Do you need to use bigger rotors on a 29er?

Following on from my post on another thread about how my Hope X2s lack power
I sort of got thinking whether or not a 29″ wheel needed a bigger rotor for the same stopping power over a 26″ – everything else being equal

Did a google and found this
Which really doesn’t come to a clear conclusion

Anyone got any ‘real world’ experience on this before I go away and buy a bigger rotor and adaptor?

26 vs 29 doesn’t make any difference IME. I run 180s on my Soul (26) and Scandal 29er cos I am a bit fat.

I’m no physicist but I’d be surprised if a slightly heavier, larger radius wheel makes any perceptible difference when slowing 100kg of bike and rider.

probably. (Rob Warner can explain why better than me 😉 )

proportionally yes, 160’s can look a bit silly with the clown wheels 🙄

functionally not ime

Yes, the maths is very straightforward. For the same braking power for a given setup and force at the brake lever, you need proportionally bigger rotors.

29erkeith. You’re wrong on the heating issue. Same amount of kinetic energy (OK, fractionally more because a 29er is slightly heavier) to get rid of = same amount of heating.

I’m no physicist but I’d be surprised if a slightly heavier, larger radius wheel makes any perceptible difference when slowing 100kg of bike and rider.

That’s fine so long as you also agree that changing rotor size on any bike also makes no perceptible difference.

I should also add, I have the same brakes on two of my bikes – 29er with 203/180 and 26″ with 183/160. Similar braking power. It was noticeable when I first built the 29er with the 183/160 combo that the power was slightly less than the 26″ bike

I have 29″ (or 700c) rotors on my road bike and they’re nowhere near as powerful as the 160 rotors on my 29er 😯

😉 They’re not rotors though. they’re braking surfaces.

I have 29″ (or 700c) rotors on my road bike and they’re nowhere near as powerful as the 160 rotors on my 29er

My 700c wheeled road bike only has rims that are ~25″ diameter, what the hell is it you have?

& you missed this bit ……….

everything else being equal

I experience no perceptible difference in braking power on the 29er with the same size brakes. Not that I have a 26er now.

Don’t worry about it.

Running 183 and 160 Tech X2’s on mine with no issues.

No,use 160mm discs on my 29er & always have done.Maybe if you got up to silly high speeds it might but otherwise nope,it’s about the same…

For an extream example, BMX brakes are shocking, whereas 29’er v-brakes are pretty potent.

29er riders don’t touch the brakes do they? I mean they’re only meant for towpaths riding anyway

That would also mean that rim brakes would be better than discs in general – bigger braking surface so it would cool better,directly on the rim of the wheel instead of in the middle,so no loss of braking energy through all the spokes ……………….Actually I may be on to something…………….Oh hold,they’re ****’ useless when it gets muddy aint they……… 😕

29er riders don’t touch the brakes do they?

Well yes, it was only whilst trying them in a moment of madness that I thought they may be a bit lacking
I’ve quarantined the bike for 48hrs just in case a wheel may explode as a result

For an extream example, BMX brakes are shocking, whereas 29’er v-brakes are pretty potent.

piss poor example more like! seeing as BMX V brakes are also pretty potent.

I went out for an hour on mine last night on some pretty flat local trails, so no need to touch the brakes. Got home & once the bike was back in the house the wheels still exploded.
There is no explanation for this phenomenon, but it is one that I think we should all take more seriously.

Clubber has it but the 10 ish percent isn’t noticeable IME.

Something along the lines of:_ To stop in the same distance at the same speed on a bike approximatelly the same weight will require the same amount of energy to be disipated” however “As a smaller area of rotor is being swept due to the smaller amount of rotation more friction will be required at the rotor”

so you probably just pull the brakes a bit harder, I can’t see lack of power being an issue with any decent brake, and you should get better modulation too!