Tuesday, April 14, 2009

5, 6 or 7? 120 or 126?

I'm in the process of sorting out wheels and freewheels for my Schwinn Sports Tourer and my Motobecane Grand Touring. And some of my understanding of rear hubs and freewheels is being challenged in the process.

I've reassigned the 27" wheelset that came with the Motobecane to the Schwinn. This is a good thing, as they fill the frame up a little better, and take a little pressure off the rear Mafac brake to reach all the way down to a 700c rim. And the plump tires I chose (1 1/4" Pasela's) should make the Schwinn's already very pleasant ride quality that much more cushy. Good stuff.

Also good stuff is that I've found that the Motobecane's frame accepts 700c rims without difficulty. More to the point, the brake bridge is located so as to allow the Suntour Superbe brakes on the back of the bike to squeeze the pads onto the rim, not the tire (just barely, but I'll take it). The new fork, though sized for a 27" rim, works fine in that regard as well, though I don't yet know if it messes up the bike's steering or handling.

At any rate, from a rim perspective, the swap is working out just fine. However, we all know that things revolve not around the rim, but around the hub. And the hubs are challenging me a bit.

The Specialized cartridge/sealed bearing hubs on the 27" rims have an outer locknut dimension(OLD) of 122mm, according to my calipers. Or did, until I added 5mm of spacers to them, 3mm on the right side and 2mm on the left. The goal was to get the hub to accept not just a 5-speed freewheel, but also a 6- or 7-speed freewheel. This, assuming that the widths of 6-and 7-speed freewheels was the same. Not, apparently, the case.

I thought I'd read that a 7-speed freewheel and a 6-speed freewheel had the same width, and that the sprockets are just crammed closer together on the 7. Same way an Ultra 6 and a 5-speed freewheel have the same width. But while adding those 3 mm to the freewheel side of the axle made the axle able to support a 6-speed Shimano 600 freewheel (an oldie but goodie), a 7-speed recent Shimano freewheel doesn't clear the locknut. It's not really even that close. In the mean time, the 700c wheelset readily accepts either a 6-speed or 7-speed, with clearance for either, and it's a 126mm wheel with a Shimano 600 hub.

So now I'm confused. I've ordered an IRD 6-speed freewheel with a nice wide gear range for the Schwinn, and we'll see if that fits. I settled on the one with more consistent gear spacing, because I figured there might be times when I missed a 28 tooth cog between a 32 and a 24, more than I'd miss a smaller gap higher up in the range. Anyway Rivendell had what I needed, so I got it, along with some hemp twine to twine the bars, and some corks to prevent the bars (hopefully) from taking a core sample of my abdomen in a crash or possibly hosting some sort of mud wasp clan someday.

I couldn't find anything that said how wide the IRD freewheels are, so I'll publish that spec when I find out -- at least the 6-speed width.

And apparently I need to sit down with some calipers to see what's keeping me from running a 7. If worst comes to worst, I can get the rear wheel re-dished at some point. I'm honestly half expecting the wheels not to hold up well, anyway, given their age and the rusty eyelets. If that happens, it'll be easy enough to justify the respacing and a new freewheel. I'll have to see how it plays out...

The weather hasn't been very cooperative recently, so I haven't gotten out yet. Am hoping for a nice Sunday morning, but the nights are still getting pretty cold. In particular, I'd like to at least get into the woods on the Paramount, where wind chill is less of a problem than out on the road on the Kestrel.

All for now,


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