Gunnar Cycles USA Message Board

Hi; I have an idea of my perfect bike, and it's a Crosshairs with disk brakes AND rear rack braze-ons. Apparently this is not an option - I have to choose a rear disk OR a rear rack.

My rationale for disk brakes is to ensure maximum stopability as a commuter in rainy Vancouver. The rear rack is to support the two or three times a year when I will go on a 2, 3, or occasionally a 4 day light touring adventure.

So I can go with standard canti's on the rear and a disk up front if I want the rack mount, or I can have disks front and rear and use a rear axle-mounted rack - something like those available from http://www.oldmanmountain.com/ (thanks to Ed at my LBS for this suggestion).

I wonder if anyone has advice for me? I do not have experience with disk brakes, only the opinions of fellow cyclists who highly recommend them. I must admit that I was ready to go with the rear catilever brakes until I saw Ed Testa's crosshairs on the gallery: http://www.waterfordbikes.com/gunnar/data/gallery/galleryshow.php?rg=1&rgid=142 how sweet is that !?

I have a Rock Tour with the disc and canti options. I tried the Avid mechanicals for awhile but finally decided I like canti's better. They "feel" better and seem to have better modulation. On the Rock Tour, I installed OMM racks with no problem. I've been successful getting them to work with either set up. PLUS, I have a 29er, Surly Karate Monkey. The OMM rack works great on it too. Call them and they can walk you through how to do it on 700c.

I finally decided that (for me) discs worked no better than cantis. I also began to think through the physics of discs too. With a fully loaded tour bike, when braking hard, all the force is applied at the hub, then transferred through the spokes. This means that spokes get stressed in order to slow the bike quickly. This becomes more pronounced when riding with a load. Essentially, the path that the force follows is: disk to hub to spokes to rim to tire to road. Perhaps this is no big deal, but I figure that spokes and conventional lacing patterns weren't designed for this type of stress. When opting for cantis, it takes the spokes out of the equation.

...Just my thoughts

It seems to me that when you brake the rim, the opposite force happens, but it still puts stress on the spokes and hub. Every piece of the bicycle (and you, by the way) is travelling at a velocity "v" and consequently has momentum "p" (p=mv), where m=mass of bike, gear, and rider. To slow down that mass, by either braking system, you must slow the entire mass down. Whether you have rim or disk brakes, your mass is attached to the wheel at the hub centers. So when you brake with rim brakes, the rim slows down first compared to the rest of the bike, which stresses the spokes and hubs (axles, bearings, flanges). This is the opposite, but probably equal force that disk braking has on hubs and spokes. From what I have read, things like chain and seat stay design needs to be disk brake ready.

Either way, a well designed system should be fine for any of us mortals. Disks do have an advantage in wet and mud, and if you bend your rim, and for long descents - no rim heating. Ask Mr. Beloki about that phenomena....

I run canti's - I don't have a valid reason for changing to disks at this point. It's all abot value added for me, and disks for me don't add any value.

Cheers!

_________________
Steve "Single Speed" Arrivo

"Somewhere there's a nice, sunny place with warm breezes and shady palms where all the second-place guys train."
Bob Kennedy
USA Record Holder, 3000 and 5000 Meter Runs

Thanks for your insights. Disks appeal to me for the stopping power in wet conditions. Cantilevers for their simplicity. I hadn't thought about the 'feel', but I can certainly see how the disk brake can remove the feedback in the system - kind of like flying-by-wire. I might have to take a spin on a disk-equipped bike and judge for myself. I'm considering a disk up front and canti's in the rear to give me the best of both.

There does seem to be some controversy about the pysics involved, but general agreement that disks stop a bike better. Since this disk is a more expensive option (makes it a custom order), and potentially adds some weight, the question is: just how much better is it? And is it worth it?

It sounds like the OMM rack will do just fine, so that shouldn't be too big a part of my decision.

It's just my opinion on what happens while braking - well mine and Mr. Molson's opinion. I didn't do a vector force analysis, but we certainly could. Sounds like a good search. I'll bet a German testing lab has tested this already.

As far as for me, we live where it is mostly flat, no long tricky downhills, so Canti's/V-Brakes are fine for me. Again, just MHO.

Steve

_________________
Steve "Single Speed" Arrivo

"Somewhere there's a nice, sunny place with warm breezes and shady palms where all the second-place guys train."
Bob Kennedy
USA Record Holder, 3000 and 5000 Meter Runs

Go with what looks the coolest bro! Thats what I do when it comes down to a choice that works well both ways. Happy trails

Gunnerluver