Let’s cut straight to the chase: do these brakes have a wandering bite point? The answer is: they did, but now they don’t.
Like quite a few of the best mountain bike disc brakes, the XT M8100 comes as a lever and a caliper in the box that you have to put together yourself. It’s a bit of a chore, and if you’re slapdash, you may have to bleed the system afterwards, which means you’ll need to stump up for the £30 bleed kit. However, on the plus side, having the hose sealed with a plastic cap means you can thread it through the frame without losing brake fluid, which definitely makes installation way easier if you have internal routing.
The shape of the lever is pretty much identical to the M6100 Deore brake. It does have extra dimples on the lever blade for grip along with a dial near the lever pivot offering tool-free reach adjustment. You also get FreeStroke adjutsment, so you can fine-tune the bite point, but this seems to have so little effect as to be redundant. The twin-pistons are also the same size as the Deore brake, it uses the same resin brake pads and even the split clamp opens in the same way, although they actually worked on this set of brakes. Oddly, the XT rotor is only offered in three sizes – there’s no 220mm option and they’re all six-bolt. Again, there’s nothing stopping you switching to an SLX rotor, which is available in the whopping 220mm size.
With so much the same, it’s no surprise that the bedding-in process was just as quick as with Deore – three or four hard stops and we were ready to roll. XT does have a slightly snappier lever feel and there’s plenty of power on tap. We noticed a bit of squeal in the wet, but when we swapped to the sintered pads the volume reduced. The brake doesn’t feel grabby and never fades, but there’s one key difference – the XT levers pulled to the handlebar now and again due to air in the system. This has been a problem with (mostly high end) Shimano brakes for quite a few years now and it can be disconcerting when you’re travelling at speed. The inconsistent performance means you can’t predict when it’s going to happen.
The front Shimano XT M8100 disc brake has always been fine, but the rear brake can develop that infamous wandering bite point that upper-level Shimano brakes have unfortunately become known for in recent years. The solution, no matter what you may read online, is a comprehensive bleed.
The only way to do a wholly comprehensive air-ridding bleed of Shimano brakes is to completely remove the bleed nipple assembly from the caliper and do a top-to-bottom gravity bleed while cradling the caliper in an old rag and rotating the caliper in every plane possible – ideally with the whole brake removed from the bike (not easy if your bike has internal hose routing). Once you’ve gone through this rigmarole, the brake should perform fine for a few months. But it shouldn’t be that hard.
When working as they should, the XT disc brakes are lovely. Much like everything else XT-flavoured from Shimano, the experience is all about ‘feel’. Maybe I just have Shimano-shaped fingers, but I can never get comfy when using non-Shimano brake levers. All other brand brake levers just feel a bit too chubby and/or hard-edged. Which is fine if you like it that way.
Anyway, back to the feel. Basically, you can clearly feel the instant where the pads meet the rotor. There’s a definite ‘thunk’ sensation, but there is no grab or snag sensation. Which makes them great for movements that are less about slowing down and more about bike handling. The rotors (not included and £31.99 for 203mm size) also play a part in this impressive level of feedback and control. There’s no pulsing of power. In this sense they make for ideal trail-riding brakes where the impressive level of interaction really improves flow and fun. All-or-nothing gravity fiends should look for something with more top-end power, though.
Living with them, post-bleed faff, has been easy. The pistons have been no trouble and there has been none of the resistance or uneven stickiness that other brands’ pistons exhibit when it comes to replacing worn-down-to-the-backing-plate pads.
So the question is… are Shimano XT M8100 disc brakes worth the painful bleed regime? We’d say no. We’d go for Shimano’s Deore M6100 series brakes instead.
With Icetech rotors and extras you’re looking at over £200 a wheel for XT, which isn’t too bad for a brake of this quality, but what stops this getting a better rating is the variable performance. Not knowing how the brake is going to feel from one moment to the next can really catch you out.