bogydave

Was looking at a "pulled from the dumpster" frame that some one here salvaged & built up a great bike .

Was out riding today & thinking about that. But I like disc brakes, Hmmmm?
A classic with disc ! (Maybe it's been done already .)

Can a regular metal frame & fork be modified to mount disc brakes ?
Can always get a disc front fork , but wouldn't be a Classic" then (hybrid classic) ([I see that on CL now & then,)

Are weld on disc brake mounts to the frame & forks possible ?

Was just thinking a "Classic" with discs , that would turn some heads

jimc101

Possible yes, cost effective, probably not.

You would need to consider - can you get the tabs (a frame building supplier should be a source for these), is the rear OLD 135mm, if not, don't bother as hubs of less than this are very hard to find/effectively obsolete; does the frame have areas in the rear triangle that strengtheners/braces can be added to? is the frames steerer 1 1/8th", as you would be need to replace the fork with a disc one; a repaint would be required.

Thinking you would be much better looking at a retro looking new bike, rather than attempting to do what is an update which requires major frame work on an old frame.

Bike Gremlin

Disc brake puts a lot of pressure on the fork and the steerer bearings. Frames and forks designed for disc brakes have this put into calculations of tubing strength and construction. The old ones don't.

jimc101

Fork yes, but there is no difference between a headset (i.e. the bearing) used on a disc or non-disc bike

Bike Gremlin

With new frames, yes. Older frames often have narrower steerer bearings. I believe think bearings can take more force.

dsbrantjr

If the "classic" has cantilever brake studs you could fit Magura hydraulic rim brakes. I have them (HS-33 model) on one of my bikes and like them a lot. No fork, frame or wheel mods needed. Might not "turn heads" but they stop great and the bike can be easily restored to original condition.

dkmatdrum

I have a 1986 Schwinn touring bike ---lugs, Columbus Tenax tubing,classic geometry- that I put a Nashbar carbon disc fork on and it made it a much better bike while retaining most of the look of the original. It stops better, steers better and no longer has any tendency to shimmy, loaded or unloaded.

fietsbob

A straight blade Heavy duty fork wont un bend from the forces that will take the rake out of a Bent fork .

+ 1 with the above .. German, Magura HS 33 rim brakes , functionally, are really Good !!

I have a Bike which has the Fittings for both .. those, and Disc Brakes. and I see No reason to change them out..


Crashing with a broken bike turns Heads , If you need attention
want disc brakes? Buy a Bike already with them.

bogydave

Have 4 with disc.
Don't weld anymore, so no modifying frames for me.
Where did some of the recumbents come from, some guys garage
who went nuts making a bike for himself, who didn't have the word "can't" in his vocabulary.

dabac

Possibly, but not an issue, nor a design driver.

Good ol' 1" headsets have all the strength needed. And there's precious little payoff from being stronger-than-required.

The reason we're seeing bigger steerer tubes and the associated changes are due to stiffness/weight considerations of fork (and frame).
Out of the same material, you get more stiffness at less (added) weight by increasing diameter than by increasing wall thickness.
And the critical joints between steerer, fork crown and fork legs can be made stronger/stiffer, which is extra important for disc brake bikes.

As a secondary issue, a wider head tube offers more options on how to design the down tube head tube/joint. Either for simply style purposes on a bike with a thick down tube, or for weight/work reduction or for strength/stiffness gains.

But bearing strength, forget about it.

jyl

If the bike is really a classic, many of the turned heads will have expressions of dismay that you modified it with disc brakes. It's not going to be admired, if that's what you're going for.

dabac

Yes-no-maybe.

With bikes, few things a impossible.

But quite a number of things aren't suitable.

Either from a sheer engineering perspective, or from a money/effort vs results balance.

With forks, you're looking at three hurdles:
1) Nice rim brake road bike forks may use quite narrow fork crowns.
Meaning the brake rotor might not clear the inside of the fork leg.
Replacing a fork crown, or making the fork bow-legged is possible, but not a sensible expenditure of time and effort IMO.

2) Nice rim brake road bike forks may use quite tapered fork legs.
They might not be happy dealing with the forces that a disc brake mount can generate.
It's possible to improve things here by careful design of the bracket, or even to make some funny cantilevered stay to stiffen the fork leg.
But it'd change the look considerably and may still not be good enough.
And for some combination of bike, rides and riders, merely adding a bracket to the original fork might be good enough as is.

3) Dropout angle.
Front Disc brakes with the caliper in the traditional position - at the rear of the fork leg - generates a downwards force at the axle.
There's been a few accidents where front wheels have been ejected while braking.
Nasty.

Newer forks tend to have either thru-axles or a slightly different dropout angle, or really deep lawyer lips to prevent this from happening.
An old fork will have neither.
Better be outright religious in checking that the front wheel is secure prior to every ride. And mid-ride.
Or do like Cotic did, and put the caliper at the front.

Frames are usually roomy enough for the rotor, but the stay might not be stiff enough for the brake forces involved. I've seen several roadbikes-turned-footies with bent stays.
Again, things can be improved by the shape/size of the bracket, and/or by installing a crossmember between the stays.
Or, for some combination of bike, rides and riders, be good enough as is.

Rear wheel spacing might be an issue. Most disc brake rear hubs are 135 mm.
And with the rotor mount needing to be a set distance from the dropout, respacing a hub is no longer as easy as for a rim brake.
You're either looking at having to machine the hub to move the rotor mount surface inwards. Easily doable for some hubs, more awkward for others. Or - assuming there's still enough clearance for the rotor - do a custom offset of the caliper mount.

Better to spread the frame, which is rarely a problem with steel frames.
Spreading aluminium frames is somewhat debated.

Let's discuss "weld" first. Frame tubing is usually quite thin, even at stays and fork.
It can usually be welded, but it takes some skill not to burn through.
Some alloys get outright unhappy by the temperatures and will need either some sort of heat treatment to regain strength, or really shouldn't be welded.
Brazing is usually an overall safer option.

If the question is "can stuff be added to a frame way after production?" rather than about how, then sure.
Ignoring alloys with funny ageing properties, and the partially destroyed paintwork, adding brackets as such is no big deal.

Slightly to the side:
if you decide to go ahead yourself, I wouldn't bother buying the caliper mounting brackets. The shape isn't that complicated.
Making them yourself gives you considerably more freedom about how to let the mount taper off, which can strengthen the design.

bogydave

I'm understanding now, that there's a lot more involved
than just tacking on a mounting bracket to hold the brake pads & use a new disc wheel set.

Maybe the ends of he fork would be cut off & one from a bike with discs would
be welded on, it'll have to fit the newer style disc wheel set which are designed to handle the stresses of braking from the center
(Same on the rear, cut off & replace)

Way more involved that I need or want to get into.
I'll look for a better winter project.

fietsbob

For my winter bike I built up Drum Brake Hub wheels , the frame , an old MTB, is un changed ..

It gets you the Non Rim brake function so welcome in Nasty Weather , without any mechanical Gymnastics.

Its been fine for 20 winters .. It lives in the basement wearing Studded tires right now..

Sunny and not raining, at the Moment.


If you still Do brazing there were plans to turn a few old frames into an Easy Racer Recumbent ..

The plans came from that company .. circa 90's..

Delmarva

+1
Not to mention it won't stop any sooner.
That "classic" will stop just fine with rim brakes that have been serviced.

CafeVelo

A classic frame would do better in fixed gear purgatory than with discs.

No bike deserves fixed gear purgatory.