Old 05-31-09, 05:58 PM
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Originally Posted by cyclistjohn View Post
I don't understand what you mean there :-(
Here's what I'm getting at:

If you measure a 50T ring, it will have a diameter of about 200 mm. This means that, if the ring is just swaged on, it will have to resist bending over a length of 100 mm--the ring's radius. (Obviously, I'm ignoring the size of the crankarm here.)

If, on the other hand, you have a 50 ring bolted to a 130 mm BCD crank, the spider's radius will basically be 130/2 = 65 mm. That means the ring will have to resist bending over a length of (100-65) = 35 mm.

The upshot of all this is that applying equal amounts of force to either chainring will be more likely to bend the swaged chainring, since the force will have 100 mm of leverage--versus only 35 mm of leverage on the bolt-and-spider chainring.

Originally Posted by cyclistjohn View Post
Yes, I realise it goes against the philosophy of a folder to take bits off & refit them. The problem though is that it isn't "normal" use of a folder, is it?

I'm sure Brompton, Dahon, et al, didn't design their folders with frequent century 21 air travel in mind :-)
If that's the case, I find that disappointing. The B practically begs to be taken on air travel, given its small, regular shape when it's folded.

I may look into the self-extracting bolt idea, though. I would have to figure some way to "hide" the loose right arm within the folded package, while keeping it secured there; however, I think that could be managed with velcro straps.

Originally Posted by cyclistjohn View Post
...After reading your post, in the absence of any pictures, I folded my M3L to try to imagine what happened to your chainring.

Since you mentioned your saddle was pushed forward, it was maybe a glancing blow which distorted the outside of your chainring?

I'm pretty sure whatever happened involved the corner of some other suitcase being dropped on the M3L's case as it was lying with the B right-side-up. After all, only the upper-left-hand part of the ring is exposed in the folded state: the rest gets covered by the front wheel from the right, and by the rear triangle from the left side.

The glancing blow thing may have happened last time: my saddle was OK this time, which inclines me to suspect a side impact happened.

Originally Posted by cyclistjohn View Post
Maybe you can persuade your LBS to take a pic' of the bent chainring?
I could call and ask, but I frankly doubt I'll be able to find time to call (classes are starting up this week), or that the LBS would be inclined to spend time taking photos rather than wrenching.


Last edited by >>ECB<<; 05-31-09 at 06:03 PM.
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