bestbike85 Posted April 1, 2020 Share Posted April 1, 2020 Say a bike comes with a crown to axle rigid fork of 483mm and the manufacturer says a suspension fork could be installed with a c-a of 501-511 (100mm). Is that 501-511 (100mm) value calculated including say a 20% sag? So if I Installed a fork with a 500 (100mm travel) c-a and had 20% sag, my effective c-a would be 480 (-3mm from rigid)? Next, if I installed a 520 (120mm) c-a fork with 20% sag, my effective c-a would be 496 (+13 from rigid)? Now if those two scenarios are accurate, which would you recommend. Going -3mm from original rigid fork, or going +13mm from original rigid fork? Thanks for any help you’re willing to provide. Quote Link to comment Share on other sites More sharing options...
mack_turtle Posted April 1, 2020 Share Posted April 1, 2020 480mm is equivalent to a 100mm suspension fork. put the amount of travel that is necessary for your riding style, so long as it is within the manufacturers' specifications for safety. a longer fork will: shorten the reach raise the stack raise the BB slacken the head tube and seat tube I don't know how accurate these are in the end, but you can compare the geo of two setups using http://www.bikegeo.net/, and you can estimate the effect on geometry on a bike with a different fork using https://bikegeo.muha.cc/ Quote Link to comment Share on other sites More sharing options...
RidingAgain Posted April 1, 2020 Share Posted April 1, 2020 Fo every 20mm of fork length increase you'll slacken the head angle by 1 degree. And you can check this out... https://www.bikecad.ca Quote Link to comment Share on other sites More sharing options...
Chief Posted April 1, 2020 Share Posted April 1, 2020 If you use a suspension fork with the same A to C as your rigid fork it will steepen head angle at sag and steepen it even more under braking and compression. I personally would go with a fork that has an A to C that is the same or slightly more as your rigid when set to desired sag. I would go +13, -3 steepens head angle. Stock head angle is also a factor. 2 Quote Link to comment Share on other sites More sharing options...
bestbike85 Posted April 1, 2020 Author Share Posted April 1, 2020 4 hours ago, Chief said: If you use a suspension fork with the same A to C as your rigid fork it will steepen head angle at sag and steepen it even more under braking and compression. I personally would go with a fork that has an A to C that is the same or slightly more as your rigid when set to desired sag. I would go +13, -3 steepens head angle. Stock head angle is also a factor. That’s what I’m thinking. The head angle is already fairly steep at 69 degrees. Also if I run a 120mm and ran 25% sag it would drop that +13 to a +7 which would be even better. seems like I have the proper train of thought, so I’ll probably go with a 120mm. Quote Link to comment Share on other sites More sharing options...
mack_turtle Posted April 1, 2020 Share Posted April 1, 2020 sounds like you would not want to go any higher than a 120mm fork. in general, an unsagged 100mm suspension 29er fork is about 500mm a-c, and a 120mm fork is around 520. a 480mm rigid fork is about the same as a sagged 100mm fork. also take into account the frame's design. my KM is designed to handle a 140mm fork, but I set mine at 120 because 140 was a bit nutty for my needs. Quote Link to comment Share on other sites More sharing options...
notyal Posted April 1, 2020 Share Posted April 1, 2020 Go big or go home. Quote Link to comment Share on other sites More sharing options...
ATXZJ Posted April 1, 2020 Share Posted April 1, 2020 (edited) FWIW, both my non-boost 29er Pike and SID forks are around 540mm A2C, unsagged. Edited April 1, 2020 by ATXZJ Quote Link to comment Share on other sites More sharing options...
bestbike85 Posted April 1, 2020 Author Share Posted April 1, 2020 28 minutes ago, mack_turtle said: sounds like you would not want to go any higher than a 120mm fork. in general, an unsagged 100mm suspension 29er fork is about 500mm a-c, and a 120mm fork is around 520. a 480mm rigid fork is about the same as a sagged 100mm fork. also take into account the frame's design. my KM is designed to handle a 140mm fork, but I set mine at 120 because 140 was a bit nutty for my needs. Oh yea, it’s either 100 or 120, nothing more. I could do a 110 and probably have the best of both worlds. I plan to push the bike hard, but I want it to ride right more that just over forking for the sake of over forking. 2 Quote Link to comment Share on other sites More sharing options...
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.