Seat Tube Angles On Sagged Hardtails

If you haven’t checked out Angles of Repose by Mike Ferrentino on NSMB.com, I’d suggest you take a look. He discussed some issues with increasingly steep seat angles, with his prime example being the 76° seat angle on the Kona Honzo causing him to have knee pain. While a seat tube angle of 76° does not sound at all extreme in 2022, it’s important to note as he did that on a hardtail (the Honzo), only the front end sags and the geometry therefore gets steeper with a rider perched atop it.

One of the user comments left below the article was that hardtails would benefit from being compared at some level standardized sag percentage, which would better reflect the bike’s geometry with a rider on it. One brand taking this approach is Cotic, who currently presents the geometry of their bikes at 25% sag. However, the majority of brands only publish the static geometry chart.

I also subscribe to the philosophy of comparing hardtails against full suspension bikes with the hardtail geometry accounting for the front end sag, and it was my motivation when I developed the Sagged Hardtail Geometry Calculator. Accounting for the sag in a hardtail’s fork to correct the geometry chart provides a good comparison against the static geometry of full suspension bikes, where both ends of the bike sag roughly the same amount. This is generally an improved way of looking at hardtails whether you’re comparing frame geometry or bike fit between hardtails and full suspension bikes.

Three of the important points you’ll find in analyzing the geometry of a sagged hardtail relative to the static geometry chart are that the reach increases, the seat tube angle steepens, and the head angle steepens. Keep all of those things in mind when looking at the static geometry chart for a hardtail. You will want to keep the reach in check, so go shorter than you would target for the same sized full suspension. An increase in reach of about 15 mm would be a reasonable expectation for a typical trail bike under sag when compared to the static geometry chart. Jeff Lenosky has a great demonstration of this reach increase for hardtails under sag.

The steepening of angles is not at all unexpected and as always you would be wise to account for the steepening when looking at your desired head angle. That steepening of around 1.5 degrees might make the super slack hardtail seem more logical than it appears at first glance, or perhaps it would rule out the reasonable head angle once you’ve determined it seems too steep with your weight over it. The seat tube angle however, does seem to be a secondary concern for riders in their search for new bikes. The recent trend for very steep seat angles on hardtails should be looked at with a skeptical eye when you see the resultant angle of a sagged hardtail. If you select a hardtail with a seat tube angle of say, 78°, which seems to be a nice “on-trend” number for a capable trail or enduro bike, make sure to account for the additional increase you’ll get from the front end sagging. It would be a costly way of finding out that super steep seat angles don’t make a whole lot of sense on a hardtail after all.

There are a few ways you can experiment with comparing hardtail geometry on this site.

1. Comparing a hardtail against a full-suspension bike? Use the Sagged Hardtail Calculator to change the static hardtail geometry to sagged and then plug the outputs of the sagged hardtail into the Bike Geometry Calculator to compare the two styles of bike more closely.

2. Comparing multiple hardtails but one of them is shown with a static chart and the other with a sagged chart? Use the Sagged Hardtail Geometry Calculator to change the static to sagged or sagged to static and then plug the outputs into the Bike Geometry Calculator to compare against the other bikes.

3. Comparing multiple bikes with some sagged and some not? You can combine both of the above approaches through a few iterations to compare multiple bikes like Cotic (sagged geo chart) to a Honzo (unsagged geo chart) to a full-suspension (unsagged geo chart).

One word of caution with this approach of comparing a sagged hardtail to a static full suspension bike is that the bottom bracket heights do not provide an apples-to-apples comparison. The calculated bottom bracket height of a sagged hardtail will accurately represent the real world scenario, since the rear cannot sag at all. However, the bottom bracket height of a full suspension bike with a rider on it will be much lower than the static geometry chart would suggest.