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-   -   Two quick questions (http://www.bikeforums.net/folding-bikes/250723-two-quick-questions.html)

Shilun 12-05-06 07:50 PM

Two quick questions
 
1: How much weight can I load on the seat tube? (the Giant Halfway RS has a very long seat tube) I have a beam rack which has a capacity of 10kg. Could I add another to the same tube, or perhaps a Carradice bag at the top of the tube? Would this put too much strain on the tube?

2: I have a Shimano rear derailleur (RD2200) which I want to attach to another folder. The Shimano website says that it is rated at MAX/MIN 26/11. However, it came on a KHS folder (F20) with a 34/11 cassette. Unfortunately, I never put that bike through its paces, so I don't know if the RD could actually reach the 34 cog. Can there really be such a large difference between the recommended max capacity and the actual max capacity?

eubi 12-06-06 07:06 AM

1: So that's an extra 20 kg (44#) or so on two racks, hanging off the seat post. Depending on how much you weigh, I can't see it being a big deal. Seatposts for folders are pretty stout.

I have a Dahon Speed 7. It's very comparable to your Giant Halfway. The actual calculation would be a bit more complex, but here's a quick and dirty approximation to consider. I weigh 230# (104kg) and have no problems with seatpost flexing on my Dahon. As long as you weigh less than 186#(84 kg) , you should be OK.

You just have to consider that you have a lot more unsprung weight on the bike. You may have to alter your riding style somewhat. For example, I would handle my bike differently if it was unloaded vs. whether it was fully loaded for touring.

maunakea 12-06-06 11:55 AM

Quote:

Originally Posted by Shilun
The Shimano website says that it is rated at MAX/MIN 26/11. ?

That means the RD has a short cage that isn't long enough for a cog larger than 26. Why the RD was mated with an 11/34 cassette is a different question, but I have not seen a 26-limit cage work with anything bigger than a 26 cog. The B-tension adjusting screw is typically the same length and pitch, so if you replaced the short cage with a long cage, you may be able to accommodate a 34 cog. Most folks just buy a long cage RD.

invisiblehand 12-06-06 12:48 PM

Quote:

Originally Posted by Shilun
1: How much weight can I load on the seat tube? (the Giant Halfway RS has a very long seat tube) I have a beam rack which has a capacity of 10kg. Could I add another to the same tube, or perhaps a Carradice bag at the top of the tube? Would this put too much strain on the tube?

2: I have a Shimano rear derailleur (RD2200) which I want to attach to another folder. The Shimano website says that it is rated at MAX/MIN 26/11. However, it came on a KHS folder (F20) with a 34/11 cassette. Unfortunately, I never put that bike through its paces, so I don't know if the RD could actually reach the 34 cog. Can there really be such a large difference between the recommended max capacity and the actual max capacity?

First, some personal experience with a 105 short cage derailer--I put a 13-30 cassette on my Nova with a 105 short cage derailer. Works fine with a little adjustment to the b-screw. I just followed the advice from Sheldon Brown's webpage.

Second, I thought that part of the maximum and minimum limits are related to using a triple crank in the front and the derailer arm having enough leverage to accomodate a cyclist shifting to small-small and big-big chainring and cog combinations. So if your KHS folder has a single or a double up front, the min/max limits may not be applicable. In the case of the aforementioned Nova, if I try to get into a big-big or small-small chainring-cog combination, the derailer arm swings to an extreme forward or rear position respectively. But in the middle chainring, I can use any cog without any issues.

Third, Sheldon Brown states that the Shimano specifications are very conservative.

Shilun 12-07-06 08:36 AM

Quote:

Originally Posted by invisiblehand

Second, I thought that part of the maximum and minimum limits are related to using a triple crank in the front and the derailer arm having enough leverage to accomodate a cyclist shifting to small-small and big-big chainring and cog combinations. So if your KHS folder has a single or a double up front, the min/max limits may not be applicable.

I think this may be the answer. The website states that the RD2200 has a 22T capacity for the front chainrings and seems to be designed for the triple 52-42-30 crank. On my KHS, the front was a double 44-32.

Leisesturm 12-07-06 10:21 AM

Overall I agree with eubi's assessment of the twin rack situation: much depends on rider weight. However some does depend on how conservatively or not the seatpost has been built. When I was researching my 1/2way (unsuspended) purchase I read a couple of reviews to the effect that the seattube had collapsed after a moderate hit (pothole). I am pretty good about unloading the seattube when going over obstacles but there are always those times... I have a Delta beam rack on my tandem and the Delta people go out of their way to say that the rack should be mounted as low on the seattube as possible. While it doesn't seem to me like it should make much of a difference, there it is stated in black and white. Perhhaps the added stress of the load center being out from the tube could be a problem for a thin walled seattube. In any case, the suggestion of the Carradice bag for the upper load is probably a better one than a second beam.

H

jur 12-07-06 04:14 PM

Regarding the derailer capacity: I took my Tiagra long cage which serviced a triple chainring and a 12-26 cluster, and installed it on a folder with 11-34 in the back. Before this, I checked the Shimano specs and Sheldon B's comments; the total capcity exceeded the 11-34T cogs, but the max cog was listed as 28. Well in my case all works fine, just on the 34T cog the pulley rubs against the 34T cog (with the chain in between the two, of course). I have the B-screw set to its maximum. It shifts beautifully slick, it hasn't missed a shift yet, but I can detect a small increase in backpedalling resistance and chain noise compared to the other cogs.


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