The Tuesday Tune Ep 8: Why We're Riding Telescopic Forks - Video
For over 100 years, telescopic suspension forks have adorned the front end of motorcycles - and more recently, mountain bikes. For just as long, alternative systems have been proposed, built, tested, sold and usually also abandoned. Most of these alternatives have been some form of linkage fork, using short links, swingarms and pivots just like the rear suspension of your bike. These have invariably been touted as solving problems that telescopic forks have always found it difficult to address, the most notable of which is brake dive - so how did it come to be that we're almost all still riding telescopic forks in spite of their accepted shortcomings?
After all, if you could remove brake dive from the equation as a variable, it should be much easier to find spring and damping rates that allow for better bump absorption and traction since the need to compromise on sensitivity in order to support the fork under hard braking is eliminated.
This is a more complex question than it may first appear. After all, nobody is using telescopic forks for the rear suspension - that idea died with the old Manitou frames. Why is it that we can easily accept linkages as a viable system for minimizing unnecessary motion of the rear suspension under acceleration/braking, but not for the front? What is it that linkage forks are yet to get right in order to achieve the level of performance and commercial success that their respective engineers always thought possible?
We suggest that the answer lies in two related aspects: the steering axis's relationship with axle path and the number of design variables. This week's Tuesday Tune is about understanding how telescopic forks came to dominate the market in spite of their widely known and inherent compromises in performance.
Note: there won't be a Tuesday Tune video next week due to the holiday break. We'll be back in a couple of weeks to bring you more tech ramblings!
MENTIONS: @VorsprungSuspension
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Interesting topic though, thanks for this series and merry christmas.
never owned a UD telescopic though friends raved about their Dorado and Shiver, and complimented the handling in the chunder where the more flexible structure helped hold chosen lines, and the small bump sensitivity from the always relubricated seal package
For a while back in the 90's I put a Noleen Girvin Vector on a KHS Yamaha. Wonder if it would still suck if fitted with one of today's air cans?
@hampsteadbandit I owned a Shiver back in the day, didn't really like its flex characteristics compared to 40s, but for its time it certainly was the most sensitive fork around. Wouldn't have hurt to have some bottom out bumpers in there though, every time it bottomed it sounded like a car crash.
@XCMark unfortunately we don't work on Leftys.
Shiver DC and Shiver SC were somewhat ahead of their time? but with some undercooked engineering...they did last forever like most Marzocchi though
I saw a Marzocchi RAC once in Cycle Surgery, Spitalfields, London. Strapped to a store wall for several years with its red carbon fibre crown. Ever ride one? Or work on one?
ep1.pinkbike.org/p5pb9350497/p5pb9350497.jpg
re. 40's I got the first year 40's strapped to the front of a Mythic (Banshee) Scream they hooked me up with in the UK.
Great FR fork because you could point it down a chute full of garbage and it would let you barge on through = hugely confidence inspiring for going 'off piste' but perhaps a little stiff on some of the off-camber wooded DH trails common to the S-East of UK
I am right in thinking the later 40's became more "refined" in terms of handling i.e. flexure across chassis?
www.bikeradar.com/mtb/gear/article/pushing-the-limits-of-fork-offset-an-experiment-45343
IMO, telescopic forks work very well & linkage forks usually are ugly as shit, so they lose.
"BMW's telelever front suspension has been the only commercially successful alternative in recent years"[2008]
newatlas.com/single-sided-front-swingarm-could-point-the-way-to-better-motorcycle-handling/10484
en.wikipedia.org/wiki/Hub-center_steering
upload.wikimedia.org/wikipedia/commons/9/93/Nessie_Kawasaki_1000_left_side_cropped.jpg
Notice how the "better" mini-link designs are becoming simpler with less exaggerated leverage curves like the early Santa Cruz VPP. Remember how they were absolutely brilliant in certain ways, but totally sucked in others, such as crazy pedal feedback? Also notice how DW's Split Pivot is a more loved design right now (Evil, Devinci) than his more complicated DW Link, even though he swears the Splitter is less advanced and a lower shelf product. There's also reliability and durability - simpler always winds in these scenarios. Many single pivot-ish bikes have impressive stiffness and bearing durability these days.
Simple for the win.
MTB only used what was already standard in moto industry. Telies had been poor industry standard long before some MTB has happened to exist and instead of proper development of various alternatives it just sticked to telies while justifying it with years long marketing work.
Just go through Tony Foale's book, or study Norman Hossack's design, or Valentino Ribi's suspension for Honda RC125M and then try to re-examine why telies are still standard in MTB. With qualities of today shock dampers, suspension knowledge and experience it's time to get into linkage forks and make the two approached find their users.
But yes, it's easier to introduce another nano-narrow 1xZilion drivetrain standard for just yet-to-come ground braking 147+eˇ3/4 x 8mm hub axle standard that will once forever solve all troubles that bother this sport.
@fluider the advantages of linkage forks are fairly well known throughout the suspension world - the problem is that everything needs to be as good an overall package as it can. Having better anti-dive characteristics doesn't count for much if you make something else worse at the same time, and that's why designers have found it so difficult to find commercial success - most if not all of those systems have some fatal flaw (often something solvable too) that has sunk the ship. For example, the Ribi forks just cost too much to make at the time, although I think that layout is where the real potential lies. The Hossack design requires frame integration and is relatively heavy, which doesn't fly in the MTB world.
Part of the problem is that the MTB industry just isn't very highly paid in general, and development resources are very spread out across many small companies. Even guys like SRAM or Fox are pissing in the ocean compared to Honda. You don't find many people in this industry that have decades of experience with suspension/chassis design and a sufficient understanding of the physics involved, with sufficient funds behind them to actually develop something like that, make it a better overall package than any of the telescopics already out there, then bring it to market and convince enough people to buy it. I personally think the Motion France fork is the closest we've seen so far, but then they have riveted bushing pivots and an apparently non-serviceable damper unit with no compression adjustability, so anything that does go wrong - and things will go wrong - isn't easily reparable or serviceable. It's also very, very expensive, and asking people to take a financial gamble that big on something you know you can't fix is a pretty tough sell.
I think there is enough educated and skilled people in MTB industry who can make valid R&D for linkage forks, and even smaller frame brands do use their own test labs. FOX must have pretty big experience data at hand from testing their dampers on various ATV vehicles. Jesus, the kinematics is well known for over 50 years! You just need to extensively test various layouts and settings.
I think Motion France fork is not the closest because it's short travel, it uses proprietary damper, it's gonna be expensive and in fact it is pro-dive in up-to-SAG point.
And it seems that vast majority of riders really don't mind it.
With linkage fork you can have very steep axle path that maintains wheelbase and increases trail when going into its travel. Telefork must lower its head angle to increase trail and this is used in todays geometries to compensate for the disadvantage of telefork, the decrease of trail while going into travel.
gifmaker.cc/PlayGIFAnimation.php?folder=2016122208qOgdsqMqTeTOTz5mxOeFHA&file=output_viwvRg.gif
It seems like if the stanchions were angled more vertically you could keep trail more consistent by adding more offset.
It also seems like a more rearward axle patch could be faster in certain conditions, maybe the stanchions should be angled more horizontally?
Probably because it is old non-patentable motorcycle technology, although I am continuously surprised what general principles used in a microscopicalky different way the US patent office will grant a patent on...
"Hey, we have this motorcycle with an anti-brakedive fork, we just dismounted the engine, can we patent it?
The USE forks had a whack axle path too - it was kind of C shaped and created a substantial reduction in steering trail. This is precisely the sort of detail that, when overlooked, sinks a whole design. Telescopics all have dive issues for sure, but being rather overdeveloped in a lot of ways to try to compensate for that has meant that they are, at the moment, still the most viable option overall.
But SPs are great these days. The biggest challenge they faced was dealing the with the multiple chainlines that 2x & 3x drivetrains cause. But with the rise of 1x, now they can all place the main pivot at an ideal location for one chainring, which solves most of their pedaling issues.
...biggest problem of todays bikes is, that time to ride them is not included in price.
What do you think about the Lauf Fork @VorsprungSuspension? It seems to be quite popular-ish
youtu.be/OUsl-qb138A?t=8m20s
I ride my fork stiff so I feel like Gwin... without his abilities that is????????
Tks Steve!