High BB height
- Thread starter sanjuro
- Start date
It will spin better! No, but really, I don't think so. But really, it will spin better.
John Cowan says a high bottom bracket provides more leverage for pumping rollers and jumps and such. At least, that's what I read in an old Decline.
It makes sense, but BMX bikes have ~11" BB heights, and they pump much better than MTBs. However, that's possibly too broad of a comparison. Head angle, chainstay length, wheelbase, and all that jazz probably determine the pump of a bicycle more than just the BB height measurement. A 14" BB isn't really bad at all, and one could adapt to that pretty quickly and easily. My XC bike has a 12.25" BB height, and I can hop on much taller bikes and ride just fine.
It makes sense, but BMX bikes have ~11" BB heights, and they pump much better than MTBs. However, that's possibly too broad of a comparison. Head angle, chainstay length, wheelbase, and all that jazz probably determine the pump of a bicycle more than just the BB height measurement. A 14" BB isn't really bad at all, and one could adapt to that pretty quickly and easily. My XC bike has a 12.25" BB height, and I can hop on much taller bikes and ride just fine.
Was it the Quake XLT? A 14.5" BB height is pretty excessive for a bike with 6.7" of travel. Not saying it's a bad bike (never ridden one), but it would rule it out for me personally.
My dirtbag is fairly hi too, just took a little getting used to and I was all good. Personally I dont think an inch or two is a huge difference, I still whack teh hell out of my bashguard.
It was a trail bike, but it got me thinking about the VP-Free, which I have been told is high.
Anything above 14.5" I've ridden just didn't settle into corners well.
They were great for flowing trails and such bet harder to set into a berm.
They were great for flowing trails and such bet harder to set into a berm.
Yes, one of the biggest things that is completely blown out of proportion these days. While there are places where you can get away with a 10" BB height on an 8" travel bike, it's not pratical to have ultra-low BBs for a lot of places that people ride, and there's a lot of other factors to consider, such as the wheelbase to BB to travel ratio, and so on. I got a 15" BB on my new freeride rig, but it also sags 2-3" into the travel, so the effective BB is not super high IMO, not to mention I put some super-sticky tires on it and I can rail turns just fine (although if I went with smaller tires I'd have a lower BB). Getting ejected when your pedal strikes a solid rock is one of the suckiest types of crashes I've had, and I've killed lots of crank-brothers products on rocks. I'm not saying that BBs should be super-high, but there are practical limits. There are some manufacturers that say "screw it, we'll lower that BB!" and they get some die-hard fans, while other manufacturers are more conservative and want to be able to sell bikes for more conditions.
Hey Patan, where in the patagonia are you at? and where do you ride? I rode my disco volante for ever, it didnt exactly have a low bb, but it made for a funner bike, more active even whilst running into the sag. When I didn't feel it as fun was in the fast open sections were the bike went crazy on me hehe
Not really so, a lower BB results in dropping the COG of a bike significantly, considering that the rider (the largest mass on a bike by a long shot) is lowered. I feel it translates into cornering pretty favourably; over the years I've gone from 15" to 14" to 13.6" BB heights on 8" travel frames, and the bikes have progressively been quicker in and out of corners and just felt faster all round as the height dropped.
The fastest racebikes on the circuit currently all have sub 14" BB heights (Sunday / M6 / etc) and with good reason. The only sacrifice you make on a DH course is where you can pedal from my experience, and at the ~13.5" mark it does start becoming noticeable, however your riding style most certainly adapts. You learn to hold speed over sections much better, pedal hard where needed, and gain a lot of time in the twisties.
How low you go is personal preference, I think 13.5 is best left to 8" bikes, and 9" bikes should be around 14", but it's definitely one of the most important geometry numbers on a downhill bike regardless.
Like I said though, it fails to take other things into account. Some designs like the chumba evo have the shock mounted way high in the frame, whereas others have it very low, you have some significant COG differences without even looking at the BB. Then you have people that set sag on DH bikes as if they were XC bikes, so you get some more significant changes there, and so on. No one of the factors here or that I talked about in the post above is going to be huge by itself, but together it means that a 14" bike vs a 14.5" can be radically different, and that 14.5" could easily outperform the 14 and even have a lower dynamic BB height. Anyhow, just saying that it's not so simple and tends to get blown way out of proportion without considering all these other factors.
Is it an important figure? Sure. Should people go selling their bikes just because one is half an inch lower? I don't think so. Does half an inch of lower BB necessarily mean you'll end up with a lower COG or dynamic BB? No.
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I still think it goes back to what the purpose of your bike is. If your running a full blown DH bike, then a low BB is nice to have, low center of gravity, Blah Blah.... But you sacrifice Clearance. Yes, The low BB is blown out of proportion, in the idea that everyone out there thinks they need a lower bb now. And they dont, its mostly hyp for them, where they can say"Hey look, I have a more race ready bike than you do".
I race on a Dirtbag, which as we all know isnt the lowest BB in the industry, according to the website its 14.35bb height, which works well for me, I cant afford to have a full on race bike, and a full on trail bike, and a full on local DH bike ETC. So I have a dirtbag, it works for where I ride, and for where I race. Would I like to be racing on a Customed out Sunday or a Customed out M6, yeah that would be nice, but that just isnt going to happen. I dont have the cash for one, and I am not good enough of a rider to get one for free.
Like I said in my first post, I already hit the bashie enough as it is, I couldnt imagine how many broken superchargers I would have if My bb was lower. But if all I did was race on this bike, I would want something differnt
I race on a Dirtbag, which as we all know isnt the lowest BB in the industry, according to the website its 14.35bb height, which works well for me, I cant afford to have a full on race bike, and a full on trail bike, and a full on local DH bike ETC. So I have a dirtbag, it works for where I ride, and for where I race. Would I like to be racing on a Customed out Sunday or a Customed out M6, yeah that would be nice, but that just isnt going to happen. I dont have the cash for one, and I am not good enough of a rider to get one for free.
Like I said in my first post, I already hit the bashie enough as it is, I couldnt imagine how many broken superchargers I would have if My bb was lower. But if all I did was race on this bike, I would want something differnt
You can't compare BB heights between 20" and 26" wheel sizes.
A positive BB rise will help with manualing and jumps because most of your weight is above the axle center line. Negative BB rise will make it harder because of leverage.
Personally I think BB height can make or break a bike. I can't stand riding a bike when I feel like I'm teetering over top of it. All that said I am starting to be of the opinion that the Geometry that you get from a full suspension bike, specially a DH bike is somewhat useless. Some of you were alluding to BB height in relation to travel and how much the bike will sag. Well the company designs a bike around a certain amount of sag it would be much more helpful to know that bikes bb height at that sag.
Also on a similar thread are top tube measurements. I can see for bikes were you are seated how this might be a very important measurement; however, I don't know about the rest of you but the seat on a DH bike is not a point of contact for me, and it is, something has gone wrong. Now I can understand that traditionally this was a useful measurement for road, and maybe even conventional riding. But it doesn’t' seem very applicable to a bike where you are standing all the time and your only points of contact are your hands and feet. I guess if you want to know the distance between your points of contact (hands and feet) you could do some trigonometry with the seat angle and top tube length but that's not exactly user friendly.
For DH wouldn't more useful numbers be based on the bikes geo at the companies intended sag, and revolve around horizontal distance from head tube to bb shell, Vertical distance between BB shell and top of head tube, BB height at sag and wheel base at sag.
Maybe someone who has some more experience with this can explain to me why this is not done (aside from the fact that it is not industry standard practice).
I only bring it up because it seems given the current numbers it is really hard to figure out what a bike is going to ride like. You could end up feeling like you have your feet above your head and riding a train.
Just look at the new V10. On paper relatively high BB, steep head angle and short wheelbase. But when I hop on my buddies that fork slackens out pretty quickly.
Also on a similar thread are top tube measurements. I can see for bikes were you are seated how this might be a very important measurement; however, I don't know about the rest of you but the seat on a DH bike is not a point of contact for me, and it is, something has gone wrong. Now I can understand that traditionally this was a useful measurement for road, and maybe even conventional riding. But it doesn’t' seem very applicable to a bike where you are standing all the time and your only points of contact are your hands and feet. I guess if you want to know the distance between your points of contact (hands and feet) you could do some trigonometry with the seat angle and top tube length but that's not exactly user friendly.
For DH wouldn't more useful numbers be based on the bikes geo at the companies intended sag, and revolve around horizontal distance from head tube to bb shell, Vertical distance between BB shell and top of head tube, BB height at sag and wheel base at sag.
Maybe someone who has some more experience with this can explain to me why this is not done (aside from the fact that it is not industry standard practice).
I only bring it up because it seems given the current numbers it is really hard to figure out what a bike is going to ride like. You could end up feeling like you have your feet above your head and riding a train.
Just look at the new V10. On paper relatively high BB, steep head angle and short wheelbase. But when I hop on my buddies that fork slackens out pretty quickly.
Yeah, I think a lot of people put too much faith in the numbers vs. the actual feel of the bike. I've ridden a V10 before and it sags way down in the rear before the front even moves. Plus, with a scraper BB height you'll be clipping everything as you go down the trail...on rocky trails where I ride, I can't imagine smashing everything in sight. My bike has an epic tall BB height, and when I slap on 24" tires, I clip everything in sight. That means if I'm at 15.5" normally, minus the 1-1.5" from the tires, I'm at 14-14.5, and 9" travel means smash smash smash. I much prefer the higher BB height so I don't have to deal with smashing pedals and chainrings and everything else....oh yeah, the Racelink has a 28tooth chainring...imagine that with 10 more teeth.
I agree on another point, oddly enough, a pure DH race bike is growing very far from a freeride/DH bike...or you could say the freeride bike is evolving from an XC bike with huge travel to a DH bike that you can ride all day long.
I agree on another point, oddly enough, a pure DH race bike is growing very far from a freeride/DH bike...or you could say the freeride bike is evolving from an XC bike with huge travel to a DH bike that you can ride all day long.
Super low seats is a fad, you need to be brigning your seats up a touch to help keep you in an attack postion, Alot of people are running the seat height no lower than an inch and a half lower than the bars.
I was saying that you never really sit down on a dh bike when you are riding, so to use a head tube to seat tube measurement doesnt' seem very usefull in giving you an idea of the cockpit. I understand that it can be a contact point, but not nearly to the same extent as your hands and feet.
Yeah I see what your saying, but still it gives you a feel as to where the proper stance is, even though your not sitting, you still need to be able to feel for where you need to be, and alot of DH bikes with teh seat about an in and a half below the stem, it gives you an excellent feel for the bike, and alsoif you should need to sit, you can without sacrificing too much. Also you want to be able to have the proper fore and aft ability of seat position, even if you slam the seat, you dont want the seat too far forward or too far back compared to your leg and foot position
My '08 V10 has a 14.8" BB but it corners SOOOOO fast compared to the '07 V10. It also hits the pedals and bashgaurd on stuff I expect to clear. Basically I wouldn't want to go any lower but I feel the improvement from the higher old bike.
remember that all BB heights are static without sag
to get the effective BB you have to take into account how much sag youll be running
14.8" isnt that low, however on the 10" travel V10 with correct it probably sits around a similar than say a Sunday with a lower static BB