Community > Thorn General
How much is a steel frame worth in scrap value?
PH:
--- Quote from: martinf on January 06, 2022, 07:42:32 am ---
--- Quote from: Bill C on January 05, 2022, 10:30:41 pm ---the fault i found was that if i adjusted the ebb to remove the slack in the chain then the pedals moved and where no longer comfortable for me i have arthritis in both knee's and they are sensitive to saddle height/pedal position
--- End quote ---
A valid comment on the EBB, and something that bothered me before I got my first Thorn. I had, however, previously owned a tandem with an EBB, so I concluded that I could live with this drawback.
To keep the saddle to pedal distance and angle the same, it is possible to move the saddle (vertically and horizontally) to match the movement when adjusting the EBB. Of course, doing that means that the reach from saddle to handlebar changes slightly.
In pratcice, this hasn't yet been a problem for me.
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That pretty much reflects my own concerns before buying the Raven, though I didn't have the tandem experience. I adjusted the saddle the first couple of times I tightened the chain, then got bored with it, I have it set to be perfect in the middle of the throw, so it's never more than a few mm out.
So yes, a valid concern and I appreciate a problem for some. But, not for the OP, they don't dislike an EBB (They're going to buy a bike with another) they dislike the set screw design of their current frame.
CycleTourer:
--- Quote from: martinf on January 06, 2022, 08:38:13 am ---The alternative to an EBB frame would be a very old mountain-bike frame with horizontal dropouts.
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A "very old mountain-bike frame" is not the only alternative. Surly has horizontal dropouts (its so-called Gnot-Boost design) on several of its current frames, as well as on some only-recently retired ones like the Troll. On these frames, chain tension is adjusted with Surly’s Tuggnut fitted into that dropout.
PH:
--- Quote from: CycleTourer on January 06, 2022, 02:05:31 pm ---
--- Quote from: martinf on January 06, 2022, 08:38:13 am ---The alternative to an EBB frame would be a very old mountain-bike frame with horizontal dropouts.
--- End quote ---
A "very old mountain-bike frame" is not the only alternative. Surly has horizontal dropouts (its so-called Gnot-Boost design) on several of its current frames, as well as on some only-recently retired ones like the Troll. On these frames, chain tension is adjusted with Surly’s Tuggnut fitted into that dropout.
--- End quote ---
I thought martinf's comment was in relation to his own requirements for a "large, inexpensive frame that permits the use of a Chainglider" rather than just a Rohloff alternative.
There's plenty of Rohloff options, probably more ways to move the hub away from the BB than the other way around. The Surly version is OK, I have an Ogre, it does mean having to adjust the brakes each time you adjust the chain, it also makes getting the wheel out with a mudguard more awkward. I'd have preferred something where the brake mount moves with the dropout (Assuming discs), Paragon Designworks offer a couple.
mickeg:
I have never found that adjusting the chain would then require an adjustment to the clamp position on the saddle rails.
Since the chain between the chainring and sprocket is nearly horizontal, adjusting the chain for elongation only moves the relative saddle poition fore and aft with minimal vertical change. Before I bought my Nomad Mk II I was concerned that i would have to adjust the saddle when I adjusted the chain, but I have never found that to be necessary.
Realistically the chainstays are specified as 466mm. Thus, if you have 1 percent chain elongation, that is a hair under 5mm that you need to move the bottom bracket spindle to compensate. I would not notice 5mm of change in spindle location fore or aft.
I have occasionally moved the seatpost up or down a few mm, but since I have several different bike shoes and they have different sole thicknesses, the difference in shoes is bigger than the difference in chain wear for saddle position.
PH:
--- Quote from: mickeg on January 06, 2022, 08:14:22 pm ---Realistically the chainstays are specified as 466mm. Thus, if you have 1 percent chain elongation, that is a hair under 5mm that you need to move the bottom bracket spindle to compensate. I would not notice 5mm of change in spindle location fore or aft.
--- End quote ---
Another way to look at it, if you don't measure chains or subscribe to the idea of changing them at a set wear point, is the maximum required throw is one chain link (Any more than that and you remove a link and start again). So 12.5mm, if the saddle is set for the midway point, your riding position will be a maximum of +/- 6.25mm
There are people for whom that makes a critical difference, I'm not one of them, I do notice it, but it isn't a problem. When I first got the Raven, I made the mistake of setting the saddle in the perfect spot, a couple of chain adjustments and it did become uncomfortable and I needed to move the saddle about 1cm forward.
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