Fork offset is relatively new on the list of MTB measurement considerations, and its place on the well-known chart is cleared without much controversy. Simply put, it is the measured distance between the steer axle of the fork and the front axle, which is adjusted using various offsets at the top of the fork. Brands have started designing their geometry with shorter offsets in mind, and today it’s hard to find a 29″ bike with over 44mm of offset. The tide has changed. But what happens if we put a 51mm offset fork on a 44mm or 41mm bike?
First, let’s take a quick look at offsets and why a shorter offset can be useful. Our feature editor Matt Miller wrote an article about offset some time ago, so be sure to check it out. In short, a shorter fork offset increases the size of the fork footprint. This is achieved by increasing the distance between the tire’s grip surface on the ground and the point where the steering axle crosses the ground. The larger track size provides more stability and better front end control. The simple idea is that the front wheel is easier to self-correct, following straight lines more naturally rather than feeling wobbly. Look, mom, it’s easier to ride a bike without hands!
A looser head tube helps reduce the sloppy feel of the handlebars, a more stable ride is often preferred on these same low gravity toys, so we now have a 29″ fork with 41-44mm offset, bigger. Most 27.5″ forks have about 37mm of travel. A shorter offset also shortens the bike’s wheelbase, making the larger bike more manageable, as well as making it easier for the rider to properly weight the front wheel for maximum traction.
I recently started testing the new 170mm Öhlins RXF38 m.2 and they sent me a 51mm fork offset. The Privateer 161 and Raaw Madonna I test require 44mm offset, but both brands say 51mm will work just fine. Performed?
I’ve pedaled two bikes with Öhlins 38 and Fox 38 and my experience can be summed up as “buying a new fork doesn’t matter”. Although you can feel the change in handling, it’s so slight that I forget it halfway through the first descent every time I change places. I’m pretty sure if I get on your bike and do a few laps, I can’t tell what the fork offset is without looking. I find myself quite sensitive to variation and nuance on my bike, having tested many different components and frames, and for this frame and fork combination, offset does not seem to be the defining performance variable.
What I feel is that the steering with the longer reach of 51mm is a bit lighter and side-to-side rollover is easier to achieve than with the 44mm fork. This dip wasn’t so big that I needed to get on the front of the saddle or hold the handlebars tighter on rough terrain. It’s just a minor difference, like a 0.5° head tube angle that’s quickly forgotten. I see that some riders respond better to a self-correcting handlebar feel and this should be taken into account.
I had no problem adding weight to the front wheels because these bikes were long enough that I already had to shift my weight forward aggressively. There are no significant changes. Again, given the fact that I love long bikes, the difference in wheelbase length doesn’t bother me. A friend of mine, a full-time mountain bike frame engineer, tried both forks on the same bike and agreed they both work fine. After jogging, he also couldn’t remember which fork he was at without looking down. Fortunately, we are adaptable creatures, and it is easy to adapt to such small changes.
If my goals were different and every tenth of a second affected my professional racing career, I would definitely choose a shorter offset fork. For those who need maximum stability and minimum performance gains to keep their paycheck, such a difference, which I forgot about, is well worth it. For many regular off-road enthusiasts like myself, chances are that the fork you already have will work great with the bike you buy, as long as it fits the bill.
My experienced colleague Matt Miller had a very different experience installing a longer offset fork on his partner’s bike. I wanted it to be the best for her, so we ended up selling the old forks and buying a used front fork with a 37mm offset.”
In Matt’s experience, this fork offset request seems to be highly dependent on the bike in question and the rider. If you already have an offset fork that is not recommended for your bike, it’s best to try it out before emptying your wallet for a new model. You may even prefer the mismatch to the expected size.
Look up the term “caster” and see how it affects steering and handling characteristics. plays a key role in the performance of the bike. Caster is a combination of HTA and Rake.
I just went through this about 2 years ago. I built a big 2018 Devinci Troy that was given a 150mm 27/29 pike with a 51mm offset. I’ve spent months trying to find a clear and fairly simple explanation of how a 46-44mm offset fork affects handling and 51mm, but nothing really makes sense to me… I upgraded to a 160mm fox 36 2019 . – 27/29 (I ride almost exclusively on mullets) with a 44mm offset.
I see a subtle difference. … I guess I made a lot of adjustments to the update schedule this year, adding 10mm of travel, adding a new offset and installing a 29 front wheel, I have a lot of variables to get my bike mullet ready. I have a set of 27.5 wheels for park days but I ride mullets all season. So I don’t really know what it’s like to be on smaller fronts. This can be a really significant difference. The shorter offset fork I used last year. I would ride the CPL once on the 29 fork with the 51mm fork, then switch to the 27.5 fork and it feels “better”… this year with less offset + more travel I could comfortably run the mullet all day long ever . I even thought about changing tires…
I just received a full suspension bike as a gift and it has a 44 degree offset. My previous bike (a budget hardtail) had a 51 degree offset. Now I know I’m comparing apples and oranges, but the difference I see is the wiggling of the front end. I did notice that in tight corners I could be neutral or slightly front-heavy, but the same on the 44 resulted in the front end diving into an uncomfortable position. So I think I’ll have to put the weight on. On any steep section, I was comfortable from neutral to slightly ahead.
I read the headline and rolled my eyes… WTH? Of course, the bike will “work” with a fork with a non-original offset. First, as the author says, the bike handles differently, and after a short opportunity to get used to this difference, it becomes second nature. Secondly, fork offset has been on the radar since the early 90s until suspension became a big thing. I remember being stunned and fascinated by my friend’s Yeti Pro FRO bike with an Accutrax fork that had 12mm offset, maybe 25mm. Processing is fast and accurate. He loved it, but didn’t ride it until his new long-reach suspension fork arrived.
Our old-timers called people’s excessive focus on grams “weight babies.” This article sounds like it was written for a “geometric pixie” staring at her belly button. oh bro…
Enter your email address to receive top mountain biking news, product selections and special offers delivered to your inbox each week.
Post time: Oct-27-2022
