Duplicating an existing frame

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sussex cyclist
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Re: Duplicating an existing frame

Post by sussex cyclist »

@Jamesh That's good to know if it comes up, thanks. I just never gave it any thought before because I had no need to change.
slowster wrote: 3 Jul 2022, 8:26pm 1. What tyre width do you want to use, and is that with full mudguards?

2. What size and year model of Langster do you have?

3. Were the Langster and your other bike(s) set up with the same position, i.e. saddle height, saddle distance behind the bottom bracket, relative height of saddle and bars, and distance from saddle to bars?

If available, a side on photograph of the Langster would be informative.
1. 23mm, on all my road bikes. I'm not exactly sure what you're asking, but I have used mudguards with all of them at one time or another (rather bodged with the Langster).

2. 56cm effective TT; slightly too big as it turned out, but I adapted.
I'm not positive about the year, but believe it's a 2007.

3. I don't immediately know the answer to those, except to say that my three road bikes all had different geometry. This would suggest that I am perhaps being persnickety about getting the measurements on a new bike exactly correct. On the other hand, the Enigma definitely felt the best, and as I'll be spending a lot of money (for me) on a new bike, it only makes sense to pattern it on that. I know there are a number of factors which contribute to how a bike feels.
Racingt
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Re: Duplicating an existing frame

Post by Racingt »

I've considered having a new frame as a copy of an old frame - and when I investigated, Brian Rourke cycles offera that very service.
I have no experience of dealing with them, but i believe their reputation is very good.
Jamesh
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Re: Duplicating an existing frame

Post by Jamesh »

I thought all frames should be 73x73° 22" !!!
slowster
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Re: Duplicating an existing frame

Post by slowster »

I think that knowing the geometry alone of the Enigma would not be anywhere near sufficient to build a frame that gave a similar feel. I imagine that being a relatively expensive custom titanium frame, it may have used butted rather than plain gauge tubing. So you would need to know the tube butting profile as well as the diameters, and those would only be valid for titanium, because the stiffness of steel is different. Bikes built with the same geometry but different tube profiles/thickness will potentially feel very different, e.g. see this anecdote of 531colin's who designs many of Spa's frames - viewtopic.php?p=1504658#p1504658.

For the record, be aware that seat tube length and angle probably won't have much impact: the saddle is a point in space linked by the seat post and seat tube to the bottom bracket shell. The saddle can usually be correctly positioned regardless of a degree or two's difference in seat tube angle by choosing a seat post with more or less set back.

I think that the numbers which determine the steering/handling (as opposed to the feel of the frame stemming from the combined effect of the stiffness of the various tubes) are:
- chainstay length (bottom bracket axle to wheel axle)
- front centre (bottom bracket axle to front axle)
- bottom bracket drop (below an imaginary horizontal line joining the axles)
- head tube angle
- fork offset

You might be able to measure all these yourself. I think some smartphones can measure angles (but take two measurements - the second one with the bike rotated 180 degrees on the same piece of floor, taking the average of the two measurements to eliminate any error from a floor which is not completely horizontal).

Small differences in these numbers are unlikely to make a significant/especially noticeable difference, and moreover I doubt that the numbers for your frame are unusual (unless you have particularly unusual body dimensions).

It looks to me as though your Enigma took a fork with a 1 1/8" steerer. The market has changed a lot in recent years, and there is much less choice of such forks for rim brakes, and probably fewer still (if any) with mudguard eyelets. It is now fairly common for carbon forks to have tapered steerers, necessitating a larger diameter head tube. The vast majority of carbon forks are made for disc brakes, and you may be much more likely to be able to find a suitable fork with mudguard mounts if you have a front disc bake as well.

Assuming a carbon fork, head tube length is arguably a matter of the length being sufficient to get the bars/stem high enough without an excessive number of spacers under the stem (most carbon fork manufacturers stipulate a maximum of 30mm of spacers, and some manufacturers also stipulate a minimum of 10mm - making the tolerance somewhat tight and making it necessary to choose a stem with suitable rise to provide any more adjustment. Note however that two forks with the same offset might have quite different A-C measurements (axle to crown), i.e. a 10mm shorter A-C measurement will slightly steepen the head angle and might warrant a 10mm longer head tube.

I can't help thinking that you are setting yourself up for a lot of headaches, and potentially disappointment as well, in trying to 'reverse engineer' your Enigma.
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sussex cyclist
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Re: Duplicating an existing frame

Post by sussex cyclist »

Thanks very much for your detailed post.
boblo
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Re: Duplicating an existing frame

Post by boblo »

Stanforth are near you in Brighton. I had a fully custom 853 frame from them starting with my old (bent) frame as a reference. I wanted a modern take on my classic 1980's 531c steel tourer (discs, thru axles, sloping top tube, filet brazed etc) and got exactly what I asked for and it's 100% custom/my choices. Here: https://www.stanforthbikes.co.uk/

The bike: Image
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sussex cyclist
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Re: Duplicating an existing frame

Post by sussex cyclist »

boblo wrote: 4 Jul 2022, 6:45am Stanforth are near you in Brighton.
They certainly do a good job triggering wanderlust.
rareposter
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Re: Duplicating an existing frame

Post by rareposter »

As mentioned above, a lot of builders are not keen to simply duplicate a design - it's a bit like asking a renowned artist to just paint you an exact copy of the Mona Lisa without giving them the opportunity to express their artistic flair in an original creation.

Also depends a lot on the components you'll be putting on it - discs vs rim brakes being the obvious one that requires a different frame design.

Best bet is to say: here's what I had before, make me something that rides in [style], looks like [design] and costs [price].

You can argue it either way that giving that brief to 5 different frame builders will result in 5 different builds so either they're all wrong or they all think they're right, or they're all building their take on your brief. 🤷🏻‍♂️
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531colin
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Re: Duplicating an existing frame

Post by 531colin »

A couple of comments on "slowster's" post......(sorry)
Seat tube angle isn't terribly important unless you are somebody who regularly finds yourself struggling to get your saddle far enough back, in which case it is pivotal.
The major determinant of steering "feel" is trail, which is governed by head tube angle and fork offset (and wheel size, but thats probably 700c). All the other things people fret about (stem length, front centre, chainstay length, wheelbase, ...) have relatively little effect.
When designing a frame for a carbon fork, I'm likely to say "show me the fork".
Once you have decided on your fork you will know what headset size you need, and therefore what head tube. You will know axle to crown height so you can design your frame to give you the right head angle with that axle/crown dimension. You will be able to match up tyre/mudguard clearance front and rear.
Carbon steerers only permit a small stack of spacers between headset and stem. Extending the head tube above the top tube works, and I don't think it looks bad....

Image_DSC0829 by 531colin, on Flickr
mig
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Re: Duplicating an existing frame

Post by mig »

do the builders give specific reasons when given this request?

i sometimes wonder if they err on the side of caution if they are subsequently then presented with a terrible frame to copy and think that they don't want their name associated with a monstrosity!
Jamesh
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Re: Duplicating an existing frame

Post by Jamesh »

Nothing off the shelf from spa, enigma, Genesis, surly, etc etc??
mig
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Re: Duplicating an existing frame

Post by mig »

most likely not but the OP doesn't specify this specifically. it could be any frame being referred to.

"can you copy my frame? it's great...fits me perfectly...etc etc" i'd think isn't the best starting point for a framebuilder. if they merely say "yes" it could be the start of a world of hurt for them.
rogerzilla
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Re: Duplicating an existing frame

Post by rogerzilla »

It will feel different if it's steel rather than titanium, but you'd have to be pretty sensitive to notice. Titanium metal is only half as stiff as steel but virtually all titanium frames use oversize tubing to counteract this, so the frame will end up about as stiff as a steel one. This means you're into the dubious world of shock absorption and "feel", rather than anything readily measurable.

It will almost certainly be a bit heavier than the titanium frame, but not by much if it's made from 853.
scottg
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Re: Duplicating an existing frame

Post by scottg »

mig wrote: 4 Jul 2022, 10:37am do the builders give specific reasons when given this request?

i sometimes wonder if they err on the side of caution if they are subsequently then presented with a terrible frame to copy and think that they don't want their name associated with a monstrosity!
One American company put themselves out of business by building shopping trolleys for people.
I rode a couple of them, yes they're were awful. Did their reputation in.
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Deutsche Luftschiffahrts-AG
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mig
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Re: Duplicating an existing frame

Post by mig »

scottg wrote: 4 Jul 2022, 11:23pm
mig wrote: 4 Jul 2022, 10:37am do the builders give specific reasons when given this request?

i sometimes wonder if they err on the side of caution if they are subsequently then presented with a terrible frame to copy and think that they don't want their name associated with a monstrosity!
One American company put themselves out of business by building shopping trolleys for people.
I rode a couple of them, yes they're were awful. Did their reputation in.
that could be the wheels, rather than the frame, though.
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