Just reminds me too much of my MX days where every ad for a Kawasaki, or Suzuki two stroke mentions a recent top end, and or...
Just reminds me too much of my MX days where every ad for a Kawasaki, or Suzuki two stroke mentions a recent top end, and or bottom end/clutch and that's out of necessity because they really are garbage compared to Honda/Yamaha.
Browse some listings for DH forks. I guarantee you'll see more more people mentioning they just rebuilt their Boxxer VS 40's.
I like how you interprete that as boxxer needing more care than fox 40, when both have comparable service intervals. Let's turn it around, what if most 40 owners cannot be bothered to service their gear? Because you know, Kashima is self lubricating 🙄
You know Ive always been curious about this. Unsure how it could be tested in a controlled way, but Ive always wondered how much stiffer are...
You know Ive always been curious about this. Unsure how it could be tested in a controlled way, but Ive always wondered how much stiffer are forks by increasing stanchion size? Or is it placebo? Going for a well built 34mm to a 35mm to a 36. Should the focus be on the stanchion size or the actual construction of the lowers to make the most difference?
It’s been nearly 10 years since I covered it in school, but IIRC the bending stiffness of a tube is Stiffness = E*(pi/64)*(OD^4 - ID^4).Because the diameters...
It’s been nearly 10 years since I covered it in school, but IIRC the bending stiffness of a tube is
Stiffness = E*(pi/64)*(OD^4 - ID^4).
Because the diameters are scaled to the 4th power, small increases in stanchion size can yield huge stiffness increases.
Crown stiffness quickly becomes a limiting factor though. That’s why a 38mm single crown works like crap compared to a 35mm dual crown fork.
There are some other things that affect fork performance too. For example, a less stiff fork will be more susceptible to bushing bind when ridden in rough terrain.
"That’s why a 38mm single crown works like crap compared to a 35mm dual crown fork." 35mm dual crown fork 🤮 I always casually browse the used...
"That’s why a 38mm single crown works like crap compared to a 35mm dual crown fork."
35mm dual crown fork 🤮 I always casually browse the used bike listings for DH bikes I don't really need.. After seeing this pic in the G Out Project, anything with an oldschool boxxer is immediatley ruled out unless the bike is a screaming deal.
The bending stiffness of a tube increases to the fourth power with respect to diameter... Ie bigger tubes are way fucking stiffer than smaller tubes.But steerers...
The bending stiffness of a tube increases to the fourth power with respect to diameter... Ie bigger tubes are way fucking stiffer than smaller tubes.
But steerers are flexy, crowns are flexy, and axle interfaces are flexy. If you put some effort into locking the two tubes together then they work together and will flex together, and this also massively increases stiffness. The keyed axle of the Mattoc or a 20mm axle with four pinchbolts like the old 36, the bulky crown like a lyrik, all help to make the most of their tube stiffness. The flexy modern 36 with its slim crown and arch and shitty little axle make for a comparative noodle.
It would be cool to see tests. Both for bending stiffness and torsional stiffness. Torsional stiffness affects the feel the most in my opinion, and that's where you get the most advantage from the crown/axle/arch rather than the stanchions.
Upside down forks disagree on torsional stiffness being a benefit... Users of them mostly say it is not a problem. Darren Murphy put it in a...
Upside down forks disagree on torsional stiffness being a benefit... Users of them mostly say it is not a problem. Darren Murphy put it in a good way - how much torque do you actually put on a fork?
I'm happy to agree that a complete lack of torsional stiffness is something that some people enjoy. I assume that they also like flexy frames like...
I'm happy to agree that a complete lack of torsional stiffness is something that some people enjoy. I assume that they also like flexy frames like Pole or Yeti or that old intense tracer that would spit you out of corners in random directions, but if you were delicate they'd track around bumps rather than over them.
Couldn't imagine anything worse myself. There's compliance which helps a tire grip in a corner, and there's compliance which spits you off your line. USD forks or fox 34s are the latter.
Upside down forks are much stiffer front to back eg under braking and are slightly less stiff laterally. They are used by most high end motorcycles for a reason! You should go listen to the latest PUSH interview about why lateral stiffness is overrated.
Motorcycles usually don't need to be as precise with line choice, the machine (and thus system) is heavier and needs more fore-aft stiffness, weight is not as big an issue so larger stanchions can be used, etc.
Still, people riding upside down forks don't seem to have much of a problem with torsional stiffness. At least in most cases.
BTW, all of this has been discussed over multiple pages before.
Upside down forks are much stiffer front to back eg under braking and are slightly less stiff laterally. They are used by most high end motorcycles...
Upside down forks are much stiffer front to back eg under braking and are slightly less stiff laterally. They are used by most high end motorcycles for a reason! You should go listen to the latest PUSH interview about why lateral stiffness is overrated.
You should go listen to the latest PUSH interview where the rationalize why they made an inverted fork whilst avoiding talking about the fact they could'nt afford a lower leg casting production run.
The lower leg casting price seems to me little overblown issue, if formula as relatively small manufacturer can sell complete lowers for 160euros, I don't think it's that crazy. I know part of it is they share lowers between multiple forks but overall numbers still must be fraction of what RS produces yet lowers for lyrik or pike cost almost double.
You know Ive always been curious about this. Unsure how it could be tested in a controlled way, but Ive always wondered how much stiffer are...
You know Ive always been curious about this. Unsure how it could be tested in a controlled way, but Ive always wondered how much stiffer are forks by increasing stanchion size? Or is it placebo? Going for a well built 34mm to a 35mm to a 36. Should the focus be on the stanchion size or the actual construction of the lowers to make the most difference?
It’s been nearly 10 years since I covered it in school, but IIRC the bending stiffness of a tube is Stiffness = E*(pi/64)*(OD^4 - ID^4).Because the diameters...
It’s been nearly 10 years since I covered it in school, but IIRC the bending stiffness of a tube is
Stiffness = E*(pi/64)*(OD^4 - ID^4).
Because the diameters are scaled to the 4th power, small increases in stanchion size can yield huge stiffness increases.
Crown stiffness quickly becomes a limiting factor though. That’s why a 38mm single crown works like crap compared to a 35mm dual crown fork.
There are some other things that affect fork performance too. For example, a less stiff fork will be more susceptible to bushing bind when ridden in rough terrain.
"That’s why a 38mm single crown works like crap compared to a 35mm dual crown fork." 35mm dual crown fork 🤮 I always casually browse the used...
"That’s why a 38mm single crown works like crap compared to a 35mm dual crown fork."
35mm dual crown fork 🤮 I always casually browse the used bike listings for DH bikes I don't really need.. After seeing this pic in the G Out Project, anything with an oldschool boxxer is immediatley ruled out unless the bike is a screaming deal.
I support this POV, as someone who recently picked up a 2022 35mm Boxxer Ultimate for $500. 35mm bad! Keep these forks cheap and introduce people like me who haven't spent time on a DH bike to the awesomeness of dual crown forks.
35mm for park/freeride. 38mm for race. (although the 38mm on the Status 170 didn't feel overly stiff or race-y imo)
Don’t most things need so amount of flex built into it? I would assume (yes, I know what happens when you assume), that is things were built not to flex, very heavy and surprise, surprise, very stiff and uncomfortable. There is an old photo of a rampage rider landing a massive drop and his aluminum bar flexed so much people thought he must have broken it. It was fine from what I remember.
One could argue that stanchion flexing is not the best place for a flex to occur, but yes, some degree of flex is good for fatigue reduction. We are strapping new gizmos to our bikes to reduce vibrations after all. And to those people that think fore/aft flex is so detrimental to fork performance need to think about how fork bushing binds because of single sided spring/damper design instead.
Upside down forks are much stiffer front to back eg under braking and are slightly less stiff laterally. They are used by most high end motorcycles...
Upside down forks are much stiffer front to back eg under braking and are slightly less stiff laterally. They are used by most high end motorcycles for a reason! You should go listen to the latest PUSH interview about why lateral stiffness is overrated.
You should go listen to the latest PUSH interview where the rationalize why they made an inverted fork whilst avoiding talking about the fact they could'nt...
You should go listen to the latest PUSH interview where the rationalize why they made an inverted fork whilst avoiding talking about the fact they could'nt afford a lower leg casting production run.
Push are kinda boneheads. My friend got into it with them at the Sea Otter because they didn’t do a dynamic bushing in their inverted fork. They claimed it makes no difference and yet it binds up pretty badly when you lightly load it in torsion. (It’s a noodle torsionally too because it’s inverted)
There were rumors that WeAreOne were leaving the frame building business due to financial troubles. Now it looks like their website doesn't have a menu item for bikes/frames anymore. https://www.weareonecomposites.com/ Also their wheels have been discount on and off 20% for almost the whole year.
The new M Series wheels and Innderdrive MTB hubs from ENVE have finally launched. Gravity wheelsets are still 6 months out but I got my hands on a set of the lighter trail wheelset last week that feel surprisingly good for how light they are. I attached some first impressions to the PR below.
Push are kinda boneheads. My friend got into it with them at the Sea Otter because they didn’t do a dynamic bushing in their inverted fork...
Push are kinda boneheads. My friend got into it with them at the Sea Otter because they didn’t do a dynamic bushing in their inverted fork. They claimed it makes no difference and yet it binds up pretty badly when you lightly load it in torsion. (It’s a noodle torsionally too because it’s inverted)
😅 We stubbornly wanted to make the sliding bushing work so bad, probably delayed the whole project by a year. At the end of the day in blind A/B testing, riders couldn't tell a difference so it was ease of service and manufacturing consistency that pushed us to fixed bushings. Mountain bikes are similar to motos in many ways but also different, so not every moto concept is a good fit for us. Sure, putting sliding bushings as a feature on our spec sheet would look cool, but if it isn't actually better we're not interested.
And yes, it is noodley in a bike stand in a sea otter parking lot. On the trail, you might feel differently.
😅 We stubbornly wanted to make the sliding bushing work so bad, probably delayed the whole project by a year. At the end of the day...
😅 We stubbornly wanted to make the sliding bushing work so bad, probably delayed the whole project by a year. At the end of the day in blind A/B testing, riders couldn't tell a difference so it was ease of service and manufacturing consistency that pushed us to fixed bushings. Mountain bikes are similar to motos in many ways but also different, so not every moto concept is a good fit for us. Sure, putting sliding bushings as a feature on our spec sheet would look cool, but if it isn't actually better we're not interested.
And yes, it is noodley in a bike stand in a sea otter parking lot. On the trail, you might feel differently.
I’d still be willing to give one a fair shake on trail. I’m always open to being proven wrong.
Out of curiosity, what was the reasoning for pursuing an inverted layout over conventional?
Opportunity for increased bushing overlap via a dynamic bushing is the main upside I see inverted offering.
Increased seal lubrication is nice but less important if you do regular service.
Cost savings because you don’t need to buy a cast part from a supplier?
I’m incredibly curious to see how the EXT DH fork turns out. We were talking to them at the sea otter and supposedly it will be using a dynamic bushing arrangement. I’d probably be lining up to throw my money at them if I hadn’t just put a 40 on my bike because I really wanted to try out the new Grip X2.
😅 We stubbornly wanted to make the sliding bushing work so bad, probably delayed the whole project by a year. At the end of the day...
😅 We stubbornly wanted to make the sliding bushing work so bad, probably delayed the whole project by a year. At the end of the day in blind A/B testing, riders couldn't tell a difference so it was ease of service and manufacturing consistency that pushed us to fixed bushings. Mountain bikes are similar to motos in many ways but also different, so not every moto concept is a good fit for us. Sure, putting sliding bushings as a feature on our spec sheet would look cool, but if it isn't actually better we're not interested.
And yes, it is noodley in a bike stand in a sea otter parking lot. On the trail, you might feel differently.
I’d still be willing to give one a fair shake on trail. I’m always open to being proven wrong.Out of curiosity, what was the reasoning for...
I’d still be willing to give one a fair shake on trail. I’m always open to being proven wrong.
Out of curiosity, what was the reasoning for pursuing an inverted layout over conventional?
Opportunity for increased bushing overlap via a dynamic bushing is the main upside I see inverted offering.
Increased seal lubrication is nice but less important if you do regular service.
Cost savings because you don’t need to buy a cast part from a supplier?
I’m incredibly curious to see how the EXT DH fork turns out. We were talking to them at the sea otter and supposedly it will be using a dynamic bushing arrangement. I’d probably be lining up to throw my money at them if I hadn’t just put a 40 on my bike because I really wanted to try out the new Grip X2.
On EXT's IG post of the inverted DH fork, someone asked when the single crown version drops and they confirmed that it's in the works.
I’d still be willing to give one a fair shake on trail. I’m always open to being proven wrong.Out of curiosity, what was the reasoning for...
I’d still be willing to give one a fair shake on trail. I’m always open to being proven wrong.
Out of curiosity, what was the reasoning for pursuing an inverted layout over conventional?
Opportunity for increased bushing overlap via a dynamic bushing is the main upside I see inverted offering.
Increased seal lubrication is nice but less important if you do regular service.
Cost savings because you don’t need to buy a cast part from a supplier?
I’m incredibly curious to see how the EXT DH fork turns out. We were talking to them at the sea otter and supposedly it will be using a dynamic bushing arrangement. I’d probably be lining up to throw my money at them if I hadn’t just put a 40 on my bike because I really wanted to try out the new Grip X2.
As mentioned earlier, the bend stiffness is greatly increased with an increase in tube diameter. Bushing overlap aside, the large upper tubes used on inverted forks will prevent bending and thus binding of the sliders in the bushings. I can image that the sensitivity from the 50%-80% travel zone would be much improved from this design choice. A sliding bushing could be better, but the jump from a conventional MTB fork design to an inverted one is likely large enough that the performance increase is immediately apparent to riders.
I’d still be willing to give one a fair shake on trail. I’m always open to being proven wrong.Out of curiosity, what was the reasoning for...
I’d still be willing to give one a fair shake on trail. I’m always open to being proven wrong.
Out of curiosity, what was the reasoning for pursuing an inverted layout over conventional?
Opportunity for increased bushing overlap via a dynamic bushing is the main upside I see inverted offering.
Increased seal lubrication is nice but less important if you do regular service.
Cost savings because you don’t need to buy a cast part from a supplier?
I’m incredibly curious to see how the EXT DH fork turns out. We were talking to them at the sea otter and supposedly it will be using a dynamic bushing arrangement. I’d probably be lining up to throw my money at them if I hadn’t just put a 40 on my bike because I really wanted to try out the new Grip X2.
To be honest, Fox and RS make really good conventional forks. We did feel that we could improve on the conventional fork a bit strictly on the low volume nature of our manufacturing, (i.e. more complex designs and tighter tolerances) but we also felt the whole industry is getting close to the ultimate performance limit of conventional forks. So we bought all the inverted forks we could find, rode them, modified them, rode them so more, etc. and at the end felt the inverted design was worth pursuing further.
Food for thought: You could do a sliding bushing in a conventional fork as well. But to answer your question, there's not really one advantage that's more important than others. We learned that everything (flex, alignment, lubrication, etc.) has to work in unison and the inverted design has a different set of parameters to allow that tuning.
Cost had no factor in the decision, and actually the opposite is true. A custom casting from Asia would certainly be cheaper than what were doing now. However, a factor we did consider, it would be near impossible to source that casting in the US.
😅 We stubbornly wanted to make the sliding bushing work so bad, probably delayed the whole project by a year. At the end of the day...
😅 We stubbornly wanted to make the sliding bushing work so bad, probably delayed the whole project by a year. At the end of the day in blind A/B testing, riders couldn't tell a difference so it was ease of service and manufacturing consistency that pushed us to fixed bushings. Mountain bikes are similar to motos in many ways but also different, so not every moto concept is a good fit for us. Sure, putting sliding bushings as a feature on our spec sheet would look cool, but if it isn't actually better we're not interested.
And yes, it is noodley in a bike stand in a sea otter parking lot. On the trail, you might feel differently.
I’d still be willing to give one a fair shake on trail. I’m always open to being proven wrong.Out of curiosity, what was the reasoning for...
I’d still be willing to give one a fair shake on trail. I’m always open to being proven wrong.
Out of curiosity, what was the reasoning for pursuing an inverted layout over conventional?
Opportunity for increased bushing overlap via a dynamic bushing is the main upside I see inverted offering.
Increased seal lubrication is nice but less important if you do regular service.
Cost savings because you don’t need to buy a cast part from a supplier?
I’m incredibly curious to see how the EXT DH fork turns out. We were talking to them at the sea otter and supposedly it will be using a dynamic bushing arrangement. I’d probably be lining up to throw my money at them if I hadn’t just put a 40 on my bike because I really wanted to try out the new Grip X2.
"Opportunity for increased bushing overlap via a dynamic bushing is the main upside I see inverted offering.
Only valid for a dual crown fork. With a single crown, you have the same space in either an upside down or a right side up fork. With a dual crown, the surface that could be used to slide is clamped in the crowns with a right side up fork. With a USD dual crown fork, the 'dynamic' bushing can protrude past the lower crown so you get a genuine advantage of this layout.
The BIG negative is that besides having to deal with the surface finish of the outer surface of the stanchion (normal for all forks out there, besides the inner surface if you are using the stanchion as the air spring cylinder), you have to deal with the surface finish of the inside of the outer tube as well. You double the parts that need to be finished to a tight tolerance, have a high smoothness of the surface AND then be surface treated for hardness.
(I'd be happy to be proven wrong on these assumptions by someone who actually had a hand at designing a fork, I did no such thing ever after all, this is all just assuming how it's done.)
@whitesq regarding sourcing a casting in the US, is the industry that far gone or are there specifics when it comes to fork castings? Geometry specific, material specific, etc.? We can get proto cast parts from basically a garage here in Slovenia and there are a few suppliers of cast aluminium parts within a 20 kilometer radius around here. Not sure about the quality, that is true, but there are options at least. Plus there's always CNC milling
To be honest, Fox and RS make really good conventional forks. We did feel that we could improve on the conventional fork a bit strictly on...
To be honest, Fox and RS make really good conventional forks. We did feel that we could improve on the conventional fork a bit strictly on the low volume nature of our manufacturing, (i.e. more complex designs and tighter tolerances) but we also felt the whole industry is getting close to the ultimate performance limit of conventional forks. So we bought all the inverted forks we could find, rode them, modified them, rode them so more, etc. and at the end felt the inverted design was worth pursuing further.
Food for thought: You could do a sliding bushing in a conventional fork as well. But to answer your question, there's not really one advantage that's more important than others. We learned that everything (flex, alignment, lubrication, etc.) has to work in unison and the inverted design has a different set of parameters to allow that tuning.
Cost had no factor in the decision, and actually the opposite is true. A custom casting from Asia would certainly be cheaper than what were doing now. However, a factor we did consider, it would be near impossible to source that casting in the US.
You can totally do a sliding bushing in a conventional fork, but conventional lowers construction doesn’t really facilitate that. You’d need to add a harder sliding surface inside of the mag casting. With an inverted fork you just have to do some extra machining inside your upper tubes.
Me and a friend have actually been toying with the idea of trying to do a sliding bushing conventional frankenfork to test the concept. We would use 40 lowers and cut/bond 40 stanchions inside to act as the exterior sliding surface. Then modify 35mm Boxxer stanchions to run inside.
The main reason we haven’t tried it is parts cost. Scrapping two forks for a pet project is hard to justify.
Edit: @Primoz On a single crown dynamic bushing setup you don’t gain increased bushing overlap at full extension but you do still gain bushing overlap everywhere else. If upper bushing is attached to the stanchion and your fork sags by 20mm, you have 20mm extra bushing overlap.
You can totally do a sliding bushing in a conventional fork, but conventional lowers construction doesn’t really facilitate that. You’d need to add a harder sliding...
You can totally do a sliding bushing in a conventional fork, but conventional lowers construction doesn’t really facilitate that. You’d need to add a harder sliding surface inside of the mag casting. With an inverted fork you just have to do some extra machining inside your upper tubes.
Me and a friend have actually been toying with the idea of trying to do a sliding bushing conventional frankenfork to test the concept. We would use 40 lowers and cut/bond 40 stanchions inside to act as the exterior sliding surface. Then modify 35mm Boxxer stanchions to run inside.
The main reason we haven’t tried it is parts cost. Scrapping two forks for a pet project is hard to justify.
Edit: @Primoz On a single crown dynamic bushing setup you don’t gain increased bushing overlap at full extension but you do still gain bushing overlap everywhere else. If upper bushing is attached to the stanchion and your fork sags by 20mm, you have 20mm extra bushing overlap.
Someone at RS did that with an old Totem single crown and maybe RS1 bits. It was very cool.
You can totally do a sliding bushing in a conventional fork, but conventional lowers construction doesn’t really facilitate that. You’d need to add a harder sliding...
You can totally do a sliding bushing in a conventional fork, but conventional lowers construction doesn’t really facilitate that. You’d need to add a harder sliding surface inside of the mag casting. With an inverted fork you just have to do some extra machining inside your upper tubes.
Me and a friend have actually been toying with the idea of trying to do a sliding bushing conventional frankenfork to test the concept. We would use 40 lowers and cut/bond 40 stanchions inside to act as the exterior sliding surface. Then modify 35mm Boxxer stanchions to run inside.
The main reason we haven’t tried it is parts cost. Scrapping two forks for a pet project is hard to justify.
Edit: @Primoz On a single crown dynamic bushing setup you don’t gain increased bushing overlap at full extension but you do still gain bushing overlap everywhere else. If upper bushing is attached to the stanchion and your fork sags by 20mm, you have 20mm extra bushing overlap.
Sounds really heavy just to have some moving bushings.
I like how you interprete that as boxxer needing more care than fox 40, when both have comparable service intervals. Let's turn it around, what if most 40 owners cannot be bothered to service their gear? Because you know, Kashima is self lubricating 🙄
Upside down forks don't flex like that😉
Upside down forks are much stiffer front to back eg under braking and are slightly less stiff laterally. They are used by most high end motorcycles for a reason! You should go listen to the latest PUSH interview about why lateral stiffness is overrated.
Indeed. I've ridden inverted forks on bikes and Motos plenty. We all get to have our opinions on how we like things to ride.
The "but Motos use them" argument doesn't really hold up imo. We use our forks so differently and ride such different terrain.
Motorcycles usually don't need to be as precise with line choice, the machine (and thus system) is heavier and needs more fore-aft stiffness, weight is not as big an issue so larger stanchions can be used, etc.
Still, people riding upside down forks don't seem to have much of a problem with torsional stiffness. At least in most cases.
BTW, all of this has been discussed over multiple pages before.
You should go listen to the latest PUSH interview where the rationalize why they made an inverted fork whilst avoiding talking about the fact they could'nt afford a lower leg casting production run.
They could have CNCd it... Intend does it.
The lower leg casting price seems to me little overblown issue, if formula as relatively small manufacturer can sell complete lowers for 160euros, I don't think it's that crazy. I know part of it is they share lowers between multiple forks but overall numbers still must be fraction of what RS produces yet lowers for lyrik or pike cost almost double.
Does it use the new suspension layout from the Altitude?
I support this POV, as someone who recently picked up a 2022 35mm Boxxer Ultimate for $500. 35mm bad! Keep these forks cheap and introduce people like me who haven't spent time on a DH bike to the awesomeness of dual crown forks.
35mm for park/freeride. 38mm for race. (although the 38mm on the Status 170 didn't feel overly stiff or race-y imo)
Don’t most things need so amount of flex built into it? I would assume (yes, I know what happens when you assume), that is things were built not to flex, very heavy and surprise, surprise, very stiff and uncomfortable.
There is an old photo of a rampage rider landing a massive drop and his aluminum bar flexed so much people thought he must have broken it. It was fine from what I remember.
One could argue that stanchion flexing is not the best place for a flex to occur, but yes, some degree of flex is good for fatigue reduction. We are strapping new gizmos to our bikes to reduce vibrations after all. And to those people that think fore/aft flex is so detrimental to fork performance need to think about how fork bushing binds because of single sided spring/damper design instead.
Push are kinda boneheads. My friend got into it with them at the Sea Otter because they didn’t do a dynamic bushing in their inverted fork. They claimed it makes no difference and yet it binds up pretty badly when you lightly load it in torsion. (It’s a noodle torsionally too because it’s inverted)
There were rumors that WeAreOne were leaving the frame building business due to financial troubles. Now it looks like their website doesn't have a menu item for bikes/frames anymore. https://www.weareonecomposites.com/ Also their wheels have been discount on and off 20% for almost the whole year.
The new M Series wheels and Innderdrive MTB hubs from ENVE have finally launched. Gravity wheelsets are still 6 months out but I got my hands on a set of the lighter trail wheelset last week that feel surprisingly good for how light they are. I attached some first impressions to the PR below.
https://www.vitalmtb.com/news/press-release/enve-releases-fifth-generat…
😅 We stubbornly wanted to make the sliding bushing work so bad, probably delayed the whole project by a year. At the end of the day in blind A/B testing, riders couldn't tell a difference so it was ease of service and manufacturing consistency that pushed us to fixed bushings. Mountain bikes are similar to motos in many ways but also different, so not every moto concept is a good fit for us. Sure, putting sliding bushings as a feature on our spec sheet would look cool, but if it isn't actually better we're not interested.
And yes, it is noodley in a bike stand in a sea otter parking lot. On the trail, you might feel differently.
I’d still be willing to give one a fair shake on trail. I’m always open to being proven wrong.
Out of curiosity, what was the reasoning for pursuing an inverted layout over conventional?
Opportunity for increased bushing overlap via a dynamic bushing is the main upside I see inverted offering.
Increased seal lubrication is nice but less important if you do regular service.
Cost savings because you don’t need to buy a cast part from a supplier?
I’m incredibly curious to see how the EXT DH fork turns out. We were talking to them at the sea otter and supposedly it will be using a dynamic bushing arrangement. I’d probably be lining up to throw my money at them if I hadn’t just put a 40 on my bike because I really wanted to try out the new Grip X2.
On EXT's IG post of the inverted DH fork, someone asked when the single crown version drops and they confirmed that it's in the works.
https://www.vitalmtb.com/features/upside-down-push-nine-one-fork-finally-here
Consider listening to the interview Vital did with Push when the fork dropped. Covers many of these questions.
As mentioned earlier, the bend stiffness is greatly increased with an increase in tube diameter. Bushing overlap aside, the large upper tubes used on inverted forks will prevent bending and thus binding of the sliders in the bushings. I can image that the sensitivity from the 50%-80% travel zone would be much improved from this design choice. A sliding bushing could be better, but the jump from a conventional MTB fork design to an inverted one is likely large enough that the performance increase is immediately apparent to riders.
To be honest, Fox and RS make really good conventional forks. We did feel that we could improve on the conventional fork a bit strictly on the low volume nature of our manufacturing, (i.e. more complex designs and tighter tolerances) but we also felt the whole industry is getting close to the ultimate performance limit of conventional forks. So we bought all the inverted forks we could find, rode them, modified them, rode them so more, etc. and at the end felt the inverted design was worth pursuing further.
Food for thought: You could do a sliding bushing in a conventional fork as well. But to answer your question, there's not really one advantage that's more important than others. We learned that everything (flex, alignment, lubrication, etc.) has to work in unison and the inverted design has a different set of parameters to allow that tuning.
Cost had no factor in the decision, and actually the opposite is true. A custom casting from Asia would certainly be cheaper than what were doing now. However, a factor we did consider, it would be near impossible to source that casting in the US.
"Opportunity for increased bushing overlap via a dynamic bushing is the main upside I see inverted offering.
Only valid for a dual crown fork. With a single crown, you have the same space in either an upside down or a right side up fork. With a dual crown, the surface that could be used to slide is clamped in the crowns with a right side up fork. With a USD dual crown fork, the 'dynamic' bushing can protrude past the lower crown so you get a genuine advantage of this layout.
The BIG negative is that besides having to deal with the surface finish of the outer surface of the stanchion (normal for all forks out there, besides the inner surface if you are using the stanchion as the air spring cylinder), you have to deal with the surface finish of the inside of the outer tube as well. You double the parts that need to be finished to a tight tolerance, have a high smoothness of the surface AND then be surface treated for hardness.
(I'd be happy to be proven wrong on these assumptions by someone who actually had a hand at designing a fork, I did no such thing ever after all, this is all just assuming how it's done.)
@whitesq regarding sourcing a casting in the US, is the industry that far gone or are there specifics when it comes to fork castings? Geometry specific, material specific, etc.? We can get proto cast parts from basically a garage here in Slovenia and there are a few suppliers of cast aluminium parts within a 20 kilometer radius around here. Not sure about the quality, that is true, but there are options at least. Plus there's always CNC milling
You can totally do a sliding bushing in a conventional fork, but conventional lowers construction doesn’t really facilitate that. You’d need to add a harder sliding surface inside of the mag casting. With an inverted fork you just have to do some extra machining inside your upper tubes.
Me and a friend have actually been toying with the idea of trying to do a sliding bushing conventional frankenfork to test the concept. We would use 40 lowers and cut/bond 40 stanchions inside to act as the exterior sliding surface. Then modify 35mm Boxxer stanchions to run inside.
The main reason we haven’t tried it is parts cost. Scrapping two forks for a pet project is hard to justify.
Edit: @Primoz On a single crown dynamic bushing setup you don’t gain increased bushing overlap at full extension but you do still gain bushing overlap everywhere else. If upper bushing is attached to the stanchion and your fork sags by 20mm, you have 20mm extra bushing overlap.
Think it’s a lot easier to get high quality surface finish on the OD of a tube with centerless grinding vs honing the ID. Certainly easier to inspect.
I never understood the benefits of trombone type bushing- minimum overlap when the fork is at its longest length. Maybe it aligns the assembly better?
Fork castings are magnesium. there’s only a few suppliers doing that in Taiwan, maybe less in the USA. Never looked.
Someone at RS did that with an old Totem single crown and maybe RS1 bits. It was very cool.
In a production environment, wouldn’t you just machine on a lathe and then use a roller burnishing tool?
IIRC that’s the way shock bodies were done when I was in the Fox machine shop. I don’t know if the process has limitations with larger diameters.
😂 I mean that’s what you put on the drawing
Tool maintenance, inspection and repetition over millions of parts is another thing
Yeah this fork that was ridden at 35mm stanchions for years is suddenly hot garbage because reasons. (marketing depts told me this is the truth)
Sounds really heavy just to have some moving bushings.
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