Do I *need* bigger rotors?

I’ve just taken delivery of a new wheelset and now need to source some six bolt rotors.

For a number of years I’ve been using centrelock resin only rotors from Shimano, and they have been OK. I can stop, modulation is good, but there are times when I’m on faster trails that I find my brakes just don’t have the power.

Now I need to buy new rotors anyway I’m considering going bigger. Unfortunatly it looks like the RT66 in 203mm are either out of stock or suprisingly expensive (as in for a tenner more I can get ice tech). Should I stick with 180mm? Or go nuts and buy the 220mm from Merlin that are dirt cheap right now? Any other brands which are worth spending more on?

Should I just suck it up and get a 4 pot rear?

I have entered analysis paralysis, so hopefuly the STW hive mind can steer me right…

SLX 71xx brakes 4 pot front, 2 pot rear.
Wheels are 29 front 27.5 rear (if that makes any difference)
Rider is probably just over 70kg laden and bike is sub 15kg.

Are you looking to fit a bigger rotor for the rear? Sorry not clear in your post

TRP rotors have been cheap in a few places recently, they’re thicker than Shimano ones and definitely better than the resin only ones

What sort of riding are you doing?

I run 220/200 for the Alps. 200/180 for UK.

Bigger rotors make a noticeable difference to me.

203/180mm on MTB and 180/160 ilon commuter bike

I doubt in a 85kgkg rider/bike you will feel the difference in weight.

Go big

Bigger and better brakes make you ride faster.

Merlin were selling the thicker Magura rotors pretty cheap recently (some notionally for e-bikes but…).  Worth a look.  As well as (I’m sure) good braking & longevity, I’m hoping they’ll stay straight more easily & avoif ting-ing so much as my old ones

If compatible with frame and fork I’d go 220mm, total bargain at a tenner from merlin and not a bad weight at 185g, I use Uberbike 220mm 2mm thick ones and they’ve been perfect so far.

I’ve not tried 220 myself but I’ve read that they could be too catchy for lighter riders and depending on how/where you ride also not get up to a decent working temperature.

TBH there’s 2 contradicting and equally valid and true schools of thought, one is that more brake = better, and that’s pretty self explanatory, you can in theory stop harder, you probably get a bit more reliability and a bit longer life since all the parts are less stressed, and it can be quite a bit less tiring since less finger creates more effect.

On the other hand I still feel like less rotor = better feel, but also that for normal bikes absolutely any quality brake set up properly has way more than enough power, and the only limit of stopping power is how well you can actually apply it and manage the brake vs grip. Basically since I replaced the cheap tektros that came on my first modern bike, I’ve never felt like “I wish I had more brake power” even once, but I’ve always been happy to add a little more subtlety and feel

I mean, I’m using the same model 15 year old formula brakes on my enduro bike and my trailbike (and my fatbike, and my commuter) as I used to use on my dh bike, with cheap basic pads. 160 on the back gives loads of subtlety and fine control but still has pretty effortless power and zero fade issues, 203 on the front is definitely more than I need most of the time but tbh I don’t feel much drawback either so I’ve tended to stay bigger as I know it’s got plenty in reserve for harder use days like uplifts or holidays. Admittedly, I am light so there’s less heat stress there but equally I’m comfort brakey.

So it’s definitely not right or wrong, it’s what you prefer. But it does seem to me like these days a lot of people feel like they <must> have 4 pots and massive rotors and vented pads and all that and it’s just a bit weird to me

FWIW I’m 106 kg.

On my 16 kg bike with 4 pot Avid Code frankenbrakes I use 185 front and rear all year round for all types of UK riding.
When I take it to the Alps I use 203 front and rear. I’ve had a couple of fluid boiling issues in the past and it is a bit scary tbh.

Braking technique has a huge effect. It took me a while to learn that dragging the rear brake is a really silly thing to do.

If it were me, I’d go for a bigger rotor and also try different pad compounds. I run 200 mm 4 pots front, 180mm 2 pots rear with sintered pads. Basically, there’s a trade off between high-speed braking power and low-speed modulation so you need to experiment and find what works for the riding you do. On my MTB, I go for the power end of the spectrum, on my commuter, modulation, with 160 mm rotors front and rear and stock Shimano resin pads.

Are you looking to fit a bigger rotor for the rear? Sorry not clear in your post

Yes, I’ve currently got 180 F/R so am considering going up a size on both.

What sort of riding are you doing?

It’s a good mix. My day to day (other than the usual bimbleing) is shorter but fast built/groomed trails with jumpy stuff thrown in. Some occasional trips to the dark peak as well as a few days a year at FOD. I’m expecting to visit some welsh bike parks this summer.

TRP rotors have been cheap in a few places recently, they’re thicker than Shimano ones and definitely better than the resin only ones

Do thicker rotors cause setup issues with Shimano that is built around 1.8mm?

I’ve not tried 220 myself but I’ve read that they could be too catchy for lighter riders and depending on how/where you ride also not get up to a decent working temperature.

I’ve read the same, which is probably the main reason I have not already bought a set! I do wonder if there is a ‘best of both worlds’ argument nestling in there somewhere. If they are not up to temp maybe they would be less grabby, and if they are up to temp, I must be going fast enough. Probably just stupid mental (in)agility on my part though.

Braking technique has a huge effect. It took me a while to learn that dragging the rear brake is a really silly thing to do.

I am a guilty of this and it’s a habit I’m trying to break. Unfortunately doing so is where I found my ability to bleed off speed on fast trails is currently mildly compromised.

So it’s definitely not right or wrong, it’s what you prefer. But it does seem to me like these days a lot of people feel like they <must> have 4 pots and massive rotors and vented pads and all that and it’s just a bit weird to me

Only quoted the last paragraph,  but read and considered all, Thankyou, a good insight. I think I’m looking for the Goldilocks zone of nice feel, ample power and reduced fatigue. It’s probably time to spend some money working out what I prefer. Discs and pads are still cheaper than new brakes!

If it were me, I’d go for a bigger rotor and also try different pad compounds. I run 200 mm 4 pots front, 180mm 2 pots rear with sintered pads. Basically, there’s a trade off between high-speed braking power and low-speed modulation so you need to experiment and find what works for the riding you do. On my MTB, I go for the power end of the spectrum, on my commuter, modulation, with 160 mm rotors front and rear and stock Shimano resin pads.

Thanks. This helps me come to the realisation that I just need to put the time into working out what I prefer and what works for me. I was hoping to avoid rabbit hole #2 which is pad compounds but looking kinda necessary! I’ve also got 160mm on my bimbleing hardtail and they are more than enough for a lot of things.

I’m 70kg and ride tweed valley steep and annual trip to alps. I’ve 200f 180r on all my bike including the ebike, all have 4pot fronts ebike and ht have 2 pot rears. I have maguras usually mt7 but the mt5/trail on the ebike. Mixture of hope discs and the fancy magura ones, which are very good.
New bike is 200 f&r with the thicker sram discs, I’m about to swap a set of mt7s onto it.
To be honest for me 200/180 is probably a good mix (I took 220/200 off the ebike).

I am now super curious about the non Shimano rotors though. Looks like the 2mm ones are more readily available from other suppliers. Does the extra thickness make setup tricky – again I’ve read conflicting reports here.

“ But it does seem to me like these days a lot of people feel like they <must> have 4 pots and massive rotors and vented pads and all that and it’s just a bit weird to me”

What’s weird to me is that adult males that ride MTBs vary so much in weight (and add women and teens and the variance is even more) yet we’re all using almost the same rotor sizes.

Convert rotor sizes in mm to weights in lbs and you’ll see what I mean! Conveniently I’m 180lbs and have a 183mm rear disc on my hardtail. But what if you’re under 160 or over 220lbs? That’s not exactly a big weight range and some bikes won’t take less than 180 and/or more than 203 on the back anyway!

Personally I use 200 f&r on the trail bike (Hightower),  Hope tech 3 E4 brakes and 220f 200r on the ebike which is heavy (Whyte E-160 which is just under 27kg)) which are Code RSC and I’m under 11 stone. When I went to buy the 200mm hope rotor for the trail bike the guy in the shop was adamant I shouldn’t need to go 200mm on the rear and went into great detail about why so I walked out and bought it from another shop. I’m more than happy with the extra stopping power although I might not ‘need’ it all the time

I’m 96kg. My 180mm rotors overheated quite severely on steeper descents. Changed to 203mm and had no problems.

While we are on the subject of size does rotor size make any difference to brake noise? Obviously there are other factors but somebody with the same bike advised me to go down to 180 from 200 to reduce noise and it worked.

“While we are on the subject of size does rotor size make any difference to brake noise?”

Temperature does so rotor wise will.

Thanks everyone. All read and digested so far.

I have a temporary reprieve as I’ve just discovered my hardtail rotors are 180mm 6 bolt instead of 160mm and of the same type as my current ones. Means I can ride my new wheels sooner which is good… and I have more time to consider my options.

TRP slate evo look interesting… and this is why I hate internally routed frames 😠

75kg 160mm rotors front and rear. Stop well every time 🤷‍♂️

200 front, 220 rear for the Alps? That isn’t a typo https://enduro-mtb.com/en/rotor-size-myth/

I quite like enduro mag and trev’s usually worth listening to but that article was ridiculous. There might be a basically reasonable idea in it for some riders and it even starts out that way, “this could be the solution for many” but then they decided to try and make it universal and clearcut and it turned into april fools’. “For aggressive enduro riders with large 29” wheels, 200 mm rotors are mandatory”, ffs.

I had 2.0mm SRAM HS2 with with XT M8100. There weren’t clearance issues with pads.

Id stay away from Icetech, they warp with heat, then have to true them (RT86). Sometimes they go back, but most of the time I’d get ching ching ching during or after a ride.

larger rotors do provide more braking torque due to the braking surface being further away from the centre of the wheel (more leverage). They also should dissipate heat better due to the larger surface area (which will improve braking performance in some situations).

Do you ‘need’ bigger rotors? Maybe not for the type of riding you’ve described (doesn’t sound like you are doing really steep stuff?) However, you could be a heavy rider, have poorly performing brakes or just have poor braking technique. Larger rotors may provide some improvement in those scenarios but may not be the only solution.

Other than cost (you’ll also need new adapters), the trade off for increasing rotor size is fairly small though (slight increase on rotational weight) so I’d probably get at least a larger one for the front.

I’ve never been convinced the rotor pattern makes any real difference. You can pick up SRAM centreline rotors shipped from UK at sub £15 for 203mm and cheaper for other sizes.

They may be OEM. they may be fakes. But they’re cosmetically identical to ones I’ve had previously. Either way ultimately it’s a steel disc and I’ve had no issues with the ones I’ve bought.

I went from 200/180 to 220 front and rear and really liked how it felt, running Code RSC’s which I already liked, I found the bigger and thicker rotors gave a better modulation and feel IMO.

Unless you’re getting brake fade you don’t need bigger rotors. What most riders need is a  stronger grip so they can pull the levers harder.

ebikes with electric power boosted brakes are coming.

I quite like enduro mag and trev’s usually worth listening to but that article was ridiculous. There might be a basically reasonable idea in it for some riders and it even starts out that way, “this could be the solution for many” but then they decided to try and make it universal and clearcut and it turned into april fools’. “For aggressive enduro riders with large 29” wheels, 200 mm rotors are mandatory”, ffs.

they certainly get a bee in their bonnet about rotor sizes. every review where the bike doesn’t come stock with 200 front and rear gets downvoted for brakes being inadequate or dangerous.

they may all be a bunch of 200lb dudes riding sustained long and steep alpine descents every ride but they do seem totally unaware that maybe, perhaps, other people don’t.

even trail bikes get panned for not having double down casings as a minimum.

What most riders need is a  stronger grip so they can pull the levers harder.

Or, what riders needs is bigger rotors and 4 pot brakes so they don’t have to pull harder…

they may all be a bunch of 200lb dudes riding sustained long and steep alpine descents every ride but they do seem totally unaware that maybe, perhaps, other people don’t.

Those guys are the most Enduro people I know to exist. Which seems appropriate.