# Road disks... 140mm vs 160mm rotors. And why?



## Waspinator

I’m using Shimano RT-99s, 140mm front and back. I weigh 200 lbs.

I haven’t noticed any trouble stopping. No brake fade. Nothing. I’m wondering why 160mm is becoming more commonplace now. 

What do you folks use, and why?


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## dir-t

My road bike has rim brakes.

When it came time to build my new MTB frame, I decided to go with new "stronger" 4-piston brake calipers and gave my old brake set to my wife to replace her lower-end discs. I think she ended up with a 160 mm rotor up front, whereas the old one was 140 mm.

The funny thing, I always felt my old setup worked great. She felt the same about hers. After the swaps, we both had the same reaction, "wow, I didn't think it would be a big improvement, but it is."

I'm not saying any brake system is inadequate, but sometimes you don't know what you're missing until you make a change.


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## Marc

You use larger disk rotors when you need more stopping power.

As in steeper/longer inclines (say MTB descents) or higher loads (as in say touring or on tandem bikes). My gravel/touring bike is spec'd with 160s. Which is nice when I'm hauling 13kg of bike, 78kg of myself, and another 30kg of panniers/stuff.


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## PoorInRichfield

How much stopping power you have all comes down to the tire's contact patch with the road. You can throw 500mm brake rotors on your wheels and it won't matter once the tire starts to lose it's grip. I suppose anti-lock disc brakes will be a thing on bikes at some point, but until they are, contact patch rules.

Reasons to go with bigger rotors:

Your total weight (bike + rider) is relatively high. My opinion would be if total weight is 200 lbs+, then use 160mm rotors.
You live in a hilly or mountainous area.
Your bike has heavy tires, like a fat bike, where most of the mass is far from the hub.
You ride in an urban area or otherwise busy traffic area where stopping quickly could be the difference between life and death!
Reasons to go with small rotors:

You're a weight weenie... logic and safety be damned! 
You're a light weight rider on a light weight bike (< 200 lbs total, IMHO)
You typically ride solo in rural areas where emergency stops are rare to non-existent.
You're trying to maximize aerodynamics, like on a TT bike.
I think this would be a good topic for the GCN Tech show on YouTube... do a test of a road bike to see when or if one ever actually 'needs' the larger 160mm rotors. GCN did do a video on this topic and showed shorter stopping distances with the 160mm front disc.

I weigh 167 lbs and have 140mm front and rear Shimano Ultegra rotors on my 2020 Trek Domane. So far, I haven't had a reason to go bigger for riding in the mildly hilly Midwest.


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## velodog

I've read elsewhere that the 160mm discs show an improvement over the 140's when used with mechanical discs. I'm a rim brake guy so no experience, but that makes sense to me.


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## Finx

Just generally speaking, a 160mm rotor will brake a little better and run a little cooler than a 140mm. There might also be some marginal gains in pad wear for the reasons stated previously.

The thing about this sort of stuff is, you generally don't need it... right up until you do. You haven't had any problems with 140mm rotors, and might never, but that one time you are bombing down a long fast decent and your pads and rotors overheat will be very thrilling. 

I cooked a 160mm rotor (and pads) on my first disc brake bike. Mostly due to lack of knowledge and experience (i.e. user error), but let's just say I haven't been down that hill since that day.


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## Lombard

Plain and simple - more surface area, more heat dissipation. If your fluid starts to boil going down a steep hill, there goes your braking power. Some mountain bikes have even larger rotors now.


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## QuiQuaeQuod

Waspinator said:


> I’m wondering why 160mm are becoming more commonplace now.


The technical aspects of rotor size are pretty simple, and mentioned. But the vast majority of people who buy a bike won't push their brakes to the limit where they will notice a difference.

Marketing reasons are also simple. Big rotor looks bigger on the showroom floor, so even noobs will believe that a bike with bigger rotors has "better" brakes.


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## Waspinator

QuiQuaeQuod said:


> The technical aspects of rotor size are pretty simple, and mentioned. But the vast majority of people who buy a bike won't push their brakes to the limit where they will notice a difference.
> 
> Marketing reasons are also simple. Big rotor looks bigger on the showroom floor, so even noobs will believe that a bike with bigger rotors has "better" brakes.


Admittedly, on a road bike, I like the look of smaller (140mm) rotors.

On my mountain bike, I like the look of larger rotors. I run 203mm rotors on it.


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## Bremerradkurier

Are tandems starting to run dual calipers/rotors on the front wheel full moto style?


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## harryman

The physics of it have already been well covered, but what you need really comes down to how much you weigh, and the terrain you ride. I find that road bike discs get the worst abuse compared to mtbs because while the grades aren't always as steep, they are much more sustained, and the speeds are higher. Where I live in Colorado, you can come into a switchback at 45-50mph on the road, and repeat that over and over. On a mtb, you brake more often, but in shorter bursts and at half that speed. Accordingly, I run the biggest rotors I can fit on a road bike and can still easily turn them purple and get the pads hot enough to start to lose friction. Which, is easily remedied by opening them up for a second, but still. I'd happily run 185mm rotors up front if I could get them to fit. 

If you live somewhere with rolling terrain and no long sustained descents, 140s would be ok if you're light and 160s perfect for everyone else.


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## mtrac

I run 180 front and 160 rear on my commuter. The only thing I can add to the other comments is that the mfr won't recommend anything it hasn't tested.


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## aclinjury

harryman said:


> The physics of it have already been well covered, but what you need really comes down to how much you weigh, and the terrain you ride. I find that road bike discs get the worst abuse compared to mtbs because while the grades aren't always as steep, they are much more sustained, and the speeds are higher. Where I live in Colorado, you can come into a switchback at 45-50mph on the road, and repeat that over and over. On a mtb, you brake more often, but in shorter bursts and at half that speed. Accordingly, I run the biggest rotors I can fit on a road bike and can still easily turn them purple and get the pads hot enough to start to lose friction. Which, is easily remedied by opening them up for a second, but still. I'd happily run 185mm rotors up front if I could get them to fit.
> 
> If you live somewhere with rolling terrain and no long sustained descents, 140s would be ok if you're light and 160s perfect for everyone else.


^This.

Road bikes can really get up there in speeds. One could really put a lot of heat into a braking system on the road, MUCH more compared to mtb, reason is because mtb tires will lose traction way before the brake system gets hot, where as on the road, the road tires (in spite of their skinnier size) can really allow a lot of braking fore before they will slide out.

Also, one thing I haven't seen mentioned in here is that a larger rotor will alow for a better modulation (everything being equaled).

However, a larger rotor does have its drawback too, it's easier to warp and get distorted (thus causing pad rubbing that you will not be able to get rid off unless you buy a new rotor). I find that when the rotor gets to the 180mm range and above, that's when the noise that it makes (when it makes it) also tend to get amplified compared to a smaller rotor.

Another reason to go 160mm front and 140mm rear is that the UCI is standarizing to these sizes. This will force manufacturers to concentrate their developements and offerings in these sizes.


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## Lombard

aclinjury said:


> However, a larger rotor does have its drawback too, it's easier to warp and get distorted (thus causing pad rubbing that you will not be able to get rid off unless you buy a new rotor). I find that when the rotor gets to the 180mm range and above, that's when the noise that it makes (when it makes it) also tend to get amplified compared to a smaller rotor.


Warping is a concern and is even more of an issue with rotors which have an aluminum spider. The purpose of an aluminum spider is to dissipate more heat - aluminum is an awesome conductor next to copper and silver. But aluminum bends more easily and can get hot enough to actually melt. Solve one problem, create another.


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## cxwrench

aclinjury said:


> ^This.
> 
> Road bikes can really get up there in speeds. One could really put a lot of heat into a braking system on the road, MUCH more compared to mtb, reason is because mtb tires will lose traction way before the brake system gets hot, where as on the road, the road tires (in spite of their skinnier size) can really allow a lot of braking fore before they will slide out.
> 
> Also, one thing I haven't seen mentioned in here is that a larger rotor will alow for a better modulation (everything being equaled).
> 
> However, a larger rotor does have its drawback too, it's easier to warp and get distorted (thus causing pad rubbing that you will not be able to get rid off unless you buy a new rotor). I find that when the rotor gets to the 180mm range and above, that's when the noise that it makes (when it makes it) also tend to get amplified compared to a smaller rotor.
> 
> Another reason to go 160mm front and 140mm rear is that the UCI is standarizing to these sizes. This will force manufacturers to concentrate their developements and offerings in these sizes.


While I agree that road bikes will normally see higher speeds and generate a lot of head in braking events mountain bike brake systems definitely see a LOT of heat. 180mm Ice Tech rotor shown:


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## PoorInRichfield

If your rotors look that bad, might I suggest a parachute?


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## Lombard

cxwrench said:


> While I agree that road bikes will normally see higher speeds and generate a lot of head in braking events mountain bike brake systems definitely see a LOT of heat. 180mm Ice Tech rotor shown:


That sure looks like gouging due to brake pads being totally worn down.


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## SwiftSolo

Waspinator said:


> I’m using Shimano RT-99’s, 140mm front and back. I weigh 200lbs.
> 
> I haven’t noticed any trouble stopping. No brake fade. Nothing. I’m wondering why 160mm are becoming more commonplace now.
> 
> What do you folks use, and why?


I switched from 140's front and rear to 160 front and 140 rear shortly after buying my disc bike in early 2014.

I live for twisting downhills and my decision had nothing to do with over all stopping power or heat. It had more to do with making lever pressure more equal on both levers during rapid deceleration. 

It can be argued (effectively) that by adding power to the front brake you are exacerbating the loss of effectiveness of the rear--after all, we are mostly riding on the front wheel during heavy deceleration on steep downhills anyway so why make it worse? The answer relates to the willingness to move ones' ass aft and below the seat to regain some of that rear wheel contact.

Admittedly this MTB technique is not widely accepted by roadies.


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## zerolight

From my experience with a decade or more on MTBs with discs and just a couple of years on disc equipped road bikes, it's less about stopping power, and more about the effort required to stop.

On my MTB I have a pair of 180mm discs, on the road bike it's 160/140 F/R. On my first real road bike it was regular rim brakes and I hit a hairpin on a fast road descent (that I'd ridden before on my MTB) and ran very wide on the corner - why? because you need to apply much more effort with rim brakes vs discs to get the same stopping power.

What I love about discs is not that I can stop quicker, but that it takes less effort. The larger the discs, the less effort you need to apply. Light controlled 1 finger braking means I can focus instead on my line, I'm more comfortable, more confident. 

You need smaller on the rear because it locks up easier than the front, so 160 back there isn't necessary. Until a recent frame change I was 160/160 on the Defy, now 160/140 on the Supersix. Where I ride, I'd not want to drop to 140 up front.


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## cxwrench

zerolight said:


> From my experience with a decade or more on MTBs with discs and just a couple of years on disc equipped road bikes, *it's less about stopping power, and more about the effort required to stop.*


That's because you have more power. And more control.


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## thisisthebeave

Waspinator said:


> I’m using Shimano RT-99’s, 140mm front and back. I weigh 200lbs.
> 
> I haven’t noticed any trouble stopping. No brake fade. Nothing. I’m wondering why 160mm are becoming more commonplace now.
> 
> What do you folks use, and why?


Modulation firstly, and ultimate power level second. I ran 160/140 on road and cx for years but my new cx came with 160/160 and I liked it. Easier to feather between lockout and firm braking. Now I even run 160/160 on road so I can exchange wheelsets between bikes without changing rotors.


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## OldChipper

I prefer 700mm rotors. They've worked fine for decades, never overheat and warp, have plenty of modulation for my needs, are lighter and more aero, and are super easy to install and adjust.


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## cxwrench

OldChipper said:


> I prefer 700mm rotors. They've worked fine for decades, never overheat and warp, have plenty of modulation for my needs, are lighter and more aero, and are super easy to install and adjust.


You'll never give up, will you?


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## OldChipper

cxwrench said:


> You'll never give up, will you?


Sure I will! When the manufacturers stop creating more problems than they're solving. It started with the proliferation of BB standard - none of which are better in the long run that threaded - and continues with stooopid and un-needed road discs. If they would continue to make both rim and disc on high-end bikes, I'm OK. Just don't force inferior tech on me so they can make more $$$.


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## Marc

OldChipper said:


> Sure I will! When the manufacturers stop creating more problems than they're solving. *It started with the proliferation of BB standard* - none of which are better in the long run that threaded - and continues with stooopid and un-needed road discs. If they would continue to make both rim and disc on high-end bikes, I'm OK. Just don't force inferior tech on me so they can make more $$$.


You mean back in the 1900s?


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## velodog

cxwrench said:


> You'll never give up, will you?


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## cxwrench

OldChipper said:


> Sure I will! When the manufacturers stop creating more problems than they're solving. It started with the proliferation of BB standard - none of which are better in the long run that threaded - and continues with stooopid and un-needed road discs. If they would continue to make both rim and disc on high-end bikes, I'm OK. Just don't force inferior tech on me so they can make more $$$.


Various bb standards are definitely not a new thing. Neither are different types of brakes. Everything else w/ brakes has settled on discs, why not bicycles?


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## TimV

cxwrench said:


> Various bb standards are definitely not a new thing. Neither are different types of brakes. Everything else w/ brakes has settled on discs, *why not bicycles?*


Because there is a certain subset of cyclists who are fierce Luddites.


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## 4slomo

Bike frames and forks are structurally rated for a maximum disc rotor size. Best to not exceed the rated diameter, even if there seems to be clearance for a larger diameter.


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## SwiftSolo

4slomo said:


> Bike frames and forks are structurally rated for a maximum disc rotor size. Best to not exceed the rated diameter, even if there seems to be clearance for a larger diameter.


What was the source of this information?

At first glance I'd question this observation.


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## 4slomo

Check with your frame and fork manufacturer(s) for the maximum brake disc diameter they recommend.



SwiftSolo said:


> What was the source of this information?
> 
> At first glance I'd question this observation.


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## aclinjury

SwiftSolo said:


> What was the source of this information?
> 
> At first glance I'd question this observation.


think logically. As the disc diameter gets larger, the caliper also needs to be moved out away from the fork leg further thus creating a higher leverage at its point of attachment at to the fork leg. This causes at least a couple issues. One, caliper will have more movement, more flexy, and 2) easier for caliper to snap off from the fork leg. You don't just make one component bigger without taking into account of the stress it puts on the rest of the system.


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## SwiftSolo

aclinjury said:


> think logically. As the disc diameter gets larger, the caliper also needs to be moved out away from the fork leg further thus creating a higher leverage at its point of attachment at to the fork leg. This causes at least a couple issues. One, caliper will have more movement, more flexy, and 2) easier for caliper to snap off from the fork leg. You don't just make one component bigger without taking into account of the stress it puts on the rest of the system.


I don't think it's that simple.

As we go to larger discs the amount of load transfer to the calipers is reduced. The total force possible is limited by tire contact patch friction. Because modern hydraulic disc brakes will easily overpower road bike tires, the caliper load question becomes one of leverage.

The distance from the road surface to the fulcrum (the axle) remains fixed. The factor that changes is the distance from the fulcrum to the caliper. It increases, thereby reducing the possible load.

Also, my newer disc brake bikes locate the caliper mounts on the compression side of affected members in such a manner that shear loads on fasteners and connections should be minimal.
It is the 30 page safety manual on my Cannondale hi-mod that causes me to question the challenged premise. With the seemingly endless ways to kill oneself outlined, I don't recall any reference to changing disc size.


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## Trek_5200

Just ordered a bike and the build is using a blend 140 & 160. I googled and saw this isn't unusual. Assume they know what they're doing and didn't question it.


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## PoorInRichfield

aclinjury said:


> Another reason to go 160mm front and 140mm rear is that the UCI is standarizing to these sizes. This will force manufacturers to concentrate their developements and offerings in these sizes.


:idea:

Ah... suddenly the mystery has been solved (Not sure how I missed reading this info when it was posted, but)...

I've been considering downsizing my bike's stock 160mm rotors to 140mm rotors, largely to reduce the bike's chubby weight. I've had 140mm discs on previous bikes and didn't have an issue.

In scouring the Interwebs, I noticed that pro bikes often had 140/140 as recently as 2019 and then all of the sudden, all of their bikes are 160/140 or 160/160. I also noticed that bikes like the Giant TCR Advanced Pro 0 came with 140/140 and then switch to 160 with the latest model. Knowing that the UCI has standardized on 160/140 answers my question on why the sudden change!

I keep reading that for *normal* roadies that 140/140 should be fine, especially if using Shimano ICE-Tech rotors... which I am. I don't live near any mountains and don't usually use my brakes for much more than stopping at stop signs, so I'm pretty sure heat dissipation is a non-issue for my riding style.

From 2019...










From 2020...

https://cyclingtips.com/2020/01/pro-bik ... part-four/


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## ono

160mm rotors are more efficient and provide shorter stopping distance. 
Here is a GCN video explaining that:


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## upstateSC-rider

Very good thread dredge with good info, and like a couple of others mentioned, modulation is better with the larger rotor.


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