…for a single crown fork?
I’m sure I’ve seen people writing that longer travel single crown forks out too much stress through the CSU, and so should use double clamps. My question is, at what travel do you think that single crowns stop being effective?
Depends on the size and stiffness of the stanchions.
32's might be limited at 120-130 mm.
38's might be good to 180.
Difficult to say.
seeing as there's plenty of 180mm 29er single crown forks about already, I can't imagine it would be too challenging to make a 200mm travel Single crown fork. Tapered steerers and bigger headtubes addressed many of the issues that led to needing dual crowns back when all DH bikes had straight 1-1/8" steerers.
I reckon a USD would be best, a new Dorado SC would be awesome...
“Depends on the size and stiffness of the stanchions.”
It does but it also really doesn’t. The main problem area is the crown:steerer interface - the thicker the stanchions, the less they bend and the more that leverage is forced through the crown:steerer junction. Just watch pinkbike’s ultra slo-mo huck to plate videos and you’ll see how much they bend there.
You can get 190mm 29” Zebs. You used to be able to get 180mm Lyriks and 36s. I wonder how long they last before they start creaking? What the pros ride is irrelevant because they never use anything for long enough for longterm issues to show up. That’s also the case with the vast majority of mag/website reviews.
i guess it depends what you are going to do with it.
to me 180 travel suggests free riding and big drops and jumps or very fast descending on rough and chunky trails.
while the best riders are smooth enough to not need the extra strength of a dual crown will probably be fine with even more travel, but the less smooth rider may require extra strength if they are going to benefit from all the extra travel
there is also the weight to consider. the crown would need to be stronger and i’d guess with a greater overlap with stanchion (that would increase the A-C measurement). this will make them heavier. there must be a point at which a 35mm dual crown will be easier to package, have more direct steering, be lighter and stronger than a 200mm travel, 40+ mm single crown.
that said, i think more people would buy a monster single crown than a “sub-DH racing” dual crown
edit: and what CGG said
Whatever Semenuk ran at Rampage, at the least
The main problem area is the crown:steerer interface – the thicker the stanchions, the less they bend and the more that leverage is forced through the crown:steerer junction. Just watch pinkbike’s ultra slo-mo huck to plate videos and you’ll see how much they bend there.
You can get 190mm 29” Zebs. You used to be able to get 180mm Lyriks and 36s. I wonder how long they last before they start creaking? What the pros ride is irrelevant because they never use anything for long enough for longterm issues to show up. That’s also the case with the vast majority of mag/website reviews.
Yeah this is what I was wondering. Is 160-170mm a practical limit for the rest of us?
if the fork lowers ran zero offset (so all the offset was in the fork crown, and the legs were further forwards) there'd be almost no downside of a dual-crown fork. You could easily make a 300mm sc fork with enough material, but why bother? imo everything over 170mm should be a dually
Fair few 190 singke ceowns out there,
....Zeb,EXT
I'm running red 180mm Lyriks with a bit more sag on my Mega, no issues or noticeable flex over 170mm or even 160mm, don't like the weight penalty of 38mm forks, whatever happened with those proto enduro dual crown Formula fork, I thought they'd be the next craze.
Feasible or rational?
Feasible - anything you like, its just engineering and what trade off in weight and packaging you're prepared to accept for the "flexibility" of running an SC fork.
Rationally, though. At sub-65kg I can feel the flex in my 35mm stanchion 160mm travel Helm 2s, and as I've already had one CSU replaced due to a creaky steerer, I doubt its the stanchions flexing I can feel. As above its the stiffness of the crown/steerer interface that's the limiting factor - especially when you consider that a 1.5" steerer is the same dia as a 38mm stanchion... Weight wise a Boxxer is 200g heavier than a Zeb, but I reckon if you took the need for pure "DH rated" away, I don't think it would be too hard to match weight of a big SC with the much increased stiffness of a DC. Pinkbike do a slowmo huck->flat series where its quite disconcerting to see how much a fork flops around.
(Anyone remember triple clamp RS SIDS and Manitou XVerts from the late '90s? I had a pair of Pace RC37MXs for 24 hrs, until they disintegrated on their first descent)
People seem to forget that the 32mm Boxxer got up to 200mm travel before the design was finally superseded. You can make a strong enough stanchion in smaller diameters, but you will sacrifice stiffness.
These days I'm using a (29") Manitou Mezzer which probably has a similar A-C to those old Boxxers and is probably a good 1kg lighter. The thing that's changed is stanchion diameters which does affect stiffness, and the steerer diameter which is a good 10mm bigger (~38mm OD) that will affect strength. Dual crowns aren't really necessary on a trail or Enduro bike. You could easily ride DH on a modern 180mm(+) travel single crown fork.
I'm running 2019 Fox 36's at 180mm on my Banshee Rune with no worries from the fork.
Headset bearings are a different matter though. At 64º I think they're the weakest link these days.
Also depends on your weight.
A 32mm stanchion fork with 130mm travel light be too flexy if you're heavy but fine if you're light.
Been running my 180mm 36s since 2017 and never really had an issue, there's some creaking started now but they are 6 years old and have been abused.
cookeaa
People seem to forget that the 32mm Boxxer got up to 200mm travel before the design was finally superseded
On 26" wheels though.
I reckon 140mm is the limit given how many creaky csu’s I’ve had.
On 26″ wheels though.
So the radial difference between 26 and 29 is ~32mm so about an extra 1.5" on the A-C and you could (and people did) drop your Boxxer in the crowns to bump up the A-C.
Honestly those stanchions were under some significant leverage and were fine...