Fork offset experimenting
- Thread starter toodles
- Start date
I've done enough experimenting with bar width, stem length and reach adjust and angle adjust headsets over the past few years to sort of know what the changes feel like. I'm not claiming anything other that a difference in feel that doesn't match what I've experienced and expected with other things I've changed.
I'm also not sure I think the shorter offset is better for all-round riding. It seems to rely on the bike lean angle more to turn quickly in lower speed situations which isn't going to work on tightly tree'ed sections or for the blind Enduro racing I've been getting into for the past few years. Sometimes quicker handling is gonna be of benefit when you read a trail wrong or there is an unexpected obstacle.
What I think it does best in my un-scientific, holistic, hippy, borderline anti-vaxxer, unprofessional opinion is a smoother, calmer turn in at speed. Which is my next point - I think its more relevant to DH bikes than Enduro or trail but there might be drawbacks I don't know about because I'm cooked and don't own a DH bike anymore. I reckon a longer reach DH bike with a 42mm offset and 29er front would be interesting to give a go though. I don't even know what offset is on the 29er DH forks stock.
Anyway, I'm going to go back to drawing scientific conclusions by scattering chicken bones in a circle of crystals and publishing them as new found Laws of Thermodynamics.
I'm also not sure I think the shorter offset is better for all-round riding. It seems to rely on the bike lean angle more to turn quickly in lower speed situations which isn't going to work on tightly tree'ed sections or for the blind Enduro racing I've been getting into for the past few years. Sometimes quicker handling is gonna be of benefit when you read a trail wrong or there is an unexpected obstacle.
What I think it does best in my un-scientific, holistic, hippy, borderline anti-vaxxer, unprofessional opinion is a smoother, calmer turn in at speed. Which is my next point - I think its more relevant to DH bikes than Enduro or trail but there might be drawbacks I don't know about because I'm cooked and don't own a DH bike anymore. I reckon a longer reach DH bike with a 42mm offset and 29er front would be interesting to give a go though. I don't even know what offset is on the 29er DH forks stock.
Anyway, I'm going to go back to drawing scientific conclusions by scattering chicken bones in a circle of crystals and publishing them as new found Laws of Thermodynamics.
Too late. That's probably why I'm in the garage hiding so often.I envy you. Don't get kids - never ever!
I haven't gone that route yet. Happy just looking like a dork riding with a massive camelback for now. *pictured here with incorrect non-lizard approved slow offset fork*
Eleventy billion.
But seriously, they're fuckin' huge. The 40 29er is, I think, 58mm. The 650b one is 52mm, which is also silly big for a DH bike.
Now we're cookin with fire! Take that RM! I mean Udi!
FWIW I agree with you when it comes to 27.5 trailbike forks with the 43-44ish offsets most of them come with...I'm fine with them mostly. It's the 29er and dh forks that are stupid.
I just put ye ole 26" 180mm fork with 27.5 wheel on when I know I'm just going to be smashing shit.
I only understand Enduro-specific bumbag compatible single crowns but aside from the Fox and Rockshox differences (apparently Fox is shorter offset?)
Stock for 29er forks is 51mm offset, "reduced" is 42mm.
Stock for 27.5 is 46mm, "reduced" is 37mm.
Both 9mm shorter for RS forks, but percentage wise the 27.5 is moving more. Apparently you can put a 42mm offset into a 27.5, and someone was speccing that setup.
I think you got what I said entirely wrong. Or maybe I'm starting to dance with that German guy who liked to misplace my dad's stuff once he got old enough.
I'm waiting for a DH fork to look like the good ole' Quadra 21. Then I'll buy a new DH fork and we can discuss offset. Until then, none of you rednecks even have a clue as to what you're talking about.
My first "DH" bike had a Quadra 21R. 2" up and down travel. 4" fore-aft travel. Imagine the difference when I upgraded to an original Z1 bomber.
Yeah CSU are compatible across wheel sizes for current generation lyrik, gives a lot of options, but a bit expensive ti test haha.
In fact, many variables such as wheel diameter and head angle also impacts steering behavior, a given offset doesn't yield consistent feel across different bikes. That's why offset % difference between 27.5 and 29 forks is irrelevant.
The metric that best describes the steering behavior is the mechanical trail which is the leverage the "ground speed" has to align your wheel with the direction you travel.
The more mechanical trail you have, the more the force generated by the "ground speed" tries to steer your front wheel towards where you go thus increasing stability. The faster you go, the greater that aligning torque will be, conversely, if you travel at an hypothetical 0 km/h speed, there will be no aligning torque whether you have 20mm or 200mm mechanical trail.
Now another factor that is also tied to fork offset comes into play at low speed, it is the effect of the vertical force generated by the rider weight on the front tire contact patch. This force also creates a torque around steering axis, but it is trying to steer you off track more and more as you steer.
At any moment these two torques are opposed and their sum is what dictates if you need to apply a force to steer or apply a force to prevent the bike to steer more than you want.
Generally speaking, reducing fork offset makes both these effects more pronounced so steering is
respectively more unstable at low speed and more stable at higher speeds. That makes it maybe less predictable/consistent as the change in steering behaviour is more marked?
In my experience, I find more mechanical trail is really beneficial at speed as I correct direction less and get a positive feel when steering, especially when traction is limited and the self aligning effect is already diminished.
In very slow-tight corners it is also kind of striking to me how I need to pay more attention as the bike try to turn in more. I feel leaning more helps as you can go around the corner steering less (less fighting against the front turning in more). When you say on slow corners it seems like you need to steer more to go around, do you mean it just steers by itself or you actually want to do so? nice to hear about your thoughts on your experiments.
I think you guys lost me at Scattered Chicken Bones
That's not hypothetical, I'm slow as shit.
When i was referring to steering/turning at low speed, I meant "bike upright-ish, handlebars turning to go around something where you couldn't lean the bike" kind of turns. The reduced offset fork makes those super low speed negotiations seem like more work, but thats not really relevant to DH or even Enduro for 99% of the time.
The trails I rode today were horrible cross-cambers lines with drops into steep corners and the bike felt pretty dialled. Kinda wish I had two forks so I could swap the offset back and forth for more trials. Swapping the CSU is a PITA.
Phil Irving, Motorcycle Engineering, 1961
I have a mix of trails where you're peddling through or around rocks and roots, chuncky not smooth single track. they are also very twisty. Not much learning area and you're not going very fast. The shorter offset requires more bar input but just like at higher speeds rocks and such require less input to fight deflection.
I’m looking fwd to a future of linkage forks with battery activated eccentric pivots that not only allow dynamic offset thru the stroke (because linkage) but also also a choice of preset offset curves depending on trail conditions and how much weight is in your fanny pack.
I dunno but that Greg Minaar dude seems to think they help a fair bit and he's won a couple of WCs...
Well we for sure know fox's 27.5 and 29 40s have too much offset.
Took him long enough.....
So I just got a 37mm offset 650b 36 for my Lowtower, and ... I have to agree with @toodles 150%. I pick lines with ridiculous ease now, off camber trail segments are a piece of cake to navigate where previously the front wheel would flop/dig sideways. Stability is improved in all speeds, but slow speed "swing around tree" moves are no longer possible. You turn the handlebar and nothing happens unless you lean the bike. The change, for me, is bigger than some would make you believe.
I don't care about other parameters, I am not changing the entire frame, just the goddamned fork.
I don't care about other parameters, I am not changing the entire frame, just the goddamned fork.
Jesus it took until the 50th post in a thread about fork offset for someone to say mechanical trail, and no one has mentioned flop over yet?
The increased flop over from the increased trail when decreasing offset is probably whats giving you guys that faster turn in feeling. increased flop over gives you the same effect as steepening the hta for turn-in, but without the negative effects on stability.
The increased flop over from the increased trail when decreasing offset is probably whats giving you guys that faster turn in feeling. increased flop over gives you the same effect as steepening the hta for turn-in, but without the negative effects on stability.
To me the lower offset helps best if you're running a short stem. With 51° the flop is terrible with a 40mm stem. 42° with a 40mm stem feels natural. And better front traction without having to lean far forward.