Is my bike frame disk brake compatible?

kmxtornado

kmxtornado

10 kW
Joined
Feb 28, 2011
Messages
563
Location
Bay Area
Here I go again with newb questions. I know my front fork isn't disk brake compatible, but what about the rear? Here's a shot of my rear dropout.

Ebike:
IMG_0890.JPG

Larger photo here: http://1.bp.blogspot.com/-dQiNyr5R2iY/TrjvaI6SWyI/AAAAAAAABz0/kAVIF_Dczck/s1600/IMG_0890.JPG

Restoration bike:
IMG_0955.JPG

Larger photo here: http://1.bp.blogspot.com/-ZBt6fwRFSW0/TsC_1gCQvrI/AAAAAAAAB-o/J21nY0t1Ad8/s1600/IMG_0955.JPG

1. I suspect that the hole being used for the white rear trunk rack and the empty one are for mounting a disk brake caliper. Is that correct?
2. Is it weird to have a disk brake in the back and a standard one in the front? Anyone else have a setup like that?

I contacted A2Z who fabricate adapters and stuff like that for mounting disk brake systems, but they weren't very helpful. They kept telling me their stuff is only for alloy frames and not steel. Firstly, they don't know mine is steel and secondly it makes more sense that disk brakes are mounted on steel frames since a majority of mountain bikes are built out of this material, right? They kept referring to my rear dropout as a fork. Shows what they know. Ugh.
 
No.

there are adapters that you could use that might make it comparable. However neither frame looks like it has the clearance for a disk. The chain stays and seat stays have a constant angle from the dropouts to where they meet the seat tube. that angle will strike the outer edge of a disk.

A problem easily solved on a steal bike with a mallet and a welder.
 
kmxtornado said:
Here I go again with newb questions. I know my front fork isn't disk brake compatible, but what about the rear? Here's a shot of my rear dropout.

I contacted A2Z who fabricate adapters and stuff like that for mounting disk brake systems, but they weren't very helpful. They kept telling me their stuff is only for alloy frames and not steel. Firstly, they don't know mine is steel and secondly it makes more sense that disk brakes are mounted on steel frames since a majority of mountain bikes are built out of this material, right? They kept referring to my rear dropout as a fork. Shows what they know. Ugh.
Click to expand...

I also contacted A2Z, no help at all. I wanted to convert my cheap chinese ebike frame to disc brakes, but ended up buying a new frame. Much easier and probably safer to start with a frame suitable for disc brakes from the beginning, unless you can weld your own frame/dropouts/brake calliper holders.

Oh, and dont forget that when including a hubmotor AND disc brakes, you need to figure out a way to fixate the torque arms. I would never use a hubmotor without at least one torque arm. When trying to adjust a frame to accept brake discs AND using torque arms is near impossible. Better to fixate the torque arm and continue using V-brakes. Even better to get a better frame.
 
nope sorry. Those are not disc brake tabs.
Those disc brake adapters are known to crack frames, that is why they are not popular.
Frames not designed for rear disc do not have the strength to handle the braking forces.

You might want to go with the biggest and strongest v-brakes for the rear of the bike.
 
BTW, if it makes you feel any better, my bike with 16lbs of battery, my 230 pound self, and mega downhill duty do just fine with a 180mm front disc plus a rear vbrake.

So, said setup could work for you unless you're significantly heavier than me.
 
Thanks fella's. Then what are those two holes for above the rear dropout?

hjns said:
kmxtornado said:
Here I go again with newb questions. I know my front fork isn't disk brake compatible, but what about the rear? Here's a shot of my rear dropout.

I contacted A2Z who fabricate adapters and stuff like that for mounting disk brake systems, but they weren't very helpful. They kept telling me their stuff is only for alloy frames and not steel. Firstly, they don't know mine is steel and secondly it makes more sense that disk brakes are mounted on steel frames since a majority of mountain bikes are built out of this material, right? They kept referring to my rear dropout as a fork. Shows what they know. Ugh.
Click to expand...

I also contacted A2Z, no help at all. I wanted to convert my cheap chinese ebike frame to disc brakes, but ended up buying a new frame. Much easier and probably safer to start with a frame suitable for disc brakes from the beginning, unless you can weld your own frame/dropouts/brake calliper holders.

Oh, and dont forget that when including a hubmotor AND disc brakes, you need to figure out a way to fixate the torque arms. I would never use a hubmotor without at least one torque arm. When trying to adjust a frame to accept brake discs AND using torque arms is near impossible. Better to fixate the torque arm and continue using V-brakes. Even better to get a better frame.
Click to expand...

Well, the purpose of my bike build was to reuse an existing bike I had laying around. I have been eyeing a Specialized Sport with stock disks, but that's just going to take up more space in my garage and it's more money spent that I was hoping I could use to upgrade my existing bike.

No need for torque arms. The hub is in the rear and my frame is full steel. It's also a fairly weak motor. Not nearly as hardcore as the rest of you guys' rides.

neptronix said:
nope sorry. Those are not disc brake tabs.
Those disc brake adapters are known to crack frames, that is why they are not popular.
Frames not designed for rear disc do not have the strength to handle the braking forces.

You might want to go with the biggest and strongest v-brakes for the rear of the bike.
Click to expand...

Good to know. Thanks for your input on them.

neptronix said:
BTW, if it makes you feel any better, my bike with 16lbs of battery, my 230 pound self, and mega downhill duty do just fine with a 180mm front disc plus a rear vbrake.

So, said setup could work for you unless you're significantly heavier than me.
Click to expand...

Nope, the total weight of me and mine definitely doesn't outweigh your setup. I have a rear hub though. The hub is disk brake compatible, but I was wondering if my frame was.
 
Haha, but why are there two holes? Different type of racks? No wonder there's holes on both the left and ride sides of the bike. Stupid me.
 
kmxtornado said:
No need for torque arms. The hub is in the rear and my frame is full steel. It's also a fairly weak motor. Not nearly as hardcore as the rest of you guys' rides.
Click to expand...
I would not count on that, those dropouts look smallish.

Since your frame is steel, it would be possible to solder some reinforcements, that could make for torque plate and IS brake caliper mount all at once.
 
If you want disc brakes on the front, just buy a fork with disc mount. I think nasbar has one for around $50.
 
Oohhhh, I see. Thanks! Learn something new every day I suppose. I had no clue. Thanks for the clarification.

chisixer6 said:
If you want disc brakes on the front, just buy a fork with disc mount. I think nasbar has one for around $50.
Click to expand...

Ooo, you weren't joking. I just took a look at it and it really is $50 + shipping/tax. Not bad at all. But then again, I'm also looking at some low price suspension forks, but unfortunately these cheap ones at $63 aren't disk brake compatible. So I guess if I'm going to go cheap, I gotta pick one or the other. Which would you guys recommend if I could only have either:

A. Suspension fork.
Maybe adding weight in the front might be a good thing.

B. Disk brake fork (reminder, that my hub motor is on the back).
I figured I should have a disk brake in the rear if anywhere since that's where all the braking is usually done and that's the wheel that's got the most torque (although my brake lever is connected to a power cutoff switch).

Thoughts?
 
kmxtornado said:
(reminder, that my hub motor is on the back).
I figured I should have a disk brake in the rear if anywhere since that's where all the braking is usually done and that's the wheel that's got the most torque (although my brake lever is connected to a power cutoff switch).

Thoughts?
Click to expand...

This isn't true. If you look at motorcycles, they'll normally have two discs in the from and one in the rear. The majority of the braking is done on the front. Others can chime in, but most will tell you that the front does the brunt of the work. Granted, for both bikes and motorcycles, it's virtually Impossible to mount two discs in the back. Many higher-end bikes will have larger rotors in the front than the back.

Tony
 
TonyReynolds said:
kmxtornado said:
(reminder, that my hub motor is on the back).
I figured I should have a disk brake in the rear if anywhere since that's where all the braking is usually done and that's the wheel that's got the most torque (although my brake lever is connected to a power cutoff switch).

Thoughts?
Click to expand...
Click to expand...

This isn't true. If you look at motorcycles, they'll normally have two discs in the front and one in the rear. The majority of the braking is done on the front. Others can chime in, but most will tell you that the front does the brunt of the work. Granted, for both bikes and motorcycles, it's virtually Impossible to mount two discs in the back. Many higher-end bikes will have larger rotors in the front than the back.

For my steel bike build, I'm looking at a Redline D440 (or similar), keeping the V-brake in the rear and adding the largest mechanical rotor disc brake (200mm or larger) to the front that I can afford. That combo will give me plenty of stopping power.

Tony
 
I have an old Fox front suspension fork for you that has an IS mount for disc brakes, with a cheap mechanic chinese disc brake caliper. I can send it to you for costs of shipping (from Basel, Switzerland).

You will be fine with a front disc brake and a rear V-brake, even with your hub motor in the rear. Just make sure not to open the throttle and brake at the same time and have e-braking implemented. No brake (disc/V-brake) can withstand the power of a hub motor.....

KR,
Henk


kmxtornado said:
Oohhhh, I see. Thanks! Learn something new every day I suppose. I had no clue. Thanks for the clarification.

chisixer6 said:
If you want disc brakes on the front, just buy a fork with disc mount. I think nasbar has one for around $50.
Click to expand...

Ooo, you weren't joking. I just took a look at it and it really is $50 + shipping/tax. Not bad at all. But then again, I'm also looking at some low price suspension forks, but unfortunately these cheap ones at $63 aren't disk brake compatible. So I guess if I'm going to go cheap, I gotta pick one or the other. Which would you guys recommend if I could only have either:

A. Suspension fork.
Maybe adding weight in the front might be a good thing.

B. Disk brake fork (reminder, that my hub motor is on the back).
I figured I should have a disk brake in the rear if anywhere since that's where all the braking is usually done and that's the wheel that's got the most torque (although my brake lever is connected to a power cutoff switch).

Thoughts?
Click to expand...
 
TonyReynolds said:
This isn't true. If you look at motorcycles, they'll normally have two discs in the from and one in the rear. The majority of the braking is done on the front. Others can chime in, but most will tell you that the front does the brunt of the work. Granted, for both bikes and motorcycles, it's virtually Impossible to mount two discs in the back. Many higher-end bikes will have larger rotors in the front than the back.

For my steel bike build, I'm looking at a Redline D440 (or similar), keeping the V-brake in the rear and adding the largest mechanical rotor disc brake (200mm or larger) to the front that I can afford. That combo will give me plenty of stopping power.

Tony
Click to expand...

I would only partially agree. When traveling in town at speeds around 35-45km/h, I always brake rear first, then add the front for more power. Front first will give me more dive, which I dont like. Also, I find it easier to modulate the rear better than the front, probably because of the different force vectors, especially with full suspension. BTW, in the end, it may well be that the front brakes get the most load... and in the dirt / downhill it may also be a different case.
 
You said it yourself: The front does dive.

This happens because when braking, the weight is transfered to the front. The weight being in the front, it is the front brake that does most of the work, more than 80% usually, and nearly 100% when you are braking very hard.

With the rear, you can only brake moderately, for any hard braking will lose traction and the wheel will lock. The front being loaded by the weight transfer, increases its traction, thus can be braked with much more power before starting to slip.

Acceleration produces the opposite, loading the rear with the weight transfer. The wost case scenario is a bike with a front motor and the big brake in the rear.

Just try measuring your braking distance at a given speed, using the front or the rear brake.
 
If you go disc/ front and vbrake/rear, that's fine...if you want to spend a little more, get hydralic disc on the front, I heard from an earlier thread that mechanical disc is not that much better than v brakes, I have Avid BB5 mechanical and I don't think it stops that much better.

Jerry
 
chisixer6 said:
I heard from an earlier thread that mechanical disc is not that much better than v brakes, I have Avid BB5 mechanical and I don't think it stops that much better.

Jerry
Click to expand...
Well, they are not so much more powerfull, but they brake in all weather conditions, and that is a big step up already.

A good set of DH rated hydro disc brakes is the way to go when you build a powerfull Ebike and want to ride fast.
 
Looks teh same as the ones that came on my DayGlo Avenger back in 2005; they've worked ok with the Fusin geared motor and with a 9C 2807 DD motor.

The Fusin at it's original lower power levels (36V <16A) only needed torque washers, but when moved up to 48V 20A it required dual torque arms.

The 9C needed only a short torque arm until I went to 48V 40A.
 
I'm always so impressed with you guys fabricating your own stuff. Am I the only one on ES that doesn't have machining equipment?
 
MadRhino said:
You said it yourself: The front does dive.

This happens because when braking, the weight is transfered to the front. The weight being in the front, it is the front brake that does most of the work, more than 80% usually, and nearly 100% when you are braking very hard.

With the rear, you can only brake moderately, for any hard braking will lose traction and the wheel will lock. The front being loaded by the weight transfer, increases its traction, thus can be braked with much more power before starting to slip.

Acceleration produces the opposite, loading the rear with the weight transfer. The wost case scenario is a bike with a front motor and the big brake in the rear.

Just try measuring your braking distance at a given speed, using the front or the rear brake.
Click to expand...

That's completely true for motor scooters and motorcycles b/c they're so heavy. I ride a Yamaha Vino 125 and you're 100% right on that. Definitely not the same with bikes though. I should know b/c I flipped over the handlebars on more than one occasion as I was stupidly holding something in my right hand and only engaged the left lever. Or maybe you mean that both still need to be used: rear first, then followed by using the front brake? I suppose ebikes fall in btw the categories since they're heavier than normal bikes but lighter than the gas powered 2-wheelers and maybe perhaps that's why it's okay to use the front brake so aggressively?

Interesting topic though. Do you guys really use the front brake more than the rear? Maybe it's time for a new thread.
 
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