How do I determine disc size?

[keitht]

Sounds like a daft question...but I have no idea.

Only ever set up cable brakes before.


Got some Hope Mono to go on my Mr XC.

Forks have post mount, for which i have an adaptor.
Rear has additonal mount also ( for bigger disc ??? )

Is there a standard formula/measurement.

 

[dyna-ti]

Big disc[rotor] goes on the front.For instance 160mm on the rear with 180mm on the front.you can run them the same size front and rear but the bigger rotor always goes on the front
A 160mm on the rear and a 180mm on the front is fine for just about everything bar downhill.Then its likely to be 180/203 or 203/203mm.Big rotors dont go on the rear as its the front that actually stops you and an oversized rotor on the rear will cause skidding

Sizes used to be called International Standard or IS these were 51mm between the centers of the mount.Then it went on to post mount with 74mm between the centers
Post mount calipers are set at 160mm rotors if you wish to increase it then you add a 20+mm adaptor

Any more questions please ask

 

[keitht]

Thank you sir.

It appears I will need a 160 rear rotor..and a little unsure about front.

I have a postmount adaptor..plus a IS extension on the front....assuming these are standard adaptors ie 20mm..then I need a 180mm or a 200/3?

 

[dyna-ti]

I would opt for 160mm rear and 180mm front.Its a set up im very familiar with and never had any stopping issues.
Do you have rotors?
I have a set of hope wavy 6 bolt fitting,R/160mm F/180mm,hardly any use.
If you're interested
All my disc set ups are for early 5 bolt rotors so these are really no good to me

 

[P20]

The hope callipers normally have a number on them. 3 is 180mm front or 160 rear. 5 is 160 front, 140 rear. Then you can work out which adapters you need.

 

[dyna-ti]

The hope callipers normally have a number on them. 3 is 180mm front or 160 rear. 5 is 160 front, 140 rear. Then you can work out which adapters you need.

I though the No5 was 160 on either the front or rear,the 140mm i dont ever remember seeing :?

There is a chart showing all the sizes,buggered where it is ive lost the link

 

[keitht]

The hope callipers normally have a number on them. 3 is 180mm front or 160 rear. 5 is 160 front, 140 rear. Then you can work out which adapters you need.

I though the No5 was 160 on either the front or rear,the 140mm i dont ever remember seeing :?

There is a chart showing all the sizes,buggered where it is ive lost the link

Anyone got the definative answer for this....seems to be some confusion...especially with me...

 

[MikeD]

Just to be clear - you've got the fork, adaptor and caliper but no rotor, and you need to know what size it needs to be?

If it's a post-mount fork with an adaptor to fit an IS caliper, then it'll be a minimum of a 180mm rotor - the adaptor adds 20mm straight off. Bigger than that is a bit special-use, so 180 is the most likely answer. The easiest way to be sure is probably to mount the adaptor and caliper and then just measure from the centre of the fork dropout to the outer edge of the brake pads. And double it

 

[keitht]

Just to be clear - you've got the fork, adaptor and caliper but no rotor, and you need to know what size it needs to be?

If it's a post-mount fork with an adaptor to fit an IS caliper, then it'll be a minimum of a 180mm rotor - the adaptor adds 20mm straight off. Bigger than that is a bit special-use, so 180 is the most likely answer. The easiest way to be sure is probably to mount the adaptor and caliper and then just measure from the centre of the fork dropout to the outer edge of the brake pads. And double it

Thank you Sir.

I shall use that method.

Regards Keith

 

[keitht]

AaaaaarrrgggggggggggggggggHHHHHH!

So just when I thnk i have it sorted in my head.

An adaptor sorted..the bolts..and a free hour or so....

Forks are Manitou Xc...Hope adaptor doesn;t fit new Marzocchi's...brake set i have is also Trials Mono..not normal..so they won't even fit on the adaptor if the adaptor fitted the forks...


Grrrrr...a bit f**ked now....not sure what to do.

Perhaps swap the brakeset for some Hayes or something..or go mad with a file ??



Any ideas..??


K