Author Topic: Building a dirtjumper  (Read 3732 times)

Building a dirtjumper
« on: 16 February, 2021, 10:12:49 pm »
I'm "helping" our lad build this...really should be based on a gnarly 90s Scott or Cannondale, but in fact it's a Planet X Jumpin Jack Flash frame, with Halo rims, Hope hubs, a borrowed cockpit and a madly powerful Magura rear brake.

Just need to get the work stand up in a bedroom somewhere...

Re: Building a dirtjumper
« Reply #1 on: 18 April, 2021, 01:31:38 pm »
The build has progressed... It's now ridable, though there're good and bad about it:
Good points
*It's light
*The wheels - rear is a Halo not the Hope as originally planned... It's specifically made for dirt jumpers with AIUI an extra "bushed" bearing for the single sprocket in addition to LH and RH cartridge bearings. Curiously no dish at all in the rear wheel.
*The hella-powerful (cheap) Magura MT5 rear brake.
*Chain line seems a cool 48mm using donated Deore cranks (c. 2005? ) and a 121mm Shimano Octalink BB (NOS off the Bay). At least the shell is easy: 68mm BSA "English threads"!

Not so good
*Bars are too wide... Nukeproof 780mm! ?
*Headset a bit tight for spinney jumps? Maybe a little directional (warped cup? Head/steerer/castor angle is high, so it *wants* to go sideways). Hard to tell... More fettling thought needed. It was difficult sourcing/fitting this... The Planet X site and help didn't offer much advice. When offering a frame it would help to spec the components in more detail eg give ISIS data so we know the bottom race is a 56/40 etc etc. More dimensions please! [On edit: improved by putting the spacer below the stem]
*Chain is a bit... slack.. It's a SS, with vertical dropouts, so needs IMHO a chain tensioner of some sort. We sourced one from "Gusset" (these BMX kids are so outrageous )  but it don't have no spring, so requires "periodic adjustment".
*Got the wrong diameter seatpost (more  "Gusset", more unspecified dimensions and possibly "measure once, fit twice" ) so it's running with a road saddle etc.

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Re: Building a dirtjumper
« Reply #2 on: 19 April, 2021, 10:12:43 am »
I can't offer any build advice, but I'm looking forward to the action photos  :)