Originally posted by Barnaby
I want to find out how my Miyata 1000 3-ring tourer would feel stripped down into a fixed-single speed format with a high tech crank set instead of the old heavy triple that is on there now. The info. that I have come across from Rivendell and others suggests that BB flex comes more from the BB axel rather than the BB shell itself. The info. also says that Q-factor ( the span measurement outside of crank to outside of crank) has alot to do with peddalling efficiency and power transfer.
The extra length of the crank axel required for triples is pointed out also in the Sierra Club Guide To Outings On Wheels as a good reason to stay with doubles even on a loaded tourer.
The non-sealed axel I now have on the Miyata is 125 mm. in a 68 mm shell with English threading. I have a sealed cartridge on my racer (70 mm shell-Italian threading), with a total length of 110 mm or so.
My question is: Are the cups interchangeable between the type of cups that sleeve over a sealed unit, and the fixed and adjustable cups that come with a non-sealed unit? The later have races for bearings that the former to not, and therefore don't seat the same over a sealed unit. Am I right?
I have put the 110 unit in the Miyata shell and loosly put the crank arms that came with the unit on as well, and the clearances seem that they would be OK with the cranks tightened. I will not know this for sure unless I get the kind of cups that come with sealed units instead of the the English cups with the races, that came with the Miyata.
Is it possible that with a new crank that a 125 mm spindle could be swapped with one as small as 110? The measurements that I have taken seem to suggest so since the chain stays are the same diameter, they flare out to the 126 mm rear drop-out over a shorter disatance in the racer ( since the chain stays are shorter), and the tourer has an indent on the right chain stay for the second ring that the racer doesn't have.
Lastly, do you think that a bike could be rejuvinated by the improved Q-factor of the shorter axel, and the improved stiffness of a sealed-unit over a loose cup and cone axel?
I think you have fallen for a bit of bull.And, what does the sierra club know about bike mechanics, theory and engineering?Ask yourself how many loaded tourers DO use triples. The difference between a typical double and triple crank in spindle length is 10mm,and sometimes less.Look at the spindle and ask yourself how much more flex are you likely to get by addding 5mm to each end, considering where the bearing support is???? There can be considerable BB shell flex, as well as crank flex,especially in some of the old stuff........The cups are not interchangable between the cartridge and non cartridge types.......Better Q factor may help,but some are more sensetive to it than others.....Certainly you can swap a new crank speced for a 110 spindle for one that was speced for a 125 spindle.....Want the ultimate in alleged Spindle stiffness,then get a shimano 9 speed octalink double crank/ BB setup with a 109.5mm spindle.