Bike Fit -- Bar height and "Stack" height in BMX and MTB-DJ/Street

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Bike Fit -- Bar height and "Stack" height in BMX and MTB-DJ/Street
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flag cmc4130
Posted: Jan 21, 2016 at 9:05 Quote
Y'all are about to get TMI, but here we go....

Bike fit for bmx and mtb-DJ/street doesn't get talked about that much, but to me, a major aspect would have to be how the "stack" height compares to your measurement of your knee to the ground. Then how tall your bars are relates to how high above your knees you want your grips to be.

While a lot of bmx racing and dirt jump riders seem to have their grips slightly above their knees, I think it's true that one current trend in bmx and mtb street riding is to have your grips more significantly above your knees--almost mid-quad. If your grips are below knee level, there would seem to be more low back strain and less power in lifting.

The "stack" on a typical DJ-mtb (for example, a Transition PBJ) is 563mm (22.16").

photo

http://www.utahmountainbiking.com/fix/fit-bike.htm

The average man's inseam is 45% of height (32.4" for a 6 foot tall man). Knee height averages around 21.3" for men, according to this: http://dtic.mil/dtic/tr/fulltext/u2/a433581.pdf

http://www.bikeforums.net/road-cycling/279617-average-male-inseam-height-ratio.html

A stance like this, his knees are well below his grips.

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Danny McAskill as well:
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Lee McCormack talked about bmx racing bike fit in his book:
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I would imagine that in DH, you'd want your knees below your grips too....
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These guys have knees below grips.
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Tall (or long leg) dudes on 20" bmx might have more low back strain when their knees are at or below grip level.
Van Homan.
Unsecure image, only https images allowed: http://cdn.bmx.transworld.net/files/2008/08/18/van-homan.jpgChris Doyle
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Grips higher than knees.
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Ryan Nyquist is a short dude, but he also ran low bars.
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Phil Sundbaum has to hunch a lot when his grips are at knee level
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Lacondeguy - When you have a long "reach" frame, then raising the bars brings the angle of your back up to normal.
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Martin Soderstrom is 6'5", but he also seems to have that body type with a longer torso and shorter legs....
photo
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Grips higher than knees.
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flag ricar
Posted: Jan 21, 2016 at 10:27 Quote
A lot of those pics are difficult to compare. Saying the grips are higher than their knees is fine, but at what point? In many of the pics the cranks are not level so it's impossible to compare. not saying you are wrong, or arguing, just that it's real hard to compare. I do think it makes sense, but spindle height to grip height would be more simple. Getting any comparison of that in pics pulled off the web would be difficult.

I find it interesting that McAskill is the only one (of the pics posted) that has any significant rise to his bar.

Hoffman back in the day
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flag cmc4130
Posted: Jan 21, 2016 at 12:41 Quote
ricar wrote:
A lot of those pics are difficult to compare. Saying the grips are higher than their knees is fine, but at what point? In many of the pics the cranks are not level so it's impossible to compare. not saying you are wrong, or arguing, just that it's real hard to compare. I do think it makes sense, but spindle height to grip height would be more simple. Getting any comparison of that in pics pulled off the web would be difficult.

I find it interesting that McAskill is the only one (of the pics posted) that has any significant rise to his bar.

Hoffman back in the day


yeah, i agree, the pics are hard to tell.

i'm not necessarily going to tell someone what the "proper" bike fit is--it's up to them to decide. but, i think it is interesting to look at the comparison across different bikes and riding styles, and to pay attention to how each rider fits with the bike, not just what a bike is "supposed" to look like in the abstract.

that was probably hoffman's first air on a run, cuz he was usually above 8 feet! Wink
flag ricar
Posted: Jan 21, 2016 at 13:14 Quote
Posting that pic was more about how similar the set up was to what it is some 30 years later. Guys used to run the bars farther forward in the 80s but frames were shorter. If memory serves I think an 86 Haro Master had a TT of 18", now the grips are in pretty much the same spot but the frames got longer.

That MUST be a set up air (or it's mid 540) but you get a good idea of where his knees are to his grips as you pointed out. I have to admit, I have never thought of that knee height/ grip height thing before.
flag ridelikeacat
Posted: Jan 21, 2016 at 19:32 Quote
i though the reason the bars should be above your knees is for proper weight distribution in the manual position. Cuz since in a manual your arms are locked straight, changing the stem length or the overall rise changes the position your body and front wheel is in when your bike is balanced during like the neutral manual position. So high bars are like a lower more steady manual that you can use for better manual to hops and long manuals or in dannys case like crazy trials stuff. I think too since manual position is like the neutral spring position for a good bunnyhop it makes the position for juumping higher more balanced and dialed too. Cuz a low front end is garbage to lift and that is directly related to how hunched over your neutral standing position is since u cant manual hunched, you have to be like somewhat standing over the bb still, so you can hang off the back of your bike. Thats also why the backsweep on the riser bars for hanging off the bike and properly like lifting and directing the bars in hops or in a manual. Man i love talking bikes, sorry for rambling. But ya u want the bars higher so you have more room to balance and move while still keeping the front wheel comfortably low enough to like hop out of manual or do a big ol tire bump without flipping off the back cuz ur front wheels so high
flag cmc4130
Posted: Jan 21, 2016 at 20:16 Quote
ridelikeacat wrote:
i though the reason the bars should be above your knees is for proper weight distribution in the manual position. Cuz since in a manual your arms are locked straight, changing the stem length or the overall rise changes the position your body and front wheel is in when your bike is balanced during like the neutral manual position. So high bars are like a lower more steady manual that you can use for better manual to hops and long manuals or in dannys case like crazy trials stuff. I think too since manual position is like the neutral spring position for a good bunnyhop it makes the position for juumping higher more balanced and dialed too. Cuz a low front end is garbage to lift and that is directly related to how hunched over your neutral standing position is since u cant manual hunched, you have to be like somewhat standing over the bb still, so you can hang off the back of your bike. Thats also why the backsweep on the riser bars for hanging off the bike and properly like lifting and directing the bars in hops or in a manual. Man i love talking bikes, sorry for rambling. But ya u want the bars higher so you have more room to balance and move while still keeping the front wheel comfortably low enough to like hop out of manual or do a big ol tire bump without flipping off the back cuz ur front wheels so high

manuals are interesting, because some people in bmx think it's all about the shortest chainstays possible. although it might be easier to pull up, it's not actually easier to lock in the position. i've had manuals down on all my bikes, but i've gotta say, i have them most locked down on 24"s and 26"s. it's okay to have that back end to pull against. the first bike i learned great manuals on was actually a bmx pro XXL race bike with a long front end and long back end. you DON'T need a bike that loops out too easily.

try lots of different setups--high bars, low bars, whatever. i think each time you adjust to a new setup, it's like "cross-training" and you become a better rider.
Wink
flag Metro-Gnome
Posted: Jan 21, 2016 at 20:25 Quote
I think it's important to also consider bb rise or drop in this equation. I mean yes, having knees under grips/high bars makes manualling a little easier, but a huge part of what factors in is the rise or drop. For instance, a shorter rider on a bike with 25mm rise is raising his knees towards the grips with the rise(if you get me) therefore closing the gap and making a high bar almost necessary. With a low bar and a bb with 25mm rise, a low bar would be farther from their center of gravity. For instance compare my 3 bikes

Majesty 26" Dirt 10bb drop, 38mm rise bar
Sub park 26" 15bb rise, 38mm rise bar
Dartmoor 24" Ghetto 25bb rise, 84mm rise bar

I didn't realize why such different bikes felt so alike...
In the standing position these bikes feel more similar than they look on paper based on geo stats alone . If you line them up on a wall, the bar height doesn't vary that much, either. Of course this isn't a fair comparison because the 24" Ghetto is a 24...but I'm doing the best I can here to explain that I can't necessarily do anything on one of these bikes that I can't do on all of them. This thread is making me think long and hard about bar-to-knee position. I used to think it was all about bar height. I've been riding short frames with high bars and low bbs. I never understood why it felt so natural, as when I ran lower bars on high bb frames it would feel like they were too far away from my center of gravity to manual as easily.---edit--- Honestly though any normal, modern chainstay is going to be short enough to make all kinds of stunts possible, bar height/bb rise is just going 'tweak' how fast you rotate in the air and with how much stability. Sorry if I'm kinda going off topic a bit

-end rant.
flag ricar
Posted: Jan 21, 2016 at 21:27 Quote
Street MTB (Szymon Godziek)
photo
4X MTB (Benedikt Last)
photo

Dirt MTB (Carter Holland)
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Street BMX (Garret Reynolds)
Unsecure image, only https images allowed: http://i1.mtbx.com.ar/foto/o/12/55/1255197978_gr7.jpg
Vert BMX (Mat Hoffman)
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Race BMX (Raymon van der Biezen)
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The biggest difference I see is in chain stay length (and stand over on the race BMX) on the race bikes compared to the other genres. That being said, there is actually less than an inch difference between Hoffman's chain says and van der Biesen's. It's hard to compare the 20" bikes but it I were better at photo shop I'd take the bikes and overlay them to see just how they line up. I am surprised at how similarly set up they look, but really, it is a pretty superficial comparison.
flag ridelikeacat
Posted: Jan 21, 2016 at 21:44 Quote
Ya metro i shoulda clarified when i was talking bars being above the knee i meant with a proper freestyle bb. Te bb height makes a big difference.

Yeah ricar the biggest dfference is that for speed bikes like to be longer with lower bb and a slacker headtube angle. For slow spinny pr bouncy trcky riding bikes like a short wheelbase with a higher bar and steep headtube angle. All bikes are basically a hybrid of a long downhill bike and a super short lil bmx. Just to varying degree. Im having a big problem with the geo of "street mtb" because it differs so much. Like ricar id call that first "street mtb" a DJ because of the fork and bar/stem but its hard cuz "street mtb" is refering to a riding style not a certain bike. I would call it a Park DJ as it is a dirtjumper with dj fork and tires but the geo has been made a bit shorter and steeper for street. A true street mtb is all rigid but then not always like my street mtb isnt wven a true one cuz it uses a park DJ frame. Im building up a true street build with parts i mentioned before (pridestreet fork and bar and an ns capital frame) to setup a good as possible mtb street geo for my body. But now i discover Anthem bikes and there 26" bmx frame and to me this is a 26street bike. But thats where the difference lies. Street mtb needs a hardtail mtb frame like a ns capital or dartmoor freaky etc but all these "frankenstein" dj/street hybrids are confusing everyone.
flag ridelikeacat
Posted: Jan 21, 2016 at 21:49 Quote
I hate the term "street mountainbike" cuz its not a mountainbike its a freestyle street bike, but that sounds like a crotch rocket. Mtbmx confuses people cuz they say "its not a bmx tho" and the riding is very different. Mtb street is super heavily dirtjumper influenced. Im tryin to like have bmx influenced 26" freestyle but im finding the fixed gear freestyle riders are doing alot more bmx oriented street riding and now riders are even riding 26" bmx frames with 75 degree headtubes and short rigid forks with 6" riser bars on a frontload bmx stem with bmx hubs and a high bb. Grindplates on chainstays....lol so cool and the geo is bmx geometry for street just on a 26" wheelset. Pretty gnarly.
flag cmc4130
Posted: Jan 21, 2016 at 22:01 Quote
ridelikeacat wrote:
I hate the term "street mountainbike" cuz its not a mountainbike its a freestyle street bike, but that sounds like a crotch rocket. Mtbmx confuses people cuz they say "its not a bmx tho" and the riding is very different. Mtb street is super heavily dirtjumper influenced. Im tryin to like have bmx influenced 26" freestyle but im finding the fixed gear freestyle riders are doing alot more bmx oriented street riding and now riders are even riding 26" bmx frames with 75 degree headtubes and short rigid forks with 6" riser bars on a frontload bmx stem with bmx hubs and a high bb. Grindplates on chainstays....lol so cool and the geo is bmx geometry for street just on a 26" wheelset. Pretty gnarly.

I agree with you, man. People are pushing different ideas and geometry, and it's very cool. And, in a lot of ways street FGFS and street MTB are converging..... and both are more progressive than a lot of 26" BMX (like the Stolen Zeke 26" and Fairdale TAJ with their long chainstays.... etc.)

Pfix & Street Fiend style with disk brakes?
https://www.pinkbike.com/forum/listcomments/?threadid=163968

photo

photo


Nice retro styling . . . but I kinda wish the head tube angle was steeper (than 71 degrees) and the back end was shorter (than 16.7").....
2015 Fairdale Taj
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Volume Hessian 26" -- shorter chainstays than other 26" BMX's
photo
flag ridelikeacat
Posted: Jan 21, 2016 at 23:03 Quote
Those bb are all so low though! They rob the bike of the pop that bmx have. Look at the bb height on these 26" fgfs frame by anthem bike co
https://instagram.com/p/83TL32AHKW/

My bb is even too low for the style. this is my bike that im soon replacing
https://instagram.com/p/BAZA3ZNEkDN/

Here is a ns capital street mtb with similar geo to what mine will be, notice stem and bars and bb
https://instagram.com/p/-SGFcQMEH_/

Heres a different ns capital from the side to etter show bb height
https://instagram.com/p/_XXm5VO0xK/


theres a new frame that will have -15mm bb height and 375mm chainstays, 8mm thick dropouts, 75 degree headtube for 26" wheels. So sick. Will be so nice to trick on.
flag auri
Posted: Feb 26, 2019 at 23:45 Quote
cmc4130 wrote:
ridelikeacat wrote:
I hate the term "street mountainbike" cuz its not a mountainbike its a freestyle street bike, but that sounds like a crotch rocket. Mtbmx confuses people cuz they say "its not a bmx tho" and the riding is very different. Mtb street is super heavily dirtjumper influenced. Im tryin to like have bmx influenced 26" freestyle but im finding the fixed gear freestyle riders are doing alot more bmx oriented street riding and now riders are even riding 26" bmx frames with 75 degree headtubes and short rigid forks with 6" riser bars on a frontload bmx stem with bmx hubs and a high bb. Grindplates on chainstays....lol so cool and the geo is bmx geometry for street just on a 26" wheelset. Pretty gnarly.

I agree with you, man. People are pushing different ideas and geometry, and it's very cool. And, in a lot of ways street FGFS and street MTB are converging..... and both are more progressive than a lot of 26" BMX (like the Stolen Zeke 26" and Fairdale TAJ with their long chainstays.... etc.)

Pfix & Street Fiend style with disk brakes?
https://www.pinkbike.com/forum/listcomments/?threadid=163968

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Nice retro styling . . . but I kinda wish the head tube angle was steeper (than 71 degrees) and the back end was shorter (than 16.7").....
Unsecure image, only https images allowed: http://fairdalebikes.com/wp-content/uploads/2014/09/bmx-26-inch-cruiser-2015-fairdale-taj.jpg
Volume Hessian 26" -- shorter chainstays than other 26" BMX's
photo

Hi there, sorry for diggin out that topic.

Did anyone already compared the height of a dirt jump bike to a "modern" BMX geometry with a 9" bar? I would like to do that just so see how serious the differences are.

I am also having trouble find the sweet spot for my Transition PBJ Stack/Bar height.

Currently i am riding a Circus Expert fork dropped to 80 mm travel combined with odyssey boss stem and a 2018 district bar. I am pretty tall (6,7') and switching back and forth between a high front and a low front. I really like to have the BMX ride, feel and look with a 26" dirt jump bike.

photo

I am still wondering how different some pro setup are. Cody Gessel f.e. rides a extremely high front setup (100 mm with a lot of spacer underneath the stem)

Edit:

I tried to do some drawing to compare the geometry of the PBJ with a district bar and a "random" BMX bike with 10" bar:

photo

The PBJ is, depending on the fork travel, generally 5 - 6 cm higher (measurement from the BB to horizontal bar height)
flag cmc4130
Posted: Feb 27, 2019 at 8:42 Quote
We can compare the "stack" between BMX and MTB-DJ.

An 100mm sus fork would typically be around 478mm (18.8") axle to crown. Let's assume both the BMX and the MTB have same head tube length (4.5"-ish). The MTB-DJ will also typically have 1" (25.4mm) of bb "drop" below axles.

Assuming some of the numbers below, the stack is 9.15" (232.4 mm) taller on the MTB-DJ.

photo
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photo
photo
flag auri
Posted: Feb 28, 2019 at 2:06 Quote
cmc4130 wrote:
We can compare the "stack" between BMX and MTB-DJ.

An 100mm sus fork would typically be around 478mm (18.8") axle to crown. Let's assume both the BMX and the MTB have same head tube length (4.5"-ish). The MTB-DJ will also typically have 1" (25.4mm) of bb "drop" below axles.

Assuming some of the numbers below, the stack is 9.15" (232.4 mm) taller on the MTB-DJ.

photo
photo

photo
photo

Thanks for your reply!

But stack does not consider the significant higher rise of a bmx bar (9-10") to a mtb bar (2-3,5"). For the feel/rating of posture on a dirt bmx/mtb it is important to consider/compare the height from BB to the height of the bar. Thats why i get a value of 5 - 6cm higher feel for the dirt jump mtb, depending on the bar height.

I was surprised of the high value of reach (466) for the bmx geometry (referring to my drawing). I guess the steep head angle of the bmx geometry does matter very much here. But that roomy feel in that case (bmx) is also determined by the bar roll (more chicago or old scool trail setup/rolled backwards).
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