Modern Mountain Bike Geometry By Transition Bikes

Bike geometry can be complicated. It's nearly impossible to know everything about how a bike will ride based on looking at these numbers alone (not to mention these numbers tell you nothing about how the suspension itself will function). But we hear it being done all too often - and to be fair, we do it too. Problems arise when riders focus on just a few of these numbers instead of how they all relate to one another.

There are no right answers here. We're opinionated about this stuff and we'll let you know it. In the end, there are preferences and our hope is that this article provides the grounds for a more informed discussion of bike geometry. We're going to keep it pretty basic, and some of you might find a lot of the topic a little too 101. But we frequently come across pretty educated riders who haven't fully considered some of this stuff. Even in the basics you might come across a few new ideas. We hope it makes you think more about all of the details in your bikes geometry - we think about it a lot.

We'll begin with a topic that we see people confused about all the time....

Effective Top Tube (ETT) is a traditional way to measure a bikes length. It measures a horizontal line, parallel to the ground, from the center of the head tube to the intersection with the seat tube or seat post. This number is useful for identifying how long a bike will feel while in a seated position.

Reach is newer way to measure a bikes length. It uses the same horizontal line as the Effective Top Tube, but instead of measuring from the head tube to the seat post, it measures from the head tube to a vertical line that runs perpendicular through the center of the bottom bracket shell to the ground. This measurement identifies how long a bike will feel while standing.

So Reach measures your cockpit anytime you're standing and Effective Top Tube measures your cockpit only while seated with your saddle at a specific height. They're both telling numbers and it's worth considering them together, but we put a lot of emphasis on Reach these days. Any time we're riding aggressively, we're out of the saddle, so it follows that this number is going to have a greater overall impact on the "handling" characteristics that define the modern trail or all mountain rider.

One of the most common problems we see is over-emphasis on Effective Top Tube length. As a whole, bikes tend to be getting longer front ends these days. But that can be done with a longer ETT, a longer reach, or a combination of both. Riders who look only at Effective Top Tube without considering reach may be selling themselves short, literally. That's because seat angle has a huge effect on ETT, but zero effect on Reach. Watch what happens when we make the seat angle slacker:

The Effective Top Tube is now longer, but the Reach has remained the same. Or to look at that in another way, it's not hard to imagine a scenario where the Effective Top Tube of 'Bike A' is the same as 'Bike B', but the Reach of 'Bike A' is actually shorter than 'Bike B' because 'Bike A' has a slacker seat angle. This happens; a lot. In these cases, Bike A may fit great while seated, but while standing, the cockpit length is too short and the rider doesn't have enough room to move around or find the bikes sweet spot.

The slack seat angle that afforded the rider adequate seated top tube length does nothing to help the rider move around on the bike while in a standing position. It has other effects as well. The riders seated weight will be further over the bikes rear axle, making the rider work harder to keep the front wheel on the ground while climbing and harder to effectively transfer power to the cranks. The taller the rider/seat post, the more dramatic this effect will be because the seat itself keeps moving rearward as the saddle height is raised. So rather than slacken the seat angle to increase a bikes Effective Top Tube, why not increase the Reach? Proper position while seated and standing.

Another problem with ETT as a whole is that, because it's influenced by seat angle, the actual feel that a listed ETT provides will vary from one rider to the next depending on how high they run their saddle, even on the same frame. Reach is more constant. Consider a rider who is 6' with two bikes; both bikes have a listed ETT of 610mm, but they have different seat angles. ETT is always measured in a parallel line to the ground starting at the top of the head tube. Now let's assume this riders actual seat height is 5" above where the ETT is measured. The bike with a slacker seat angle will actually feel longer while seated than the bike with the steeper seat angle, even though
they have the same effective top tube on paper. So saying that you prefer a bike to have a particular ETT isn't really considering all the necessary information.

Longer Reach also means that the measurement from the BB to the front axle will be longer.

Let's assume that you take a frame and increase the Reach by 25mm. The distance from the BB to the front axle will grow as a result and you now have a bike with a longer wheelbase. You can now shorten the bikes chainstay length to get the wheelbase back to where we started. Same overall footprint, just with more bike out in front and less in the back. Same stability at speed, but a lot easier to push the rear end around in corners and get the front wheel off the ground when you want to. Decreasing the chainstay without increasing the reach would shorten the wheelbase, potentially sacrificing stability at speed. And a slack seat angle combined with the shorter chainstay is going to shift rider weight even further over the rear axle.

With a longer reach dimension, riders can run a shorter stem while still having enough room in the cockpit, whether seated or standing. Short stems provide stability, which is a good thing when you're hanging on for dear life down a high-speed singletrack descent or pointing it through a technical section of trail. When climbing, your tire is less likely to get knocked off line by a root or ledge in the trail. We're going to make a blanket statement here that's intended to offend plenty of people...anyone who doesn't consider themselves a purely XC rider shouldn't be running a stem over 60mm on a mountain bike. That's being generous too. Really we think that max stem length
should be closer to 55mm, maybe even 50mm, but we'll leave some wiggle room in there.

We see people defying this rule regularly - probably because their bike's reach is too short so they put on a longer stem to provide enough room to move around. Or because their bike came spec'ed with a 90mm out of the box and they never changed it.

2013 Transition Carbon Covert Announced

Transition Bikes unveils the new carbon Covert. See the bike in action as well as some of the new features and design inspiration that went into creating Transition Bikes first carbon bike.

The 2013 Carbon Covert is Transition Bike’s first carbon frame offering. The 160mm travel Covert was the perfect candidate to bring to carbon as it allowed the bike to shed weight, improve strength, add new features, and update the look at the same time. 

“In my mind, this bike really represents the ultimate no holds barred quiver killer. It's really everything I would want in a single do-everything type of bike and we've tried pretty hard to ensure all the right features are there without including things that don't really matter. A big goal of ours with this project was to develop something with very unique lines that you don't often see in bicycle frame design...and we feel we've really accomplished that. This was a long development effort so we're pretty pumped to finally unveil our first carbon frame.” Says Kyle Young, Transition Bikes owner.

Transition Bikes took the essence of the previous Covert but started from the ground up to produce something all new and extremely exciting. For design inspiration they looked outside the bike world towards Italian super cars. The carbon material allowed a no compromise design approach that allowed them to achieve exactly what they envisioned; powerful lines and a unique bold look. The frame uses some exciting new materials and an evolved suspension platform for the best possible performance on the trail.

The 2013 Carbon Covert is the first bike on the market to offer both C.O.C.K. and B.A.L.L.S. technology. The Completely Optimized Carbon Kinetics utilized in production of the carbon structure are an industry first; only available on Transition Bikes. The careful use of C.O.C.K. makes the Carbon Covert one of the strongest frames on the market today. The Basically Aligned Linear Leverage System suspension works with the shock making the suspension incredibly easy to tune; once again, only available on Transition Bikes. Our B.A.L.L.S. are only there to make sure you have fun on the trail. Unlike other suspension systems, our B.A.L.L.S. aren’t overly complicated, it’s just the right suspension technology to keep the ride smooth and predictable.

“When we first met in the lab to develop these new technologies, I didn’t realize just how big they would become. I am proud to see this bike released so everyone can experience the ultimate package.” Says Sam Burkhardt, Transition Bikes product manager. 

Working in conjunction with the B.A.L.L.S. suspension system, the 2013 Carbon Covert features a longer 8.5” x 2.5” custom tuned Fox CTD Adjust rear shock. The longer shock helps contribute to improved suspension performance and easier shock setup for riders of any size. The rear travel has been increased from 150mm to 160mm further expanding the performance in gnarly terrain. For riders looking for ultimate downhill performance, an optional Fox RC4 coil shock is available as well. The B.A.L.L.S. suspension system uses a higher main pivot placement for improved pedaling performance with modern 2x10 and 1x10 drivetrain setups. An all new hardware system, with single allen key tightening, has been developed to keep the pivots tight. While the front triangle features full internal cable routing, including the Reverb Stealth routing for clean looks and integrated performance.

FEATURES

• Carbon Front Triangle with Carbon Seatstay and Alloy Chainstay and Rocker
• 160mm Rear Travel
• 8.5” x 2.5” Fox CTD Adjust Custom Tuned Rear Shock
• Optional Fox RC4 Coil Shock Available
• All Front Triangle Cable Routing is Internal
• Reverb Stealth Seat Post Routing
• New Pivot Hardware System
• 12 x 142mm Dropouts (10 x 135mm Dropouts Sold Separately)
• Press Fit 30 Bottom Bracket Shell
• Frame Weight 6.75 lbs (Including Rear Shock and Rear Axle)
• PRICE: To Be Announced
• C.O.C.K & B.A.L.L.S Technology (Only Available From Transition Bikes)

GEOMETRY 
Head Tube Angle: 66.5 Degree (Fox 36 160mm) / 67 Degree (Fox 34 160mm) 
Chainstay Length: 430mm 
Seatube Length: Sm 563, Md 593, Lg 623mm 
Reach: Sm 378mm, Md 406mm, Lg 431mm 
Wheelbase Length: Sm 1106mm, Md 1137mm, Lg 1169mm 
Bottom Bracket Height: 349 mm

"This is definitely the most exciting bike we have ever done. It took much longer than we anticipated but when doing full suspension carbon you can't rush anything. Seeing carbon bikes being produced in person really makes you appreciate the massive amount of work that goes into each frame. I think there is a misconception that these bikes just pop out of molds and are good to go and that couldn't be further from the truth. Each frame is like a sculpted work of art.” Says Kevin Menard, owner of Transition Bikes. 

The 2013 Carbon Covert will be available in three colors (Lemon Lime Metallic, Stealth Black & Matte White) with multiple build kit options to meet different rider preferences and price points.

• TRANSITION BIKES
• 2641 Delta Ring Rd.
• Ferndale, WA 98248 USA
• (360) 366-4960