are 160mm forks too much?

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Comments

  • peter413
    peter413 Posts: 5,120
    b45her wrote:
    your clever picture is irrelevant , the sx trail comes from the factory with 66's and the guy has put 888's on there , the a2c difference is just 3mm i.e that accident would have happened longer forks or not , its the a2c length thats immportant not the travel figure .

    How can you know the exact a2c length with a dual crown fork, it can change. And I was always under the impression that dual crown forks put more stress through the frame than a single crown fork.
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  • YeehaaMcgee
    YeehaaMcgee Posts: 5,740
    b45her wrote:
    your clever picture is irrelevant
    Eh? Clever? What?
    And it is relevant, you said...
    b45her wrote:
    unless your name is josh bender your never going to "rip a headtube clean off" even if you put 200mm forks on, .
    So I showed you an SX trail with the headtube ripped off. It does happen.
    My photos
  • bennett_346
    bennett_346 Posts: 5,029
    b45her wrote:
    YeehaaMcgee wrote:
    b45her wrote:
    unless your name is josh bender your never going to "rip a headtube clean off" even if you put 200mm forks on, .
    Well, here's an SX trail...
    http://ap1.pinkbike.org/p4pb5428691/p4pb5428691.jpg

    It does happen on occasion. The longer fork doesn't just increase leverage, it also slackens the head angle, meaning that the force of landing a jump is going to apply more twisting force.
    There's been plenty of crash videos on youtube where you can see the headtube coming off the frame.
    It doesn't happen to everyone, but you'd have to be foolish to just suggest that everyone will be fine with far longer forks than intended.

    your clever picture is irrelevant , the sx trail comes from the factory with 66's and the guy has put 888's on there , the a2c difference is just 3mm i.e that accident would have happened longer forks or not , its the a2c length thats immportant not the travel figure .
    Made sense to me, it shows that you can rip a headtube off with long travel DCs
  • 386ka
    386ka Posts: 479
    YeehaaMcgee wrote:
    b45her wrote:
    unless your name is josh bender your never going to "rip a headtube clean off" even if you put 200mm forks on, .
    Well, here's an SX trail...
    http://ap1.pinkbike.org/p4pb5428691/p4pb5428691.jpg

    It does happen on occasion. The longer fork doesn't just increase leverage, it also slackens the head angle, meaning that the force of landing a jump is going to apply more twisting force.
    There's been plenty of crash videos on youtube where you can see the headtube coming off the frame.
    It doesn't happen to everyone, but you'd have to be foolish to just suggest that everyone will be fine with far longer forks than intended.
    Actually, the longer fork stresses the frame more by slackening the head angle. The longer a2c doesn't mean much without that.
    A much loved, Giant Trance X3 2010
  • b45her
    b45her Posts: 147
    what i'm saying is that the 888's were not a factor in the front of that bike failing wheather it had the standard 66's or the 888's the forces acting on the weld would be the same ,the leveage and head angle are generated by the axle to crown length and not the travel . if anything the 888's would have made the failure less likley due to them having 2 more inches of travel to dissapate the impact and a near identical headangle .
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  • rockmonkeysc
    rockmonkeysc Posts: 14,774
    Slackening the head angle will not increase the stress on it. You can make it any angle you want and the stresses will stay the same. It will change the direction of the force relative to the angle of the head tube but your going to have to change it a lot before it causes a failure which wouldn't have happened anyway.
    That picture doesn't really prove anything, the front end could have snapped even with the standard forks, you don't know how it happened. I have seen a lad snap the head tube off a Cube hardtail. Forks were 10mm longer than standard. He was stupid enough to ride a step down jump with a 25 foot gap & 10 foot drop, pretty sure that would have snapped anyway.
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  • YeehaaMcgee
    YeehaaMcgee Posts: 5,740
    The picture proves everything that was needed - that headtubes do get ripped off on occasion, even if you're not Josh bender.
    My photos
  • rockmonkeysc
    rockmonkeysc Posts: 14,774
    The arguement was that fitting longer forks will cause head tubes to fail. If I get bored after my friday lunch time pint I will do some quick calculations to prove the very minimal extra force transmitted to the head tube by longer forks.
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  • anj132
    anj132 Posts: 299
    RockmonkeySC wrote:
    The arguement was that fitting longer forks will cause head tubes to fail. If I get bored after my friday lunch time pint I will do some quick calculations to prove the very minimal extra force transmitted to the head tube by longer forks.

    This isn't a sarcy reply. Could you, it sounds quite interesting. :)
  • rockmonkeysc
    rockmonkeysc Posts: 14,774
    If the boss is out of the office...
    Fairly simple calculation to be honest. It will be a fairly small increase in loading unless your going for a stupid increase in travel.
    If you put a 300mm travel Super Monster T on a lightweight XC race hardtail you would probably break it but it would also ride better as a unicycle than with the daft fork fitted.
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  • anj132
    anj132 Posts: 299
    RockmonkeySC wrote:
    Slackening the head angle will not increase the stress on it. You can make it any angle you want and the stresses will stay the same. It will change the direction of the force relative to the angle of the head tube but your going to have to change it a lot before it causes a failure which wouldn't have happened anyway.

    Trying to get my head around this but I would have originally thought that say landing a slacker head to flat would create more stress on the headtube (HT).

    But due to the wonders of suspension, this is elimanted, the suspension absorbs the impact. If say on a rigid fork doing the the same flat drop, then a slacker head angle will have more stress on the HT. Applying the logic to a bottomed out fork however due the fork compressing the head angle isn't as slack as when "not-compressed" so there is little difference say between a 120 fork and a 160 fork - the actual difference is the bottomed out HA (i.e. longer sanctions must go somewhere). Infact, you could argue that bottoming out a 120 fork is more likely to give more stress where as a 160 fork wouldn't have bottomed out.

    However I admit I don't know a lot about this and my logic could be very flawed & overally simplistic and doesn't consider other variables such as handling due to higher BB.
  • YeehaaMcgee
    YeehaaMcgee Posts: 5,740
    RockmonkeySC wrote:
    If the boss is out of the office...
    Fairly simple calculation to be honest. It will be a fairly small increase in loading unless your going for a stupid increase in travel.
    If you put a 300mm travel Super Monster T on a lightweight XC race hardtail you would probably break it but it would also ride better as a unicycle than with the daft fork fitted.
    It's not as straightforward as you may think, since you need to consider where the back wheel touches the floor, and the wheelbase, in order to figure out the change in head angle. As the fork increases in length, th eentire bike rotates around the rear wheel - which is what causes the forces acting upon the front fork to be aligned to better force the headtube away from the frame.
    It's not rocket science, but it's not entirely trivial either.
    My photos
  • b45her
    b45her Posts: 147
    YeehaaMcgee wrote:
    The picture proves everything that was needed - that headtubes do get ripped off on occasion, even if you're not Josh bender.

    nope , you claimed that longer travel forks would make a failure more likley , then posted a picture of a bike which you thought had longer than recommended forks bolted to it .

    you fail to grasp that the travel is not the measurement that affects the head angle and stress on the front of the frame , the a2c measurement is the immportant number .

    the point i'm trying to make is that if you ride hard enough to snap the frame of your bike its likley to break longer forks or not.

    the only comment i made was why worry about warrenty's when its simple enough to bolt the old forks back on before you go bike in hand to the shop for a replacement .

    hell ive cracked 2 frames and snapped a rear triangle clean in half and not once did the bike shop even question how i did it they just asked me to bring the frame to them so they could send it off for replacement .
    ribble sportive for the black stuff

    Canyon Strive AL 8.0 for the brown and green stuff.
  • b45her
    b45her Posts: 147
    RockmonkeySC wrote:
    Slackening the head angle will not increase the stress on it. You can make it any angle you want and the stresses will stay the same. It will change the direction of the force relative to the angle of the head tube but your going to have to change it a lot before it causes a failure which wouldn't have happened anyway.
    That picture doesn't really prove anything, the front end could have snapped even with the standard forks, you don't know how it happened. I have seen a lad snap the head tube off a Cube hardtail. Forks were 10mm longer than standard. He was stupid enough to ride a step down jump with a 25 foot gap & 10 foot drop, pretty sure that would have snapped anyway.

    can't really agree with this , slackening the head tube will increase the stress on the headtube weather the forks are longer or not , its all about leverage and the angle the force acts on the lever.

    think of it like putting a wheel brace on your car standing square to it and trying to undo the wheel nut with the brace at 5 o'clock ,its hard right ?

    put the same wheelbrace on the same nut closer to 3 o'clock and its a damn sight easier , same force exerts more torque because of the shallower angle .
    ribble sportive for the black stuff

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  • YeehaaMcgee
    YeehaaMcgee Posts: 5,740
    b45her wrote:
    YeehaaMcgee wrote:
    The picture proves everything that was needed - that headtubes do get ripped off on occasion, even if you're not Josh bender.

    nope , you claimed that longer travel forks would make a failure more likley , then posted a picture of a bike which you thought had longer than recommended forks bolted to it .
    Actually, I posted the picture in response to THIS, BY YOU!!
    b45her wrote:
    unless your name is josh bender your never going to "rip a headtube clean off" even if you put 200mm forks on, .
    So, I posted a picture of a bike, not ridden by Josh Bender (as far as I know), which has the headtube ripped clean off.
    It doesn't matter what forks were on the bike, the headtube has been ripped off.
    My photos
  • anj132
    anj132 Posts: 299
    Ok sorry but I am going slightly off topic but interested in all this a2c stuff...

    1. If you were to increased a fork internally i.e. came as 120 but increased it to 140. The a2c is the same? So doesn't create extra stress on the frame (warranties shouldn't be effect) but I see this increasing the HA?

    2. So, with a travel adjustment fork, they are often sold as 'climb on 110, descend on 150' but the a2c stays the same so same logic as above - no extra stress no matter what 'mode' it's in?
  • b45her
    b45her Posts: 147
    dude your making a fool of your self , i mentioned the name josh bender because he's a very well know loon on a mountain bike ,everyone knows headtubes break clean off but the people who do it either do it in a big crash or while attempting a rediculous jump of some sort hence the refrence to josh bender .

    the initial question asked by the chap who started this thread was weather he could safely put 160mm forks on a bike designed for 150mm forks ,the answer to which is yes .
    ribble sportive for the black stuff

    Canyon Strive AL 8.0 for the brown and green stuff.
  • styxd
    styxd Posts: 3,234
    the only comment i made was why worry about warrenty's when its simple enough to bolt the old forks back on before you go bike in hand to the shop for a replacement

    It might not be simple enough if you've disabled yourself after crashing due to the headtube being ripped off by using forks that are longer than the manufacturer has specified.
  • b45her
    b45her Posts: 147
    anj132 wrote:
    Ok sorry but I am going slightly off topic but interested in all this a2c stuff...

    1. If you were to increased a fork internally i.e. came as 120 but increased it to 140. The a2c is the same? So doesn't create extra stress on the frame (warranties shouldn't be effect) but I see this increasing the HA?

    2. So, with a travel adjustment fork, they are often sold as 'climb on 110, descend on 150' but the a2c stays the same so same logic as above - no extra stress no matter what 'mode' it's in?

    the a2c is the length between the axle and where the forks join the headtube , when travel adjust forks are lengthened /shortened the a2c changes, wouldn't be much point in having travel adjust if it didn't .

    as far as i'm aware there arent many forks that can be increased internally although lots can be reduced quite easily .
    ribble sportive for the black stuff

    Canyon Strive AL 8.0 for the brown and green stuff.
  • anj132
    anj132 Posts: 299
    b45her wrote:
    the a2c is the length between the axle and where the forks join the headtube , when travel adjust forks are lengthened /shortened the a2c changes, wouldn't be much point in having travel adjust if it didn't .

    Thanks for the reply but I don't think it's to the headtube as the 'c' part means crown.

    i.e.

    http://wheelworks.co.nz/wp-content/uplo ... CN7615.JPG

    http://wheelworks.co.nz/wp-content/uplo ... CN7614.JPG

    But I take it back if I'm wrong
  • anj132
    anj132 Posts: 299
    Yeah im wrong. :)

    Just confusing myself... making a swift exit :lol:
  • b45her
    b45her Posts: 147
    styxd wrote:
    the only comment i made was why worry about warrenty's when its simple enough to bolt the old forks back on before you go bike in hand to the shop for a replacement

    It might not be simple enough if you've disabled yourself after crashing due to the headtube being ripped off by using forks that are longer than the manufacturer has specified.

    your kind of missing the point , the frame in question is designed around a 150mm fork ,do you really think that slackening the static head angle less than 1 degree is going to make the frame catastrophicly fail?

    by the time the sag is set correctly the headangle difference is around 1/2 of 1 degree if a change that small is going to break the thing in half i think felt should employ new engineers .

    i'm not saying that going out and putting fox 40's on an 80mm xc frame is fine but panicking over such slight changes to a frame designed for all mountain use is just paranoia .
    ribble sportive for the black stuff

    Canyon Strive AL 8.0 for the brown and green stuff.
  • rockmonkeysc
    rockmonkeysc Posts: 14,774
    Bollox to it. I'm going to put some Super Monster T's on a 80mm travel carbon XC race bike.
    Do schools not teach (very) basic mechanics?
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  • mickus
    mickus Posts: 199
    Well I wasn't expecting quite this response... But I think I've got a satisfactory answer!

    My main concern was overloading the frame but I was also interested in how much it was likely to effect handling and general feel of the bike.

    I've bought the forks, as they were too good a deal to pass up, and will give them a try. If it handles like a bag of cap then I'll down size slightly.

    Thanks for all the help.
  • YeehaaMcgee
    YeehaaMcgee Posts: 5,740
    b45her wrote:
    everyone knows headtubes break clean off
    So what the farking fark was your farking point?
    Sadly, the technology doesn't exost which allows me to reach through your monitor and give you a slap, so please go stand in front of a mirror and do it for me.
    Bloody muppet.
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  • b45her
    b45her Posts: 147
    my point was you claiming that putting 160mm forks on a 150mm bike is going to make it snap in half you fucking halfwit.
    then you trying to prove your point by showing a picture of a bike with a broken headtube even though the fork on it has the same measurements as the standard forks , do you not have any grasp of mechanics ??

    nice of you to use part quotes out of context to try and back your own flawed argument too . as for the slap i'll pm you my address if you like and sent you bus fare .
    ribble sportive for the black stuff

    Canyon Strive AL 8.0 for the brown and green stuff.
  • YeehaaMcgee
    YeehaaMcgee Posts: 5,740
    b45her wrote:
    my point was you claiming that putting 160mm forks on a 150mm bike is going to make it snap in half you ******* halfwit.
    then you trying to prove your point by showing a picture of a bike with a broken headtube even though the fork on it has the same measurements as the standard forks , do you not have any grasp of mechanics ??
    All I said was that a longer fork increases the chances of failure. You said frames don't fail anwyay, unless you ride like Josh Bender, so I showed you photographic proof that such failures do happen.
    If the forks are the same length, then that just goes to show that these things happen anyway - do you really want to increase the chances even more so?
    My photos
  • Chunkers1980
    Chunkers1980 Posts: 8,035
    What an offer. PM me the address and time too if it happens, I'd like to watch.
  • supersonic
    supersonic Posts: 82,708
    There are a few points here:

    - Warranty. One reason some frames are not warrantied for longer forks is because some manufacturers expect the rider to ride the bike harder with them. Harder plus the extra leverage increases the stress.

    - Head angle. Slackening the head angle does increase the leverage from some types of landings.

    I have seen dozens of snapped frames and ripped off headtubes. The majority had forks fitted that were longer than intended, or triple clamp forks when designed around a single clamp. Usually quite a bit longer mind!

    It is a combination of factors why manufacturers have limits. If in doubt, don't do it.
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