2018 Racing Rumors

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5/22/2018 10:48 AM

Pull-shocks are like gearboxes - better in theory, but not enough to justify the marketing risk

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5/22/2018 11:04 AM

You can see the yellow ohlins spring, so def not pull shock.

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5/22/2018 11:27 AM

Thanks unskilled, forgot about that. But it falls into the same category if you ask me, complicated, nonstandard designs that cause issues when it comes to time to service. Even brands like BOS and in the end even Ohlins have servicing issues here in Slovenia. There are shops that wrench them now, but a few years back you had to send BOS to Germany or France. That's why i'm a diehard fan of Rock Shox, because i can service them cheaply and well nearby.

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5/22/2018 11:46 AM

Wooyek wrote:

Pull-shocks are like gearboxes - better in theory, but not enough to justify the marketing risk

But how are they better in theory? There are issues as to where to put the squishing factor. You can make a pull-spring, but you have to fasten it somewhwere. Easier to grind it down and make it a squish spring. Same goes for air, you can make a vacuum chamber to increase the force by extension, but you can only go so high (1 bar or thereabouts), before you 'run out of steam'. That would require a mighty large piston cross section. So you have to compress the thing, which means longer piston rods, usually even more seals than with push designs, etc.

Also, gearboxes are inherently worse, even theory wise, than the regular chain and sprocket wise. They have about the same amount of losses as a well lubricated standard system in the middle of the cassette (but gain some when you're at the cassette extremes), but you have more bearings in the gearbox, let's say a few more seals (given you have disconnected crank and output sprocket ratios, so you need to seal both) and a ton, granted inactive, but still, gear pairs.

Each of these things adds some inefficiencies to the whole drivetrain, in ideal conditions all of the above have an efficiency of about 99 %. These efficiencies multiply with each other. So for a Pinion gearbox, before you have the final output sprocket, you have say at least 3 seals, at least 4, but more likely around 6 bearings and at least two active gear pairs. Just that nets an efficiency of at most 0,99^9 = ~91 % (4 bearings, 2 gear pairs and 3 seals), if not more. The 99 % efficiency is taken from my engineering classes, which could be a number that's quite high, but logically, 99 % is a great efficiency. That's why gearboxes feel sluggish (TBH haven't ridden one, but i would love to, yet nevertheless the numbers don't lie).

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5/22/2018 1:35 PM

Primoz wrote:

But how are they better in theory? There are issues as to where to put the squishing factor. You can make a pull-spring, but you have to fasten it somewhwere. Easier to grind it down and make it a squish spring. Same goes for air, you can make a vacuum chamber to increase the force by extension, but you can only go so high (1 bar or thereabouts), before you 'run out of steam'. That would require a mighty large piston cross section. So you have to compress the thing, which means longer piston rods, usually even more seals than with push designs, etc.

Also, gearboxes are inherently worse, even theory wise, than the regular chain and sprocket wise. They have about the same amount of losses as a well lubricated standard system in the middle of the cassette (but gain some when you're at the cassette extremes), but you have more bearings in the gearbox, let's say a few more seals (given you have disconnected crank and output sprocket ratios, so you need to seal both) and a ton, granted inactive, but still, gear pairs.

Each of these things adds some inefficiencies to the whole drivetrain, in ideal conditions all of the above have an efficiency of about 99 %. These efficiencies multiply with each other. So for a Pinion gearbox, before you have the final output sprocket, you have say at least 3 seals, at least 4, but more likely around 6 bearings and at least two active gear pairs. Just that nets an efficiency of at most 0,99^9 = ~91 % (4 bearings, 2 gear pairs and 3 seals), if not more. The 99 % efficiency is taken from my engineering classes, which could be a number that's quite high, but logically, 99 % is a great efficiency. That's why gearboxes feel sluggish (TBH haven't ridden one, but i would love to, yet nevertheless the numbers don't lie).

Pull shock like on the cannondale jekyll just have their air chamber on the opposite side of the air piston than the regular setup.
The inefficiency of gearboxes does not come from the number of seals or bearings ( normal transmission have also 4 bearings and 4 seals, 2 of each in the bottom bracket and the freewheel) it comes from the fact that all gears are in mech at all time even if just one set is connected to the output shaft creating friction...

I think the prototype suspension setup is a four bar link suspension with the shock driven by a rocker and link, kind of like a canyon sender

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5/22/2018 2:18 PM

The freehub bearings and seals (in the case of Pinion) remain. I mentioned you decouple the output from the crank, which means you have MORE seals in a gearbox than with a standard BB, which was my point. Same goes for bearings. For a Pinion, you need to support the input shaft relative to the housing, the layshaft relative to the housing and the output shaft relative to the housing and/or the input shaft (since they are concentric). And you also need to support the inactive gears, which spin freely (but produce less inefficiencies due to them not being loaded, like the power path is).

Therefore the constant mesh, while it is a contributing factor, i'd say it is not the significant factor with a gearbox.

As for the proto suspension, i kind of agree. The 'looks like a session' comments should become the standard, since it's the most logical layout - you have all the pivots in a close vicinity to the vertices of the (front) triangle, making a stiff and light frame. The spacing of the rear triangle also makes it relatively stiff. I'm not sure another link set is needed.

For XC, trail and similar short travel bikes a top tube mounted shock could prove to be beneficial, since it should give more space in the triangle for two water bottles. And it'd make sense to avoid mounting the shocks to the downtube for obvious reasons.

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5/22/2018 3:00 PM

Big Bird wrote:

Can't see the shock layout. I'd love to find out it's a pull shock design. It's time.

I’m with big bird, shock technology has come such a long way since back in the day and a pull shock would open up lots of other suspension designs ?

GT should have just made a modern day 27.5/29” lobo full carbon, super low standover height with a pullshock from RS like back in the day and every person in the world would be talking about it like the good ol days

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5/22/2018 3:19 PM

Is that a wishbone thing driving the shock between the swingarm and rocker?

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5/22/2018 4:58 PM

metadave wrote:

Is that a wishbone thing driving the shock between the swingarm and rocker?

I hope not, it could just be a jerry rigged mud guard to keep stuff off of the shock and linkage.

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2017 Specialized Stumpjumper FSR expert 29er
2015 Specialized Camber Comp Custom Build

5/22/2018 6:34 PM

Not to beat a dead horse in the wrong forum but...

Pull shocks are superior. Here's why.

Imagine that your shock absorber is a piece of rope. If you try to compress it like a "standard" shock, it wants to deform to the side, not compress. So in a "standard" frame one has to design in extra stiffness into the frame to keep the shock compressing in a straight line. More stress on the frame, seals and mounting bushings.

Now imagine that your piece of rope is a pull shock. The harder you actuate the shock, the more it just wants to be straighter. Frames can be made lighter because they don't have to take care of keeping the shock in line and there's less friction and thus wear on the seals and bushings.

Back in the days of the LOBO and the Lawill Schwinns, I don't recall Rock Shox having any issues with the shocks. Our shop never had to send back a blown one that I recall. Before enduro blew up, a friend at Rock Shox said they were working on a new generation of pull shocks, but that project was sidelined by more enduro products. Now a little bird says that the new pull shock might just be on the way.

Now to dust off that old, pre enduro, full size frame drawing of a high pivot pull shock DH bike and redraw it to fit 29" wheels. Bring 'em on Rock Shox!

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5/22/2018 9:30 PM

While there is a point in the rope analogy I can't help but think that if pull shocks are so vastly superior, why aren't they used in racing? Both motorcycle and car racing.

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5/23/2018 8:07 AM
Edited Date/Time: 5/23/2018 8:33 AM

The present Commencal DH Supreme uses a pull linkage arrangement.

Pull linkage good, pull shock I’m undecided as yet, but it is my belief because of limited usage the forward development of the technology will be limited & not embraced by the masses.

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5/23/2018 8:17 AM

we're definitely not working on pull shocks.

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5/23/2018 8:32 AM

Few minutes of Photoshop later...

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5/23/2018 8:34 AM

The boys at Ride.io spotted Koas Seagrave on a 29-inch Transition DH bike:

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5/23/2018 8:59 AM

Dave_Camp wrote:

we're definitely not working on pull shocks.

but a guy on the internet knows someone who knows someone who says you are. i'm sure he's correct.

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5/23/2018 9:27 AM

Actually it would only make sense for your post to be true.

Though Dave probably does not post on this forum in an official role, any public communications about future products from a company should be deny deny deny, at least on the record. It's off the record where rumors start.

It doesn't mean Big Bird's statement is true (and that Dave is only covering it), but regardless if RS is in fact making a pull shock or not, this is exactly the scenario of how rumors about (a real) one would start and become more public.

qblambda if you're making that silhouette any more detailed, the bottom link (there should be one connected to the vertical one) should be quite long for the shock to have full stroke.

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5/23/2018 9:37 AM

Developing a complete pull shock chassis for a single frame is a big project for little return in sales. I'm impressed Fox and Cannondale made it happen (DYAD).


We are not working on pull shocks. Imagine how stoked everyone would be if there was a pull shock 'standard'. haha

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5/23/2018 9:56 AM

Primoz wrote:

Actually it would only make sense for your post to be true.

Though Dave probably does not post on this forum in an official role, any public communications about future products from a company should be deny deny deny, at least on the record. It's off the record where rumors start.

It doesn't mean Big Bird's statement is true (and that Dave is only covering it), but regardless if RS is in fact making a pull shock or not, this is exactly the scenario of how rumors about (a real) one would start and become more public.

qblambda if you're making that silhouette any more detailed, the bottom link (there should be one connected to the vertical one) should be quite long for the shock to have full stroke.

ha. pretty sure dave would not have come on here to deny pull shock development if rockshox was actually doing pull shock development. completely different than "deny deny deny" if he was directly asked. i'll take dave's word over conspiracy theory

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5/23/2018 9:57 AM

I can definitely see your point and agree with it.

Though regarding the Cannondale thing, it's not all that uncommon. Granted, the last two generations of Scott's Genius bikes (and all Sparks as well) has used relatively unchanged shock in the grand shceme of things, but they were nevertheless custom. Then you have the pullshocks of the previous two generations of Genius frames. And the wholly custom (but still squish) shock for the Ransom (the Equalizer). Then the current custom Fox shocks for Cannondale, the custom Trek shocks (both the Reactive valving and the current through shaft designs). And let's not forget about Specialized (And yes, i know there's a ton more of these cases left.)

Olivier Bossard made an interesting comment about how these days nobody develops a complete rolling chassis platform, like they did in the Nico times with Sunn. But i guess there just isn't enough money to do it solely for racing and you can't sell completely custom stuff to the masses, at least because of servicing reasons.

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5/23/2018 10:39 AM

Thru Shaft shocks are the future!

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5/23/2018 4:13 PM
Edited Date/Time: 5/23/2018 4:14 PM

With the news that Rock Shox is out on pull shocks, we're going in 100%!

Noah Sears
MRP (Mountain Racing Pullshocks)

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MRP - Brand Manager
Pivot Cycles - Team Rider

5/23/2018 5:18 PM

NoahColorado wrote:

With the news that Rock Shox is out on pull shocks, we're going in 100%!

Noah Sears
MRP (Mountain Racing Pullshocks)

+100

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5/23/2018 6:44 PM

qblambda wrote:

Few minutes of Photoshop later...

I'm thinking the upper link goes through the seat tube and compresses the shock from the front. The rear end of the shock is attached to the chainstays. It's not a dual short link system, but a Horst Link with the chainstays/main pivot possibly on the bb.

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5/23/2018 9:51 PM

What is the point of the vertical piece then? Plus if you look closely at the photo, you can see the vertical link gets thicker or bigger towards the bottom, where the shock eyelet is. There is no such thing on the chainstay visible.

Plus that having a link on the chainstay on such an angle would put immense stresses on the chainstay (with it being just a link between two pivots, it's in fact mainly a 'pull link' only, plus the torsional stresses - having the shock mounted to it would cause severe bending stresses, making the part heavier to carry to loads).

And given the top link and shock orientation, the top link would have to be bent upwards quite a lot to get the ETE of the shock in. That would mean the shock would be mounted in both ends (by the chainstay and by the rocker) at very shallow angles, which is never a good thing for force transfers (you would be having massive axial forces in all links when squishing the shock).

It's possible of course, it just doesn't make sense.

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5/23/2018 11:40 PM
Edited Date/Time: 5/24/2018 3:29 AM

qblambda wrote:

Few minutes of Photoshop later...

slimshady wrote:

I'm thinking the upper link goes through the seat tube and compresses the shock from the front. The rear end of the shock is attached to the chainstays. It's not a dual short link system, but a Horst Link with the chainstays/main pivot possibly on the bb.

I was wondering the same, like a bigger rocker linkage til I noticed the front shock mount is actually attached on the downtube. You can see it bulky there, looking like the previous generation of Demo.
And like Primoz said, that vertical link would have no sense then. Some pivots might be hidden around the bottom bracket...

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5/23/2018 11:49 PM

Sorry, I ditched my photoshop talents for that one. It might be that way

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5/24/2018 1:49 AM
Edited Date/Time: 5/24/2018 1:50 AM

qblambda wrote:

Sorry, I ditched my photoshop talents for that one. It might be that way

Yup, you're right guys. Having two links scissoring the shock forward (one running from the seatstays/upper link to the shock, another from the shock to the BB area) when the wheel moves upwards makes sense. I didn't notice the forward shock mount until you mentioned it.

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5/24/2018 1:07 PM

FWIW, the Sender has an almost exactly the same layout.

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5/25/2018 3:53 AM

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