MTB Tech Rumors and Innovation

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Primoz
Posts
4519
Joined
8/1/2009
Location
SI
4/11/2025 11:23pm
There are a few people who I eagerly await pre-season race footage of, top of the list is Loic and based on his recent story I'd...

There are a few people who I eagerly await pre-season race footage of, top of the list is Loic and based on his recent story I'd say we aren't disappointed. New/Raw brake calipers, possibly uncovered rear shock finally, new chainstay, new/kinked seat tube? There's too much and yes I am hoping someone posts the screenshots for me. 

MTBrent wrote:
IMG 6628IMG 6627

That fork coating is reminiscent of the older rockshox 26in models. What is it? I forgot if it was Titanium Nitride or something else.

Reminds me of the coffee related named Marzocchi models from before they were bought out by Fox... 

3
Primoz
Posts
4519
Joined
8/1/2009
Location
SI
4/11/2025 11:52pm
whitesq wrote:
Forgot about that and props to Primoz, it is an insightful post. However, it is only looking at wag and not roll. If he did include...

Forgot about that and props to Primoz, it is an insightful post. However, it is only looking at wag and not roll. If he did include roll, I'd venture to guess the results would be similar though, the USD is not as stiff as a RSD. But the nuance of the whole game is what is the right amount of flex/stiffness/compliance? 

I think a lot of the roll in the rear wheel is generated by the way the frame is designed and I would not be surprised there is fairly little (compared to the rear) roll going on with the front wheel. You would be twisting the wheel basically towards the stanchion where the fork is the strongest. I'd guess most of the loading generated in this direction would be deflected to a different axis/plane just due to the structure of the fork, it buckling out of axis, etc. 

If we are talking about roll specifically, I would not be surprised if roll was a much bigger factor with USD forks (no bridge) than with rsu forks (I also tested a bridge less RSU fork in that analysis and it's a noodle) but at the same time I would be surprised if the main factor generating roll was rider's inputs vs. The fork itself - the forces generated by the spring are not the same as the forces generated by the damper, on the return stroke they are not only not the same scale, they are even working one against the other so actually working really strongly to generate roll. With an USD fork the stanchion-interface-to-dropout, dropout itself, the axle (diameter and thickness) and it being clamped into the dropout and the hub assembly is the only thing preventing roll generated by the stanchions moving unsynchronised. 

2
Primoz
Posts
4519
Joined
8/1/2009
Location
SI
4/11/2025 11:56pm
Etney wrote:
Fox USD fork confirmed (or at least they are showing it as a prototype)Pic borrowed from the pink site

Fox USD fork confirmed (or at least they are showing it as a prototype)

Pic borrowed from the pink site
31fc0f259a3010a5c8e6fdefeb87daef 0.jpg?VersionId=lGN4DkcPvBlrXuWQyrrvAgKOsQ6Y

TEAMROBOT wrote:
I can't figure out why anyone making an inverted fork in 2025, especially a single crown inverted fork, wouldn't use the Manitou hex axle to add...

I can't figure out why anyone making an inverted fork in 2025, especially a single crown inverted fork, wouldn't use the Manitou hex axle to add torsional stiffness. The patent is expired and it adds almost no weight. I imagine a 15mm hex axle is significantly stiffer in torsion than a round 20mm axle, and doesn't require a new front hub. Especially if you're already doing pinch bolts, you can do it the way the Dorado has been doing it since 2002? It's so simple!

Manitou Axles - S4 Suspension

We'd finally settled on Boost 15mm as a trail bike front hub, and now it's blowing up again. Sigh.

They axle isn't really in torsion though (that would be both legs rotating opposite way around the hub) so I'm not sure how helpful is? A...

They axle isn't really in torsion though (that would be both legs rotating opposite way around the hub) so I'm not sure how helpful is? A 20mm axle or maybe torque caps are probably the better options out of what already exists

Clamping down on the axle is what improves torsional rigidity of an usd fork. Besides bending the stanchions also twist a bit and also twist around the axle. Clamping that down makes it a bit stiffer. 

3
Jakub_G
Posts
352
Joined
8/7/2019
Location
SK
4/11/2025 11:56pm
TEAMROBOT wrote:
This looks like a good way to get rid of the vulnerable pull link that was hanging out under the BB on the last version of...

This looks like a good way to get rid of the vulnerable pull link that was hanging out under the BB on the last version of the Demo prototype. But I'm surprised to hear it has "pretty high anti-rise," and I'm also curious what numbers you think are pretty high, aka above or below 100%

Specialized has been on the very very low AR program for a long time, in the 40-60% range on the Demo, Enduro, and Stumpjumper for years and years. I would be shocked if they went above 100% on the new Demo, and that would represent a big change in suspension philosophy for them.

They were also promoting very low anti squat (or even pro squat), no chain growth, very little to no progression at all etc. And here we are 🤷🏻

4
Jakub_G
Posts
352
Joined
8/7/2019
Location
SK
4/11/2025 11:57pm
Carraig042 wrote:

With a 15mm hex axle.

 

It's not hex axle, more like square with rounded edges. Nothing new from them, it's a same design as helm forks used from the get go.

1
Jakub_G
Posts
352
Joined
8/7/2019
Location
SK
4/12/2025 12:00am

They dont hold asa back 

There's a chance he is so fast because he wants to finish before his cranks explode.

17
Jakub_G
Posts
352
Joined
8/7/2019
Location
SK
4/12/2025 12:04am Edited Date/Time 4/12/2025 12:11am
Primoz wrote:

Reminds me of the coffee related named Marzocchi models from before they were bought out by Fox... 

Nah cappuccino coating was more like bronze color and also very shiny. This looks almost like matt in appearance and shade is also very different. Performance wise dlc/pvd would be most likely the best option and not too hard to get, colour options are in that region as well 17444414194893215229351337521937.jpg?VersionId=x8MX8nt6BpWDqNcWVLqaGE2p8eXZYB

2
B Rabbit
Posts
50
Joined
1/13/2024
Location
Sydney, NSW AU
4/12/2025 2:04am Edited Date/Time 4/12/2025 2:05am
karlbrodie wrote:

The big question regarding all these new USD forks is, where are we putting the mudguard?  

Your chin is the mudguard now 🤷‍♂️

7
alex_o
Posts
8
Joined
1/18/2025
Location
Lisboa PT
4/12/2025 4:49am Edited Date/Time 4/12/2025 4:49am

Will it be the return of frame mount mud guards?

3
slimshady
Posts
146
Joined
9/16/2011
Location
AR
4/12/2025 5:07am
Primoz wrote:

Reminds me of the coffee related named Marzocchi models from before they were bought out by Fox... 

Jakub_G wrote:
Nah cappuccino coating was more like bronze color and also very shiny. This looks almost like matt in appearance and shade is also very different. Performance...

Nah cappuccino coating was more like bronze color and also very shiny. This looks almost like matt in appearance and shade is also very different. Performance wise dlc/pvd would be most likely the best option and not too hard to get, colour options are in that region as well 17444414194893215229351337521937.jpg?VersionId=x8MX8nt6BpWDqNcWVLqaGE2p8eXZYB

Actually, it was called espresso 🤓. I had a 350, good sliding but boy that thing went down as fast as butter on a hot toast.

5
Jakub_G
Posts
352
Joined
8/7/2019
Location
SK
4/12/2025 5:27am Edited Date/Time 4/12/2025 5:28am
Primoz wrote:

Reminds me of the coffee related named Marzocchi models from before they were bought out by Fox... 

Jakub_G wrote:
Nah cappuccino coating was more like bronze color and also very shiny. This looks almost like matt in appearance and shade is also very different. Performance...

Nah cappuccino coating was more like bronze color and also very shiny. This looks almost like matt in appearance and shade is also very different. Performance wise dlc/pvd would be most likely the best option and not too hard to get, colour options are in that region as well 17444414194893215229351337521937.jpg?VersionId=x8MX8nt6BpWDqNcWVLqaGE2p8eXZYB

slimshady wrote:

Actually, it was called espresso 🤓. I had a 350, good sliding but boy that thing went down as fast as butter on a hot toast.

Heh not it seems the Mocha one is the closest I think from the color palette I posted above. As long as it's not latte macchiato coloured it's fine by me 😁

2
TannerVal
Posts
128
Joined
2/6/2016
Location
Hampton, NH US
4/12/2025 5:27am
Primoz wrote:

Reminds me of the coffee related named Marzocchi models from before they were bought out by Fox... 

Jakub_G wrote:
Nah cappuccino coating was more like bronze color and also very shiny. This looks almost like matt in appearance and shade is also very different. Performance...

Nah cappuccino coating was more like bronze color and also very shiny. This looks almost like matt in appearance and shade is also very different. Performance wise dlc/pvd would be most likely the best option and not too hard to get, colour options are in that region as well 17444414194893215229351337521937.jpg?VersionId=x8MX8nt6BpWDqNcWVLqaGE2p8eXZYB

slimshady wrote:

Actually, it was called espresso 🤓. I had a 350, good sliding but boy that thing went down as fast as butter on a hot toast.

Yeah, cappuccino would be much lighter

2
Skepex
Posts
1
Joined
4/12/2025
Location
Heidelberg DE
4/12/2025 5:45am

Does anyone know something about a new Megatower?

1
monarchmason
Posts
283
Joined
5/24/2022
Location
Nevada City, CA US
4/12/2025 6:35am
Skepex wrote:

Does anyone know something about a new Megatower?

Towers are not tall enough. Said to be a new 32”. Going to be called MegaSkyScraper. Remember me as I just leaked the companies biggest news. Theyre coming for me. 

18
3
monarchmason
Posts
283
Joined
5/24/2022
Location
Nevada City, CA US
4/12/2025 8:20am

I actually hope this USD fork excitement brings the revival of the all mountain Lefty. Maybe Im the only weird one on this.

15
5
4/12/2025 8:24am
Skepex wrote:

Does anyone know something about a new Megatower?

Don't know anything about the Megatower, but 2026 colours and builds have been released. The newest gen 2025 Hightower was released in September 2024, so if I had to guess the new Mega would be released during the second half of 2026. I have the current Mega and it's a sweet bike. 

2
sspomer
Posts
6030
Joined
6/26/2009
Location
Boise, ID US
4/12/2025 10:10am

some really interesting stuff w/ dakotah and his bike setup (the rim stuff was cool)

8
TEAMROBOT
Posts
1348
Joined
9/2/2009
Location
Los Angeles, CA US
4/12/2025 10:44am Edited Date/Time 4/12/2025 11:23am
Primoz wrote:
Clamping down on the axle is what improves torsional rigidity of an usd fork. Besides bending the stanchions also twist a bit and also twist around...

Clamping down on the axle is what improves torsional rigidity of an usd fork. Besides bending the stanchions also twist a bit and also twist around the axle. Clamping that down makes it a bit stiffer. 

Hey all, learned a lot about bending and tube shapes in this discussion. To your point, clamping a tube is extremely effective at preventing rotation, i.e. the handlebar/stem interface or seatpost/seattube interface. No one makes hexagonal seatposts or handlebars, because bolts and clamps seem to work just fine. Not a lot of rotation if things are clamped down properly. 

I disagree with @TheSuspensionLabNZ (which doesn't happen very often, or ever?) that the axle of a USD is not experiencing significant torsional loads. I think the front wheel on any MTB fork is experiencing tremendous torsional loads because of one-sided disc brakes. I learned this on an illuminating and frightening road ride on an early-generation disc cyclocross bike with a QR front axle. I like road rides that are steep, hilly, and fast on the descents, but this fork was twisting dramatically in the wag/yaw axis whenever I jammed on the brakes, so much that I was being pushed wide on turns at 40+ mph, which was horrifying. I had to ride at basically half speed on all the descents because the front of the bike would wander and push/pull so much when I braked. Yikes.

That's an extreme example, and thank God no one makes QR disc forks anymore (for road or mountain bikes), but the lesson remains. When you make a USD fork, by removing the arch from a traditional telescoping fork, you're asking the axle to do all the work in preventing that torsional wag/yaw force under braking. I think that's more of a concern for than rider input forces, but when you combine all those [braking, trail, and body input] forces together it gets really bad. And then add in the left/right imbalance in forces from single-sided dampers and springs that others have mentioned, that are adding roll forces at the axle. It’s a lot  

Imagine a steep set of grippy jagged rocks that you have to brake through into a turn, where you're braking, compressing, decelerating, setting up to turn, and leaning the bike all at the same time, with body inputs in every direction, and maybe stuffing the front wheel into some weird rock shapes that want to deflect the front wheel in the wrong direction, too. That's the scenario where a set of overbuilt and "too stiff" Fox 40 lowers are going to be your friend. By comparison, when you're coasting and not braking on a slippery off-camber, the USD fork is going to be brilliant and the Fox 40 is going to deflect. Trade offs. And this trade off is going to be amplified when we're talking about a single crown USD fork. Color me suspicious of these new single crown USD forks. Would love to try one to see if I’m wrong. 

9
TEAMROBOT
Posts
1348
Joined
9/2/2009
Location
Los Angeles, CA US
4/12/2025 10:50am
TannerVal wrote:

Yeah, cappuccino would be much lighter

Other Fox stanchion color options for the U.S. suburban market:

This may contain: starbucks drinks with different toppings and names on the cups, all in different colors

23
Robstyle
Posts
85
Joined
1/2/2023
Location
Invercargill NZ
4/12/2025 11:50am

If y'all ever want to test what real torsional flex feels like, just take a usd fork for a ride with the pinch bolts loose 😬

The different front axle configurations are interesting, iirc intend dropped the 20mm option because it didn't yield a significant gain. 

8
dolface
Posts
1656
Joined
10/26/2015
Location
CA US
4/12/2025 12:03pm
Primoz wrote:
Clamping down on the axle is what improves torsional rigidity of an usd fork. Besides bending the stanchions also twist a bit and also twist around...

Clamping down on the axle is what improves torsional rigidity of an usd fork. Besides bending the stanchions also twist a bit and also twist around the axle. Clamping that down makes it a bit stiffer. 

TEAMROBOT wrote:
Hey all, learned a lot about bending and tube shapes in this discussion. To your point, clamping a tube is extremely effective at preventing rotation, i.e...

Hey all, learned a lot about bending and tube shapes in this discussion. To your point, clamping a tube is extremely effective at preventing rotation, i.e. the handlebar/stem interface or seatpost/seattube interface. No one makes hexagonal seatposts or handlebars, because bolts and clamps seem to work just fine. Not a lot of rotation if things are clamped down properly. 

I disagree with @TheSuspensionLabNZ (which doesn't happen very often, or ever?) that the axle of a USD is not experiencing significant torsional loads. I think the front wheel on any MTB fork is experiencing tremendous torsional loads because of one-sided disc brakes. I learned this on an illuminating and frightening road ride on an early-generation disc cyclocross bike with a QR front axle. I like road rides that are steep, hilly, and fast on the descents, but this fork was twisting dramatically in the wag/yaw axis whenever I jammed on the brakes, so much that I was being pushed wide on turns at 40+ mph, which was horrifying. I had to ride at basically half speed on all the descents because the front of the bike would wander and push/pull so much when I braked. Yikes.

That's an extreme example, and thank God no one makes QR disc forks anymore (for road or mountain bikes), but the lesson remains. When you make a USD fork, by removing the arch from a traditional telescoping fork, you're asking the axle to do all the work in preventing that torsional wag/yaw force under braking. I think that's more of a concern for than rider input forces, but when you combine all those [braking, trail, and body input] forces together it gets really bad. And then add in the left/right imbalance in forces from single-sided dampers and springs that others have mentioned, that are adding roll forces at the axle. It’s a lot  

Imagine a steep set of grippy jagged rocks that you have to brake through into a turn, where you're braking, compressing, decelerating, setting up to turn, and leaning the bike all at the same time, with body inputs in every direction, and maybe stuffing the front wheel into some weird rock shapes that want to deflect the front wheel in the wrong direction, too. That's the scenario where a set of overbuilt and "too stiff" Fox 40 lowers are going to be your friend. By comparison, when you're coasting and not braking on a slippery off-camber, the USD fork is going to be brilliant and the Fox 40 is going to deflect. Trade offs. And this trade off is going to be amplified when we're talking about a single crown USD fork. Color me suspicious of these new single crown USD forks. Would love to try one to see if I’m wrong. 

 I don't know enough about this stuff to have an informed opinion but fwiw Darren Murphy (of Push) posted a bunch of stuff about flex and torsion when they were developing the Nine One. His conclusion was that the real-world torsional deflection on their fork wasn't significant enough to offset the other gains the design offered. (Can't find links atm but I do remember that that the "hold the front wheel w/ your knees and turn the bars" test was one he was pretty adamant had almost no bearing on real-world performance).

5
4/12/2025 12:58pm
Skepex wrote:

Does anyone know something about a new Megatower?

Pon are all in on ebbbssss the MT is dead.

2
2
majorjake
Posts
33
Joined
5/25/2018
Location
Burlington, VT US
4/12/2025 1:15pm
karlbrodie wrote:

The big question regarding all these new USD forks is, where are we putting the mudguard?  

Onawalk wrote:
What was old is new again!I had a silver "carbon fibre" coloured version on a Marzo Shiver SC on my Giant AC-1!This is the best, and...

What was old is new again!

I had a silver "carbon fibre" coloured version on a Marzo Shiver SC on my Giant AC-1!

This is the best, and only way!

https://www.google.com/url?sa=i&url=https%3A%2F%2Fwww.reddit.com%2Fr%2F…

I'll make you feel young again; Acerbis fenders on a chromo Mongoose IBOC.

5
sspomer
Posts
6030
Joined
6/26/2009
Location
Boise, ID US
4/12/2025 1:23pm

Frameworks sea otter bike check with Fox usd fork

8
4/12/2025 3:20pm
TEAMROBOT wrote:
Hey all, learned a lot about bending and tube shapes in this discussion. To your point, clamping a tube is extremely effective at preventing rotation, i.e...

Hey all, learned a lot about bending and tube shapes in this discussion. To your point, clamping a tube is extremely effective at preventing rotation, i.e. the handlebar/stem interface or seatpost/seattube interface. No one makes hexagonal seatposts or handlebars, because bolts and clamps seem to work just fine. Not a lot of rotation if things are clamped down properly. 

I disagree with @TheSuspensionLabNZ (which doesn't happen very often, or ever?) that the axle of a USD is not experiencing significant torsional loads. I think the front wheel on any MTB fork is experiencing tremendous torsional loads because of one-sided disc brakes. I learned this on an illuminating and frightening road ride on an early-generation disc cyclocross bike with a QR front axle. I like road rides that are steep, hilly, and fast on the descents, but this fork was twisting dramatically in the wag/yaw axis whenever I jammed on the brakes, so much that I was being pushed wide on turns at 40+ mph, which was horrifying. I had to ride at basically half speed on all the descents because the front of the bike would wander and push/pull so much when I braked. Yikes.

That's an extreme example, and thank God no one makes QR disc forks anymore (for road or mountain bikes), but the lesson remains. When you make a USD fork, by removing the arch from a traditional telescoping fork, you're asking the axle to do all the work in preventing that torsional wag/yaw force under braking. I think that's more of a concern for than rider input forces, but when you combine all those [braking, trail, and body input] forces together it gets really bad. And then add in the left/right imbalance in forces from single-sided dampers and springs that others have mentioned, that are adding roll forces at the axle. It’s a lot  

Imagine a steep set of grippy jagged rocks that you have to brake through into a turn, where you're braking, compressing, decelerating, setting up to turn, and leaning the bike all at the same time, with body inputs in every direction, and maybe stuffing the front wheel into some weird rock shapes that want to deflect the front wheel in the wrong direction, too. That's the scenario where a set of overbuilt and "too stiff" Fox 40 lowers are going to be your friend. By comparison, when you're coasting and not braking on a slippery off-camber, the USD fork is going to be brilliant and the Fox 40 is going to deflect. Trade offs. And this trade off is going to be amplified when we're talking about a single crown USD fork. Color me suspicious of these new single crown USD forks. Would love to try one to see if I’m wrong. 

Thomas Sowell quote: There are no solutions; there are only trade-offs.

3
2
RaggedEdge
Posts
80
Joined
12/5/2017
Location
Austin, TX US
4/12/2025 3:21pm

Both of those vids are great. Neko, FW, and the team are the coolest thing to happen in a long time!

4
4/12/2025 3:23pm

I actually hope this USD fork excitement brings the revival of the all mountain Lefty. Maybe Im the only weird one on this.

No, I love the Lefty too. Dual crown, inverted, great torsional stiffness, all at that cost of having to deal with Cannondale's customer service. 

All these forks have the air spring on just one side anyways, so why not put the damper over there too and dump the other leg?

What patents does Cannondale still hold on it?

2
luisgutrod
Posts
332
Joined
5/8/2017
Location
Paris FR
4/12/2025 7:49pm
TEAMROBOT wrote:
Hey all, learned a lot about bending and tube shapes in this discussion. To your point, clamping a tube is extremely effective at preventing rotation, i.e...

Hey all, learned a lot about bending and tube shapes in this discussion. To your point, clamping a tube is extremely effective at preventing rotation, i.e. the handlebar/stem interface or seatpost/seattube interface. No one makes hexagonal seatposts or handlebars, because bolts and clamps seem to work just fine. Not a lot of rotation if things are clamped down properly. 

I disagree with @TheSuspensionLabNZ (which doesn't happen very often, or ever?) that the axle of a USD is not experiencing significant torsional loads. I think the front wheel on any MTB fork is experiencing tremendous torsional loads because of one-sided disc brakes. I learned this on an illuminating and frightening road ride on an early-generation disc cyclocross bike with a QR front axle. I like road rides that are steep, hilly, and fast on the descents, but this fork was twisting dramatically in the wag/yaw axis whenever I jammed on the brakes, so much that I was being pushed wide on turns at 40+ mph, which was horrifying. I had to ride at basically half speed on all the descents because the front of the bike would wander and push/pull so much when I braked. Yikes.

That's an extreme example, and thank God no one makes QR disc forks anymore (for road or mountain bikes), but the lesson remains. When you make a USD fork, by removing the arch from a traditional telescoping fork, you're asking the axle to do all the work in preventing that torsional wag/yaw force under braking. I think that's more of a concern for than rider input forces, but when you combine all those [braking, trail, and body input] forces together it gets really bad. And then add in the left/right imbalance in forces from single-sided dampers and springs that others have mentioned, that are adding roll forces at the axle. It’s a lot  

Imagine a steep set of grippy jagged rocks that you have to brake through into a turn, where you're braking, compressing, decelerating, setting up to turn, and leaning the bike all at the same time, with body inputs in every direction, and maybe stuffing the front wheel into some weird rock shapes that want to deflect the front wheel in the wrong direction, too. That's the scenario where a set of overbuilt and "too stiff" Fox 40 lowers are going to be your friend. By comparison, when you're coasting and not braking on a slippery off-camber, the USD fork is going to be brilliant and the Fox 40 is going to deflect. Trade offs. And this trade off is going to be amplified when we're talking about a single crown USD fork. Color me suspicious of these new single crown USD forks. Would love to try one to see if I’m wrong. 

yeap, you definitively need to try one of the new single crown USD ones.. keep in mind the crowns are massive, not comparable to conventional and do better job that crowns in conventional that are kept slim and lean for weight targets.. normally.. ..(I can only talk about intend, look at the flash)..Push seems equivalent...

3
Primoz
Posts
4519
Joined
8/1/2009
Location
SI
4/12/2025 11:00pm
Primoz wrote:
Clamping down on the axle is what improves torsional rigidity of an usd fork. Besides bending the stanchions also twist a bit and also twist around...

Clamping down on the axle is what improves torsional rigidity of an usd fork. Besides bending the stanchions also twist a bit and also twist around the axle. Clamping that down makes it a bit stiffer. 

TEAMROBOT wrote:
Hey all, learned a lot about bending and tube shapes in this discussion. To your point, clamping a tube is extremely effective at preventing rotation, i.e...

Hey all, learned a lot about bending and tube shapes in this discussion. To your point, clamping a tube is extremely effective at preventing rotation, i.e. the handlebar/stem interface or seatpost/seattube interface. No one makes hexagonal seatposts or handlebars, because bolts and clamps seem to work just fine. Not a lot of rotation if things are clamped down properly. 

I disagree with @TheSuspensionLabNZ (which doesn't happen very often, or ever?) that the axle of a USD is not experiencing significant torsional loads. I think the front wheel on any MTB fork is experiencing tremendous torsional loads because of one-sided disc brakes. I learned this on an illuminating and frightening road ride on an early-generation disc cyclocross bike with a QR front axle. I like road rides that are steep, hilly, and fast on the descents, but this fork was twisting dramatically in the wag/yaw axis whenever I jammed on the brakes, so much that I was being pushed wide on turns at 40+ mph, which was horrifying. I had to ride at basically half speed on all the descents because the front of the bike would wander and push/pull so much when I braked. Yikes.

That's an extreme example, and thank God no one makes QR disc forks anymore (for road or mountain bikes), but the lesson remains. When you make a USD fork, by removing the arch from a traditional telescoping fork, you're asking the axle to do all the work in preventing that torsional wag/yaw force under braking. I think that's more of a concern for than rider input forces, but when you combine all those [braking, trail, and body input] forces together it gets really bad. And then add in the left/right imbalance in forces from single-sided dampers and springs that others have mentioned, that are adding roll forces at the axle. It’s a lot  

Imagine a steep set of grippy jagged rocks that you have to brake through into a turn, where you're braking, compressing, decelerating, setting up to turn, and leaning the bike all at the same time, with body inputs in every direction, and maybe stuffing the front wheel into some weird rock shapes that want to deflect the front wheel in the wrong direction, too. That's the scenario where a set of overbuilt and "too stiff" Fox 40 lowers are going to be your friend. By comparison, when you're coasting and not braking on a slippery off-camber, the USD fork is going to be brilliant and the Fox 40 is going to deflect. Trade offs. And this trade off is going to be amplified when we're talking about a single crown USD fork. Color me suspicious of these new single crown USD forks. Would love to try one to see if I’m wrong. 

dolface wrote:
 I don't know enough about this stuff to have an informed opinion but fwiw Darren Murphy (of Push) posted a bunch of stuff about flex and...

 I don't know enough about this stuff to have an informed opinion but fwiw Darren Murphy (of Push) posted a bunch of stuff about flex and torsion when they were developing the Nine One. His conclusion was that the real-world torsional deflection on their fork wasn't significant enough to offset the other gains the design offered. (Can't find links atm but I do remember that that the "hold the front wheel w/ your knees and turn the bars" test was one he was pretty adamant had almost no bearing on real-world performance).

Vital MTB podcast content. Apparently there's very little twisting torque coming in from the contact patch to make steering too vague with an usd fork, making it a non factor. 

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