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#166
05-28-2013, 09:17 PM
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#167
05-29-2013, 12:00 AM
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Can you speak to the conversations you had to get the chain stays that you had spec'd special for you? I know Steve Hampsten builds a frame out of the MAX tubeset, but makes some alterations... basically selecting lighter tubes in some areas (chain stays, etc.) while keeping the beefy chain stays. Seems like you're both getting at the same thing, a bike that has a stiff drive train and a bit more compliance in the seat stays, although going about it differently. I won't pretend to know all the inner workings of tube manufacturers, but it seems they are missing the boat on the tubesets they've designed if two respected builders (and I have to assume others as well) feel that the best possible frame comes from synthesizing a frame from various tubes.
__________________
And we have just one world, But we live in different ones
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#168
05-29-2013, 10:54 AM
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I could go on for much longer than anyone would want to read about chainstays and how they effect the feel and performance of the bike. I think they have a huge effect on both feel and performance and can make or break the ride. Having stays made to my spec's was pretty simple. I have a very long relationship with Reynolds and we have traded thoughts and ideas back and forth for a few decades. I feel privileged that they will often contact me with ideas for new tubes to get my opinion - they are great to work with. So when I told them what I was looking for they set up to make them and then I had my own part number. Those guys are great. Tube manufacturers are under huge pressure to offer lighter and lighter tubes, even if they don't produce a better ride, because builders have a constant pressure from the market to make lighter and lighter frames. The issue of course is that you can only remove so much of the material before the performance and/or feel suffers. I think that in the case of 953 that many builders are choosing it due to its low weight and consequently want the lightest possible tube set that can be safely produced........ and that means super thin and light c-stays. And these super light and thin stays are of course less stiff and I personally don't favor the ride they produce. This is one of the larger reasons that I wanted my own stays made and why I was willing to suffer a slight weight gain to get the ride I wanted. Making a bike lighter is seldom a bad thing but if it just weighs less and doesn't ride well it's all for naught. It took me a minute to find it but there is an old thread from back in the day were we discuss frame stiffness, drivetrain stiffness, performance and weight and I think it holds up pretty well. The thread has real value for a number of pages and then goes off the rails (as so many do over time) so don't hesitate to get into it...........you don't need to go through all 10+ pages to get the point. http://forums.thepaceline.net/showth...stay+stiffness I hope that helps and answers your question. Dave
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#169
05-29-2013, 07:54 PM
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Dave, thanks for this reply and the link. I have a question about seat stays... what do they contribute to the package and how do they influence the ride (assuming straight stays)? Does their length or attachment have any effect (side tack vs fastback vs GT style triple triangle; pivot or solid dropout attachment etc)?
And while I'm asking... what about the chainstay bridge? Round/flat/minimalist/none... It looks to me like this would influence the flex characteristics of the stays, and their torsion resistance? Last edited by Mike748; 05-29-2013 at 09:23 PM.
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#170
05-29-2013, 10:18 PM
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I'm sure I've said it before, but I'll say it again - thank you for putting the time and effort into tuning the JKS series the way you have. I may not be the fastest rider to ever throw a leg over one of your bikes, but that "jump, snap" wasn't lost on me when I took it for the first spin, nor any ride since.
__________________
VeloBase.com
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#171
05-30-2013, 11:56 AM
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Seat stays - the job of the seat stays is for the most part to hold you up and they mostly work in compression. The bending loads on them are small which is why they can be so small in diameter. The stays themselves, when not stuffed into a frame, are shockingly flexible. Most folks tend to think that it's a metal tube so it must be stiff as can be but you can flex them noticeably in your hands or over your knee - they move a lot and easily. But they work very well as columns with an axial load end to end. The length of the stays would have some effect on ride but I can't think of any builder that changes the design of the bike so that the stays are a different length. In other words the length of the stays is a result of other stuff (c-stay length, seat angle, seat tube length, BB drop and to a small extent attachment method) and not something one usually designs in to the bike. S-stay attachment method - this will have very little effect, if any, on the ride, performance or feel of the bike. Once they are rigidly attached they don't really care how. I'm sure one could measure a difference in stiffness from one type of attachment to another with the proper equipment but the numbers will be very small and inconsequential in the end. The one exception to this is the GT Triple triangle......having the stays attach twice at the top does change things a bit and should make the frame slightly laterally stiffer. At least in principle they should. Whether that is a good thing or not could be debated and whether it offsets the increase in weight, labor, and cost is another matter. The GT Triple triangle first came about with their BMX bikes of long ago as a way of dealing with breakage problems they had with a pierced top tube design. It was effective at both stopping the breakages as well as being a very good marketing deal as it can be instantly seen and recognized as a GT. Interestingly I raced a GT for awhile back in my BMX days and the original design was less stiff laterally and worked better as it allowed the rear end to hook up better and the triple triangle set up tended to have the rear tire skip and bounce more while sprinting. Bolt on s-stays to drops - if the stays are straight I'll bet there is not much going on here. I've never tested it but as long as everything bolts up tight it should be as effective, or nearly so, to a welded/brazed attachment. All this changes of course if the stays are curved as the bolt then doubles as a pivot and would allow for more s-stay flex and wheel travel. C-stay bridges - they can make a large difference in the stiffness and feel of the bike depending on the material being used and the length of the stays. If the stays are long as in a touring bike then a c-stay bridge can make a big difference by supporting the stays and effectively making the triangle shorter and thus stiffer. The shape of the bridge matters little - it just needs to have a large enough attachment surface area to the c-stay so that it doesn't want to punch through the tube. They act mostly in compression so their shape isn't that important and they can be round or flat or aero.....or whatever. With most carbon and steel bikes one can usually get by very well with a small reinforcement behind the BB.......say between the c-stay BB sockets and they will be very effective on a short stayed race bike. Ti is a bit of a different beast as the material is much less stiff than a similarly sized steel stay (harder to generalize with carbon as so much of it depends on layup) so they really benefit from a bridge. I remember very well when we at Serotta made our first Ti MTB's. I got one of the first ones and we tried it without a bridge in hopes that it would save time and money and the bike wasn't very good in my eyes.........the tail wagged WAY too much. We then added a bridge to the bike and it was much, much better. We eventually went to a larger stay and a bridge and it was very good. Ti is different. I see little benefit in terms of resistance to torsional c-stay flex with a bridge. The bridge is in most cases so close the the BB that it will have little influence here. With a touring bike and long stays it might add up but I've not tested it. Time for me to get to the bench - thanks for reading. Dave
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#173
05-30-2013, 05:42 PM
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dave
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#175
06-04-2013, 01:36 PM
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#176
06-11-2013, 12:04 PM
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Surprise! I bet you didn't see this coming.
Ten Years - part 8 is up. Dave http://www.kirkframeworks.com/blog/2...-years-part-8/
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#178
06-13-2013, 08:37 PM
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Dave
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#180
06-17-2013, 10:17 PM
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