Fitting disc brakes

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Misterbit
Posts: 1
Joined: 18 Oct 2021, 8:20pm

Fitting disc brakes

Post by Misterbit »

Is it possible to fit disc brakes to a frame built with rim brakes?
The frame is a Marin Bolinas Ridge
Thank you
KM2
Posts: 1323
Joined: 23 Oct 2008, 5:38pm

Re: Fitting disc brakes

Post by KM2 »

eBay
Disc brake bracket converter
Lookrider
Posts: 147
Joined: 1 Aug 2019, 6:10pm

Re: Fitting disc brakes

Post by Lookrider »

I believe you have to be certain that the forks and heafset will be able to take the extra forces implied on it
Not just a case of buying converting brackets ...could be serious safety issues so please speak to a professional befure you attempt this
Tompsk
Posts: 195
Joined: 6 Nov 2014, 9:35am

Re: Fitting disc brakes

Post by Tompsk »

Misterbit wrote: 18 Oct 2021, 8:26pm Is it possible to fit disc brakes to a frame built with rim brakes?
The frame is a Marin Bolinas Ridge
Thank you
With disc brakes the forces on the forks are massively different to rim brakes (assuming 26" or larger wheels). So for the front you need to at least change the forks, perhaps look at the headset too, especially if it's a 1" steerer.
KM2
Posts: 1323
Joined: 23 Oct 2008, 5:38pm

Re: Fitting disc brakes

Post by KM2 »

The converter is for the rear.
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andrew_s
Posts: 5795
Joined: 7 Jan 2007, 9:29pm
Location: Gloucestershire

Re: Fitting disc brakes

Post by andrew_s »

Rear brakes are relatively safe to convert - the wheel locks up before the forces get too large.

Front brakes would need a new fork, probably, but the headset/steerer shouldn't need any change.

The problem with the forks is the fork blade folding at the top of the disc tabs, or excessive flex giving handling problems.
The forces at the headset are the same for a given rate of deceleration regardless of the type of brake, and you can't decelerate faster than would lift the back wheel, which you can do with rim brakes in clean conditions.

"More powerful" disc brakes get you lower hand force and better control, but only actually stop you faster when the braking surface isn't dry.
Dr pepper
Posts: 59
Joined: 29 Jul 2020, 11:41pm

Re: Fitting disc brakes

Post by Dr pepper »

I fitted them to the front of my old trek and they've been fine, and went into the detail at the time.
I tried the ebay brackets didnt fit, being handy with a weld set and seeing as the forks are steel I cut the ebay bracket and welded it on.
The biggest safety concern I found was the front wheel being forced out of the forks, the second the original weld from the fork to the steerer tube can fail with the increased force.
Neither of these has happened to me even with a 180mm disc, and I've grabbed a handful of brake a few times.
Rears can also cause trouble with the frame, some bikes meant for rear discs have a strap on the frame rails to strengthen up, so a bracket would need to be strong here, and preferably with a circular hole that goes over the axle, I think there are such things.
Mine is mechanical, I wouldnt recommend a hydraulic caliper for this unless you manage to get a kit designed for it.
I certainly wont go back to rim brakes.
Lookrider
Posts: 147
Joined: 1 Aug 2019, 6:10pm

Re: Fitting disc brakes

Post by Lookrider »

Dr pepper
I dont want to challenge your welding skills etc
Safety wise any weld on steel changes the echanical metal properties next to the weld this area is known as the heat affected zone HAZ
The only way to help with this is to have the welded area subjected to heat treatment in a controlled environment where the temperate of heat relief is calculated based on carbon content and thickness etc
The metal is heated then held for a given time and slowly allowed to cool
This helps prevents minor cracking and or fatigue cracks in the HAZ
All you have done is make this area HAZ
Extremely brittle and very unsafe
The continuing vibrations through the fork will one day result in a fatigue crack and the ultimate failure of the fork
I'm sorry to make you aware of this but I would think seriously about replacing your fork
I'm sure you will read up online the effects of welding and the HAZ
Des49
Posts: 799
Joined: 2 Dec 2014, 11:45am

Re: Fitting disc brakes

Post by Des49 »

Dr pepper wrote: 21 Oct 2021, 1:00pm The biggest safety concern I found was the front wheel being forced out of the forks, the second the original weld from the fork to the steerer tube can fail with the increased force.
You have given enough reason not to in your post, I would have the brake mount on the front of the forks so the wheel was forced into the dropouts not out.

I second the post above by Lookrider.

The main enemy is fatigue, this will build up slowly until things break, potentially pretty disastrous for forks.

Years ago I looked into adding discs to my MTB (over 30yr old custom steel frame), certainly getting new forks made for the job would be fine but would change the ride quality from needing to be stiffer/stronger. But the rear triangle would be vulnerable, the frame builder really did not recommend doing this to my frame, they would have needed to have added a brace but even then did not recommend it.
NickJP
Posts: 797
Joined: 24 Sep 2018, 7:11pm
Location: Canberra, OZ

Re: Fitting disc brakes

Post by NickJP »

Dr pepper wrote: 21 Oct 2021, 1:00pmI fitted them to the front of my old trek and they've been fine, and went into the detail at the time. I tried the ebay brackets didnt fit, being handy with a weld set and seeing as the forks are steel I cut the ebay bracket and welded it on. The biggest safety concern I found was the front wheel being forced out of the forks, the second the original weld from the fork to the steerer tube can fail with the increased force
This is what can happen when fitting disc caliper tabs to a fork not designed for them:

Image

Image
Des49
Posts: 799
Joined: 2 Dec 2014, 11:45am

Re: Fitting disc brakes

Post by Des49 »

NickJP wrote: 23 Oct 2021, 2:36am
This is what can happen when fitting disc caliper tabs to a fork not designed for them:
That is frightening, hope the riders were ok. Thanks for posting these examples, hopefully they serve to put anyone off considering adding discs to a bike not already designed for them.
Dr pepper
Posts: 59
Joined: 29 Jul 2020, 11:41pm

Re: Fitting disc brakes

Post by Dr pepper »

The internet is full of disaster stories.
My forks are much wider I'm not overly concerned about the same happening to mine, however the steerer tube weld does concern me a little, thats why I pull it apart and check it now & again.
Good V brakes which I had initially could probably provide just as much force, the only difference I get is better brakes in the rain.
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