Heresy corner: Are we riding discs that are too big?

Given the number of posts on here about pads that fall apart and the number of replies that say you need to bed them in by braking hard (Ok that’s a simplification, but probably a valid one)…
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Why don’t we just ride smaller discs which would have the effect of working the pads (and discs, granted) a bit harder thereby speeding the bedding in process? After all the big heavy lads say they don’t seem to have bedding in / premature wear problems.

Discuss.

isn’t the pad wear & ‘bedding’ only dependent on the actual braking force used and not the disc diameter ?

I am over 16st, I run 203 rotors, you wouldn’t expect me to use 140mm would you….

Loddrik – I’m 16st too by the way and a 180/160 mix seems to give me the greatest pad life.

SfB – Yes, but I’m assuming that with smaller discs you’ll have to squeeze harder to get the same braking effect – leverage effect of the distance from the axle and all.

This sounds wrong, but I lack the physics to know why. 😕

my rear pads were weasring at an alarming rate on a 185mm disc, swapped to 160mm and now fine

Quite right, a lot of people are over-disced and they tend to be the one going through pads. I met a slim lady on the South Coast with 8″ brakes front and rear who’d never ridden outside the Purbecks! I am double her weight, live in south Wales and have never dreamt of having such big rotors. I have survived a week in the Alps on borrowed 160/160.

I have 180/160, 160/140 and 160/Vee all of which pull me up when required.

I was just thinking more disc must be passing through the pads with larger discs and more wear. But the extra power -less braking needed?

Also a smaller disc will run hotter when used more by heavy riders.

Then the random varibles of each rider is huge.

We need a controlled experiment running wheels and pads and recording data-would be easy to do-suprised bike mags don’t do it just to see if bigger discs run at the same force and distance wear pads out quicker than a small disc.

My hardtail is 160 fr/rr

Rigid SS is 185fr / 160rr – I want it to stop regardless of pads as long as its not to extreme.

I weigh 10st and have 210/190, yet get 4/5 months out of a set of pads?!

Maybe I don’t go fast enough!

suprised bike mags don’t do it just to see if bigger discs run at the same force and distance wear pads out quicker than a small disc.

Cos it’d be very difficult to replicate accurately and scientifically (and with “real world” significance), it’d probably also be the most boring article imaginable!

Me – Member

I weigh 10st and have 210/190, yet get 4/5 months out of a set of pads?!

Maybe I don’t go fast enough!

From my experiences (as a relatively light bloke of between 11 and 12 stone) lighter guys go through pads much slower than heavier guys. Sorry to all the fatties out there, but if you want your disc brake pads to wear, lose some weight! Mine have always lasted a good length of time, even got 2 full weeks of DH riding in Morzine/Les Gets out of a full set of disc pads before (well, I changed them with a day to spare, but there was enough in them to have lasted), whilst others I were riding with went through 2 or 3 full sets each. I know I wasn’t breaking less, or that I’m some kind of god of a rider (far from it), just that those that were munching through their brake pads were significantly more portly than myself.

FWIW, it will be harder to “bed in” pads with larger rotors, due to their size meaning its harder to get the heat into them. But once they’ve bedded in, pads should last longer with larger rotors because you won’t be getting them so hot so frequently. Or some such reason like that anyway.

I’m probably over-rotored.

But at 16 stone I feel a 203 at the front and 160 at the back means I will never have a 20p-50p-20p-50p moment when I wish I did have bigger rotors.

better safe than sorry. I don’t care about pad life, I stick them in and they work and swop them out when they need to be swopped out. Never felt short changed by the lifespan of them.

pads in my c2’s seem to last forever, whilst they last about 6-8 months in the minis on another bike – both bikes are ridden similar amounts, both are 180/160 combination, and though one is a HT and the other a FS, the amount I swap components around, they have have spent as much time on each bike as well

as for the avid cable disc, I don’t know if they’ll ever wear out, 160mm on the front of SS and still the originals of 5 or 6 years 😯

i presume cable disk pads last longer as theres probably an order of magitude less force going though them.

C2’s last ages, gues because there’s a bigger gap between the pads and rotor when your not braking. That and th pads are massiiveeeeee.

180/160mm shimano dsk on my curent bike, replced 8″/6″ hayes hfx’s. Tried 8″ rear and it was just impossible to do anything as it locked up at barely any pressure.

would say the avid is more capable of sending me over the bars due to lack of modulation – very on/off

i keep thinking i am running too big discs
i wish i could run too four discs.

203 front and back (the disks and adapters were free and I didn’t want to run 160 in Whistler), weigh 10st, replace the pads every 6-7 months.

203 front, 180 back. Ride a bit of everything including some big mountain stuff. Love the big rotors. Change pads about every 9 months or so… which was about the same when i was running 160s on this bike. I dont think the size of the rotor has any effect on how quickly I wear through pads.

What compound pads you use does have a huge effect!!

I have a cunning plan to bed in my disc pads, swap the 203mm rotor for a 160 and bed them in using that, only worry is the pads wont leave stuff behind on the 203mm disc, but it’ll be there already wont it?

I have to ask Saccades, what’s a 20p etc moment. I’m lost!

I’m definitely finding that the front disk needs more “warm up” time now that I’ve moved from 160 to 185.

20p-50p-20p-50p
-£1.00?

Y.A.W.N

i presume cable disk pads last longer as theres probably an order of magitude less force going though them.

Mmmm not sure on this one. Aren’t the forces required at the pad/disk interface to slow the rider are the same whether they are applied using hydraulics or a cable?

I use BB7s, because being of the larger persuasion, I have an inherent fear of boiling brakes.

One big advantage of being small and light, is that it takes less energy to slow me down, and therefore much longer pad life. Yippee!

160 rotors seem to be plenty powerful enough to slow me down, and I could possibly get away with 140 on the rear, certainly on flatter ground. In fact, decent Vs are ok for me, in dry weather, in somewhere like Epping forest.

I have big (203/180) rotors, and weigh 16 stone, and I don’t get through pads very fast.

I am a fat git and I found a 160mm front disc just wasnt quite powerful enough I was never quite sure I would make it round a bend at the bottom of a descent on my local ride. Went for a 180mm and I have had no problem with this bend. Mind you it could just be a confidence thing.

17 stone. 180/160. Too steep for that and I’m walking anyhow 🙂

12.5 stone. 180/160 rotors and Hope sintered pads last a very long time.

12 stone, 160/160 on my xc bike, and I did more than 2k before i changed pads, WTF are you boys doing, dragging through the corners…..

Am I being stupid or are the larger rotors just so they don’t heat up as much and cook the fluid in the brakes? the smaller the rotor the hotter it will get as it is touching the pads more frequently.

If it’s the size of the rotor V brakes should be **** mint cos they have a huge rotor to stop on (in the dry)! I know this is crap, but u see what I mean?

like a previous post. If you wanna stop better a good pad and disc are the main things. If you do big stuff you want a bigger rotor so the breaks don’t cook and stop working.

Please correct me if I am wrong 🙂 If so, explain how a bigger rotor diameter makes you stop faster. To me its one material connecting with another. If it causes more friction it will stop faster so unless you rag the breaks you don’t need bigger rotors.

A bigger rotor has more leverage than a smaller rotor. Think about stopping the rotor with your fingers (carefully, don’t try this at home), if you could squeeze a large rotor at the outside edge it would be easier and if you stopped it at the hub you need more effort on the hub sized rotor, it is the same as spinning a wheel up. If you spin from the hub you need more effort to get it going. You can probably tell I’m not a teacher.

Aimed at Giddy rob^^^^

Blimey, there are some fat barstuards on this forum! No wonder people go on about wearing stuff out.
I’m somewhere between 9.5&10 stone and find it difficult to wear anything out. I have more spare and half worn pads hanging around in my spares box than anything (must chuck them).

I did go through a brand new set of Deore pads in half a ride though. Dorking>Winter>Brand new Rocky Mountain Switch

aye, that makes sense. Though I have a 203mm rotor up front and soon got through my avid pad.

It does stop like ****, but I don’t have a 160mm (for e.g.) to compare it to. Well, I do but it ain’t avid so wouldn’t be a fair test.

Though, I never ran out of power on my hardtail with 160mm rotors. Though, I probably never went as fast as I do on a fs.

End of the day 203mm looks cool on the front of your bike! Most of the time I don’t need it, but sometimes I guess it gets me out of dodge with the stopping power.

With boobs theory, imagine how good rim brakes would be if they used the same materials to stop as disc brakes! Damn!!!!

“Pitching In!”

LOL – flamejob!

“step away from the pie!”

I’m in the process of changing both my bikes to 203 front & 185 rear – from 185 – 160, and 160 – 160.

I used to ride mainly cross country, and the 160s were fine. I ride Wales and Peaks much more now, and want more stopping power.

I can’t see any way at all that a smaller rotor will give longer pad life – it must be much the other way, as the pad is working less hard with the extra leverage. While that makes sense to me, brakes turn forward energy into heat – so there should be the same heat made, whether the rotor is large or small. I’ll have to think on that bit.

🙂

Flamejob,
Why would you throw away pads that are only half worn?

iamtheresurrection & proteus

I think that Saccades is refering to the pucker factor!

I don’t know, I think a controlled experiment to determine how rotor size effects pad wear [factoring in all the variables] would be interesting.

Thought about the heat thing. For a given stopping force, the pads will need to squeeze harder on a smaller rotor – but on a larger rotor which is moving past the pad faster, the smaller force is applied over a greater area – both producing same heat.

Bedding in argument asside(do I need to bed sintered, which I always run, as sintered are heat treated anyway?) I think wear should be the same for both sizes.

If with big discs they are not getting to the optimum temperature then it could cause premature pad wear. Certainly the big discs on the tandem get used very hard and pad life is thousands of miles. Small discs on the solo never found wanting either.