Inverted Fork

[east or bust]

Thought this was kind of cool.

Some of you may have already see this but here it is.



Link to article:

http://reviews.mtbr.com/first-ride-r...-inverted-fork


Not really geared toward us regular joe's yet (at $1,865 MSRP) but this could create some nice trickle down tech.




If this has already been discussed I'll delete.

[Gripen]

Inverted forks are nothing new, Dorado, Maverick, etc...

Lots of motorcycle forks are inverted.

[stuckathuntermtn]

WHYYYYYYYYYYYYYYYYYY

[jm2e]

So which end of the fork gets scratched the easiest again? Is it the end that's closest to the rocks?

[Ted Striker]

WHYYYYYYYYYYYYYYYYYY

To sell you more stuff.

On motorcycles the reduction in unsprung weight makes a difference, but with such a small weight diff on an mtb fork, it seems unnecessary.

[rod9301]

i had a maverick inverted fork, and it was flexy and sticky when you hit a square bump, was much happier with the fox that replaced it.



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[Jethro]

It is one thing to do an inverted fork on a motorcycle, with triple clamps and oversized fork tubes. Scaled down to mountain bike size, the loss of the fork arch leaves the setup a little flexy.

[Hugh Conway]

Some of you may have already seen this

Which time around?

[beast]

It is one thing to do an inverted fork on a motorcycle, with triple clamps and oversized fork tubes. Scaled down to mountain bike size, the loss of the fork arch leaves the setup a little flexy.

RockShox fixed the flex issue with their "Predictive Steering" tech on the RS-1 fork. There's a solid hub axle that locks into place in the dropout using some knurled teeth, essentially bonding the two legs together and eliminating any flex. In terms of precision, it felt like a 24" BMX cruiser fork. The thing is far stiffer than any other suspension fork I've ridden to date.

[east or bust]

Obviously I've seen this on motos , just never on an mtb.

So which end of the fork gets scratched the easiest again? Is it the end that's closest to the rocks?

...

[toast2266]

If this thing is actually the bees knees when it comes to suspension, why did RS debut it in a cross country package? XC racers have repeatedly demonstrated that they don't give a fuck about the quality of their suspension. My useless internet speculation: the suspension is neither all that great nor can it maintain adequate stiffness in longer travel formats.

[jono]

I guess all those motos were short travel? Better guess is that they wanted to highlight the lighter weight first and after people remark on how 'surprisingly stiff' it is you'll see a long travel version. Paying a little attention to the trends in the last couple decades would show that larger diameters and thinner walls are the path to lighter weight. Or do the math, that's even more compelling. The limit is when the walls are too easily dented, hence aluminum over steel (math again). Look at this fork again and you'll see that concept displayed.

The connection between the two sides, if it's rigidly attached, should be stiffer than the combination of a big heavy horseshoe over the top and an axle half its diameter. Then there's the fact that the upper stanchion can be larger in diameter and, being the portion that's in heavy bending, that's going to stiffen the whole thing, too.

This looks like a two-sided Lefty; it will be interesting to see which results in the better combo of (stiffness x travel / weight) in the long run. The only technical downside to this approach (not to say this particular execution of it) is the larger wheel bearing being a little less efficient, and I'm guessing no one is worried about that.

[toast2266]

I guess all those motos were short travel? Better guess is that they wanted to highlight the lighter weight first and after people remark on how 'surprisingly stiff' it is you'll see a long travel version. Paying a little attention to the trends in the last couple decades would show that larger diameters and thinner walls are the path to lighter weight. Or do the math, that's even more compelling. The limit is when the walls are too easily dented, hence aluminum over steel (math again). Look at this fork again and you'll see that concept displayed.

Motos purposefully build in a bit of torsional flex to the forks - it makes them ride better. Otherwise they feel harsh at the bars. But more to the point, Moto forks are massively more stout than Mtb forks. The issue isn't making an inverted fork stiff enough, it's making a 3.5 lb inverted fork stiff enough.

The connection between the two sides, if it's rigidly attached, should be stiffer than the combination of a big heavy horseshoe over the top and an axle half its diameter. Then there's the fact that the upper stanchion can be larger in diameter and, being the portion that's in heavy bending, that's going to stiffen the whole thing, too.

I'm impressed that you were able to assess the theoretical stiffness of different fork designs so easily. Does NASA know you're doing FEA analyses in your head? They'll pay you for that you know.

It's not like this is the first inverted fork to have a funky, oversized axle design. Manitou did hexagonal axles, Maverick did massive oversize axles, and some other company (Risse?) also did oversized axles. And those were all on forks that were far more overbuilt than this one (and longer travel). But they all sucked (with the potential exception of the Dorado, but that depends on who you talk to).

This looks like a two-sided Lefty; it will be interesting to see which results in the better combo of (stiffness x travel / weight) in the long run. The only technical downside to this approach (not to say this particular execution of it) is the larger wheel bearing being a little less efficient, and I'm guessing no one is worried about that.

You have no idea what you're talking about. Other than being a piece of carbon and metal that attaches to the front of your bike, this thing has basically zero similarities with the lefty (i.e. doesn't use square sliders, runs on bushings instead of bearings, damping might actually work, etc.). The very fact that you're excited that this thing might give the Lefty a run for its money shows that you have no business talking suspension, since the Lefty's suckiness is only outdone by the headshocks that they replaced.

[kidwoo]

How many leftys you ridden toast?


By the time they got those manitou tpc dampers in them, they didn't suck. They're stiffer than any fork you've ever had on a trail bike. I was actually looking into what it was going to take to get one of their new ones. (turns out it's a mental tolerance for fucked up steerer tubes) Their weak point has always been the dampers but the high end ones are worth doing. The chassis is kind of ridiculous awesome. I'd much rather have one of those than anything fox has made in the last 3 years.


And yeah that hub attachment system is kind of like a lefty.

[creaky fossil]

RockShox fixed the flex issue with their "Predictive Steering" tech on the RS-1 fork. There's a solid hub axle that locks into place in the dropout using some knurled teeth, essentially bonding the two legs together and eliminating any flex. In terms of precision, it felt like a 24" BMX cruiser fork. The thing is far stiffer than any other suspension fork I've ridden to date.

so first we had to get 15 which actually improves on 9

but then we had to blame 20 for being tubby and eliminate 20 everywhere below 180mm travel

now we get something like the Maverick axle, proprietary

on a pimpmonster chi-chi legshaver fork

all change is not progress

*********

on all moto vs mtb attempts at analogy/parallel

moto has an engine, the entire package of chassis dynamics assumes external energy source

[toast2266]

How many leftys you ridden toast?


By the time they got those manitou tpc dampers in them, they didn't suck. They're stiffer than any fork you've ever had on a trail bike. I was actually looking into what it was going to take to get one of their new ones. (turns out it's a mental tolerance for fucked up steerer tubes) Their weak point has always been the dampers but the high end ones are worth doing. The chassis is kind of ridiculous awesome. I'd much rather have one of those than anything fox has made in the last 3 years.


And yeah that hub attachment system is kind of like a lefty.

A few. Aside from the damping issues, there's also the fact that if you get one little bit of sand into the bearings they feel like shit. And they're a pain in the ass to rebuild.

[reckless toboggan]

toast2266 totally on-point once again.


So true:

The very fact that you're excited that this thing might give the Lefty a run for its money shows that you have no business talking suspension, since the Lefty's suckiness is only outdone by the headshocks that they replaced.

[kidwoo]

A few. Aside from the damping issues, there's also the fact that if you get one little bit of sand into the bearings they feel like shit. And they're a pain in the ass to rebuild.

I've never owned one so never had to deal with sand in there but to compare those things to a headshoK is a little rough (even though they're structurally very similar ).

I wasn't kidding, I really would rather have one of those than the constantly thinning walled and flexier fox stuff.


I don't know......an 1800 sid is a little silly but I'm open to the idea that some good concepts from it could be used.

[toast2266]

I don't know......an 1800 sid is a little silly but I'm open to the idea that some good concepts from it could be used.

Yeah - there certainly could be something good to come out of this, but every couple of years someone unveils a new inverted design and announces that they're going to revolutionize mountain bike suspension. None of those designs have ever caught on, because they all suck for one reason or another. Both Rockshox and Fox have proto'd inverted Boxxers / 40's, and from what I've heard, both companies have abandoned (or at least shelved) those programs because they couldn't build something that was better than their current offerings.

I've never laid hands on this new RS so I'll withhold final judgment. If Beast says it's torsionally stiff, then I'm inclined to believe it, but I'm skeptical that this thing will be useful in longer travel applications. And that skepticism isn't because this fork is new and different, it's because inverted designs have been done over and over by perfectly competent engineers and they all sucked.

P.S. I did fondle that inverted X-Fusion and it was pretty stiff. And it's a mere $1,776. Haven't ridden it though.

[jono]

Sorry to offend your sense of alpha poster there toast, but it doesn't require FEA to get the stiffness vs. weight numbers, only to do the details on the design. I have software for FEA, but I've done the torsion and cantilever beam numbers so many times that the relative impacts of the different variables are just ingrained now. This is a little like law that way: it takes practice, but eventually you get good at it. It helps that some of the variables get third or fourth powers attached to them; feels like cheating. If you think it's a problem to make an inverted fork stiff in comparison with a regular one at the same weight you should stick to writing arguments because the facts aren't changed by clever persuasion.

Kidwoo has laid out the facts about the Lefty comparison pretty well: anything you might complain about on those is about the damping, not the structure. Obviously this arrangement lacks the preloaded metal on metal of a Lefty's sliding mechanism, and that has its pros and cons, but I was referring to the hub connection. Get that solid and preloaded enough so that there is no gapping in use and this thing will have legs.

Also worth noting that they've added material to the outside of the front and back of the stanchions at the top where bending moment is at its highest. That's a good step for better stiffness to weight ratio as well, and a lot cheaper to manage on an inverted carbon where you can meaningfully increase the area moment of inertia in that region without having to create an internally ovalized butt shape...which sure sounds like a nightmare to me.

The devil's in the details and this thing may suck, but not for the reasons being complained about so far.

[creaky fossil]

I would hope people paid to engineer (vs design) forks actually are seeking improvement when they problem-solve in their role as, y'know, engineers. So on this naive hope, I expect it's possible to incrementally improve a design and prior implementation of something that, ultimately, still isn't superior to what exists presently. On what ground is upside-down actually an improvement outside moto fork designs?

You're not problem-solving if you have to create the problem that your imagined solution solves.

[frorider]

Random questions...since the weight reduction is modest, what's this offer to the xc Lycra crew? Ie what Creaky said. And why intro it w/o guards for the lowers? The knurled axle interface helps rigidity...but manitou has hex axle for years, and while it helps, it's no panacea.

For a given weight, invert forks do have superior front/back rigidity, but I'm not sure that's a limiting factor with short travel xc forks anyway. And if a seal leaks, this will mess up your brake pads in the middle of you ride.

[Hugh Conway]

I'm impressed that you were able to assess the theoretical stiffness of different fork designs so easily. Does NASA know you're doing FEA analyses in your head? They'll pay you for that you know.

It's pretty basic fucking engineering (like intro level coursework) - no need for fancy colored computer models to show to 'tards like you toast.


creaky - it's a consumer product in America. marketing tells the nerds what to do and the nerds do it. cart driving horse. Then they truck out the nerds to give toasts buzzwords.

[jamal]

The highest bending force is up at the crown so the once piece carbon deal should be stiffer than two tubes bolted to a standard crown/steerer, and there will be less force on the bushings. Also less unspring weight, which would have an effect similar to lighter wheels. I guess it would be neat to try but it doesn't offer me a whole lot over my current fork which is actually lighter than this thing.

[jono]

I expect it's possible to incrementally improve a design and prior implementation of something that, ultimately, still isn't superior to what exists presently. On what ground is upside-down actually an improvement outside moto fork designs?

The common goal in bike forks (from a high level view) is more stiffness, strength and travel and less weight. Math speakers might compare different implementations using a statement like stiffness x travel x strength / weight. Or you might tweak that a little, but the point is that you can trade weight for any of those others and you can get more stiffness with less travel etc. But those compromises are specific to a design. At the high level, where things like the basic layout are considered, that goal is common to all bike forks.

Inverted forks give more stiffness at a given weight, because they put the larger diameter on the upper portion, which carries the higher bending moment (bending due to applied load [not braking], force x distance, increases linearly from zero at the hub to max at the bottom of the headset). Further, local strain up high results in exponentially more deflection at the hub due to the increased distance. (To keep this even a little bit simple, I'm assuming a basic understanding that larger diameters give better strength to weight ratios; Google area moment of inertia and cantilever beam equations for more.) To achieve the goal with an inverted fork you need to keep the axle stiff enough to handle the lateral loads, but as it turns out those loads are small since the rider's COM usually stays fairly close to being in line with the wheel. Take that free increase in stiffness/weight ratio and trade either stiffness or weight for travel as needed and the same arrangements that do well in one travel can be made into longer or shorter travel designs, but it requires a whole redesign.

The details aren't always done right and as Hugh is always saying "innovation" these days comes from better marketing not better engineering. That market success has more to do with belief than reality should surprise no one.