FSA OS-99 Stem

We got this stem from FSA about a year ago, and while it’s always nice to get schwag, I had no idea how to review it. At $99, it’s cheaper than most stems, and at a claimed 99 grams (probably for a 100 mm, the 120 mm test sample was 123 g), it’s competitive with the lightest stems out there. It’s a straightforward forged and machined aluminum stem with ti hardware, so maybe that’s why it’s reasonably priced. Perhaps people would rather pay more for something with some carbon on it, even if it’s heavier and more expensive. But all that is info you can get from the web in a couple of minutes. All I’d be able to add is that it felt stiff enough, but I’m skinny and weak, so that’s not terribly enlightening. So I just rode with it for a year, falling over a couple of times and hitting a pothole hard enough to crack a frame. The stem survived those encounters unscathed.

Then it occurred to me that, like sharks, the stem would probably be more awesome with lasers, so I put one at each end of the stem. I mounted the bike on a trainer, steadied the front wheel, and put 45 pounds of weights on one end of the bars. As the stem flexed, the two laser dots pulled farther apart. Then I did the same with a 120 mm Thomson on a mountain bike. The Thomson is a 170 g (claimed) stem that’s supposed to be safe for freeriding, so it figures to be much stiffer.

With the laser dots 1930 mm away from the stem, the FSA dots deflected 8 mm, the Thomson 6.5 mm. That means the FSA twisted .24 degrees, the Thomson .19. At 210 mm (one end of a set of 42 cm bars) the bars on the FSA would flex .83 mm, .15 mm more than the bars on the Thomson. Now you can say that the FSA flexed 23% more than the Thomson, but I say a .15 mm difference is imperceptible.

The cliché is “light, strong, cheap: pick two”. It appears that FSA, with this unassuming stem, has hit the trifecta.

 

 

15 Comments

Anonymous

that the twist didnt involve the frame, bars, fork, wheels etc. if you used two diff bikes for this test?
Chris M (apparently as bored as you today, only with less engineering skill so I just surf the web…)

Anonymous

Two points aren’t enough to distinguish between rotation and deflection. If the weight was placed on the front of the bike, it would have rotated slightly around the rear wheel as the front tyre gave way a bit and the stem deflection angle would have been less than what you measured. You could try getting around this by using three lasers and measuring the difference in the angle the two line segments make. Just my 2 cents worth. Keep up the awesome homebrew science!

Andy

Not in mine either, but it’s still on the cheap end of the scale (50-300+?). Which is sad, but that’s a whole other discussion.

Anonymous

The 0.15 that is imperceptable maybe the distance that takes the stem to the point of no return and can leave you face planted on your next ride? Then again it might be fine or whithin its limits. Either way I wouldn’t ride the Test stem no matter the price of the stem.

Remember, it might be perfectly fine, but you really need to get the materials specs before going around testing it to know where you are in that respect.

Andy

It’s .15 at the ends of the bars, so it’s 1/20th that distance at the stem itself. And 45 pounds is definitely less than the force you’d put on the bars while riding. I’m sure that stem has gone through hundreds of cycles with more force than that over the year. But if I do snap it I’ll let you know for sure (not being sarcastic).

Anonymous

You know, I have one simple request. And that is to have handlebars with frickin’ laser beams attached to their ends! Now evidently my cycloptic colleague informs me that that cannot be done. Ah, would you remind me what I pay you people for, honestly? Throw me a bone here! What do we have?

Anonymous

how about one of these as well? I want to know which bar will withstand the force of my massive biceps.

Anonymous

that review was “shit my pants” funny. (I think Cadence is replicating your laser test and does not know that you were kidding)

Anonymous

that the weakest part of the stem is near the bolts that attach it to the handlebar. I’ve had a similar stem break at that location.

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