# Disc brake tabs: Seatstay vs Chainstay mounting



## bee (Apr 7, 2008)

Most frames are made with the disc brake tabs on the seatstay. I've noticed a growing number of frames with the tabs mounted on the chain stay and trying to figure out which is really the ideal place for mounting. Seatstay or chainstay? What are the considerations when choosing?


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## jgerhardt (Aug 31, 2009)

bee said:


> Most frames are made with the disc brake tabs on the seatstay. I've noticed a growing number of frames with the tabs mounted on the chain stay and trying to figure out which is really the ideal place for mounting. Seatstay or chainstay? What are the considerations when choosing?


I like the look of chainstay mounting, however I know there can be a an issue with having enough room for the caliper between the chain and seat stays.


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## dru (Sep 4, 2006)

I put my mount on the chainstay and love how clean it looks. However Mr. Gerhardt is quite right. My old Deore 555 fits just fine, but my Xtr 975s from my 29er will not fit. The 975 caliper is thin vertically but very fat. The 555 has most of its mass to the outside of the rotor, vertically. 

Drew


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## 3wfab (Aug 1, 2010)

ducking to get slammed......but I believe there is also consideration to the physics and forces on the stays as mounting on the chainstay is more rigid than on the seatstay: you find the additional support/brace (not always) with seatstay mounts but the idea is the under braking, the force is driving the seatstay towards the chainstay (if mounted on the seatstay). If mounted on the chainstay, since the force is coming from 'inside the triangle', it already has the extra 'support/brace' built in.

....I probably should never be a technical writer......but if you understand the above, you get it.


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## Drew Diller (Jan 4, 2010)

There's also the hassle factor of aligning the caliper when installing the brake. People I've talked to with chain stay mounts are split about it being more difficult than seat stay mounts.


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## ade ward (Jun 23, 2009)

On my estay 29 er I drew up the dropouts so they were long enough to get the calliper mounting on the rear side this means they are in the same orientation as the wheel mounting


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## Blaster1200 (Feb 20, 2004)

3wfab said:


> ducking to get slammed......but I believe there is also consideration to the physics and forces on the stays as mounting on the chainstay is more rigid than on the seatstay: you find the additional support/brace (not always) with seatstay mounts but the idea is the under braking, the force is driving the seatstay towards the chainstay (if mounted on the seatstay). If mounted on the chainstay, since the force is coming from 'inside the triangle', it already has the extra 'support/brace' built in.
> 
> ....I probably should never be a technical writer......but if you understand the above, you get it.


I am actually a technical writer, but we all have our bad communications days. :thumbsup:

I understand what you're saying (I'm used to rewriting documents written in Jenglish ). However, I disagree. Forces applied inward to a triangle have the save effect as forces applied outward.

I believe the reason a brace is not needed on chainstay mount is because chainstays usually have thicker walled tubing than seat stays and therefore stronger.

On a semi-unrelated note, I can't figure out why I always want to use "chainstays" as one word and "seat stays" as two words.


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## rbemiss (Nov 19, 2008)

many times in my world i am also taking into account fenders and or rear racks. a pita when mounted on seatstays (one word. lol ) i am a firm believer in having all your design thoughts figured out before any metal cutting. good luck with your final desision


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## pvd (Jan 4, 2006)

Unless you need to mount racks and bags, seatstays are the way to go. Chainstay mounting forces spacial problems with the rider and are hard to work on. They also force some pretty lame dropout designs. For any type of performance riding seatstay is the only way to go.


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## blackgt (May 27, 2010)

pvd said:


> Unless you need to mount racks and bags, seatstays are the way to go. Chainstay mounting forces spacial problems with the rider and are hard to work on. They also force some pretty lame dropout designs. For any type of performance riding seatstay is the only way to go.


I agree, while some people like the look of chainstay mounted (as it is/was unique), they are a pain to work on, seatstay mounted gives the best versatility.
Jeremy


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## Live Wire (Aug 27, 2007)

Not to mention the cable/hose routing from the dt to the chainstay almost never looks right.


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## Blaster1200 (Feb 20, 2004)

pvd said:


> Unless you need to mount racks and bags, seatstays are the way to go. Chainstay mounting forces spacial problems with the rider and are hard to work on. They also force some pretty lame dropout designs. For any type of performance riding seatstay is the only way to go.


Spoken from a person who truly knows lame dropout designs.

So exactly how does the location of the caliper affect "performance riding"?



Live Wire said:


> Not to mention the cable/hose routing from the dt to the chainstay almost never looks right.


You don't always have to route from the DT to the CS. :thumbsup:
This bike was built to carry a rear rack as well as a baby seat, and the seatstay mounted caliper would have been in the way, forcing too many compromises.


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## pvd (Jan 4, 2006)

Blaster1200 said:


> Spoken from a person who truly knows lame dropout designs.
> 
> So exactly how does the location of the caliper affect "performance riding"?


I guess that I probably know a lot less about dropout design than some others. I should put some work into that.

Besides having issues with rider heal clearance and being closer to mud, I don't see the CS mount sharing much of the bending load with the seatstay. I would want a brace in there, but then it starts getting really crouded. It's all opinion, but I've done one bike with them and swore to never do another without good reason. It also looks crappy to me.


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## bee (Apr 7, 2008)

Blaster1200 said:


> Spoken from a person who truly knows lame dropout designs.
> 
> So exactly how does the location of the caliper affect "performance riding"?
> 
> ...


That build looks great. Haven't seen top tube routing with a chainstay mount. Clever solution to avoid the issues with rear rack and baby seat. Does routing along the top tube and mounting on the chainstay only work for a certain type of brake (i.e., hydraulics)? What about mechanical disc brakes? Could you use those brakes on a chainstay mounted disc frame with routing along the down tube instead?


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## itsdoable (Jan 6, 2004)

bee said:


> ... Does routing along the top tube and mounting on the chainstay only work for a certain type of brake (i.e., hydraulics)? What about mechanical disc brakes? ...


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## Howley (Nov 23, 2005)

Very cool drop out solution-Anyone have a photo of the similar mount between the 2 stays? Not sure what post it was seen in and tried to search for it- Looking for the image of a single braze on on each stay to mount the disk brake...


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## bee (Apr 7, 2008)

pvd said:


> I guess that I probably know a lot less about dropout design than some others. I should put some work into that.
> 
> Besides having issues with rider heal clearance and being closer to mud, I don't see the CS mount sharing much of the bending load with the seatstay. I would want a brace in there, but then it starts getting really crouded. It's all opinion, but I've done one bike with them and swore to never do another without good reason. It also looks crappy to me.


After thinking about this for awhile, I don't think that is very accurate. Rider heal clearance should not be an issue at all with chainstay mounted disc brakes. Why would they be? Look at the pics above. No way that a person's foot would even come close to even touching the disc brake when pedaling.


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## CBaron (May 7, 2004)

bee said:


> After thinking about this for awhile, I don't think that is very accurate. Rider heal clearance should not be an issue at all with chainstay mounted disc brakes. Why would they be? Look at the pics above. No way that a person's foot would even come close to even touching the disc brake when pedaling.


Its because there can be no inward bending of the CS until it gets fwd of the brake caliper mount. When caliper is mounted on the SS then the inward bending (angle) of the CS can begin at the dropout&#8230;as long as it clears the disc rotor.

Cheers,
CJB


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## dru (Sep 4, 2006)

CBaron said:


> Its because there can be no inward bending of the CS until it gets fwd of the brake caliper mount. When caliper is mounted on the SS then the inward bending (angle) of the CS can begin at the dropout&#8230;as long as it clears the disc rotor.
> 
> Cheers,
> CJB


That's not entirely true either in all cases; my frame uses CS mounting for the caliper and the CS starts inward right at the dropouts because my IS mount is parallel to this disc, not the CS. The IS mounting tab sits on the CS at an angle to account for the bend in the stay.

Also, like the previous poster said, heel clearance is a non issue. Nothing on my caliper sticks out past the CS itself. There's absolutely no way you'd snag your foot on the caliper, unless you were trying to stuff your foot in the spokes..

My only beef with CS mounting is the fact that not all brands and models of caliper will fit in the CS position.

Drew


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## pewthers (Jul 7, 2009)

itsdoable said:


>


Am I just high, or does it look like moving the angle of the cable pull 90 degrees clockwise would diminish the ability to adjust the BB7? It just looks like maximum force would be generated very early in the lever pull and that there would be a lot less rebound travel (which might not be a huge issue if your rotors were very true).

I'm not bashing anyone's work, I'm just curious if this set-up has any drawbacks stemming from the removal of the brake's built-in housing stop and the alteration of the angle from which the cable is pulled.

-Matt


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## CBaron (May 7, 2004)

dru said:


> That's not entirely true either in all cases; my frame uses CS mounting for the caliper and the CS starts inward right at the dropouts because my IS mount is parallel to this disc, not the CS. The IS mounting tab sits on the CS at an angle to account for the bend in the stay.
> 
> Also, like the previous poster said, heel clearance is a non issue. Nothing on my caliper sticks out past the CS itself. There's absolutely no way you'd snag your foot on the caliper, unless you were trying to stuff your foot in the spokes..
> 
> ...


We've yet to run into too many problems with either setup. You are correct in that you need to be mindful of what brake model will be run in the CS mounted setup. However, I think the issue is not heel=to-caliper interference but rather millimeters less of heal clearance at the mid-stay point. Its not uncommon for riders to graze the CS's with their pedaling and thus removing 2-4 mm of clearance (mid-stay) would exacerbate this.

FWIW, I'm cool with running it either way now that paragon has developed their CS mounted DO. Prior to that I did not like putting those stresses directly into the CS.

Later,
CJB


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## dru (Sep 4, 2006)

CBaron said:


> However, I think the issue is not heel=to-caliper interference but rather millimeters less of heal clearance at the mid-stay point. Its not uncommon for riders to graze the CS's with their pedaling and thus removing 2-4 mm of clearance (mid-stay) would exacerbate this.


I'm guessing what you're saying's true since scuffed up XTR cranks are also indicative of some rider's body english with the foot but it's something that has never happened to me.

I have my cleats set up so my shoe is completely straight and never touch the cranks or the frame unless I'm unclipping in the process of bailing.

Having just gone to the basement to look at the bike I can say that the front caliper bolt does stick out more than the CS itself. Conceivably if I rode with a different style and cleat position I could snag a foot.

Drew


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## itsdoable (Jan 6, 2004)

bee said:


> After thinking about this for awhile, I don't think that is very accurate. Rider heal clearance should not be an issue at all with chainstay mounted disc brakes. Why would they be? Look at the pics above. No way that a person's foot would even come close to even touching the disc brake when pedaling.


Typically heel clearance is not an issue, neither is the CS shape. However, some riders do graze thier heel against the outer most part of the caliper, and in the pictured caliper above, where the adjuster sticks out past the seat & chain stay, we have had more than one rider "adjust" the capiler during a ride. One rider would have to back off the adjuster every few km's so the rotor would not rub. A hydraulic caliper, or a different mech caliper worked fine. SS mounted calipers are beyond reach of your heel.



pewthers said:


> Am I just high, or does it look like moving the angle of the cable pull 90 degrees clockwise would diminish the ability to adjust the BB7? It just looks like maximum force would be generated very early in the lever pull and that there would be a lot less rebound travel (which might not be a huge issue if your rotors were very true).
> 
> I'm not bashing anyone's work, I'm just curious if this set-up has any drawbacks stemming from the removal of the brake's built-in housing stop and the alteration of the angle from which the cable is pulled.


That setup was done, just because we could - and to see how well it worked (which was fine). The Avid mech arm can be re-installed every 60 deg, becasue it sits on an hex key. The return spring was re-positioned to provide a similar return force. The frame was designed to handle the earlier version of BB7 caliper, which had a longer arm, but I did not have one handy to modify by the time this project happened. The pictured setup is on a MTB tandem, and there is no shortage of braking power. If you look closely at that picture, the tandem was in SS mode at thiat time.


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## pewthers (Jul 7, 2009)

itsdoable said:


> That setup was done, just because we could - and to see how well it worked (which was fine). The Avid mech arm can be re-installed every 60 deg, becasue it sits on an hex key. The return spring was re-positioned to provide a similar return force. The frame was designed to handle the earlier version of BB7 caliper, which had a longer arm, but I did not have one handy to modify by the time this project happened. The pictured setup is on a MTB tandem, and there is no shortage of braking power. If you look closely at that picture, the tandem was in SS mode at thiat time.


Very cool, I didn't know that the lever could be moved.


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## mickuk (Jul 6, 2007)

There are some very tidy cs disc mounts here - particularly impressed with the reworking of the Avid.

There is also a slight (theoretical) benefit of cs mount with singlespeed dropouts, where the brake reaction force is perpendicular to the dropout slot. With seatstay mount, the force is acting in line with the slot. However with the majority of load transfer onto the front wheel during braking, I don't think we ever generate enough rear wheel torque / reaction force for this to become an issue (I've never shifted a rear wheel under braking in 8 years of riding seatstay mounts with horizontal dropouts).

Anyone any thoughts on "long" cs mount dropouts (like Blaster's but I am in no way disrespecting his fantastic work) where there is a big distance between the ends of cs and seatstay (so they don't come close together forming a true triangle). The dropout itself becomes a short 4th member. As a fatigue engineer I'd say this was bad, but real life there seem to be plenty of bikes with this layout for a number of years and no apparent problems.


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## Blaster1200 (Feb 20, 2004)

Like itsdoable's bike, the blue bike I pictured is also on a tandem. It's an 8" brake disc, as well, further adding strain on the mount. I can't say that this bike has seen a lot of use, but with as burly as those stays are, I'm not worried a bit. 

I slightly changed my method of construction for my latest bike. Heel-to-chainstay clearance isn't an issue whatsoever. But although the seat stays are fairly narrow, I have seen some heel marks on the seatstays where they bow around the tire, which tells me that even though I apparently occasionally ride with my heels in, the chainstays aren't a concern. 

These two bikes are the only ones I've used the low caliper mount dropouts on, but I'm really liking them more and more. Now when I see calipers mounted in the normal position, they look like an excess growth hanging on back there.


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## titaniumgearsolid (Mar 13, 2008)

Here's my own design..


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## brant (Jan 6, 2004)

One problem I've found is the fact that if you step off the back of the bike when you've finished a long downhill, a chainstay mounted brake is less likely to protect your calf muscle from being "branded" by the glowing hot disc rotor.


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## bee (Apr 7, 2008)

mickuk said:


> Anyone any thoughts on "long" cs mount dropouts (like Blaster's but I am in no way disrespecting his fantastic work) where there is a big distance between the ends of cs and seatstay (so they don't come close together forming a true triangle). The dropout itself becomes a short 4th member. As a fatigue engineer I'd say this was bad, but real life there seem to be plenty of bikes with this layout for a number of years and no apparent problems.


I'm not sure how long a chainstay needs to be to get optimal braking, or it that is even an issue. I do know that the placement of post-mount fittings is a huge issue sine the mounting have to be 5mm inward, or was is outward, of the face of the dropout. Not to worry though. Paragon Machine Works is coming out with a post-mount dropout so you don't have to do the 5mm in/out thing. You would just have to weld up the dropout and you are good to go.


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## Blaster1200 (Feb 20, 2004)

mickuk said:


> There is also a slight (theoretical) benefit of cs mount with singlespeed dropouts, where the brake reaction force is perpendicular to the dropout slot. With seatstay mount, the force is acting in line with the slot. However with the majority of load transfer onto the front wheel during braking, I don't think we ever generate enough rear wheel torque / reaction force for this to become an issue (I've never shifted a rear wheel under braking in 8 years of riding seatstay mounts with horizontal dropouts).


This is a valid concern, or benefit of CS mounted calipers with horizontal dropouts. I've seen quite a few wheels (brake side) get shoved backwards as a result of the forces when brakes are applied. Oddly, most of the situations where I've seen this was 4X/DS racers using horizontal dropouts. And I actually experienced it as well a few times until I went with a bolt-on hub.


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## D.F.L. (Jan 3, 2004)

Heel clearance can be an issue with Avid mechanicals that have an outer adjustment knob.

Otherwise, not.

Expect your CS-mounted brake to last longer than an unbraced SS-mounted version and to die before a braced SS position.


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