ZRACE XG4 flat mount 4-piston brake calipers – a quick review

The ZRACE XG4 flat mount 4-piston calipers have been out for a while now, but I had a hard time finding a thorough non-YouTube review, so here we go. I installed these on my parts-bin gravel bike which uses Shimano 105 ST-R7020 mechanical 2×11 shifters and a GRX 1x RD. Brake rotors are 160mm Shimano RT76 (I think). The previous brake calipers were a mismatched set of 105 and Ultegra road calipers, because again, parts bin build.

TL;DR: a significant upgrade from stock Shimano 2-piston calipers. More power and easier modulation on descents, with no real downsides so far. A worthwhile upgrade if you ride in the mountains.

Installation was a breeze. My existing hose olives were in pretty good shape, so I reused them, and just threaded the existing Shimano hose end fittings into the ZRACE calipers rather than using the included fittings and hoses. Make your own decision about this; I didn’t have much hose to spare, so I didn’t want to lose any length and risk having to replace the hoses. So far there are no sign of leaks but I’ll be keeping an eye on it.

Compared to the previous calipers, these seem to be more sensitive to caliper centering and rotor trueness. It took several tries to get both rotors to spin without rubbing, and I had to straighten out a wobble in the front rotor which had not been a problem with the old calipers. Maybe it’s the calipers, maybe less pad clearance, maybe just new pads being thicker than used? In any case, I got it sorted in about 15 minutes.

I cannot comment on the bleeding procedure, because the universe smiled upon me, and both front and rear systems firmed right up when I installed the oil funnel and gave the levers a few pumps. I did orient the bike to put the levers at the top of the system, and gave the calipers a dozen or so taps with a rubber-coated wrench handle to help dislodge any bubbles. So far so good, but I’ll be monitoring this also and will bleed them if it becomes necessary.

The good part – riding. I went out to one of my favorite North Carolina mountain rides today, starting at Bent Creek and riding across Bent Creek Gap to Mills River and back. It’s a 20 mile out-and-back route on a reasonably well-maintained Forest Service road where you climb for 5 miles, descend for 5 miles, and then do it again in reverse. Roughly 2200ft of climbing according to Garmin. The road is wide enough and smooth enough to let you build up some real speed on the descents, while having enough hairpin turns and washboard sections to require good brake performance.

Performance of the new brakes is significantly better than the old. I found that it took much less lever pressure to achieve the necessary braking, which also allowed for better modulation, since you’re not just cranking on the levers as hard as you can. I set Strava PR’s on several (maybe all) of the descent segments, probably because I was comfortable carrying more speed for longer before slowing down for the tighter turns. The only real issue was that I locked up the rear tire more often than usual; not exactly surprising with more powerful brakes, and I’m sure I will adjust, but the extra power from the 4-piston caliper is probably just overkill for the rear. Maybe think about the matching 2-piston XG2 for your rear brake instead. Or just leave whatever you have now if the mismatch doesn’t bother you.

One thing to note, not necessarily an issue, is that the front brake would give a pretty good squeal when first applied after not being used for several minutes. Conditions today were an interesting thing I can only describe as “damp and dusty” with fairly high humidity. Every front-facing surface of the bike ended up coated with a thin layer of damp grit; it’s possible that some of this was building up on the front brake and causing the squeal. Whatever the cause, performance didn’t seem to suffer, and the squeal only lasted a second or two before clearing up each time. If it happens in drier conditions I may try different pads.

Happy riding!