Remember back when all that we cared about were headtube angles and chainstay lengths to see if a bike was shred-ready? NBD on the HTA, offset is the argument these days. This measurement is the distance of the front wheel axle in front of an imaginary line running through the head-tube. The fork offset is a result of both the fork crown and lowers having their own offsets, so depending on the fork manufacturer, it might be easier or harder to change the offset for fine tuning your ride.
During the dark ages of fully rigid mountain bikes, fork offsets and lengths were used to change the steering geometry of each bike based on the manufacturer’s desired ride quality. Fork offset and headtube angle play together with the wheel/tire outer diameter to establish the trail measurement for a given bike. Basically the trail measurement is the distance of the steering axis in front of the front tire’s contact patch. In general, lower trail numbers mean a snappier handling bike and higher trail numbers make for a more stable and slower turning bike. Keep in mind that, generally, more trail makes the steering heavier/slower while reducing fork offset actually INCREASES steering trail.
Like most things with bikes, it’s not recommended to look at a single measurement and make a larger statement about the rest of the bike. A bike is a sum of its parts and the steering feel of a bike is affected by the fork length, head-tube angle, fork offset, handlebar width, stem length, bottom-bracket height, front and rear centers, and by and large your own weight distribution on the bike.
Early into the development of 29er mountain bikes, higher offset forks were successfully tested in order to reduce the trail measurement on the larger wheel so the bikes would turn in as snappy as the best 26” bikes on the market without needing to steepen the head-tube angle of the bike. For example, Fox used 40 mm offset on 26” bikes, 51 mm on 29” bikes, and eventually 44 mm on 27.5” bikes in order to keep turn-in comparable between all three wheel sizes.
Benefits of a longer fork offset:
- Increased maneuverability
Benefits of a shorter fork offset:
… Sooo what’s our preference? …
Knowing that this was all coming, Matt, our Chief Enginerd, armed himself with a few Cane Creek Angleset cups, two MRP Ribbon forks with two different offsets, and a handful of travel reducing spacers in order to test a bike in two different configurations. Lap time difference was zero seconds, and while both work well, the 51 mm offset is a little easier handling at low speed, while both are stable at high speed with our made-for-goin’-fast wheelbase length. This means our testing has told us that the 51 mm offset provides the best combination of slow speed and high speed handling with our bikes. So we recommend the well-rounded performance of the 51 mm offset fork on our 29er bikes.