Does anyone have expertise/ insight on bearing loads? I made some inquiries with Enduro Bearings but they are unable to help (assuming due to liability issues)
I posed this question: I have an intense tracer 279 that uses these: https://cycling.endurobearings.com/collections/suspension-bearings/products/63800-llu-max-bo for the trunion side eyelet which each has a static load rating of 340lbf so with two bearings that brings you to 680lbf. This force would be exceeded at just past 50% of shock travel for my 500lb spring (standard on size Large). At full travel, that force would be 1280lbf.
I've looked at other bearings used such as the 6900 series on the fox eyelet bearing kit (2 bearings) and each is listed at 477lbf. So again that's 954lbf. On a DH shock (75mm stroke) and 500lb/in spring you're looking at about 1475lbf at full travel. In a bottom out scenario that force will spike even higher.
Often, the loads at the pivots exceed that experienced at the shock eyelet. There are some bearings with higher load limits available but not by much. My thought is that the loads on the pivots/shock should not exceed the load limit rating of the bearings but it appears that this actually does happen and by a fair margin. It also doesn't seem to be an issue so I'm clearly missing something. But that is making it difficult to design a frame since I can't determine what loads would cause a bearing issue/failure.
I think it's a case of "deal with it" and replace the bearings as needed... All these guidelines and data is relevant for continuous operation and for calculation of bearings that don't get replaced, etc. But we all know we replace bearings more or less on a yearly basis (though mostly due to contamination).
Does anyone have expertise/ insight on bearing loads? I made some inquiries with Enduro Bearings but they are unable to help (assuming due to liability issues)...
Does anyone have expertise/ insight on bearing loads? I made some inquiries with Enduro Bearings but they are unable to help (assuming due to liability issues)
I posed this question: I have an intense tracer 279 that uses these: https://cycling.endurobearings.com/collections/suspension-bearings/products/63800-llu-max-bo for the trunion side eyelet which each has a static load rating of 340lbf so with two bearings that brings you to 680lbf. This force would be exceeded at just past 50% of shock travel for my 500lb spring (standard on size Large). At full travel, that force would be 1280lbf.
I've looked at other bearings used such as the 6900 series on the fox eyelet bearing kit (2 bearings) and each is listed at 477lbf. So again that's 954lbf. On a DH shock (75mm stroke) and 500lb/in spring you're looking at about 1475lbf at full travel. In a bottom out scenario that force will spike even higher.
Often, the loads at the pivots exceed that experienced at the shock eyelet. There are some bearings with higher load limits available but not by much. My thought is that the loads on the pivots/shock should not exceed the load limit rating of the bearings but it appears that this actually does happen and by a fair margin. It also doesn't seem to be an issue so I'm clearly missing something. But that is making it difficult to design a frame since I can't determine what loads would cause a bearing issue/failure.
Primoz has pretty much hit the nail on the head here. The radial/axial load ratings of bearings quoted by the manufacturers are based on continuous 24hr operation over a lifetime, even the static load rating. Generally in rotating machinery design, the output for a calculation is the expected lifetime of a bearing based on operating loads and conditions - depending on the application it's always nice when the output comes out as "inifinte"...however, in my experience (designing heavy duty winch drums and selecting gearboxes for them) bearing failure seems to be much more to do with how they're mounted than anything else e.g. bearing type, arrangement, spacing and accuracy of axial alignment as a function of manufacturing tolerances.
Bearings in an MTB application are an outlier case - for starters they never see a complete rotation which means you're preferentially wearing the balls and groove in one specific quadrant of the bearing. Secondly, it's a wild west in terms of how they're mounted. When it's done well, the location of each bearing relative to the other on its axis will be controlled with a decent degree of accuracy - easily done by machining, almost impossible if fabricating. One of my old frames used to eat through chainstay yoke bearings because the bearing axes for the pivot were totally off. But the biggest killer is dirt and water ingress. The water washes away the grease and what grease remains mixes with fine dirt particles to form a cutting compound and grinds the balls/races away, eventually leading to play.
In answer to your question, I think frame manufacturers know that the bearings are going to fail due to contamination before any cyclical loading beyond limit so take some liberties with the rated loads. They are also prioritising weight above bearing life and speccing bigger bearings with higher load ratings for each of your pivots will pile on the pounds quite quickly.
The folks who I personally believe have pivot design nailed are Deviate, who use a combination of labyrinth seals and o-rings to fully seal the cartridge bearings within. Dirt still eventually gets in, but the grease ports allow you to fill the entire void with enough grease to suspend the contaminants more effectively and prolong the inevitable. I owned a Highlander for the best part of two years (in rainy Scotland, ridden 2-3 times a week in the summer and at least once a week in winter) and didn't have to replace a single bearing.
Primoz has pretty much hit the nail on the head here. The radial/axial load ratings of bearings quoted by the manufacturers are based on continuous 24hr...
Primoz has pretty much hit the nail on the head here. The radial/axial load ratings of bearings quoted by the manufacturers are based on continuous 24hr operation over a lifetime, even the static load rating. Generally in rotating machinery design, the output for a calculation is the expected lifetime of a bearing based on operating loads and conditions - depending on the application it's always nice when the output comes out as "inifinte"...however, in my experience (designing heavy duty winch drums and selecting gearboxes for them) bearing failure seems to be much more to do with how they're mounted than anything else e.g. bearing type, arrangement, spacing and accuracy of axial alignment as a function of manufacturing tolerances.
Bearings in an MTB application are an outlier case - for starters they never see a complete rotation which means you're preferentially wearing the balls and groove in one specific quadrant of the bearing. Secondly, it's a wild west in terms of how they're mounted. When it's done well, the location of each bearing relative to the other on its axis will be controlled with a decent degree of accuracy - easily done by machining, almost impossible if fabricating. One of my old frames used to eat through chainstay yoke bearings because the bearing axes for the pivot were totally off. But the biggest killer is dirt and water ingress. The water washes away the grease and what grease remains mixes with fine dirt particles to form a cutting compound and grinds the balls/races away, eventually leading to play.
In answer to your question, I think frame manufacturers know that the bearings are going to fail due to contamination before any cyclical loading beyond limit so take some liberties with the rated loads. They are also prioritising weight above bearing life and speccing bigger bearings with higher load ratings for each of your pivots will pile on the pounds quite quickly.
The folks who I personally believe have pivot design nailed are Deviate, who use a combination of labyrinth seals and o-rings to fully seal the cartridge bearings within. Dirt still eventually gets in, but the grease ports allow you to fill the entire void with enough grease to suspend the contaminants more effectively and prolong the inevitable. I owned a Highlander for the best part of two years (in rainy Scotland, ridden 2-3 times a week in the summer and at least once a week in winter) and didn't have to replace a single bearing.
The grease port also supposedly acts as a flusher pushing the dirt out and replacing it with new grease.
It also probably flies out through the path of least resistance (I have heard a comment it's hardly beneficial in practice...) and mucks up the gap between the two moving parts with lots of grease.
Interestingly the lower link of SC bikes uses a single shield bearing with a gap between the shield and inner ring and a cover over it that also doesn't have any seals. So it's designed to be greased fairly often to push out the dirt. And is anything but sealed (compared to standard sealed bearings and additional labyrinth and rubber seals).
I was thinking about designing suspension for a full size range of bikes to give the same experience to riders of all sizes and weights, and started thinking about leverage ratio. I had an idea that for larger riders, having a slightly lower initial leverage ratio could be good, allowing them to run lower spring rates or shock pressures to achieve the same suspension performance, what are your thoughts? Am I misguided?
I was thinking about designing suspension for a full size range of bikes to give the same experience to riders of all sizes and weights, and...
I was thinking about designing suspension for a full size range of bikes to give the same experience to riders of all sizes and weights, and started thinking about leverage ratio. I had an idea that for larger riders, having a slightly lower initial leverage ratio could be good, allowing them to run lower spring rates or shock pressures to achieve the same suspension performance, what are your thoughts? Am I misguided?
I like the concept, but what if you have a rider that is 6,0 and 160lbs on a large vs 5,10 220lb. Or on a small size 5,5 140lb female vs 5,6 200lb older guy?
Seems like you can open a can of worms where one rider gets a great leverage ratio and then next will struggle. I guess same way it is now, but starting with the best kinematics for the average rider seems like the safest option.
If you really want to go this deep, is it possible to design the frame in base of the best kinematic possible and then offer 2-3 other links and let the rider pick based on their height and weight.
Another thing I've been thinking about are trunnion mount shocks, and traditional shocks. I've seen a lot of people expressing dislike of trunnion mount shocks, and I am not sure why. What disadvantages does trunnion mounting have over traditional eyelets?
Very solid mounting by bolting the shock directly onto the frame with two bolts spaced widely apart.
And that is a disadvantage? Does it restrict suspension movement or cause more load to be supported by the shock leading to needing more maintenance or higher failure rates? More friction in the pivot bearings due to higher loads?
I was thinking about designing suspension for a full size range of bikes to give the same experience to riders of all sizes and weights, and...
I was thinking about designing suspension for a full size range of bikes to give the same experience to riders of all sizes and weights, and started thinking about leverage ratio. I had an idea that for larger riders, having a slightly lower initial leverage ratio could be good, allowing them to run lower spring rates or shock pressures to achieve the same suspension performance, what are your thoughts? Am I misguided?
Raaw does precisely this, for each size you can select a lower leverage or (slightly) higher leverage rocker depending on rider weight:
Thank you, that makes sense. Do you see any benefit of trunnion over standard eyelets?
They created trunnion shocks to have a more compact package. The overall length of the shock is shorter for the same shock stroke. It is therefore easier to fit inside a frame design. No issues there, unless you have a flexi frame that puts a lot of sideloads on the shock.
Here's a question, how do you feel about size specific chainstays or chainstay length in general? I like my chainstays to be about 435mm long, paired...
Here's a question, how do you feel about size specific chainstays or chainstay length in general? I like my chainstays to be about 435mm long, paired with a 480-490 reach, and I'm a 6'1 man with a long torso, but there has been a big push for longer stays for a "more balanced feel". What are your thoughts?
I've had a lot of debates on this.
I've always preferred bikes with shorter rear ends as I think they are more rewarding to ride and flick into corners.
My bike friend who runs an unnamed bike company completely disagrees and thinks longer back ends are better as they give a more balanced weight distribution.
I think the weight distribution thing is nonsense, I think every rider rides in a dynamic centre of gravity and their body position will adjust to suit this and spread the weight effectively.
One thing I observe is when bikes have too long a reach ppl end up lifting the bar height which essentially is the equivalent of shortening the reach in terms of shifting weight loading and correcting the body position.
I've had a lot of debates on this.
I've always preferred bikes with shorter rear ends as I think they are more rewarding to ride and...
I've had a lot of debates on this.
I've always preferred bikes with shorter rear ends as I think they are more rewarding to ride and flick into corners.
My bike friend who runs an unnamed bike company completely disagrees and thinks longer back ends are better as they give a more balanced weight distribution.
I think the weight distribution thing is nonsense, I think every rider rides in a dynamic centre of gravity and their body position will adjust to suit this and spread the weight effectively.
One thing I observe is when bikes have too long a reach ppl end up lifting the bar height which essentially is the equivalent of shortening the reach in terms of shifting weight loading and correcting the body position.
I'm very curious about it all.
Back in the 26" aluminum tank days, my DH bike had pretty short chainstays, while my other bike was the Gen 2 magic link Kona Coilair. This bike had 455mm chainstays, super long for the time. On my local DH track, there was a segment about 3 min long that was fast, rough, and loose. Speed rarely dips below 20 mph. I was noticably faster, in both feel and actual time, on the Kona. This is despite having worse suspension, worse brakes, and cheaper tires on it. I honestly believe its due to the long chainstays.
That being said, my Kona was dual duty as my trail bike, and pedaling it on tame trails, with switchbacks, sharp berms, smaller & lippy jumps, etc. it was downright hard to maneuver around.
I've had a lot of debates on this.
I've always preferred bikes with shorter rear ends as I think they are more rewarding to ride and...
I've had a lot of debates on this.
I've always preferred bikes with shorter rear ends as I think they are more rewarding to ride and flick into corners.
My bike friend who runs an unnamed bike company completely disagrees and thinks longer back ends are better as they give a more balanced weight distribution.
I think the weight distribution thing is nonsense, I think every rider rides in a dynamic centre of gravity and their body position will adjust to suit this and spread the weight effectively.
One thing I observe is when bikes have too long a reach ppl end up lifting the bar height which essentially is the equivalent of shortening the reach in terms of shifting weight loading and correcting the body position.
Back in the 26" aluminum tank days, my DH bike had pretty short chainstays, while my other bike was the Gen 2 magic link Kona Coilair...
Back in the 26" aluminum tank days, my DH bike had pretty short chainstays, while my other bike was the Gen 2 magic link Kona Coilair. This bike had 455mm chainstays, super long for the time. On my local DH track, there was a segment about 3 min long that was fast, rough, and loose. Speed rarely dips below 20 mph. I was noticably faster, in both feel and actual time, on the Kona. This is despite having worse suspension, worse brakes, and cheaper tires on it. I honestly believe its due to the long chainstays.
That being said, my Kona was dual duty as my trail bike, and pedaling it on tame trails, with switchbacks, sharp berms, smaller & lippy jumps, etc. it was downright hard to maneuver around.
Yeah totally if I were racing fast loose tracks or if that was my usual riding I would want longer chainstays. They are stability at the cost of nimbleness and vice versa.
But short stay bikes I find way more fun to ride and flick around.
Most my riding is steep tight & twisty and when I've ridden long cs stay bikes it's taken some of the fun away.
I am experimenting with designs with the help of Linkage software, and while I have been able to get wheel paths and leverage ratios that I want, I am at a loss with anti rise and anti squat. I know what they are, and how they affect the ride, but I don't know how to properly calculate them and manipulate them. Does anyone know of a good resource to learn how to do these calculations? I'm studying engineering in college right now, but none of the classes I have already taken have gone over anything like this.
This is what I have been working on so far. I know it is a bit complicated, but it gives me the progression that I want and the axle path that I want. I would love some feed back on it!
This is what I have been working on so far. I know it is a bit complicated, but it gives me the progression that I want...
This is what I have been working on so far. I know it is a bit complicated, but it gives me the progression that I want and the axle path that I want. I would love some feed back on it!
Great work using the program. Does it seem overly complicated? Are you getting special numbers from this layout you can’t achieve my reducing some of those links.
if you want, you can share the charts, Anti-rise, AS?
It explains how to map out antisquat (depending on where in the travel you are of course, as it's not static), but the TL;DR is, the higher the pivot point,t he more geometric antisquat you have, which is then refined by the amount the chain grows going through the travel to get the final antisquat value - a high pivot bike without an idler will have A LOT of antisquat. A low pivot bike with a high mounted idler will have very low antisquat numbers (effectively pro-squat if the chain is routed above the line from the rear axle to the pivot point).
As for your design, first, you're in the i-Track patent area (idler on a moveable link that is not the swingarm). Second, what is the distance between the two main pivots, centre to centre? When designing bikes clicking around in Linkage is all fine and dandy, but will you be able to package it all together? Or will it require 10 mm outer diameter bearings with very thin walls to make it work which will require 5 mm thick axles and thin section bearings that will all explode the first time you sit on it?
This is what I have been working on so far. I know it is a bit complicated, but it gives me the progression that I want...
This is what I have been working on so far. I know it is a bit complicated, but it gives me the progression that I want and the axle path that I want. I would love some feed back on it!
I find this visualisation really helpful to understand anti-squat and anti-rise.
I just linked the yeti video as it was the first to come up, but he did videos on other suspension types too.
This is what I have been working on so far. I know it is a bit complicated, but it gives me the progression that I want...
This is what I have been working on so far. I know it is a bit complicated, but it gives me the progression that I want and the axle path that I want. I would love some feed back on it!
Great work using the program. Does it seem overly complicated? Are you getting special numbers from this layout you can’t achieve my reducing some of those...
Great work using the program. Does it seem overly complicated? Are you getting special numbers from this layout you can’t achieve my reducing some of those links.
if you want, you can share the charts, Anti-rise, AS?
Absolutely, I made a few little changes since uploading that gif. What I was going for was a slightly rearward axle path that ends in about the same position as it starts, and a leverage ratio that begins around 3.2 and is 26% progressive.
Having a few more minutes, the link I gave above does cover it, but I think the PB variant is even clearer:
https://www.pinkbike.com/news/definitions-what-is-anti-squat.html
It explains how...
It explains how to map out antisquat (depending on where in the travel you are of course, as it's not static), but the TL;DR is, the higher the pivot point,t he more geometric antisquat you have, which is then refined by the amount the chain grows going through the travel to get the final antisquat value - a high pivot bike without an idler will have A LOT of antisquat. A low pivot bike with a high mounted idler will have very low antisquat numbers (effectively pro-squat if the chain is routed above the line from the rear axle to the pivot point).
As for your design, first, you're in the i-Track patent area (idler on a moveable link that is not the swingarm). Second, what is the distance between the two main pivots, centre to centre? When designing bikes clicking around in Linkage is all fine and dandy, but will you be able to package it all together? Or will it require 10 mm outer diameter bearings with very thin walls to make it work which will require 5 mm thick axles and thin section bearings that will all explode the first time you sit on it?
Doing the math the center to center distance between the two pivot points is about 30.9 mm. It is very tight, but I think that an appropriatly sized bearing would fit in the space. This is why I posted it here, to have more eyes on it while I am experimenting and people to bring up things I may not have thought about. The I-Track pattents weren't something that I was aware of either, and that will be important to keep in mind. I wouldn't want to develop an idea to find out that parts of the design are pattented by someone else far down the line.
Having a few more minutes, the link I gave above does cover it, but I think the PB variant is even clearer:
https://www.pinkbike.com/news/definitions-what-is-anti-squat.html
It explains how...
It explains how to map out antisquat (depending on where in the travel you are of course, as it's not static), but the TL;DR is, the higher the pivot point,t he more geometric antisquat you have, which is then refined by the amount the chain grows going through the travel to get the final antisquat value - a high pivot bike without an idler will have A LOT of antisquat. A low pivot bike with a high mounted idler will have very low antisquat numbers (effectively pro-squat if the chain is routed above the line from the rear axle to the pivot point).
As for your design, first, you're in the i-Track patent area (idler on a moveable link that is not the swingarm). Second, what is the distance between the two main pivots, centre to centre? When designing bikes clicking around in Linkage is all fine and dandy, but will you be able to package it all together? Or will it require 10 mm outer diameter bearings with very thin walls to make it work which will require 5 mm thick axles and thin section bearings that will all explode the first time you sit on it?
Doing the math the center to center distance between the two pivot points is about 30.9 mm. It is very tight, but I think that an...
Doing the math the center to center distance between the two pivot points is about 30.9 mm. It is very tight, but I think that an appropriatly sized bearing would fit in the space. This is why I posted it here, to have more eyes on it while I am experimenting and people to bring up things I may not have thought about. The I-Track pattents weren't something that I was aware of either, and that will be important to keep in mind. I wouldn't want to develop an idea to find out that parts of the design are pattented by someone else far down the line.
Like @earleb said it's not an issue if you don't sell it, but still, maybe something to keep in mind.
30,9 mm gives you enough space to use two 28 mm OD bearings with a 1 mm wall on the link and 0,9 mm clearance between them to over all the tolerances and have some gap. Frames are trending towards 20+ mm ID bearings lately for the main pivots, you can imagine what that means for the OD. Santa Cruz is using 6902 bearing (15x28x7 mm) in their lower link for the Hightower, Megatower & co which would leave you a 1 mm wall thickness around the bearing. This is way too thin even for something like steel, let alone aluminium.
You are of course free to try it, but if you have a look at what bearings most bikes use you will at least get a feeling for the size needed.
All those graphs looks great. I love the numbers you can up with. I do think you can make a much more simple design and achieve something very similar but much more simplicity.
I feel like the rear end could have some major issues with flex also loading all the bearings in a turn with how you have it, could cause binding.
Norco have been moving the main pivot to vary the CS length for many years now. Owen of Forbidden was a designer at Norco when they started doing it.
Does anyone have expertise/ insight on bearing loads? I made some inquiries with Enduro Bearings but they are unable to help (assuming due to liability issues)
I posed this question: I have an intense tracer 279 that uses these: https://cycling.endurobearings.com/collections/suspension-bearings/products/63800-llu-max-bo for the trunion side eyelet which each has a static load rating of 340lbf so with two bearings that brings you to 680lbf. This force would be exceeded at just past 50% of shock travel for my 500lb spring (standard on size Large). At full travel, that force would be 1280lbf.
I've looked at other bearings used such as the 6900 series on the fox eyelet bearing kit (2 bearings) and each is listed at 477lbf. So again that's 954lbf. On a DH shock (75mm stroke) and 500lb/in spring you're looking at about 1475lbf at full travel. In a bottom out scenario that force will spike even higher.
Often, the loads at the pivots exceed that experienced at the shock eyelet. There are some bearings with higher load limits available but not by much. My thought is that the loads on the pivots/shock should not exceed the load limit rating of the bearings but it appears that this actually does happen and by a fair margin. It also doesn't seem to be an issue so I'm clearly missing something. But that is making it difficult to design a frame since I can't determine what loads would cause a bearing issue/failure.
I think it's a case of "deal with it" and replace the bearings as needed... All these guidelines and data is relevant for continuous operation and for calculation of bearings that don't get replaced, etc. But we all know we replace bearings more or less on a yearly basis (though mostly due to contamination).
Primoz has pretty much hit the nail on the head here. The radial/axial load ratings of bearings quoted by the manufacturers are based on continuous 24hr operation over a lifetime, even the static load rating. Generally in rotating machinery design, the output for a calculation is the expected lifetime of a bearing based on operating loads and conditions - depending on the application it's always nice when the output comes out as "inifinte"...however, in my experience (designing heavy duty winch drums and selecting gearboxes for them) bearing failure seems to be much more to do with how they're mounted than anything else e.g. bearing type, arrangement, spacing and accuracy of axial alignment as a function of manufacturing tolerances.
Bearings in an MTB application are an outlier case - for starters they never see a complete rotation which means you're preferentially wearing the balls and groove in one specific quadrant of the bearing. Secondly, it's a wild west in terms of how they're mounted. When it's done well, the location of each bearing relative to the other on its axis will be controlled with a decent degree of accuracy - easily done by machining, almost impossible if fabricating. One of my old frames used to eat through chainstay yoke bearings because the bearing axes for the pivot were totally off. But the biggest killer is dirt and water ingress. The water washes away the grease and what grease remains mixes with fine dirt particles to form a cutting compound and grinds the balls/races away, eventually leading to play.
In answer to your question, I think frame manufacturers know that the bearings are going to fail due to contamination before any cyclical loading beyond limit so take some liberties with the rated loads. They are also prioritising weight above bearing life and speccing bigger bearings with higher load ratings for each of your pivots will pile on the pounds quite quickly.
The folks who I personally believe have pivot design nailed are Deviate, who use a combination of labyrinth seals and o-rings to fully seal the cartridge bearings within. Dirt still eventually gets in, but the grease ports allow you to fill the entire void with enough grease to suspend the contaminants more effectively and prolong the inevitable. I owned a Highlander for the best part of two years (in rainy Scotland, ridden 2-3 times a week in the summer and at least once a week in winter) and didn't have to replace a single bearing.
Thank you this is very helpful!
The grease port also supposedly acts as a flusher pushing the dirt out and replacing it with new grease.
It also probably flies out through the path of least resistance (I have heard a comment it's hardly beneficial in practice...) and mucks up the gap between the two moving parts with lots of grease.
Interestingly the lower link of SC bikes uses a single shield bearing with a gap between the shield and inner ring and a cover over it that also doesn't have any seals. So it's designed to be greased fairly often to push out the dirt. And is anything but sealed (compared to standard sealed bearings and additional labyrinth and rubber seals).
I was thinking about designing suspension for a full size range of bikes to give the same experience to riders of all sizes and weights, and started thinking about leverage ratio. I had an idea that for larger riders, having a slightly lower initial leverage ratio could be good, allowing them to run lower spring rates or shock pressures to achieve the same suspension performance, what are your thoughts? Am I misguided?
I like the concept, but what if you have a rider that is 6,0 and 160lbs on a large vs 5,10 220lb. Or on a small size 5,5 140lb female vs 5,6 200lb older guy?
Seems like you can open a can of worms where one rider gets a great leverage ratio and then next will struggle. I guess same way it is now, but starting with the best kinematics for the average rider seems like the safest option.
If you really want to go this deep, is it possible to design the frame in base of the best kinematic possible and then offer 2-3 other links and let the rider pick based on their height and weight.
Another thing I've been thinking about are trunnion mount shocks, and traditional shocks. I've seen a lot of people expressing dislike of trunnion mount shocks, and I am not sure why. What disadvantages does trunnion mounting have over traditional eyelets?
Very solid mounting by bolting the shock directly onto the frame with two bolts spaced widely apart.
And that is a disadvantage? Does it restrict suspension movement or cause more load to be supported by the shock leading to needing more maintenance or higher failure rates? More friction in the pivot bearings due to higher loads?
Frame alignment is an issue and can create huge sideloads in the shock, wearing it out.
Thank you, that makes sense. Do you see any benefit of trunnion over standard eyelets?
Raaw does precisely this, for each size you can select a lower leverage or (slightly) higher leverage rocker depending on rider weight:
https://raawmtb.com/en-us/collections/madonna-v3/products/madonna-v3-fr…
They created trunnion shocks to have a more compact package. The overall length of the shock is shorter for the same shock stroke. It is therefore easier to fit inside a frame design. No issues there, unless you have a flexi frame that puts a lot of sideloads on the shock.
Love this thread.
I'm a mechanical engineer with a background in design (mostly rotating machinery).
Also have friends in the bike industry and know a couple bike designers.
I've had a lot of debates on this.
I've always preferred bikes with shorter rear ends as I think they are more rewarding to ride and flick into corners.
My bike friend who runs an unnamed bike company completely disagrees and thinks longer back ends are better as they give a more balanced weight distribution.
I think the weight distribution thing is nonsense, I think every rider rides in a dynamic centre of gravity and their body position will adjust to suit this and spread the weight effectively.
One thing I observe is when bikes have too long a reach ppl end up lifting the bar height which essentially is the equivalent of shortening the reach in terms of shifting weight loading and correcting the body position.
I'm very curious about it all.
Back in the 26" aluminum tank days, my DH bike had pretty short chainstays, while my other bike was the Gen 2 magic link Kona Coilair. This bike had 455mm chainstays, super long for the time. On my local DH track, there was a segment about 3 min long that was fast, rough, and loose. Speed rarely dips below 20 mph. I was noticably faster, in both feel and actual time, on the Kona. This is despite having worse suspension, worse brakes, and cheaper tires on it. I honestly believe its due to the long chainstays.
That being said, my Kona was dual duty as my trail bike, and pedaling it on tame trails, with switchbacks, sharp berms, smaller & lippy jumps, etc. it was downright hard to maneuver around.
Yeah totally if I were racing fast loose tracks or if that was my usual riding I would want longer chainstays. They are stability at the cost of nimbleness and vice versa.
But short stay bikes I find way more fun to ride and flick around.
Most my riding is steep tight & twisty and when I've ridden long cs stay bikes it's taken some of the fun away.
I am experimenting with designs with the help of Linkage software, and while I have been able to get wheel paths and leverage ratios that I want, I am at a loss with anti rise and anti squat. I know what they are, and how they affect the ride, but I don't know how to properly calculate them and manipulate them. Does anyone know of a good resource to learn how to do these calculations? I'm studying engineering in college right now, but none of the classes I have already taken have gone over anything like this.
This is what I have been working on so far. I know it is a bit complicated, but it gives me the progression that I want and the axle path that I want. I would love some feed back on it!
Here's something. Pinkbike also has some explainers I think.
https://www.bikeradar.com/features/the-ultimate-guide-to-mountain-bike-…
Great work using the program. Does it seem overly complicated? Are you getting special numbers from this layout you can’t achieve my reducing some of those links.
if you want, you can share the charts, Anti-rise, AS?
Having a few more minutes, the link I gave above does cover it, but I think the PB variant is even clearer:
https://www.pinkbike.com/news/definitions-what-is-anti-squat.html
It explains how to map out antisquat (depending on where in the travel you are of course, as it's not static), but the TL;DR is, the higher the pivot point,t he more geometric antisquat you have, which is then refined by the amount the chain grows going through the travel to get the final antisquat value - a high pivot bike without an idler will have A LOT of antisquat. A low pivot bike with a high mounted idler will have very low antisquat numbers (effectively pro-squat if the chain is routed above the line from the rear axle to the pivot point).
As for your design, first, you're in the i-Track patent area (idler on a moveable link that is not the swingarm). Second, what is the distance between the two main pivots, centre to centre? When designing bikes clicking around in Linkage is all fine and dandy, but will you be able to package it all together? Or will it require 10 mm outer diameter bearings with very thin walls to make it work which will require 5 mm thick axles and thin section bearings that will all explode the first time you sit on it?
I find this visualisation really helpful to understand anti-squat and anti-rise.
I just linked the yeti video as it was the first to come up, but he did videos on other suspension types too.
Absolutely, I made a few little changes since uploading that gif. What I was going for was a slightly rearward axle path that ends in about the same position as it starts, and a leverage ratio that begins around 3.2 and is 26% progressive.
Doing the math the center to center distance between the two pivot points is about 30.9 mm. It is very tight, but I think that an appropriatly sized bearing would fit in the space. This is why I posted it here, to have more eyes on it while I am experimenting and people to bring up things I may not have thought about. The I-Track pattents weren't something that I was aware of either, and that will be important to keep in mind. I wouldn't want to develop an idea to find out that parts of the design are pattented by someone else far down the line.
If you are not planning to sell bikes you can ignore any patents and build whatever you want for yourself.
Like @earleb said it's not an issue if you don't sell it, but still, maybe something to keep in mind.
30,9 mm gives you enough space to use two 28 mm OD bearings with a 1 mm wall on the link and 0,9 mm clearance between them to over all the tolerances and have some gap. Frames are trending towards 20+ mm ID bearings lately for the main pivots, you can imagine what that means for the OD. Santa Cruz is using 6902 bearing (15x28x7 mm) in their lower link for the Hightower, Megatower & co which would leave you a 1 mm wall thickness around the bearing. This is way too thin even for something like steel, let alone aluminium.
You are of course free to try it, but if you have a look at what bearings most bikes use you will at least get a feeling for the size needed.
All those graphs looks great. I love the numbers you can up with. I do think you can make a much more simple design and achieve something very similar but much more simplicity.
I feel like the rear end could have some major issues with flex also loading all the bearings in a turn with how you have it, could cause binding.
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