My new bike build is progressing nicely and i need to get disc rotors to go with my new shiny groupset. Now i’ve never ridden discs on a road bike, and these are my first new hydraulic brakes in well over 10 years, and they were Avid Elixir’s.

What size rotors would you be speccing, i’m pretty sure i won’t need anything more than a 140mm on the rear, but i’m undecided between 140 and 160 on the front.

Any advice gratefully received.

Do your forks allow a 140 front? Many don’t.

I’d always go 160 front, it’s not just the power, I find the larger rotor much easier to modulate the braking on

Really? Not heard of that before, i was under the impression with the flat mount system that it just depended on which way up you mounted the mounting plate.

@momo that was my thinking, i’m just totally unaware of the performance of these new brakes.

I think I have 160mm front and rear on my Cube and they are amazeballs. I’m 88kg and I have hills. There’s a 45-50mph descent on my local loop with a right turn half way down and I keep going faster and braking later just to see how fast I can stop. I’ve not found a limit yet. This on a descent where I used to drag the rim brakes all the way down just to have any confidence I could make the turn.

Lol, just checked a couple of recordings of the same descent – 48kph old bike, 68kph new bike, and I wasn’t trying on that most recent attempt.

I would go larger just for heat dissipation. The weight increase is likely to be negligible.

I’m experimenting with 140mm front and rear on my CX bike (84kg here), logic being I never brake hard anyway and smaller rotors might actually heat up MORE which would assist in wet weather scenarios (e.g. drying rotors off quicker). I’m also curious to see if they squeal less as they should be stiffer?

I have a 160mm rotor on order as backup though…

My gravel bike has 160 fr&rr, they don’t lack power, in fact they are pretty much perfect.
I’m 125kg.
If you’re a fair bit lighter then 140 should be perfectly viable.
I have no idea if they’ll fit though, sorry.

I’m also curious to see if they squeal less as they should be stiffer?

Probably just squeal a different note 🙂

I have a feeling that ice-tech rotors and sintered pads won’t squeal. This is based on the fact that my cheap rotors squeal but also flutter at low speeds, and cheap rotors also fluttered at low speeds on my MTB but ice-tech ones didn’t.

Just built up a new disk road frame and went 140/140 mainly because im 65kg but what influenced the decision the most was an eBay voucher meant they were cheaper!
Went for ultegra disks but I’m using sram brakes.
Unless you are a pie eater I doubt you will feel underbraked using 140 on the front.

I’m 82kgs ish with Shimano hydraulic brakes. Think they are rs785 calipers or something like that (flat mount front / post mount rear) with Ultegra Di2 levers. 160mm disc front and rear. I wouldn’t downsize personally – there are a few hills locally where they work fine but I just feel like they’re having to work really hard.

Maybe my accidental move from the original sintered pads to organic replacements hasn’t helped my cause as I’m sure they felt more confidence inspiring before that change (old ones were worn out and I was going to be bleeding brakes anyway as swapping from mechanical to di2 stis).

Deffo go 160mm on the front, 140mm on the rear should be fine for a road bike

Just built up a new disk road frame and went 140/140 mainly because im 65kg but what influenced the decision the most was an eBay voucher meant they were cheaper!
Went for ultegra disks but I’m using sram brakes.
Unless you are a pie eater I doubt you will feel underbraked using 140 on the front.

Same weight, same disc sizes, mine are XTR centrelock though – got them for £20 each on eBay 🙂 !

Probably just squeal a different note

Hmm…. good point! However hopefully it will fall out of the resonant range that turns it from a slight squeak into a howl, or something (IANAcoustician)

Deep down I just wanted to try 140mm front and rear, I just love the look of tiny discs 😎

I have 160/160 with the absima airotors- they’re probably lighter than a 160/140 from most manufacturers. That’s with the Hy/rd tektros. Tons of power, great feel, and I’ve never managed to overheat them. Probably I could go smaller but I did the same as I do on mtbs and went with a bit more than I probably need, for margin for error

But then I don’t do any Epic Descents- perhaps if I was to take this setup which works great for me and went to the alps or even a big highlands pass I’d die.

I’ve got 140/140 Ultegra Freezatech rotors on my road bike with R8000 brakes and they’re superb, I can’t see why I’d ever want any more power.

On my gravel bike I have 160/160 with GRX brakes as that’s what it came with, so I don’t see the point of changing.

My 29er FS XC bike has 160/160 XTR rotors with M9100 race brakes and thats more than enough power for me.

I’m not exactly light at the moment at 78kg

Thank you for all your replies, i’ve decided on 140mm front and rear.