150mm forks on a Giant XTC3?

davenewcastle1973 Posts: 146
edited February 2011 in MTB workshop & tech
I'm thinking of putting a set of Rock Shox Domain 318 150mm forks on my XTC3 to replace the Tora 100mm forks on their as standard.
My thinking is that this will raise the front and make it more trail friendly - is there any reason why I shouldn't do this?
Apologies if this over simplifies!

Ragley mmmBop
Yeti 575


  • nicklouse
    nicklouse Posts: 50,675
    lots of reasons.

    I till handle like a barge. it will not climb. and you will lose any warranty and may also lose your face.
    "Do not follow where the path may lead, Go instead where there is no path, and Leave a Trail."
    Parktools :?:SheldonBrown
  • But apart from that its all good?! :shock:
    Ragley mmmBop
    Yeti 575
  • stu8975
    stu8975 Posts: 1,334
    But apart from that its all good?! :shock:
    Yes, but remember its a criminal offence not to put pictures of your smashed in face on here when your headtube gets ripped off and you faceplant the ground :lol: , or maybe that just applies to geordies :wink:
  • supersonic
    supersonic Posts: 82,708
    No offence, but insane idea! A freeride fork on an xc frame?! Don't do it, stick to 100mm forks.
  • You can reduce 150mm RS forks to 130mm with travel adjust spacers, and at 130mm it'll be fine for use on a 100mm frame. But a bit hefty. If you can live with the weight though,
    @130mm you set 30%sag which is 39mm 130-39= 91mm. @100mm 25% sag is 25mm = 75mm.
    Head angle change is typically 1 deg for 1"=25.4mm

    So you'd barely get half a degree head angle change which is well within the frame's safety limits and will make the bike more supple up front and descend with more stability. It might climb slightly worse, but not by much, because it'll keep weight over the front and track the ground better with the more supple initial to midstroke action of the fork.
  • supersonic
    supersonic Posts: 82,708
    But do you know the frame warranty? If wanting a longer fork, I'd get a Recon or Rev, not a Domain, warrantly allowing. Frame safety limits work on full crown to axle length (usually quoted as a max travel figure as the general consumer doesn't really understand that measurement), as they will extend when riding and do not sit at sag all the time.
  • Frame safety limits are usually good for up to 2 degrees head angle change from the major manufacturers. And Crown to axle height on RS products is usually similar for a given travel. (it is worth checking with the frame manufacturer, and i have done so for many fork upgrades I've carried out)
    Pike 454 140mm had the the same CTA as Revelation 130mm QR despite a 10mm travel difference.
    The Domain and Lyrik won't be far off the same at 130mm. (maybe less with 20mm dropouts mounted higher up on the lowers than QRs)
    Fox 36 travel adjusted to 140, 120 or 100 are similar to 32's for CTA too.

    The frame is designed around "dynamic ride height" so the angles are correct at the sag point and the bike will handle as it was designed to . The original forks will fully extend in use too, it's factored in to the design.
    A16mm difference is negligible. It will just produce more stability at high speed and very slightly slower steering at low speed for a more supple midstroke action with ramp up later in the stroke than a 100mm for with the same spring rate.
  • NatoED
    NatoED Posts: 480
    there is a really good reason they have put 100mm travel forks on that frame. stick to 100 or 110 travel max . go for recons or magura make a nice light 100mm forks too
  • supersonic
    supersonic Posts: 82,708
    Frame safety limits are usually good for up to 2 degrees head angle change from the major manufacturers.
    The frame is designed around "dynamic ride height" so the angles are correct at the sag point and the bike will handle as it was designed to . The original forks will fully extend in use too, it's factored in to the design

    This is simply not the case with many manufacturers and models. Many quote a maximum travel rating for warranty terms, [which is based on the average CTA at full extension of common forks] not what you are riding at sag. Specialized for example with the Rockhopper and Hardrock are not warrantied for more than 110mm of travel. Giant, from doing some reasearch with the XTC, do not warranty forks of more than 110mm of travel either.

    If 2 degrees was correct, then all 100mm designed XC frames would be able to take 150mm forks. Thay can't.

    You simply cannot put on longer forks and run more sag to try and reach what the frame is maximally designed for as you will invalidate the warranty. Full extension leverage may be more than the frame can handle and you are running a softer spring rate to compensate.
  • Anonymous
    Anonymous Posts: 79,667
    There's a good reason WHY the frames aren't warranted for longer forks. They don't just pluck numbers from thin air.
    Years ago, when bikes were generally more overbuilt, you could get away with a bit more messing about, but as bikes have got lighter and lighter, the tolerances have been tightened up.
  • I'm not suggesting you fit longer forks to change the bike's use and go hucking it. I'm not even saying it should be done. Just that it CAN be done.

    I'm saying that if you adjust the fork to suit the bike's geometry, you can dial in more favourable ride charactheristics like small bump sensitivity that you don't get from some basic OE forks to smooth out rougher sections and get the front tracking better through them. With the penalty being a small angle change. But within safe limits.
    The 2 degree angle change I had in mind was for steepening or slackening the angles by a degree either way on frames with adjustable forks and there seem to be more of them fitted OE these days, which gives more scope for this kind of tuning If you've got a version with fixed travel forks fitted.

    If your 100mm fork is tall on CTA (some are 500mm) with a max of 110mm travel the CTA will be 510mm. Domains @120mm run CTA @505mm.
    A Fox Van 32 @130mm is 500mm which opens up the possibility of using them in place of forks with a 490mmCTA like the MX Comp 105, 4X, or DJ forks from Marzocchi. The MX and DJ forks have been fitted to bikes as OE in the past.
    So it can be done safely if all the figures are taken into account.
  • supersonic
    supersonic Posts: 82,708
    The frame is not warrantied for it! If out of warranty you can do what you like, but if you went back to the shop with a broken frame and a Domain with 130mm travel they would not replace it.
  • cavegiant
    cavegiant Posts: 1,546
    Although implied above, I thought I would spell it out clearly.

    The increased torque produced by a longer fork can cause your frame to snap.

    The only people who know what their frame will take is the designers.

    Ask the designers what you can add, they might say you can fit max 100,110 or even 150.
    Just because someone on-line speculates what your frame can take, unfortunately does not make it true.

    You could get seriously injured if you fuck this up.

    The worst thing about fitting a fork too long is you cannot trust your bike, you do not know what drop will cause it to snap!

    My last frame was desiged for 140, I have been OK'd with 8" dual crown. The frame before was OK'd at 135, it snapped when I put a 150 on it (only 15mm why would that make a difference ;-) )
    Why would I care about 150g of bike weight, I just ate 400g of cookies while reading this?
  • Thanks for all the advice - I've decided not to go ahead with this! I think that the idea of having to post photos post face plant was what really put me off....

    Instead, going to go for a Ragley mmmBop and put the Domain on there.

    One bike for getting to work, and the other for fun!
    Ragley mmmBop
    Yeti 575