wrong size rotors? big mistake?

Damo152003

hi im new on here! i need some help please! basically i have just started getting back into mtb riding and i brought some hope m4 off ebay the other day fitted to my bike and there 203mm ones.

Basically i thought bigger would be better and look better and that was it. But reading more into it tonight im a bit worried i have just wasted my money. I have read 203 rotors only fit certain bikes for the strengh of the forks etc and they go to your weight etc?

The bike is only a carrera krackhan 2008 model with suntour xcr forks and im a real light weight.

The question is have i just wasted £110 on brakes which wont work on my bike forks or something? i dont understand why they will break the forks and also will they make braking worse or something as i read most people use 180mm? will it really make any more diff?

Sorry to go on and maybe this might be a simple answer but im in the dark with it all lol

thaks for reading. Damien

delta5

I don't think you need to worry about the breaking the forks, but as you're light you may well find that 203 rotors have too much braking power - that can make it difficult to 'feather' the brakes on descents, and risks your wheels locking up and washing out.

203 rotors are normally only used on the front. The rear rotor is usually 180 or 160.
As you said, for most MTbikes 180 on the front and 160 on the rear is normal, and that provides plenty of braking - especially on a HT, and with forks like the Suntour XCR which will not offer the traction you'd get with better forks.

That said, I don't think you've wasted your money. If your Hopes with 203s are working okay give them a chance and see how it goes. If they do prove to be too powerful maybe you could just use the Hope calipers with your original 160 mm rotors. Also you can always move the Hopes to another bike if/when you upgrade from the Kraken.

Damo152003

ok thanks for the reply much appriciated,put my mind at ease. As we speak it still has a 180mm on the back or 160mm which i will be upgrading to hope soon anyway.

Regarding the front il just give it a go.Problem i have it a 203mm standard caliper from hope. If its no good for me il just have sell it and get a 180 like you said.

Im pretty good with my brakes so hope its all ok cheers.

stubs

Why not just buy a smaller rotor and a brake adapter. Superstar are doing them cheap at the moment
brake adaptors clicky
rotors clicky

You need to work out if your forks are post mount or IS mount but with M4 brakes you will be able to fit a 180mm front and 160mm back no problem thats how most people run them for XC.

Damo152003

can i do that i know if you say had a standard 160mm brake you can up it to whatever.

My hope m4 brake is standard 203mm without any adapters. so can i get an adapter to go 203 down to 180mm? it is brake to is fork,

thanks for the reply really helpful.

stubs

Sorry just realised you mean you have the old fashioned M4. :oops:



The only way of getting them to fit a smaller disc is to split the caliper and fit the half for the size you want. Email Hope they might be able to help they are usually pretty good if you ask politely. info@hopetech.com

Damo152003

ok thanks for the advise. my fault maybe i should of said but to be honest i didnt realise they were the old ones lol! not to worry il give them a whirl and see what happens! il post on thursday to let you know how i go..............over the handle bars............

cavegiant

It is a great brake, I would still use it.

shm_uk

Damo152003 wrote:

hi im new on here! i need some help please! basically i have just started getting back into mtb riding and i brought some hope m4 off ebay the other day fitted to my bike and there 203mm ones.

Basically i thought bigger would be better and look better and that was it. But reading more into it tonight im a bit worried i have just wasted my money. I have read 203 rotors only fit certain bikes for the strengh of the forks etc and they go to your weight etc?

The bike is only a carrera krackhan 2008 model with suntour xcr forks and im a real light weight.

The question is have i just wasted £110 on brakes which wont work on my bike forks or something? i dont understand why they will break the forks and also will they make braking worse or something as i read most people use 180mm? will it really make any more diff?

Sorry to go on and maybe this might be a simple answer but im in the dark with it all lol

thaks for reading. Damien

There's nothing wrong in principle with fitting a 203mm rotor on the front.

They will be more powerful than you need, but that doesn't matter (I've just fitted a 203mm front rotor, for no other reason than just because I wanted to )

Suntour state a maximum rotor size of 185mm for all their XCR forks:
http://www.srsuntour-cycling.com/SID=si282b537323243c73dec626548b3ae2/index.php?screen=sh.product_series&tnid=2827

Beyond this the warranty is void & any damage caused to the fork (or you!) resulting from using the large rotor is not covered by warranty or 'fit for purpose' legislation.

In theory the fork may break and possibly cause you to have a massive crash, but in reality I've no idea how likely that is...


If you're not convinced enough to use the 203mm rotor, e-mail service@hopetech.com to find out what caliper number you need for a 185mm front rotor (IS to IS mount). I've always got a really quick & helpful response from Hope.

I think it's a Number 3 caliper you'd need for IS to IS 185mm front rotor, but not 100% sure


If you go down the 185mm route, I have a no-longer-needed 185mm rotor you can have for a tenner, and depending what caliper is required I have a spare Number 5 if you need ...


Cheers

shm_uk

One other thing I meant to mention...

The 1st-generation M4 calipers, as per the example pic posted by stubs, were sized for 165, 185, 205mm rotors (maybe 203mm for a Boxxer fork using Caliper #6)

I think the subsequent Mono M4's & Tech M4's use 160, 180 or 200mm rotors.

Make sure you know which version of the M4 you have if you decide to speak to Hope, so that they can quote you for the correct setup.

Damo152003

thanks for the help. right i went my local bike shop with my caliper i got off ebay and to order the correct rotor. After fitting the rotor it very slightly rubs on the caliper at the top...........so i rang hope and the say the model i have is 200mm mentioned above. 203mm is for the later ones and the number on the back of my caliper is (8). The caliper is 200mm standard size without any brackets so im quite p.....d off my local bike shop didnt know this as i have just brought 203mm floating rotor which is now no use to me!

Regarding the brake it self it isnt brill the stopping power just dosnt feel100%. My mates hope 2pot caliper is a million times better than mine. Is there any common faults with the hope brake? i have replacedbrake fluid and bled. pistons move ok and pads half worn and everything seems ok! wish i hadnt brought it now! lol any ideas?

peter413

Could be that new seals are needed or the pads are not contacting the rotor properly because the rotor is the wrong size or the caliper is mis-aligned

My Mono M4 lost a lot of power when it needed a new diaphragm and also when I got a new mount to fit it to a PM fork and that meant I needed a 183 rotor instead of the 180 rotor that was standard

shm_uk

Regarding lack of brake power, I have been using a set of 1st-generation M4's for years, with no problems with swapping rotors, calipers, pads etc.

As far as I am aware, and as far as i have experienced over the past 6 or 7 years with my M4's, there's no reason for the brakes to lose power if they're set up properly.

Key things to check:

1. Are you sure ALL of the air has bled out of the system?

2. Give the disc rotor a good de-grease & clean

3. Just in case the pads are contaminated, use some fine sandpaper to sand the surface of each pad to remove a thin layer of the pad (there's a chance the pads might have got brake fluid or something on them).

4. Make sure the caliper is aligned centrally so that all the pads contact the rotor at pretty much the same time when the brake is applied

shm_uk

... I'd also suggest going back to the bike shop for a refund or something as they've sold you something that's completely wrong

... if not, find an alternative LBS to use in future :-)

clodhoppa74

i was told, flatly, by my lbs that 180 would be the max size for any suntour fork below the raidon, as they're just not built for the stress, and the wheels/hub aren't that great either (i have a vulcan).

can't vouch for their validity, but they've been right about most things.

Damo152003

im pretty sure all the air is out but il try it agen! already sanded the pads etc still no good!!
I work in a garage so understand how it all works but i get the feeling im missing alot on theses brakes lol!!! How do you align the caliper?? daft question i know but theres just to allen keys bolts with no adjustment available unlike my old disk brakes which had quite alot of room for adjustment.

The disk itself dosnt sit central in the caliper. like mentioned above there is no adjustment?

I didnt no aboutforks taking a certan disk size untill i had brought them and read about it on here lol!!!

peter413

Use shims between the caliper and fork mount

Damo152003

ya i thought that but i need it come the other way so i cant use them. Il wait till i get the correct disk!

I have just had a play around with the caliper pistons move, one side moves alot quicker than the other tho and the big piston moves on its own with one pull of the lever and then on the second pull it moves the little piston so that could be why it has less power as its only moving one piston with one pull of the lever so i assume it wants bleeding agen.