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If one were using 160mm discs on a 26er should one then change to 185mm discs for a 29er? It seems the additional rotating mass would merit the switch, no? 200lb rider on rough, hilly singletrack.
 

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Yunkie said:
If one were using 160mm discs on a 26er should one then change to 185mm discs for a 29er? It seems the additional rotating mass would merit the switch, no? 200lb rider on rough, hilly singletrack.
while not necessarily true the swap for you size makes tons of sense whether on a 26er or 29er. Better modulation and bite with better stopping power and feel. Changing pad compound from an organic to a semi metallic on a 160mm rotor will be beneficial if you don't want to upgrade the rotors.
 
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basically i look at rotor size in terms of leverage

that is

a larger rotor provides more leverage

and for me... what that equates to is less pressure on the rotor at the pad
which (in my mind) equates to less wear on the pads.

since i dont own a car
and i ride a ton
i get tired of going thru 3 pairs of pads a year, etc...
which is about $120/yr in brake pads!

so 203's and EBC metallic pads have been my personal choice.
i also have some DiscoTech ceramic pads that i have yet to try

thats my 2 cents

peace...d
 

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Mashers Only!!
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I have been on my 29er for just under 3 years on 160mm rotors and perfectly happy. I just built a new bike(Leviathan) and used 180mm on front and stuck with 160 on the rear. The increase in stopping power and modulation was (to my surprise) a significant gain. I like it so much I ordered the parts to convert my Moots to 180mm in front! I am also 200lbs....

HUGH
:)
 

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Jacob 34:19
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Go bigger.

Also 200lbs. I run 160/160 on my single speed. 160r/185f on my geared bike. BB7's on both bikes and the larger rotor up front makes a noticeable difference. You might also try a search on this forum as this topic has been discussed ad nauseam. I think the consensus is bigger rotors work better on bigger wheels.
 

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Always Learning
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Padre said:
I weight 210lbs and run 160mm front and rear.
But you're confirmed as the world's largest weight weenie.:thumbsup:

Have you ever tried 160 front 140 rear with those Ultimates? I'm thinking of a 140 something or other in the rear since I run a Crow or other minimal tread in the rear as it is. No point in having too much brake back there for me without a tire to bite during XC racing.

BB
 

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meh....
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I'm 150 plus gear, I've had brake fade with 203f/185r, so I'd most likely never go smaller unless it was a ride with no real big descents, or I was really looking to lose as many grams as possible for some big ride.
 

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Just going by feel here are my thoughts. I am weigh 200 pounds. I went with a 185f/185r on my sir9 ss and a185f/160r on my geared Karate Monkey. These rotor sizes are not overkill at all. The rotors don't get overwhelmed by the increased wheel size and seem to handle their braking duties like a 160mm on a 26er. Bottom line . . . I really like having 185s and its more fun to ride when I can brake with gusto or with one finger while the other three and my thumb hold on for dear life!!!

On paper, here's why I think it's reasonable to go up a rotor size when going to a 29er . . .
When braking, the force created between your tire tread and the trail acts on a 11.5% longer moment arm for a 29er versus a 26er. The force between the brake pad and a rotor acts on a 15.6% longer moment arm for a 185er than a 160er. So rather than being at a 11.5.% mechanical disadvantage by staying with the same rotor size, I think its good to go up one rotor size when using a 29er wheel where you actually gain a little bit (4.1%) of moment arm to do the same job.

I think rotational mass does make a difference too, but I don't know how to calculate its effect. I'm sure it eats into the 4.1% gain.

I think folks using canti or V brakes don't have to worry about this because rim brakes almost the same distance away from the hub as the tire/ground contact patch.

Finally, I wonder how our hubs will hold up. Has anyone experienced hub failure due to all that 29er rubber on the ground plus bigger rotors????
 

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Recovering Weight Weenie
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BruceBrown said:
But you're confirmed as the world's largest weight weenie.:thumbsup:

Have you ever tried 160 front 140 rear with those Ultimates? I'm thinking of a 140 something or other in the rear since I run a Crow or other minimal tread in the rear as it is. No point in having too much brake back there for me without a tire to bite during XC racing.

BB
That wouldn't work for long here. I think the 140mm would turn red and bend or at least just disintegrate in a few rides. Our steeps are too steep and long.
 

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The rotor size depends on your weight, your riding style and your riding places.

200 lbs and agressive style in the mountains are not the same thing that 150 lbs and smooth style in a flat groud.

At the start, I think that you must change your pads.
 
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