21/04/2022 - Cotic Ebike Project Update - Steel Prototype

Ebike Project Update - Steel Prototype

Cotic Ebbike Steel Geometry Prototype

Seeing as we 'outed' our ebike project a few months ago (if you haven't heard, head over to Our news story for details, or watch Guy Kes and I test and compare the prototypes in his excellent video further down this story) we decided we would be as open as we can be about the project development and where it's getting to.

The first ebike prototypes were signed off in mid 2019, but didn't arrive until late 2021. They were broadly an ebike version of the Jeht, with a 5mm higher BB (22mm BB drop static instead of 27mm on the Jeht). The thinking being we wanted an all round trail bike for our first ebike, and because you can pedal more up climbs you might want a slightly higher BB. It also had a slightly slacker seat angle than the Jeht because it was signed off about a year before the actual Jeht was, and in that time we learnt that we preferred the rider sitting a little further forward. Just as the production bikes eventually will, they use a Shimano EP8 based power system and an aluminium front triangle to house the internal battery in the down tube.

cotic ebike, ebike prototype, shimano STEPS, shimano EP8

Following a bunch of testing, we found we didn't need the ground clearance quite as much as we thought. Firstly, because the power of the eeb means you don't need long cranks, and we have been using 165 and even 160mm cranks, where our regular bikes are designed around 170mm cranks. Also, the Jeht doesn't have a super slammed BB to start with, because we ride up knobly tech climbs and we don't want to catch our pedals all the time, so going higher than the regular bike wasn't really necessary in reality. This is why we prototype!

Also, the higher BB made initiating turns a little more difficult, which is exaggerated by the down tube battery. Having 5kg of battery and down tube with it's centre of gravity high up and forward of the cranks means there's a fair bit of inertia to overcome in order to move it away from it's upright position and lean the bike over for a turn. I got busy with offset bushings and different shock lengths and strokes to see what I could work out. Certainly dropping the BB helped, but another option I tried for dropping the BB was to mullet the bike - put a 27.5" rear wheel in. I started out with a 2.8" rear tyre to do the geometry changes in smaller steps, but have ended up with a regular 2.5", but with no offset bushings or anglesets involved otherwise. This has resulted in slacker angles and a 12mm lower BB (now 34mm static), but still with no pedal clearance issues because of the short cranks.

What this has also done is transformed the ability of the bike to turn in. The big advantage of a smaller rear wheel is that it makes turns easier to initiate, at the expense of a bit of grip once you're settled in the corner (smaller wheel = less inertia/gyroscopic effects, but smaller contact patch). Being tall, and with my style of riding, I can never feel this effect on a regular bike no matter how many times I test it. I can just drop a full 29er into a turn with no issues at all. I know shorter riders have preferred it on our bikes, which is why we now offer a mullet option on our droplink bikes. However, on the eeb, with the added battery weight resisting turn in as well, the effect is obvious and very noticable. Even using various adjustments to match geometry, the mullet setup just drops into corners so much more easily compared to the full 29er, and once it's lent over and set it just rips around. The extra sprung mass on an ebike generates impressively increased grip compared to a regular bike.

What's Next?

Off the back of all if this testing, plus some discussions about what we want out of the bikes and where the market is going, we concluded that the production bike would specify as follows:

Even though these are relatively minor changes in the grand scheme of things, it was important we double check the changes and the quickest, easiest way to do with that was to go steel, hence the steel eeb geometry prototype.

Cotic Ebike Steel Geometry Prototype, shimano STEPS, Shimano EP8, steel bike, uk made ebike

This front triangle was built by our friends at Five Land Bikes in between building our UK production RocketMAX frames. It's full 853 - basically a RocketMAX tubeset with a slightly thicker wall down tube - with an external Shimano STEPS battery slung under the down tube so I can get our regular droplink suspension packaged in. Ironically in spite of it's looks this arrangement actually has better/lower centre of gravity position than the down tube internal battery.

The shock/linkage angle might look a bit odd, but it's just where my "join the dots" fell in order to replicate the proposed production kinematic using our toolbox of stock UK made links and shock mounts combined with the original ebike prototype rear end. On a bike carrying as much weight as a full power ebike, the 38mm chassis of the Zeb is just the tool for the job.

I told Five Land to paint it with whatever was going through at the time it was finished. Callum claims this was just using up "what was left in the gun". I suspect he was also showing off a bit, but I actually kinda like it!

Cotic Ebike Steel Geometry Prototype, shimano STEPS, Shimano EP8, steel bike, uk made ebike

First couple of rides have been encouraging, but have also raised a couple of questions about the proposed kinematic now it's giving out more travel on a longer shock, so there's some tweaks to try out. I'm still having no crank clearance issues on 165 cranks, despite having ridden straight up Devils Elbow (my usual suspension test track, but riding down) a few times, so wondering if there's scope to drop even lower on the BB. It's really interesting to see where these limits lie.

As for production, that's still looking like Autumn 2023. Our production slot is booked, but because delivery is driven by Shimano availability this is giving us the time and space to make these changes and hopefully make the bike as close to what most people want from one of these things.

As always on these kind of things, I super interested to hear your thoughts and feedback on where we're going with this. Do get in touch. Email cy@cotic.co.uk and let me know what you want out of a Cotic ebike, and what you think of the steel prototype.