MC#5 – Heyride’s 29er trail(ish) bike

BikeCAD of the frame

The next frame in the queue is for Heyride. He borrowed and seemed to really dig MC#1, so I’ve tweaked a few things on this bike to make the geometry of #1 even better (IMO).  It’s a hair over a 19″ frame (seat tube center to center) instead of frame #1 which was a 17.5″ frame that had a 24.6″ top tube (Gorilla sizing = long torso and arms & short legs). In addition to giving it a more ‘regular’ standover height and seat tube length, I slackened the head tube by a half-degree to 69.5 degrees.  He’s getting the new Rock Shox Reba 110 with 51mm of offset (awesome they are starting to make these bigger offset forks whereas before only Fox was allowed to make them for Trek) so the trail will be around 83mm –4mm more than was on my first frame so should handle more the way I like it.  I considered a 69 HT angle bringing the trail up to 86mm or so but decided against it since the TT length would get too short and he liked the way 79mm of trail rode. The other thing I changed pretty considerably is the front-center (distance from the center of BB to front axle). I shortened it almost 1cm to 688mm…which also happens to shorten the top tube when keeping all other things constant.  But with the slack head tube angle, it needed to be done in order to keep the wheel base short-ish (1122mm/44″) and a little shorter than the MC#1.  I also changed the seat tube angle to 72 instead of 73.  This was to also change the rider position on the bike more aft, which i hope will make the top tube not seem as short as it is (616mm/24.25″) and make it more wheelie-able.  All this should keep the bike handling the way he likes it – flick-able, wheelie-drop-able, and FUN, but not so short that it’s unstable over rough terrain.

Front Triangle mitered and braze-ons (mostly) added...

The chainstays are not exactly short but they are definitely not long at 440mm (effective CS length is about 17.2″).  Most production 29ers (and even many custom ones that come in stock sizes) have 17.5″ chainstays (445mm) since it is easier to build for  because there’s no offset or bent seat tube necessary and a front derailleur will not get in the way.  But with the 440mm chainstays it should be ok, especially since I offset the seat tube by 5mm.  The idea behind the short chainstays is that it makes a 29er easier to wheelie and flick and place the front wheel where you want it.  It also keeps the wheel underneath the rider more making climbing traction better than the same bike with longer chainstays.  But short chainstays also can make the bike handle less like a Cadillac over rough stuff (all other things equal).  This may be important to guys mostly bombing down rocky fire roads in Norcal – like I grew up doing, but less important to people riding tight rooty singletrack.  Bikes have definite personalities, and one ain’t going to be perfect for everyone.  If you’re like most people I know, you have multiple personalities and want a bike to match each! Cross bike, trail bike, touring bike, rigid singlespeed…and so on…

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