Why Measuring MTB Sag at the Shock Is Costing You Performance
If you’re still relying on the O-ring at the shock body to set your sag, it’s time for a serious upgrade. Most mountain bike manufacturers base sag recommendations on the shock stroke—not the actual movement at the axle. That might be convenient, but it’s not accurate.
Here’s the problem: MTB rear suspension systems use non-linear linkages that multiply or reduce shock movement through leverage ratios. So even if you think you’re running 25% sag at the shock, you could actually be sitting at 21% or 29% at the axle. That’s a huge difference—and it directly affects how your bike handles and the suspension performs through the stroke.
The Problem with Shock-Based Measurements
It’s not just the leverage ratio that throws things off. Measuring sag at the shock is full of built-in flaws:
- You can’t properly settle the suspension because you can’t pump the suspension to settle it before taking the measurement. That means the bike often isn't fully settled when you measure throwing the measurement off.
- The shock area is tight and awkward to access. Trying to measure at the shock body often leads to 1–2mm errors which get amplified by the leverage ratio. This applies to both air shock and coil shocks.
- It’s easy to nudge the O-ring just by reaching down to set it initially or as you carefully dismount, throwing off your reading without even realizing it.
And here’s the kicker: a 1–2mm error at the shock becomes 4–6mm at the axle due to the leverage ratio. That’s a 3–5% swing in sag—enough to dramatically change your suspension feel and handling.
Real-World Validation
I thought I had my Evil setup dialed using the slider they provide on the linkage and the fork O-ring, but I was actually running about 5% too much sag. Once I switched to the Slacker Digital Sag Scale with the Virtual Fender Mount, I corrected the settings—and the bike instantly felt firmer, more responsive, and way more confidence-inspiring.
Even better, Forbidden Bikes reached out in the first week of launch and is now using the system for in-house testing and on their demo tours to make sure customers get the best experience possible. That’s a strong endorsement from one of the most progressive brands in the MTB space.
Precision at the Axle, Where It Matters
The Slacker Virtual Fender Mount eliminates all the guesswork by providing 1:1, real-time sag readings right at the axle. It removes human error, bypasses the linkage math, and gives you a direct measurement of the percentage of sag right on the handlebars using the wireless remote or your smart phone.
And to top it off, we offer a 30-day money-back guarantee, so there’s no risk in trying it for yourself.
Ready to ride like your bike was meant to?
👉 Shop the Slacker Virtual Fender Mount now and experience suspension tuning the way it should be—simple, fast, and precise!
