Hey everybody welcome back to another Tuesday tip we're in this week's video
We're gonna be talking about modern BMX frame geometry and what all of the numbers that are used to build your frame actually
Mean so if you're new here every Tuesday
I try to make a tips and tricks video on everything from learning about your bike itself
To tips and tricks for working on your bike to tips and tricks for actual tricks while riding your bike
So like I said before this week
We're gonna be talking about modern BMX frame geometry and what all of these
numbers mean throughout the years BMX frames have changed for a variety of reasons a couple of those being
Just to fit the trends of the time or to make bikes feel better for certain disciplines. Whether it be
Park Street or trails or for certain styles of riding so to get right into what all of the
geometry and numbers mean on your BMX frame
Let's talk about the pieces and parts that make up a BMX frame
And we'll start from front to back and that's how we'll talk about the numbers as well so starting at the front
We've got the head tube
The top tube the bottom tube the seat tube the bottom bracket tube cable guides if you have them
chainstays seat stays brake mounts if you have them they can also be on the chain stays and
Dropouts moving our way back to the front of the frame
Let's talk about head tube angle first
To measure head tube angle you draw a line from the middle of the head tube
And then you draw a line from the middle of the dropout and where they meet the angle of that
Is your head tube angle?
This is something that has a huge
Impact on the way that your bike feels and how certain tricks can feel while you're riding your bike
generally the numbers range from about
74 to 76 degrees with most frames falling somewhere in the 74 point five to
75 degree angle so the way this works is the steeper the head tube angle
the closer the tire is to the rest of the bike and the easier and
Quicker it reacts as you turn the bars and on the opposite side of the spectrum
The mellow or the head tube angle the further the front tire is
Away from the rest of the bike generally speaking steeper head tubes help with things like nose manuals and other front end tricks whereas
mellower head tube angles help with things like trails and
Jumping and that's because when your front tire is closer to the rest of your bike your bars
Have a quicker effect when turning
Which is something that helps whenever you're in a nose manual or doing front-end tricks it gives you more control
With those tricks and with a mellower head tube angle your wheels are further apart
Which makes for less responsive turning which is something that you want if the trails so that you feel like you have more control?
Whereas when you're in a nose manual?
And you need to correct quickly you'd want more of a responsive feel
Coming from a steeper head tube angle when it comes to top tube angle on BMX bikes we see everything from 18 inches
up to
21 and a quarter to
21 and a half inches top tube length is measured using that same line that we drew through the middle of the head tube before
From that center point of the head tube
To the center point on the seat tube and this has to do with how comfortable it makes your bike feel so it kind of
Goes hand in hand with how tall you are
But when it comes to the shorter top tubes like 18 and 19 inches we mostly see those in flatland
And then when you get into 20 point 5 to 21 inches
That's what we see more commonly when it comes to
their Park Street and trails and things like that and like I said those usually have to do with how tall you are
But a shorter top tube can do the same thing as a steep head tube and it can bring your wheels closer together
Giving your bike a more responsive feel and that's why we see Park riders
Who are doing crazy spins and tail whips and things like that?
running shorter top tubes
And then when it comes to a longer top tube it can do the same thing as eight mellow head tube and it can
Spread your wheels apart further giving your bike a less responsive feel so that it feels like you have more control and stability
For things like trails, you can definitely tell when someone's riding a frame
That's way too big or way too small for them because they're either
Hunched over to reach the bars or they're reaching really far to get to the bars unless we're talking about flatland
we're
18 and 19 inch top tubes are
The norm when it comes to down or bottom tubes the length directly correlates to the top tube and seat tube
So there's really nothing to say about this because this generally isn't something that we change when working with BMX
geometry
So we'll move right on back to the seat tube height also known as stand over and the seat tube angle for this video
I'm just gonna call a stand over and what this is is the measurement from?
the center of where your top tube connects to the seat tube to the
center of the bottom bracket and on frames this can range anywhere from six and a half inches at the low end to
Ten inches on the top end and really. This is something that is up to the rider because
Shorter stand overs are known for making things like tail whips easier
So this is another thing that you'll see a lot of Park riders doing is having
Shorter stand overs whereas a taller stand over could be known to be stronger
That's up for debate, but it's also something that can raise your seat up and make things like bar spins easier
I don't it's really personal preference and everything to do with what you like and how you feel that it affects your riding
So now we'll move on to seat tube angle
this is
Measured using that same imaginary line that we drew from the center of the drop out up to the point where it meets the line
Going through the head tube
How you measure this is you have this line right here that goes from the back to the front?
And then you've got a line through the middle of the seat tube the angle from the line on the seat tube
to the line going from the back to the front this angle that it creates is your seat tube angle and
We see everything from 69 to 70 to 71 degrees on the seat tube angle
seat tube angle combined with other things such as head tube angle can change the way your bike feels because a
Steeper head tube angle combined with a steeper seat tube angle can make the top tube feel longer than it really is
Other than that it's another thing
That's up to personal preference and the way that it can change the look and the feel of your bike
Next we'll talk about bottom bracket height, which is the measurement of how much higher your bottom bracket is then your axle to axle wheelbase?
Generally, this is anywhere from eleven point five inches to eleven point seven five inches with some frames being lower
Or higher than that number
This is another thing that you might not think has an effect on the way that your bike feels
But it's something that definitely does a lower bottom bracket brings your whole bike
Closer to the ground which is something that a lot of trail riders like because a lower bottom bracket makes your bike feel
more stable and less twitchy
Whereas on the opposite side of the spectrum a higher bottom bracket can make your bike feel more twitchy or more?
Responsive so this is another thing
That's up to personal preference
But it does have an effect on the way that your bike feels another thing that can affect your bottom bracket height is
your tire tread believe it or not because a
bigger tire with bigger tire tread puts your axle to axle wheelbase higher
Therefore bringing your entire bike in your bottom bracket height higher moving on from bottom bracket height
We can talk about the seat stays
This is another thing that is dependent on other aspects of the bike
So this isn't something that we typically change, but there is a seat state bridge
That is something that we change on custom bikes or some frames put their own seat state bridge on there
This is one of the first frames to ever include one of these. This is a scavenger bridge
Which is called the bridge because it's got a bridge going across the seat stays
So there's not much to talk about with this other than if your brake mounts are on here sometimes
They're removable or welded on which is another preference that you can make or decide on
When you're buying a frame some frames also don't even have brake mounts at all or the option for brake mounts
Without of the way, we can move down and talk about chain stays
This is something that has a huge range on BMX frames anywhere from
12.5 inches on the shorter end to 14 and a half
14.5 inches on the longer end chainstay length is the measurement from the center of your bottom bracket?
To the center of where an axle would be in the drop out when it's slammed and I slammed
Axle means that your wheel and your axle are is far forward in the dropout as possible so again
That's the measurement from the center of the bottom bracket to the center of a slammed
Axle this measurement directly affects your wheel base from axle to axle and makes it shorter or longer
Depending on your frame, which has a big effect on the way that your bike can feel
which is why you see street in park frames with shorter chainstay lengths and
Trail based frames with longer chainstay lanes a longer chain stay means that your wheels are further apart
Which makes your bike feel more stable?
it's harder to loop out and it's easier to keep underneath of you while jumping at the trails and
Obviously having a shorter chain stay brings your wheels closer together, which generally makes your bike feel more responsive
And it has an effect on manually and it can make bunny hopping easier
So if you write everything from Park to Street to trails you might want to consider something in the middle of the road which on
A lot of frames is around
13.5 inches, but if you ride more Street and Park than you do trails you might want to consider something shorter
And if you ride more trails you might want to consider something longer
All that being said the last thing that we need to talk about with BMX frame
Geometry are the dropouts so when it comes to dropouts they can be deeper or shallower
depending on the frame
So that's something that you're gonna want to consider because the shorter the dropout the less
range you have and where you can put your wheel and your chain is something that can directly affect this so if you have a
Shorter dropout and your chain stretches or the links just don't line up
You could be faced with a axle that sticks out of your dropout
And you either have to buy a new chain or take a link out and maybe you have to put a half
again because an entire link puts it further forward, then it can go and
This is something you definitely want to take a look at because it can cause a lot of frustration
If you don't have the money to just go out and buy a new chain if things don't line up
Perfectly with a longer drop out obviously you don't have to worry about that as much
There's also some technology that we can talk about with dropouts some frames have built-in chain tensioners and a chain tensioner is
Usually a bolt or a pin inside the drop out that you can tighten or loosen
to not allow your axle to move forward any further, so it makes lining up your wheel a
Million times easier than doing it all by hand
But this is also something that can be bad because they can break or get stuck or something like that
I haven't had any bad experiences with them really
But I know that when you take off your wheel sometimes you have to loosen them and tighten them
And it's just it can be a pain to have them
But it also can help a lot to have them so that's another thing you want to consider
also, there are solid dropouts like this one or these ones that you can see where it's just one piece of metal or
On like the sunday frames, they have super thick dropouts that are hollow in the center which are supposed to be stronger
But that's another thing that you can look at because a thicker dropout
affects your axle and your wheel and if you have a solid axle and
A hub guard and all of these things it can have an effect on how you put your wheel on your bike and that's not
Something that you would generally think about when you're buying a frame other than that there's a couple non
Geometry specific things that we can talk about such as another feature of this frame is the fact that there's no
Tube up here to put a seat clamp on so you have to use I think animals wedge
Seat post is like the only one that you can use that's like modern
You can't put a seat post clamp on here, so you have to find some other way to do it
They're also used to be frames with built-in pivotal seat posts
So you couldn't change the height of your seat at all without
Cutting it and figuring out a way to get a seat post in there
I'm not sure if those are still
But it's worth mentioning and then the last thing that we can talk about
Doesn't have anything to do with geometry but a lot of frames nowadays have head to badges
and
This is another thing about this frame. Is it's one of the first ones that had a head to badge, and these are cool because
Look at it. I think it's pretty cool to have one of these on your bike and
There's a lot of custom designs for different bikes
Fbm has some really cool head tube badges, so that's another thing to consider
I mean I guess if that's something that has an effect on the frame you buy
It's just a cool feature that you can have on your bike
I just remember a huge one that we haven't talked about yet
When it comes to chainstays there's different methods of connecting the chainstay?
To the bottom bracket tube some frames are built so that both chainstay tubes well directly to the bottom bracket tube
But there's other frames that are designed with what is called a wishbone design where the chain stays come together
Into one tube that is welded to the bottom bracket itself. This is something
That's said to be stronger
There's some frames like the barcode frame from terrible one where there's wishbone designs on both the top and the bottom
There's also frames that have dual top tubes. There's frames with platforms
there's tons of things that you can get into when it comes to specific designs and features on frames as well as
Frames can have gussets on the inside or the outside
Of the tubes a gusset is a piece of metal welded to the down tube or the top tube and then
The head tube on a frame
designed to add
Strength and just make it less likely for the frame to break in those places and like I said they could be inside
The tubing they could be on the outside they could be in the middle they can be on the top tube
Also, there's frames that have the top tube and the bottom tube connected with a gusset
And then there's frames like the sundae Soundwave like what I ride where it's a huge gusset that goes down here
And then the bottom tube has a wave in it and the top tube has a wave in it
and then there's a wave on the underside of the top tube all meant to add strength to the frame itself and
Resist bending and dents like these on the bottom of the frame
So I think that about covers it when it comes to BMX frame geometry and other features
to do with frames in their geometry
so
Hopefully I helped you learn about
BMX frame geometry, I'm gonna keep saying it BMX frame geometry and
I hope I didn't miss anything if you like this video consider subscribing
It's free and there's no reason not to I want to give a huge shout out to
Kurt at BMX Union because almost all of this information came from his insight article on the website about
BMX frame geometry, and I literally couldn't have made this video without it
It's a huge article and all of the information
I talked about is in it
And it would have taken forever to compile it on my own so Thank You Kurt Thank You BMX Union
Thank you for watching
remember to subscribe if you liked the video and
We'll see you next time goodbye
You