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International Standard Brake Mounting IS Better (TT.3)

(From MeatEngines)

Wait, what? But, but Drew-Bob, but, but what about all those grams from having two extra bolts‽ And Post Mount (PM) and Flat Mount (FM) brake standards both look so much cleaner. And PM brake mounting has been around since the late '90s on forks and it's almost never a problem.


I started writing this issue of Tunnel Talk (TT) fifteen minutes before my shift this morning, when I arrived at the shop and saw a bike in the rack with the front brake removed and a note that one of the brake mounts is stripped. There's only one fix, fresh lowers for the Fox 34 in question.


And I've seen it enough times, over every brand's forks, that it drives me crazy. No, it's not 'common' but I'd still bet you that over a thousand sets of fork lowers get binned every year because of brake posts being stripped. Bolts that are too short, bolts that are too long, bolts with messed-up threads, bolts being forced in at an angle, I've seen multiple examples of every possibility.


And it's all completely unnecessary waste because in every case if those forks had a set of International Standard (IS) mount brake tabs then stripped threads just mean a new adapter. Easy. And threading the cheap-and-easily replaced part as insurance against mechanical misadventure isn't even the best part about an IS setup.

The same rules apply as with PM|PM adapters, a front is just a rear +20mm. So an IS|PM adapter for a 183mm rear rotor has you covered for a 203mm front.

My favourite feature of using an IS to PM brake system - let's be clear, I'm not advocating a return to IS|IS brake mounting and the endless shimming of calipers and rotors that accompanied that setup - is how much it simplifies service.


For example, if I want to bleed, reset the pistons, or change the pads on the front brake of my rigid Waltworks I don't even remove the wheel. I just unbolt the brake adapter from the fork and my caliper stays perfectly in alignment, still attached to the adapter while I do whatever work I need. Then I bolt the adapter back on and away I go.


There's no need to realign the system or remove the wheels. This is an added benefit for folks that don't have a workstand at home, but I find it much more efficient all the same.

Guerilla Gravity is one of the few high-end bike manufacturers still using IS tabs. I think their system looks very clean and it can't be understated that a bad bolt is ruining a sub $40 adapter (for a nice NSB one) rather than an entire seat stay assembly.

There's also a significant increase in the range of adjustment. Sure the current side-to-side range of your Post Mount caliper is going to be sufficient for most bikes but I've had to space out rotors (thankfully 6-bolt hubs were involved) in order to center the caliper on some very, very expensive PM frames.


With an IS mount setup, it's easy to add spacers between the adapter and frame or fork to move the caliper inboard. And in the cases where it's necessary to move the caliper outboard there's at least the option to file an adapter narrower.


On my classic scratch-and-dent pile Kona Roast I had to file my adapter at a massive angle in order to interface with an IS brake mount that was welded on anything but straight but all it took was elbow grease to get it perfect. I've seen enough examples of PM and FM mounts that aren't straight to know in both cases you're SOL.

Okay, fine, use Flat Mount (Ugh) or Post Mount on super high-end frames if you have top-level QC/QA, but on budget-friendly bikes give the local shop a chance to make them rideable if things aren't perfectly square from the factory. This Marin is great, but I've seen lots of bikes at this price point that aren't.

And fine, usually, normally, most often there's no issue with an FM or PM frame mounting setup. I'll acknowledge that. But over an infinite number of bicycles, the number of stripped threads and out-of-spec setups will be legion extrapolating from the number I've seen in my time in shops and there is no good reason not to just use IS frame and fork mounting combined with the side-to-side adjustability of a PM caliper.


The lowers on that Fox fork are going to be somewhere around $400 and a fresh, top-end, brake adapter from NSBillet would have been thirty-six bucks. Some companies know this, for example, Fox resisted switching from IS to PM until 2008 for a reason, and even today there are multiple frame manufacturer's still shipping bikes with IS mount including folks like Guerilla Gravity operating at the premium end of the activity.


What more can I say? When it comes to mounting PM brake calipers to frames or forks, I think it's absolutely the case that two bolts are lesser than four. It's really too bad that direct Post Mount has taken over.


Cheers,

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