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flag NickBosshard
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Posted: Jul 10, 2019 at 13:51 Quote
First post for me but been reading and watching a lot and I have to say hats off to you guys for all those awesome builds!

Now it's time for me to build one and before I'm getting to much into the design I thought I might get some opinions from you guys on what I've done so far. The plan was a progressive 29er trailbike with similar travel numbers to my exisiting Pivot Mach 5.5 to have something to compare it to. As a reference, I'm 176cm (5'9'') tall.
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Rough frame shape in Linkage to get a feel, final clearance check and design will probably be done in Blender as I know my way around it quite well.
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Intending on running it with a coil shock, but might go with a MRP progressive spring, some insights on the progression of lev.-ratios for coil shocks would be welcome.
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Antisquat above 100% for a good portion of the travel in lower gears...
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...and all below 100% in the higher gears for going downhill, I'm not much of a sprinter.
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For building it, I plan to make it from chro-mo tubing and fillet braze it with brass. The bikeshop I work at is going to expand and get a framebuilding shop this autumn which I'll be able to use.
flag R-M-R
Posted: Jul 10, 2019 at 14:20 Quote
NickBosshard wrote:
First post for me but been reading and watching a lot and I have to say hats off to you guys for all those awesome builds!

Now it's time for me to build one and before I'm getting to much into the design I thought I might get some opinions from you guys on what I've done so far. The plan was a progressive 29er trailbike with similar travel numbers to my exisiting Pivot Mach 5.5 to have something to compare it to. As a reference, I'm 176cm (5'9'') tall.

Rough frame shape in Linkage to get a feel, final clearance check and design will probably be done in Blender as I know my way around it quite well.

Intending on running it with a coil shock, but might go with a MRP progressive spring, some insights on the progression of lev.-ratios for coil shocks would be welcome.

Antisquat above 100% for a good portion of the travel in lower gears...

...and all below 100% in the higher gears for going downhill, I'm not much of a sprinter.

For building it, I plan to make it from chro-mo tubing and fillet braze it with brass. The bikeshop I work at is going to expand and get a framebuilding shop this autumn which I'll be able to use.

Geometry
Looks like you based it on a Large Mach 5.5. Keep in mind stack affects reach, so it will be between a Large and XL Mach 5.5. Not unreasonable for someone your height, especially with the steep seat tube angle. The combination of long reach and slack head angle will make it feel a lot longer on tight trails. If you want to make it more agile, go steeper on the head angle, don't reduce reach.

Anti-squat
- Your centre of mass looks a bit low, so anti-squat will be a touch higher than your current numbers, but still below current averages. I favour very high anti-squat.
- Is your model in "horizontal mode"?
- You must be using an idler if your pedal kickback is so low. If you're using an idler, why not use more anti-squat, since pedal kickback will be nearly zero?

Brake squat
It's high. Consider adding mounts for a floating brake to allow you to incorporate this later, if you choose.

Leverage
- Average: Looks good.
- Curve: For a coil, more progressivity is better, but there's only so much you can do without a shock link. I recommend a shock with position-sensitive damper, such as an EXT Arma / Storia v3 or Fast Fenix.

Overall packaging
I like it. Rear triangle is compact, seat tube isn't compromised, shock is accessible, room for a water bottle - nicely done.
flag NickBosshard
O+
Posted: Jul 10, 2019 at 16:23 Quote
Geometry wise I deliberately went a bit extreme especially compared to my medium Mach 5.5 (445mm reach) as I can always make another front triangle if it doesn't quite work, probably gonna make a rough prototype just to ride and test before the final version.

R-M-R wrote:
Your centre of mass looks a bit low, so anti-squat will be a touch higher than your current numbers, but still below current averages. I favour very high anti-squat.

Thanks for pointing out the COG. height! Anti-squat is deliberately somewhat low as this bike probably won't see a lot of climbing.

R-M-R wrote:
Is your model in "horizontal mode"?

Please explain, I'm still kinda new to suspension design and working with Linkage.

R-M-R wrote:
You must be using an idler if your pedal kickback is so low. If you're using an idler, why not use more anti-squat, since pedal kickback will be nearly zero?

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No, not using an idler, trying to keep it simple. Now with the updated linkage(to get proper anti-squat with the new COG.) it's a bit higher but still low. Also a reason why I prefer the lower anti-squat

R-M-R wrote:
Brake squat
It's high. Consider adding mounts for a floating brake to allow you to incorporate this later, if you choose.

Kinda fixed that by playing around with the rest Big Grin

R-M-R wrote:
Curve: For a coil, more progressivity is better, but there's only so much you can do without a shock link.

photo

Setteled on an even flatter curve and will probably go with an air shock but might try my progressive coil from my Mach 5.5.

Thanks for the quick, in-depth feedback!
flag R-M-R
Posted: Jul 10, 2019 at 17:55 Quote
NickBosshard wrote:
Geometry wise I deliberately went a bit extreme especially compared to my medium Mach 5.5 (445mm reach) as I can always make another front triangle if it doesn't quite work, probably gonna make a rough prototype just to ride and test before the final version.

I wouldn't call it extreme; just wanted to put it into context.

NickBosshard wrote:
Thanks for pointing out the COG. height! Anti-squat is deliberately somewhat low as this bike probably won't see a lot of climbing.

That's reasonable. More anti-squat will also produce a more rearward axle path, so it can have a dual benefit. Fears of pedal kickback interfering with suspension function are greatly exaggerated and can largely be addressed with a low-engagement hub.

NickBosshard wrote:
Please explain, I'm still kinda new to suspension design and working with Linkage.

There's a checkbox in the upper right for "horizontal mode". With it unchecked, the rear suspension curves are calculated with the suspension in pitch (rear compression only); with it checked, the curves are calculated with the bike in heave (both ends simultaneously).

NickBosshard wrote:
No, not using an idler, trying to keep it simple. Now with the updated linkage(to get proper anti-squat with the new COG.) it's a bit higher but still low. Also a reason why I prefer the lower anti-squat

Ah, I see now. I mistook the 32/10 kickback curve for 32/50. It's far too low for 32/50, hence my assumption you were using an idler, even though the bike image didn't show it. Now that I realize the curve was for 32/10, it makes sense.

NickBosshard wrote:
[Re: brake squat] Kinda fixed that by playing around with the rest Big Grin

How so?

NickBosshard wrote:
Setteled on an even flatter curve and will probably go with an air shock but might try my progressive coil from my Mach 5.5.

A progressive coil will help a little. Might as well try it, since you already have one.

NickBosshard wrote:
Thanks for the quick, in-depth feedback!

Salute
flag Kustomango
O+
Posted: Jul 12, 2019 at 5:51 Quote
Amazing work as always.

Just wondered if anyone has been building with the new Trunnions shocks in mind? And if so, has anyone got measurements for the mounting widths and bearing choice ? Tried to find them through shock manufacturers but so far no luck.
flag scotteh
O+
Posted: Jul 12, 2019 at 7:07 Quote
NickBosshard wrote:
Thanks for the quick, in-depth feedback!
RMR is the real MVP. By far the most educational and awesome active user of PB.
flag ktm87
O+
Posted: Jul 12, 2019 at 7:20 Quote
scotteh wrote:
RMR is the real MVP. By far the most educational and awesome active user of PB.


^^^^ this RMR has helped me a ton. knows his stuff
flag jibb
Posted: Jul 12, 2019 at 8:05 Quote
Couldn't agree more serious depth of knowledge and awesome enough to give time towards others tup
flag Kustomango
O+
Posted: Jul 12, 2019 at 9:33 Quote
R-M-R wrote:
Leverage
- Average: Looks good.
- Curve: For a coil, more progressivity is better, but there's only so much you can do without a shock link. I recommend a shock with position-sensitive damper, such as an EXT Arma / Storia v3 or Fast Fenix.

I didn’t realise the Storia was position sensitive? I though it was still shims and a secondary piston for the HBC. Would be amazing to see some more info/explanation on this if you have it.
flag Arnoodles
Posted: Jul 12, 2019 at 10:56 Quote
Kustomango wrote:
R-M-R wrote:
Leverage
- Average: Looks good.
- Curve: For a coil, more progressivity is better, but there's only so much you can do without a shock link. I recommend a shock with position-sensitive damper, such as an EXT Arma / Storia v3 or Fast Fenix.

I didn’t realise the Storia was position sensitive? I though it was still shims and a secondary piston for the HBC. Would be amazing to see some more info/explanation on this if you have it.
Seconded.

I was under the impression the Millyard shock was essentially the only position sensitive mountain bike shock out there.
flag EuanBisset145
Posted: Jul 12, 2019 at 11:37 Quote
History forgets shocks like the old dhx 5 air which was position sensitive. If we look at our motocross cousins most shocks on the market are operating using both position and speed sensitive elements. A hydraulic bottom out mechanism is classed as a position sensitive element due to the fact that it only operates in say the last 20-30% of travel.
flag R-M-R
Posted: Jul 12, 2019 at 17:28 Quote
Aww, thanks y'all. Fab

EuanBisset145 wrote:
History forgets shocks like the old dhx 5 air which was position sensitive. If we look at our motocross cousins most shocks on the market are operating using both position and speed sensitive elements. A hydraulic bottom out mechanism is classed as a position sensitive element due to the fact that it only operates in say the last 20-30% of travel.

Yep, this man knows his shocks. The Arma and Storia v3 have a hydraulic bottom-out. Some Manitou forks have had this, my 2007 Marzocchi 888 had a hydraulic bottom-out, some shocks (not sure about on bikes) use a tapered chamber that allows a decreasing amount of bypass. The MRP Ramp Control is a combination spring + position-sensitive damper, as are the foam volume reducers recently coming to market. Lots of ways to accomplish it! Some are more effective than others, of course, but always a sound concept.
flag NorCalNomad
O+
Posted: Jul 13, 2019 at 13:23 Quote
EuanBisset145 wrote:
History forgets shocks like the old dhx 5 air which was position sensitive. If we look at our motocross cousins most shocks on the market are operating using both position and speed sensitive elements. A hydraulic bottom out mechanism is classed as a position sensitive element due to the fact that it only operates in say the last 20-30% of travel.

I loved my DHX air on my old Marin Quake. Helped make that bike feel bottomless.
flag joose
Posted: Jul 29, 2019 at 19:42 Quote
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Critique and ask questions. Want to make sure I'm not missing anything before getting too invested. Took some inspiration from the o.g. Corsair konig. This frame is meant for good ole xc single track, shitty washed out fire roads and the such.
flag R-M-R
Posted: Jul 29, 2019 at 23:52 Quote
joose wrote:
Critique and ask questions. Want to make sure I'm not missing anything before getting too invested. Took some inspiration from the o.g. Corsair konig. This frame is meant for good ole xc single track, shitty washed out fire roads and the such.

Quick thoughts:

Note: I prefer the "Horizontal mode" setting in Linkage (top left).

1. Those pivots may be too close to each other and the tire to fit bearings and housings.
2. The minimal vertical offset between pivots will reduce stiffness / require additional material.
3. Most people prefer a more progressive leverage curve.
4. Trail is low. Hopefully, the fork offset in your model is high, which would give you room to increase trail with an extremely low offset fork.
5. Interesting blend of long (for XC / gravel) front-centre and steep head angle. Should be good for the intended purpose of XC and fire roads.
6. The short rear-centre will create a more rearward weight bias than most bikes, especially on less steep descents, which is probably this bike's intended purpose.
7. It would be nice to see the anti-squat curve (using horizontal mode, the intended chainring size, and a slightly higher centre of mass).

The pivot placement may send you back to the drawing board. Ensure you have enough room for stout bearings and housings before bothering with anything else.

 


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