- Bike Checks
by AJ Barlas
For the last four months we have been having a blast and beating on the Santa Cruz Bikes Blur TRc. Having had countless friends speak very highly of the old Blur 4X, and preferring a trail bike with a little less travel, yet still with angles and construction burly enough to inspire confidence on aggressive trails, it seemed like a no-brainer to give it a go.
Throughout the process of getting to know the bike, it made sense to learn more about this updated trail weapon, its design, and the relationship with the Blur 4x (for those unaware, the TRc is often dubbed the new 4x). Follow on below as we chat with Santa Cruz's Scott Turner and dig a little deeper into the creation of one of the most popular rides on the trails.
SCB: Yes, but mostly in spirit. We have always felt like the Blur 4x was a bike ahead of its time. Released at Interbike 2004, it was unlike most any other bike out there. Shorter travel (115mm) to keep it quick, slacker steering angles for stability at speed and in the steeps, short seat tube (pre-dropper posts), low BB for great cornering, strong enough to take a lot of abuse, and the ability to run longer forks if you wanted to.
The riders that had them, loved them and it definitely earned somewhat of a cult status, but it never sold in huge numbers, especially when compared to the original Blur and the Blur-LT that followed it. The 4x moniker didn't help as it kind of pigeon-holed the bike from the start as some sort of 4x or Dual Slalom specific bike when in actuality it was also a great aggressive trail weapon.
Longer top tubes and shorter chainstays, fine-tuned the geometry for modern tastes, and longer seat tubes helped make it more useable as a trail bike.
The largest improvement (besides weight) is to the rear suspension. Our newer designs offer more support in the midstroke, and a more linear overall feel compared to the VPP1 bikes. The result is a bike that is more responsive and playful. In addition, the bike performs better under pedaling. We also incorporated the VPP2 collet pivot axle system which gives an added boost to bearing life and ease of serviceability.
This is not unusual for us. The Tallboy Carbon came out 18 months before the Tallboy Aluminum, the Highball Carbon came out 10 months before the Highball Aluminum.
We like going all-out with carbon first, then working backwards and trying to mimic the performance aspects in aluminum. The weight of course doesn't match up, but we want the performance to be the same regardless of material, and to be able to offer it at a lower cost.
Some of this is about understanding where the limits of carbon are. The XC was our first carbon frame so we were on the conservative side but as our experience with the material grew we were able to better understand where material could be removed without sacrificing performance.
We came up with a new way of forging aluminum links which allows us to make them within a few grams of the carbon links. Since the upper link requires a threaded shock bolt hole and you can¹t thread carbon it simplifies some of the manufacturing. It also helps with getting the right press fit for the bearings.
One of the things that makes the Blur TRc so special is how it combines progressive geometry and stiffness with light weight and all-day capabilities. The weight really helps with the playful, agile feel of the bike. To achieve this we had to look at all possible weight-saving areas, and keep the bike minimalist. In retrospect, we probably should have put tabs on there, but we weren't really sure who would be buying the bike.
At that time, most aggressive riders were on six-inch bikes exclusively, and XC riders were on 29ers. We made a bike in no-mans land, and we weren't sure who (if anyone) would buy it. As it turns out, the bike became a favorite of riders coming off longer travel bikes, and is being ridden in a similar manner. If we were using press-fit bottom brackets like most of our competitors, we certainly would have put tabs on there. But since our reliably awesome thread-in BB's allow for easy chainguide mounting without ISCG, there are plenty of options for everyone. We did add ISCG to the Blur TRa when the time came.
We weren't against through-axle frames, but we didn't really see the benefits in stiffness with our one-piece swingarm designs. There were issues with compatibility and lack of options that we felt outweighed the "neato" factor of a rear through axle. Once the 142x12 was more widespread in the market, and no longer difficult to find for our customers, we made the switch.
The suspension was developed in-house. Of course it's awesome to have FOX around the corner for quick custom tune turnarounds, but we do the experimenting and testing within our group. We always try to get production bikes under certain riders at FOX once they are available, as the tune process continues over the life of the bike due to rear shock technology changes and product updates. We're actually making a minor change to the tune for next year—a slight increase in Boost Valve pressure to firm up the midstroke even more. Feedback from FOX also gives us some more data points for future products.
We work on tunes while we are developing the bikes. To achieve this we order various shock tunes in our required size (light and medium compression/rebound tunes in different combos) and we can get the boost valve pressures fine-tuned with a quick trip to their facility. One of the most important tuning tools is the air volume spacers, which we can change here. This is typically the item we work with first while developing a frame design, and can fine tune the damping tunes a little later in the process.
The travel is obviously different so the shock rate and shock tune both need to get considered. Shock tune is discussed above. To talk about shock rate development you first need to understand that shock rate is the ratio of shock movement to rear wheel movement. This ratio works out to being the same as the ratio of shock force to rear wheel force. Shock rate is the inverse of leverage ratio. We prefer to use shock rate because if the shock rate is high then the amount of force required to move the rear wheel is also high so it is more intuitive for us than leverage ratio (which is the opposite).
Our shock rate curve literally looks like a happy face. It falls in the beginning to sag and then rises towards bottom out. This allows you to get a low shock rate around sag where small bump sensitivity is important without getting the harsh bottom outs.
To answer the question, different types of bikes have different shock rate requirements. For us an XC bike has a flatter shock rate curve which makes the bike feel a bit sportier when pedaling but also sacrifices a bit of bump performance. A bigger travel bike has a bigger portion of the mid stroke that is at a lower leverage ratio to give you more of a super plush feel.
This was one of the engineering departments major projects during the big 2007 VPP2 development (during the redesign for the Blur-LT2). We all made a long list of any possible issues anyone and everyone had about maintaining a full suspension pivot system and the engineering and design team went to work trying to eliminate all of them. We wanted our frames to be easily serviced and be disassembled and reassembled with a decent multi-tool.
As you note, the two bottom pivots come out from the left side, so you can remove the lower link without removing the crank set. The upper link axles come out on the right. Then there are the custom seals we tooled up. We wanted a full contact seal that would allow a grease purge, and labyrinth sealing keeping the bearings clean and out of the elements. There are 8 molded rubber seals, and 8 aluminum seal caps per frame, all easily serviced with the grease gun via the grease ports. We are pretty sure that the full system is a good step beyond what anyone else is doing out there in bike world. The shit is dialed!
For more information about the Blur TRc, including a great run through on the carbon frame build process, head over to the Santa Cruz Bicycles website. Also be sure to stay tuned for our in-depth ride review, set to drop not long after the Sea Otter Classic!