advice on chainstay clearance for rear tire

[Brian Rowe]

Hi everyone, I would appreciate your input on this question, thanks.

 

About two years ago I converted my 1981 Bianchi Limited to 650B. Since then I have ridden it many thousands of miles; on brevets, a few fast group rides, long and short training rides, etc. The bike performs wonderfully.

 

Here is my issue. With 38mm tires (Soma B-Lines), there is only about 2 millimeters of clearance between the chainstays. Is it too risky to have such a tight clearance? In particular, on brevets and long rides I get very far from home, and if the rear wheel developed a slight wobble that I couldn't fix, that would end my ride. (I do carry a spoke wrench and a Fiber-Fix spoke). 

 

So my first option is to pay a knowledgable mechanic or framebuilder to dimple the chainstays to give me a bit more room.  As I understand it, that is not a risk-free job. Something could go wrong and ruin the frame. The second option is to just leave it alone. The bike has proven itself over many long rides and I'm not sure the clearance needs fixing.

 

What do you think I should do?

 

Brian

 

[satanas]

Personally, unless the chainstays are cracked or corroded I think it should be virtually risk-free to *carefully* indent them a bit; of course, things can always go wrong, but if it was me I'd be happy to take the (IMHO very small) risk.

The other point of view is "don't fix it if it isn't broken."

Later,
Stephen

[Ed Braley]

I have a couple of 650B conversions like this, including my own Bianchi Limited. I just ride them as they are. Plenty of other things might cause the unexpected premature end of a ride, you're just aware of this one possibility. If anything, 650B machines with plump tires are less likely to have this kind of problem.

 

Look at the tight clearances on some of the production 700C bikes these days. Low spoke counts, and narrow tires on those bikes, too. No one seems to care...

 

Ed.

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[Peter Weigle]

Ed said,,,

>Look at the tight clearances on some of the production 700C >bikes these days. Low spoke counts, and narrow tires on those >bikes, too. No one seems to care...

This is somewhat true,,,

but many of us with wider 650b tires seem to get lured off the pavement and enjoy a bit of rough stuff, dirt roads and maybe a little mud thrown in,,,

more clearance,, both chain stay,, (and also fender clearance) is a real nice thing to have in these situations.

Just saying..

ptr

[somervillebikes]

I have a 650B conversion which is ridden daily. It has 42mm Hetres which leave 2mm of clearance with the chain stays.  The bike has seen brevets, commuting, tons of gravel, hard climbs, fast descents, mud, rain, you name it.  The tires haven't once touched the stays, at least as evidenced by the lack of paint scuffs at the area in question.  The only downside I experienced was that when riding in mud, mud and debris would cake up there.  It never caused harm, and after getting through the mud I'd kick it off.

Granted, it doesn't leave a lot of room for error, for example if the wheel goes out of true on the ride.

Anton

ridingthecatskills.com
 

On Thursday, June 5, 2014 1:17:05 PM UTC-4, EdBraley wrote:



[William Lindsay]

Don't be shy about dimpling.  Nothing's going to get ruined.  The way I did it (on a Miyata 912):

1.  Get a small length of 2x4

2.  Drill a 1" hole through the 2" thickness of the 2x4

3.  Rip the 2x4 on your table saw bisecting that hole

Now that half-circle is a wooden cradle for the outside surface of your chainstay.  

4.  Use a big C-clamp to squeeze a dimple into the inside of the chainstay.  The outside doesn't squish because it's cradled by the wood and the c-clamp is pushing on the wood on that side.  

5.  For extra credit find or make a projectile to shape your dimple the way you want.  Squeeze that thing with the c-clamp.  That way you really make a dimple rather than just flattening the inner surface

All this is done with the crankset and rear wheel off the bike of course.  

Go for it!  Check frame alignment before and after with the string method to make yourself feel better.  Brace the rear end with a bare rear hub if you are particularly nervous.   

[Brad]

There is always the opiton of going with the Pneu Confreriale.
http://www.xxcycle.com/tyre-hutchinson-confrerie-des-650b-275-650-b-ts,,en.php
Hutchinson 32 x 584 aka 650B x 32.   That will get you up to 5 mm of clearance per side if I do my math right.

[Brian Rowe]

Thanks everyone. Its good to know that I'm not the only one putting a lot of miles on a bike with tight clearances.