Could Evan Turpen’s designs change the future of mountain bikes?

Last year former pro downhill racer Evan Turpen set out to design a mountain bike that could pedal over roots, rocks and hills faster than other suspension bikes. Turpen revealed his frame designs to the media last year. His frames generated plenty of interest, but the bikes were not yet available to the public. Evan had built two prototypes when we contacted him to see if we could try one of his bikes. He didn’t have one available for us at that time, but he was willing to share his plans with us as he prepared to launch his bike company in the spring of 2022.

This is the first prototype of Evan Turpen’s Contra mountain bike. The steel frame weighed close to 13 pounds, so Evan left it unpainted to keep from adding any more weight.


What are the main advantages of your frame design?

The rearward axle path, due to the high and forward pivot location, is the most noticeable advantage of the design. It allows the rear wheel to move up and back, which is more similar to the movement of the front wheel. It helps the bike carry speed through rough sections much better than a “normal” bike that has a mostly forward-arcing axle path. This is because the rear wheel on this bike moves in the direction that the bump is pushing the wheel (up and back). It hangs up less on square-edged hits and transfers less impact to the rider because of this.

Very good pedaling is also an advantage of this design. This bike achieves 100 percent anti-squat in every single gear at the statically loaded sag point in travel, and the anti-squat curve is very stable around sag. This means no matter what gear you are in and even what sag percentage you prefer, you always get very efficient pedaling performance with little to no bobbing.

The idler pulley is necessary for the design in order to reduce any pedal kickback that would occur if you had the same pivot location but with a normal drivetrain (without the idler). The bike has very low-pedal kickback, which means you can pedal through bumpy sections smoother than if it were a normal bike. It disrupts your pedal stroke less.

The idler pulley is also oversized, at 22 teeth, to help with drivetrain efficiency, smoothness and durability. Since it is positioned so far forward, it helps to reduce the angle your chain sees when it is in the furthest ends of the cassette (climbing and descending gears). This helps to increase drivetrain efficiency compared to other high-pivot bikes.

How much travel does it get?

There are two different shock mounts that achieve 140mm of travel and 164mm of travel respectively. They use two different-size shocks to do so (210x55mm and 230x65mm). The geometry adjusts correctly in each position for the increase or decrease in fork travel depending upon each setup.

What wheel size is it now, and what’s it going to be later?

This bike is a full 29er. The next bike will also be a full 29er but will have the option of running a mixed-wheel combination for shorter riders and those who prefer that setup by utilizing a different swingarm.

What kind of rider is the bike designed for?

This bike is aimed at aggressive trail and enduro riders and racers—people who want a bike that climbs well and descends even better. It is versatile with its travel adjustment so it can be a shorter-travel bike for all-day epic adventures but also be configured for bike-park days or enduro races in the long-travel mode.

How well do you like it so far?

I love this bike! It was the first one I designed and built, and it lived up to my expectations. My main complaint with this first prototype was that it was very heavy, at about 13 pounds for the frame, shock, idler pulley and axle. It needed to go on a serious diet to eke the most out of the design’s advantages.

What are you planning to change when you start production?

The design has already changed to be much lighter (by about 3 pounds) while maintaining performance characteristics and stiffness similar to that of this first prototype. I also improved pedaling and braking performance even more. Suspension performance improved drastically as well because of the unsprung weight being reduced by 600 grams (the weight that has to move every time the bike absorbs a bump). The shock-leverage ratio has also improved to make it even easier to tune for shocks from all different manufacturers.

How much do you think you’ll charge for a frame when you start selling them?

Pricing is still being determined. They will most likely be priced similar to high-end carbon frames but be made in the USA in small batches instead of mass-produced in Asia.


We reached out to Evan again to see how things are going now. He currently expects to be able to offer his bikes to the public this summer. Read on to learn more about the latest changes to his frame design and his plans for Contra Bikes.

What’s the main advantage of your latest frame design?

Suspension performance, mainly carrying speed and maintaining control and grip through rough sections of trail. The latest frame design combines as many positive suspension characteristics as I could into one bike.

Realistically, there is not just one thing that makes the bike work great. It is the combination of all of the characteristics that make a really great-riding suspension design. The axle path, leverage ratio, anti-rise, anti-squat, frame geometry, unsprung-to-sprung-weight ratio, frame stiffness, and even tolerances and smoothness of the suspension linkages are all things that I worked hard to optimize.

What is the main advantage of having an idler pulley?

The idler pulley is what allows for the high-pivot location and rearward axle path to work well on a chain-driven bicycle. Without the idler pulley, there would be greater degree of chain growth and pedal kickback on a high-pivot bike, and the suspension wouldn’t work so well. With the idler, you can independently control the way the bike pedals and also reduce the amount of chain growth and pedal kickback. It adds an additional tuning element when designing a full-suspension frame, and if the designer takes advantage of this, he can achieve some really unique performance benefits.

The striking looks of Turpen’s first prototype generated plenty of interest in the mountain bike community.


How do you explain the term “anti-squat” to people who aren’t familiar with it?

Anti-squat is a suspension system’s mechanical resistance to compressing during acceleration. Take your average car for example. When you mash on the gas pedal and accelerate hard, the front end of the car rises and the back of the car squats down as the suspension compresses. The same thing happens on bicycles when you pedal, since every pedal stroke is a little acceleration. Since pedaling is a rhythmic motion, this can cause unwanted and repeated compression, then extension of the suspension with every pedal stroke. This equates to an inefficient feeling on the bike, since some of your pedaling force is going into moving the suspension instead of propelling you forward. You can minimize this unwanted movement by locking out the suspension using a climb switch or a lockout lever on your rear shock, but this is merely a band-aid and doesn’t actually solve the root cause of the problem. Instead, a skilled frame designer can carefully tune the anti-squat of the rear suspension design and can nearly eliminate all unwanted movement of the suspension. All of this is built into the suspension design without ever having to touch a lockout switch to make your bike feel efficient.

Can you describe what it feels like to ride a bike with good anti-squat performance?

It’s a very enjoyable experience. The bike feels very efficient when you are pedaling with very little unwanted movement of the suspension. I never need to use a climb switch. It also generates a lot of grip up steep climbs, and I think this is due to there being more consistent pressure on the rear tire’s contact patch.

You said that your first prototype of this bike felt like the best bike you’d ever ridden. What was it that made it feel so good?

It was a number of things. At the time, it was the best bike I had ever ridden from a suspension performance standpoint. Weight-wise, though, it was very heavy at around 12.5 pounds for the frame, including the shock and no paint. The leverage ratio on that bike had a very nice shape and a balanced amount of progression. It used its travel very efficiently, and I can’t recall ever experiencing a harsh bottom-out. The pedaling performance and grip while climbing were surprisingly good, too—shockingly good. Also, performance in the rough on big bumps was something that would make you smile. The bike carried speed really well.

The non-drive side of the bike reveals some of the workings of the suspension system.

When do you expect to complete your first batch of bikes for sale?

As of right now, it is looking like sometime this summer. I don’t want to set an exact date just yet, because anything could happen. There could always be delays in this current COVID-affected supply chain. Lucky for me, I already have the majority of raw materials I need to make the first frames, but I still need to decide on a rear shock or shocks to spec and purchase those. I have been doing a lot of rear-shock testing over the last few months.

Do you have any idea how much you’re going to sell them for?

The price isn’t set yet, but it is looking like they will be very similar to carbon fiber frames like Santa Cruz or Yeti. They will be very handmade here in California in small batches instead of mass-produced overseas.

Has it been hard to get the parts you need to complete the bikes?

It has been hard to get parts to build up complete bikes, and that is why I will currently offer them as a frame only.

Are your bikes designed more for racing or trail riding?

This first bike is a big-hitting enduro bike that will be capable of being raced at an EWS-level race or ridden hard in a lift-accessed bike park, but it will also be quite fun to ride on less challenging trails. You can really tailor the intended use of the bike with the build kit that you choose. For instance, you can reduce the rear travel from 164mm all the way to 147mm with a simple shock swap. Combining with a lighter, shorter-travel fork with 150mm or 160mm of travel steepens the head angle and lowers the bottom-bracket height, and you have an entirely different ride.

Without a doubt, the first bike is going to be a great enduro race bike. It could also be used for downhill races that are less demanding. There is also a hack to convert it to a proper Sea Otter slalom race bike. I am excited about this!

As a former pro downhill racer, Evan is making sure that his bike can handle the rigors of off-road use.


What do your bikes do that make them work better than other bikes?

A number of things; the bike really is doing everything it can to help you maintain control, speed and grip through the rough. It does all this by balancing all aspects of the suspension kinematics to truly create what I like to call a “smart mechanical system.” It pedals very efficiently despite being made out of steel and having a lot of suspension travel. Compared to other high-pivot bikes, I focused a ton of energy into optimizing drivetrain efficiency and smoothness, and I think it is the smoothest idler drivetrain on the market. The geometry is also something I pored over endlessly to really get the most out of the suspension layout. It corners amazingly and climbs shockingly well. I think a lot of people will be really surprised when they ride it.

How many people have tried your bike so far?

Only a handful of other riders. There is only one test bike, so I currently do the majority of riding and testing. Feedback so far on the bike has been overwhelmingly positive, but I am still pushing to make it better. There will be further improvements before it goes to production.

Is it possible for someone to try out one of your Contra bikes before ordering it?

Initially, it will be possible for people to try the bikes on a case-by-case basis in and around Santa Cruz County. I will have a few complete bikes early on for media sources to ride and review. After they are done riding them, they will serve as short-term demo bikes before later being sold to recoup costs. In the future, I would like to have an authorized demo center out of a local bike shop, but people will have to travel here to try them or track down a buddy that has one. I am a one-man show at the moment.

How can someone order one of your bikes?

I will be selling direct through Currently, the website is just a landing page with an e-mail sign-up. It will get updated with information and a web store as I get closer to launching.

You said in an interview last year that you were out of money and might have to go back to working in a bike shop again. Did that happen?

Nope! Luckily, we figured out that housing prices had increased so much in Santa Cruz County that we could do a cash-out refinance on our home. This should be enough funding to get things off the ground.

Can you say who the investors were?

Us! Myself and my fiancé.

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