Fitting a front Avid mechanical disc and caliper to the rear?- Mtbr.com
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  1. #1

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    New question here. Fitting a front Avid mechanical disc and caliper to the rear?

    Hi,

    Can this be done? I want to put my 165 mm system on the back so I can upgrade to 185 on the front. Does anyone know if it'll be compatible?

    Muchas gracias!

  2. #2

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    Why?

    Quote Originally Posted by BenP
    Hi,

    Can this be done? I want to put my 165 mm system on the back so I can upgrade to 185 on the front. Does anyone know if it'll be compatible?

    Muchas gracias!
    You need the same caliper up front with a different adaptor for the 185mm rotor. Geta rear rotor.

  3. #3

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    OK, but then I have to get a new rotor, a new rear combo (caliper + rotor) and an adaptor. Can I get an adaptor to go from 165 to 185? (2002 model) Also, I'll have a disc left over...

    it is really impossible to just stick my current brake at the back? It would save me a lot of trouble...
    Last edited by BenP; 04-23-2004 at 07:09 AM.

  4. #4
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    Quote Originally Posted by BenP
    OK, but then I have to get a new rotor, a new rear combo (caliper + rotor) and an adaptor. Can I get an adaptor to go from 165 to 185? (2002 model) Also, I'll have a disc left over...

    it is really impossible to just stick my current brake at the back? It would save me a lot of trouble...
    Not a problem. All you need is the standard rear adaper (which will work with either new style 160 or old style 165mm calipers and rotors). You can pick one up out of a QBP catalog for a few bucks if none of your shops have one laying around.

  5. #5

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    Cool, thanks... errrm is that an adaptor from front to rear or from 165 to 180??

  6. #6
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    Quote Originally Posted by BenP
    Cool, thanks... errrm is that an adaptor from front to rear or from 165 to 180??
    Buy the 185mm complete brake kit plus a 160/165mm rear adapter. Use your old caliper on the rear with the 165mm rotor, and the new caliper on the front. Check Speedgoat's site for a list of all the available adapters.

  7. #7

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    Art thou reading my mind?

    (Bolting the new caliper to the front that already has a 185mm rotor, the old caliper and new 160mm rotor on the rear. Taking a break right now... Also switching them pesky bolts over too.)

    Speaking of bolts, did you find out about them from Avid f*nŠtik?

  8. #8

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    Sorry for sounding stoopid, but what's the 160/165mm rear adapter for?

  9. #9
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    Quote Originally Posted by Schtoojp
    Art thou reading my mind?

    (Bolting the new caliper to the front that already has a 185mm rotor, the old caliper and new 160mm rotor on the rear. Taking a break right now... Also switching them pesky bolts over too.)

    Speaking of bolts, did you find out about them from Avid f*nŠtik?
    Did I read that wrong? I think he's currently got a 165 in front.

    I spoke to Avid about the bolts, and both Kylee and Paul didn't know what grade they were using. So I asked specifically if SS would be ok, and they offered, "why don't we just send you some new bolts!" Mike, the engineer & designer, is no longer with the company. He would have been the go-to guy for info like that. Kylee says she's been getting this question alot, so maybe the next person who calls will get an answer.

  10. #10
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    Quote Originally Posted by BenP
    Sorry for sounding stoopid, but what's the 160/165mm rear adapter for?
    Let me guess, you've got a Manitou fork?

    The Avid calipers by themselves are 74mm post mount compatible, which mean they'll bolt directly up to a Manitou fork and use a 165mm rotor (version 1 calipers, 1999-2002) or a 160mm rotor (version 2 calipers, 2002+).

    If you want to use them in any other combination or with any other fork or frame, you need an adapter. In the case of rear tabs, there are IS 160/165, IS 185 and IS 203mm adapters available. For IS forks, there is the same list of adapters.

    To confuse matters even more, you can run a 140/145mm rear rotor by using a front 160/165mm adapter to mount the caliper to the rear position.

  11. #11

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    Aha! I'm with you. You mean the adaptor that comes with the brakes. So i need a rear adaptor for a 165 mm rotor as this isn't the same a front adaptor for a 165 mm rotor (which I already have). Am I right?

    My fork is a Rockshox by the way, but hopefully it'll turn into a Fox very soon.

  12. #12

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    [QUOTE=f*nŠtik]Did I read that wrong? I think he's currently got a 165 in front.

    Confused the hell outta me...

  13. #13
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    Quote Originally Posted by BenP
    Aha! I'm with you. You mean the adaptor that comes with the brakes. So i need a rear adaptor for a 165 mm rotor as this isn't the same a front adaptor for a 165 mm rotor (which I already have). Am I right?

    My fork is a Rockshox by the way, but hopefully it'll turn into a Fox very soon.
    Gotcha, yes, the black forged adapter/bracket that fits between the fork and the caliper. Yes, the front 165 adapter is different from the rear 165 adapter.

  14. #14

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    Yes he does, but when he grabs a new disc set, he should switch his old caliper to the rear and use the new caliper up front. Mix and match to get the new stuff up front and the already owned stuff up the back. Which is what I just did.

    The bolts, the bolts are drving me crazy! Well, not quite. First store only had SS bolts (I have reverted back to bolts even though Machinery's handbook 25 says they should be referred to as screws), next store had 12.9 bolts, but only 4 and I need 6 to bolt up the rear adapter too. I had a close look at the original bolts, and darned if they look similar to the 4.4 stuff you can buy here, AKA mild steel and also made in Taiwan, but with a different head (designation on the head). I would suspect that they are not 4.4, as that would be plain dangerous, but they might also be only 8.8, which is only about 12-15% 'tougher' than a A2-70 SS bolt (8.8 being 116,000psi, A2-70 being 100,000 psi. The 12.9 comes in at 164,000, IIRC. Tensle strength, not shear). I could not find values for 8.8 nor A2-70 SS, but the 12.9 has a shear strength of around 5,000 psi IIRC. So, given the size of the bolt shank, these 6mm things would have around 3% of that, so about 150psi shear strength. Spread over two bolts, plus not all of the shear load is borne by the bolts due to static friction in the washers, mounts, etc. and the loading is not equally borne by both bolts (the lower wearing more load), I doubt you would get close to overloading and sheariong off a 12.9 bolt. To that point, even if a SS bolt had only half the shear strength (and A2-70 SS is a hardened Austenitic bolt, so prolly a little more than half) you *might* shear it off if you were running a 160mm rotor, were a clyde and grabbed a really big handful of brake.

    I know I kinda went unscientifc at the end there, but I am not an engineer, but I can visualize things pretty easily in my noggin. What it all work out to is that I don't think the SS bolts would have sheared off with my 180lbs and a 185mm rotor, but maybe, just maybe they might have if I managed to really load them up. The point is moot now as the original bolts are in there now, until I get a hold of some fresh 12.9 bolts and remove all doubt.

    Even more concerning are the rotor bolts. They are only 5mm, and as such have only about 115psi of shear strength each IF they are 12.9 bolts. Multiply by 6 due to six bolts, and that's only 690psi at about 1" from the axis of rotation. If they are only 8.8, figure that you have 400psi of shear, and the margin between safety and disaster becomes smaller still. Again, I am not an engineer, and this is purely speculation from a mildy stressed mind, albeit one who is enjoying actually having to nut something out for a change rather than just idling along.

    During this install, I have also gone crazy with grease and threadlock. A little too much oxidization in the mountings, and the CPS washers were showing signs of galling. Also, the new bolts have no threadlocer, so they got a dose. Hoping that I can reduce the oxidization, reduce rusting bolts (alot of rain in these parts) and make sure the things never come off without my say so. As it stands, nothing has gone even a little bit wrong with the brakes, but I'd rather have perfect brakes and a broken driveline that a perfect driveline and borken brakes. Self preservation is a strong motivator...

    Thanks for trying to find out for us. Maybe the mystery bolts will be cleared up in the near future. Not that i will switch out the bolts anyway, unless I can find some 12.9 rotor bolts from somewhere that also have a shoulder to locate the rotor correctly. That's going to be a tall order methinks.

  15. #15

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    ok. now we're rolling.

    thanks for the advice

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