Possible Solution to Shimano GRX Lever Compatibility With Post/IS Brakes

Posted on November 3rd, 2019 by Jeff Whitfield | Comments

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In a previous post, I talked about the upgrades to my Marin Nicasio which included a full drivetrain upgrade to Shimano GRX cranks and derailleurs. One of the problems I ran into had to do with the GRX levers.

I recently talked about problems surrounding flat mount brakes and getting them to work on a frame that only accepts IS or post mounts. In a nutshell, if your bike doesn’t accept flat mounts and/or can’t be adapted then good luck getting any of the new Shimano GRX brake calipers to work.

Hope is not lost though.

In that same post I made about flat mount brakes, one commenter mentioned possibly using a different brake caliper. I can’t believe I didn’t think about this myself. The idea would be to use a MTB caliper like the Shimano SLX 2-piston brake caliper. The goal is to use a caliper that can be post mounted which in turn can be adapted to IS mounts as well.

Technically, this should be possible. However, you’ll have to make for damn sure that the GRX levers support the pistons. If they don’t then you might be setting yourself up for some serious brake failure. If you’re really dying to upgrade to hydraulic brakes and can only use post/IS mounts then this might be a possible solution. However, do so with caution!

I’ve already upgraded my bike using Shimano 105 levers and TRP Spyre brakes. They’re not as good as hydraulics but, after a bit of tweaking, they have plenty of stopping power. I likely won’t bother with hydraulics this time around. Instead, I’ll just wait and upgrade my frame to one that accepts both flat mounts and thru axles. That combination in my opinion is a better way to go.