tdong

i am still not very happy with the saddle angle on my birdy bike even when I move everything forward and add extra washers at the back suspension. Here is a dump idea please tell me what you think ?

Basically i will cut the tube and drill through for two bolts so that i can move the tube to the front. i can add the metal ring around the two tubes if need to. The M2Racer Power Module would be perfect but i can't find it for sale anywhere as the company closed long time ago

smallwheeler

what about the fit of the bike you trying to correct? if you're trying to shorten the reach, the easiest solution would be to change the stem. you could experiment by rotating the the stem 180º.

probably what you need is a stem insert that has 0 forward stem length.

tdong

no it is not about the reach it is about the seat angle is it way too far back. my handle bar is a butterfly i can move it at any distance i wish

smallwheeler

fietsbob

I dont have that seat post ... plain 7/8 top type offers the option of mounting the saddle clip ahead of the seatpost.. Or to the rear ..

you may seek out someone with aluminum welding experience to modify or fabricate a replacement .

Bike Friday is advantaged by having several frame sizes , most/all others just one .. yours seems that.

yes butterfly bar, horizontal, will be a shorter reach.. as shown vertical just up/down

tdong

here is the image overlay. see what i mean about the seat angle ?. the welder is asking like $100. i think i will go ahead with my mod and will see. since i can buy another birdybike seattube if i mess up

smallwheeler

yes, i understand the issue.

tdong

those are for road bike won't fit the birdy tube

smallwheeler

i'm providing you with images for ideas.

you can visualize cutting the seatpost then bolting it back together but, you cant conceptualize how to modify the 33.9 seatpost to accept a 27.2 seat post?

anyway, maybe this is all you need. you'll have to experiment.

tdong

thanks for your input smallwheeler. I think my question should be with the way i just about to do by cutting the tube and bolt them together would it still be safe and hold the weight ?

BruceMetras

As s/w intimated, it would be much easier/safer to install a negative setback post in the Birdy tube.. As the 35mm Birdy seatpost is open at the top, a simple sleeve and clamp would be all that is needed to modify .. your idea of bolting two round tubes together is not good (IMO) .. normal riding would attempt to shear/twist the bolts.. making the bolts bigger to offset the levering/twisting will weaken the tube more.. the engineer types might comment to say it would work and I'm wrong .. I'd go the easy, safe route that could be undone easily..

smallwheeler

i think it's not a good idea. it will never be stable and you will have destroyed the seatpost.


i could be wrong, but to be clear, i think what you need is a seatpost with setback that has a pivoting clamp. you can rotate the seatpost 180º. that will give you 3-4cm of forward reach.

birdy seatpost with setback:

fietsbob

NB Problem Solvers

you can take apart that saddle clamping hardware and / or saw off the end of the tubing square
or maybe even just turn it over the other end is probably cut off square

shim the ID of your seat post tube to take a common sized seat post as there is being shown .. ^^above^^

Or have a tube, the same size, made and welded up to get the pushed ahead saddle mount you desire ..




Father was a machinist .. so making rather than internet shopping seems better..

welding on a 7/8" diameter tube Horizontal on top and buying one of Brompton's excellent Penta clip saddle clips
which is stepless, secure and works in 360 degrees will have your saddle positioned above the horizontal tube.

Then the saddle set back adjustment range can be user chosen..
Idea, modeled after Brompton's own Saddle adapter pin..

Which offers the horizontal tube when fitted to a post, which also has a 7/8" top diameter

As most tube seat posts do.

tdong

thanks for all the input. i won't cut the tube as it seems like a dumb idea. I would either go with the Rspeed which sell on ebay or will talk to my brother in law about bending the tube a bit since he is working for a steel tube company

1nterceptor

If you mod the seat post in any way; you may not be able to push it all the way
down. Negating one of the attributes of a folder, compact size for storage/parking.
From your pic; looks like you can still move the saddle forward. You can also try
another seat that has longer rails; Selle SMP is one.

tds101 

I was just about to create a thread asking about a more forward riding position on one of my bikes (Puma Nevis, it's a pedal forward bike, but it's too far back and causes me knee pain). Now I'll just start Google'ing and find a more forward position seat post. The bike is well worth it - it's built like a tank!

Dynocoaster 

Dahon had a 2 piece seatpost that had an internal diameter of 27.7.

jur

I see the seatpost is not actually a Birdy original. The original has a setback-setforward possible mounting, making a huge difference. Check out SW's pic of a more modern birdy's seatpost.

tdong

It is the original post of birdy green classic.


i am going to leave it as is. . Looks like too much work for a few cm

energyandair

If its an old style Birdy the seatpost slopes back further than in the Monocoque and the seatpost clamp sits on open top of the seatpost. The nature of the clamp is such that there is a limit to how far forward you can tip the seat

When they changed to the monocoque, they made the seatpost more upright and introduced a seatpost that is a bit longer and is closed on top by an offset clamp. With the offset set back, you can achieve a similar position to the original Birdy at maximum height. If you want the seat further forward, you can turn the seatpost so that the offset is forward. In both positions, you have a better range of seat tilt angle.

The seatposts are interchangeable in fact the offset post that came with my monocoque is a better fit in my older Birdies than the original posts are. It also has height markings which is very handy.

I think that if you buy one of the new posts, it may solve all of your problems.

If you look here "Models", they show the new style post facing forwards and back. They also show an old style seatpost on the folded grey monocoque beside the Birdy Orange 9 speed.

tdong

thanks energyandair

bhkyte

I found a good selection of telescopic seatposts for a konga on ebay. I managed to get a suspension seat post fitted to my mezzo cheaply by simply using a 25.4 inner diameter standard length seatpost insert.
Presumably something could be achieved in the same manner to achive layback.