I dont think BB drop matters much honestly, what matters is absolute BB height. BB drop is irrelevant as it relates to the center of gravity, which is much higher on the bike and is the dominating force.

 

Agreed, saddle height is usually set by the extended leg on the lowest point of the pedal stroke. Lower the BB by 5mm, and your saddle will be 5mm lower too. That'll put your center of gravity nearly 5mm closer to the roll axis, which is why the handling changes. (You'd need to also lower the stem 5mm to get all 5mm drop in COG.) Since the roll axis is the line between tire patches, this is determined by absolute BB height. Changing the height of the gyroscopic effect of the wheels (by changing wheel sizes) will have some effect on handling too, but that is independent of BB height. BB drop may reflect both changes in BB Height and wheel size, but tells you nothing much about handling changes.

It's interesting to read what Bike Radar had to say about it in their Ultimate Guide to Bike Geometry and Handling:

The bottom-bracket drop itself is less important than some people have supposed. The distance by which the bottom bracket hangs below the wheel axles is seen by some to directly determine the stability of the bike in turns, as if the bike’s roll-axis (the line about which it turns when leaning into a corner) was at the height of the axles. This argument was used in the marketing of 29in wheels, claiming that because the bottom bracket sat slightly below (not above) the axles, the bike was far more stable.

In fact, the roll axis is – roughly speaking – the line connecting the tyre contact patches. The important measurement for cornering is the height of the centre of mass above this line, and not the height of the bottom bracket relative to the axles.

Fitting smaller wheels reduces the bottom-bracket height but doesn’t affect the bottom-bracket drop. This makes a bike significantly quicker to change direction of lean because the centre of mass of the bike and rider is lower.

Interestingly, some bikes (such as Pivot’s Switchblade) feature height-adjustable ‘chips’, which compensate for different wheel sizes. Using these, the bottom-bracket height remains similar with the smaller wheel size, but the bottom-bracket drop changes. This results in a much smaller change in the bike’s handling, suggesting bottom-bracket height is important, not bottom-bracket drop.

Bottom-bracket drop is still a useful measurement, though. Bottom-bracket height is affected by not only wheel size but also tyre choice – comparing bottom-bracket drop between bikes of a given wheel size removes this variable.

 

It is a interesting measurement when comparing frame geometries. All other factors being equal bb drop determines how much lower or higher the bb will actually be comparing brands.

Thus the discussion.

I'm trying to get a handle on idea on what is too much drop.

So... please respond with your bikes bb drop, travel and whether you consider it to low, about right or too high.

That will help with this discussion.

 

My input to the discussion, is that there really shouldn't be a discussion about BB drop, because it is not a relevant force within bike handling or performance. Not trying to be condescending or anything, but I would hate for people to get the impression that it provides any tangible difference to the bike. The reason it doesn't is explained thoroughly in the bike radar article linked above.

Bb drop is very relevant as it allows comparison between geometries of bikes. Bike manufacturers are not publishing's bb height these days. Bb drop allows you to calculate bb height given the set up that you intend to use.

Bb drop directly affects bb height. Saying it is not relevant is incorrect.

What isn't helping this discussion is not listing your preferred bb drop.

 

What isn't helping this discussion is not listing your preferred bb drop.

Sorry I am detracting from meaningful discussion by offering a viewpoint? To specifically answer your question, I dont have a preferred BB drop (explained) but I do have a preferred BB height.

 

since we're talking drop, it'd be important to know what the drop is in relation to... so

what wheel size?

 

But... you didn't mention your wheel size, and even that isn't enough. How much ground clearance do you have?

If we're going to ignore clearance: is there anyone that wouldn't accept a 200mm drop? Would be nice and stable. More is always better, but then we need to mitigate for the reality of clearance.

bb drop is a compromise based on how much ground clearance you need.

Probably real question: whats the min distance you can tolerate between chainring and ground? And how long is yur crankz.

 

My 15-20mm wis based on 27.5 165mm travel. I'm expecting that 29 could push to 25mm to have the same clearance.

 

I’m generally inline with those numbers but sag/suspension progressivity is also a factor.

My Spur has 40mm of drop but it’s only 120mm of rear travel, the flex stays make it very progressive and I’m not throwing it down the chunkiest/steepest stuff. I don’t even have 165 cranks on it and all is well despite the big BB drop number.

 

Considering BB drop is the product of wheel size in relation to BB height I prefer less drop. I would like to be around 13.75" or 14" height for 160mm. BB drop will be whatever it will be to have the clearance I want.

I've had too many pedal smacks at speed a few resulting in good crashes. I run 165mm and thin pedals to help but I would still prefer a taller BB. Sure lower bb's feel great in the corners but I would rather have more clearance and get used to cornering with a higher COG. Maybe we would stop sanitizing trails so much if BB's trended up?

 

+100%. I could not have said this any better. I have had 2 big crashes in the last 2 years and both were from my pedal grabbing a embedded rock in the ground and stopping the bike suddenly. This of course was riding downhill at a good speed. I also run 165mm cranks. Thou, crank length doesn't really matter riding downhill as the pedals are level. YMMV...

Considering BB drop is the product of wheel size in relation to BB height I prefer less drop. I would like to be around 13.75" or 14" height for 160mm. BB drop will be whatever it will be to have the clearance I want.

I've had too many pedal smacks at speed a few resulting in good crashes. I run 165mm and thin pedals to help but I would still prefer a taller BB. Sure lower bb's feel great in the corners but I would rather have more clearance and get used to cornering with a higher COG. Maybe we would stop sanitizing trails so much if BB's trended up?

 

Never been much of an Enduro sort- tend to ride mostly within XC to Mountain range.

On FS 29er's with 120-145 mm fork travel and 100-150 rear travel, BB drops range ~30-50... I don't notice much difference.



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I can tell you my Stumpjumper Evo BB is too low. I can tell you my Commencal Meta BB is just right. I don't remember ever riding a bike and thinking "this BB is too high" but maybe I just forgot.

 

Old school FR bikes were too high. Other than those, I'm with you. I would be happy to see every 140 to 170 bike bumped up 10 to 15mm. I would like to try super short cranks but I kind of see them as a silly work around for a problem that's easily solved. They make sense for DH bikes because there's just noway to have good clearance without jacking the BB up so high it will really hurt cornering, but for 140 to 170, we can just raise the BB.

 

BB inline with axles.
All bikes.

 

Madness. Sheer madness.

 

The bikes travel makes a difference too, because 30% of 180mm is more than 30% of 100mm.

Most long travel 29’ers are between 29-35mm of bb drop. But some have over 40mm of drop (stumpy evo in low).

I’d be really interested to try lower bbs with shorter cranks, and see how that felt.

 

What's the bb drop of the bikes you are riding now?

 

My SJEvo was really problematic with 170mm crank, even with the Cascade link that improves progression and rides higher.

Now I run the Williams Racing Mullet link which lowers the rear axle about 1" to correct for a 27.5" wheel, but with a 29" rear wheel. Then I placed the bike in the 'Low' position.

The end result is the BB height from the ground is 345mm/ 13.8" which is just heavenly. It's a HUGE improvement in ride performance, and not just pedaling.

Like DGUSMC pointed out, the low BB height on my Spur is no problem just because the effective ride height is higher because of less travel and the bike just sits higher.

I'm not stoked on super low BB heights and I'm not the only one. It's a common complaint that I hear these days.

 

 

I like higher BBs.

The industry trend of stupidly low BBs causing pedal strikes on everything is just ridiculous.

14 inches is great. Paired with 160/5 cranks, even better.

Plenty stable and keeps the pedals off the rocks.

 

Completely Agree!
It seems like SOME Eripean , german and Canadian brands keeping more or less normal BB height, Most USA brands making stupid low bbs..

Look at my Liteveille 301 MK11 frame from 2013 , it has 36sm BB heigh and even with 175mm cranks it was aweosome to ride any rockgardens..

 

My last few frames BB drop did not match manufacturer specifications. They all had less drop which was probably a good thing. I recently purchased a Pole Evolink. The current v1.4 has a -3mm drop, my v1.3 has 20mm. Deciding to get the older model was solidly based on the lower BB height of the older model. I do get strikes more often than not and wonder if the move to the taller BB height would have been a positive move.

 

{ too high, just right, too low} in this order
Road bike (28mm tire): { 67mm, 74mm, 81mm}
Gravel bike (42mm tire): { 73mm, 79mm, 85mm } -- gravel bike have much taller tire than road bike, so it deserve some more bb drop.
Short travel Mountain bike (29" wheel with 2.4" tire): { 31mm, 42mm, 53mm } -- relatively tall to compensate for suspension movement and uneven terrain.

 

I have a 29er and 27.5 bikes. I run the high setting for my suspension. On my 27.5, I tested the low setting and I did have more pedal strikes. No BB strikes though. I can't say there was a major difference between a high and low BB when you adjust it. It may feel different for bikes that have low BB built in like Whyte bikes.

In the past, I built an Intense Recluse. Great bike but wow...the BB sat so high. I felt like I was riding too high! At least I had ground clearance.

 

I think most modern bikes are too low. Easy!

Maybe they're designed for people that ride groomed trails, with stiff suspension, and mostly downhill so they don't need to pedal and worry about pedal strikes. But for riding on pedaly trails, with camber, and roots, higher is better.

 

my Hard tails
Nordest bardino 2 LTD has a 55mm drop
Octane one Prone 27.5 has 45mm drop

my 2018 Scott genius 940 is apparently 20mm but I cannot find an exact figure. the bike is a work in progress for me

 

The new Pole bikes have zero BB drop or BB height. Can’t remember which. Leo says it helps you change direction quicker. I’d definitely like to try one of those bikes just to see how it would ride

 

Less hard crashes that lead to attempts to get warranty work or crash damage discounts knowing Leo.

 

345mm bb height for 27.5 bikes with 160 rear travel worked well for me and my 29er now is 170 travel and 351mm bb height, running ~30% sag for each size. So not much bb drop, 10mm and 21mm if the geo charts are correct? Newer 2.5 and 2.4 tires on the 29er give a few more mm ground clearance than the 2.3 tires I ran on the 27.5 bikes. New England riding with a ton of pedal catchers everywhere and always running a well used bash guard too.

 

Mostly all mountain/enduro with lots of natural rocky stuff and loamy off-piste.

My V1 Megatower has a 29mm drop in its "neutral" configuration (160mm fork and flip chip in high position). That was too low with 175mm cranks and I was catching pedals everywhere.

I swapped in some 170mm cranks (which is what SC specs on their completes) but it still wasn't quite enough, so I increased fork travel by 10mm and it's been fine ever since.

So the perfect BB drop for me on this bike is roughly 26mm as it turns out, 3mm higher than stock thanks to overforking it, but I could maybe get there with thinner pedals or 165mm cranks without affecting the geo. It doesn't feel any different to me though.

It's not something I considered when I bought the frame. It will be moving forwards (along with stack, but that's another topic).

 

Always find this Paul Aston interview interesting when discussing BB height and drop (both of which I have no idea what mine are):

The BB is currently about 375mm. Blasphemy! I'm not a super fan of low bottom brackets, especially in Finale where there are plenty of things to catch a pedal on. My theory is that low bottom brackets were great to improve stability on tiny bikes with small wheels a few years ago, nowadays we mostly use bigger wheels so we instantly have higher axles and more BB drop, plus this bike is so inherently stable that a higher BB lets me ride through rocks and ruts with much more confidence.

I find it also switches direction easily with my style of riding: I pump the bike a lot and unweight it between corners, at full extension I am standing above the axles and so it tips over easily. This also keeps the bike leant over in turns better: if you are standing far below the axles your weight pushing through the BB is trying to stand the bike up.

 

I though BB drop was an alternative measurement used by manufacturers to disguise ridiculously low BB heights?

 

It's nothing more than a measurement which exists beneath the span of the axles on the frame. No accounting for sag and/or sags, no accounting for rear-axle movement during articulation.
It is a wannabe measurement.

 

My favorite is a custom full suspension frame. 26", 13.25 BB and 175mm cranks.

 

Nothing is more embarrasing than having to call the AAA to get an off road bicycle off the speed bump in front of the package store...
Before you bought the beer for the afternoon!!

 

I'm riding 29" wheels with 142mm rear 160mm front. 25 to 30mm bb drop is good for me cuz I like the ground hugging effect, but I also run 170mm crank arms to mitigate pedal strikes. This is a good fit for me.