Is it possible to shorten a bicycle frame?

[horizon]

The recent thread on SandS couplers got me thinking.

Although I have now pretty much nailed the make and type of bike that works best for me (Took you long enough horizon! Ed.) it leaves me with some bikes which I would love to cut in half, take out a cm or two, stick them together again (no need for couplers) and make them shorter.

AFAICS I am talking about the top tube and down tube.

Purely as a matter of interest what stands in the way of doing this, even with replacement forks?

[Cyril Haearn]

If the top tube is shortened the down tube will have to have a double kink
Maybe the couplers justify the price after all if they can get round that

[drossall]

It's basically a triangle. If you shorten two sides of a triangle, you need to shorten the third as well, or else change its shape significantly. So you'd have to take the whole frame apart at the lugs and start again. Which is generally not worth it!

[Samuel D]

Purely as a matter of interest what stands in the way of doing this, even with replacement forks?

Geometry! If you chop bits out of two non-parallel tubes fixed at their ends, they will no longer line up. They’d need to pivot at the joints.

[AndyA]

You could in theory cut the headtube off, mitre the TT and downtube a few cm shorter, fit new headtube. The headtube would be longer, and hence raised if you reused the original fork. To maintain original geometry you would need a shorter fork.
There are a few pitfalls - if the tubes are butted you might end up with the joint or heat affected zone in the thin section of the butt. You're also putting the tube through another heat cycle.
Definitely cheaper to track down a used frame that fits too!

[horizon]

Thanks all - I hadn't even tried it out with matchsticks!

I was still thinking along the lines of the couplers not apparently affecting frame strength and parting the frame in exactly the right places - this was my overarching image! A quick slice and put it back together ...

[Brucey]

there are substantial practical difficulties. In addition to those already stated, you may find that you get toe overlap with the revised geometry.

Using a stem that is 1-2cm shorter is a lot easier....

cheers

[drossall]

I suppose that, theoretically, you could replace the couplers with telescopic extension fasteners, preferably in all three tubes. This would give an adjustable size frame. To set against that benefit, it would almost certainly be heavier, less rigid, prone to "down-sizing" at unexpected moments and in need of elasticated brake cables - what's not to like?

[Vorpal]

Why not have a frame builder make you one, based on your preferred bike, but with the cm taken out?

[pete75]

Why not have a frame builder make you one, based on your preferred bike, but with the cm taken out?

Exactly. Custom sized frame go to a custom builder.

[reohn2]

Why not have a frame builder make you one, based on your preferred bike, but with the cm taken out?

Exactly. Custom sized frame go to a custom builder.

I agree,if Horizon's requirements are so unique going custom built is the only answer.

Horizon
After the many threads on you're riding position/frame requirements,I'd really like to see either a photo of you on the bike or a list of your ideal/preferred measurements ie; saddle top to BB,nose of saddle behind BB,reach from nose of saddle to handlebar at the stem,height of handlebar in relation to saddle top,all measurements taken with the bike on a level surface.
I think that's the only way a consensus of opinion could determine if the forum can be of any help or give advise on whether you need a custom built frame.

[NATURAL ANKLING]

Hi,
I agree with Brucey & R2.....?
Once you sort the saddle to BB the rest is rather academic, as you can achieve the top half body fit with the components.

That said what type of cycling are you doing..............how long have you been at it and what is your favourite type of event / ride........how long in saddle etc.
Because unless you are stressing yourself a lot on the bike, the top bike position matters less.
Is it that you always cycle in that position and / or have you just got stuck in that position.

I am rather laid out on my bikes that is that my top half of body is long compared with my height, my old cycling mate was same height but legs were two inches longer, we probably couldn't swap bikes comfortably for reach, but reach can be adjusted in the stem bar area, if not then you bend your elbows or keep hands on the top of bars if you were pushed.

Now tell me that you have flat bars.

Some camps say that you move the saddle back to get more comfort, in extreme it will make you look like a granddad with disabilities' , go the other way and equally silly like you stolen a childs bike, all this affects ergonomics of your bottom half and constant dislike if not pain for your favourite bike.

If you really have given up adjusting the components then buy a cheap frame the right size for your likes and then duplicate.
I don't really believe that a standard frame the right size will not suit you, unless you are not telling us something....

A picture as said will get some constructive comments for sure.
Good luck.
P.S.
Getting a comfortable position or the lack of may simply be a stiffness lack of flexibility, I put a lot of weight also on how hard you ride too, if you don't press hard on the pedals or cant because of extreme road conditions (off road) then the contact points become sore after just an hour.

[horizon]

I agree,if Horizon's requirements are so unique going custom built is the only answer.

I'm certainly not unique but I am off normal. I have a 34" inside leg on a 5'10" height. That means I have long legs. To accommodate my legs I shift the saddle back - you have to do this or you just sit off the back of the saddle. I'm not the only person who moans about a 73 deg seatpost angle (see 531colin's posts!). I deal with it by using a VK adaptor. Sorted.

But having moved back, it means I can no longer comfortably reach the bars (especially drops). So I use a very short stem. Almost sorted - I just need another cm or two adjustment on a regular touring frame. A smaller frame doesn't quite work as the reach doesn't diminish in proportion to height.

It took me ages to sort that out - mainly with thanks to 531colin and this forum. And it took me a long time to understand frame dimensions and how I sat on a bike. There are so many variables - even during the course of a day's cycling.

Custom build? There are two bike builders who understand the problem and pretty much sort it for me with off-the-peg frames: Spa (thanks to 531colin) and Thorn. But I do want to be sure before splashing out. And don't worrry, I'm still cycling and I'm OK on my bikes - just not quite as 100% as I would like to be. I've also stuck with drops and that's a bit of an indulgence as converting to straight bars on a drop-barred bike actually pretty much solves the problem.

Without the forum I don't think I could have got my head round it but it has still been a steep learning curve for a non-technical person.


Note: I've just read NA's post (thanks, NA) and you can see how many variables could be considered.

[reohn2]

You didn't give us any (optimum) measurements,sorry to push but without them we have no idea of your ideal.

[pwa]

I know it can cause some people problems if they muck about with their cleats / foot position on the pedals, but if you nudge your cleats back on the shoes by 15mm that has the same effect as reducing the top tube by 15mm in that it brings your upper body 15mm closer to the bars. I tried it some time ago and to my surprise the feeling on the pedals was okay and I got no adverse reaction in my knees or elsewhere. It reduced reach to the bars and luckily I had enough room not to encounter toe/wheel overlap.