First of all, regarding bottom bracket drop... your resulting bottom bracket height is one of the things, if not the biggest thing that dictates your center of gravity. Certainly from a cornering perspective, this is what has the biggest impact on how the bike swaps direction perpendicularly to it's direction of travel. However, that totally ignores the fact that we also deal with a fore/aft balance and the polar moment of inertia (for lack of a better way to describe it) in how we weight the front/back of the bike. Since the overall vehicle weight (bike/rider) center of gravity is so dynamic, you can't just view the bottom bracket height as sole determining factor in how a bike feels.

Regarding bb height vs bb drop... bb drop is the best way to compare bike to bike as it removes the differences in bb height measurements presented by mfg's for sag, tire squish etc. Shoot, even different pedal, shoe and (gasp) cleat stack height have an impact on this. So the safest thing as a consumer is to understand what your desired bb drop is for a given travel amount and wheel size.

Brining it full circle, I like seb stott... but I can't figure out several things he says in that geometry article. He says that a bike with more stack and the same reach is going to feel shorter. While this is true in some regards as if saddle height remains consistent, the measurement from hip position to hand position could be as long or longer. That being said, we all have target saddle and hand positions where we are comfortable, so if you control not only saddle height but also hand position, then a bike with the same reach, and larger stack will end up being longer when adjusted for hand position.

I digress... I would say that trying to determine how a bike is going to feel based on a geo chart is a fools errand. If you're using bb height I guarentee you're looking at a cooked number that's measured differently from mfg to mfg. The best way is to take into consideration bb drop and sag % to estimate your own resulting bb height with a fixed assumption on tire/wheel diameter.

TLDR: Don't trust the intertubes or forums or geo-charts. ride the bikes, goe charts lie and there is more to how a bike feels then just "i want this bb height".

 

First of all, regarding bottom bracket drop... your resulting bottom bracket height is one of the things, if not the biggest thing that dictates your center of gravity. Certainly from a cornering perspective, this is what has the biggest impact on how the bike swaps direction perpendicularly to it's direction of travel. However, that totally ignores the fact that we also deal with a fore/aft balance and the polar moment of inertia (for lack of a better way to describe it) in how we weight the front/back of the bike. Since the overall vehicle weight (bike/rider) center of gravity is so dynamic, you can't just view the bottom bracket height as sole determining factor in how a bike feels.

Regarding bb height vs bb drop... bb drop is the best way to compare bike to bike as it removes the differences in bb height measurements presented by mfg's for sag, tire squish etc. Shoot, even different pedal, shoe and (gasp) cleat stack height have an impact on this. So the safest thing as a consumer is to understand what your desired bb drop is for a given travel amount and wheel size.

Brining it full circle, I like seb stott... but I can't figure out several things he says in that geometry article. He says that a bike with more stack and the same reach is going to feel shorter. While this is true in some regards as if saddle height remains consistent, the measurement from hip position to hand position could be as long or longer. That being said, we all have target saddle and hand positions where we are comfortable, so if you control not only saddle height but also hand position, then a bike with the same reach, and larger stack will end up being longer when adjusted for hand position.

I digress... I would say that trying to determine how a bike is going to feel based on a geo chart is a fools errand. If you're using bb height I guarentee you're looking at a cooked number that's measured differently from mfg to mfg. The best way is to take into consideration bb drop and sag % to estimate your own resulting bb height with a fixed assumption on tire/wheel diameter.

TLDR: Don't trust the intertubes or forums or geo-charts. ride the bikes, goe charts lie and there is more to how a bike feels then just "i want this bb height".

reach has nothing to do with your seat to hand position, think of trials bikes with no seat at all, it is a standing position factor.

 

BB drop is important because it removes tire variation from the equation.

Trek is putting 2.6 tires on the Fuel EX for instance and this is how they measure BB height, if you put more normal 2.4 tires on it, all of the sudden the measured BB height is maybe 10mm lower, but the BB drop has not changed as it's measured from a horizontal line between the axles.

I think someone needs to do some math to figure out what BB drop they like with their preferred tires and wheel size. I'll try and run a string between my axles and measure my own preferred BB drop. Since I'm likely to always be on 29" tires and have definitely located my favorite tire set up, plus I seem to really like about 150-160mm travel & 170mm cranks, that BB drop should continue to be my ideal spot (right now I really like my SJEvo with a Mullet link, but running a 29"wheel, but the frame in the low setting).

 

Exactly.

 

the notion that bikes are systems is just silly. i reduce all my bikes to just one variable: head tube length. doesn't matter where any other single variable or combination of variables lands, through extensive blind testing, i have determined that head tube length alone determines everything about how it performs.

 

BB drop will influence how a bike handles. eg trying to manual a low bb bike is harder than one with a high bb, this is due to most of your weight being on your feet.

high speed cornering when out of the saddle tends to "feel" better with a low BB as your center of gravity is lower.

BB height really comes down to (hark spit) Feelings

 

It’s the strangest thing. You bb drop advocates don’t seem to understand that axle height has no bearing on handling. Change your tires and bb height changes - which changes your leverage against the ground through the tire, and yet Bb drop remains unchanged.

bb drop has no meaning until you’ve got all the parameters necessary to compute bb height.

why not just talk sagged bb height? What makes that inferior to bb drop? Bb height will let you compare every bike, not just bikes with same exact tires, sag, wheel size and color.

 

Bb drop allows you to compare frames and removes several adjustable variables. Tires, cranks, pedals. Those variables are adjustable. Frame drop is not ( ok it is if you change fork height and wheel size). It gives you a direct comparison between frames as to how much lower/higher the bb will be.

Often the manufacturer doesnt publish bb height and if they do it might be with differe t tires than what you will use.

Also the bb drop dimension for me is giving me a pedal strike potential data set. What I want to know is what is too low. What bikes should I rule out because the bb drop is too low? ..... at the moment I'm rolling out 30mm + bb drop as to low on a 160mm travel 29er frame.

 

Plummet makes sense here. So many variables as to what the actual BB height will be on the bike once you build up the frame.
As you increase the travel of a bike, I would expect more tendency to pedal strike, no? No matter how high the BB, eventually you're going to need to stutter pedal, or you will strike something.
Before dropper posts were popular I had a hardtail that had a high bottom bracket, it felt like I was riding on the top step of the ladder. If you have ever ignored the "Do Not Stand Or Sit On The Top Step" warning sticker on a ladder, you know the feeling. I exaggerate, and the feeling went away at speed.

 

It's not that bad riding downhill, keeping the pedals level, etc...but it's "that bad" like almost everywhere else...that you have to pedal, especially uphill, where you are bottoming out your pedals constantly on stuff that you should just be able to smoothly pedal over. Yeah yeah, clock the pedals and whatever, but when you suddenly have to trials over everything, else bash pedals, it just gets to be ridiculous after a while. My carbon Turner RFX was "just right". Not so low that everything else became ridiculous, but low enough it cornered and handled great. My current GG is too low for general stuff, with 170 cranks. Running it in the lesser travel setting helps, but in general this has gone too far IMO. Not asking to return to 14+ BB heights though. Some of the 2000s stuff was equally ridiculous on the other end of the spectrum.

 

Plumb It also is insisting that any bike is in an imperfect state until tires are swapped out and insists that rigid geometry numbers apply evenly across all bikes. There's articulating wheel suspension at either one or both ends of bikes on topic here - how's a dynamic number like suspension wheel path supposed to factor in?

Over and over Plum Bit reiterates it's a measurement... okay - but also that it influences handling. That's overstating the obvious in that it's a factor in bike geometry as opposed to a firm indicator of performance - as with an endurance / sprint / climbing road bike. Or a gravel bike. ...on paper.

'Front Center' is also a complete bicycle measurement but - if a rider swaps out a fork for 3mm less fork offset then - another variable!! This entire thread is pointless other than forcing new or other less-involved riders to assume there's a lasting disconnect in finding a bike that fits.

BB Drop as being implied on a MTB is a reading off of a frameset only - and pragmatically it's instead a road frameset. Somewhere, somehow, the number has been attached to mountain bike, here and now it's being used as if to insinuate how distant mountain bike and / or riders are from common sense.

Go find that guy or gal and ask for an exclusive interview. I'm sure the mounting pressure from this thread has them ready to crack. ...or begin a crack smoking habit.

 

 

Interesting discussion! Personally I think there’s so many variables in either measurement that they can’t be taken as absolutes - the value is just a way to compare bikes (hopefully with some accuracy). What is frustrating is comparing one geo table where height is used against another where they list only drop —- what’s the correct conversion????

I also find it interesting that so many posters agree that current BB heights are too low (especially because they’ve been trending slightly upwards after reaching a nadir a few years back…). Same with me, I stuck a longer shock on my current ride, a V1 Megatrail, in order to bring BB height to a comfortable place.

To answer the question, on 26” wheels- exactly 0 drop, or 13.5” unsagged. When talking full suspension, especially longer travel, so much changes with sag, dynamic sag while riding, pedaling inputs, etc - coming from rigid and hardtail bikes, I had NO way to anticipate what the unsagged measurement would translate to out on the trail- I had to just try it.

Also find it interesting that so many talk about cornering feeling good/different with a lower BB. I don’t notice a difference— then again my home trails, in the Eastern US, don’t really have corners, just “changes of direction.” To me, bottom bracket height matters for these issues:

-Rollover clearance on rocks, logs and ledges
-Center of gravity on steep-steeps like low-speed rock rolls
-Pop for wheelies, bunnyhops, and lofting the wheels — too low feels sluggish here.

So high enough to not bash the chainring all the time, low enough to point downhill and not fly OTB - and hopefully that’s the right height that handling feels good.

 

2022 Canyon Neuron CF9, XL, 140F/130R. BB drop is 38mm. Pedal strike is annoying, but not anywhere near what my 2014 Anthem Advanced was.
2016 Salsa Mariachi SS, XL, 100F/hardtail. BB drop is 60mm. I rarely ever worry about pedal strike.

Different geometries, so different riding styles. I feel like I'm riding "in" the Neuron, while I feel like I'm riding "on top of" the Mariachi. I've pretty much relegated the Mariachi to non technical trails. Since getting the Neuron, how I approach technical features has become habit and doesn't transfer safely to the Mariachi. Also the Mariachi beats the holy **** out of my 40+ year old wrists and back.

 

I'll admit I find this thread a little frustrating. Not enough dudes are listing their preferred bb drop. Instead they prefer to rant on about how there's lots of variable, admit that bbs on certain bikes are too low but then never list their own preferences, therefore not contributing to the data set.

How about you guys that dont like using bb drop as a measurement, list your bb height instead. bike, wheel size tire used and travel.

I can then back calculate that to a bb drop equivalent to the data set.

 

its because a blanket answer to your blanket question is useless. BB drop is 100% inversely related to frame travel. It decreases as travel increases. to know what BB drop makes people feel warm and fuzzy inside so you that you can validate your own warm and fuzziness, you need to tie it to travel.

 

BB drop definitely changes the way a bike feels. Imagine a bike with 200mm of drop. (This is not practical on most bicycles because the pedals will hit the gound easily.) You will feel so IN the bike that lofting the front or rear tire over object will be nearly impossible. It will feel VERY stable at speed, though.

Now picture a bike with –200mm drop, which could be described as "rise." Super squirrely, right? But shifting front -rear weight balance would become incredibly easy. Too easy, in fact.

The ideal is somewhere in the middle: low enough to be stable but not so low that the bike becomes difficult to shift your weight around on it or the pedals start hitting the ground.

I don't know what to say about actually numbers because it depends on the type of suspension on the bike.

I have a custom Marino incoming. I designed it around 29x2.6 tires and a 495mm rigid fork, which should feel about the same as my 120mm suspension fork at sag. BB drop figures for a bike like that range from 70mm to 50mm, so I went right to the middle at 60mm of drop. If I find that this is too close to the ground, I'm fine with getting shorter cranks. I doubt it's going to feel too low from an handling standpoint.

 

I don’t think anyone is saying changing a frames bb drop doesn’t change handling, the problem is that the bb drop number lives independent of what really matters which is bb height.

Consider a bike with 2” skateboard wheels, and a 36er. One has huge negative drop, the other huge positive drop. The bb drop depends on axle height and axle height has nothing to do with a riders leverage to the ground. The leverage is bars and pedals to tire, lower bb gives you more.

For a given axle height (wheel size and tire), for a given suspension curve, for given crank length, wheelbase, yes, now you can compare frames but to what end, it’s a number that needs too much context to be useful, and literally you have enough context exactly once you can compute bb height.

I’m seriously thinking this entire thread is a troll.

 

I find BB drop a pointless measurement in some ways. I looked up some of my older bikes and it's not even listed. BB height is much more relevant. Would a BB drop of 30mm on one bike prevent you from buying it over one with 25mm?
I'm no good at maths but my old Enduro's BB was 351mm with 26" wheels. My new bike is 340mm with 30mm of BB drop. Which one is the better handling bike? Well one of them has 170mm of travel and the other 150mm.

At least with BB height you can probably infer from the amount of travel and crank length if you're at risk of pedal strikes.

 

At least with BB height you can probably infer from the amount of travel and crank length if you're at risk of pedal strikes.
View attachment 2017843

Wow, that's scary low.

 

Thanks to those that contributed to this thread regarding bb drop. I'll start another thread and frame another question that might yeild more usefull data for those who cant get their head around bb drop.

 

Tell me how to insult my audience from whom i am asking for data without directly insulting the audience from whom i am asking data?

From the framing of your your last post, it appears that you might have the answer to the very question you asked. So, instead of allowing the rest of us to embarrass ourselves, why don't you tell us what your preferred BB drop is and why it works for you?

 

This is an interesting thread. Does make me think of the War song Low Rider.

Anyway I’m looking for my first FS bike. Thinking trail. I like to pedal through the rough stuff on my hard tail and don’t want pedal strikes. I figure and BB drop is and easy way to look at pedal clearance. Use the tables for tire size for rolling radi. The subtract from this the BB drop, crank length and pedal height. Then just ball park the suspension travel to figure the clearance.

I’m looking at ‘22 TF and EX. In large both low. TF BB 31mm height 343. EX BB drop 27mm and 346. These two are close. With Shimano PD520 pedals at 15mm. For the TF the clearance goes from 129mm down to 29mm. The EX goes from 153mm to around 21 to 23mm. I know with the EX the proper setup should make it more equal but I wanted to compare when bottomed out.

I’ve bike shop test road both. The TF is more nibble to me but the EX is oh so plush.

 

@plummet i appreciate the spirit of this thread, but I suspect a lot of people don't appreciate the nuance. Trying to explain it is throwing pearls before swine, to coin a phrase. (That was a joke.) Don't worry if people don't to get it.

 

I don't have a preferred BB drop as it is subjective to a particular bike/frame and the purpose of said bike/frame

 

This reminds me of the thread asking what your preferred tires pressure is.

 

My last bike (a 27.5 hardtail with a 130mm fork) had an extremely low bb. The bb drop wasn't listed in the geo table, but the bb height with the stock 2.3/2.25 tyres was 300mm, 5mm lower than manufacturer spec. Even with 170mm cranks I had plenty of contact with the ground. The fact that the stock fork had a huge negative spring that sagged on it's own exagerrated the problem. Eventually I upgraded the fork to a 10mm longer one that also needed less sag to work well and that gave me around of 4mm more ground clearance and a higher dynamic ride height and the issue disappeared. This bike cornered very well before and after the fork change. Switching to a mate's ht with a 315mm bbh felt akward in comparison (I first rode it, then checked geo online).

My current bike is a 27.5 fs with 150/140mm f/r. BB drop is listed as 15mm which is average for the travel I believe. Static bb height is around 340mm, although I have a 2.6 front tyre fitted and this gives some extra mm's. I built this one from the frame up, so went for 165mm cranks for various reasons including ground clearance.

Hardtail geo is easy to compare, but I feel there's too much going on on fs bikes to really be able to draw safe conclusions. For example mine has very high anti squat values, so it rides high when climbing. Suspension setup can obviously change dynamic ride height.

One could argue that current ultra long enduro bikes are so stable that they can afford or even benefit from a higher bbh. I believe this is what Pole is going for with their latest models.

 

Trying to understand what you guys are talking about "BB drop". Newbie question. Are you talking about the smaller distance from the wheel axel to the crank ? Thank you. ( that's not my bike )

 

That is correct.

 

@BansheeRune - Thank you, appreciate it.

 

Is there a standard for measuring bottom bracket drop with suspension? Sagged or unsagged or...?

 

Unsagged.

It seems it would be helpful if the manufacturers provided BB drop at sag as well.

 

Standards 🤣

 

How useful are RAD and that Front:Rear ratio you got in that spreadsheet, ocnLogan?

I felt that RAD was a way to sell those RipRow machines, ensuring that trained range of motion works on a bike. I habitually upsize since I almost always find that larges feel naturally easier at carrying higher speed through corners and in the air than size mediums and smalls (very few exceptions, like SB150 and 2018 Jekyll 27.5 in med). I never have ridden a small that I liked better; smalls seem to lock me into slower-speed riding, sessioning, and stunt stuff as opposed to the kind of mtb exploratory trail sampling experience I wanted. Lee and Alex seem to have gone quiet after that Revel bikes experiment, where they chose size smalls... yikes.

I saw that F:R ratio thing in a vorsprung video, but found that it didn't correlate well with actual measured weight distro, using a scale under each wheel and doing a ratio on the weight readings. It'd work as a comparison between bikes with very similar wheelbase, but then it'd be just easier to just do what I currently do: find the magic CS-WB combos that correlate with real world weight distro measurements.

I credit the weight distro balance for the magic, where I can ride gnarly stuff with far less work besides simply carrying speed. My natural standing pedaling position is in the right place for this stuff. For 90+% of normal stuff, there's no need to move/hold my body forward to weight the front for blazing a corner super fast, nor any need to move/hold my body rearward to unweight the front to prevent an OTB or weight the rear to climb out-of-the-saddle. Only need to shift weight for actual techniques.

Just saying, they both stink of even more oversimplification. I'd rather have the original numbers, which you have, and am struggling to find any use for those composites. Something with longer wheelbase will naturally have a bigger F:R ratio, but it doesn't mean that since a 1.83 ratio works well for a 1230mm WB 29er that it should also work for a 1150mm WB bike, 1300mm WB bike, nor even a 1230mm WB 27.5 bike. From my set of measurements, I find that heavier riders want even lower ratios than lightweights. I also find that smaller wheeled bikes do better with higher ratios.

I feel that the perceived benefits of mullet have a lot to do with BB drop. People have mentioned a feeling that a well designed mullet can corner like a centrifuge. Check out the old Foes Mixer reviews. People think it has to do with the traits of different wheel sizes. They're not wrong, but I'd technically credit the BB drop. I bet that you can get a 29er to feel more like a 27.5 if the BB drop was reduced to a similar level.

The other mullet difference is how the BB drop to front axle is more the BB drop to the rear axle. I feel this synergizes with my preferred riding style of heavy-feet and light-hands. The front will be more stable, to require less from me to hold the front, but the agile rear will be more responsive to movements that originate from my hips/core. A well-designed mullet wouldn't be a conversion, but one that tunes the rear kinematics to work with this trait, to maintain a balanced suspension feel.

Sorry for the ramble, but I prefer a bigger picture discussion, touching on the many things that you have to juggle to create a well-rounded bike.

 

How useful are RAD and that Front:Rear ratio you got in that spreadsheet, ocnLogan?

I felt that RAD was a way to sell those RipRow machines, ensuring that trained range of motion works on a bike. I habitually upsize since I almost always find that larges feel naturally easier at carrying higher speed through corners and in the air than size mediums and smalls (very few exceptions, like SB150 and 2018 Jekyll 27.5 in med). I never have ridden a small that I liked better; smalls seem to lock me into slower-speed riding, sessioning, and stunt stuff as opposed to the kind of mtb exploratory trail sampling experience I wanted. Lee and Alex seem to have gone quiet after that Revel bikes experiment, where they chose sizes smalls... yikes.

I saw that F:R ratio thing in a vorsprung video, but found that it didn't correlate well with actual measured weight distro, using a scale under each wheel and doing a ratio on the weight readings. It'd work as a comparison between bikes with very similar wheelbase, but then it'd be just easier to just do what I currently do: find the magic CS-WB combos that correlate with real world weight distro measurements.

Just saying, they both stink of even more oversimplification. I'd rather have the original numbers, which you have, and am struggling to find any use for those composites. Something with longer wheelbase will naturally have a bigger F:R ratio, but it doesn't mean that since a 1.83 ratio works well for a 1230mm WB 29er that it should also work for a 1150mm WB bike, 1300mm WB bike, nor even a 1230mm WB 27.5 bike. From my set of measurements, I find that heavier riders want even lower ratios than lightweights.

The short answers are "I found them very useful trying to buy a bike during covid that I couldn't sit on or demo" and "its a work in progress".

The slightly longer answer is that after 3 years of thinking "I kind of feel like my bike is too small for me", I came across the RAD videos. And after doing some testing, I found that my bike then was almost a full inch too small for me, which explained my discomfort in longer trails (I was getting the rounded/hunched back feeling on longer downhill segments, like the feeling of wishing I could just fully stand up). So RAD (and the trig to figure out how a bike would fit me in my spreadsheet), was super useful. My Banshees frame is 17mm larger than my Kona, and that plus stem length + bar in my calc, puts me about an inch larger. And it is definitely more comfortable.

Also, my Kona had a WB of 1222mm, and a F/R ratio of 1.88. The Titan has a WB of ~1268mm, and a F/R ratio of ~1.8. And the Titan definitely has more weight on the front, even with a 1.5 degree slacker HTA than the Kona. It also had more front grip than the size L Transition Sentinel I got to ride (WB of 1263mm, F/R ratio of 1.87). Beyond that I don't have much data. So you're right, I have no idea if the 1.8 ratio is something I'd desire on a much smaller WB bike. Small devils advocate moment though... I don't think I'll be riding anything with dramatically smaller wheelbases anytime soon. Even the XC bikes now have wheelbases about as long or longer than my Kona (Trek Top Fuel L is 1215mm, and Rocky Mountain Element XL is 1263mm).

Its also been useful to see how I could fit a L, or XL of almost any brand, by fiddling with the cockpit enough.

I really wish I had a magical set of all the bikes I was interested in, in both L and XL, available to ride on my local trails, where I didn't get fatigued, and could just get some really great data on what I actually prefer. But since that isn't an option for me as a non-bike reviewer/sponsored athlete/billionair, for this last bike I went with a size large.

So to return to your question again. After riding it for a year, I think my next one will be a smidge larger (either a larger L, or an XL). And I don't feel like adding ~40mm of wheelbase made riding my trails any harder.

I did the scale thing with the Kona (in a response to you actually IIRC). I should drag the scale out to the garage and test the Banshee sometime just to see how different it is in comparison.