Recently comparing 2 bikes i was wondering about the effectiveness of massive brakes off road.

bike 1 has very progressive 180/160 brakes and the other had very good 200/180 brakes. I allways find the limit of braking is in the tire to dirt and not the actual brakes themselves. An i doing something wrong? why the need for massive brakes?

Heat dispersion.

There is truth in the ‘heat management’ argument.

Bigger/heavier discs don’t get as hot for the same energy input.

However on a mountain bike we have lot’s of airflow/cooling passing over the disc hence it’s less of an issue than on a car (for instance).

But there is no other advantage in bigger brakes. Once you can lock the wheel you have sufficient power and modulation is a tuneable attribute – changing pads, lever lengths and hydraulic ratios can create more or less modulation on the same brake system.

Heat dispersion and how hard you have to pull on the brake lever to get a certain amount of braking.

I use a front 203, don’t need it, 180 is more than adequate but I find the 203 needs a little less effort which is good on long descents/stages. And it gives a load of overhead/margin for failure, I did a day at BPW on half-functioning brakes but because my brakes are way stronger than I need normally, half-functioning was enough. 160 on the back though usually.

Oh, and also my new bike won’t take a 160 rear! What’s up with that? Stupid imo.

Quite like the 203 on the front of the Voltage I tend to bury the bike into corners turn it and fire 🙂 it out

I try to minimise the time spent braking and big brakes work well for me.

Zees on the HT have been a revelation

I took my weight weenie escapades a step too far a few years ago…went form 203-180 to 180/160. Total disaster. You don’t appreciate good brakes till they’re gone.

I hardly use my front brake, but it’s got a 203 on it, when I use it generally means I want to stop, so I want to be able to stop…

But there is no other advantage in bigger brakes.

I disagree, once you work out how much more grip a decent / soft compound tyre has on the surface you are riding , you can really haul on the anchors- without skidding. Big rotors very useful on difficult/steep/fast, they also offer more modulation.

I have 203/180 (and 2015 Deore brakes) on my hardtail.

I’m not a ‘weight weenie’ and am more interested in power/performance than weight.

I can’t imagine a scenario when I’d need more braking than this set up can provide.

Not my words but from an ex railway braking engineer, now an aerospace braking engineer, I know who wrote about this to me recently.

The primary advantage with larger diamater discs is leverage.
There are also significant benefits in heat management, and increased frictional losses due to swept length.

I appreciate its “appeal to authourity” but he does know about brakes..

Bigger discs creates more leverage or power. You don’t have to use the brakes as on off switches so scrubbing same amount of speed off as a smaller disc but with less effort at the bar. All helps with control and less forearm pump. Extra power in reserves for when you need it.
Tyre grip is always the weak point but as you brake weight is transferred to the front increasing the grip you have, opposite for the rear end which relates into bigger discs on the front compared to rear.

more difficult to bed in the pads and prevent glazing with bigger rotors.

love the percieved difference between very progressive and very good 🙂

I put 203mm on the front and back of my bike. Used to get the odd bit of brake fade on the rear with 180mm so thought for the extra few grams it was worth it. Can’t see a reason why you wouldn’t go for the largest rotors you can fit unless you are an XC racer or something.

As a Clydesdale sized rider I find that anything below 180mm disc they just fade/ overheat on any decent high speed descents and pad life is reduced as is the life of the calipers in the case of Hayes brakes.
I certainly would not do an uplift day without at least a 203mm on the front and 180mm on the rear but am fortunate to have speccd my uplift/Alps bike with floating twin rotor Hope V4s and can still single finger brake by the bottom of any decent, ie no arm pump issues or brake fade. Pads last like pads should with this set up.
The downside of course is that set up is very heavy compared to my hard tail 180mm at each end cheapo brake set that at the bottom of a big fast decent I may end up two finger braking because of the fade issues.
Ultimately if you have to compromise ie can’t run two bikes for very different riding styles you have to either compromise on out and out stopping ability at the bottom of the hill/weight/cost/durability of pads….same as any other componentry on a bike.

If you think about it bigger discs offerless leverage. They effectively shorten the distance from tyre to caliper.

Yeah, if you think about it incorrectly 😉

ex railway braking engineer, now an aerospace braking enginee

Classic…quoting from experience pretty different to bikes…

Yes. I’ve got 203s on the front of both my bikes (FS 160mm tank and a 140mm HT). I know I don’t need them, ’cause I’m not quick enough, but I’d rather have too much brake just in case than not enough- live to fight/ride another day! I’ve been on a motorcycle with cooked brakes and it’s not fun with leathers and a FF lid on, stuff booling down a hill in t-shirt and shorts at 20-odd mph and not being able to slow down! 😯

If you think about it bigger discs offerless leverage. They effectively shorten the distance from tyre to caliper.

Hmmmm…are your discs attached directly to your tyres?

A caliper applies the same force to a disc regardless of where it is. A larger disc has greater leverage and therefore needs less of the caliper’s force to give the same braking effect as a smaller disc. Therefore with a larger discs you get better braking and more control. You’re making better use of the braking force the caliper can provide

The only issue with going too large is discs and pads not getting up to temperature often enough and thus increasing pad wear. 183/160 works well on my hardtail but I had to go to 183/183 on the full sus.

For the hard of thinking compare the disc to a cassette. Which gives more leverage (and makes it easier to get up hills) – the big cog or the little cog?

It’s much the same thing when put in reverse and used to slow you down. There’s also the added advantage of more contact distance for any given amount of travel meaning, in theory, better modulation.

As people above have said there are very few downsides to big brakes – what is the weight difference between sizes anyway?