Banshee Spitfire front triangle
This kit replaces the aluminum front triangle and lower linkage on a Banshee Spitfire v2 trail bike. This provides the opportunity to customize aspects of the frame geometry, run mixed wheel sizes and modify rear wheel travel and suspension characteristics.
The kit contains:
- Front triangle, powder coated
- Lower pivot linkage, pivot hardware, axels, bushings and bushing extractor tool
- Seat clamp
- Handmade in Bristol, UK
- Reynold 631/853 tubing
- Stainless 316L AM shock mount, pivot mounts & pivot linkage
- Main pivot uses 2x plain bushings
- External brake and gear cable routing
- Internal dropper seat post cable routing
Custom options
- Fork travel (140-160mm)
- Rear travel (130-150mm)
- 650b/650b or 650b/29″ wheel sizes
- Head tube angle
- Seat tube angle
- Reach
- Seat tube length
- BB drop/rise
Project origins
My Banshee Spitfire V2 (size L) in all her glory.
This bike first released in 2014 remained relevant in an industry that was rapidly experimenting with significant frame geometry changes, for many years after its release. Described as “the downhiller’s trail bike”, the Banshee V2 was far more capable than its 140mm of rear travel would suggest. I ran a 160mm fork on mine. Interchangeable dropouts provided not only 3 head angle/BB height adjustments but also the ability to run 26″ or 650b wheels, 142 or 148 hub spacing.
A common failure of these frames was for a crack to develop around the ST/DT gusset. My frame eventually suffered the same fate. I cut the gusset off, removed the paint, and to my dismay the crack had made its way through the downtube.
I reverse engineered the rear triangle by putting the frame in my LCFF, clamping the rear axel in the jig and setting the CS distance and BB drop to the static values in the Banshee datasheet.
I took a photo to obtain the approximate pivot locations in the Z plane. I then took a calibration measurement (distance between any of the two pivots locations) using a steel rule and scaled the image in CAD to suit fit the measurement. Maybe an accuracy of +/- 1mm? (designers also tend to use round numbers for nominals)
I wanted to make a few changes to distinguish my design from the original this design and I was keen to try a 29 front wheel on a bike I was very familiar with.
I decided I wanted:
- a slacker front end (spitfirev2 is 66deg in slackest setting)
- steeper seat tube
- 29″ front wheel
- easy to service
- keep the suspension kinematics as similar as possible to the original design*
- don’t break
*or not
Linkage is such a good bit of software. Its pretty cheap for the personal license, $20 or something
Initial designs
I started to sketch out the geometry I had settled on from my Linkage experiments, and developed a solid model which had a rear triangle that could be dynamically adjusted to sweep through it’s full range of motion.
My first designs relied on a seat tube that was cut and rejoined at an angle so that I could put the main lower pivot through the center of the lower section of the seat tube. I made a cutting jig to cut the 87 or so degree cut with a hacksaw.
I also tried a few designs with the AM lug type of idea.
But it seemed like a lot of metal, and it would be expensive to develop
I really like laser cut plate shapes. I was pretty close to making this one. I designed the tooling and paid for it to get SLS printed. What put me off in the end was I thought I’d struggle to weld on the inside of the two parallel plates (probably with bronze)
The tooling that never was.
The last couple pictures show a hole through the downtube and seat tube for a bearing mount. It was around this time when I saw a 2019 Ancillotti scarab 29evo on pinkbike.
This bike is sick.
It has adjustable geometry (HT angle and BB height) and two rear suspension travel settings (150mm and 165mm)
All the linkages, and moving parts are right around the bottom-centre of bike, around the bottom bracket. The rear tringle is small, stiff and light weight, with no extraneous moving parts, pivots or fastenings.
This is also what I realised I really liked about the banshee v2 suspension design (and that short 4-bar system in general); the rigid rear triangle. It just makes sense to me to not shake a load of fasteners, preloaded and stressed aluminum parts and ball bearings down a bike trail and expect it all to stay together.
Another fairly uncommon feature of this bike is that all its rotating elements run on plain bearings (aka bushings) rather than ball or roller bearings.
Bearings and bushings both eventually wear and effect suspension performance. But in different ways.
Ball bearings will fail by crushing balls or breaking the cage or both. Once one ball becomes cracked the rest won’t be far behind, this completely seizes the bearing, meaning that as the bike is ridden it is the inner race of the bearing and the outer diameter of the axel of the pivot that move relative to one another. You won’t know when this happens unless you’re paying close attention to your suspension, or take the shock out and wiggle the back end up and down.
Bushings don’t fail like that. The axel wears a bigger hole into the bushing and the joint becomes sloppy. This sloppiness is quite noticeable and often noisy (creaks and cracks). When this happens in your shock bushings, you change the bushings.
So a message to all bike designers: make it easy to replace the bearings (whether ball or plain or whatever
It’s also possible for bushings to be a bit squeaky when first installed and take a certain about of time to wear in. This is a characteristic of the Ancillotti frame too. I suspect that this problem of audible noise from the pivots is soluble, possibly by tightly controlling the parallelism of the pivot axes, or just by finding a different material combination.
I was more than happy to experiment. I designed the lower pivot short link pivot on the frame to run on 2 plain bushings pushed into a reamed hole.
For the rotating axel, A chose a plain stainless steel cylinder, bought off the shelf from Misumi.
The smaller the axel, the greater Hertzian stress is applied to the bushing material (more wear). So bigger axels are better?
