phobus

I have a bike with a little less tire clearance at the chainstays than I'd like. As far as I know, it's made of True Temper OX Platinum - the frame is a 2009 Gary Fisher Presidio. It's identical to the Lemond Poprad when they were built with TT.

Now, I don't actually know for sure if the stays are OX Platinum, or only the main triangle. But if they are, is it a bad idea to attempt to dimple them? Is there a higher chance of causing damage compared to a non-hardened steel, or is it just more difficult?

Any advice is welcomed. I've researched dimpling stays on this forum and elsewhere, but the materials question has me wondering if it's even feasible.

Andrew R Stewart 

The wonderment as to whether the stays are OX Plat is a valid one. Many frames likely only have two tubes of it, the top and down tubes. All the others often need some forming or machining during the build and that goes easier with more common 4130.

Have you dimpled any stays yet? How many MMs of added clearance, per side, are you seeking? What tool would you use? Andy (who has used a broom handle and a hammer to do this before)

unterhausen

if it is oxplat, dimpling it successfully will be difficult. you will probably dent it

phobus

I haven't. This frame has tons of clearance everywhere else in the rear triangle, but I would be happy with even a modest increase - say, 3mm per side. 5mm would be great. I'd probably use a clamp with wooden forms.

If it helps - the chainstays are approximately 31mm x 18mm oval at the bottom bracket, transitioning to 12mm round at the dropout.

Andrew R Stewart 

Being already fairly ovalized I'd be hesitant to further narrow them down too much. 5mm out of 18mm is a lot even before brazing them up. Even if just 4130. I might consider an inside only indent of about 3mm. I would do this with a localized contact form or rounded blade. Not a wood form. But it's your bike and whatever happens is what happens. Andy

phobus

Thanks for the advice. I fully expected to be told it was a bad idea, I think I'll shelve this for now.

Cynikal 

How much clearance are you trying to get? I have 40 mm Nanos on 23 mm rims on my OX Plat Poprad. They are snug but work really well.

Nessism

According to info on the Henry James website the tall 30mm chain stays are made from Verus heat treated steel. I've worked with this material before and it's nowhere near as hard as the OXPlatinum alloy. I think you could dimple it 3mm but I agree that localized dimpling would be preferable over flattening the stay over a large area.

phobus

How snug is snug? I'm surprised you are able to make that work.

Currently I have 37mm WTB Riddlers mounted on 17mm internal-width rims. They measure 37mm wide at the knobs, and only have around 2mm clearance on either side. Ideally I'd like to be able to fit a 38mm or 40mm tire on a wider rim with a little more clearance than this.

phobus

Thanks, I also saw that chart but wasn't sure if it that could have changed over time.

When you say localized dimpling, can you provide a picture with an example? I interpret that to mean a dimple that doesn't extend very far along the length stay.

Cynikal 

There is probably 2 mm on either side. The tires are mounted on H plus Son Archetypes. I've ran this setup for about 5 years without issue but it definitely doesn't work when mud is involved.

Andrew R Stewart 

Here you go with a few photos.




These two shots show a couple of different tools I've made for crimping. The thick block tool was #1 and for pre brazed stays works really well. The erector set tool fits an already made frame and also works well but with more bits going on takes longer to set up. Note the indenting forms, they are hand cut and filed. I decided that the crimps I will do will tend to be rather localized to clear at a specific point for a specific tire or ring need.



Here's a shot showing both tire and ring crimps as I am setting up a chainstay fit/brazing. This frame is a fixed gear rollers bike and has rather tight clearances overall, note that the stays are not ovalized much to begin with.

I did try to make a crimper out of a large channel lock pliers. I brazed a cupping piece of tubing on one jaw and the form on the other jaw. But for the stay wall thicknesses I played with found that I didn't have enough strength to indent much at all. So onto screw pressured tooling I went. If you were local to me I'd offer to help you out. Andy

TiHabanero

I just made a crimping tool from an old Vise-Grip. Had to crimp in steps so that the tool could be closed, but it did work. The form was the wrong shape so I have to redo it and make it more like the form in the picture above.