UKC

I'm fairly set on getting a pair of these for my bike, but not sure which ones.
I have a Kona One20 Primo frame with RS Rebel forks. Hubs hold a 6 bolt rotor.
Does anyone have any suggestions for what size rotors would suit me best and subsequently what mounts I'd need to get?

Cheers

In reply to airbournegrapefruit: The size of the rotor/mount will all depend on your size/weight and if your riding trails, cross country or full on downhill. A general rule of thumb is that a bigger rotor will stop you quicker but if its too big it will throw your weight forward at the wrong time. Best speaking to your local bike shop for some free advice. hope this helps
cheers

In reply to airbournegrapefruit:

The only disadvantage to larger rotors is an increased price and marginally increased rotational weight. If you are not too bothered about weight, and can afford the extra cash, then bigger is undoubtedly better. The difference between a 160mm and 200mm disk is really noticeable, especially on longer descents.

The mounts you get will depend on the style of mount that is present on your fork and frame. Modern hope disk callipers use a post-mount. You can choose the adaptor based on your frame mount style, and disk size, here, (for example):
http://www.chainreactioncycles.com/Categories.aspx?CategoryID=563&Brand...

You can identify a 'post' mount on your frame or fork as two holes that drill direct into the tube, where the International Standard (IS) has holes that are side on i.e perpendicular in the vertical axis) from the tube.

Well done on upgrading your brakes, by the way. IMO the brakes and the forks are the two best places to spend money on your mountain bike.

In reply to Alun: Cheers for the advice and I agree about brakes and forks. The factory brakes (shimano M575) were a bit shit, so much so that the rear one had a bit of a seal failure mid descent at the weekend.
I was thinking 203mm rotor for the front and 183mm for the back. My riding style is that area between DH and XC, in other words I like going fast down XC trails and a 'normal' speed down DH trails. So was thinking this would be a best of both words set-up.

In reply to airbournegrapefruit: Big is always better in this case,anything less than a 200mm rotar on a m4 is pointless.

In reply to airbournegrapefruit: generally its best to have a bigger rotor on the front but having the same on both is common too but just check the frame's rear mounting maximum rotor size as if you excdeed this it can fatigue the frame and cause a nasty accident!

In reply to airbournegrapefruit:

That's exactly what I have (with Shimano XT front and M4 rear) and it has worked like a charm for dozens of days riding intense DH in the bike parks of the Pyrenees.

In reply to airbournegrapefruit: I think for a 120mm bike M4's with 200mm discs are massively OTT. You'll have no real need for that much braking. You'd be as well off just buying XT brakes with 180mm discs front & rear. They'll save you money, be lighter & less trouble to maintain in the long run. However if you are insistent on going with the M4's don't bother going over 180mm disc size & you'll probably be fine running 160mm in the rear.

As in simple terms the bike will die long before you ever get to the point where you're testing the limits of the brakes.

In reply to Frank4short:

I never understand this attitude. How can your brakes be too powerful?

I can understand wanting to save money, but that isn't really an issue here. Larger rotors aren't that much more expensive. I just can't understand willfully choosing to buy an inferior product, which isn't much cheaper, just because "you'll have no need for that much braking".

If you're going to buy disc brakes (which, according to the OP's choice, cost around 150 quid per wheel, excluding rotors) why save a tenner by choosing a smaller disc? The weight you save is effectively nothing, and the performance difference between a 160mm disc and a 203mm is more than noticable!

In reply to Alun: This was pretty much my thought when I paid last night, but had to go with the 183mm back and front due to stock levels at the companies I got them from.

But upgrading the front rotor at a later date isn't that big an issue, so we shall see how these fair up for now.

In reply to Alun:


it's not the power that you can have too much of. you don't NEED big brakes for trail centres and most natural trails in the uk where the descents aren't that big and your brakes won't heat up too much because of that fact. Even Steve Peat (downhill champion) doesn't use big rotors because of the added weight of dinnerplate size rotors.

if you are going to the alps and doing descents in excess of 10 mins where you are constantly braking you might want to consider bigger rotors as they will be less likely to warp under the heat generated.

In reply to higherclimbingwales:

You may not NEED them but you'll find that if you do have them then you will find youself getting progressively faster on the desents,there is huge difference betwen the way someone from a x-country background rides downhill sections and someone who rides with an aggresive all mountain style rides these same sections,the 1st dos,nt require over large disks the other does.

In reply to Frank4short:

I'll back you up on this. It IS possible to have too much power in your brakes, even for DH use. A few of my mates who race DH and are very very quick, and even they sometimes find the new Shimano Saint brakes too powerful; sometimes just a touch of braking is needed but it's hard to modulate the power when just a dab of brake can near enough lock the wheel. I went for Shimano SLX for this reason (and budget admittedly).

So yeah, with 203mm discs and powerful brakes you may find you are locking wheels at unfortunate moments, especially if you get a bit wild, panic, and grab a load of lever. Same thing in muddy/low traction conditions. For XC/AM riding I wouldn't go bigger than 185mm up front, and most modern brakes will still easily lock a rear wheel with a 160mm disc.

In reply to Dirk Didler:


That's just a load of cack. Size of brakes does not affect speed, riding ability & style does. Granted more powerful brakes may enable you to brake later into corners in reality for most people this means skidding. Skidding is under no circumstances whatsoever an efficient or highly skilful way to slow down or go through corners. Just cause it might be all the rage in the downhill freeride videos these days you still won't find a world cup DH racer worth their salt skidding through corners when racing.

In reply to Frank4short:

Cack...Cack, how dare you sir,ride off at a place of your choosing sir,my overly large 203's against your poverty induced 165's.
On a more thoughtful note though riding ability and style does...of course it does Frank but you put someone who can ride on two bikes with the only difference being brakes and i'll put money on him/her going quicker on the bike with more powerful brakes,"of course i,m talking about a route/course with a descent dh section" for the simple reason it takes some off the work out of it,as for skidding thats a skill in its own right and the DH mention is mute as they try not to use brakes at all.

In reply to Dirk Didler:

Yes & No. The OP said he was upgrading his brakes due to the fact he felt his current ones weren't up to the job. Fair enough. However my point is buying the biggest most powerful brakes with the biggest discs he can possibly buy is excessive in the extreme. Granted with better brakes you are likely to ride faster. I wouldn't dispute this fact my point is once you go beyond a certain point any gains you will be making in braking power are, unless as pointed out elsewhere you're doing a lot of mega long alpine style descents, wasted. Having brakes that will lock up your wheels at the slightest touch are unnecessary on all but the toughest trails. And further to that for most people may even be a retrograde step as they'll end up skidding an awful lot more than they should.

Which leads me back to my original point - want to upgrade your brakes? Fair enough but on balance one would probably be better off getting a good pair of brakes that weigh less for the money rather than spending all your money on a pair of super tanker anchors with massive discs that far outpass ones need & ability & also at that weight twice as much. E.g. the difference between say the M4's with 200mm discs & a set of SLX or XT brakes with say 180mm on the front & 160mm on the rear. Which incidentally is what i'm running & I can honestly say more often than not it's my tyres & conditions which are the problem rather than the brakes but then again i'm not prepared to get 2.4/2.5 DH tyres which would overcome this as on long rides the benefits of the extra grip are far more likely to be outweighed by the rolling benefits of a 2.1 or 2.2 tyre. If or when i decide to upgrade my brakes it'll be for a lighter pair of similar stopping power as opposed to a stronger braking pair.

In reply to Frank4short:

That wasn't what the OP asked. He said that he had pretty much settled on buying M4s, and wanted to know whether it was worth buying larger or smaller discs.

And my point is - if you're going to spend 150 notes per wheel, it is daft to save an extra 5 quid, and 50 grams, on getting a smaller disc.

If you're not going to go riding in the proper mountains, then a set of Deore's would be fine for most people. But that's not what the OP asked!

PS larger discs have nothing to do with warping (as somebody suggested above) and everything to do with brake fade. On my 'local' trails in the Pyrenees, a 160mm front XT disc is useless within a couple of minutes of descending, whereas the 203mm will stay powerful for a whole run.