let's talk about geometry of the frame

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6/28/2018 11:31 PM

Hi guys!!
I am riding since 2 years ago a bsd soulja.
Lots of people in my country are riding now bsd because they are not too much expensive and because they have a short back end, which is kind of a trend.
From the begging, I have felt like the bike reacted better: easier to pull up the front wheel, easier for rotation/spin.
But now, I am realizing that maybe this is not the best..because Since the frame it’s shorter, and smaller, I’ve find harder to get more balance when I am doing tricks.
Is this only my thought or it could be the reality?
I am riding mostly in street and not in park.
But..at September I would get another frame…which one could be? Maybe a cult or wtp?
Thanks!

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6/28/2018 11:42 PM
Edited Date/Time: 6/28/2018 11:53 PM

There's literally only 5 or 6 factories in Taiwan that make all aftermarket bmx frames (obviously excluding American made. S&m, fbm, standard etc). So which brand really doesn't matter that much. Just support the brand you like the most.

But, yeah. I don't like a super short chainstay either. With responsiveness you lose stability, and short chainstays sacrifice hop height. You can hop quicker, but not as high. So, it really depends what you want to do. Most bsd frames have a slacker seat tube angle too, so bear that in mind if you're comparing geometry. A slacker seat tube angle reduces the effective toptube length, so a 21" toptube will feel shorter.

Almost everything will affect something else. Steeper head tube angle will increase the effective toptube (by angling your bars forward a touch), but decrease the wheel base (by moving your front wheel back a touch). Overall making the frame more responsive (easier to nose manual too). Same goes for just about everything, but how noticeable it is varies between riders. Some people notice little changes in one thing, but not in another.

Bar height also matters with regards to ease of lifting the front. Taller bars act similarly to short chainstays. Easy to lift the front, less balance, lower hops.
I'd say anything over 9" is excessive unless you're over 6' and like tall bars. I'm 6' and use 8.85 bars and a front load, works perfect for me, but it's personal preference.

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6/29/2018 4:09 AM

Oh my gosh You were awesome!
I mean.. now I have found out a thing!
All my friends that tried my bike said that was too small for them and I have said but toptube it’s 20.9.. and they are riding 21. So we weren’t able to explain that. Now I understand why..
Which frames are you riding? Like as you said, Maybe having a shorter chainstay it’s not probably the best. I can bunnyhop like usual.. so it Didn’t affect me too much but, main problem, it feels small. When I am doing bar I need to lay back a lot, otherwise I will hit my knee with the bar.
Is there any frame you’d suddgest? If I go for a wtp or cult are more standard frame?

Many thanks!

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6/29/2018 5:00 AM

Sounds like you need a longer frame, long top tubes and short chainstays makes wonders, roomy and stable but still quick to spin and stuff, also keep a high BB (11.7" and up) to get a poppy bike because ~ 13" cs and low BB makes the bike feel sticked to the ground and makes it really hard to go high on hops.
Maybe go for 0.25" (one halflink) cs more, on your current frame which starts at 12.8" you should have your wheel about 13", maybe get a frame who starts a 13" to get your wheel at ~13.25 (from 13.1" to about 13.5").

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6/29/2018 5:26 AM

Thank you so much for your reply.
Do you know which frame could fit on theese specs?

Thank you!!

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6/29/2018 5:47 AM
Edited Date/Time: 6/29/2018 5:47 AM

Quick question
What specific discipline of bmx are you using the frame for (e.g. flatland, vert, etc)?
Edit: street, my bad, I read that earlier and then came back and forgot

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6/29/2018 6:03 AM

mattiabmx wrote:

Thank you so much for your reply.
Do you know which frame could fit on theese specs?

Thank you!!

There are plenty, first figure out the specs you are looking for, it should narrow it down to a few frames then pick the one you like the most depending on the color, the frame finishes, the price...

So i don't know what tt size you ride but look for 0.25" to 0.5" bigger than what you usually ride.
Of course with a 71° seat tube angle to get the real size
21" +. 71° = 21"
21" + 69° = ~ 20.75"
71° being the classic, good to catch the seat on barspins, 69° means more room for your legs if you are a turndown addict.

Then 13" slammed chainstays
11.7" or 11.8" BB
Here are the most important measurements, now

75° or 75.5° head tube angle, yours is 75.2° so you have a rare inbetween, but globaly coming from a 75° to a 75.5° angle is just like taking off 2mm of fork offset, so a bit quicker handling and shorter total wheelbase which is good for tech stuffs and pop into noses

And finally any standover you like, most of frames these days are around 9" and it's great unless you like low slung scooter like frames.

I don't have time right now but I can make you a small list later,I just need to know what size of the soulja frame you ride right now.

Waiting for it you now have everything you need to search for your dream frame.

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6/29/2018 6:08 AM

Personally, I ride a custom fbm with pretty relaxed geometry (considering it's for street). It's hard to say what will suit you really. Some street frames still have 13.75 chainstays, which is pretty long. 13.5 chainstays, 11.75 high bb, 21" toptube (with a 71 seat tube angle) would probably suit you? But personal preference is a big part of it. Strangely, some street frames have a low bb.
If you like cult and want to support them, get a cult, if you like federal, get a federal etc. There's really not much difference these days

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6/29/2018 8:09 AM

mattiabmx wrote:

Thank you so much for your reply.
Do you know which frame could fit on theese specs?

Thank you!!

Francky wrote:

There are plenty, first figure out the specs you are looking for, it should narrow it down to a few frames then pick the one ...more

Thank you so much for all your details. I wrote them down and Now I'll start looking for a frame.
I mainly ride in street, sometimes on park..but I can only do few things on ramp/quarter.
I like doing barspins and hang5s..that's it.
My soulja is 20.9

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6/29/2018 8:12 AM

grumpySteve wrote:

Personally, I ride a custom fbm with pretty relaxed geometry (considering it's for street). It's hard to say what will suit ...more

I ride mainly street..like ledge, some stairs and bank. And sometimes I like ride on quarters aswell..but I am not good with it smile
what's the difference between high and low bb?
Also, I can't say which toptube fit for me..with my frame now I would say that 20.9 it's a lil bit short for me and I would like to get something longer..but since you told me that seat tube angle affect the lenght on the tt, I can't say which one could be right now.

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6/29/2018 9:14 AM

High bb is better for spins and hops, low bb is better for stability. Your best bet is going fairly middle of the road like we suggested really. And a 21" with a 71° seat tube angle will feel longer. What rise bars/stem have you got? That's another thing you can play with to make your bike feel more stable, or more responsive. Some people like their bike to be easy to throw around, but I like it to feel more stable. I have to put more effort in, but it feels more dialled. But, I don't have particularly great balance myself. I had a responsive frame and tall bars, and found it harder to land stuff cleanly, even though it was easier to do the trick, it felt sketchy. But everyone is different really

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6/29/2018 9:41 AM

grumpySteve wrote:

High bb is better for spins and hops, low bb is better for stability. Your best bet is going fairly middle of the road like we ...more

but wait..my bsd it's already 71 seat tube.

Check the specs here:

– Short rear end slammable to 12.8”
– 7mm thick invest cast dropouts optimised for plastic pegs
– Extra wide rear end for up to 2.4” tires
– External gussets
– Engraved headtube
– Removable brake mounts

– Toptube sizes : 20.6″, 20.9″ and 21.2″
– Headtube angle : 75.2°
– Seattube angle : 71°
– BB height : 11.7″
– Chain stay length : 12.8 to 13.2″
– Weight : 5 lbs
– Colours : Surplus green, matt grey and matt black

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6/29/2018 12:24 PM
Edited Date/Time: 6/29/2018 12:27 PM

Go for a 21.25"
Why not your current frame but bigger ? if you feel right on it, that 21.2" soulja could be a great option.

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6/29/2018 1:10 PM

Hmmmm with the steeper head tube angle, it should feel more like a 21" too. Maybe it's the short rear end? Or bar height/position?

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