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Old 03-20-07, 07:09 PM   #1
achc
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Disc brake rotor size

This question is always in my head and I cannot find a firm conclusion to it.

If I move a disc brake caliper from front to rear or vice versa, how do I adjust rotor size?

What I have tried to put a rear caliper design for 160mm rotor size and put it to the front. It ended up fitting a rotor of 185mm on front.

With calipers like Avid, I can change the adapter to fit it easily. But some calipers like Magura or Hope, you cannot esp if you want to go from large to small.

Has anyone tried similar things and have an answer to this?

I am thinking of putting a caliper design for 8" rotor (205mm) on front to the rear of a bike.

Thanks
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Old 03-20-07, 08:08 PM   #2
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There is no such thing as a caliper specifically designed for 6"/7"/8" rotors. Nor is there such thing as a caliper specifically designed for the front or rear.

All calipers use brake adapters that will allow you to run your caliper either front/ rear or 6"/7"/8" rotors depending on which brake adapter you use.

edit: Nevermind. I think I might be a little ********.

Last edited by FreeRidin'; 03-20-07 at 09:45 PM.
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Old 03-20-07, 08:59 PM   #3
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Quote:
Originally Posted by FreeRidin'
There is no such thing as a caliper specifically designed for 6"/7"/8" rotors. Nor is there such thing as a caliper specifically designed for the front or rear.

All calipers use brake adapters that will allow you to run your caliper either front/ rear or 6"/7"/8" rotors depending on which brake adapter you use.
SOME caliper can use adapters like Avid but some cannot. Take this one as an example...


This caliper is design to fit on the front with a 203mm rotor. IF I put a 180 rotor on it, it will not work. The pad will not touch the rotor as the caliper will be extended out and the rotor just spin in the inner circle.

If I put a bigger rotor, yes I can put an adapter to make it work. That just extend the caliper but what about the other way?
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Old 03-20-07, 09:43 PM   #4
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Haha wow I just got P3WN3D, I completely forgot about older hope brakes (they no longer use that design).

So your answer is no. You can not run anything smaller than an 8" rotor on the hope caliper posted above.
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Old 03-21-07, 07:26 AM   #5
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I have Hope Mono Mini (the new hopes) and its the same thing. They do not just adapter either. I also have Magura Marta/ Marta SL/ Louise FR. They are new brakes but they again do not use adapters like Avid.

I have Avid BB7 and Juicy 7 on some of my other bikes and those I can swap adapter and make them fit front or rear, and what ever rotor size that Avid design for.

So Freeridin', my main question of the post was if I put that Hope caliper (the one i post a link to) to the REAR of the bike, what rotor size should I use? Yes I have to get the correct size lever or just left side and rear and get a longer brake line and bleed the system. But my main concern is what rotor size will I have to use with the front design caliper to the rear...

I put a rear design for 160mm rotor caliper to front and ended up with 185mm rotor to fit it. So if its 203mm front design, should I just put 175 rotor (if there is such thing)?
There has to be some relation.

What I have heard before is ...
Front caliper mount to rear - use a smaller rotor
Rear caliper mount to front - use a bigger rotor

By using smaller/bigger rotor, I mean use a large diameter rotor then what the caliper was orginial design for at its end (i.e. 180mm rear caliper on front, use 203mm on front)

Last edited by achc; 03-21-07 at 12:48 PM.
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Old 03-21-07, 11:50 AM   #6
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Quote:
Originally Posted by achc
I have Hope Mono Mini (the new hopes) and its the same thing. They do not just adaptor either. I also have Magura Marta/ Marta SL/ Louise FR. They are new brakes but they again do not just adatpors.
By new I meant 2007...like anyone is riding them yet.

Quote:
Originally Posted by achc
So Freeridin', my main question of the post was if I put that Hope caliper (the one i post a link to) to the REAR of the bike, what rotor size should I use? Yes I have to get the correct size lever or just left side and rear and get a longer brake line and bleed the system. But my main concern is what rotor size will I have to use with the front design caliper to the rear...
I really can't help. Chances are you could get something to fit, but it would take some trial and errors. And take into consideration the amount of money you would need to spend to make this happen...

Lever=$90
Line=$30
Rotor=$40

Total=$160

Quote:
Originally Posted by achc
should I just put 175 rotor (if there is such thing)?
Hope only makes a 140, 160, 180, 183, 200, 203, and 205mm.

Hayes makes a 178mm and Shimano makes a 170mm, but I have never seen a 175.
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Old 03-23-07, 11:09 AM   #7
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Quote:
Originally Posted by FreeRidin'
Haha wow I just got P3WN3D, I completely forgot about older hope brakes (they no longer use that design).

So your answer is no. You can not run anything smaller than an 8" rotor on the hope caliper posted above.
Actually, I just check the 07 Hope series.
http://www.hopegb.com/voir_hbm_image...deimage_1.html

These are just adaptor to increase rotor size, and change mounting style like IS to POST. They are still not making it like Avid where ALL calipers are the same as long as its the same model and you just snap a bracket on it.

To answer my own question which I THINK you appear to be wrong, yes I found out I can run rotors smaller then 8" on the caliper posted above. I just have to mount it at the rear instead of front.

What I have also done last night was put a Avid BB7 caliper with front 160mm adapter onto the rear of a bike and also want to put 160mm. I don't have the rear 160mm adapter in hand so I just used the front. The result was that I had to use a VERY long bolt and put about half an inch of spacers on them.

Proof that when you put front caliper to rear, decrease rotor size
rear caliper to standard front fork, increase rotor size.

Last edited by achc; 03-23-07 at 09:02 PM.
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Old 03-23-07, 11:14 AM   #8
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Why not just run 8" on the rear? Problem solved.
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Old 03-23-07, 11:57 AM   #9
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Originally Posted by dminor
Why not just run 8" on the rear? Problem solved.
There are a couple answers to this in my situation...

- I do not have a 8" rotor
- front brake is suppose to be stronger then rear unless you ride backward
- unless you have a FR/DH frame, chances are you cannot fit 8" rotor on your frame
- I ride XC and have 7" on front
- 8" is heavy

but the most important***

when you mount a front caliper to the rear, you will need to reduce your rotor size to mount it unless you are like me. Put a huge spacer and use long bolt to increase rotor size.
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Old 03-23-07, 01:40 PM   #10
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Quote:
Originally Posted by dminor
Why not just run 8" on the rear? Problem solved.
This was my first thought as well.

Since this won't work for you though, I'm thinking it might be time for a different caliper or rear brake assembly to fit your frame and needs, rather than trying to cobble it together.
I think it's either that or your long bolts and washers for spacers.
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Old 03-23-07, 01:59 PM   #11
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Quote:
Originally Posted by achc
Actually, I just check the 07 Hope series.
http://www.hopegb.com/voir_hbm_image...deimage_1.html

These are just adaptor to increase rotor size, and change mounting style like IS to POST. They are still not making it like Avid where ALL calipers are the same as long as its the same model and you just snap a bracket on it.
The entie 2007 Hope line up uses 74mm post mounts....
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