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Old 01-01-05, 10:47 PM   #1
Everest
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Converting To Disc Brakes

Im considering switching from v to disc brakes on my mountain bike its a gary fisher tassajara which had a disc model so i assume my frame and fork have the required tabs. Im just wondering what all i would need to purchase to make the conversion. Of course i will have to buy rotars calipers and levers but will i have to change hubs?
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Old 01-01-05, 11:39 PM   #2
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If you have the hubs with a flat face and 6 bolt holes on the left side then you have the wheels. Otherwise you will need new hubs or rims. A new disc wheelset is not too expensive anymore. I saw a Sun Rhynolite/Shimano Deore hub wheelset at my lbs for 130.
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Old 01-02-05, 09:18 AM   #3
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Quote:
Originally Posted by Everest
Im considering switching from v to disc brakes on my mountain bike its a gary fisher tassajara which had a disc model so i assume my frame and fork have the required tabs.
You might want to look to be sure.
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Old 01-02-05, 10:13 AM   #4
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I'm sure this has been answered before.
(Assuming you have the appropriate mountings on your bike)
If you want cable discs, you'll need calipers, rotors (with pads), and cables
If you want hydraulic discs, you'll need calipers, rotors, hose (and oil), and levers
If you don't have disc hubs, you'll need to get some.
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Old 01-02-05, 04:14 PM   #5
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Not neccesarily the hose and oil. My hydros came pre-hosed and bled
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Old 01-02-05, 04:45 PM   #6
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i have the right mountings however the hubs dont appear to have the necesssary holes so this projects price just made a significant price jump. is it really worth the upgrade? Unless somone has some disc stuff they want to let go for cheap i'm now thinking i'll have to settle for upgrading to higher quality v's any recomendations.
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Old 01-02-05, 04:52 PM   #7
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Quote:
Originally Posted by Everest
Im considering switching from v to disc brakes on my mountain bike its a gary fisher tassajara which had a disc model so i assume my frame and fork have the required tabs. Im just wondering what all i would need to purchase to make the conversion. Of course i will have to buy rotars calipers and levers but will i have to change hubs?
Are you sure that you want to do this? Most equipment upgrades don't make economic sense.

1. Have you perchance filed the lawyer tabs off of your fork? If you have, you might want to rethink the whole project. Disc brakes have an unnerving tendency to eject the front wheel right out of the dropouts. A smooth bottom fork with an ordinary quick release isn't adequate to hold your fork in place.
2. Take a look at your wheels. If they have radial spokes or if you can't see any disc mounts (my bet), you'll need a new wheelset for starters.
3. Now take a look at your brake levers. If they are combined with the shifters, which is common on bikes in this price range, You're either limited to cable actuated brakes or add a set of shifters to your shopping list.
4. Take a hard look at what is included in whatever brakes you are interested in buying. If you're planning to do front and rear, make sure that you're getting front and rear. Do you need an adapter for the caliper? If you do, what exactly do you need? Are you positive about your answer to the last question?

After you price out all of this componentry, consider the cost of a brand new bike that's already equipped the way that you want. Keep in mind that you're getting a brand new bike with all brand new components, everything is designed to work with everything else and you get a new bike warranty.
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Old 01-02-05, 04:53 PM   #8
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Quote:
Originally Posted by Everest
i have the right mountings however the hubs dont appear to have the necesssary holes so this projects price just made a significant price jump. is it really worth the upgrade? Unless somone has some disc stuff they want to let go for cheap i'm now thinking i'll have to settle for upgrading to higher quality v's any recomendations.
Avid Single Digit 7's. They're good and they're cheap.
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Old 01-02-05, 04:58 PM   #9
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Disc brakes have an unnerving tendency to eject the front wheel right out of the dropouts. A smooth bottom fork with an ordinary quick release isn't adequate to hold your fork in place.
Not that runaround again. If your skewers are that loose you need help.

www.Jensonusa.com has Sun Rhynolite/XT disc wheelsets for $130
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Old 01-02-05, 05:02 PM   #10
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Disc brakes have an unnerving tendency to eject the front wheel right out of the dropouts. A smooth bottom fork with an ordinary quick release isn't adequate to hold your fork in place.
a) this is really really REALLY rare
b) that rule of thumb only applies to 8in rotors on crappy forks built without the stresses of disc brakes in mind. New forks don't have any issue with 6in and personally I have one dh fork with 8 in front rotor and a standard QR and never have issues (the fork has been running for 3 years through various owners too) The general warning is against 8in rotors on a standard QR and even then I don't know anyone who has had this happen. And most people I know run 8in rotors up front

I do agree thoguh, unless you are riding stuff that needs discs I find v's work fine. So really the cost of the upgrade just ends up not being worth it
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Old 01-02-05, 06:30 PM   #11
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Originally Posted by Maelstrom
a) this is really really REALLY rare
That's what I used to think too. In fact, the first time I heard it I thought it was crazy. I don't think that it's all that rare anymore and I definitely wouldn't file the lawyer tabs on any disc brake bike.
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Old 01-02-05, 07:10 PM   #12
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Quote:
Originally Posted by Retro Grouch
Are you sure that you want to do this? Most equipment upgrades don't make economic sense.

1. Have you perchance filed the lawyer tabs off of your fork? If you have, you might want to rethink the whole project. Disc brakes have an unnerving tendency to eject the front wheel right out of the dropouts. A smooth bottom fork with an ordinary quick release isn't adequate to hold your fork in place.
2. Take a look at your wheels. If they have radial spokes or if you can't see any disc mounts (my bet), you'll need a new wheelset for starters.
3. Now take a look at your brake levers. If they are combined with the shifters, which is common on bikes in this price range, You're either limited to cable actuated brakes or add a set of shifters to your shopping list.
4. Take a hard look at what is included in whatever brakes you are interested in buying. If you're planning to do front and rear, make sure that you're getting front and rear. Do you need an adapter for the caliper? If you do, what exactly do you need? Are you positive about your answer to the last question?

After you price out all of this componentry, consider the cost of a brand new bike that's already equipped the way that you want. Keep in mind that you're getting a brand new bike with all brand new components, everything is designed to work with everything else and you get a new bike warranty.

The whole "front wheel beiong ejected" urban myth actually occurred.

The person Screaming blue murder about how dangerous it was and "it happend to me!" even put up on his own website all the gory details, well not everything.

It turned out that the silly SOB did it to himself, he commissioned somone to build him a disc fork for his tandem, then proceded to ride it down a steep hill, oh did you also know that he either removed the lawyers lips or had them romoved because it slowed down tire changes.

He pretty well set it up to blow up in his face, and then started this campain of how bad disk brakes are without a bolt on axle.
and oooh, I'll PM you, some cat has avid disc's, both front & rear going for 135 or so on Ebay.
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Old 01-03-05, 11:31 AM   #13
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I upgraded the front to Avid discs this past weekend. Total investment (Avid BB7 disc and SD7 levers) was under $100 out the door from Cambria. Of course, I didn't need the levers, but they came highly recommended.

My bike came with disc-ready hubs.

The caliper was a snap to set up, and no screeching sounds yet. I put ~12 very wet, very muddy miles on it right away, and am impressed with the performance. Really what I like is how much smoother (and quieter, and stoppier) the action at the caliper is compared with how a v-brake works on a wet and muddy rim.

And the SD7 levers were a great investment. So much adjustability, and they provide great modulation even to the v-brake on the rear. Light years better than the Tektro levers I took off.
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Old 01-03-05, 12:46 PM   #14
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Quote:
Originally Posted by Scooby Snax
It turned out that the silly SOB did it to himself, he commissioned somone to build him a disc fork for his tandem, then proceded to ride it down a steep hill, oh did you also know that he either removed the lawyers lips or had them romoved because it slowed down tire changes.
Not exactly...

No, he's not a silly SOB; he's a pretty smart guy with a PhD in environmental sciences (or something like that) who has been riding for many years and who, along with his wife, have successfully campaigned their Ventana and Calfee off-road tandems in events like the TransAlp and TransRocky Challenges, to name but a few of their accomplishments. Note: I have known James for 6 years via tandem cycling discussion forums and was one of the first to hear about their wheel ejection on our off-road tandem enthusiast's forum.

Yes, it was a custom fork and it truly was an awful design relative to the drop-out orientation and "other things". No, he didn't remove the tabs; there were none to begin with. The fork was fabricated for use with a custom Calfee Tetra Tetra enduro tandem and was intended to be used for touring and non-technical dirt paths and trails with a disc brake.

It's also noteworthy that this same Calfee Tetra Tetra tandem was also fitted with a Marzocchi DirtJumper "Frankenstein" fork with 20mm axle for technical off-road riding and it was in this more robust configuration that they completed the TransRocky challenge.

Back to the failure, it's important to note that the disc brake being used was a four pot downhill hydraulic from Hope with 203mm rotor which moved the disc caliper contact point with the rotor well behind the fork blade (photos on his Website).

What was and remains a valid issue from the event is the need to carefully evaluate the various fork drop-out configurations being used or modified for use with disc brakes because disc brakes do, in fact, alter how brake energy acts on the front axle of a bike. The further you clock around the brake caliper's contact point with the braking surface -- in this case a disc brake caliper and rotor -- the more you alter the brake energy's path. Remember, the caliper leverages the axle when it is applied to the brake surface to slow or stop the rotation of the wheel. What stops a bike is friction between the tire and ground. Both of these sources of brake energy act together against the axle which, on a bike with rim brakes mounted above and forward of the axle, cause the axle to be pushed back into a conventionally oriented drop-out. It follows, as you move a brake caliper's location clockwise or counter-clockwise, the brake forces acting on the axle shift with it. If you move it too far back or forward (not that I know how you'd do that) and don't correct orientation of the drop-out as you change in brake caliper position, you will reach a point where the axle is no longer being forced into the deepest part of the drop-out and, instead, against only one tang or perhaps towards the opening in the drop-out. Clearly, a quick release skewer is not designed to deal with strong shearing forces.

You can read Jame's take on the issue at the aforementioned Website: http://www.ne.jp/asahi/julesandjames...quick_release/

Details regarding the background and supporting data that suggests that QR skewers can work themselves loose are outlined here: http://www.ne.jp/asahi/julesandjames...ase/diary.html

Anyway, while not defending the notion that there are an inordinate number of wheels being pulled out of forks by disc brakes (I'll let others hash that out), I would note that under the right (or wrong) conditions a disc brake "could" increase the probability that a wheel could be ejected from a disc equipped bike with an improperly tightened skewer or just a bad combination of fork, brake, and skewer, or a bike with a rear wheel disc brake mounted behind the seat stay that has rear-facing drop-outs (been there, done that).

My personal take -- provided elsewhere in the archives -- is this: I think any concerns regarding wheel ejection can easily be addressed by the average, informed cyclist who uses quality components produced by recognized brand-name manufacturers per their instructions. At a minimum, drop-outs on disc-compatible forks should be parallel with fork blade or canted forward and incorporate supplemental tabs or recessed flats to preclude a skewer pull-out while subjected to shearing forces. Ti or super-lightweight quick-release skewers should not be used to secure a disc wheel and the cyclist should make a point to read the manufacturer's instruction regarding proper use and closure of the skewer. Finally, anyone using four or six-pot downhill disc brakes like the Magura Gustav M and Hope's Enduro or Ti-6 with 185mm or larger rotors must be absolutely sure they are using a disc-specific fork with properly aligned drop-outs and supplemental retention features since these particular caliper installations create severe brake force & brake force path issues. Moreover, if someone truly needs downhill brakes they probably need a bolt-on hub. IMHO, single piston XC disc brakes are usually not of great concern for the average rider assuming all other things have been addressed AND skewer position and tension are checked before and after each ride. For tandem teams, advanced, heavyweight, or super-aggressive riders, closer attention may be warranted. In any event, if anyone finds that their skewer shifts or feels loose, they should inspect their drop-outs for any damage and pay close attention to their skewer on subsequent rides. If the skewer continue to shift or loosen they should replace the skewer and monitor the new skewer for movement during use. If it stays put, resume the prudent process of just double checking the skewer before and after each ride. If it continues to shift, they should carefully evaluate if they have selected the appropriate fork/axle retention system for the type of riding they are engaged in.

Last edited by livngood; 01-03-05 at 04:47 PM.
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Old 01-03-05, 01:04 PM   #15
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I stand Corrected, It was all the fork makers fault!!
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Old 01-03-05, 03:08 PM   #16
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Originally Posted by Scooby Snax
I stand Corrected, It was all the fork makers fault!!
I don't think it's that simple. It makes it easy to dismiss the original crash from Dec '02, but it doesn't address other rider's who have experienced wheel extractions or discovered loose skewers where the common link is disc brakes vs. rim brakes.

Bottom Line: Prudence dictates that anyone who has disc brakes be attentive to the care and use of their equipment. A loose skewer discovered after a ride or fall should not be dismissed as "rider error" and should warrant close attention on subsequent rides.
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Old 01-03-05, 03:22 PM   #17
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As I said before, common sense applies. Disc or no. I have known several friends who have dropped front wheels off V-brake bikes, so the percentages in my experience are jaded the opposite way. Whichever form of stoppers, The QR should leave a nice big "Ow that was hard" indentation in the hand. If you dont strain a little when taking it on and off, it is too loose(that does't neccesarily apply to the bodybuilding oafs. But to average people).
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Old 01-03-05, 03:23 PM   #18
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Quote:
Originally Posted by mtbikerinpa
Whichever form of stoppers, The QR should leave a nice big "Ow that was hard" indentation in the hand. If you dont strain a little when taking it on and off, it is too loose(that does't neccesarily apply to the bodybuilding oafs. But to average people).
Good advice.
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Old 01-04-05, 01:24 PM   #19
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"lawyer tabs"?
If you're looking to go cheap, then have a look on ebay. You could go one wheel at a time. Starting at the front is probably best, but up to you really. A front new disc hub is fairly cheap, then it's a case of rebuilding up your wheel (or just buying an entire new front wheel). If you have integrated brake/shifters then just go for cable discs, otherwise you'll end up spending way more.
But like Retro Grouch said, is it really worth it?
mtbikerinpa, technically you do still need a hose & oil, but most of the time that comes with the brake. Same for some other stuff though.
Cheers
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Old 01-04-05, 02:06 PM   #20
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I have upgraded to discs on two bikes, It's not riding in rain, mud, or snow that drove me to it, It's the simple pleasure of not having to undo the V brake to get the wheel and tire off that makes me smile!
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