Rudge 'Bi-Frame' -a 'Proper' Folding Bike....?

For discussions about bikes and equipment.
Brucey
Posts: 41500
Joined: 4 Jan 2012, 6:25pm

Re: Rudge 'Bi-Frame' -a 'Proper' Folding Bike....?

Postby Brucey » 1 Oct 2020, 6:53pm

those shifters look pretty nasty but they may serve a purpose. The FSA FD looks like a 'road' FD so it may not reach out over a triple chainset. Still it isn't going to be a very expensive experiment.

FWIW I bought one of these

Image
I think this is a Sachs 'Centera' model

a while back when CRC were selling off old stock; it is an 'old' (6/7/8s) style MTB/touring mech, so is designed for a triple with a MTB chainline and a big ring size in the 46-48T range, and uses bottom pull; such mechs are comparatively rare in braze-on format, despite being listed by most manufacturers. This one will (if necessary, with a small tweak) manage something close to a 'road' chainline too. I have no idea if it is compatible with any indexed shifters or not (and I'd expect that to vary with chainline anyway). It does however fit on my BiFrame and work very well. Needless to say CRC have no stock left now, but it is an example of what fits and works OK.

edit; I think this is the Sachs Centera groupset from which the FD comes, circa 1995-1997 (although the FD shown is top pull format)

Image

The RD is rather odd; it looks like it has a bit missing! And the chainring teeth look worn out before you start.... :shock:

cheers
-------------------------------------------------------------------------------
~~~~~~~~~~~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~

DevonDamo
Posts: 443
Joined: 24 May 2011, 1:42am

Re: Rudge 'Bi-Frame' -a 'Proper' Folding Bike....?

Postby DevonDamo » 1 Oct 2020, 11:36pm

Brucey wrote:The FSA FD looks like a 'road' FD so it may not reach out over a triple chainset.


Thanks Brucey - the Sachs groupset does look a lot like the Suntour kit on the Bi-Frame, in terms of weird 80s styling. I had a look for one of their front derailleurs on eBay but couldn't find that exact model. The cheapest FD I could find that looked like it had a fighting chance of coping with a triple chainset was a Shimano 2300:

https://www.ebay.co.uk/itm/Shimano-2300-Front-Derailleur-Braze-on-mech-Triple-chainset-Road-Bike/133525831096?hash=item1f16c27db8:g:XkEAAOSwaEhfaPq6

It's supposed to cope with up to a 52 chainring. As far as the clamping angle is concerned, I'm not sure how Shimano measure this, but their specification sheet says something about a chainstay angle of 61 to 66 degrees. I might just buy that one and take a chance.

Brucey
Posts: 41500
Joined: 4 Jan 2012, 6:25pm

Re: Rudge 'Bi-Frame' -a 'Proper' Folding Bike....?

Postby Brucey » 2 Oct 2020, 12:04am

the 61-66 degree angle is the chainstay angle, i.e. the angle between the seat tube (in a normal frame) and the chainstay. This is not easy to compare with a BiFrame because of the way the seat tube is done, but since the chainstays are near-horizontal on 26" wheeled MTB-esque things the chaisntay angle usually comes out close to the seat tube angle. 61-66 degrees is a typical angle for a 700C wheeled road bike with a lowish BB. 65-70 degrees is the usual range for a 26" wheeled MTB-like thing. In practice it doesn't really matter what this angle is, except for two things;

1) if affects the capacity of the FD and
2) it affects the chances of the FD hitting the chainstay.

So FD-2300 might work for you but the capacities won't be quite right and it also may not reach out far enough to manage a MTB chainline triple (which is usually about 3mm wider than a road triple).

cheers
-------------------------------------------------------------------------------
~~~~~~~~~~~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~

DevonDamo
Posts: 443
Joined: 24 May 2011, 1:42am

Re: Rudge 'Bi-Frame' -a 'Proper' Folding Bike....?

Postby DevonDamo » 2 Oct 2020, 10:37am

Brucey wrote:So FD-2300 might work for you but the capacities won't be quite right and it also may not reach out far enough to manage a MTB chainline triple (which is usually about 3mm wider than a road triple).


Okay - thanks: it was worth checking-in here before rushing out and buying anything. My tacky Chinese thumb shifters aren't due to arrive for at least another month, so I'll keep an eye on ebay for a braze-on front mech designed for an MTB triple.

DevonDamo
Posts: 443
Joined: 24 May 2011, 1:42am

Re: Rudge 'Bi-Frame' -a 'Proper' Folding Bike....?

Postby DevonDamo » 10 Oct 2020, 2:41pm

I read through this entire thread, and no-one has actually mentioned using these things off-road... Having restored my new large-framed model, I've ended up with two sets of wheels so now I can quickly swap between off-road and on-road configuration. I just got back from a test ride on one of my local mountain bike trails, which is reasonably steep and technical in places. Obviously, an old bike with no suspension and ancient tyres is not going to set any records, but it was really good fun - very nimble, surprisingly good brakes and it all felt rigid and composed. If you could get dropper posts to fit 26.6 seat tubes, I think I'd actually buy a set of decent tyres and start doing some 1980s-style mountain biking a bit more regularly.

By the way - I'm now left with a spare small frame for one of these - as described and pictured on p7 of this thread. If anyone know any smaller riders who'd be interested in building it up as a project, I'd flog it for £50. It would need wheels, chain-set, bottom bracket, seat, seatpost and front derailleur - i.e. the bits you'd want to replace anyway to make a trick custom version.