Another thread about mounting disc brakes to a frame...
 

I apologize for starting another thread on disc brake frame conversions but I was just hoping for some comment on the feasibility of two frames for conversion. My wife and I have steel bikes we used for Audax riding, general road riding and touring. We have recently spent more time mountain biking and both find the braking on our road bikes frustrating and are looking to upgrade them anyway. We got some feedback from a local frame builder but was interested in any comments others might have on the forum.

My bike is a Fuji World 2004. It has a Reynolds 853 main triangle. I was told the problematic part for a conversion is the rear dropout. To remove the wheel you pull it forward. I was told they could be cut off and replaced by welding in new ones (possibly through-axle). The current fork is carbon/alloy and would need to be replaced. There are a few options around for 1 1/8” steerer in carbon. The nearest to what I have (just from looking at it) is a Ritchey adventure fork but I imagine small differences in the geometry of the fork can make a bit of difference to the ride?

My wife’s bike was a Bioracer shipped out from Europe back in 1998. I don’t have specifics on this one. It’s made from Columbus steel, with a steel fork, had a horrid paint job which delaminated after a few years and had to be re-coated. That said, my wife did PBP on it and plenty of cycle touring. The frame builder I spoke to pointed out his issue with this frame was the front end which has the old style steerer and stem. The fork would need to be replaced and he was not willing to make up a new one as in his opinion discs should not be fitted to a fork with a steerer less of than 1 1/8”. Any thoughts on this? He also said it would not be worth replacing the head tube.

Thanks in advance for any feedback you might have.

I'd say the builder is more right then wrong. I could quibble about the rear dropouts and such but the bottom line is axle placement being consistent (and of course the braking load paths on stays not intended to handle them) and how the disk can be slid out of the caliper.

Some of the disk wanting mania reminds me of the hot rod era. Put a big engine is a family car and all kinds of other issues become real important real fast. Andy

I have a disc audax bike planned, and I'm going to use a 1" steerer for that bike. My rationale is that braking loads on that bike will not be too severe. I think that if I was going to do touring on it, I would want a 1 1/8" steerer. I thought about this for quite a while and then found that Crust bikes has a 1" steerer disc fork, so I figured if they were still in business, people weren't dying because of it. I can understand why a builder wouldn't want to do this though.

Putting discs on a road bike is a pain. They aren't made with space for a disc. If you really want this, it's probably best to get new bikes.

If you do go with discs you will need new wheels and the standard now is pretty much 100mm axle in the front and 142 mm in the rear. If I were to do this I would make a new fork for the wider axle and legs made for disc brakes. In the rear you should be able to get away with a set of the Paragon drop outs for disc brakes.

https://www.paragonmachineworks.com/...12-mm-hub.html

Those dropouts are not that easy to get on a new bike. I'm struggling with that right now. I don't see how it's really practical to try on an existing bike, especially assuming it has straight stays. It would take some pretty extreme cold setting, which is not that easy on an existing frame. I have seen you mention replacing dropouts a couple of times now, have you done it? Do you have pictures somewhere?

I think the only way to get discs on an existing road bike is to cold set the dropouts to 135 and go with a seat stay mounted tab. There are adjustable tabs for horizontal drops, but as Andy says forward facing drops might have a problem with wheel ejection. Paragon had some vertical dropouts with built in stay mounted tabs, but I'm not sure they still make them. Probably some people out there have some spare ones.

I have a couple of frames that I have thought about replacing the chain stays on. Seems like a silly amount of effort. I might still do it, dunno.

I know this is a bit off topic but, what problems are you having? This is how I attach my 3/4" stays to the dropouts. I know you are not welding, but you could still braze a plug into the end of the stay and then notch it at an angle, with the dropout being flush with the outside of the stay.
https://cimg5.ibsrv.net/gimg/bikefor...fad8803dd0.jpg

My next step is to make something like your fixture. It would be a lot easier if I bent my own stays. Pre-bent sbend stays aren't meant to be that far out where they have to be to hit the front of the dropouts. This is good for tire clearance and bad for crank clearance. It's too bad nobody none of the U.S. suppliers got the columbus low mount stays.

And I'm also set on using a lugged bottom bracket shell. I'm not actually worried about the connection with the dropouts. I need to prove to myself that the stays will give me the tire clearance I want while leaving crank clearance

Not the Paragon dropouts but the new cast ones from Nova etc. See pic below. I initially tried to install a set of the Paragon dropouts but for quick release on my 89ish Raleigh Peak mtb. I tried to weld them on before taking a frame building workshop. Once the workshop was finished the the Peak got set aside. I bought the cast dropouts to use on a new build but did not like them. I was between frames and as I had everything needed to convert the Raleigh to 27.5 I decided to try to fit the cast dropouts. It is a slow build and I needed to figure out the cable routing.
https://cimg4.ibsrv.net/gimg/bikefor...65b4ab4cc9.jpg
This is the Raleigh Peak 650b disc conversion
https://cimg7.ibsrv.net/gimg/bikefor...09135431c2.jpg
3/4 straight CS 1 1/2 inch round Paragon dropout
https://cimg1.ibsrv.net/gimg/bikefor...7749fe4afd.jpg
New build Paragon disc dropout

Thanks. Are you tall?

I like making my own stays, because I can bend them any way I need them. I'm planning an aluminum frame next and I'm not looking forward to having to use pre-bent stays that I can't manipulate.

Also, I agree that wsteve464 must be tall with the angle on those seat stays.

Was now down to 6'3" from 6'4" :). I am having a hard time finding my fit. I need a tall head tube for a more upright position. I think I may have one that fits, the one with the round dropouts has a 550mm toptube as opposed to my other with a 580mm TT. I can't stretch out like I used to.

I was mostly curious if you were tall because the angle of those seat stays is pretty big for a mountain bike. Road bikes generally have steeper seat stays.

Good Point. All I'm missing is the big engine! I must admit though, most of my cycling challenges over the years involved going rather than stopping. That said, the canti's are damned annoying.

Thanks. Yes I was expecting that. New wheels, new groupset (full hydraulic). Realistically all I'd be doing on each is keeping the main frame and the stem/handlebars. That's about it. Thanks for the info on the drop-outs. How to they allow for the 142mm spacing, by how they are welded to the stays or by doing something to the stays or a combo of the two?

Your stays have to be bent out. 130 to 142mm wide.

I really wish people would understand that the inside of the dropout face is in the same place with 135 and 142. The only difference is that the 142 thru axle dropouts have a 3.5mm recess on each side for the hub end cap to seat in. It is just like the dropout slot in a QR dropout. The inside of the dropout faces are still 135mm apart, only the faces of the slot are 142mm apart.

Yes, you're right. The real issue with retrofitting chain stay mount (low mount as Paragon calls them) dropouts is getting the stays out to the front of the dropout. If you go with seat stay mounting, this might be a little less depending on what it takes to clear the disc. The old-school vee brake mountain bikes tend to have decent clearance for the disc, so maybe the low mount dropouts will work. I feel like a road bike would pose more of an issue unless it's for 140mm discs. Which is to say that someone that doesn't do this all the time is going to have to do a lot of fiddling beforehand and I can understand why they wouldn't really want to do it or at least charge a reasonable rate for their time.

OK. Thanks. This would explain why the framebuilder didn't seem too fussed about that.

Has anyone got any further comment on the suitability of a 1" steerer for a fork with disc brake mounts? Remember this is for a bike that will be going touring.

Do you overpack?

I think you already got your answer about the 1" fork, your builder said no. You're going to have to put in some research to find someone that will make one for you. Retrofit is out unless the existing fork is an overbuilt unicrown fork. Most forks built for rim brakes are very marginal for disc, it's not unlikely that it would fold under heavy braking.

The Ritchey fork has Axle-Crown: 393mm. Good news is it has 50mm rake, because that A-C is likely to push the front of the bike up and reduce the head tube angle.

I'm a little surprised I'm the only one who thinks you shouldn't put this much effort into major modifications on a $1500 bike. Does your framebuilder work for free?

Ask the framebuilder if using a thicker walled steerer tube would work. A standard steerer tube appears to have a maximum wall thickness of .090" and is made of crmo. You can get 1 inch crmo tubing up to .188 inch wall thickness. You would need to use a threadless stem and probably a shim to 1 1/8" over the steerer tube to make the stem fit and have a nut welded in to the top of the steerer to allow the stem cap to be tightened to set the preload as a star nut would not fit, just a thought.

With the cost of the rear disc dropout conversion and the custom fork it would probably end up costing more than a new bike.

I'm not sure it's worth it either and no, the framebuilder doesn't work for free!. My wife and I want Ultegra/GRX800 level components. The only cheaper (than the frame mods) but reasonable option here in Australia that I know of is the Norco XR Steel. It's a lesser steel than my frame, my wife has rejected the dull grey colour and I don't understand why a steel bike has a press-fit bottom bracket. Other options start around the same price as my frame modification but still not Reynolds 853 or equivalent.

Thanks for the suggestion. I'll look into that.

So the idea is that because the caliper is all that way further down there's more torque on the steerer?

If the weight, fit and ride are what I wanted, I wouldn't worry about whether it's 853 or not. It wouldn't have a discernable effect on the ride - especially with our new fat tires. Also, speculating a bit, my limited experience with 853 is that it's too hard (as in material hardness) for efficient post weld machining. 853 ST and HT's are difficult to quickly/easily ream and it wears out tools faster. If this is the case, your current bike might only be 853 in the DT/TT (I'm guessing here but...seems likely).

It looks like the XR is made from 725 which is a similarly high end heat treated tubeset. The XR would be a full upgrade from your current bike including braze-ons, wheel fitment, headtube size and fork. It's any easy choice for me - aside from the $$.

I'm less sure what to tell your wife about the paint! :-) You could have a painter put some accents on it for relatively little $.

any thoughts about just having the framebuilder do a custom frame? how much cost differential would that be from the conversion. and theoretically the result would be better and more integrated and to purpose

I have had some discussions with a well known framebuilder who has done a lot of pioneering work with disc on road bikes. He noted that to meet his safety standards, especially the forks he has to build stronger and his disc frames are are heavier. disc vs caliper is all up to planned usage