Saturday, April 15, 2023

Why I Don't Like Telescopic Front Forks For Gravel Bikes

The Otso Waheela S
 Several years ago telescopic front forks for gravel bikes were introduced with the Fox AX model being the most prominent player. Although there were others in the niche as well, Fox, and now Rock Shox, with its limited travel Ruby fork, are now the main purveyors of this tech for gravel. 

I have tested and ridden the previous Fox AX model enough that I have a pretty good handle on what this idea can and cannot accomplish for the typical gravel rider. But first, let's get into why you might want this in the first place.

I'm going to summarize in the way I describe what is going on when you ride rougher roads and gravel, so I am not trying to dive into the science here too much.  Please forgive my broad brush strokes here, but I will try to give you enough to chew on that the rest will make sense. 

Gravel, unpaved roads, or even rough, broken up paved roads cause vibrations. While your tires can and do deal with some of that, some of the energy that is created by you to pedal gets transferred into energy that is known as vibrations and that has to be dissipated somehow. Most of the time this happens in your muscle tissue and that energy is turned into heat, which then has to be dealt with by other means in your body as well. You can see this happening when the muscles in your arms are shaking while riding rough grounds, and that is energy being transferred to you, which you damp out, and that is not an ideal way to handle this for the cyclist.  

So, maybe you can see how a telescopic suspension fork might prove to be an advantage here because it dissipates the energy, not you. Well, ideally it would do this. That is the goal, but these devices don't damp everything out. But you get the picture, hopefully. 

Okay, so back to these "gravel specific" telescopic fork devices. Almost universally they have been hamstrung by what is seen as the necessary geometry for gravel bicycles, which itself is derived from road cycling, and which is focused on aerodynamics and efficiency of the rider, primarily. This means, for this discussion, that a limitation on the axle to crown height of a fork, (acceptable for aero/geometry reasons) is imposed which in turn limits travel on a telescopic design to around 40-50mm of travel. Basic stuff and completely understandable for gravel bikes. 

Now, let's talk some history. Back in the early 1990's, suspension for MTB was in its infancy. The "standard" amount of travel was about 60-65mm, with Rock Shox settling in at 63mm for its famous Mag 21 model. I rode the equivalent Specialized Future Shock model, (a rebadged Mag 21, basically), and it was woefully over its head on "real" mountain bike terrain. The damping on my fork was modified to be such that it would not "blow through its travel" but still, it wasn't enough. Travel that is. This is why you cannot buy a 63mm travel MTB fork anymore. Many think 80mm is too little, and most "XC" forks now are at 100-120mm of travel. Why? Because to actually be effective, the telescopic design needs that much distance to travel to dissipate energy effectively instead of the rider doing that.

The Fox AX was overwhelmed easily by bigger hits if set up to deal effectively with normal gravel

 Okay, now back to my experience with the Waheela S and the Fox AX fork. This fork had tunability and in my experience, it could be set up in several ways. It made sense to me to have the fork working all the time to absorb as much of the vibrations as possible. This would make up for the added weight of the fork over that of a typical fork for gravel, which was anywhere from a pound to a pound and a half difference. (Depending on the rigid fork) Okay. That was great until you hit something bigger than crushed rock. Then the fork would bottom out violently with a loud "clunk" and forget about it being an advantage in Level B road ruts, pot holes, or washboard where the travel was completely overwhelmed. (Remember my MTB Future Shock here)

Now, I could have opted for the damping to only take effect on the bigger stuff and just lived with the buzz of normal gravel, but that sort of defeats the purpose of pushing around the extra weight on, what normally is, most of my rides. Notice; You may have a differing opinion here, but for me? The suspension fork is a no-go. Not as it is currently configured in 2023. 

From Rock Shox social media

Now let's talk about another issue that any suspension fork, (besides the Lauf leaf spring fork) brings to the table, and that is maintenance.

 The image to the left here is a Rock Shox posting on their social media describing what the foam rings do on their forks and how often you should service those. The foam rings help prevent dust from entering the fork's internals where dust would be detrimental to the inner workings. Now, you all know how much dust gravel riding generates, right? So, maintaining good foam rings would be even more challenging in a gravel riding scenario, one could assume. 

Rock Shox states that these foam rings need servicing after every 50 hours of riding. Now, I don't know about you, but that would be about twice a year, at least, for myself. Just roughly guessing here, but at least twice is a safe bet. 

Ever look up what suspension servicing costs at your local bike shop, (if they even do that at all)? It seems from a quick search on the internet that you could expect this to be a $75.00-$100.00 repair. That is a minimum of $150.00/yr for me, and how many days without the bike the fork is on? Maybe a couple weeks? Hard to say.

I don't know about you, but I can find better ways to spend $150.00+ bucks and however many days of downtime that it would incur to do fork maintenance. I just don't see the performance benefits of telescopic front forks for gravel bikes as being an advantage that is worth more than the initial costs, ($500.00 - $850.00) and the maintenance costs of those types of forks. Especially when I can get what I want in terms of vibration damping out of a Redshift or Cane Creek suspension stem, have no maintenance costs, and a lot less initial cash outlay. I also could opt for the venerable Lauf fork, have no maintenance costs, but yeah, it does cost $990.00! 

Verdict: For my money, the best solution here is a tire that works well and a suspension stem, like the Redshift ShockStop stem, which does a great job at the vibration reduction thing. It is also tunable for your ride style and weight. The ShockStop is also swappable from bike to bike in most cases as well, making it more versatile over the long haul for its owner. I do not need a specific "suspension compatible" gravel frame, nor are there any proprietary limitations. 

To make the telescopic fork actually work on a gravel bike, it would necessarily need to have more travel to work with to dissipate both high frequency, mid frequency, and big impact inputs. Only then would its weight penalty, cost penalty, and maintenance penalty over a suspension stem make it a consideration. However; to gain that function the fork would have to have an axle to crown height that would nullify any aerodynamic efficiencies that a gravel bike needs to have.  (Think about how a Fargo or Cutthroat with suspension would do in a headwind vs a typical gravel bike) Yes- you could do this and maybe be a happy rider, but there is no denying the physics here. And still you have all the economic and practical issues to deal with as well.


Nooge said...

There are ways to make the suspension be supple at the beginning of the travel and ramp up to firm as the fork compresses. For example, adding internal spaces that reduce the volume of the air chamber at the top, AKA tokens. There’s also calling that races different for low speed and high speed hits. But that adds more cost and complexity and development.

Overall I agree with you. For most people, the juice isn’t worth the squeeze. Given the current sales slump, I think it’s safe to say nobody is going to poor that money into R&D for a product that for which there isn’t much demand. So we are left with these underwhelming products for the foreseeable future.

Guitar Ted said...

@Nooge - I agree with you, but I think asking for all of what you are saying to happen in 40mm of travel is too much. The compromise in travel would make changing from "supple" to "ramping up" such a drastic and finely grained transition as to be nearly impossible to pull off without some major technological advancements in fluid dynamics and electronics. I am not aware of a suspension system with that little travel that can do what we are talking about well, or at all. Perhaps someone does? I'd be interested to read about it.

Nooge said...

They could use an inverted fork to allow short stack height and longer travel, though that might require a down tube with a kink. Alternatively, they could use rheomagnetic fluid like MagneRide. Once electronics are involved you can use accelerometers to alter the stiffness and damping based on the bump size and use almost your entire travel fairly optimally for both small and large bumps.

So there are engineering solutions. But is there enough profit to be made in it and will some company commit the funds to develop it? I don’t think so for the next 5+ years.

Guitar Ted said...

@Nooge - Good examples. The inverted design has been tried, as you probably are well aware, to not much success in the bicycle world. The battle to have light weight components versus stiff, durable components is where that design runs afoul I think.

Electronics have been applied to bicycle suspension in various forms with middling success at best. I think at some pint it will be a thing that is commonplace, but we are not there yet in the bicycle world.

So, yeah. The foreseeable future doesn't look promising for gravel bike telescopic front suspension tech, not that it matters. ;>) And I feel this is the salient point here. Other solutions will prove to be more attractive due to less expense and easier to apply technologies.