Starling Cycles Staer
HIGH PIVOT PROTOTYPE
Words by Robert Johnston
Photos by Findley Forrest & Nico Turner
When it comes to testing bikes, few things conjure up more excitement than the opportunity to test a prototype machine, especially when there’s some outside-the-box thinking involved in its design. When Starling cycles uploaded a video introducing their latest creation – a 170mm travel steel 29er using a unique high jack pivot (explained below) – I had to have a go. Luckily, after testing Starlings’ production Murmur 29er, I had built a rapport of sorts with owner Joe, who kindly agreed to lend me this prototype model for a few weeks thrashing all over the UK. Since testing, Joe named this prototype the “Staer,” the Old-English word for a Starling bird.
So let’s get to the bike, and what makes it so special. Joe is not afraid to admit that the inception of this machine was a result of an error whilst attempting to fabricate a frame suitable to accept an effigear gearbox (look out for that bike soon). A mistake in the order of some machined parts required to accept the gearbox resulted in Joe having a collection of steel bits that weren’t suitable. The idea popped into Joe’s head that an “enduro” version of his Sturn downhill bike could be made possible utilizing these machined bits, and so the Staer was born. As with all Starling bikes, the frame is constructed from a collection of steel tubes of various alloys, selected for their optimal properties in each frame area.
Whilst the pivot point on the Staer prototype is not super high, such as on the Commencal Supreme DH V4, the design principles and functionality share similar traits. By positioning the pivot point above the chain line, the movement of the rear wheel in the initial part of the travel becomes primarily rearward. In theory, this allows the rear wheel to move out of the way of obstacles with less resistance, but the effectiveness of this is not entirely clear. What is unarguable however is the stabilizing effect that this rearward movement has, as the wheelbase extends for a considerable portion of the suspension travel. Stability when you’re under compression, such as pushing hard through a berm or coming through a g-out, can only be considered a good thing, allowing limits to be pushed a little harder with reduced risk of an uncontrolled wobble.
The downside to this extending rear end is that the chain is then put under a lot of tension (known as chain growth), which can be felt as a kickback force through the pedals. This effect will reduce the ability of the rear end to conform to the trail, and likely undo any positive effect of the high pivot positioning. To resolve this issue, an idler system can be used. By positioning a cog on the same central axis as the suspension pivot, and routing the chain over this cog, the chain growth is eliminated, and the rear end is left free to react without the effects of the chain forces. What makes the Starling truly unique is the execution of this idler system – the jack pivot. A left-hand drive Profile Racing bmx crank is used, driving a bmx half-link chain on to a cog on the left side of the pivot. An axle, free to rotate, solidly connects this left cog to an identical cog on the right side. Finally, a second, geared chain runs from this right side cog to drive the rear wheel. Complicated to look at, but very simple in operation. To allow for the left side chain to be tensioned sufficiently, an eccentric bottom bracket is used: allowing for some movement of the crank axle; and some extra tuning of effective bottom bracket height and the front-rear length ratio.
Geometry of the Staer as standard is in keeping with the times, but far from the most extreme that Joe has experimented with – a 64 degree head angle, 73.8 degree effective seat angle, 475mm reach and 450mm stays combine to produce a stable package, without getting into ultra long and slack territory. During testing, the bike was fitted with a headset that slackened the head angle by 1.5 degrees, pushing the head angle well in to downhill bike territory at a raked out 62.5 degrees.
An EXT Storia rear coil shock and Ohlins RXF EVO coil fork made for some seriously supple suspension off the top, with high quality tuneable damping that offered a huge range of set up options. Chris Porter, the extremely knowledgeable director of Mojo Rising and renowned bike fettler, provided a great help in getting the rear shock set up to perfection, resulting in a 500lb spring rate being supported by 5 clicks of low speed compression and 7 clicks of high speed compression. Each click on the Storia shock makes a noticeable difference, perhaps accentuated by the simplicity and free-moving nature of the single pivot rear end – finding a balance between steering and stability involved some focused set up on a single piece of familiar track, but following Chris’ guidance resulted in some noticeable improvement over an afternoon of set up. Chris offers this wisdom to anyone purchasing an EXT shock from Mojo Rising – really adding value to the service.
Joe had the Staer set up with a single-speed Project 321 rear hub and cut down 10 speed cassette to make a 5 speed cluster on the rear, offering an 11-36 gear spread. When mated to the 28t front cog, this produces a similar low gear to the 11 speed set ups that were so common just a couple of years ago, before the eagle soared to the top. It was manageable, though certainly didn’t offer the low speed leg-spinning capabilities of the gear systems that are now common place. Gear shifting wasn’t good with this set up, since the synchronized shift ramps on each of the 5 cogs had lost their sync due to the missing gears in between. The mindset of running the bike single-speed on the downhills was necessary to avoid the dreaded “skip” as a cog jumps unexpectedly to the next gear when under power. A normal rear wheel and 11 or 12 speed gear system could be fitted to this machine to produce a more normal ride in this respect, though there is definitely something to be said for keeping your thumb off the shifter on a descent and getting on with the gear you’re in.
Braking and seatpost duties were the task of the Magura MT5 brakes and the Vyron wireless dropper. The performance of the brakes was nothing short of outstanding, without a single hint of fade or changing feel throughout testing – just gobs of well modulated power. The Vyron dropper had issues however, and was replaced by a 9point 8 Fall line dropper that is also being tested for a feature coming soon.