Welcome to the dungeon
I will keep this up to date with my personal projects and some of my entertaining customer builds as well.
DH BIKE
The unofficial winter training ground of some of the fast DH racers around is a mere 50 minute drive from my shop. Prior to starting wzrd I would be up there up to 10 times per winter. Last winter I only made it out twice (on my pink and purple hardtail) but this year I have already made it up four times (on my show bike, and hope to get back up once this winter storm passes. Prevost is only open when there is no fire hazard, so its a balance of that and snow.
While my hardtails hta’s in the 61 degree range, and 1300mm+ wheelbases can soak up a lot of steepness and speed, the lack of rear travel still gets in the way. I nuked two rear wheels last winter, and have already killed one this year - something needs to change!
This is where the DH bike comes into play. Its primary home will be Prevost in the winter, but will also see Whitler and some of the smaller lift access bike parks in the summer. The plan is to build something on the planted & fast side of things, rather than a more playful park/fr bike.
Front end geo will have a steeper hta and a shorter reach then my current hardtail, but the same length unsagged chainstay length. With a 44mm head tube and the fox 40’s straight steerer I will be able to adjust the hta and reach a fair bit with different headsets.
Reach - 500
Stack - 650
HTA - 62.5
BB height - 345mm (294 sagged)
CS length - 450mm (455 sagged)
Wheel size - 29/29
The current plan is a single pivot with a non-concentric idler attached to the chainstay. The pivot will be high and quite far forward sitting above & in front of the chain ring in the downtube. This layout will get me 209mm of travel from a 260x75mm shock.
Being a DH bike, I will be able to run a 84mm bb shell with external bearings for the cranks, gaining me a lot of room to play with for the pivot construction. I want this pivot to be as stout as possible as I fear the already high single pivot forces will only be exasperated by my chainstay length. So, the plan is to use a 68mm t47 shell with a 24mm internal bottom bracket. Being able to use my frame jig to make sure the main pivot gets brazed in centered and square is a bonus. Spinning up a 24mm pivot spindle with a clean m12 compression bolt shouldn’t be too hard either (for whoever I pay to do it as I do not have a lathe haha).
I want to add a downward curve to the chain stays to avoid any chain interference issues, but haven’t figured out curves on planes yet in Fusion. If someone has a good tutorial they can point me to on this topic I would be eternally grateful.
I am still stuck on coming up with cable routing that doesn’t suck. I have worked on dual suspensions that the cables saw into the frames (yetis) and others the saw into the cables (ibis aluminum). I normally run my cables in the top tube into the seat stays, but there will be way too much movement for that on this bike. I am considering through the down tube, through the main pivot and then into the chainstays. My only beef with that is then the brake line has to teleport from in the chainstay to on top of the seat stays. Cable routing keeps me up a night. I need professional help.
Anyways, here are the drawings and charts I have so far. Unfortunately I yeeted my PC last week, so I have had made a few small changes since these screen grabs.
Let me know what y’all think.
okay, talk soon.
