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EXT Inverted Fork

Jm_

sled dog's bollocks
Jan 14, 2002
19,267
9,904
AK
Man, I thought we already did this. I love the idea of inverted forks, but they just don't work as well for mtb as they do for moto.

I think the only way they would work is to have a 30+mm axle, like the foes did, to combat independent axle movement. You'd still have to deal with fore/aft stiffness which may not be as good, ever, in a weight/stiffness battle.

The lefty worked well because it was a strut, not a traditional fork. It had 4 roller bearings that rode on carriers in between flat surfaces of the slider and fork itself. This limited travel to about 100mm. To get maximum stiffness, they put the bearings right next to the axle, which is why they had the accordion boot. Later they changed it so the bearings are up higher and there's a lower bushing as well. Now they didn't need the boot but I don't know if it was still stiff. I think the last ones had like 140mm of travel. I had a lefty and loved it, but it was short travel and the damping kind of sucked.

Now I have a linkage fork and all my problems are solved :rolleyes:
Fore/aft stiffness is where inverted DC is good...except it's just not a landslide thing, since you can make bigger stanchions on a right-side-up like the Fox 40 or new 38mm boxxer...and get the same result, AND you take a big hit in torsional stiffness with inverted. The real issue you run into is as you keep increasing travel on a conventional fork, you run out of enough bushing overlap for...pretty much everything. Having the space to run overlap in the space between the crowns is where DC inverted forks come in...but if we aren't going much over 8" of travel...it's not really needed. For the purpose of overlap, this is wasted space on a normal DC fork. If we were going 9-12" of travel is where it would matter. Once you go to single-crown inverted...it's just stupid. Now you don't have more overlap than a conventional fork and you take an even bigger hit on torsional rigidity for...no good reason.
 
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englertracing

you owe me a sandwich
Mar 5, 2012
1,590
1,086
La Verne
Fore/aft stiffness is where inverted DC is good...except it's just not a landslide thing, since you can make bigger stanchions on a right-side-up like the Fox 40 or new 38mm boxxer...and get the same result, AND you take a big hit in torsional stiffness with inverted. The real issue you run into is as you keep increasing travel on a conventional fork, you run out of enough bushing overlap for...pretty much everything. Having the space to run overlap in the space between the crowns is where DC inverted forks come in...but if we aren't going much over 8" of travel...it's not really needed. For the purpose of overlap, this is wasted space on a normal DC fork. If we were going 9-12" of travel is where it would matter. Once you go to single-crown inverted...it's just stupid. Now you don't have more overlap than a conventional fork and you take an even bigger hit on torsional rigidity for...no good reason.
I agree with all that, and I think there is a "critical mass" where with enough bulk a DC has an inherently decent amount of stiffness.
I don't think the size fork used on a trials bike meets that, so they are still using a conventional.
 

Jm_

sled dog's bollocks
Jan 14, 2002
19,267
9,904
AK
I agree with all that, and I think there is a "critical mass" where with enough bulk a DC has an inherently decent amount of stiffness.
I don't think the size fork used on a trials bike meets that, so they are still using a conventional.
As evidenced by MX forks that have no steerer and carry all the stress in between the crowns through the uppers.
 

Westy

the teste
Nov 22, 2002
54,831
20,692
Sleazattle
Regular moto forks don't use a crown so the torsional rigidity issues are pretty much the same as a USD.
 

Westy

the teste
Nov 22, 2002
54,831
20,692
Sleazattle
Tell me more about this.
Not something I exactly have intimate knowledge with. Just was thinking that I don't think I had ever seen a regular style motorcycle fork with an arch. I have had some street bikes where a flimsy plastic fender is bolted between fork legs, but that ain't going to do much. Which really puts all of them in a similar category as a USD fork.



1686364765965.png


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1686364993442.png


I had an older version of the SV650 in the last picture above. My generation bike only had a 17mm diameter axle on a 450lb bike. Any issues I had with that fork was with the orifice damper, which is much less of a big deal when you have 400lbs of shit between you and the suspension. Now each one of those fork legs probably weighs a lot more than a complete DH fork and in the worse case scenario only has to deal with a 21" wheel.
 
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Jm_

sled dog's bollocks
Jan 14, 2002
19,267
9,904
AK
Not something I exactly have intimate knowledge with. Just was thinking that I don't think I had ever seen a regular style motorcycle fork with an arch. I have had some street bikes where a flimsy plastic fender is bolted between fork legs, but that ain't going to do much. Which really puts all of them in a similar category as a USD fork.



View attachment 195014

View attachment 195015

View attachment 195016

I had an older version of the SV650 in the last picture above. My generation bike only had a 17mm diameter axle on a 450lb bike. Any issues I had with that fork was with the orifice damper, which is much less of a big deal when you have 400lbs of shit between you and the suspension. Now each one of those fork legs probably weighs a lot more than a complete DH fork and in the worse case scenario only has to deal with a 21" wheel.
No no, tell me more about not having a crown, like you did above :D
 

HardtailHack

used an iron once
Jan 20, 2009
6,926
5,892
Fore/aft stiffness is where inverted DC is good...except it's just not a landslide thing, since you can make bigger stanchions on a right-side-up like the Fox 40 or new 38mm boxxer...and get the same result, AND you take a big hit in torsional stiffness with inverted. The real issue you run into is as you keep increasing travel on a conventional fork, you run out of enough bushing overlap for...pretty much everything. Having the space to run overlap in the space between the crowns is where DC inverted forks come in...but if we aren't going much over 8" of travel...it's not really needed. For the purpose of overlap, this is wasted space on a normal DC fork. If we were going 9-12" of travel is where it would matter. Once you go to single-crown inverted...it's just stupid. Now you don't have more overlap than a conventional fork and you take an even bigger hit on torsional rigidity for...no good reason.
There were some old right side up forks that had the casting that ended quite a bit lower than the axle height.
That would be no issue on a single crown fork but to get a low offset on a DC fork you'd have a pretty poor Max steering angle as you'd have to have zero offset or maybe negative crowns.
 

Happymtb.fr

Turbo Monkey
Feb 9, 2016
1,959
1,318
SWE
About bushing overlap, some (maybe all? Idk) inverted moto forks have sliding bushings: one bushing at the bottom of the slider and the other at the top of the stanchion. The more you compress the fork, the more bushing overlap you get.

Most inverted mtb forks have fixed bushings. Why? The only inverted fork with sliding bushings I know about is the one made by CRconception
 

PUSHIND

PUSH Industries (Duh)
Dec 5, 2003
221
251
Colorado
I wonder if Push will use one. Could the axle conundrum* be what killed the Fox USD project and now the hex axle could bring it back?
We prototyped round axles, hex axles, steel axles, aluminum axles.....on an on. After hours and hours on our torsional test rigs along with months of field testing...well, you can see from the various photos and videos from Sea Otter that we're not using a hex.

Most companies making or that made inverted did it because its cheaper and easier than cast lowers.
Definitely not. Diecast lower legs are far less expensive.

Here's a look at just one of our 3 setups required to machine the outer tube:

OuterTube.jpg
 

iRider

Turbo Monkey
Apr 5, 2008
5,654
3,101
Cornelius from Intend (a big fan of Manitou products back in the day) said he tried different axle types/designs/materials and found that a steel axle provided the stiffness to weight that he was after for an inverted fork.
 

Jm_

sled dog's bollocks
Jan 14, 2002
19,267
9,904
AK
We prototyped round axles, hex axles, steel axles, aluminum axles.....on an on. After hours and hours on our torsional test rigs along with months of field testing...well, you can see from the various photos and videos from Sea Otter that we're not using a hex.

Definitely not. Diecast lower legs are far less expensive.

Here's a look at just one of our 3 setups required to machine the outer tube:

View attachment 195038
We did a thread here were those in the industry posted a few prices of the equipment and it was upwards of a million for that kind of equipment. CNC machines are not cheap either, but it's my understanding the cost and complexity of investment casting is a good few levels above CNCing. My comment said "most", to leave some exception, as there have been lots of companies that came and went making inverted forks and it seems to me to be a lot easier to machine some tubes rather than have to pour, cast and machine lowers out of aluminum or magnesium. Avalanche, Risse, Hanabrink, Stratos, Mr. Dirt, Foes, just to name a few. My theory is they had access to CNC machines/operations and this was the far easier way for them to produce suspension parts, rather than having to cast parts. A more complex design, like Intend, might be a little more "equal" in cost...but being able to crank out *and change* cast lowers doesn't seem "cheaper" to me.
 

PUSHIND

PUSH Industries (Duh)
Dec 5, 2003
221
251
Colorado
@PUSHIND , when are you folks going to release full details on the fork?
Once they're available for sale to customers.

We did a thread here were those in the industry posted a few prices of the equipment and it was upwards of a million for that kind of equipment. CNC machines are not cheap either, but it's my understanding the cost and complexity of investment casting is a good few levels above CNCing. My comment said "most", to leave some exception, as there have been lots of companies that came and went making inverted forks and it seems to me to be a lot easier to machine some tubes rather than have to pour, cast and machine lowers out of aluminum or magnesium. Avalanche, Risse, Hanabrink, Stratos, Mr. Dirt, Foes, just to name a few. My theory is they had access to CNC machines/operations and this was the far easier way for them to produce suspension parts, rather than having to cast parts. A more complex design, like Intend, might be a little more "equal" in cost...but being able to crank out *and change* cast lowers doesn't seem "cheaper" to me.
Not familiar with the thread you're referring to, but I am very familiar with the costs of both standard CNC machines, as well as building a completely automated production machining facility.

While the molds for diecasting are expensive, the per-piece price is extremely low. This lends the ability to pay for the tooling upfront or it can be amortized over the production parts depending on the vendor you work with. If you pay $60,000 for a mold and order 12,000 parts, you're only amortizing $5 per lower leg into the COGS. Also, because you're ending up with a component that is very close to the final net shape, minimal machining is necessary for features such as bushing seats, seal glands, etc. In fact, with form tooling, the lower seat, bushing area, and seal gland can all be machined in one single operation as they are concentric features. It is set up to be a very cost-effective, streamlined production process for complex part designs which is one of the reasons why it's used.

On the other hand, the materials, programming, tooling, and cycle time involved in machining carry much greater costs. This is why you often see extrusions and forgings being used in high-volume machined parts so that you're at least starting with a rough net shape of the finished part.
 

norbar

KESSLER PROBLEM. Just cause
Jun 7, 2007
11,465
1,679
Warsaw :/
Once they're available for sale to customers.

Not familiar with the thread you're referring to, but I am very familiar with the costs of both standard CNC machines, as well as building a completely automated production machining facility.

While the molds for diecasting are expensive, the per-piece price is extremely low. This lends the ability to pay for the tooling upfront or it can be amortized over the production parts depending on the vendor you work with. If you pay $60,000 for a mold and order 12,000 parts, you're only amortizing $5 per lower leg into the COGS. Also, because you're ending up with a component that is very close to the final net shape, minimal machining is necessary for features such as bushing seats, seal glands, etc. In fact, with form tooling, the lower seat, bushing area, and seal gland can all be machined in one single operation as they are concentric features. It is set up to be a very cost-effective, streamlined production process for complex part designs which is one of the reasons why it's used.

On the other hand, the materials, programming, tooling, and cycle time involved in machining carry much greater costs. This is why you often see extrusions and forgings being used in high-volume machined parts so that you're at least starting with a rough net shape of the finished part.
While you are correct many smaller companies probably went with CNC because they couldn't/didn't want to field a big up front investment even if the per unit cost was lower. I think that was his point. Obviously molds scale better
 

canadmos

Cake Tease
May 29, 2011
21,024
20,178
Canaderp
While you are correct many smaller companies probably went with CNC because they couldn't/didn't want to field a big up front investment even if the per unit cost was lower. I think that was his point. Obviously molds scale better
And when they go under, that CNC machine can be auctioned off. That mold, probably not?
 

Jm_

sled dog's bollocks
Jan 14, 2002
19,267
9,904
AK
And when they go under, that CNC machine can be auctioned off. That mold, probably not?
If you even owned one in the first place, most are contracting w/someone to make their stuff usually, avoiding that huge capital cost. Trickstuff is a great example. Push seems to own at least one, so not in the same category, but again, the main reason the inverted design has been pursued/persisted over the years…
 

canadmos

Cake Tease
May 29, 2011
21,024
20,178
Canaderp
If you even owned one in the first place, most are contracting w/someone to make their stuff usually, avoiding that huge capital cost. Trickstuff is a great example. Push seems to own at least one, so not in the same category, but again, the main reason the inverted design has been pursued/persisted over the years…
Should come visit one of the buildings at my work here, the one has 50+ cnc machines. The flow forming machines are the magic ones - metal goes in one end and a formed part comes out the other. :confused:
 

PUSHIND

PUSH Industries (Duh)
Dec 5, 2003
221
251
Colorado
If you even owned one in the first place, most are contracting w/someone to make their stuff usually, avoiding that huge capital cost. Trickstuff is a great example. Push seems to own at least one, so not in the same category, but again, the main reason the inverted design has been pursued/persisted over the years…
Having CNC automation had nothing to do with our decision to build an inverted fork. Designing, prototyping, and manufacturing a conventional fork would have been a much easier path.

And yes, we have at least one...actually.....a large number of them :D:D We take a lot of pride in being a manufacturer, and have an incredibly talented staff!

Our most recent DMG Mori installation as part of our facility expansion here in Colorado:

DMGInstall.jpg
 

PUSHIND

PUSH Industries (Duh)
Dec 5, 2003
221
251
Colorado
Oooh, and nice machines.

I can usually spot something made on a Haas machine because of the shitty surface finish from torque ripple.
No way Bro, they have an F-1 team, must be the best in the world! :p

Haas is like the Ford of the machine tool world.
Friggin machine snobs! :D

I will say that had it not been for Haas equipment it would have been very difficult for us to begin manufacturing. They make very good equipment and provide good value for their price point. On top of that, a great programmer and setup machinist with a Haas can produce better parts than an average programmer and setup machinist on a Mori, Okuma, etc! We still have a 4 axis trunnion Haas VF2 on our floor and it still makes great stuff.

That being said, there is a point at which you level up, especially if you're looking into automation like we were. The precision and capabilities of our Mori's, Citizen, and Tsugami machines are next level for sure!
 

englertracing

you owe me a sandwich
Mar 5, 2012
1,590
1,086
La Verne
Not something I exactly have intimate knowledge with. Just was thinking that I don't think I had ever seen a regular style motorcycle fork with an arch. I have had some street bikes where a flimsy plastic fender is bolted between fork legs, but that ain't going to do much. Which really puts all of them in a similar category as a USD fork.



View attachment 195014

View attachment 195015

View attachment 195016

I had an older version of the SV650 in the last picture above. My generation bike only had a 17mm diameter axle on a 450lb bike. Any issues I had with that fork was with the orifice damper, which is much less of a big deal when you have 400lbs of shit between you and the suspension. Now each one of those fork legs probably weighs a lot more than a complete DH fork and in the worse case scenario only has to deal with a 21" wheel.
An sv650 is the sport bike equivalent of a wallmart bike.
If a wallmart bike has a qr skewer AND a shit damper of course the damper will be more obvious
brace-fork-stabilizer-for-honda-xr650l_12_1200x.jpg

Fork braces were a thing.
 
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konastab01

Turbo Monkey
Dec 7, 2004
1,254
308
I’m surprised they didn’t spec more travel, but it’s cool to see the options continue to grow for these bikes.
They need options as they are too much for DH parts, the amount of fucked forks ive seen from these electric bikes is wild.
 

konastab01

Turbo Monkey
Dec 7, 2004
1,254
308
Damn. Bent backward from front end impacts or bent forward/outward from landing hard? Surron kids are hard on their stuff. They expect parts to have the durability of their 1998 CR250. Manitou rates the alloy legged models for non-throttle ebike use, but not the carbon model I use. Interesting that the stantions are the weak point.
I dont even think its because they are harder, in think its the extra weight and the power that makes it easy to do stuff that fucks them.
 

konastab01

Turbo Monkey
Dec 7, 2004
1,254
308
Friggin machine snobs! :D

I will say that had it not been for Haas equipment it would have been very difficult for us to begin manufacturing. They make very good equipment and provide good value for their price point. On top of that, a great programmer and setup machinist with a Haas can produce better parts than an average programmer and setup machinist on a Mori, Okuma, etc! We still have a 4 axis trunnion Haas VF2 on our floor and it still makes great stuff.

That being said, there is a point at which you level up, especially if you're looking into automation like we were. The precision and capabilities of our Mori's, Citizen, and Tsugami machines are next level for sure!
Excited to see the finished DH fork Darren, Ill defo be keen on one.

I have a Intend for a build and have rode it for a weekend and its been a magic fork, super plush and ride really nice with tracking and stuff.