Any way to convert a rim brake fork to disc brake?

Sunder

Sunder

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Joined
Sep 6, 2011
Messages
3,054
Location
Sydney, Australia
I bought a RockShox Paragon RL "Disc brake" compatible fork from eBay. Everything on the website suggests there is only one model. Even when I type in the serial number, it shows that it's rim brake only, then the disc brake mount type, minimum and maximum rotor size. No wonder it's confusing, so I don't even totally blame the seller.

Unfortunately, I was sent a rim brake version, and the seller is unwilling to help, and I'm past my 60 day return limit.

eBay can't help
RockShox can't help

In other words, I just wasted $400 AUD (About $300 USD).

That's it for me, no SRAM gear, no Zipp Wheels, no RockShox forks. End of the relationship as far as I'm concerned...

So, now I'm stuck with it. I also bought some carbon wheels with no brake surface to go with it, so staying with rim brakes isn't really an option.

What are my options?

There seem to be some pretty dodgy looking "Universal" adaptor kits.
I don't know what half these holes are for, but I'm not going to use them, so I could possibly prototype a custom adaptor between these two points, then CNC machine it up? Probably cheaper to get a whole new fork...

brake.jpg

Any ideas?
 
Best option probably is to sell the fork and start over. Otherwise I think you'll spend a lot of time fabricating something that won't work well enough when you consider the overall percentage of stopping power required for the fork.
 
Check out Turbotd04's thread which has both a successful and failed attempt of adding disc brakes:

https://endless-sphere.com/forums/viewtopic.php?f=6&t=102534
 
Brand new fork with V-brake bosses when you wanted disc brake mount fork.

Options as I see it

- Sell the fork

- Find an old disc brake fork, grab the angle grinder and cut it so it fits snuggly on your brand new fork and figure out how to attach it. Might mean you have to take the brand new fork apart, and weld but welding would... can?/might?/high potential? of warping the casement of the shock so no smooth action, may bind.

- Hose clamps, dicey I know

- Sell fork, eat the price difference lo$$

- Sell the wheels and go V-brake

- When trying to figure out how to mount disc brake mount, maybe incorperate a long piece of metal, that mounts to the V-brake bosses, and good all the way down, following the fork leg curvature and if you got a mount on the dropout bosses for the axle, even better. Otherwise its the same old issue that many people have encountered and no real solutions have been found, other then cheesy hose clamps or outright welding.

- Maybe you might score and find a disc brake fork housing tree that fits your fork internals.
 
ever4ything on Sram's website says that model should be disk compatible. Have you contacted Sram/Rockshox to see if they can help identify what you were sent? If it's a compatible model, maybe you can just switch the lowers.

Otherwise, sell the fork. Nothing you can do to safely add disk brakes to that fork without changing the lowers.
 
There is a 160mm post mount bracket for this fork, so I guess there must be some holes to screw it on.
 
Thanks everyone. You've all confirmed three things for me:

1. The SRAM/RockShox website is confusing as hell. Now that it's business hours, I've confirmed with their local dealer that I'm not insane - the same part number covers both Rim and Disc brake, and only the serial number differentiates them.

2. ALL adaptors, including any I make would be dodgy as hell, and when you're doing 45-50km/h (Which is why I'm even investing in shocks and carbon rims), I don't want anything dodgy. LBS asked me if I wanted a cheaper Suntour, since most RockShox are out of stock in Australia, but when I told him it was electric bike at high speed, he warned me against it.

3. My best bet is to probably sell it, cop the loss and get the proper fork. Problem is, nothing in Australia at the moment suitable for commute (high quality, low travel fork). Anyone want to argue 100mm is NOT to big a travel for high speed on poor quality (but still sealed) roads, and a small amount of low kerb mounting (1 to 1.5inch mostly). I feel at this point a persuasive argument could convince me to get a cross country fork instead of a commute fork.
 
For up to 20MPH (fastest I go), the Suntour XCV(3) I used on CrazyBike2 (and later SB Cruiser trike) 26" front wheel worked ok; it was a post-mount type disc brake fork (that I used with clamped-on rim brakes).

It's a 100mm travel, and for very small things at low speeds it worked ok, like driveway edges, etc., but at 20MPH on potholes it didn't really help all that much. It was fine on regular road surfaces, but what I really needed was something that worked on big potholes...still don't have one of those. Keep in mind that the bike itself was a long cargo bike with me in the middle-rear, that weighed around 400lbs with me on it (as half the weight), and had no suspension on the rear 20" wheel. So whatever I used would have to be made for that. :/


Anyway, if you don't have bad roads, just regular ones iwth some small defects, small bumps and holes, etc., it would work fine for you.


(I did eventually break teh fork at the crown in a crash on the trike, but a head on collision even at walking speed with 500lbs+ of trike is enough inertia to do that to any singlecrown fork. :/ )
 
Yep. Very confusing, and very unusual too. I mean, for Rock Shox to manufacture a fork with open dropouts and rim brake mounts. That is 20 years old tech IMO.

About 100mm travel to ride the streets. That is the travel I limit my DH forks on commuters. I find it is perfect, as most street motorcycles are with 3’’ to 5’’ travel forks. I have been using a Rock Shocks DHO for a long time on a commuter. That is a 20+ yr old 4 inch travel, double crown fork, through axle with both rim and disc brake mounts.
 
MadRhino said:
I have been using a Rock Shocks DHO for a long time on a commuter. That is a 20+ yr old 4 inch travel, double crown fork, through axle with both rim and disc brake mounts.
Click to expand...

I've forgotten, did the DHO come out before or after the dual crown Judy? I've had a mid 90's 100m travel Judy for so many years that I've worn out a couple of bikes, rebuilt it, and moved it on to the next bike. I modded them slightly to take a 29er wheel when there were zero 29er forks on the market, and the tires were still being listed as 28". Good times. Lots of memories with that fork. It sucks by almost any standard compared to modern forks, but it's just as good now as it was new... and it's been an on road only fork for the last decade for me. 100mm is commuter bike suspension travel, for an ebike.
 
Many years ago, I used the Disc Break conversion seat like this：
O1CN01gDndkc1RfhlDHDtlj_!!2206872132139.jpg
At low speeds there was no problem. need to add non-slip gaskets.
But I haven't tried high speed.The price is about 1-2 dollars.
My bike has been given to my friend, and I found similar pictures online. Hope this is helpful. :thumb:
O1CN01dn6A742F5jT4FvYHY_!!54098829.jpgO1CN01FlOqRR2F5jTBXC3ZI_!!54098829.jpg
 
Thanks. But those types of "P clamp" adaptors might work for the rear, but I doubt would be very good for the fork.

Given I now want to avoid RockShox, what's another reputable brand that won't cost me an arm and a leg?
 
Drunkskunk said:
MadRhino said:
I have been using a Rock Shocks DHO for a long time on a commuter. That is a 20+ yr old 4 inch travel, double crown fork, through axle with both rim and disc brake mounts.
Click to expand...

I've forgotten, did the DHO come out before or after the dual crown Judy? I've had a mid 90's 100m travel Judy for so many years that I've worn out a couple of bikes, rebuilt it, and moved it on to the next bike. I modded them slightly to take a 29er wheel when there were zero 29er forks on the market, and the tires were still being listed as 28". Good times. Lots of memories with that fork. It sucks by almost any standard compared to modern forks, but it's just as good now as it was new... and it's been an on road only fork for the last decade for me. 100mm is commuter bike suspension travel, for an ebike.
Click to expand...

At the time they were high end, expansive MTB forks. The DHO is the DH racing version of the Judy. They came on the market together in 1997 I believe and yes, it is a system that proved very good and reliable. My DHO is still working good, and had survived many bikes like your Judy. It is on the wall now, but I often think of giving it a fresher look and put it on a new build.
 
Sunder said:
Any ideas?
Click to expand...

Use a rim brake and a real wheel? They can work as well as or better than disc brakes.

Use a good linear-pull brake with high quality pads like Kool Stop, and a booster arch. If that's not gimmicky enough for you, use a Magura hydraulic disc brake.
 
Sunder said:
...
Given I now want to avoid RockShox, what's another reputable brand that won't cost me an arm and a leg?
Click to expand...
Buy a used one. I mean, I always preferred riding an old top of the line fork to a new entry level. Rebuilding a fork is not complicated nor very long, and rebuild kits are easily available for expansive forks.

You may have had a bad experience with a seller who didn’t clearly show a picture of the actual fork that you purchased, and SRAM who brought on the market a weird product. But many Rock Shox forks are proven very good and reliable.

Fox are good, more maintenance but very fine tuning and slick action. Older Marzzocchi are very easy to service and long lasting.

Racers are always riding the latest, most expansive forks, and sell their previous one for cheap in the adds on Pinkbike.

The worst you can do is buying a Chinese fork, attracted by the low price. They don’t work smooth, don’t last, and parts are almost impossible to find.
 
MadRhino said:
The worst you can do is buying a Chinese fork, attracted by the low price. They don’t work smooth, don’t last, and parts are almost impossible to find.
Click to expand...

My experience in the bike shop is that most suspension forks, by the time they are badly in need of rebuilding, are no longer supported with spare parts by the manufacturer.

It’s how you know these things are toys and not serious vehicle parts.
 
Looks to me like it has a disk mount, one so old school and obsolete it may have been made only one year. Before disc brakes themselves got standardized.

What I see is half of an old style disc mount, the upper hole. Then maybe the made for a few months brake used that and the lower hole?

Joys of old bike stuff, at one point it was changing so fast in mtb bikes. More recently it got pretty standard, so they had to start putting out stuff like 27.5 wheels, and tapered headsets. So you can't buy old stuff and use it on your bike anymore.

Seems to me you will be running a rim brake this season. Its getting really hard to find a shock in 1 1/8 straight headset that isn't a bike shaped object fork. Pretty soon I'm going to have to throw out two perfectly good bikes. Even now I'm running shit front shocks on both. My nicer ones wore out.

Its part of why I just said f--k it, and bought the honda 100 last winter.
 
Balmorhea said:
Sunder said:
Any ideas?
Click to expand...

Use a rim brake and a real wheel? They can work as well as or better than disc brakes.

Use a good linear-pull brake with high quality pads like Kool Stop, and a booster arch. If that's not gimmicky enough for you, use a Magura hydraulic disc brake.
Click to expand...

Zipp 302s don't have a rim brake compatible surface.

I have to date been running Shimano XTRs. In the dry, they are perfect from a stopping point of view. Can almost go high side. But they are extremely dusty, my wheel needs truing every 2-3 weeks unless I want a fair bit of free-play, and in the wet, again they are fine if I recently cleaned the wheel, but if the brake dust mixes with rain, stopping power is severely compromised.

The first iteration of this bike had the same Alex Rim wheels, professionally built by EMEV3. At that time, I had a slightly lower speed, (about 35-40km/h vs 45+ now), shorter ride (12km/day vs 36km/day now) and a much smoother path to travel. The wheels would be trued once every 6 months, and the brake dust was manageable, and the stopping power in the wet was fine. I think between the exponential function of braking from a higher velocity, as well as triple the distance and rougher road, means that what would be fine for a push bike or low speed eBike, is no longer good enough for my current use case.

Anyway, I'm too far down this path to go back to go back. The Zipp 302 alone cost me $500. The disc brake kit $350, and the fork $400. I'd rather sink another $400 if I had to, in order to finish it, than roll back and have two mid range track components just sit there.

dogman dan said:
Looks to me like it has a disk mount, one so old school and obsolete it may have been made only one year. Before disc brakes themselves got standardized.
Click to expand...

Please don't get my hopes up. This is a 2015-2019 fork, so I doubt it's old and non standard. I'm pretty sure the tabs are for front paniers, and the one hole (which has one on each fork) might be for a dynamo or something.

dogman dan said:
Seems to me you will be running a rim brake this season. Its getting really hard to find a shock in 1 1/8 straight headset that isn't a bike shaped object fork. Pretty soon I'm going to have to throw out two perfectly good bikes. Even now I'm running shit front shocks on both. My nicer ones wore out.
Click to expand...

Boom. I think you hit the nail on the head. At one point, I was like "f*** it, I'll sell this on eBay at half price and cop the loss". Then realised 2/3rds of the LBS' stock is out, and the remaining 1/3rd is all top end DH gear, $1200-2k for a fork, not suitable for a commute.

Anyway. Bit over it at the moment.
 
Balmorhea said:
MadRhino said:
The worst you can do is buying a Chinese fork, attracted by the low price. They don’t work smooth, don’t last, and parts are almost impossible to find.
Click to expand...

My experience in the bike shop is that most suspension forks, by the time they are badly in need of rebuilding, are no longer supported with spare parts by the manufacturer.

It’s how you know these things are toys and not serious vehicle parts.
Click to expand...

I have rebuilt my 2001 Marzocchi Shiver DC last January. Found everything required cheap and easy, even had choice of upgrades. It is better than ever now, and 1.5 lbs lighter.

I have an old Boxxer that had been rebuilt many times and I am not worried about the next.

Many suspension components are quickly obsolete and parts impossible to find. But the best are surviving even after the manufacturer disappeared.
 
Sunder said:
Given I now want to avoid RockShox, what's another reputable brand that won't cost me an arm and a leg?
Click to expand...
If you just want to get riding, and don't mind single-crown forks, the Suntour XCV(3) or other XCx (XCT, XCM, etc) should work fine, until you can get a much better one. It's not the same kind of suspension (just elastomer/spring), so it wont' give as good a ride, but is probably $100-$150USD at a guess. It is a 1-1/8" threadless steerer AFAIK; not sure if it's available in any other form.

Sorry I don't have experience with anything better that's still produced and available.
 
Go to a fabrication shop and see what the cost would be for them to make something for you. There are good welding techniques that will highly reduce warpage. Sometimes they inject the tube with gas, other times they use a paste. I doubt thats a risk you want to take with such an expensive fork. Wouldn't hurt to talk to a fab shop though.
 
Thanks Markz. Given that I can't get the right fork probably for a couple months, I might do just that. But rather than weld, see if I can do the prototyping on a 3d printer and CNC something up. That way, I don't irrevocably change the fork in case I do want to sell it later, or it doesn't work out.

There was a place in China that I did some CNCing from before quite cheap, but it was a relatively simple design. Can't hurt to get a quote at least.
 
RockShox fork lowers are usually made out of cast magnesium. No welding recommended if this one is.
 
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