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  • Bottom bracket. How low is too low? On 29er
  • Premier Icon james1992
    Free Member

    Bottom bracket. How low is too low? On 29er?

    There is a few brands are pushing the low BB It seems to have pros and cons, and yes it depends on what you genitally ride. However how low is too low?

    Premier Icon SirHC
    Full Member

    335-345 works for me. Don’t forget you have to consider the effect of sag, the BB height on my G1 drops more than my Smuggler, so G1 starts higher and they end up pretty similar.

    Not a fan of really low Bb’s, find it makes the bike harder to turn in.

    Premier Icon zezaskar
    Free Member

    I’ll speak about BB drop which is my point of reference.
    Over the last few years I’ve went through a lot of different drops and, as it is, I would not go over 30mm (as in lower BB).
    I’ve had a bike with an adjustable 39-47mm drop and it was awful to pedal uphill and going downhill was an hazard as well sometimes, like sprinting out of a corner.
    My current bike has a 25mm drop which feels perfect, but I guess that’s also related with it being a pretty long bike which negates the need to have lots of BB drop to be stable.

    I think some of the really low BB bikes are a product of today’s groomed trails. Going up and down actual natural trails makes things very different.
    That’s why I prefer length/wheelbase vs BB drop for stability

    Premier Icon jameso
    Full Member

    Don’t forget the ‘lorry on a bridge’ effect – for a given BB height a longer wheelbase means more pedal strikes on some ground / in some situations.

    Premier Icon thols2
    Free Member

    and yes it depends on what you genitally ride.

    Useless without pics.

    Premier Icon james1992
    Free Member

    @thols2

    Was Typo – “generally ride”

    Premier Icon james1992
    Free Member

    @SirHC

    Good point about the different sags can balance things out

    Premier Icon andybrad
    Full Member

    very low bb’s i like on trail centre stuff. for actual riding i find them a pain. its the reason i didnt get an evo stumpy when they came out

    Premier Icon oikeith
    Full Member

    Raaw Madonna V2 has a BB drop of 35mm with a BB height of 335-340, I’m not sure of many other bikes which have a greater BB drop.

    My bike has a BB drop of 28mm and BB height of 347mm and I have no problem getting the odd pedal in here and there, this is with 170mm crank arms.

    Premier Icon Hob-Nob
    Free Member

    Raaw Madonna V2 has a BB drop of 35mm with a BB height of 335-340, I’m not sure of many other bikes which have a greater BB drop.

    Same as the new Stumpy Evo in the high setting. The low is 40mm drop.

    Also depends on how the bike uses is travel – a decent shock that holds the bike nicely at the sag point will be better than a bike with a higher BB a sh*tty shock/suspension curve.

    I run my stumpy in the low setting, with a decent shock & it’s fine – I wouldn’t go lower though, as it makes the bike hard to pull out of fast corners when leant over. But around 35-40mm drop seems to be about the sweet spot for me anyway & I don’t run long cranks so pedal strikes arn’t an issue.

    Premier Icon SirHC
    Full Member

    @andybrad the last gen stumpy evo was a bit of dogs dinner to be honest, sizing was miles off with the tiny head tubes, pushing you too far back, a very linear leverage curve. I bought one, rode it twice and moved it on, no where near as good as my enduro was.

    Premier Icon chiefgrooveguru
    Free Member

    It’s definitely the dynamic ride height that matters, not the nominal BB height or drop.

    So with less travel you’ll have less actual sag (and often less % sag too) so the sagged height is higher for a given BB drop.

    With a shock+leverage curve that has more mid-stroke support you’ll have a higher ride height in practice even if all else when statically sagged is the same.

    With a suspension design that has more anti-squat you’ll have a higher ride height when pedalling, even if everything else is equal.

    My Levo with a 160mm fork only has 24mm BB drop so it’s on the higher side of things. But having fiddled around a fair bit with the suspension (and I think I’m pretty good at setting up bikes for how I ride), I’ve found myself running 30% sag on the fork and 37% on the shock (which sounds like a massive amount but maybe ebikes like more sag because of the better sprung:unsprung ratios?)

    So that’s about 44mm sag front, 56mm sag rear, which equates to about 52mm sag at the BB, so a BB drop of 76mm. And with a 2.4” tyre on the back that works out as somewhere between 290 and 295mm BB height.

    With the sag I’m running the mid-stroke is fairly firm so it doesn’t collapse under pumping. There isn’t all that much anti-squat with the power off but it has short cranks which give some clearance. With the power at max it stands a fair bit taller, you can definitely feel it jack up.

    Conveniently my hardtail seems to have almost exactly the same pedal clearance as the ride height sits fractionally higher but the cranks are 5mm longer.

    I think you get really tuned into pedal clearance if you ride bikes with very similar BB heights. If you usually ride taller bikes and then switch to a low one you’ll take a while to adapt and vice versa.

    One more thought – trail centres etc much better suit low BBs than natural trails if you’re going flat out. But I think natural trails and low BBs are fine if you’re not racing. For racing I think slightly higher BBs help you get critical pedal strokes in and give you more margin for error when you’re already on the ragged edge. EWS bikes are rarely super low.

    Premier Icon mudeverywhere
    Free Member

    I keep thinking the current crop of suspension Oranges must be too low at 320-330 depending on the model? But not read any complaints yet.

    Only bike I’ve had a problem with so far was a Whyte S-150. Forever smacking the pedals even on flat-ish singletrack. It’s no lower than other bikes I’ve had, higher than some. So as above it must result from travel, sag, anti-squat, the way the suspension moves and length of the bike. Leaning rather than steering longer lower slacker bikes through corners must also have an effect.

    Premier Icon chiefgrooveguru
    Free Member

    “ I keep thinking the current crop of suspension Oranges must be too low at 320-330 depending on the model? But not read any complaints yet.”

    I think they’re probably a great example of dynamic ride height vs unloaded BB height. Linear suspension so having to run less sag to avoid bottoming out, and also good mid-stroke support and high anti-squat. So sagged they don’t drop as much, when pumping they stay high and when you pedal they jack up.

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