MRP AMg Chain Guide

MRP AMg Chainguide

Test Locations: Washington & British Columbia

Test Duration: 4 months

Compatibility: Bikes with ISGG-05 tabs and 28 to 36-tooth round or 26 to 34-tooth oval chainrings

Blister’s Measured Weight (including mounting bolts):
AMG SL, Small: 119 grams

MSRP:

AMG SL: $99.95
AMG SLR: $159.95

Bolted to: Nicolai G1, BTR Ranger, Canfield One.2

Reviewer: 6’, 170 lb (183 cm, 77.4 kg)

Review Navigation: Specs // Intro // Design & Features // On-Trail Performance // Bottom Line

Intro

MRP has been making chain guides for decades, dating back to the days when setting them up was frequently a major headache. The chain guide market as a whole has gotten vastly more refined in the years since, but MRP still saw some opportunities to make their AMg upper guide + bash guard easier to set up and use, and the latest version has some clever new features to streamline the whole process.

Design and Compatibility

MRP offers three different versions of the AMg, spanning a range of materials, weights, and price points. The most basic AMg CS uses a stamped steel backplate but also features a different upper guide design than the updated AMg SL that we tested, as well as the top-spec AMg SLR. The latter two just differ in terms of backplate material, with the AMg SL getting an aluminum one, and the SLR subbing in carbon fiber to save a claimed ~30 grams. Since the AMg CS uses a substantially different design from the two fancier variants, and we’ve not tested it, we’re going to focus on the AMg SL and SLR here.

Both the AMg SL and SLR are offered for ISGC-05 tabs only and feature an adjustable upper guide that wraps over the top of the chainring to keep the chain in place, and then a fiber-infused plastic bash guard underneath to protect it and the chainring. The bash guard is available in two sizes, with the Small size covering 28 to 32-tooth round chainrings (26 to 30-tooth oval ones) and the Large handling 32 to 36-tooth round / 30 to 34-tooth oval rings. The backplate and upper guide are shared across both sizes, so you only need to replace the bash guard itself if you want to swap sizes down the line. The backplate doesn’t protrude above the upper guide no matter the chainring size setting (for cleaner looks), and the upper guide sits lower and (at least in my opinion) looks a lot better than the prior-generation AMg.

That’s all pretty normal, but things get more interesting when it comes to the design of the upper guide. In particular, MRP has made a point of streamlining the installation and adjustment process, with a layout they’re calling “Forefront.” The molded plastic upper guide (which features some softer interior padding to deaden chain noise) attaches to a slider that moves up and down to adjust for chainring height and secures with a set screw that’s angled forward to make it easily accessible behind the chainring. The height settings are labeled by chainring tooth count on the aluminum AMg SL, but the carbon AMg SLR has to go without the markings. A second sliding interface allows for quick and easy adjustment of the alignment of the upper guide relative to the chainring. It’s a clever and simple design, with a hexagonal bar fitting into a recess on the back side of the upper guide, so that its clocking is held steady. A set screw in the upper guide presses on the hex bar to lock the upper guide in place. Finally, the upper guide has a tool-free pop-up slider for the outer half of the guide, so that the crank can be removed without removing or disassembling the guide.

David Golay reviews the MRP AMg for BLISTER — MRP AMg — Slider Set Screws

All of that does make the AMg very easy to install and align. The backplate is split, so that you can slip it over the bottom bracket shell of most frames without removing the crank. You bolt the backplate on, adjust the vertical slider to the appropriate setting for your chainring size (the labeled sizes are for round chainrings; go two teeth bigger for an oval one), and then adjust the horizontal slider so that the chainring is centered on the upper guide. Some frames will still need to have the backplate spaced out on the mounting bolts — the adjustment range of the horizontal slider is finite, and the upper guide feels stiffer in settings where there’s more overlap between the hex bar and the upper guide, as compared to having it set out quite far. But MRP includes with the guide some spacers for that purpose, and the built-in adjustability means that you only need to get the spacer configuration in the right ballpark, rather than relying on it to precisely dial everything in.

On The Trail

I’ve run the AMg on several different bikes over the summer and it’s been quiet and generally trouble-free, with no dropped chains during my time with it (despite deliberately running the derailleur with the clutch turned off for a while, for testing purposes). The bash guard has done its job admirably, taking some big rock strikes without issue. Going into the test, I’d wondered if the relatively small set screws that secure the sliding mechanisms would be up to the task, or if they’d come loose at some point, but I’ve had no issues there, either — everything has been very set-and-forget.

The only quirk I’ve had with the AMg is that I’ve had a small pebble get thrown off the rear tire and wedged in the upper guide a couple of times. Both instances happened in almost exactly the same spot on a fire road climb that’s comprised of unusually finely crushed gravel, when running a Continental Kryptotal Rear tire, which has knob spacing that catches an unusually high number of rocks on that same exact section of climb. (I ride it all the time and notice a very distinct difference in pinging from flung rocks when running Kryptotals as compared to most other tires.) So I think it’s mostly a flukey confluence of a patch of gravel that’s exactly the wrong size, and a tire that’s especially good at flinging that size of gravel, but it still can happen. In both instances, the rock got wedged just a little bit too tightly to eject it by backpedaling, but it was quick and easy to poke out.

But again, I’ve spent a ton of time on multiple AMgs over the course of the summer, and the wedged rock thing only happened twice on the same part of the same climb that I ride multiple times a week at a minimum. Given that it’s worked well otherwise, is notably easy to set up, and comes in at a reasonable price and a competitive weight, that wouldn’t stop me from riding one or recommending it to someone else. It’s a good guide and I’m still happily using it on my hardtail without issue.

Bottom Line

MRP has been making mountain bike chain guides for longer than just about anyone, and their latest iteration of the AMg does its job well. I’ve had no dropped chains, it’s quiet, the installation and setup are very easy, and the bash guard has shrugged off some big rock strikes without issue. The couple of times that I’ve gotten a small pebble wedged in the upper guide were a small irritation, but I think those were much more a flukey confluence of factors rather than an issue that is going to crop up for most people. It’s a good guide that’s notably easy to set up and comes in at a respectable weight and price.

Share this post:

MRP AMg Chain Guide