Avid disc install on Cannondale

[Mr_Cheeze]

I am installing both front and read Avid Disc on my Cannondale F900. It does have wheels with Avid compatible hubs. The front installed no prob. My problem lies with the rear caliper. It does not seem to sit in the proper position resulting in the disc always being in contact with the inside pad. Yes, the CPS bolts are loosened. Does anyone know if there is some kind of shim or spacer that goes between the bike frame and the mounting bracket for this particular bike?

[C.P.]

Hey Cheeze,
It sounds like you need a disc spacer kit, for your hub. The avid rotors require hubs with a 10.16mm front offset and a 15mm offset for the rear. Some wheelsets require a spacer kit to achieve the necessary offset. For further information regarding spacers, you can contact the wheel or hub manufacturer. I had to install a spacer on my rear hub, it is about 1 mm, and is installed on the hub to move the disc outbound. 'hope this helps.
I took this info from the Avid website, where they recommend this modification for their disc brakes...

I would refrain from spacing the rotor on your hub. Most Cannondale bikes need to have the disk brake adapter spaced. Sometimes as much as 1/8 inch or more.
Make sure the caliper and adapter are spaced and centered over the rotor. With the rotor mounted directly onto the hub.

There is a huge amount of force generated by your rear brake and having your rotor mounted directly to the hub really is optimum strength/performance for most hubs.
The caliper/adapter mounted to the frame with proper spacers is utilizing the frame for strength. Considering the amount of force generated by the Brakes.

[Mr_Cheeze]

CP is right, Sparkster. Avid Bikes has it right on their website about hub spacer kits possibly being necessary. The specific hub manufacturers, Specialized, in my case, should have the kits available via their distributors.

In my opinion, I think that the integrity of the brake will not be compromised one bit with a disc spacer as opposed to a caliper bracket spacer. I am going to space the bracket in the meantime just so I can ride, but I would feel safer with the rotor kit.

The offset for the hubs is the distance from the rotor mounting surface to the outer lock nut. Most hubs you will find will have similar dimensions and may vary ever so slightly.
I think there are a few schools of thought here. I personally and professionally would never shim a Rotor unless that specific hub required it.
I have assembeled and Installed many Avid Disk brakes on a variety of bikes/hubs and have never run into any problems shimming the calipers. It is Standard Operating Procedure in our shop to shim calipers and caliper adapters for a variety of Brakes...Hayes, Shimano, Magura, Formula as well as Avids.
Happy Braking!

[Mr_Cheeze]

According to Avid, the rear hub offset needs to be 15mm. That seems like alot according to your definition of the term. Furthermore, does not 15mm seem like an awful lot to be spacing out a caliper? Obviously I would need that much longer bolts whichever way I decide to do it, correct?

With a rear hub offset spec at 15mm. That refers to the distance from the Rotor mounting surface to the Outer Lock Nut on your hub. That does not mean you would space the calpier 15mm out towards the rotor.
It means that from where your rotor mounts to where your axle mounts in the dropout (disc side) = 15mm
Generally spacing the caliper adapter does not require longer bolts.

[Mr_Cheeze]

Got it. It seems like I am actually going to need about 6-7mm offset in either case. You think I can easily get away with offsetting the caliper at that without needing longer bolts?

One question that still begs is why would Avid suggest offsetting the rotor as opposed to the caliper, which seems much easier to do?

[C.P.]

I've been away from this discussion, it looks as though you guys have sorted most of this out...As I have been following your posts, I did come to the same conclusion however, and have the same question, why would Avid suggest spacing rotor rather then caliper...so I sent an email to Avid's tech question service on their website. I'll share the response (if I get one).

I know from doing my hub, (and specifically in reading the Avid Manuals) that if you add a spacer to the rotor on the hub for offset, Avid Stronglyrecommends using longer strength hardened bolts (similar but longer then the strength hardened bolts supplied) to fasten the rotor and spacer when correcting spacing of a rotor/hub offset. They indicate that the hub manufacturer should supply these.

Hey C.P. >>Did you use individual shims on each bolt for spacing the rotor? Or one shim ring with 6 holes?
I'm waiting to hear from someone @ Avid now. I will post what I learn.
I just had a lengthy discussion with someone over @ Formula USA.
Older style Magura Hubs offset was 2.6 mm less than what is now an international standard of 15mm rear and 10.16 for front. They supply a ring shim 2.6mm thick for compensation of that measurement for using their hubs. Shimming 6 bolts to align the rotor proper center makes for a lot of "Lack of precision". Shimming two caliper bolts to get proper center seems much easier??
On another note. Your disk tab mounts should be machined free of paint that can vary in thickness on the mount tabs a make for difficult set up as well. There is a tool made by Magura for facing the disk tabs. ;D

[Crash and Burn]

Mechanically, I think either method will work without compromising too much strength. One reason Avid might suggest offsetting the rotor away from the spokes is so there is more clearance between the spokes and the inside dial of the caliper. I shimmed the caliper out to align with the disk about 3 mm and it is awful close to the spokes. I'd feel more comfortable with a rotor spacer for my specific WTB hub, but it works fine for now.

[C.P.]

I used 1 shim/spacer ring with six holes. It is machined similarly to the shape of the rotor mount on the hub, and the bolt fit is nearly interfearance type fit through the spacer, for the longer bolts supplied have a small unthreaded portion of their shank to make the fit aligned and centered where they enter/exit the spacer - I'm thinking that design feature will keep things from getting jiggy too, and the shaped machining of the spacer attempts to make it not so noticeable (from afar) when mounted, (although the shop only had black ones, and I have a polished hub so you can certainly see mine). I'll try to get a close-up shot of the hub today, and post it.

Got it. It seems like I am actually going to need about 6-7mm offset in either case. You think I can easily get away with offsetting the caliper at that without needing longer bolts?
Hey MR. Cheeze
If your shimming the adapter to mount on a Cannondale frame. You should be all set. Though Cannondale's have been the most difficult for us here at the shop to shim (more shims needed then norm with a variety of different brake manufacturers -VS- other bike Frames i.e. specialized, Fisher, Trek etc...) You should be all set with standard caliper/adapter bolts. If your bolts get good thread contact with the adapter and necessary shims, you should be all set. If you are only getting two or three threads of the bolt in the adapter/caliper. Naturally use a longer bolt.

As I type this I just spoke with Lonnie over @ Avid Tech.
The shim recommendation pertains to older style hubs that do not have international standard off set. 15mm rear and 10.16 front.

[AGENTGRAPE]

here is another thought i have heard that the fork tabs should be dressed. it was explained by a mechanic that this is the process of removing the paint from the fork where the caliper bolts to the fork tab. this is supposed to give the caliper a level surface and will help reduce drag. this is supposed to be important if you go from vbrakes to discs. i kinow this is a very small amount to be removed but does anybody do this or is this just a line of b.s. i was fed by a guy to make a couple of xtra bucks.

[C.P.]

That sums it up, as I just recieved a similar reply from Avidtech via email. We can all agree right now, that Avid Tech has great product support!
So, Sparkster, you still agree with shimming (an older six bolt hub that doesn't meet IS) or are you stickin with the caliper shim? Another post notes that the shim for a hub also gets that inside (fixed brake-pad) adjuster knob away from the spokes. In my case, it would have been in contact with spokes if I didn't shim the hub. Check out my (oops I said rearhub earlier) front hub photo.
This was a good technical forum discussion. Kept my otherwise boring work day interesting. Thanks guys!

[Crash and Burn]

Thanks for all the research CP, My front caliper even closer than that because I shimmed it out towards the disk. I'll have to get the disk shim from Avid to be safe.

[C.P.]

here is another thought i have heard that the fork tabs should be dressed. it was explained by a mechanic that this is the process of removing the paint from the fork where the caliper bolts to the fork tab. this is supposed to give the caliper a level surface and will help reduce drag. this is supposed to be important if you go from vbrakes to discs. i kinow this is a very small amount to be removed but does anybody do this or is this just a line of b.s. i was fed by a guy to make a couple of xtra bucks.

Were talking about Avid CPS discs, if you follow CPS set-up, facing is un-needed entirely, and wouldn't even make a difference for caliper alignment, as the CPS (caliper Positioning System?) does that - check out Avids Websight. It could be specific for another make/model disc caliper, but I don't know any other disc manufacturer spec requirements....Sparkster? Anyone?

Agent Grape is correct ALL Frame Disk Tabs and Fork Disc Tabs should be Faced free of paint. Magura Makes a SHOP QUALITY tool for this process.
Avids still use a Caliper Adapter that mounts directly to the frame or fork. That surface the adapter mounts to is the surface you want machined by your LBS. Then you can mount adapters/calipers to the frames/forks with proper spacing/shims to achieve correct center.

C.P. I would shim an older style Hub with a rotor shim recommended for that specific hub. 1 shim w/ 6 holes, If a shim was available from the Manufacturer. Otherwise I would shim Caliper/Adapter for proper center. To disagree with you on one thing though The CPS will not ensure that your Frame/Fork tabs are faced and this process of paint removal and square and true machining of the Frame/ Fork will be necessary for Optimum Performance/set up. It is very similar to facing a Headtube before installing a head set, Or Bottom Bracket Shell b4 installing BB.
As far as having the rotor close to the spokes. It comes down a couple of things.....Here we go!
Wheel Lacing Pattern, Disc brake wheels should be laced Symmetrically,(reverse pattern) Pulling spokes Disc side inside hub flange. Remember now Forces are reversed on disc hubs/disc side due to brake force direction. So having the spokes in proper lacing pattern matters. Having 3-4mm or more of clearance between Calipers and spokes is normal with proper lacing of the wheel. Your spokes would have to catastrophically fail to get caught up in your caliper....If that happens then there are other issues of concern..... Basically all this equals two sides with spokes two different patterns. Allowing for proper caliper clearance and The wheel being able to withstand the huge forces disc brakes put on them...
Follow??
This was a good Tech topic....Hope We all helped eachother!

[C.P.]

Avids still use a Caliper Adapter that mounts directly to the frame or fork. That surface the adapter mounts to is the surface you want machined by your LBS. Then you can mount adapters/calipers to the frames/forks with proper spacing/shims to achieve correct center.

I respectfully disagree. The CPS positioning bolts have hemispherical washers that would allow for any caliper position as long as the offset spacing has been met. Just ensuire that the caliper adapter is mounted to a clean surface(not necessarily faced etc) and tightened to the correct torque and your set. Centering? That is achieved when you loosen the CPS bolts and tighten the pad adjusters firmly so that the pads are firmly positioned on the disc. At this point the facing you mentioned wouldn't have any impact at all, even if you faced one side off 1 degree, there's probably enough adjustment in those hemispherical washers to make up the difference and center the caliper.
Next, You then tighten the CPS bolts, and loosen the pad adjusters. All set, the brake is centered , you can't tell me any different here. No need for "facing" either now, the pads are centered no matter what...Like I said, facing requirements could be different for other brake manufactureres...magura perhaps.
It is very similar to facing a Headtube before installing a head set, Or Bottom Bracket Shell b4 installing BB.

again, it is not similar to installing a BB or Headset Shell, as these items don't have hemispherical washers that allow for adjustment and "centering" as you call it that is the very reason for naming these brakes CPS! No offense here, and it's just simply understanding the Avid brakes better, Sparkster, look at the CPS closely you will see what I mean.
Again, the criteria for hub offset must be met before you position the CPS bolts.


The wheel being able to withstand the huge forces disc brakes put on them...

The forces that a disc brake put on a "wheel" are going to be similar to the forces that a rim brake puts on a "wheel" afterall, the "wheel" is still carrying all of the forces necessary to stop you either way.
No?
Okay, admittedly, My Mechanical Engineering degree is very rusty these days, I think a quick looksee in general WHEEL forces will change possibly change your quote...
Short of the extra material added to a disc hub to mount the disc brake mount - strength needed here b/c of the torque applied when braking, Explain to me how much less force there is in a wheel,(I mean the hub/spokeflanges/spokes/nipples/eyelets/rim) when braking with discs, vs braking with rim brakes as forces are transmitted through from tire contact patch to the axle, I may be wrong here, but it would seem as though the differences are not worth noting, b/c of the changes that have been made (or not made) to wheel systems as a whole.
The only difference is where the forces originate and get slowed down by the brake system chosen, so the necessity of different spoke lacing patterns. So the huge forces you mention are actually nearly the SAME forces for each braking system, and just different as to where they originate and end.
Okay, now I'm tired, I'm takin a nap, that was too much brain cell activity...Lookin forward to your reply...

Ohh Boy....
Machining disk brake mounts on frames or forks with Avids is not necessary...There I said it. You are correct!
I guess ethics would play in to my reasoning and Quotes from previous posts. I look at it from a precision stand point. I like to know that my disc tabs, head tubes,bottom bracket shells, on my bike or any other bike I may build or repair would be properly faced paint free and machined true. It is Most Crucial with other designs that do not use the CPS. If my bike had Avid brakes....I would machine the tabs regardless. Thats just me though....... ;D

As far as Wheel Forces goes...Together we have opened up a big can O worms.... ;D
There are a lot of different schools of thought here. Not that mine is THE way by any means....
To clarify my previous posts Wheel forces disc-vs-rim brakes are similar in that it is relative to where force originates from, you are correct. However, I was referring to spoke lacing patterns to compensate for Disc brake forces originating closer to the hub. As they (lacing patterns and their different spoke positions) would be relative to the distance from the outer crossing spokes to Disc brake calipers.
Example: Rear wheel lacing....Disc hub,disc rim
drive side spokes that take force from the direction of drive should be heads out facing you, spoke elbows inside of hub flange. (direction of drive being clockwise) Can you picture the pattern? The contact between each individual spoke and the hub flange is stronger on the inside of flange closer to the center of hub rotation. The crossing spokes on the drive side will have heads facing inward of the flange and have Elbows outside of the flange facing you. These spokes (3x pattern in mind) will go over two spokes and under one...(the third x) and into the eyelet/niple in a counter clockwise rotation. (If I were building a non disc wheel i would build it with the patterns identical to each other...Asymmetrical lacing, a mirror image of itself. Direction of drive force (drive side) at the hub being greater than brake force in rear wheels with rim brakes) Now, disc brake rotor rotation looking at the wheel from the disc side is counter clockwise. Brake force is applied in a clockwise direction. The spokes taking the force of the brake direction will be elbows inward of hub flange, heads facing you. The crossing spokes would be heads inward of flange elbows out facing you. These spokes same 3x pattern will go over two spokes and under one....This is where the distance from caliper to spokes will vary with different lacing patterns...and proper lacing will mean no need to space rotors with shims (International Standard hubs) to accommodate more space for the calipers as well as take the force the disc brakes put on the spokes closer to the hub. You could ask a lot of people who build wheels how they do it and you will get a lot of different answers, opinions, and ideas. I have built a lot of wheels both disc and non disc and adopted personal standards and ethics to my circus act. Again for the benefit of myself and customers who trust in me for precise accurate repairs and builds. Now I'm tired and hungry and frankly done thinking bikes until tomorrow.....9 a.m

[C.P.]

Sparkster,
You tha Man! Great description on correct lacing for a "true" international standard disc hub, makes a huge difference when lacing for disc hubs. I laced a wheel or two in my day as well, and have even worked at a few bikeshops in my day, (Belmont WheelWorks, nearly 11 years ago). I did learn the hard way last year about the required spoke lacing change that must be made when lacing my first disc specific wheel, luckily without any injuries, just a lot of frustration of having to repeatedly true my wheel, it was a lesson for the stubborn yankee in me...(I can do it myself, no-one's gonna tell me how I should do it etc)
Oh how I miss starting my work day at 9, working in a bikeshop...
C.P.

C.P.
I'm definitely NOT the man just one of them....
Writing that description took more energy than all the work I did today at work....Winter in a bike shop :P

[Mr_Cheeze]

Wow, this discussion gave me much more more than I bargained for. And CP's oversized image screwed up the 1st page's format, dammit!!

One final thing for Crash And Burn... Avid does not carry any hub spacers. You have to look to the individual hub manufacturers. Just found out from my guy today that Specialized does not even have a hub spacer, as their techs have always recommended to just space the caliper. Done and done.

Now everybody get back to work.