Inverted Fork

[toast2266]

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

So removing 1/3 of the bracing on the fork but slightly increasing the diameter of one of the remaining braces will increase torsional stiffness, and that's super basic stuff despite the fact that you know nothing about the execution of that design, and despite the fact that other companies have been doing that for years with poor results. Got it. Way to gargle RS's marketing jizz.

[toast2266]

On what ground is upside-down actually an improvement outside moto fork designs?

Like Jono said - the main benefit is there's an increase in lateral rigidty. Less fore-aft flex under load means the fork binds less on compression and will absorb bumps more smoothly. Also, the inverted design does a better job at keeping the seals lubed up and running smoothly.

I still think the downsides (decreased torsional rigidty among others) outweigh that benefit. And it's $1,800, so fuck that.

[Hugh Conway]

So removing 1/3 of the bracing on the fork but slightly increasing the diameter of one of the remaining braces will increase torsional stiffness, and that's super basic stuff despite the fact that you know nothing about the execution of that design, and despite the fact that other companies have been doing that for years with poor results. Got it. Way to gargle RS's marketing jizz.

Way to be your usual content free lawyer self toast. I don't know shit about this application - nor do I give a fuck. Because I'm not a preening cunt like you gargling jizz to get free shit and I'd rather pay your mother for 1800 blowjobs than buy this piece of shit. So go have a fucking rice cake.

[creaky fossil]

Those moto forks can be heavy because they are on a thing propelled by burning gasoline rather than a thing propelled by eating clif bars and drinking water. Can the mechanical and performance advantages available in the "we can build it heavy" moto mode translate to "we don't burn gasoline" bike mode?

[toast2266]

Those moto forks can be heavy because they are on a thing propelled by burning gasoline rather than a thing propelled by eating clif bars and drinking water. Can the mechanical and performance advantages available in the "we can build it heavy" moto mode translate to "we don't burn gasoline" bike mode?

My speculation: yes, the advantages can be obtained while sufficiently limiting the downsides, but it'll come at the cost of lots of engineering and expensive materials. This new XC fork is 50% more expensive than RS's previous top end xc model. To get worthwhile performance in a longer travel fork where 1) the disadvantages matter more, and 2) the stresses are higher, the cost would be prohibitive. And by "the cost will be prohibitive," I mean they'll probably build it anyways because some idiot will buy it.

[jono]

Those moto forks can be heavy because they are on a thing propelled by burning gasoline rather than a thing propelled by eating clif bars and drinking water. Can the mechanical and performance advantages available in the "we can build it heavy" moto mode translate to "we don't burn gasoline" bike mode?

I just made a rather lengthy post on the subject of the trade-off between weight and stiffness... maybe it's clearer to just say that which achieves stiffness without adding weight can also achieve lower weight with adequate stiffness. Where RS chose to land on that spectrum is unknown.

And, no toast, I did not say lateral rigidity. My comments apply more to fore-aft rigidity, although some of the same things help lateral rigidity, too. The net lateral feel will be largely driven by the torsional stiffness of the axle (ETA: around the bike's longitudinal axis), though, and we don't know that by looking. If they did this right (and that's the unknown here) then higher weight here compared to similar travel forks could easily mean they opted for more stiffness.

[kidwoo]

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.

I call it the 'five year flex cycle'

The irony in all this is of course that RS forks need structural advancement right now the least.

I was just talking to a buddy the other day who got a brand new 34. Both of us remember without question the first three or so years of 32mm fox forks being WAY stiffer than those pieces of shit. He's still got an old vanilla on a dirtjumper and it's pathetic how much better that chassis is. I'd easily believe this rs thing is stiffer than any current 34 based on the ones I rode last year. I swear it's like fox had some crazy turnover about 4 years ago with an influx of 120lb spando 29er hardtailers. They haven't done anything that's a real linear improvement (IE not just something better than what they just fucked up on) in eons. The 40s are the only real suspension devices they've made in a long time.

[jono]

they'll probably charge $1800 because some idiot will buy it.

FIFY. Higher price of this version says nothing about the cost to realize the noted advantages otherwise; it just means their marketing guys think they can sell it at that price and then when it trickles down you'll think you're getting a deal.

[toast2266]

There's no way a longer travel (i.e. Boxxer) version of this will be $1800. Boxxer WC is already $1,700. Adding a bunch of carbon and new tech to it means $2500+

[kidwoo]

I don't think they'd make that anyway since you'd have a fixed axle-crown height.

[jono]

My use of $1800 was a reference to this one, sorry for the mix up there. This doesn't need carbon to survive, though, so there's a lot of second order speculation...this included: To some extent a longer travel version may be possible by simply lengthening the pieces and adding another layer to the crown, since the outside of the high stress part is accessible for that. They might have built the axle strong enough for a higher travel application already, just because adequate stiffness required it, especially since longer travel applications don't need to be much stiffer at the axle, if at all...I'll be interested to see.

All that said I've never been a huge fan of RS stuff for one reason or another, so if this turns out to have some issues it isn't really going to surprise me, either.

[stuckathuntermtn]

I don't even know what unsprung weight means.

[Hugh Conway]

There's no way a longer travel (i.e. Boxxer) version of this will be $1800. Boxxer WC is already $1,700. Adding a bunch of carbon and new tech to it means $2500+

toast lulz.

[Conundrum]

I'm not an engineer nor have I ever ridden a lefty but I found this YouTube intriguing. I'm sure some will find some reason it's wrong but visually this video makes Leftys seem to make some sense.

http://m.youtube.com/watch?v=_WlRqcAQr2w&feature=share

[toast2266]

I'm not an engineer nor have I ever ridden a lefty but I found this YouTube intriguing. I'm sure some will find some reason it's wrong but visually this video makes Leftys seem to make some sense.

http://m.youtube.com/watch?v=_WlRqcAQr2w&feature=share

In theory lefty's are a pretty good idea, and stiffness is certainly not a problem on them. In practice though, the bearing vs. bushing thing doesn't work very well in real world conditions. It gets dirty and jams up.

But while the lefty is inverted, it's apples and oranges to pretty much every other inverted fork. The Lefty derives a lot of its stiffness from its square leg - I don't know of any other fork that works like that. The closest I can think of is the X-Fusion that has keyed stanchions.

[shirk]

The RS1 is heavier than the SID XX WC.

The fork isn't really for racers in that notion.

It looks good so it has that going for it.

[jono]

Nice visual explanation. I think the fact that most of the Lefty-buyers I know are ME's reflects the fact that Cannondale never has done an adequate job of explaining that stuff in laymen's terms. (They're not alone. Oy.) Engineers see that 1.2^4 > 2 and that gapping is an unavoidable source of major deflection with plastic bushings and immediately see where eliminating one side might make sense. Laypeople just think "yeah, right." Results say it better.

ETA: I've never had a problem with a Lefty getting anything in the bearings after a combined 15 years with those as my wife's and my primary MTB's. A little maintenance (in her case almost none) goes a long ways; but I do keep an eye on the boots and filters and mine has been rebuilt 3 or 4 times.

[Hugh Conway]

In theory lefty's are a pretty good idea, and stiffness is certainly not a problem on them. In practice though, the bearing vs. bushing thing doesn't work very well in real world conditions. It gets dirty and jams up.

But while the lefty is inverted, it's apples and oranges to pretty much every other inverted fork. The Lefty derives a lot of its stiffness from its square leg - I don't know of any other fork that works like that. The closest I can think of is the X-Fusion that has keyed stanchions.

lawyer playing engineer lulz.

[toast2266]

ETA: I've never had a problem with a Lefty getting anything in the bearings after a combined 15 years with those as my wife's and my primary MTB's. A little maintenance (in her case almost none) goes a long ways; but I do keep an eye on the boots and filters and mine has been rebuilt 3 or 4 times.

But to offer a contrary view, a good friend went through 3 or 4 of those forks last summer alone. And that was just racing regular xc - not doing anything weird or overly aggressive.

[jono]

Current gen I assume? I haven't gotten past test rides in the new version, but those are certainly different in the seals. Old version only goes bad in seals internally, which is a pain but not much risk to the bearings. New version lost the boot, so I have to imagine it requires constant attention to the lower. Details.

[creaky fossil]

I just made a rather lengthy post on the subject of the trade-off between weight and stiffness... maybe it's clearer to just say that which achieves stiffness without adding weight can also achieve lower weight with adequate stiffness.

Well thanks, but it really didn't tell me anything other than a slightly reworded "light, cheap, strong... pick two." So you get two darts to throw at a 3-pie-piece dart board. Then what? Why has each attempt in single crown forks previously fallen flat? Lack of adequate salesmanship? Lack of buyer courage? Lack of bike journo stokage?

They're really stuck when they consider how to improve their existing line, and so this project was a better use of their propeller-beanie brainpower?

Pet project of someone who always was jonesin' for the Marzocchi RAC?

[jono]

Um, no. My rather lengthy post said this was a way to avoid that compromise and get an improvement in weight or stiffness or a little of both.

I did not address cost since I don't see any reason for it to be different apart from volume. Which would then bring on the questions you're raising now, the answer to which is I don't know and I don't see any correlation to this product. The bike industry is littered with good ideas that failed in the market before making it and your guess is as good as mine, but history seems to indicate that an approach that doesn't suck fundamentally may eventually win out.

[toast2266]

Current gen I assume? I haven't gotten past test rides in the new version, but those are certainly different in the seals. Old version only goes bad in seals internally, which is a pain but not much risk to the bearings. New version lost the boot, so I have to imagine it requires constant attention to the lower. Details.

Yeah, current gen - 2013 models I think.

But back when I worked on those things semi-frequently, we'd always have problems with the boots. The boots would tear or come unseated, and it didn't take much contamination at all to make them feel horrible. And they were a significant pain to rebuild (not sure if the newer ones are better on that front), so getting the contamination out was a bit of a chore.

[frorider]

well one thing's for certain...the tgr brain trust will determine the success or failure of this sram product. so we've got that going for us.

at least sram is making an effort in mtb R&D investment, arguably. the vivid air tried to address the heating up issue of air shocks. XX1, while overpriced, did shake up the drivetrain world. etc etc.

no idea if this sram invert fork will eventually be the first truly successful single crown invert, but I look at how Fox has generally just repackaged existing technology (the fact they positioned CTD as some sort of breakthru was a triumph of marketing) and I'm not impressed.

Purists will invariably scoff at the new CTD design, saying it removes a level of customization and fine-tuning available with the current models' collection of individual adjustments. While there may be some truth to that (we'll get to our ride impressions later), CTD's simplified interface takes the guesswork out of the process and will make it easier for the majority of FOX suspension users to extract more performance.

yeah and now the new 36 eschews CTD right? which then makes it desirable, since it's 'CTD Free'.

[raisingarizona13]

[QUOTE=toast2266;4237263]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.

NASA? I think you misspelled it, it's NAYSA, as in the guys that own space.