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flag Will-narayan
Posted: Dec 14, 2023 at 14:13 Quote
R-trailking-S wrote:
Will-narayan wrote:
Interesting, but with a concentric idler do you get some antisquat ?

If the idler is concentric, then the antisquat is mostly determined by the pivot location. Likely that frame has around 130% juding by the picture. Antisquat is determined by just drawing a line from the rear contact patch through the main pivot and determining the height at which that line intersects a vertical line through the front axle and comparing that height to the height of the system center of mass. Then depending on the gearing, the chain pitch angle from the cassette to the idler can add or reduce antisquat. On a concentric idler, if the rear cassette gear is bigger than the idler, the chain adds antisquat, usually as much as 30% difference.

This one is pretty firm in all gears

I'm really not sure. I tried doing a similar bike in Linkage, except with a pivot instead of flexible stays as linkage can't do this, and I end up with an AS going from -70% on 10T to +105% on 51T.
But maybe it's a limitation of Linkage.
flag R-M-R
Posted: Dec 14, 2023 at 19:58 Quote
mrti,

Great looking bike and I'm impressed by your work, especially the fully boxed chainstays. Concerns about the kinematics, though.

mrti wrote:
- The antisquad is between 97 and 114% depending on gear and rear wheel compression. I admit that I will make sacrifices in kinematics for aesthetics, Since I am a designer and not an engineer, this just seems to be my nature.

Pedaling anti-squat is rarely such a discrete number, as it varies with sprocket combination, position in the travel, and the rider's centre of mass (different riders and different postures for the same rider).

Simulating this design, no sprocket combination produces 114%, even at full droop (0% sag). I can produce 114% with a 51 tooth cassette sprocket and the Linkage default centre of mass location, but only at full droop. The Linkage default CoM is too low for most riders and anti-squat is most relevant at a more realistic sag position. There's no industry standard for this, unfortunately; I favour a position pretty deep in the travel, as that's the suspension state on a steep climb, when most people are most concerned about pedaling performance.

The motion rate curve (or leverage curve, if you prefer) is also a concern beyond about 120 mm of travel.

Once again, it's a great looking bike and I hope we can help create a ride quality that matches the looks!
flag mrti
Posted: Dec 14, 2023 at 20:53 Quote
I am wondering how you get anything above 120mm, as the frame only has ~114mm of rear travel.
flag R-M-R
Posted: Dec 14, 2023 at 21:35 Quote
I didn't know how much travel it has, so I allowed the model to move through a whole lotta travel. If 114 mm is what it has, then all's well ... with the motion ratio curve. Would still recommend higher pedaling anti-squat, especially for the smaller sprockets.
flag Will-narayan
Posted: Dec 15, 2023 at 2:42 Quote
Again, unless my attempt to emulate your geo in linkage is wrong (or linkage makes a mistake or is not programmed to handle it this way), I think the idler should not be concentric, to get a good 110-140% AS value over the whole range, the idler should be moved downward and rearward by about half its diameter, like most high idler bikes.
If you intend to 3D print the yoke parts that would not be much of an issue to modify.
flag DanAlmberg
O+
Posted: Dec 15, 2023 at 8:42 Quote
Hi so havent bulid any bikes latly but now winter is here in Sweden i desigend & build this conversion kit. Took me a week from fideling with it till i was on the mountain with it. Really fun and super scary to ride ofpist on the local DH tracks Smile
And i put it on my mates Curtis


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flag mrti
Posted: Dec 15, 2023 at 20:23 Quote
Thanks for all the comments to my bike, I would like to address some of them, as it seems that some of you might not understand my approach.... and rightfully so, as it might not be the most obvious one.

First: I am a designer, not an engineer. That does not mean that I do not understand all the points that were brought up regarding kinematics, but for me the visual appearance of the frame are on the very top of the list. I wanted to create something that is as simplistic as possible. and therefore I set myself a couple of boundaries, that are different than the ones an engineer would set for himself.

- the concentric idler - not ideal
- the lower linkarm around the BB- not ideal for many reasons.
- the upper shock mount concentric with the idler and the main PP - again, not ideal.
- even using a high pivot layout on a very short travel bike - very much questionable
- the flexstays - controversial for many people
- the frame material for a short travel "light weight" bike - far from ideal

So from the start I was well aware that I would have to make compromises on the kinematics. However the one high pivot bike that have some experience on is the Norco Range, which uses a concentric idler and is far from a bad bike! At least in the lower gears, where it matters the most for me, the level of antisquad is quite similar.

Maybe give it a try and understand my approach and please don´t get mad, because some guy on the internet designed the bike that he wants and not the bike that some of you think is the best.
flag Grumposaur
Posted: Dec 16, 2023 at 1:41 Quote
mrti wrote:
Thanks for all the comments to my bike, I would like to address some of them, as it seems that some of you might not understand my approach.... and rightfully so, as it might not be the most obvious one.

First: I am a designer, not an engineer. That does not mean that I do not understand all the points that were brought up regarding kinematics, but for me the visual appearance of the frame are on the very top of the list. I wanted to create something that is as simplistic as possible. and therefore I set myself a couple of boundaries, that are different than the ones an engineer would set for himself.

- the concentric idler - not ideal
- the lower linkarm around the BB- not ideal for many reasons.
- the upper shock mount concentric with the idler and the main PP - again, not ideal.
- even using a high pivot layout on a very short travel bike - very much questionable
- the flexstays - controversial for many people
- the frame material for a short travel "light weight" bike - far from ideal

So from the start I was well aware that I would have to make compromises on the kinematics. However the one high pivot bike that have some experience on is the Norco Range, which uses a concentric idler and is far from a bad bike! At least in the lower gears, where it matters the most for me, the level of antisquad is quite similar.

Maybe give it a try and understand my approach and please don´t get mad, because some guy on the internet designed the bike that he wants and not the bike that some of you think is the best.

In that line of thought you could also drop the idler and use an O-chain?

Anyway who's mad? I'm reading some pretty well founded feedback. And you dont have to do anything with that feedback, it is your bike design. But still interesting to discuss it.
flag MTBLegend92
Posted: Dec 16, 2023 at 5:00 Quote
mrti wrote:
Thanks for all the comments to my bike, I would like to address some of them, as it seems that some of you might not understand my approach.... and rightfully so, as it might not be the most obvious one.

First: I am a designer, not an engineer. That does not mean that I do not understand all the points that were brought up regarding kinematics, but for me the visual appearance of the frame are on the very top of the list. I wanted to create something that is as simplistic as possible. and therefore I set myself a couple of boundaries, that are different than the ones an engineer would set for himself.

- the concentric idler - not ideal
- the lower linkarm around the BB- not ideal for many reasons.
- the upper shock mount concentric with the idler and the main PP - again, not ideal.
- even using a high pivot layout on a very short travel bike - very much questionable
- the flexstays - controversial for many people
- the frame material for a short travel "light weight" bike - far from ideal

So from the start I was well aware that I would have to make compromises on the kinematics. However the one high pivot bike that have some experience on is the Norco Range, which uses a concentric idler and is far from a bad bike! At least in the lower gears, where it matters the most for me, the level of antisquad is quite similar.

Maybe give it a try and understand my approach and please don´t get mad, because some guy on the internet designed the bike that he wants and not the bike that some of you think is the best.

Heck. I am an engineer and I don't focus much on most of that stuff too. It's a bike, not a rocket, and I build them for fun, not so I can do more work outside of work. Bikes that look cool/unique get a lot more attention and oogling at the trailhead than bikes that just hit certain metrics.
flag R-M-R
Posted: Dec 16, 2023 at 11:05 Quote
mrti wrote:
Maybe give it a try and understand my approach and please don´t get mad, because some guy on the internet designed the bike that he wants and not the bike that some of you think is the best.

No one is mad. Read over the feedback again and notice how much positivity and support is being given. We're all in this thread because we do, we love, or we are impressed by those who take the initiative to design and/or make bikes. We all need to recognize that our own opinions and preferences are a sample size of one, and it's possible these opinions and preferences are outliers. Maybe there are opportunities to improve the bikes via crowdsourced - often unsolicited - feedback. Might as well at least consider it, then, if you choose, you can discard it - your bike, your rules!

The harshest and most unfair criticisms of your design have been from you!

• the concentric idler - not ideal
I disagree. Concentric pivots are a great way to minimize frame fittings and hardware, when appropriate. For example, compare the slightly more efficient design of Giant's Maestro vs. Banshee's similar KS-Link.

• the lower linkarm around the BB- not ideal for many reasons.
Nothing wrong with that. Specialized uses it on DH bikes, among several other applications. Packaging can be a challenge and it helps to use a press-fit BB to maximize pivot bearing offset, but that's not insurmountable.

• the upper shock mount concentric with the idler and the main PP - again, not ideal.
Love it.

• even using a high pivot layout on a very short travel bike - very much questionable
True. My opinion, in terms of performance, is that if you're going to take on the downsides of the indirect drivetrain for a short-travel application, it's ideal to have an extremely rearward axle path and extremely high pedaling anti-squat. The short travel facilitates these things without excessive rear-centre growth or pedal kickback. But then you might lose the concentric mounting points and aesthetic.

• the flexstays - controversial for many people
Love it. Big fan of flex pivots, especially when there's so little movement. You could extend the flex zone to reduce the strain, but the movement is minimal in this design. You might consider putting the flex zone on the upper tubes and moving the caliper to the lower to reduce brake squat, if that wouldn't create a packaging fiasco.

• the frame material for a short travel "light weight" bike - far from ideal
Weight is overrated.
flag Will-narayan
Posted: Dec 16, 2023 at 12:41 Quote
The Norco Range indeed seems to have a concentric idler (I mean it looks like it but I thought there would be a twist), those I found in linkage web library have weird AS values (or similar to your geo) so I don't know, either Linkage is missing something, or Norco made the Range so that there's some decent AS in easiest gears to climb and no AS and minimum KB in bigger gears when you hit jumps and compression, I don't know, I'm no engineer either, just trying to understand things.
flag R-M-R
Posted: Dec 16, 2023 at 14:20 Quote
Pedaling anti-squat on the Range is slightly higher, but similar.

Reducing the size of the idler sprocket will increase the pedaling anti-squat.
flag ktm87
O+
Posted: Dec 18, 2023 at 11:23 Quote
Here is a frame I am currently working on. Pretty much a modified Pivot Mach 4. Made changes to geo and slight tweak to suspension and added a pinion gearbox. 120mm rear 130mm front. First frame will be a steel front triangle and machined aluminum rear end. But want to make a aluminum lugged one with carbon tubes next. Still a little ways to go on design side before I start machining but 3d printing full size proto at the moment to test fitment.

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3d print proto to test assembly

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flag EarninTurns
Posted: Jan 26, 2024 at 21:29 Quote
Fork Dimensions - Where do you all find them? I'm hoping to model a pike.

I found some 3d Models on GrabCad and a few other spots but can't find the source spec to double check. The dimensions I'm looking for are the stanchion CL to stanchion CL and the crown offset. Looks like the crown is an 11.5mm offset and the overall offset is 51. As modern forks are now 44, would the crown still be accurate?? A2C on a 150mm pike is 561 so that's another issue but easy enough to mod.
Hoping someone can slap the actual fork dim drawing in here that I can't seem to find.
I found some fox dimension drawings that weren't exactly what I was looking for but a lot closer. https://www.ridefox.com/fox17/help.php?m=bike&id=805

This is the best looking model I could grab but can't find anything to double check the dimensions:
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