Saturday, June 29, 2013

on weight limits and the TriRig Mercury Pedal

There's a new pedal out called the TriRig Mercury, a continuation of a theme which began with the Aerolite in 1979 (and still available!), continued with the UltraLite Sports, essentially attach a cleat to a bare pedal spindle. You lose pedal float, but it's the lightest solution around: you spare the added mass of the pedal body.

Here is it:

TriRig Mercury

Originally this was advertised as 71 grams, but now it's been upgraded to 93 grams. The cleats adds only 58 grams, so the total solution is very light. But not as light as they were when they were 71 grams...

So what happened?

What happened is they eliminated the "weight limit" of the original design. Of the 22 additional grams, 18 are due to a change from a hollow to a solid spindle, 4 due to a shift in the flange from the bearing sleeve (nylon)to the spindle and retaining screw (metal). As the web page describes:

The additional material adds just 9 grams of weight to each spindle, but makes a world of difference in terms of strength and durability. And most importantly, it allows us to remove the Mercury rider weight limit! That's right, now anyone can get on board with the coolest pedals on the market.

Now while I've outgrown the weight limit on my childhood BigWheels, I fit well under the limit of even the sketchiest after-market weight weenie bike bling.

The truth is everything is designed to some sort of strength limit. An NFL lineman is likely going to find that a lot of commercially available bike parts are going to have reliability issues when subject to his close to 150 kg of bulk. So there's a number there, but it's typically not quoted, because it is assumed most purchasers of high-end racing-focused cycling stuff are going to have a certain minimal degree of fitness and therefore their mass falls within some reasonable bounds. If not, then they're probably not at a place where a few seconds saved on a long climb is going to matter, progress from training alone will be measured in minutes or even tens of minutes, not seconds.

But the reality is there's plenty of riders on their packing more than a few 10's of kg, who despite this, feel it's important to spend $5/gram or more to cut mass from their bikes. It's hard to understand, but it's true. So maybe the limit is somewhere around 120 kg. There's not that many avid riders heavier than that, even if in a typical Texas Steak House a mass that low would earn you the nickname "Slim".

That means when you design your parts to a certain strength-reliability standard, you tend to build for heavy. I'm around 57 kg (I've not checked since my injury, and I'm not going to until I'm riding again) so I want parts built to the limits experienced by a 57 kg rider (add on weight from clothing, a backpack perhaps, etc). A part designed for a 100 kg rider is obviously way over-built for me; it's too heavy. If it's not over-built for me, then it's under built for the 120 kg guy. There's no way a load-bearing part is going to serve both of us well, assuming we value low weight.

So when I see a company brag about how they "removed the weight limit" from a part by increasing the mass, I react in two ways. One is they're lying: there's a limit but it's relatively high. Two is that the part is not designed for me, because I'm not close to that heavy.

Maybe TriRig will come out with a second version of the pedal: a hollow-spindle version designed for riders who aren't going to stress the part as much as those at the heavy tail of the distribution curve.

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