I was interested in getting some fatter tires on my 2008 Lemond Poprad. The Poprad is designed for 34c tires with True Temper OX Platinum tubing. The fork is carbon with the canti-posts about 78mm apart, and the rear seat stays have the canti posts about 74mm apart. Relative to vintage touring bikes, this is huge.

I wedged a 38mm tire in there with a couple of mm on either sided, but eventually these stretched, and I rubbed the paint off the inside of the stays --- mainly from those little nubs that come on new tires.

The problem is that the chain stays are too narrow near the bottom bracket. There is a subtle bend in them near the bottom bracket, but they are not indented for extra clearance. The obvious thing to do is to make the indentations.

The little motobecane I had for sale had excellent indentations for clearance, and these were common on 1970s stee bikes. With some advice from [MENTION=73614]rhm[/MENTION] [MENTION=45088]nlerner[/MENTION] and [MENTION=30734]zaphodbeeblebro[/MENTION]x, I decided to do it.

Plenty of bikes have straight stays, and with all the fattish tire kool-aid flooding the taps, this is my solution to getting extra clearance. It’s meant as a tutorial and denting the stays is not difficult.

The first thing is to make a tool for indenting.

A 3" piece of steel is what I used. I ground it down to a tapered wedge.


Then I finished it by hand with a set of files. The result was intentionally asymmetric lengthwise, but nearly symmetric in cross section. I wasn’t sure which end would be more valuable in dealing with the angled stays. I also made a wooden cradle for the outside of the stay out of a piece of leftover red oak flooring.





I marked the stays for the rim and tire. The rubbing from the fatter tires had created a “center,” so I lined up the wedge with that. I was going to use a bench vise, but there is not enough of a gap at the bottom bracket for my vise to fit. I also put a hub in the rear dropouts to prevent any weird bending of the triangle. I took the rings off the crankset because I figured I had enough clearance that way. I was going to use a wood clamp to hold the stays close to the bottom bracket, but there was not enough room.



I wound up using two clamps, and my thinking on this evolved while I was working. I started out holding the red oak, foam, and steel wedge with both clamps. This didn’t work so well. Instead, I used the quick grip spring clamp to hold the red oak cradle with a little bit of closed cell to the stay. Then I lined up the wedge and used a C-clamp to make the indentation. The C-clamp went from the outside of the stay across the oak to the steel wedge.

The steel wedge, C-clamp, and stay are a slippery combination, so that the angles need a lot of adjustment before clamping. Once they are lined up, making the indentation is not hard.





View from the bottom (potato quality)


On the second side, lining up is done the same way, but to make the stays symmetric takes some practice. From the photos, I got close on the first time I did this, but it isn't something that I would notice.

In the future, I would take off the crankarms. I needed all the space I had, and those extra inches would have been useful. The wedge I made is sufficient. I’m not exactly sure how to improve it, perhaps by having more of a “flat spot” at the first contact point to prevent slipping.

The final indentations:


The final fit:
Non drive side,


Drive side,


The change in the width at the tire went from about 40mm to about 50mm. I could have made larger indentations ... but maybe next time.

Sweet! I have a Trek 460 that I've considered converting to 650b and I think I need a bit more denting to fit 38c's.

I say, "Do it!" There are a lot of old frames that aren't particularly valuable that could ride a lot better with plump tires. The hard part is the symmetry, but it's easily covered by a fat tire

You could just buy a beach cruiser.

Great motivation to try this some day! I have a few bikes with chain stays that are too short for fatter tires without denting, I'll pick a tester some day and try it.

Someone on the CR list did something similar. But he welded the wedge to a clamp which eliminated a lot of hassle.

Thanks, but I'll stick to my 23mm tires at 140 psi.

Touche!

Nice effort and result!

I'm surprised that you could only get a 38 in there. My 05 Poprad fits a 40mm Nano on 23mm rims. Nice job on the crimping though.

Great tool development and workmanship. It's not any easy operation. A "don't try this at home" warning applies, IMO.

Did this recently on a Bianchi Eros frame I am converting to 650B. I shaped a piece of dogwood instead of steel. Worked like a charm. Space is certainly tight.

I did pretty much the same thing except I welded the wedge to the clamp, worked great! I too put a hub in the Dropout's, but did notice that the rear end was tighter after crimping the chainstays (130 to 127).
Cheers,
Chris

Nicely done!

A framebuilder I know uses a similar technique. He uses the cut off head from an old golf putter to form the dent.
Brent

Great result!

Thanks, guys, for the support and kind words. The old putter sounds like the easy thing to do. What I made is very much like one of those mini golf putters.

In my effort to figure out how to do this, I contacted Mark Bulgier who did something similar recently. Because it was an experiment, he used one of his lower quality C clamps. After 2 frames, it started to get crunchy. My goal was to use the vise, but there isn't enough clearance.

How is your C clamp fairing, and how many frames have you done? I'm curious because I was thinking of going that route. I have at least one more frame to do.

Nicely done. Thanks for the step by step.

Funny you should ask. I've done two frames, the first was an 86' Rock hopper, this was for practice. The second was a Bruce Gordon Hikari that I'm converting to 650b. Yes, the cheap C-Clamp is getting pretty wonky. My next crimping tool will be made out of a large pair of Vice-Grips.
Cheers,
Chris

Nicely done, [MENTION=238716]TimmyT[/MENTION]! I've read a few informative and encouraging threads about this on the 650B Google group, but am still summoning the courage to try it on my bike.

My conversion project sat idle for six or seven months while I mustered up the courage to do the deed... All's I can say is, just do it!!!

Cheers,
Chris

Ooh, can I borrow your wedge? It worked well for you. I have 37mm tires on my International, and the clearance is only 1 or 2mm, and I probably won't be able to keep them and install fenders. Maybe I could if I dented in this way.

let's play pass the wedge . i'm about to do this to an old tandem as i have 35 mm tires in 37 mm of clearance lol. would love to try stuffing a 40 in there.

you nailed it though. great job.

Chris, did you consider crimping the Woodrup frame?

I was in a hurry to crimp stays similarly on my aluminum CX200 recently. My "forming tool" was a 1/4" drive, 5/16" socket (i.e. a steel tube about 3/8" diameter by 1.25" long). On the opposite side, I supported the tube with a soft jaw for my vise. To apply force, I used a single 6" C-clamp. To keep the small parts in place, I just duct taped them to the frame. It was quick and the finished product looks and works great.

Ah, the Woodrup, actually it had quite a bit of clearance already. What kept me from doing a 650b conversion on it was too much reach for the brakes. It would probably be great for a conversion if you were to braze on bosses for cantilever or center pull brakes

Cheers,
Chris