As per title really.

I’ve just gone 180/160 same as my 26er was, but sometimes feel I’m bot scrubbing speed quick enough compared to before.

Seen mention once or twice of the need to upsize, any truth in this?

No

No.

wheel size: bigger

fork travel: shorter

head angle: steeper

disc size: same

overall: better.

No

Nope

So No… I’m going quicker why would I want less braking power? 😉

I went smaller. Bike came with a 180 front, replaced it with a 160

Yes and there’s a valid reason why. Bigger wheels turn slower for the same speed so taking work done (eg amount of kinetic energy your brake is converting to heat) = force x distance, if the force (how hard you pull the lever) is the same then to get the same work done, you need the distance to be the same. Since the wheel is turning slower, you need to increase the size of the disk to get the same distance.

Of course that many are fine with changing to a 29er without upsizing is probably just down to the fashion to have everything sized up – eg bars, travel, rotor size – beyond what’s really ‘necessary’.

no

I went smaller as that’s how the bikes came. My 26 Stumpy fsr is size L & came with 200/180’s. My 29 Stumpy fsr is size M and has 180/160.
No problem stopping now after brakes were bled by LBS but ate the rear (organic) pads before completing lap of Dalby. Sintered now fitted!

Yes, for the reason Cougar explained, 140mm wasnt enough anymore!

Pretty resounding then!

My understanding was as ‘clubber’ has said, but wondering what other peoples experience was.

Had XT before and Deore now so that could be playing a part.

In no rush to start spending money anyway.

no

Smaller here

Yes- 185mm Front 160mm rear- I would recommend it. Using anything smaller on the front I’m slower- I like the improved feel and power and I’m less likely to cook the brakes. I really don’t see the point of trying to save a tiny fraction of weight on a brake by downsizing, but the majority of people don’t ride as fast as me 😉

thisisnotaspoon – Member
Yes, for the reason Cougar explained, 140mm wasnt enough anymore!

Awaits cougars response to see if thisisnotaspoon can look into the future!

What are Fridays Euro lottery numbers? 😀

The answer surely depends on what is the limiting factor – energy dissipation or mechanical force.

If it’s energy dissipation then there is no difference unless the combined weight of the bike and rider are different as you are still dissipating the same energy.

If it’s the mechanical force that can be applied then a bigger wheel has a larger moment arm so is thus more capable of overcoming the friction that can be applied by the brake (depends on the Coef. of friction and pressure).

However there is also the mechanical grip available so if both bikes had the same mechanical grip that was unable to sustain full braking power then no difference. But if the 29er has more grip (most/all of the time) then it can take more powerful brakes but is this still up to the limit of the smaller rotor?

Another question is will the rider be going faster on the 29er?

In all honesty I would still choose brake diameter based on what the bike is used for. DH – 200ish, trail etc 180, XC race bike 160 and a size smaller on the back and this is due to a combination of energy dissipation and braking power.

That is my view anyway.

180 f+r. Overbraked on rear so changing to 160 on rear.

I could tell you but I’d have to kill you til you were dead and I don’t think you’d like that.

Same:180/160

went from hope 183F 160R X2s, to 183F 183R M4s.

I found the 29er so much quicker than my old 26er its alot easier to scrub the speed with better brakes with great modulation.

No. 160mm Shimano XTs are more than enough.

Bigger are disks are enduro, 29er are not enduro. So no.

Yes, upgraded from 180/160mm to 200mm front and rear. Worked great in the alps last year.

Didn’t notice any difference braking using xts. I do notice I’m going a lot faster!

No to op

Good summary, andyl, except that you missed out lever pressure.
To take it to the extreme, even a 140mm disc on a 36″ wheel could potentially generate more braking force than the tyre could cope with, but the lever pressure would probably be more than most people could sustain for a long descent.

I’m heavy, but I’ve got a strong grip, so 180/160 on a grown up 29er, same as I had on the old 26″ training wheels, is fine for me.

Yes….203 $ 180
29er is faster…my weight 95 to 100kgs…..equates to better and or later braking or me feeling more confident