- 29er Riders did you increase disc size?
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’.Posted 4 years agoPete BMember
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.Posted 4 years ago
No problem stopping now after brakes were bled by LBS but ate the rear (organic) pads before completing lap of Dalby. Sintered now fitted!kharimMember
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 😉Posted 4 years agoandylMember
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.Posted 4 years agoMidlandTrailquestsGrahamMember
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.Posted 4 years ago
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