_b77

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Given in your initial description of the issue I would hazard a guess that the rotors were contaminated, to which you appear to have used with new pads in the new callipers, that may well have subsequently contaminated the pads. The rotors then changed so everything is now contaminated, try new pads and a nice clean set of rotors.

This.

I would start with a really good bedding in of the pads/ rotor. 20 hard stops at least. Should easily lock up a 29er wheel on tarmac under a small sized rider. Any shimano rotor should produce decent braking, not just ice-tech. The ice-tech ones just manage heat better. The M6100s are servowave too so should have good power once the pads contact the disk. You can try an IPA clean of the rotors, and sand the pads to get a 'fresh' start before the bedding in if you suspect contamination. Once you have tried a good bedding in and if they feel good at the lever, but still squeal with no power, then they might have a caliper leak. 

Re the lockring tool. Try removing the hub endcap first. Might just pull off depending on the hub. Or a different tool will be needed with a thinner/deep wall. 

The M6100s are servowave

I stand corrected, I thought that was the difference between deore and SLX, the 6100 has servo wave, the 4100 doesn't.

Thanks for the replies everyone. I notice that my links to pictures of the lockring+tool were removed but it seems I now have the ability to upload so here are some pics of the lockring tool and axle nut.

The issue isn't so much the depth of the tool but more the thickness of the wall failing to clear the axle. It's hard to see how there could be a lockring adapter with a thinner wall that this but perhaps I need to have a shop around.

With regards to the braking power in general, that is encouraging.
I have always run 160mm on the rear on all my 26" bikes and was able to lock the rear easily enough to do cool skids in the street. I used to run 145mm I think on my GT LTS 25 years ago.

It is entirely possible that the old rotors contaminated my brand new pads, which then contaminated my brand new rotors.
I always felt that it's easier to just swap the pads than try and decontaminate them but I might try a light sanding as they probably only had about 200m of rolling on the contaminated rotors. And I was under the impression that bathing those old questionable rotors in Peaty's brake cleaner before running them with the new pads would do a decent enough cleaning job but clearly that's not the case.

I will persist with cleaning, replacing and bedding in the pads/rotors and let you know how I get on.

that's a cup and cone setup? take the lock nut and cone out, keep hold of the bbs and you'll have all the space in the world

Those cheap Shimano stamped steel rotors are notoriously bad, you can see how shiny they are as they're almost too smooth to create friction. 

Ah ok. That front rotor needs to get in the sea - generally, those low-end 'resin pads only' rotors aren't great. Better off with something like a RT64 (SLX level) that can take metallic pads, although for a smaller/lighter rider resin pads should still be fine. I've never had great success with those cheap resin-only rotors.

Looking at photo above, the locknut on the axle needs to come off for any tool to reach the splines on the locking. Once off, I'd swap to an external locking to avoid same problem again. 

hmm thought i replied

looks like cup and cone, remove the lock nut and cone, take the ball bearings out and keep safe, you'll have all the space in the world then

My hunch is that you need better pads. I’ve got 160mm rotors on my gravel bike and cheap rotors. It’s Tiagra levers and posh but still single piston shimano brakes. I’m not short of braking force

I'm surprised a small is too big at 160mm. My daughter at 157mm is on a small chisel with enough room for a 150mm dropper. She is also running 160mm rotors front and rear with m6100 brakes and appears to have plenty of power.

I'd bet a lot of the weight is in the wheels, mostly the hubs. That and the lower end forks tend to be the boat anchors.

A brief update on this.
I swapped the SM-RT54 rotors out with the RT64 and that has made a big difference. Sanded down the pads to give a better surface and then spent some decent time actually bedding them in this time with some hard stops. I can come to a nice stop and lock the rear. Front is not as good but even on my 26" machines I'm used to a 180mm rotor on the front so I can't expect the same performance on 29" with 160mm.

So we're all good here.

Oh, and the hub was indeed a regular hub and cone so I loosened the opposite side to remove the axle to get full access for my lockring tool. Gave the bearings a good clean-down and re-grease for good measure and added the new rotor using an externally-splined lockring.

Thanks all for the help and advice!