Bicycle Mechanics - need info on discs
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I'm considering putting 1 disc on my touring bike. It will likely be on the rear, since I don't want to upgrade a perfectly nice (and light) fork. Also, my low-rider racks would likely interfere. The bike is an old Cannondale, with fat shainstays, and ovalised seatstays. The dropout spacing is 126mm. I am using a Blackburn rack on the rear.
Are there any disc hubs which will fit? How much weight will it add? Is this even feasible?
Comments welcome, flames ignored.
Does your bike have disc brake mounts on the seat stays?
Here are a couple of points to consider:
-If you are only adding one disc, the front wheel is the way to go since it provides 70% of your stopping power.
-If your frame doesn't have disc mounts for the rear, you can buy an adaptor but it will add weight, and most importantly, your frame was not designed for discs, so the rear chainstay is not reinforced for the additional stress it will see. I've seen a picture of a Rocky Mountain frame which broke from the stress. In this case the person had disc mounts brazed on, but it's still something to think about since a touring frame is not built as strong as an MTB frame.
-Unless you get the frame spread, most disc hubs are made for MTB spacing (135mm I believe, but you can confirm on www.sheldonbrown.com). You might find a high end road or cyclocross hub to fit or possibly a bmx hub.
-If you don't want to upgrade your fork or use a disc adaptor in the rear, I would suggest buying a nice set of Avid V-brakes and levers. That alone can make a world of diff. in stopping power. (this would be my recommendation)
Well, the old Diacompes are pretty good, but an upgrade to v-brakes would make sense for pannier clearance. I was looking at a disc setup simply for a descent brake. I'm a little worried about rim heating (being a mechanical engineer, this worries me, especially the rise in tyre pressure due to heating).
As of right now, I alternate between front and rear for braking on really steep hills. However, next year, I'm planning on a long tour, heavily loaded, and would like to have better heat dissapation, at the very least. Maybe a disc isn't possible on this bike. The stays are very stout, though.
If you are running cantis, V-brakes will make a huge difference and the benefit to cost ratio is good.
If you are really interested in a disc for the rear, check www.paulcomp.com for their rear disc adaptor. I think this may be made for horz. dropouts only, but it is the same idea as other adaptors I have seen.
If money is not a concern, a nice light rigid disc fork is made by Vicious Cycles. I'm considering going this route for one of single speeds to make it the ultimate winter MTB. However, the fork runs about $190 plus a new hub and a new brake means around $400 for the whole upgrade. Quite a bit of $$$ for new brakes on the front end.
Another thought is a lot of tandems use drum brakes in the rear for extra stopping power. Not sure about details on that, but I'm sure Sheldon Brown's site has info.
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