Steel Frame modification – frame builder advice?
As far as I am aware it’s platinum OX tubing throughout. Up until very recently 853 stays were not widely available but true temper have always had them as an option.
I know steel frames are re-weldable and repairable but its a very light frame 4lb frame.
Oh. It’s a hand made Chromag frame for reference.Posted 4 years ago
I know there are a few frame builders on here.
I have a steel mtb frame which is made of high end true temper platinum ox tubing (like 853). I would to have the chain and seat stay bridges removed and either :
– new ones installed closer to bb shell/further up the seat stays
– or replaced with a nice flat plate on both chain and seat stays, shaped to bb chain stay junction.
Either way it will enable more tyre clearance on the frame.
Spoken to a few roadie frame builders and they don’t seem to know much about the true temper tubing and only give me patchy info.
Is it possible and how much would this type of minor work cost?
Can anybody help?Posted 4 years ago
How are the bridges attached? If they’re TIGed, then they have to be carefully cut off and the welds filed back, which is always a pain on thin tubing. If they’re brazed it’s generally easier.
Is the bridge clearance the only problem? the spacing between the stays is okay?Posted 4 years ago
If its got discs all these bridges do is hold mudguards. If you dont need them to hold mudguards then cut, file and be happy.
you could get away without a chainstay bridge but you’ll need a seatstay bridge.
If it’s a decent frame it’ll probably be fine but there’s a chance that the welds could be undercut in which case cutting out the old bridges isn’t going to be a great plan.
When I used to do this sort of stuff I’d charge a minimum of £50. Not including paint obviously.Posted 4 years ago
I’m not a human finite element machine but just trying to visualise the forces I can’t see what usefull function these bridges serve short of another stress raiser
Stiffens the rear triangle. Without a seatstay bridge, the rear end will flex more than will be good. It’s arguable whether a chainstay bridge is needed since the bridge is so close to the BB it’s not really shortening the effective stay by much. Seatstays are generally smaller diameter than chainstays too. For what it’s worth I always fit seatstay bridges and I’ll leave out the chainstay bridge unless there’s going to be mudguards.Posted 4 years agochiefgrooveguruMember
Interesting info from Cotic re. chainstay bridges:
“…discussions with another frame designer and further research on frame design using the FEA models shows that the worst fatigue feature on the frame is the chainstay bridge. Deleting the bridge removes this problem and massively improves mud clearance, but it it also moves the stress ‘hot spot’ to the outer edge of the chainstay/BB welds. Addition of gussets at these locations solves this, and another now classic Cotic feature is born with the bridgeless chainstay design. Enormously proud of myself for this sweet little solution, it’s only several months later that I discover Keith Bontrager had been doing the same thing on his steel frames since about 1990. A doffed hat to Mr B!”Posted 4 years ago
Shand – can I drop you a line about my frame? Or are you too busy with full builds?
Hi Rik, I’m afraid we’re running behind on our own bikes at the moment and have had to take the decision to stop all other repair/renovation/repaint work for the moment in an attempt to catch up.
Ben Cooper at Kinetics would be the guy to contact.Posted 4 years ago
I’d say in general seatstay bridges are more important than chainstay ones – the SS bridge prevents the relatively slender stays from bowing outwards. CS bridges are less about triangulation – the stays are quite beefy anyway – they’re about making the whole area more rigid. As Cy says, you can do without the bridge completely, but you need to stiffen it elsewhere, either with gussets or large fillets, or a more traditional lugged frame with a web between the stays.
I don’t think I’ve ever seen a frame fatigue at the bridge, but badly-designed bridges can collect water and rust through that way – older Bromptons were notorious for that, for instance, because the bridge had a vent hole facing the tyre.Posted 4 years ago
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