There was an article on the Dirt MPORA website a few months back about offset shock bushes for slackening the head angle of full sus bikes and in turn, lowering bottom bracket heights, it went as follows:
Want to slacken the head angle on your mountainbike but can’t afford an AngleSet? We might just have the answer for you, so read on.
Jones@Dirt bumped into a fella called Kevin Coughlan from Dublin, Ireland who although being an Elite Downhill rider and full time student somehow finds time to run his small engineering business. Kevin produces a wide variety of bits and bobs to customize the geometry of your bike but we were particularly interested in these off set shock bushings.
Jones reckons Vouilloz was running a similar set-up in his Zesty last year to get the geometry in order to run a longer travel fork and drop the bottom bracket. They’ll cost you 20 Euros which is about the same price as a replacement bush anyway.
Here’s what Kevin told us:
Basics first… The bushings works on 2 styles M8 bolts and M6.
An M8 bolt can run a max offset of 2mm per bushing. M6 can run a 3mm offset. I also make diff offsets, you can get a 1, 2 and 3 mm offset so if you have a few bushes you can swap them around for different geo to suit different tracks e.g. steep, flat, rocky etc.
When fitted they make the eye to eye of your shock shorter. M8 with two bushes is 4mm shorter M6 is 6mm. And based of the leverage ratio of your bike it will change the geo. The average DH bike with M8 bolts a 3inch stroke shock and 9 inches of travel will get about a 0.5inch BB drop and about 1 – 1.5 degree slacker HA.
So the more travel you have with smaller shocks will make the most difference.
The bushes are made of 6082 T6 alu. This means it’s a hard surface and the type of alu is very stiff with no flex. Hard surface means corrosion resistant and long wear life. They are drilled and reamed to exactly 8 and 6mm holes so it gives the best possible fit on the bolt (less knocking). Each bush is ground/sanded and polished for smoothest surface finish and lowest friction (MOAR plush suspension)
Click the link and have a read of the comments, there are some interesting ones, amongst the daft ones! The discussion continues here and there is a lot of positive feedback. When i first read about them, i was tempted to buy myself a set to have a bit of a fiddle, but at £35 a set, it struck me as a rather expensive experiment, when my Heckler is plenty slack enough, and the Banshee is currently 65 degrees with a ton of adjustability. I wondered though with the Banshee if i would be able to achieve the same head angle without the loss of travel.
When I actually applied my mind to it though, they would be no help with the Banshee anyway, as it is, the seat yoke is close to colliding with the seatpost, and it has all the adjustment built in for sitting the bike into it’s travel to lower the BB height and slacken the head, but at the expense of travel. This is how it is currently set, running around 7″s.
My mate has just ordered a set for his Giant Trance, and looking at the design of the frame, it will be interesting to see what effect they have, it all depends on the rear axle path
Short of the tyre connecting with the seatpost, there is nothing to impede the travel of the wheel, so it will be interesting to see the result when fitted, watch this space….
Also of note, Burgtec are selling titanium offset bushes off the shelf for the following bikes, at £45 a pair:
- Commencal 4X, Meta, Supreme 6, FR, Mini DH, Supreme DH
- GT Fury 10-11
- Lapierre 720/920 08-10
- Lapierre 720/920 11
- Orange Five, Patriot, Alpine 160, 222, 223 and 224
- Santa Cruz V10 05-10, VP Free all, Blur LT2, Heckler 07-09
- Santa Cruz V10 11 Carbon
- Scott Gambler 08-10
- Solid Mission 9 All years
- Transition TR250 and TR450 all years
- Yeti 303 06-08