Von Sothen Racing Fat Mouth Stem Review

    The Von Sothen Racing Fat Mouth stem is the most interesting product to have hit the market of late. It seems that we have something to break through the carbon frame, carbon rim and disc brake obsession that is currently clouding the BMX race industry.

    It’s great to see we finally have a stem on the market that’s breaking the mold and isn’t just another variation of an S&M or Profile stem.

    Von Sothen Racing, operating out of Santa Cruz, CA and Founded by Michael Von Sothen specializes in the design and manufacture of CNC machined aluminum BMX parts. In the past Von Sothen Racing has manufactured parts for Tangent, Bullseye, JAD, Throdwn and others.

    Wide bar clamping

    The “fat mouth” of the Fat Mouth is the obvious differentiator. In VSR’s own words “Wider bar clamping so you get more stiffness out of your standard diameter handlebars than you would get with those silly looking 31.8 bars that cost too much, and are limited in rise/sweep options.”

    Greater clamping power

    If you look at the side profile of the Fat Mouth stem you will see the front of the clamp has a larger gap to the rear. This feature trickles down to the VSR Micro/Mini top load stem as well. This is new to BMX but apparently common in MX. The idea is to maximise surface clamping for greater clamping power. I have only seen this one other time on a BMX stem and that was on a CXP stem out of New Zealand.

    Fitting the stem

    A small thing I had trouble with initially was centering the bars in the stem. My normal process is to center it in the knarled area as the knarling normally extends outside the clamp of the stem, I find this easier and more accurate than doing it by eye. With the Fat Mouth exceeding and completely covering the knarled area I had to use the old clamp marks on the paint of the bar to help me find the center. Aside from that it went on perfectly.


    I’m not a weight weenie, to me function and reliability far exceeds the need impressing the BMX community with how light the product is. The Fat Mouth is significantly wider while offering the same length. Common sense says there’s more alloy in the stem so it must be heavier.

    Profile Push Stem 53mm297g/10.45oz
    S&M Race XLT 55mm298g/10.5oz
    Alienation Vault Stem 53mm289g/10.2oz
    BOX Delta Stem 53mm299g/10.5oz

    So how does the Fat Mouth really compare? You’d be as surprised as me to see the 55mm Fat Mouth weighs in at just 344g/11.7oz, very close to some of the more popular stems on the market. It’s far less than the 400g weight I was expecting to see given the difference in size. You only have to look at the underbelly of the stem to see where they were able to save so much weight. It’s not simply just another stem but wider, a truck load of thought has gone into the Fat Mouth, and if you look at other VSR products they tend to have the same approach across their entire range.


    Does having a wider clamp limit the bars you can use? It’s not until your clamp is wider than the knarled clamping area of your bars do you start to wonder if the clamping area for the stem is too narrow. Having a quick look at the bars I have laying around it’s fine, and it’s probably just me being paranoid.

    How does it ride?

    To test the stiffness of the stem I put it on the stiffest bike I have a Supercross ENVY BLK Carbon V1 with Supercross ENVY BLK Carbon V2 forks. I know stiffness is difficult to measure but theoretically this set up isn’t going to flex for Godzilla.

    After spending many weeks with the stem using it in various scenarios; sprints, jumps, gates I couldn’t feel any flex! I also couldn’t make the bars move!

    Manufacturer’s Description

    • Pro StemĀ 1 1/8″
    • Stiffer, Same 7/8″ bars and about the same weight as standard BMX stems
    • VSR lifetime replacement guarantee
    • Colours
      • Raw
      • Black
      • Red
      • Blue
    • Sizes
      • 40mm
      • 45mm
      • 50mm
      • 55mm
      • 60mm
      • 65mm


    Rating 19.5/20

    Value for money:5/5


    • If you are looking for a stem that will offer the ultimate in stiffness the VSR Fat Mouth is perfect and on top of that VSR offer a lifetime replacement guarantee.
    • Sure it’s a little heavier than other stems but that’s the price you pay for wider bar clamping.
    • You would be hard pressed to find a stem that has this much clamping power.
    • The wider look of the VSR Fat Mouth might make it the ugly duckling of stems if it wasn’t for the effort of the VSR team to make the unique stem stunning with detail.

    Would I spend my hard earned cash on a VSR Fat Mouth? You bet your carbon rims I would!

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    review by Shane Jenkins/26 April 2019