Long range planning is underway for a extra fast hardtail mountain bike (MTB-LT32/29) that should be completed in the spring. Similar to the Corsair, it will have a 686mm BCD tire on the front rim. Suspension forks for such a bike are expected to reach the consumer market around then.
One of those forks, a 120mm fork for 32″ wheel, may have a slider plane 1.5° angle from the head axis. A pitched slider as I’m referring to them.
It isn’t common in bicycles or motorcycles to pitch the sliders. Typically, the slider plane is aligned with the head axis. This makes it very easy for the designer and tuner to make predictive changes to the geometry at minimal cost. The math is easier. The parts are easier to communicate. Pretty much, this is the right way to do things.
It does happen, though. Some chopper motorcycles pitched sliders (‘raked trees’) to give the bike a particular look, but this adds a huge cost and challenge to set the triple trees correctly. Early RockShox RS-1 and MAG 21 forks did, to present more like the rigid forks that preceded them. Recently, new gravel forks produced by several top suppliers have used sliders planes set at an angle to the head axis. I wrote about that in 2023:
In that post, I discuss the geometric concerns for using this type of fork in a bike design. Basically, how we ensure our geometry is what we say it is when it’s being planned and constructed with pitched sliders. How the change in offset at a particular point in the travel is dealt with. This was relatively straightforward.
The question then arises, what effect does pitched sliders produce in the system and why would we implement it? In the case of the current gravel forks, it’s clearly being done to clean up the visual aesthetic of the fork to make it more palatable for the consumer. Having an inline connection of the axle to the slider significantly cleans up the look of the bike and may make the low travel system a little lighter.
In the new situation, A mountain bike suspension fork is going to be released that will look like any other mountain bike fork but has pitched sliders. The essential architecture of the fork is otherwise identical to those slider plane is aligned to the head axis. Why would this choice be made?
I did some calculations for this based on my upcoming MTB-LT, the Warthog. So that it is clear what values may have been used in my calculations, I’ll include a print of that bike design.
I can gain some understanding of what happens with the front end geometry and crank axis height as the fork is cycled by doing some basic math. The entirety of the bike’s geometry was used to do these calculations to ensure precise representation. Honestly, the main value that I get from this is for producing a highly optimized crank axis height in my design.
Let’s make a comparison. I’ll look at just the front wheel trail and front wheel flop with the system and a slider aligned with the steerer and with it pitched. Offset adjusted so that both forks are 44.1mm at 30%. Nothing else changed. I show that below.
While the wheel flop changes a trivial amount, the front wheel trail change is measurable. Both have 90.8mm of trail at 30%. At 100% compression: 68.3mm with the pitched slider and 65.9mm the parallel slider. Trail is 3.5% less with the parallel slider fork. Does this mean anything?
Looking at this another way, there was a 24.8% reduction in trail for the pitched slider and 27.4% reduction in the parallel slider. A 2.6% difference in the reduction at 100% from 30% travel.
Looking at the difference in trail change alone, one would imagine that this is enough of a marginal gain to be worth the effort. Who wants their bike to become less stable in the most extreme of situations, even by just a little bit? I don’t.
But the bike is a system and all changes have knock on effects. If you rob from Peter, your going to have to pay Paul. What costs are you paying for this imagined advantage?
Most obvious is that geometry planning of the bike is more complex. This is acceptable for me if the effort is worth it but most folks have a very hard time with basic planning. I discuss this in the post above about the new gravel forks. Is the geometry confusion really worth the imagined gain if it results in a poorly planned system that actually negates that gain?
Think of it this way, as of this writing, BikeCAD Pro 24.5 is available but has no provision for a pitched slider in the fork geometry. Other than manually adjusting the offset at a given point, you can’t specify this. I’m sure that this will be remedied soon but it does tell you how much effort has been put into this idea in the last 20 years.
But here’s the real cost of pitched sliders, worse suspension performance. Telescoping forks have serious problems dealing with forces that aren’t aligned with the sliders. Aligned forces are an exceptional condition, not the most common. If the forces are misaligned (almost always) here will be some component of stanchion bind. That’s when the sliders resist sliding due to the bending forces going through the fork. For a long time, this wasn’t a huge issue for mountain bikes. Head angles were sufficiently steep and other factors were more problematic. Stanchion bind was rarely discussed. In 2026 and in the last 10 years, it’s become a real problem. Some bikes have head angles as low as 63° or 62°. The only time forks on these bikes work well is when pointed down a steep chute. Traversing on flatter terrain, they resemble a rigid fork. Good in a gravity race, terrible everywhere else.
Ona gravel bike, that 5° pitched slider may be aligning the slider to the angle of the forces….but it’s probably not. Again, my mountain bikes are on the low side of what is common for gravel bikes (70°-72°) and I ride some very aggressive and rocky descents. I’m not looking for a lower angle of attack for my sliders. A bike that is generally dealing with small surface bumps on flatter terrain is going to want sliders oriented steeper for best function. We are only left to believe that the 5° reduction in slider angle is making gravel bikes work worse in favor of appearance, not better.
While a deep dive into whether low head angles are an advantage or not is the topic of another post, it should be clear that using a fork that reduces the slider angle to earth 1.5° – 5.0° degrees is not wise for at least 98% of a given offroad ride.
My Starfighter MTB uses a 68° head angle. The Warthog should have a 70.5° head angle. I’ve been looking for ways to increase head angles in the last 7 years to reduce flop and advantage suspension over most of the ride. I’ve got the least to loose using this fork. Others will not be as lucky.
Will you be seeing steeper head angles on new 32″ model bikes? Definitely not. My prediction is that most 32″ wheeled bikes will have even slacker head angles or very short front centers or both. We’re already seeing this happen. Why? Simply, handlebars, stems and pour design remain the big problem in commodity bike designs.