First post and I’m hoping to tap into the collective wisdom here!
My wife and I have an old Santana road tandem that fits both of us great but has really poor rear tire clearance. Also a previous owner did a pretty hamfisted job of dimpling the seatstays so I’m thinking of replacing them.
The frame currently fits a 30mm tire with about 3-4mm of clearance. 38-40mm tire clearance would be ideal but we could live with 35mm if we had to.
My current plan is to remove the fastback SS’s and do a traditional semi-wrap around at the seattube cluster. This would give the SS’s enough clearance to run 38’s at least.
The main question I have is if I can safely dimple the chainstays and if so what extent is safe on a tandem? I’m apprehensive to try on a tandem due to stiffness and the forces involved, but perhaps I’m too worried given how beefy the CS’s seem. The chainstays currently limit the frame clearance to 30mm so to hit my target I would have to dimple 4-5mm. The CS dimensions where the center of the dimple would be is 35mm x 22mm. As a team we weigh around 325lbs. I already have a dimpling tool that I’ve used successfully a few times, albeit on much lighter tubing.
If dimpling is inadvisable, then I suppose I could replace the vertical dropouts with a set of horizontals. By rough measurements I could gain about 5mm clearance by replacing the dropouts (the CS length would grow about 12mm).
A main concern I have with dropout replacement is I don’t want to introduce too many variables into the mix as I have limited fixturing right now. I’ve taken a framebuilding course and built two frames but have mainly stuck with modifications, so I don’t have access to a jig right now. I do have some lengths of 80/20 and could probably make an ad hoc jig for the rear dropouts but I’d rather not.
Why not using a hole saw to cut a notch on the chainstays and seatstays and then close it up with a plate? That would avoid a lot of work and most likely give you the clearance you want.
I would definitely test the lateral stiffness of this solution, you may need to reinforce it somehow but I would still try this before removing the whole rear stays
I don’t think 5mm of dimple is very much so would be surprised if that was a problem. But this is not based on any real science or anything
As for the seat-stays, make sure you keep the V-brake bosses about the right distance apart (it’s supposed to be 80mm, although there is some latitude). Unless you’re running disks anyway in which case you might as well get rid of them.
Thanks Matt, That’s an interesting solution! Unfortunately there wouldn’t be much seatstay left after cutting out a chunk for clearance - the stays are maddeningly close together.
Guy, I agree 5mm isn’t much, I’ve definitely done that much before on single bikes but for some reason I’m apprehensive to do it on a tandem. I’ll probably just go ahead and do it but just wanted to see if it’s a terrible idea. As for the canti posts, that would be a secondary benefit of new SS’s!
Santana chainstays are ridiculously large and heavy. It is absolutely “safe” to indent them for clearance, but it will be difficult. Your indenter will need to be stout.
@Matt‘s solution is a good one. It’s similar to what Dave Levy has done a number of times, he calls it the potato chip, with two separate pieces welded to the stays, not joined in the middle like on Matt’s example. Dave uses thick pieces as the potato chips, so the final strength/stiffness is similar to what you had before the repair. The final shape is not as efficient at transferring loads, so he basically throws more metal at it to make up for the deficiency of the shape. Probably not how Dave would describe it, that’s my analysis. I think it’s a good way.
But again those Santana stays have a lot of strength and stiffness in reserve, so you can stand to lose some.
Thanks all! I’m thinking the plan is to try out dimpling the stays and see how it goes. If it proves too difficult, I’ll try the potato chip method. I don’t have access to a mill right now and my drill press isn’t up to such a job, so it’ll have to be freehand with a file if it comes to that.
On to trying to source some seatstays! The current ones are surprisingly spindly, so I’m curious what the wall thickness is.
I’ll try and circle back with an update when I’ve made some progress.
