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Discussion Starter · #1 ·
I have Avid BB7 disk brakes on the Dummy and would like more front brake. I have a 203mm rotor on a wheel I'm not using that I had on the Xtracycle. I'm wondering if this is overkill vs. a 185mm. I assume I need a different adapter for the caliper mounting.

I haven't swapped disks before so I'm a little vague about what is needed, and would appreciate the guidance. Also, best sources for getting the stuff, or if you have stuff lying around, etc...

Thanks

Marc

(out on the BD yesterday in the mid-teens - kinda brrrrr!)
 

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Derailleurless
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I don't think that a 203mm front is overkill if you're anticipating carrying the 200 pound load that the Big Dummy is rated for. I'm building my Xtracycle with a 203 front / 185 rear for the same reason, though I'm betting that for the most part, 185 up front would be sufficient. But with the extra 15" wheelbase, the bike is half-way between solo bike and tandem in length, so there is a lot more weight over the front end and the rear end will be much more difficult to lift under hard braking.

All you need is a 203mm front IS adapter. Any of the regular web retailers, and any local shop, can get that for you. In fact, you may find that your local shop has the adapter you need on the shelf. Should cost you $10 to $20, depending.
 

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ballbuster
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I think...

NHpug said:
I have Avid BB7 disk brakes on the Dummy and would like more front brake. I have a 203mm rotor on a wheel I'm not using that I had on the Xtracycle. I'm wondering if this is overkill vs. a 185mm. I assume I need a different adapter for the caliper mounting.

I haven't swapped disks before so I'm a little vague about what is needed, and would appreciate the guidance. Also, best sources for getting the stuff, or if you have stuff lying around, etc...

Thanks

Marc

(out on the BD yesterday in the mid-teens - kinda brrrrr!)
... SelfPropelledDevo runs 205s on the front of his BD. Maybe rear, too.

Here's a pic:

 
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my thinking has been that
a larger rotor requires less clamping force to provide the same amount of braking force.

that is
to achieve x amount of braking force
with a larger rotor
disc brake pads endure less clamping force with a large rotor
vs
a small rotor, and more clamping force at the pad

the rotor is like a lever
a bigger rotor provides more leverage

so what does this mean?

small rotors wear out brake pads faster
why?
more braking force is applied to the pads

so what?

$20/wheel in pads
$40/for a set

i go thru at least 3 sets a year
= $120/yr in brake pads.

thats crazy!

so far the best pads had been EBC Gold
currently I'm on a set of Avid Metalic
 

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Just a couple pertinent points from the Surly BD Spew:

"Rotor size- We've had no problems or inadequacies using standard 160mm rotors. However, the Big Dummy accepts 180mm and 203mm rotor sizes if you feel the need"

"! It should be noted that using the front brake only could cause the fork or frame to fail under heavy load conditions. Use both brakes and keep your speed under control !"

There is such a thing as too much front brake...:eekster:
 

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It aint gonna ride itself
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585 Posts
I've got 203 rotors front and rear. It's correct that you just need to swap out the caliper adapter and the rotor.

Given to do again, I think I'd go 160 front and 203 rear given the way weight is distributed on a longtail. The 203 rotor on the front tends to rub a little in turns, and I'm not sure I would want to put additional stress on the fork if indeed a 203 gives the brake more emergency stopping power.

The main advantage to 203s in my mind is better heat dissipation, which is good when running loaded...

 
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