Turpen's High-Pivot 29er Prototype 6

As a former Vital MTB tester, we know Evan knows what's up. It's great to see his ingenuity in version one of something he plans to produce in the future. In its current form, the 29-inch steel frame delivers 140 or 160mm or rear travel. Dive into some details from the creator himself:

What inspired the design of this prototype?

Evan: A few things...the biggest influence was my 20 years of racing experience during which I had a never-ending quest for better performing bikes and components. During my racing career I also worked on and off as a professional bike mechanic since I could never make money racing bikes! This helped mold certain design decisions I made along the way about durability, serviceability, and ease of (or lack of) maintenance in this design. But it was also a prototype and made only for me so I could do whatever I wanted. There's some proprietary stuff that I maybe wouldn't do in a production bike...

Specs and Geometry

Why go with a high single-pivot?

During the time that I decided to start this project (2018), Amaury Pierron was dominating the World Cup field on his high-pivot Commencal and it just looked right! It looked noticeably better under Amaury. High-pivot bikes have always interested me, but they've had some weird and undesirable traits in the past.

What solidified my decision to go high-pivot was borrowing a friend's Commencal Supreme SX to ride for three weeks. It was a 180mm travel, 27.5" wheeled freeride/park bike with a dropper post and Eagle gearing so you could still climb it. I rode that bike a ton and was super impressed with how it carried speed through the rough, but there were a lot of other things that really sucked about it. Namely drivetrain drag and noise, strange anti-squat and pedal kickback, not enough progression, too high of anti-rise, slightly dated geometry, and not enough tire clearance or stiffness out of the back-end. Plus I generally prefer a 29er for a trail or enduro bike although mullet setups are also pretty sweet! I felt like if I could take the positive attribute of carrying speed amazingly well and eliminate all of the negative attributes I had experienced, it would lead to a very awesome and FAST bike.

The speeds it allows you to comfortably reach are very high. I am struggling to relearn what is possible on a bike!

What sets it apart from others?

Pretty much everything. The anti-squat is one of the biggest differentiators. My anti-squat curve is 100% at sag in every single gear combination. Most high-pivots and most bikes in general pedal quite differently in different gears. Mine doesn't. My anti-squat curves are also very stable outside of the exact sag range so regardless of where you run your sag it is going to pedal very efficiently. It also has 100% anti-rise at sag which leads to super stable and predictable braking.

Pretty much all high single-pivots on the market have high anti-rise numbers which means they actually dive down into their rear travel when you apply the brakes. On my bike it is just stable. You don't have to shift your weight far back or forwards under braking. It really rewards a centered riding position. My leverage rate is also tuned for increased small bump sensitivity off the top combined with enough progression to eliminate hard bottom-outs all the while avoiding deep stroke harshness. This bike really feels like it paves ultra-rough sections of trail. It is a very cool feeling to experience and it is fully coil shock compatible.

Also, I can't forget to mention the idler. It has 22 teeth compared to the 16 teeth on the Forbidden and 18 teeth on the Deviate. This not only increases durability by distributing the loads from the chain over a larger surface area, but it also reduces friction from less chain-link angle change. It has a really nice low friction large double-row bearing that can more than handle the force applied from an Olympic track sprinter sprinting for gold, all day long. Since my idler is positioned so far forwards this reduces the angle that the chain sees and therefore frictional losses when in the extreme ends of the cassette (climbing and descending).

How many iterations did you go through?

Virtually...an absurd amount! Hundreds upon hundreds of slight variations early on. Once the design was finalized and I ordered my CNC parts there wasn't much wiggle room after that! Although I did end up adding the two uprights that connect the main pivot to the shock mounts. This was after learning how to use FEA (Finite Element Analysis), testing my frame and realizing that my bike would have actually bent from hard bottom-out forces with the original design. I'm really glad I figured that out and found a solution before riding it!

Describe the on-trail ride experience.

Next level. It turns so good, carries speed better than any bike I've ever ridden, pedals like a rocketship, creates grip where you wouldn't think is possible, and it feels as if it is doing everything to keep you in control despite however hard you push. The speeds it allows you to comfortably reach are very high. I am struggling to relearn what is possible on a bike! Best way for me to describe it is as if I was plopped into Aaron Gwin's body with his skills and speed, but still my understanding of what is possible. It's scary fast!

What are your hopes for this bike? This suspension platform?

That it piques people's interest, but that it also teaches me what I need to know so that I can apply it to the next version. The one that will be much closer to a production bike...I am a firm believer that bikes can ALWAYS be better so despite this bike riding amazingly well, the next one will be even that much better. As for the suspension platform, I aim to have my final non-provisional patent submitted and eventually granted for this design. I already submitted my provisional patent before the bike was out in public. This gives the bike "Patent Pending" status and allows me to apply the date of that application to my final patent. I'm hoping this will get the message across to larger bike companies to ****-off!

Do you plan to make a production model?

For sure! It will probably look different than this one since it will most likely be aluminum to save weight and will take all that I learned from this bike and integrate those improvements. As of right now, once the bike is fully developed and thoroughly tested I plan to make a small production run of 25-50 high-quality frames all made entirely in the USA and then move forwards from there.

Keep an eye on instagram.com/turpentime for more project updates.