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  1. #1
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    What is the best rotor size for the 29er ? Is it 160mm or 180mm ? Thanks...

    What is the best rotor size for the 29er ? Is it 160mm or 180mm ?
    I'm doing XC on single or double trail.

    Thanks....

  2. #2
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    What is the best rotor size for the 29er ? Is it 160mm or 180mm ? Thanks...

    Depends on your weight, style of riding, and type of brakes you'll be using. The heavier and faster you are, the more power you'll probably want. Go with 180. If you're on the lighter side, like modulation over power, and aremore XC oriented, 160 is just fine. If you run XT brakes and go with the IceTech stuff, 160 would be good.

    I'm 175 geared up, ride a 125mm travel 29er with a 140mm fork and ride/rode dual 180s on X0 Trail/XT IceTech stuff. I'm probably over-braked for 90% of the stuff I ride, but I'm happy to have the power when I need it.
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  3. #3
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    ^^ This!

    Unless you're really counting grams, just go with a 180.

  4. #4
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    If you're heavier, and ride any big descents, you'll want a big rotor up front. I'm about 270 lbs with all my gear. I'm currently using XT brakes and IceTech rotors (203 front / 180 rear). If you're a lighter rider, and not doing any long fast downhill trails, you'll be fine with 180 front and 180/160 rear.

  5. #5
    Always Learning
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    Quote Originally Posted by edle View Post
    What is the best rotor size for the 29er ? Is it 160mm or 180mm ?
    I'm doing XC on single or double trail.

    Thanks....
    Depends where you live and ride your XC trails. I use 160mm front/140mm rear on all of my 29"ers (weigh around 180 - 185 and ride in the Midwest).

  6. #6
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    I'm 6' 2" and about 230 and went 160r/180f on my 29er build. I have 160 f and r on my 26er and they work just fine as well.

  7. #7
    ballbuster
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    I'm 210#, ride XC in NorCal, I ride down steeps, sometimes way too fast. I run 160/160 on most of my bikes, and that works just fine. My 'Trail' bike (Was a RacerX29er, now a Titus Rockstar 29er) I run 180 in front, 160 in rear. The only time I cook my brakes is if I ride at altitude in the Sierras, like Downieville. I use Shimano brakes on all my bikes except the singlespeed, I have Hope Mono Minis. I use sintered (semi metallic) pads all around. I found it was way to easy to overheat organic pads. I've been experimenting with those cheap Disco Brakes Kevlar pads, and so far they are pretty good, especially considering the money... they go for like $12 a set, and a bit cheaper if you buy a bunch at once. They are a bit honky when they get really hot or get wet, tho. I got sick of paying $30 a set for XTR pads, or $35 for Hope Mono Mini sintered pads, which are getting hard to find anywhere, even online.

    Yeah, it all depends on your weight, your riding style, where you ride, etc. That would be the same for 29ers as 26ers. If you used a brake rotor combo on 26ers that worked for you, do that on your 29er.

    That said, the only real downsides of brakes that are 'too big' is a bit of extra weight, and less modulation. As in, the line between brakes on and brakes off is finer. Bigger rotors are grabbier.

    Me, I like having better modulation. I ride a lot of tight techy stuff that takes a feather touch on the brakes. Even 160mm rotors give me plenty of stopping power, and only occasionally do I overheat them... and I generally have to try and overheat them.

  8. #8
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    160 F/R and I weigh in at 210 lbs and ride long socal fire roads up/down and happy with it.

  9. #9
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    Quote Originally Posted by pimpbot View Post
    If you used a brake rotor combo on 26ers that worked for you, do that on your 29er.
    I'm not sure i'd completely agree with you on that. On my 26'er I felt fine on 160mm rotors, but on my 29er they were much more borderline with a similar brake system and the same size rotors. Technically the 29er wheel has more leverage over the brake because of the increased diameter, and i'm assuming that's the reason for the question.

    With that in mind, i guess my answer would be: if a particular combo was borderline for you on a 26er, go bigger with a 29er.

  10. #10
    1*14*29*2.1 & 1*1*29*2.4
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    I haven't found any differences in 29 vs 26 but I run 180 for mtb just due to a couple of brake fading descents here. 180 seems to help with that otherwise I would not have bothered...I weigh 75kg.

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    13 Lenz Lunchbox punkass

  12. #12
    ballbuster
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    Quote Originally Posted by Porch View Post
    I'm not sure i'd completely agree with you on that. On my 26'er I felt fine on 160mm rotors, but on my 29er they were much more borderline with a similar brake system and the same size rotors. Technically the 29er wheel has more leverage over the brake because of the increased diameter, and i'm assuming that's the reason for the question.

    With that in mind, i guess my answer would be: if a particular combo was borderline for you on a 26er, go bigger with a 29er.
    More leverage (slightly) but with a slower traveling rotor (slightly). At the end of the day, it's just simple physics. You're turning momentum into heat with the brakes... Doing work. Since the bike and rider weigh pretty much the same (maybe add one pound or two with a 29er with a total weight of around 220, give or take... So 0.5% to 1% difference), your brakes are doing the same amount of work to bring your speed from whatever to zero.

    Conservation of energy, like. Simple physics.

  13. #13
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    You're just wrong about this one. Think of it like a lever pivoting around the hub. Bigger wheels exert more force because of the bigger diameter wheel so you need a bigger rotor to balance that force.
    Yes, you use the same amount of energy to slow you down but that's where the similarity ends. Next are you going to tell us that gearing makes no difference in the necessary force exerted to get up a hill? The energy expenditure is the same so the force in all gears must be the same right?!

    To the OP, it is pretty common practice to go up one size in rotors when switching from a 26" bike to a 29er unless you felt that you were over-braked on the 26er.
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  14. #14
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    +1 on Bog's analysis. The resultant force required to stop a wheel with a shorter lever arm (ie smaller diameter rotor) is indeed greater on a for a larger diameter than a smaller.

    To that end, on my Epic, I was running crappy Avids with 185/160. I'm 235ish geared up. After a few 10 mile descents they would fade horribly. I then tossed a 203 on the front and moved the 185 to the rear. The larger rotors made a tremendous difference! Then I found a deal on XT's and swapped. WOHA! Now I'm considering switching back to the 185/160 combo. Talk about true 1 finger breaking. Modulation is very nice, but I am way over braked. That's okay...More is better right?

  15. #15
    ballbuster
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    Quote Originally Posted by bog View Post
    You're just wrong about this one. Think of it like a lever pivoting around the hub. Bigger wheels exert more force because of the bigger diameter wheel so you need a bigger rotor to balance that force.
    Yes, you use the same amount of energy to slow you down but that's where the similarity ends. Next are you going to tell us that gearing makes no difference in the necessary force exerted to get up a hill? The energy expenditure is the same so the force in all gears must be the same right?!

    To the OP, it is pretty common practice to go up one size in rotors when switching from a 26" bike to a 29er unless you felt that you were over-braked on the 26er.
    Actually, it does take the same amount of energy. Just when you use a lower gear and you go slower, you're spreading out that energy over more time. If you're going the same speed, you're turning the cranks slower but you have to use more torque over a smaller distance at the pedal to do the same job.... Where your muscles are way less efficient. That is, measuring at the pedals. Of course your muscles use a lot more energy because they are wasting more as heat right in the muscle, and not converting it to work that is used to push the bike.

  16. #16
    bog
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    I'm exactly the same weight as you and I found that 180/160 doesn't leave me with enough braking power on the back wheel on long descents. I tried that for a while (as well as 203/180 which was too grabby up front) and have settled on 180/180 on both of my 29ers and I'm really happy with that. There is a tad bit too much power on the rear tire but it can actually help if I ever need to slide the rear wheel a bit (not destructive skidding on sensitive trails, but rear wheel steering on gravel roads and trails that can handle it).
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  17. #17
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    Great info.
    I'm 135LBs and we don't have long decent here.....I think the 160mm rotor will do the job for me.
    Thanks...

  18. #18
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    180lbs kitted up. Tallboy LTc and I run 180/160 w/ a 4-pot Saint (M820) caliper up front and a 2-pot XTR (M985?) caliper on rear. I also have a backup set of customized Elixir w/ a 4-pot Code caliper for front and a 2-pot Elixir CR caliper on back.
    I have an identical 180/160, 4/2-pots set up on a Blur LTc.

    My trails are at the base of the Rocky Mountains...so typical ride is big up/big downs.
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  19. #19
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    What is the best rotor size for the 29er ? Is it 160mm or 180mm ? Thanks...

    Quote Originally Posted by Pau11y View Post
    180lbs kitted up. Tallboy LTc and I run 180/160 w/ a 4-pot Saint (M820) caliper up front and a 2-pot XTR (M985?) caliper on rear. I also have a backup set of customized Elixir w/ a 4-pot Code caliper for front and a 2-pot Elixir CR caliper on back.
    I have an identical 180/160, 4/2-pots set up on a Blur LTc.

    My trails are at the base of the Rocky Mountains...so typical ride is big up/big downs.
    Interesting setup. Why not go with the Saint/Code on the rear, too? Do the others modulate better?
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  20. #20
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    What is the best rotor size for the 29er ? Is it 160mm or 180mm ? Thanks...

    175lbs undressed, tallboy LTc in norcal. Ride pretty gnarly trails aggressively, big up, big down. Race enduro-open cat 1, usually top 1/4 of field. I run xtr 980 brakes with 203mm up front and 180mm in back. Started with 160 front and rear and finally happy with the 203/180 setup after warping and cooking the smaller sizes. All rotors are the xt 6 bolt ice tech.
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  21. #21
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    I am 220 and went 180 rotors and Hope M4's front and back, can stop on a dime.

  22. #22
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    140 up front and 203 out back. More aerodynamic this way.

    But in the real world, I'm ~210 and have 180 up front and until my ride today had 160 in the rear, just went up to 180 as I didn't feel the bite to be sufficient with the 160's. I'm happy with the 180's F and R as the bite is extremely strong with little lever pressure.

  23. #23
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    29er's roll faster downhill, so if your braking downhill you need more power.

    I went with 180's f/r, with hope m4's and they have been fabulous
    I weight 220 geard up and ride hard

    The rear was a little overpowered, So I flipped the back tire in the opposite direction.

    Now I get a lil fishtail action instead of stopping and its perfect!

    Go with the 180's youll be staisfied
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  24. #24
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    Just a quick bit of input. I used to ride pure xc rolling singletrack, but have been riding more all-mountain in the last year or two. What I mean is that the uphills have gotten longer, and the downhills longer, steeper, and faster (and a mix of technical and non-technical). I ride a fairly stock tallboy ltc (180 rotor in the front, 160 in the rear). A few months ago, I did a lift served ride (not my norm) and a mix of technical and non-technical downhill that left me REALLY wanting more braking power all around.

    I wasn't really sure though if upgrading the rotors would be overkill for the rest of my riding since that ride was on the extreme end of the downhill stuff I do. Anyways, upgraded front to a 203 and rear to a 180, and LOVE it all around. It gave me wayyyyyy more modulation room even in xc rides. I don't have a clue of the weight penalty, but I thought it was a great (though small and easy) upgrade.

    Summary: upgrading the rotor size didn't present any problems (like brakes that are too touchy or powerful), but did give me TONS of modulation. It will definitely be my standard set up on future 29ers.

  25. #25
    transmitter~receiver
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    Rotor size is not the only variable.
    Brakes and brake set-ups (variations of rotor design and brake) vary widely in power, modulation, etc.
    Larger rotors offer more mechanical advantage, which may or may not be a good thing, and better heat dissipation, which may or may not be relevant.
    Quote Originally Posted by pvd
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