What size are your disc rotors? Bigger: better or overkill?

[ryan]

I'm planning a pretty beefy build and I have a front 160mm mechanical disc (Avid BB7) ready for install but I'm thinking this may not be enough. How should I think about disc brake size?

So far I'm just thinking one disc in front and v-brakes in the rear. 99% of the time I'm on a paved road without much gravel to deal with. And while I might be able to go 50mph, I expect to cruise mostly at 30.

 

[Andje]

203MM is a huge upgrade in stopping power over 150 imho. i have the avid bb7 cable pull on my front wheel, and upgrading to the larger rotor made a huge difference in my stopping ability, more stopping power before lockup is how it feels. I would never go back to the 150mm just for the weight difference at this stage, at least on the front wheel.

I currently ride with a v brake in the rear and a disk up front. I also use regen. I have it all hooked to one brake leaver, it's set to trigger regen first, then front brake and rear v brake is only there to lock the rear wheel if I want to. I'm finding I have about a 15 foot full stop from 95km/h.

 

[liveforphysics]

I smoke 220mm rotors into warped destroyed rubbish in 5 minutes of riding.

Motorcycle rotors are all that I've found that holds up.

 

[ryan]

Looks like I need to upgrade my rotor to 203.

I'm not ready to fabricate a motorcycle brake onto a bicycle just yet. So hopefully the 203mm will have enough stopping power for us mortals.

 

[MadRhino]

I smoke 220mm rotors into warped destroyed rubbish in 5 minutes of riding.

Motorcycle rotors are all that I've found that holds up.

I use Gustav M 210mm Magura brakes on the bike I ride the harder in the mountain, they hold well and have outstanding braking power, yet my bike and I together are about 230 pound and the fastest I have to stop is a tad above 50 MPH. I love this setup, but I feel that it would not need much more weight and speed to become less than ideal.

I can understand that being faster and bigger like you are, is calling for thick disc and higher oil pressure.

 

[liveforphysics]

I never really had a "stopping power" problem with bicycle brakes, they generally modulated well and offered great control and stopping.... for the first time stopping...the second and third time stopping they are smoking, 4th time the rotor is red and warping and the pads and fluid are both boiling in the caliper.

If you were a drag-bike or something that only needs to slow down once every 5 minutes, they would be a fantastic choice, as the feel and stopping power is great. It's just thermal limitations that cause them to fail in a few minutes for my application.

 

[ryan]

There are a whole lot of 203 rotor options.

Is there a particular geometry I should look for?
Will most all of these be compatible with my Avid BB7 brake?
Any particular one to recommend?

 

[liveforphysics]

If you can't draw a straight line from the inside mounting flange to the outside disk area, and stay on spoke webbing, you don't want it.

 

[ryan]

Thanks.

Looks like my options are the Avid G2, XLC, or Shimano XTR.

 

[ryan]

Ordered the Avid G2 because I could get another brake for basically same cost. Now I'll run 203 in front and 160 in rear. Thanks everyone.

 

[hjns]

I have a rear HT3525 with a 203mm disc (Avid), front wheel does not yet have a hubmotor and is equipped with a 160mm disc. Shimano Deore XT and Juicy Seven hycraulics are perfect for me. Modulation is much more important for me at higher speeds than abrupt stopping of the wheel due to slipping. Having to brake suddenly at 35mph brings me to a full stop within a guestimate of 5 meters (not scientifically measured). As soon as my front 9C 2810 has arrived it will get an Avid 203mm rotor as well.

 

[Lebowski]

why not use the biggest disc possible (your rim) and get hydrolic rim brakes ? Or are those no good ?

(I've no clue. Just noticing that in the motorcycle world discs get bigger and bigger, some even
mount to the inside of the rim. So I've always assumed that disc brakes on bicycles are nonsence
as rim-brakes kind of act as the biggest disc brake possible)

 

[hjns]

Because heating up the rim while braking continuously driving downwards a long hill will make me afraid for my tires...

 

[Lebowski]

Because heating up the rim while braking continuously driving downwards a long hill will make me afraid for my tires...

but you're spreading the energy over a much larger amount of material (big rim instead of small disk) which would mean less heating ..... ?

Close to my house is the 'Albis' pass, it's a 350 meter hight difference. I've never checked the temperature of my
rims after coating down it, maybe I should...

 

[hjns]

of course. buy i dont care for the difference. I only care about the absolute temp increase close to my tires.

Because heating up the rim while braking continuously driving downwards a long hill will make me afraid for my tires...

but you're spreading the energy over a much larger amount of material (big rim instead of small disk) which would mean less heating ..... ?

Close to my house is the 'Albis' pass, it's a 350 meter hight difference. I've never checked the temperature of my
rims after coating down it, maybe I should...

 

[Alan B]

Both types of brakes have problems, but rim brakes seem to have a few more problems than disc brakes.

Rim brakes fail when wet.

Rim brakes wear out your rims which is expensive to fix.

On really big descents rim braking can cause tire failure.

Rim brakes are easy on your spokes.

Rim brakes pick up a lot of grit from being so close to the road.

 

[Kingfish]

Rim brakes are just plain messy. I thought going to disc would be better, but I have had even more issues with warpage or misalignment or lack of proper clearance by the hub motor mfr. However – disc brakes do stay cleaner than rim, and they stop just as well; I run 203mm on F & R. The ebrake greatly extends the pads.

~KF

 

[amberwolf]

Both types of brakes have problems, but rim brakes seem to have a few more problems than disc brakes.

Rim brakes fail when wet.

Rim brakes wear out your rims which is expensive to fix.

On really big descents rim braking can cause tire failure.

Rim brakes are easy on your spokes.

Rim brakes pick up a lot of grit from being so close to the road.

To add to this:
Rim brakes don't work well on poorly-trued or damaged wheels. Break a spoke and you may have to disconnect the brakes to be able to ride home.

Disc brakes can fail when wet too, but are much less likely to *get* that wet than rims, as they are farther away from the road.

 

[Lebowski]

Rim brakes wear out your rims which is expensive to fix.

I hear this often... I got 40000 km on my (rim brake) bike and am still on my original
front wheel with original rim. The rear wheel popped too many spokes so I had to
replace it at 35000km but the rim was fine. And I use this bike a lot for climbing 300 - 400m
hills... A complete rear wheel, spoked and everything only cost me $100

 

[amberwolf]

Part of how fast the rims wear depends on how much road-crud gets on the rims/pads and what kind it is. Here in Phoenix, it's flinty and carves up metal pretty well; it's kind of like having really good sandpaper instead of pads. :lol: I've never worn out a rim by braking, but probably only because I break the rims or bend them up on potholes first.

 

[Russell]

Both types of brakes have problems, but rim brakes seem to have a few more problems than disc brakes.

Rim brakes fail when wet.

Rim brakes wear out your rims which is expensive to fix.

On really big descents rim braking can cause tire failure.

Rim brakes are easy on your spokes.

Rim brakes pick up a lot of grit from being so close to the road.

All good points. I wanted to get disc brakes because rim brake pads picking up crud has been a major pain for me, especially in late winter/early spring when the roads are full of meltwater. The melting snow has many particulates in it from months of plowing which embed in the pads and can quickly destroy a rim. On my latest ebike only the front brake is disc but that's ok since for some reason I have more problems up front. Perhaps the front tire parting the water before the rear tire comes through has something to do with it. Anyway my bike came with a front 160mm rotor and I would have stayed with that however I needed to get a 203mm adapter and rotor for the caliper to clear the spokes. I thought this wouldn't be a problem since I have a small Bafang motor however it is wide which places the spokes out further than a conventional hub. So far I'm not all that impressed with the performance compared to good V-brakes, but then the caliper is a cheapie. BTW the salmon colored "wet weather" rim pads do work quite well in the rain however mine squealed like a banchee when dry! (toe-in didn't help either) Oh well nothings perfect but if I lived in a sunny, dry climate, or just rode on such days, I would have stuck with V-brakes all around for simplicity sake.


-R

 

[Alan B]

I changed the rear V brake pads recently on my bike which has very few miles on it. The pads were full of amazingly bad grit. It would have done a sanding job on the rim. It probably came from the chip and seal gravel as there was some roadwork on the commute path.

So I suppose that pad grit varies a lot depending on your road condition. I have not ridden in the wet, so this stuff managed to get into a high seatstay mounted V brake in dry conditions.