will a disc brake rip the QR from front fork and kill me?
cooperplace
Posts: 34
I'm talking to XACD (excellent people) about making a Ti 'cross disc fork for my road bike. Because of concerns others have raised about the possibility of the quick release coming out of the fork during hard braking, I've asked XACD to revise their design so the disc mounts are on the _front_ of the fork not the rear. The way the physics looks to me, this should cause the force imposed on the axle by the disc to be perpendicular to the fork instead of _down_ and out of the fork. I am however puzzled because every disc fork I see has the mounting points at the back. Am I missing something?
I would be pleased to hear comments from those who understand the relevant physics and engineering.
I would be pleased to hear comments from those who understand the relevant physics and engineering.
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Stay away from one of Ti forks. There is a reason no major manufacturer makes road or mtb forks from Ti. The amount of manipulation required to get a fork that is rigid in all the right directions, yet also forgiving is intense. Look at any old steel road fork, they are not made out of standard straight gauge tubing, they are custom drawn into the shape of fork blade and come as part of tube sets from the manufacturer. Even steel forks are very rare these days as carbon forks are just so much easier to manufacture well and cheaply. I know the idea of a Ti fork sounds nice, but I would not trust one, especially with a disk brake on it as this concentrates all the braking forces around the bottom of the fork greatly increasing the bending moments in the fork blade. As for the quick release question, mountain bikes nearly all run front disk and QR set-ups, I've never known anyone's wheel to pop out. Looking at the physics of it, its unlikely to happen even with the QR undone.
DO NOT put the brake calliper on the front of the fork, this will just put the bolts holding it on under tension, and could quite easily cause them to rip out under heavy breaking.
My suggestion would be to stop trying to redesign the fork as it is clear that you don't have that strong a grasp of the fine details involved and XCAD don't seem to be in the business of providing much feedback or input into the design process. Buy a carbon road fork or 29er MTB fork with disk mounts and be happy.
http://www.universalcycles.com/shopping ... p?id=262840 -
I disagree, it's fairly clear that if you brake hard the forces will push the wheel down (actually, down and backwards). If your QR is not done up tightly then your wheel will fall out. I think On-One now make their disk brake forks with a horizontal drop out for this reason.
As for putting the brake on the front, I've no idea. Have you asked XACD about it?0 -
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Down/Up wrote:As a 110kg mountain biker I've never experienced and issues with my disk brakes and QR, and have never met anyone who has.
There have been a few cases - one springs to mind straight away:http://www.bikeradar.com/news/article/russell-pinder-accuses-suspension-fork-firm-of-negligence-19107
Forward facing dropouts (as in the top photo) and make sure the QR is done up nice and tight and like Down/Up, you should not have a problem, but keep the disc mount on the rear - there's a reason every other fork manafacturer keeps it there...0 -
forks for disc brakes often have ridges/tabs on the drop outs (lawyer lips) to stop the wheel being forced out even if the qr isn't tight
mine have these, no idea if they work as i keep the qr *tight*, but they certainly mean i have to slacken-off the qr by a huge amount to get the wheel outmy bike - faster than god's and twice as shiny0 -
Mounts on the rear have a "pushing" the forks forward effect when braking; front mounted have a "pulling" effect. This can be used for different purposes but it needs frame geometry, rake, suspension etc all to be put into the equation.
If you're worried about the QR, then get a Lawyers Tab put in as per USA.CAAD9
Kona Jake the Snake
Merlin Malt 40 -
I've been using a XACD ti disc fork for nearly 5 years - it doesn't have lawyer tabs or forward facing drop-outs - I've never experienced wheelslip and I still have all my teeth! The whole issue of lawyer tabs and non-QR wheels was down to incompetent users - people were riding sus-forks for 10 years without this nonsense. There have been numerous attempts at ti forks - cheap carbon and steel forks have killed-off the market - there is nothing intrinsically wrong with them. Do use a steel QR though.
I would also pay more attention to someone who is an experienced designer and fabricator of titanium than a forum 'expert' with 2 posts!Make mine an Italian, with Campagnolo on the side..0 -
DO NOT put the brake calliper on the front of the fork, this will just put the bolts holding it on under tension, and could quite easily cause them to rip out under heavy breaking.
I don't see why this should be so, can you please explain why this is the case?0 -
As for putting the brake on the front, I've no idea. Have you asked XACD about it?[/quote]
XACD are quite happy to put the mounts on the front.0 -
but keep the disc mount on the rear - there's a reason every other fork manafacturer keeps it there...[/quote]
and that reason is?????????????0 -
Buckled_Rims wrote:Mounts on the rear have a "pushing" the forks forward effect when braking; front mounted have a "pulling" effect. This can be used for different purposes but it needs frame geometry, rake, suspension etc all to be put into the equation.
why? unlike a suspension front end, geometry doesn't change during braking0 -
I would also pay more attention to someone who is an experienced designer and fabricator of titanium than a forum 'expert' with 2 posts![/quote]
YES!!0 -
I may only have 2 posts on this forum but I'm a structural engineer and do have some understanding of the forces involved.
My understanding is XACD are reasonable fabricators, but not designers. This may be wrong but everything I've read about them seems to say that the customer need to supply nearly all the design input.
Anyway I wouldn't be trusting forks from a company that has a decent history of fork failures. Check out this thread on MTBR, Spicer/Sibex forks made by XACD failing through the top of the blades at the welds. http://forums.mtbr.com/showthread.php?t ... ght=spicer
I'd be more worried about this happening to my fork than the disk brake forcing the wheel out of the drop-outs.
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Horton wrote:Down/Up wrote:As a 110kg mountain biker I've never experienced and issues with my disk brakes and QR, and have never met anyone who has.
There have been a few cases - one springs to mind straight away:http://www.bikeradar.com/news/article/russell-pinder-accuses-suspension-fork-firm-of-negligence-19107
Forward facing dropouts (as in the top photo) and make sure the QR is done up nice and tight and like Down/Up, you should not have a problem, but keep the disc mount on the rear - there's a reason every other fork manafacturer keeps it there...
does anyone know who the legal team is that represented mr pinder?0 -
This is one scary thread, just stop now, you clearly have no idea of what your doing. If you don't have a basic understanding what putting the caliper on the front will do in terms of changing the forces and stresses on the caliper, the holding bolts and fork, then you really shouldn't be getting into this.My understanding is XACD are reasonable fabricators, but not designers.
Seconded fabricators will build anything you want, it is up to you to ensure the design is fit for purpose. And I mean everything from correct materials, wall thicknesses, weld specifications the lot.0 -
eh wrote:This is one scary thread, just stop now, you clearly have no idea of what your doing. If you don't have a basic understanding what putting the caliper on the front will do in terms of changing the forces and stresses on the caliper, the holding bolts and fork, then you really shouldn't be getting into this.My understanding is XACD are reasonable fabricators, but not designers.
Seconded fabricators will build anything you want, it is up to you to ensure the design is fit for purpose. And I mean everything from correct materials, wall thicknesses, weld specifications the lot.
Well, are you able to offer any suggestions as to what putting the disc on the front will do and why?0 -
Could read Cotics explaination http://www.cotic.co.uk/geek/ - done the work for you.0
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Soul Boy wrote:Could read Cotics explaination http://www.cotic.co.uk/geek/ - done the work for you.
sorry, that link doesn't seem to be working, can you please give me an idea of what they say?
thanks0 -
cooperplace wrote:Soul Boy wrote:Could read Cotics explaination http://www.cotic.co.uk/geek/ - done the work for you.
sorry, that link doesn't seem to be working, can you please give me an idea of what they say?
thanks
I take that back, it's now working0 -
Soul Boy wrote:Could read Cotics explaination http://www.cotic.co.uk/geek/ - done the work for you.
if you look at
http://www.cotic.co.uk/geek/#forks
you see they have done just what I want to do, put the disc mount on the front, for the same reason I want to do it.
Now we can all wait and see if disasters, as some seem to predict, will happen.0 -
Hello,
I am not an engineer (not the real sort anyway) but I notice from the Cotic page that their forks are rather on the beefy side.
I was reminded of this : http://www.canyon.com/_en/technology/project68.html
Where they have an interesting discussion of braking forces applicable for more traditional road forks - including the amount of deformation (you really don't want to be able to make the front wheel touch the frame...) and the amount of twist that having one brake creates (you really don't want to turn left every time you hit the brakes!)
They don't discuss the forces pushing out the wheel (as Cotic do) but from the picture it looks like there might be a though axle.0 -
They don't discuss the forces pushing out the wheel (as Cotic do) but from the picture it looks like there might be a though axle.
No it is QR but they won't have a problem as they have twin discs , with one facing forward and one back (primarily to counteract the twisting forces on the fork), but they will act in opposite directions hence reducing the possibility of forcing the wheel out.
That Canyon article shows nicely why it is not just a simple case of bunging a caliper on and off we go. Notice they are running a very different system from any stock mtb i.e. twin discs, smaller rotors, 4 cross spoke lacing, etc.
The Cotic article is poor, as they haven't addressed the complete change in loading on the caliper fixing points. Not really a surprise from a small company with limited engineering experience (see Helmlock failures as an example).
(NB: Before Cy gets grumpy, thats not to say some of the bikes Cotic make aren't very nice e.g. the Soul is pukka, but it also uses well known materials, techniques etc)0 -
Can't answer the question sorry but why has the OP asked the question and then seemingly disregarded any responses suggesting that the idea isn't sensible :?0
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A really interesting thread. I think you need to take a majority decision on this. I can't think of a disc mount that is on the rear. The photo's in above threads show a V brake mount not a disc. I would have thought the direction the dropouts face would be more crucial, hence why they face down or forwards, causing the wheel to be pushed on to the bike under braking. Yes, I know the rear may face backwards, but this is also under load from the chain.
If I understand correctly that the fork is to be fitted to a cross bike, try Pace forks as I know they make a rigid MTB fork. This might work. Though I don't know that they use Ti.
Martyn0 -
thehairs1970 wrote:I can't think of a disc mount that is on the rear. The photo's in above threads show a V brake mount not a disc.
most disk mounts are on the rear....and the photos above show a fork with v- mounts and disk mounts....0 -
Have you contacted Burls or Sabbath Bikes. Both do bespoke titanium and may give you a steer on if what you want is a good idea (or not). No doubt cost more than XACD but you will get their design input.The revolution will not be televised0
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Pross wrote:Can't answer the question sorry but why has the OP asked the question and then seemingly disregarded any responses suggesting that the idea isn't sensible :?
You have put it very well: "suggesting" the idea isn't sensible.
What possible use to me is it for people to suggest the idea isn't sensible??
I'm keen to hear well-reasoned responses, based on fact, knowledge, and actual experience. I'm quite capable of speculating all by myself.0
