The RXL’s sole is a carbon/fibre glass composite and is a 9 on Bontrager’s stiffness scale, which goes all the way to 12 by Paul Horta-Hopkins · 13/06/2016 The RXL’s sole is a carbon/fibre glass composite and is a 9 on Bontrager’s stiffness scale, which goes all the way to 12 Share this:FacebookTwitterWhatsAppPinterestTumblrLinkedInPocketEmailRedditLike this:Like Loading...