Upgrading discs to 203 mm - worth it?

Hello,

I have a 160 mm disc brake in the front with a TRP HY/RD hydro-mechanical caliper. I'm having some issues with vibrations in the front fork when I brake hard, which I need to sort out. I'll try cleaning with isopropyl but I'm also thinking of getting a larger size rotor for even better stopping power. Me and my bike weigh about 130 kg.

Is there any reason not to go bigger, except for weight and money? My bike is a heavy cruiser so adding a little weight isn't really an issue.

I reckon I'll need a 203 mm rotor and an adapter to make my IS mount a PS 203 mm.

Go for it, the easiest way to get better braking.

I can't say that a 203mm rotor will solve your vibration problem but I would not see any reason to not run a 203mm rotor.

However, I should point something out.
Obviously a 203 will give the brakes better leverage to stop the tire and depending on your tire size could lead to a brake that locks up easily.

I had 203s on the front and rear of my mountain/commuter bike and I could hardly use the rear brake without the tire locking up.
This was on a 29er with 29x2.1 tires.

Of course the rear does not do most of the braking and will get lighter under heavy braking but it could be possible that the front could get a little twitchy given the right conditions.

Probably on a heavy cruiser with big tires it will work just fine.

This may not help about the vibration in your fork, might even make it worse.

Upgrading to a larger rotor gives better braking power and cooling. Upgrading to a better caliper might be necessary, for better braking power is making modulation range shorter. The larger the rotor, the more precise the caliper needs to be and the more adjustment range is required with the brake lever.

Rotors are cheap, good brakes aren't. You can find a 225mm Hope floating rotor for 50$, but building a perfect fit with a good brake to match, might squeeze the wallet. Then, a fork that is sound and safe to stand that new braking power, might also cost you big bucks if yours can't be.

See, uprades to a bike is some sort of a chain reaction: One upgrade leads to two other, that are soon leading to rebuilding a complete bike on a better frame.

Going to a bigger rotor does NOT give you more braking power, unless the smaller rotor was not capable of locking the wheel. Braking is a function of the tires grip on the road. A brake that can lock the tire is maximum braking force. There is nothing more maximum than totally locked up. They can give you finer modulation, but there is such thing as too much of a good thing. To big and the brakes will lock up too easy.
Running cooler isn't always a good thing. Disk brakes need to get hot to work right, and work better the hotter they get up to the point of over heating. If your brakes get blazing hot but you don't experience brake fade when the rotors are glowing, then you have the right size rotor. if they stay cool all the time, you have the wrong brakes.

Going too big on the rotor can make them vibrate and chatter.

The problem you're describing isn't a symptom of a rotor being too small, so going larger won't cure it. Actually the normal cure is to go down a rotor size. But other things can be the cause, too:

Wrong pad compound.
Miss-aligned caliper.
Miss-adjusted caliper.
Lose rotor.
Worn out pads.
Glazed or contaminated pads.
Glazed or contaminated rotor.
Worn out rotor.
Wrong setting on suspension.
Lose, worn forks.
Lose headset bearings.
Lose front axle bearings.
Or they are just Tektros.

Drunkskunk said:

Going to a bigger rotor does NOT give you more braking power...

Click to expand...

It does, I mean it does give more braking force. As a result you need less finger pressure to stop the wheel, making for shorter modulation range.

Riding faster and heavier, a rider does appreciate the extra braking force, yet need to tune a fair modulation range to avoid locking the wheel on wet or loose surfaces. Hence the after market expansive brakes.

Overheated rotors like to get bent. I always like using oversized rotors even if i don't use the extra stopping power for that reason.

I'd go with 203mm, at least in the front.. make sure that your fork is up to the task though, as that's a lot of torque.

MadRhino said:

Drunkskunk said:

Going to a bigger rotor does NOT give you more braking power...

Click to expand...

It does, I mean it does give more braking force. As a result you need less finger pressure to stop the wheel, making for shorter modulation range.

Riding faster and heavier, a rider does appreciate the extra braking force, yet need to tune a fair modulation range to avoid locking the wheel on wet or loose surfaces. Hence the after market expansive brakes.

Click to expand...

No, but yes. I know what you mean, but it's not more force, it's actually less force. The larger rotor needs less pad pressure, so less line pressure, and therefor less Braking Force to stop the wheel. Since the larger disk has greater mechanical advantage, the pad needs less pressure to reach the point of lockup. It's also traveling over a larger surface area of the disk at that lower pressure allowing better modulation in some cases. (Or worse, depending on conditions.)
Marketing Gurus who can then spin that less force needed into More Braking Power!

neptronix said:

. make sure that your fork is up to the task though, as that's a lot of torque.

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The torque placed on the fork from a tire at the edge of locking up is exactly the same regardless of the disk size. That Maximum torque needed to skid the tire, referenced to the center of rotation (The axle), is a constant. The brake caliper mounting point on the fork is the same distance from the axle regardless of the rotor's size, so the pressure being placed on it at that point will remain the same. The pressure on the rotor and pad change, but they actually become less the further away from the axle they are.

Picture it another way. You have a 100 pound weight you want to lift with a Fulcrum and lever. you have a level 16.0 feet from the fulcrum, and another 24.0 feet long. It doesn't matter which lever you use, only 100 pounds will be lifted, and the fulcrum will only have to support 100 pounds.


I'm not trying to say bigger brakes are bad. They are no more bad than a bigger hammer is bad. Sometimes you need a bigger hammer. Sometimes a bigger hammer just means a flatter thumb, a bigger hole in the wall, and nail you completely missed.

The only explanation I can think of for having a maximum disc size for a fork is that with a larger disc the calliper is increased cantilevered from the mounts on the stanchion. However, as you say, the reaction force on the calliper diminishes as the radius grows, so I'm not sure if the force on the stanchion mount would increase.

Larger rotors are more likely to warp and to make noise. This is borne out by my observation of a fleet of pedicabs with about a hundred disc brakes among them. We have had much less problem with warping and brakes rubbing since phasing out 203mm rotors in favor of 160mm rotors. These vehicles have working loads of up to a thousand pounds or more, and there are some hills here.

You probably won't notice a significant difference in braking power based on the size; you might notice a difference based on the cleanliness of the new rotor. The perimeter of a 203mm disc is only about 25 percent larger than that of a 160mm disc, and that means it's unlikely to be the most decisive factor in braking. As others have noted, vehicle dynamics and the limits of traction pose more substantial constraints on braking power.

As for reducing or eliminating vibration, it would probably pay more dividends to try different pads than to try a bigger rotor. I gotta point out that correctly working rim brakes are MUCH quieter and smoother than correctly working discs.

It's not the size of the ship it's the motion of the ocean... wait, sorry I'm in the wrong forum. Anyway, I tried to engineer a way to get my 310mm Hayabusa discs to work on my bicycle. Couldn't find a way. Besides it would have been overkill.

Its more likely you have something lose or slightly out of place causing the vibrations. My little knowledge on bicycle mechanics leads em to belive its not the rotor.

Wow, such great response. I'll address them below, but first I just want to point out that I was a bit sloppy with the wording in my original post. I do have an issue with vibrations in the fork when braking hard, and I'd also like to have a bigger rotor to supposedly get more stopping power and for looks. It'd suit the fat, heavy-looking bike better.

MadRhino said:

This may not help about the vibration in your fork, might even make it worse.

Upgrading to a larger rotor gives better braking power and cooling. Upgrading to a better caliper might be necessary, for better braking power is making modulation range shorter. The larger the rotor, the more precise the caliper needs to be and the more adjustment range is required with the brake lever.

Rotors are cheap, good brakes aren't. You can find a 225mm Hope floating rotor for 50$, but building a perfect fit with a good brake to match, might squeeze the wallet. Then, a fork that is sound and safe to stand that new braking power, might also cost you big bucks if yours can't be.

See, uprades to a bike is some sort of a chain reaction: One upgrade leads to two other, that are soon leading to rebuilding a complete bike on a better frame.

Click to expand...

I believe my calliper is a very high quality one. I read a lot of reviews about the TRP HY/RD where it received much praise, which is ultimately why I got it to upgrade my mechanical disc brake. At the time, I didn't know it was made for road bikes, but I don't see why that distinction should matter. I liked the idea of having a cable actuated hydraulic brake so that I could use e-brake sensors with it. Anyway, the quality of the calliper should be good, I think.

I certainly agree about the upgrade chain reaction. This is getting expensive.

Drunkskunk said:

Going to a bigger rotor does NOT give you more braking power, unless the smaller rotor was not capable of locking the wheel. Braking is a function of the tires grip on the road. A brake that can lock the tire is maximum braking force. There is nothing more maximum than totally locked up. They can give you finer modulation, but there is such thing as too much of a good thing. To big and the brakes will lock up too easy.
Running cooler isn't always a good thing. Disk brakes need to get hot to work right, and work better the hotter they get up to the point of over heating. If your brakes get blazing hot but you don't experience brake fade when the rotors are glowing, then you have the right size rotor. if they stay cool all the time, you have the wrong brakes.

Going too big on the rotor can make them vibrate and chatter.

The problem you're describing isn't a symptom of a rotor being too small, so going larger won't cure it. Actually the normal cure is to go down a rotor size. But other things can be the cause, too:

Wrong pad compound.
Miss-aligned caliper.
Miss-adjusted caliper.
Lose rotor.
Worn out pads.
Glazed or contaminated pads.
Glazed or contaminated rotor.
Worn out rotor.
Wrong setting on suspension.
Lose, worn forks.
Lose headset bearings.
Lose front axle bearings.
Or they are just Tektros.

Click to expand...

Thanks for that expansive list! The calliper and the rotor are both pretty much brand new and was bought together, so nothing should be incompatible or worn. The bike is only a year old and everything is tightened properly, and there's no suspension.

I did clean the rotor, but I got some isopropyl today and clean it and the brake pads more thoroughly tomorrow to see if that helps. I should also point out that the vibration only happens when braking as hard as I can. "Normal" braking is fine. I also noticed that while standing still and locking the brake by almost braking as hard as I can, the rotor sometimes slip and makes a noise as if there were notches in the mechanism when I push the bike. It's a bit hard to explain. Maybe I can catch it on video.

When browsing today, I came across this assessment of the TRP HY/RD by http://ambmag.com.au/tested-trp-hyrd-disc-brakes/:

If I had one complaint about the Hy/Rd disc brakes, it would be that they delivered a little too much power with the 160mm rotors on my Soma Wolverine test bike. When I was really on the anchors, the powerful front brake overwhelmed the slender steel tubing of the fork, causing a heavy shuddering sensation as the fork flexed back and fourth.

Click to expand...

Maybe that's it? That my fork simply isn't strong enough to cope with the braking forces when braking as hard as possible, causing the vibrations. Also, since the setup is almost brand new, it hasn't yet gone through the break-in period recommended in the manual. Might that be a cause?

Lastly, the 160 mm disc isn't able to lock the wheel, so would I do right to go bigger?

Chalo said:

Larger rotors are more likely to warp and to make noise. This is borne out by my observation of a fleet of pedicabs with about a hundred disc brakes among them. We have had much less problem with warping and brakes rubbing since phasing out 203mm rotors in favor of 160mm rotors. These vehicles have working loads of up to a thousand pounds or more, and there are some hills here.

Click to expand...

Were they mechanical brakes, by chance? mechanical brakes DO have a tendency to do this since they side load the rotor significantly. All it takes is one super hard stop ( lots of heat ) with the rider death gripping the rotor, to sort of heat-press the rotor one way. Hydraulics are less prone to this.. ( case in point, i have stopped my 60mph bike multiple times with the front 203mm rotor alone and have never experience warpage. )

I had this problem as well with large rotors and mechanical calipers. The rotors simply aren't made stiffly enough. Bicycle component manufacturers are always trying to shave grams, and while this may be okay for a regular weight rider on a regular bicycle, it's not okay for a heavier ebike traveling at faster speeds.

I have piles of dead 203mm rotors. They all did a great job of controlling heat and preventing brake fade than my 160's, but also were not up to the task of repeated braking from 40mph.

The hydraulics on the other hand.. do such a damn good job that my braking power and thermal limits have been replaced by worries of physics.. ie being thrown off the bike like superman if you put a death grip on the lever.. :lol:

I forgot TRP is Tektro.....

Another thing to add to that list is Air in the system. Get a bubble in the piston, and it can feel spongy and chatter/vibrate. it might also be impossible to fully lock up the wheel. Try bleeding the brakes again.

But after your further description of the problem, I'd suspect it's just a brake compound issue. Those Tektro semi-metallic pads are one of the reasons I have so little love for Tektro. Replacing them with a full metalic pad should improve their performance. especially a pad from another manufacturer. Koolstop makes great pads, and they have the 3 standard compounds for it. KS-D620S is the sintered full metallic.

Drunkskunk said:

I forgot TRP is Tektro.....

Another thing to add to that list is Air in the system. Get a bubble in the piston, and it can feel spongy and chatter/vibrate. it might also be impossible to fully lock up the wheel. Try bleeding the brakes again.

But after your further description of the problem, I'd suspect it's just a brake compound issue. Those Tektro semi-metallic pads are one of the reasons I have so little love for Tektro. Replacing them with a full metalic pad should improve their performance. especially a pad from another manufacturer. Koolstop makes great pads, and they have the 3 standard compounds for it. KS-D620S is the sintered full metallic.

Click to expand...

TRP is Tektro's high performance brand, apparently, but still, the reviews are all great. In any case, I won't be replacing it any time soon since it was so expensive and it actually does stop the bike very quickly.

TRP says it's Shimano M515/M525 compatible so I should be able to find some compatible pads. Why don't you like semi-metallic? And isn't organic supposed to be quieter? As you can tell, I'm quite new to this.

Do you think it's inadvisable to go to 203 mm?

neptronix said:

mechanical brakes DO have a tendency to do this since they side load the rotor significantly. All it takes is one super hard stop ( lots of heat ) with the rider death gripping the rotor, to sort of heat-press the rotor one way.

Click to expand...

That doesn't account for why 203mm rotors warp more severely and frequently than 160mm. The smaller ones are under more stress at a given amount of lateral deflection, and they get hotter. I think it's just that the big rotors are spindlier and easier to distort, whether thermally or by impact.

Most hydraulic brakes on bicycles are single-piston, and thus deflect the rotor just the same as a single piston mechanical brake. And of course, the opposed-piston mechanical brakes out there work equivalently to an opposed-piston hydraulic brake (except they don't oil their rotors or leak their brake cables onto the ground).

The hydraulics on the other hand.. do such a damn good job that my braking power and thermal limits have been replaced by worries of physics.. ie being thrown off the bike like superman if you put a death grip on the lever.. :lol:

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I reckon the actual risk of that has more to do with the fact that your short wheelbase monkey motion bike sags down in front and rises up in the rear under hard braking than it does to do with your brakes.

brickwall said:

TRP says it's Shimano M515/M525 compatible so I should be able to find some compatible pads. Why don't you like semi-metallic? And isn't organic supposed to be quieter? As you can tell, I'm quite new to this.

Do you think it's inadvisable to go to 203 mm?

Click to expand...

I don't dislike any brake pad compound. Semi-metalic are great at what they do. But you're having some brake problems that sound like they could be helped or cured by full metallic pads. Organic are quieter, but would likely make your specific problem worse.

Shimano make decent pads, too. Much better than Tektro pads. I can chip off chunks of the tektro pads with my thumb nail.

It sounds like you want to go to a bigger rotor just because you really just want to do it. It makes no practical sense to do it until you get your current brake working, assess your true needs, and then pick the right size rotor for your bike.
So advisable? No. You don't have enough information yet.
But if you really want to do it for illogical reasons, like you like the way it looks, why look for an excuse? Just do it. You don't need an excuse. If it doesn't work, you can always change back.

brickwall said:

I believe my calliper is a very high quality one....

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Wrong. It is a good brake for a light weight bike on flat surface, nowhere near the precision required for a heavy bike speeding on a slope.

brickwall said:

Lastly, the 160 mm disc isn't able to lock the wheel, so would I do right to go bigger?

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It should lock the wheel easily at moderate speed. If it doesn't it might be that your brake pads are new or corrupted, the rotor dirty with lubricant, or there is an air bubble in your brake line.

Manufacturer's recommendations and rated spec are to be considered. Some forks are not rated for larger rotors, for a longer adapter does apply greater stress on the fork IS mount. Some brakes are not recommended by the manufacturer to mount with larger rotors, for they don't have the precision to modulate normally with them. Some bike frames are not recommended to use larger rotors on the rear and some just can't because of the chainstay design, but that is another story.

What I meant in my previous reply, is that a larger rotor does require better caliper precision, stiffer and more precise mount too. A 1mm variation at 2 inches from the fork lower, becomes a much greater variation with a longer bracket.

I won't be upgrading to a larger disk, but I'll keep my caliper. Will replace brake pads to see if that stops the shuddering.

[bump]... Galfer Bike Floating Discs Now Available in New Colours:
https://www.pinkbike.com/news/galfer-bike-floating-discs-available-in-new-colours.html

(They say

The Glafer Bike floating discs were launched in 2016 in ø180mm and ø203mm with green anodized aluminium pins. Now Glafer is launching more colours so it gets easier to customise all bicycle parts.

From 2018 Glafer floating Disc Wave will be available in 5 colours and 2 sizes...

Click to expand...

... and:

The Glafer Bike floating brake discs stem from the Motocross and are designed for the challenging enduro and DH disciplines, where the braking needs are more demanding than in any other MTB discipline. The discs can also be used in electric bicycles because they're heavier and the brakes get hotter.

The TF (True Floating) System is based on the slight axial movements between the braking surface and the carrier which, if needed, achieve the exact alignment between pads and discs when braking. These movements avoid vibrations; the braking is powerful, precise and stable; and the brake pads wear is uniform throughout its useful life. Besides, the thermal break between surface and carrier avoids warping.

Click to expand...

... they say. (Guess there's some confusion whether the things are spelled as "Glafer"... or as "Galfer"... :lol:

Floating rotors are pretty common, although not so many manufacturers are making them. The best that I have found are Hope, and one that doesn’t exist anymore because it didn’t sell enough, the Magura Venti that I still use on my dirt bike. A new manufacturer offering some is welcomed, for it might help spreading their use, and keep the price low.

Personally I never had good success with galfer rotors. They tended to warp with amateur track day riding (mc). The oe components would usually hold up better for longer. But that's mc, perhaps galfer has come some way and perhaps the bike components are different this was 10+ yrs back.

On the other hand brake tech is ultimate porn.

Their cmc ceramic composite are super light, supposedly work well in dry and wet, work well hot out cold, and look amazing! I would hope they trickle down to bikes....

If you have to ask if it's worth it, then definitely not. You will know without any question when you reach the limit of your brakes.

Unless you overheat your brakes, I think you'll get better feel from smaller rotors. My big rotor brakes haven't been usefully stronger than other brakes, but they have a more abrupt onset that's a little bothersome. Scour and clean your rotors with brake cleaner, and replace the pads with new semi-metallic pads. Your brake will more than likely feel fine.