Still in a quandry...203 or 185 front rotor on an XC bike...

Iain C

My plan...my other half wants discs on her Rockhopper, so I was going to give her the Deore discs on my bike and upgrade to some Avid Juicy Carbons for me. But I have some questions about what size I should be going for.

My bike...2007 Trek Fuel EX7 full suss

Me...34, could be fitter but definitely getting there, about 85kgs in weight, unlikely to get much lighter regardless of fitness! Not light, and usually carrying a Camelbak with lunch, tools, tubes, camera, waterproof etc!

My riding...been riding (this time around!) for about 6 months, obviously no super hero yet but getting there, mainly XC...local bridleways etc (boring stuff, power is not important, mud resistance is!) but also riding Cannock etc regurlarly and wanting to hit some proper Welsh hills very soon and have something up to the job.

The question...160mm, 185mm, or 203mm? To be honest I have had a few moments when a bit more power than my current 180F/160R Deores had to offer, either very wet off road, or really fast descents on road, so I was going to go bigger...either 185F/185R or even 203F/185R.

What do people recommend?

Thanks in advance.

nicklouse

185/160 they are more powerful ant way.

or if you want better brakes get some Oros.

Iain C

Committed on the Avids, they are 2nd hand, but thanks for the tip, it's the conclusion I was coming to!

Iain C

Still in a quandry here guys!

Basically the Avids are 2nd hand and come with one single 185 rotor and I need to order another, either 203 or 160.

Hooligan side of me thinks "185 for the back, 203 up front" however looking through almost every bike catalogue spec I have, there's not one single XC bike with that configuration, regardless of price.

The only bikes running 203s on the front are either proper DH bikes or some of the hardcore all mountain things with bigger weight and twin crown forks. There must be a reason for this...I could see that too much power, especially up front, could be bad news for the type of riding I do, but then on the other side of the argument the rotor is only a measly 9mm larger each side, will it really make that much difference? Coming from muddy V brakes before, I could not believe that anyone could ever want more power than my Deores could give me, but here I am a few months down the line wanting exactly that.

I'd hate to be in the position where I've got used to the brakes and then started to think "hmmm, maybe a bigger rotor would have been fine". Are there any other considerations apart from a bit more weight, different adaptor, and a slight price difference that I have not thought about? It's only 9mm bigger each side, will it make that much difference? And as I'm having to buy one new disc anyway, in many ways I'd rather it was the one up front that was new...

I do see people's XC bikes on forums where they have upgraded to 203s up front but not really factory bikes. Are these upgrades the same as fitting a winch and snorkel on a Land Rover that never goes off road, all for show, or will there be that one time that you are really glad you had it?

nicklouse

Too much braking is a bad thing. it can put you over the bars.

I am still considering coming down from 203's on the DH rig to 185 and 160.

you do not need 203 on the front go 185 both or as originally mentioned 185/160.

SuperCove

Iain... I run a 180 rotor on the front and 160 on the rear on my XC bike and have never been in a situation where these were not powerful enough to do the job required of them.

I recently moved from a Magura brake set up over to XTR and the difference is amazing, the control that these offer is far superior to that offered by my Magura's and have never looked back.

I'd keep your rotor diameter the same!

Iain C

OK guys quandry over, thanks for your expertise.

185 up front it is then.

allthegearnoidea

ive recently upgraded mine from 165/145 (yes i know! 145 is tiny! and i had to upgrade it as it often got scared when people pointed at it!!!;)) to 185/165 and they are brilliant! so mch better! on talking ot the other guys about sizes prior to upgrading they all said that 203 was far too big for xc,

Anonymous

I disagree that a 203mm rotor is "too big" for anything. As long as your brakes have enough modulation to allow control, then they're fine.

Whether or not you actually need a 203mm disc though, well, that's another issue!

papasmurf.

I've been meaning to upgrade my Front to 180, but haven't felt the need yet as running F160 R160 on the meta has been perfectly fine even with 16stone me on it. But then oros rock anway.

chrisga

nicklouse wrote:

Too much braking is a bad thing. it can put you over the bars.

That is one of the funniest things I have heard all day. Why did people bother inventing disc brakes? For more braking power or cos they look really really cool? Thats like saying too much power in your car will make you drive too fast, the power won't do that on its own....

I agree with Yeehaamcgee and couldnt have put it any better myself. I have a xc bike with 203 rotor on the front and 160 on the back and have never had any problems with it. Alright I am probably bigger than the average jockey on here but i can stop with one finger braking, and havent been over the handlebars once yet (well not because of my 4 piston hydraulic brakes which seem way over the top for a mountain bike but do look very cool).
My motorbike though has double discs, massive calipers and probably a shed load more grip on the road than a mountain bike on a loose surface and even with the extra weight, the brakes are light years ahead of mountain bike disc brakes in terms of power and modulation and guess what - I havent been over the handlebars on that either.....

I think that you can have whatever size discs you feel comfortable with but personally out of choice I went for the biggest as they seemed to offer the most stopping power. Ok 99% of the time yes I agree that I do not NEED that much as the tyre breaks traction anyway but on the one occasion I might need it I will be glad to have it.

I guess its like the guy who drives to work everyday in his porsche with ceramic brake upgrade kit. He doesnt need ceramic brakes for the majority of the time he uses them but one day perhaps he might be in a position that he does need them but much more importantly he can tell his mates in the pub that his brakes are better and look far far cooler than theirs and he bought them because he can!

Anonymous

chrisga wrote:

Ok 99% of the time yes I agree that I do not NEED that much as the tyre breaks traction anyway but on the one occasion I might need it I will be glad to have it.

same here, I run a 203mm on the front. Reason I bought a larger disc, was because I found my old my old hope C2s a little lacking on quarry descents and so on, and it was cheaper than upgrading the whole braking system.

But, as you say, most of the time, I don't need that kind of power, but it's nice to have it in reserve.

cee

Ahem. I could be wrong, but is the extra power you get from a bigger disc directly proportional to an increase in braking force, or just the amount of power it takes to lock up the wheel?

surely if I can lock up my back wheel with a 160, then slapping a bigger disc on there just means that i will be able to lock it up by exerting less force on the brake lever.

I was under the impression that locking it up was NOT what I wanted to do....In my experience, especially in slippy conditions, locking the wheel up does not result in the braking that you might want!

Then again, folks hands are different to other folks, so maybe you need to exert more pressure on the lever to acheive the same braking force as me (or maybe your fingers get sorer than mine from braking, during long descents).

Anonymous

if you cn lock up your back wheel, you dont need a bigger disc at the back, it would just make it easier to lock up (which is not what you want)

a bigger front disc obviously improves power but it might not be necessary and bigger discs, weigh more.

chrisga

Yes, less force needed on the lever is what we are trying to say is better. You can lock your wheel with v brakes, but its a whole lot less effort locking your wheels with discs. Obviously you dont want to lock your wheels and lose grip but thats ultimately down to the person pulling the lever not the brakes themselves.

http://www.carbibles.com/brake_bible.html

There is a bit in here about why bigger rotors are good (though i appreciate on a mountain bike a bigger rotor does not mean more surface area for pad contact). Noone has mentioned heat dissipation yet......

cee

Good. Im not going mad then. So the moral of the story is -

If you want to pull the brake lever with less pressure and still realise the same braking force, then a bigger disc is the way to go!

If you are happy enough with how much force you need to pull the lever, then dont go bigger.

But...either way...you do NOT increase the amount of braking force at the contact patch. This talk of power is a bit confusing to be honest. The marketing seems to suggest that the brakes work better. They don't......the levers need less effort to pull them.

And....if youve got mitts like a pound of sausages (like me...thanks dad!) maybe the bigger disc would be a bad thing (what with locking the wheel up too easy and pulling a Ghost-Bike-Endo-Superman)

By the way..... I baggsy the tm on the GBES trick!

chrisga

Yep, agreed, having bigger rotors doesnt increase the "braking force" of the pad touching the disc, that is I guess, dictated by the design of the brake, reservoir size, piston size etc etc, but with a bigger rotor the pad touches the disc further away from the centre of the hub, which increases the amount of leverage or "larger rotors mean that the brake pads make contact further away from the axle of rotation. This provides a larger mechanical advantage to resist the turning of the rotor itself." So i guess it does kind of increase the "braking force" at the point of contact between tyre and ground but not between disc and pad. And this is all before heat build up comes in to play....

I think my point is get whatever size discs you are happy with Iain (I know you will anyway and they would be carbon if you could find them).....

Anonymous

as chrisga says, it's the mechanical leverage that is affected, but from the rider's point of view, it's as though the brakes are more powerful with larger rotors.

But, the less force you have to exert on the brake lever, the more control you have over that force, up to a certain point - but different manufacturers' levers offer different amount of modulation anyway.

abbots_mike

i think that the comparison to motorbikes is inappropriate here as
1. motorbikes frequently way 10x as much as the average mountain bike
2. the weight on most motorbikes is distibuted a lot farher behind the front wheel and a lot lower down, again making it harder to go over the front.
3. 2 large, vented discs offer much better heat dissapation (sp?) than one single piece of steel. i think that if you used a mb disc brake to slow that much weight from high speed all sorts of horrible things would happen.

Anonymous

eh? have I missed something? what comparison to motorcycles?

abbots_mike

chrisga wrote:

My motorbike though has double discs, massive calipers and probably a shed load more grip on the road than a mountain bike on a loose surface and even with the extra weight, the brakes are light years ahead of mountain bike disc brakes in terms of power and modulation and guess what - I havent been over the handlebars on that either.....

not a major part of the discussion but just a point i found interesting yet felt was inaccurate
oh no, i'm turning into another one of these damn pedants!

Anonymous

yeah, sorry, I noticed after my last posting! :oops:

I don;t think it's inaccurate though.

badblood

body has mentioned Fork warranty, What forks are you running on the Fuel ex? They may only be warrantied up to 180mm anyway which pretty much makes you mind up for you.

I had Hope M4's on my old steed with 203/180mm rotors and never felt over braked. Having said that, I am running 180/160mm rotors with normal Hope minis on my new (faster) toy and haven't encountered any braking problems and I must weigh neigh on 16 stone fully loaded. THB 203's look mint but like I said your fork warranty may decide for you.

Iain C

Forks are '07 Rockshox Recon airs...

loddrik

Got 203's front and rear on my 575, prob more than I need but would rather have more than I need than find myself with not enough.

badblood

Just checked, your forks are warrantied up to 210mm rotors so it all depends if you dont mind the extra little bit of weight. I would say go for it!!

Iain C

Nice one, where did you find that warranty info?

badblood

www.SRAM.com just follow the links to the Rockshox section, says it on the spec of the revelations

Iain C

I'd looked all over the tech manual and could'nt find it, thanks!