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I've always been lead to believe that short chainstays are the key to making it easy to loft the front over things, but I'm wondering now whether BB drop might be the more important factor. Does anybody have any experience with bikes that had either long chainstays or a large BB drop, but where it was still easy to loft the front over stuff?
Higher BB makes front lift easier.
Shorter Chain stays make front end lift easier
Long and low makes front end lift harder.
This is progress.
So it's definitely a combination of the two factors then and is another example of "new geometry" not being better, just better in some areas. But I still wonder which is most important. Most reviews will talk about chainstay length and how that affects ability to lift the front end up, but ignore BB drop.
Also, I can see why a longer chainstay makes things harder. You are pivoting around the rear contact patch (not the rear axle if I remember correctly) so you need your body weight to be behind that. The further back the contact patch the more you have to move your body. But why does a lower BB make it harder to lift the front?
But why does a lower BB make it harder to lift the front?
Because the BB has to go over centre and the lower the BB, the higher the force required to lift it over centre-
https://en.wikipedia.org/wiki/Bistability
I think.
But why does a lower BB make it harder to lift the front?
Because your weight is lower compared to the rear axle.
There's always a trade-off between stability and manoeuvrability. A lot of people are chasing stability these days which is where long and low comes from, but it doesn't come without taking away from other areas despite what designers might say (apart from Brant up there it seems).
Basically you’re asking for ‘cake’.
A bike that is stable at speed, climbs well, descends confidently and makes it easy to lift the front.
And with Bold New Graphics!
Hmmm cake !
No I get that you can't have everything, I'm just trying to understand the negative effect of a low BB. It's all about your centre of mass and the forces that applies to the contact points right? I can see how having the BB below the axles means that you tend to drive the bike up and over obstacles when you hit them (rather than sending yourself out the front), but I can't see why it makes it harder to pivot the bike around the rear contact patch by applying a force to the bars, which I guess is what you are doing when you lift the front, but maybe not.
You're right that both chainstay length and BB height are key factors in a bike's manuability (how easy it is to pop sick manuals for the babes)
The trend for steeper seat angles should mean you can have shorter chainstays.
Shorter chainstays should improve the ability to get the front up, allowing designers to get the BB as low as possible, for a low centre of gravity giving optimal cornering and fore-aft stability whilst taking into account crank clearance.
A steeper seat angle should also result in a longer virtual chainstay during seated climbing, improving traction and reducing the tendency for the front of the bike to lift during seated climbing.
Given the trend for longer, lower, slacker bikes, the question is, does a longer front centre/reach and the ratio between reach and chainstay length give you more leverage to heft the bike up?
Perhaps more important than all of this is the fact that the potent combination of short chainstays and a low BB is best for generating rad roost.
I can’t see why it makes it harder to pivot the bike around the rear contact patch by applying a force to the bars, which I guess is what you are doing when you lift the front, but maybe not.
When you try and lift the front wheel (pedaling, pumping, pulling the bars, whatever) the BB has to go upwards (obviously). The larger the BB drop the more it also has to move forwards, effectively lengthening the chainstays and making it harder to lift it further. Once you've got the BB up past the axle the chainstays effectively start shortening again, making it easier to get it higher and higher (and by this point your effective seat angle is slacker, reach is shorter, stack is higher which also contribute.
Roverpig, yep when you manual you’re effectively rotating the bike around the arc of the contact patch, but that contact patch is rotating around it’s own axle (the rear dropout, at the end of the chainstay) and you’re applying leverage from the cranks/BB at the other end of the chainstay.
A quick sketch would show that would give you different arcs depending how long the chainstay was and how far above/below the axle the BB sat. Think about how you move your weight back when pushing the bike out - I think the crucial point is probably that a shorter chainstay keeps you closer to the wheel axle and the leverage ratio is lower. I’ve never really thought about this before, though...
A steeper seat angle should also result in a longer virtual chainstay during seated climbing, improving traction and reducing the tendency for the front of the bike to lift during seated climbing.
Nicolai Geometron has both a long chainstay and a steep seat angle. Front end will stay down on super steep seated climbs without having to change your position.
Long reach and front centre but tough to manual
I’ve always been lead to believe that short chainstays are the key to making it easy to loft the front over things, but I’m wondering now whether BB drop might be the more important factor.
Doesn't matter how long/low/up/down blah blah blah - technique is what you really need. Best thing is it's free (or you can pay for someone to show you if there's something wrong with your head 😛 )
I can’t see why it makes it harder to pivot the bike around the rear contact patch by applying a force to the bars, which I guess is what you are doing when you lift the front, but maybe not.
It's pivoting about the rear axle, not the contact patch, and the BB shell describes an arc about this point. The lower the BB shell, the further it has to travel to get past horizontal and start travelling backwards. The BB shell actually has to travel forwards slightly as well as upwards in the case of bikes with a BB drop, relative to the rear wheel axle, before it can start travelling backwards into a sick manual or sweet bunny hop. This is partly why a DJ bike is generally easier to hop and manual than a LLS [s]barge[/s] gnarpoon.
edit- but yeah, technique and mad skillz are what you need really. Hoodie and can of monster optional...
Its not bb drop exactly it is chainstay angle that is the thing (as well as chainstay length).
So small wheels are your friend.
No one has mentioned wheel size yet…
Jinx!!
OK, thanks, I think I'm starting to understand a bit more now. Or at least get a better idea of what I don't understand 🙂
Part of the issue is that manufacturers quote effective chainstay length, so a larger drop means a longer actual chainstay (for the same effective length).
There is also the fact that you don't just apply force to the bars to lift the front end. You are also applying an (opposing?) force through the pedals, so that has to be taken in to account.
Then we have the question of whether the bike is pivoting about the rear axle or rear contact point, where opinion still seems divided.
The point about skills is obviously a fair one. It's one of the (many) reasons why I find it hard to part with my old 26" Five. It has 425mm chainstays, no BB drop and a relatively short reach (by modern standards) but I still can't reliably lift the front out on the trail. I can loop it out in the garden, but that's not the same as knowing that I can always do it when it matters.
I love a monster truck. It's part of the reason why I spend so much time on my fatbike. It's great to be able to blast through stuff without having to do much more than enjoy the ride. But part of me thinks that I need to nail this skill on the Five before swapping it for something longer, lower and slacker.
When you have a proper long, low & slack shred sled you don't really have to worry about "lofting the front wheel", you just lift the bars a little bit, lean back a touch and the bike trucks on over.
The thing is, right, is that LLSer bikes aren't necessarily 'better', they're just different. It's just what's selling/being sold at the minute. I'm not a massive fan of LLS bikes, my old BFe 275 (on 26) is about as LLS as I'd want to go as it's my only bike that gets used for all sorts of stuff.
to be fair while its harder to lift the benefits of a lower bb and longer bike out way the odd occasion you need to lift the front.
it is harder but it doesnt take long to get used to the weight transfer.
I`m shit at manuals but dont like wet feet so can muster a decent puddle length manual even on the barge when necessary.
a high bb bike feels wierd now .
a high bb bike feels wierd now .
A 90s MTB felt weird after years on a BMX, and a newly fangled LLS bike felt weird after years on a 90s MTB, FS feels weird (to me) after years on a HT... 😆
BB drop/height & Chainstay length don't simply work in isolation...
"New" or "LLS" geometry doesn't really seem all that differrnt to "Old" geometry when it comes to the heights of BBs (relative to the ground)... I'd even contend that chainstays haven't really grown that much in length once you consider the the difference in wheel radius from 559 - 584mm (or even 622) rims really...
It's much more about the layout of the whole frame, how much longer and lower the front triangle is (compared to a few years ago) also how much Slacker the HA is (it's worth noting that more upright SA's will also have the effect of increasing a bikes wheelbase, on top of reduced HA and increased TT/ETT)...
In theory it's about improving the mechanical advantage the bike gives the rider over the contact points, and how that revised layout positions/distributes a rider's weight on the bike relative to the axles/tyre's contact patches...
As with anything, you change one thing it affects at least two others...