We Chat To Evan Turpen About His High Pivot Prototype.

Former World Cup racer, spanner and industry cat Evan Turpen turned a bad day at work into his own prototype high pivot enduro machine.

Pete caught up with Evan Turpen to find out how a less than ideal day at work spawned several months of learning how to put a bike together the hard way before the concept became reality.

What was the starting point for this project?

The starting point for this project was having a bad day at work. About two years ago I was the lead mechanic at a local bike shop and for whatever reason I was having a bad day. That day I met my girlfriend for lunch at a local sandwich shop and ended up running into a co-worker from a bike shop I had worked at in the past.

He said he had just got hired at Fox Racing Shox in their test department working on future shock and fork development projects. When I heard this, without even thinking I lashed out and said straight to his face, “Looks like everybody has my dream job except me…” It was very childish of me. I should have been proud for him, but instead I was being a dick.

That’s when I realised I was miserable with where I was going. The shop I worked at was the best in town, but I still wasn’t happy. I had been a bike mechanic for too long, was burnt out and I needed a change. It wasn’t for a little while longer that I decided to pursue a long-time dream of mine of making bikes. It started as a note in my cell phone. I created a wish list of what I thought would make the perfect bike and soon after the real work began.

Once you had made that decision, what happens next?

Initially I spent about three months in Linkage Design. Linkage is a 2D bike suspension design and analysis software. I was already super familiar with using it since I am a massive bike nerd. Eventually I was able to create a design that achieved all the goals I had set for myself and more. After the initial 2D design had been decided on I realised I needed to take it to 3D.

I looked into hiring people to do it, even had someone working on it for me for a bit, but ultimately decided to do the 3D design myself. I taught myself Creo Parametric 3D design software and eventually was able to put together a rough 3D assembly of the frame and move the suspension to check clearances.

Then it was trying to find someone to fabricate it… I got a quote back from a major U.S. frame manufacturer and it would have ended up costing me around $20,000 for the first few prototypes which was out of the question for me. I decided I needed to see about making it myself…

How did you learn what you need to in order to get this bike built?

Lots of YouTube videos, patience, and tons of discussions with knowledgeable custom frame builders. I also have a friend who is an engineer that offered me tonnes of guidance and help along the way. There was a lot of trial and error. Tonnes of mistakes and wasted parts and tubing. Being a bike mechanic definitely helped though as I was already mechanically savvy and had a high attention to detail.

Even though I want to learn, I left the actual welding of the frame up to a local custom frame builder (John Caletti of Caletti Cycles). The last thing I wanted was a catastrophic failure because of my lack of welding experience. I also had a local machinist (Dave Mather of Mather Machining) CNC my links and idler pulleys. He far exceeded my expectations for the finished parts and was able to nail the tight tolerances I had specified for the parts.

What did you know you did and didn’t want to do with the bike?

Most of my decisions are based on almost two decades of racing and wrenching on bikes. You learn a lot in that amount of time. I raced pro downhill for 7 years and even went as far as racing World Championships in 2006 in Elite Men’s Downhill for team USA. As a privateer racer I was always focused on having the best bike possible and constantly looking for an edge with my equipment wherever I could.

For this bike I wanted to create the fastest bike possible for its intended use, but also a very durable and easy to work on bike. This bike is an aggressive trail bike but also has settings to turn it into a long-travel enduro/bike-park machine. The bike has double double-row MAX type bearings in the swingarm pivots that exceed the requirements for the loads seen on them. They shouldn’t wear out anytime soon.

There are also only 4 washers on the entire bike making disassembly and service a little easier. Basically I listened to what I wanted in a bike and let that guide me. I created the bike that I wanted above all else and since I’m really picky, I think other people will like it too.

How did you arrive at the frame layout?

Months and months of staring at a computer screen…but also learning FEA (Finite Element Analysis) was a big influence. Early on I was designing the bike by the seat of my pants. Making it look like what I thought a strong bike was.

After suggestions from my engineer friend I taught myself FEA and started virtually testing my frame and links. I learned that some of my early designs would have actually bent from hard bottom-out forces. Not good…

Using FEA allowed me to methodically design the frame and components to make sure they could handle the loads they would actually see (at least in theory). On some parts I actually was able to lighten them up by being smart with where the material was placed.

How hard was it to narrow down suspension platform options?

Pretty hard, but since I was in control, I had the freedom to go down whatever path I desired. I spent about three weeks riding a Commencal Supreme SX which is a high-pivot park/freeride bike. I saw certain advantages with the high-pivot layout that I really liked, especially how it carried speed so good through the rough.

I also noticed a ton of disadvantages like too much brake squat, bad drivetrain efficiency and noise, strange anti-squat behaviour, and lack of swingarm stiffness to name a few. With my design I only wanted the positives of the high pivot layout and worked hard to eliminate all of the negatives. In the end I actually far exceed all the positives of other certain designs that I liked.

How did you nail down the geometry and sizing?

Lots of research, but mostly through real world experience riding all different geometries on lots of different bikes. Before making this bike, I had a very custom Specialized Stumpjumper EVO 29 in size S3. It had a different link for different geometry, a different shock, different travel, even shorter than the already short stock offset fork.

There were certain aspects of the geometry that I had with that bike that I really enjoyed, but things I knew I wanted to change. Also the suspension performance on that bike was terrible in the rough. Not enough progression and an almost entirely forward axle path. After riding my first prototype I can confidently say that I am very happy with the geometry and would only like to try a mullet version of the swingarm in the future with shorter chainstays for a more whippy riding option.

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How many prototypes have you made?

This is the first prototype and first bike I have ever made.

Beyond prototypes, what form did your testing take?

FEA is one form of testing, linkage analysis is another form of virtual testing, but now it’s all real-world performance and durability testing through riding and racing. I’m signed up to race the first California Enduro Series race at China Peak in about two week’s time.

I’m not afraid to put the bike against the clock even though I am out of shape, un-trained, and out of practice. Once I can secure the next round of funding, I am going to fabricate the next version utilising what I have learned from this bike. It will be aluminium, much lighter, and much closer to what a production bike will be.

Once I’m fully happy with the next version then I will have to do a batch of pre-production samples for actual fatigue, strength, stiffness, and impact testing. It will be hard to break the bikes since it is expensive, but it is a necessary step to ensure that they are safe and entirely up to the task of going to production.

Did you have any outside help for testing?

Not yet. I am going to research what labs perform frame testing in the US, but also look into creating my own tests. I used to work at Santa Cruz Bicycles building media bikes and I’ve seen what strict standards they test their bikes to. The destructive testing is brutal, but necessary. I also have quite a few friends who already test bikes and suspension for major companies that I would like to get on the bike for their feedback.

How did you settle on the spec for the complete bike?

This is my personal bike so it’s a mixture of parts I already had on my last bike and a few new parts I wanted to try. I had X01 Eagle drivetrain on my last bike and was really curious how Shimano’s 12-speed compared to it, so I bought that. I custom built the wheels and actually robbed the rear hub off of an old downhill bike I had. The Renthal cockpit, 110 headset, WTB Silverado saddle and Bike Yoke dropper were some go-to items for me from the past.

Did that affect any decisions you made on the frame design?

No. But since this bike is a one-off prototype, I had no issues using Super-Boost cranks paired with a DH 157mm rear hub. This was necessary on this first prototype to get all the clearances I needed using basic straight chromoly tubing. It would have been so much easier to get clearances in carbon! I would have preferred it to be 148mm for ease of compatibility, but honestly the feel of a dish-less DH rear wheel is really nice.

Does the bike or ‘brand’ have a name?

There isn’t a specific bike name yet, but there is a potential brand name. I just can’t say what it is yet for trademark reasons…but it’ll be announced soon enough. The logo looks rad.

Favourite moments?

Having all the mitred tubes and machined parts 100% mounted in the front triangle frame jig and ready for welding. This was a very proud moment and the culmination of many months of fabrication work by me.

Also, the first off-road ride. I was grinning from ear-to-ear and it felt like a massive weight had been lifted off of my shoulders. I knew it was going to be good, but the actual performance on trail far exceeded what I thought was possible. It was shockingly fast.

Any disasters?

Many, but the biggest almost disaster was me cross threading the tap into the first main swingarm pivot after the whole frame had been fabricated and welded. I thought I had ruined the frame, but luckily I was able to safely fix my mistake.

I learned to thread the part before it was set to be welded so it could be perfectly straight from the beginning. I did learn a clever way though to ensure I could tap all the pivot threads perfectly even after welding going forwards.

Anyone to thank?

Todd from Black Cat Cycles. I still owe you a nice bottle of whiskey and some cash for your time helping me brainstorm.

John Caletti of Caletti Cycles for welding the frame and offering me tons of advice.

Dave Mather of Mather Machining for making such nice parts for me at a price I could actually afford.

Bjorn for letting me have unrestricted access to your workshop and the crazy amounts of help and teaching you gave me.

And last but not least, my girlfriend Margaux for believing in me, putting up with all the late nights I spent working on this when I should have been home, and being so stoked for me along the way.

You can keep tabs on Evan by following his Instagram feed here.

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