[Crispy01]

Hi, a while ago there was a thread about Ti flex plate dual suss bikes, and why the isnt any with a resonably placed pivot.

Now I have made one. Only moving parts on the frame are the shock.

I set the plates up so it was neutral at 30% sag. With the pressure required to push out the travel it is pretty stiff. I can only get about 70% travel doing bunny hops in the car park. Have not ridden it on the trails yet. Race this weekend to test it out.

Stuff all rear end twisting flex.
I love it so far

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[Eric Malcolm]

Nice - Passive springing.

How much designed travel do you have there?

Eric

 

[HoffmanBikes]

This is neat. Please do give a ride report.

 

[Crispy01]

Hi Eric, 110mm travel. But cant measure it...

 

[adarn]

Why did you go this route instead of using pivots? Looks neat...

 

[Crispy01]

Adarn, cause it is different. And I can haha. Cant wait until sundays race to try it out properly.

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[jcaino]

Pretty cool.

 

[G-reg]

How much is the air spring in the shock used? Would be cool if you could use just a pure damper, ie. a coilover without a spring.

 

[Crispy01]

Hi G-reg, this is my main problem atm. To get a reasonable amount of travel with a short spring it was welded at 30% of the travel. To push that out all the way so it would sit at 0% I need over 250 psi in the shock. Then I am only getting about 15% sag.
Now with the flex plates and the air shock working together it ramps up quickly. Like I said doing a bunny hope and landing hard I can at most get through 70% of the travel.
I think the seat stays are absorbing alot of the force. There may be another plate going in at the top of the seat stays to give them more movement... see how it rides for a while first

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[Crispy01]

Sorry double post

 

[Crispy01]

Well race today was a DNF, not because of the frame. But because the derailleur that was guiding my single cog on the back moved over and the screw was not long enough to get it back... ohh well. Besides that I set a pb on the track by 40 sec whilst I am fighting the onset of a chesty cold. So not bad.
Looking at the shock it seams I only at most used 60mm of travel. The track is know as technical and duallys are usually the prefered race bike. Pedals awesome. Tracks perfect, feels like 100mm of travel.
But I think this bike will be set up as a fun bike with gears for hitting rough and jumpy trails and leave my rigid single speed for xc racing because... idk. I feel like it haha. Maybe because I prefer the cred of being a hard bastard and not a clever #$*@ at the races.

But I think I may modify the seat stays and install some ti flex plate near the top to aid in reducing the force to move through the travel.

Any ideas??

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[TrailMaker]

Let's see;

If I read you right, you are looking to increase compliance of the rear end, i.e. it is too stiff? Why not just shave down the existing plates until you are happy? I wonder if, choosing a very specific shaping profile, you might introduce some amount of progressive spring rate?

 

[sbitw]

Impressive.

In the photos I've seen of a Funk (?) with dual flex plates, the upper plate was fixed to the frame at the bottom of the plate, opposite to what you've got. Here it looks like the upper flex plate is going to try and spread the chain stays and seat stays as the shock compresses. I'm no engineer, so probably way off base, but do you think that could be contributing to the reduced travel?

 

[hmcleay]

I think the majority of your stiffness would come from the lower plate, due to its shortness. If you could make that plate thinner (or narrower), then you should get some additional compliance.


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[Gilarider]

Looks like a fox shock? A large volume air can should screw right on there and make it less progressive. From there you could send the shock for a tune of the compression damping.

Can you actually bottom out the shock if you let all the air out or will it not flex enough?

 

[PeopleForScience]

I imagine that a company like push could take your shock and tune it with input from you on frame and linkage geometry and designed leverage rate then get your preferred ride feel and make a perfect shock.

Wow that is a run on sentence if I have ever seen one.

 

[coconinocycles]

Ask Brendan from Siren……
- Steve Garro, Coconino Cycles

 

[Crispy01]

Sorry for the reply, been working on money earning stuff....

Firstly thanks for the input, some of these ideas have got me thinking alot

Ok, Trailmaker, I am pretty cautious about cutting into/out voids or slimming down the plates as that will create higher stress points along the plates and may accelerate fatigue in those areas... if you know what I mean. Keeping it parallel and an equal amount flex along the plate.

sbitw, Thanks If you knew of any photo's of something along those lines it may help. I cannot find anything out there with dual flex plates??
The reason I went with the seat post cluster mount is to fit a bottle in for xc rides, the amount the stays open up would be no more than 20mm at bottoming out... there should be more than enough flex in over 800mm of 20mm stays to accommodate that without getting over 50% of the yield, or contributing to much to the ramp up.

hmcleay, Before I welded in the seatstays I could move the chainstays through the full travel with about 15kg of force, so I do not think this is the cause of the problem.

Gilarider, Thanks, This is my best be so far I think, with the air out and myself bouncing on the seat I can get it to withing 5mm of bottoming out, I have got my LBS chasing up an up sized air can for me, would you know specifically what I need? It is a float rp23.

PeopleForScience, Thanks, I think this will be me second pursuit if the first fails.

coconinocycles, Can you please elaborate?

Thanks again for everyone's input
Now back to crazy inventions that may make money

 

[sonic reducer]

I am pretty cautious about cutting into/out voids or slimming down the plates as that will create higher stress points along the plates and may accelerate fatigue in those areas... if you know what I mean. Keeping it parallel and an equal amount flex along the plate.

its never going to have an equal amount of flex on the entire plate with it being straight due to leverage points. seems to me like you would want to isolate the fatigue areas towards the middle, away from the HAZ of your welds? say with a very slight, fair curve. I dunno, not an engineer. for instance many car/truck leaf springs have shape to them to better distribute the flex over the entire spring. not apples to apples of course...

sweet project!!!