Making New Waves, Resurrecting Old Ones
Could this seemingly obvious technology potentially change the way mountain bikes are designed?
April 17, 2022
It was October 31st, 2019 and I was busy carving out a new business model for my MTB service shop in a pre-COVID world where so many small retail bike shops had been on life support for years. "Different" was quite literally my biggest goal. Just be unlike anything else in a very significant way, because if I was going to sell new bikes then duplicating the norm would likely lead to another slow death for yet another small retail shop. Locate rurally I thought. Low overhead with some extra space to carve out a little terrain park would be cool -- and different. As I was breathing life into this vision, little did I know that those initial back and forth emails with Charlie at Berd on October 31st would eventually have the biggest impact on how I would ultimately shape a very key aspect of this new retail direction for my service shop.
I'd envisioned a specialty shop that would be the go-to place in the Midwest to buy one -- mabye even two -- particular brands of bikes, but they had to be small MTB specific brands. What I didn't want is the typical small-shop lineup where operating capital was stretched out across four to six brands because most imperative would be that my relationship with sales reps would be rock solid, fluid, and valued by both sides -- no uphill battles or ego driven moods to navigate. We'd crush it year-in and year-out for their brands, or wisely move along to another. Having already ridden a lot of bike brands (and then riding more out of due diligence) I opened a dealer account with Yeti Cycles. Yeti had a strong reputation for a rear suspension platform that was firm at the sag point and pedaled particularly efficiently before opening up and getting active deeper in the stroke when things got rowdy which really smoothed things out at speed. Speed is certainly requisite with Yeti, and having come from moto, I loved speed. Here in the Midwest we pedal almost constantly. No lung-busting climbs, but consequently not much to go down either. So because we pedal a lot, Yeti appealed.
The Yeti SB115 is a short travel 29er with a short wheelbase that excels at carving tight and twisty singletrack, hovering through Midwest rock gardens, and has just enough suspension to stick four foot drops-to-flat with plenty of confidence.
I could talk a lot about the high-end hubs and carbon rims I'd initially sent to Berd for them to lace up with their patented spokes, because those wheels rode great, spun up fast, and dampened vibration very well -- and it was a clear and noticeable difference vs. rigid spokes. But in October of 2020 I'd realized that it was high time to let these professional engineers who had a specific rim spec'd for their unique spokes to go ahead and lace both of their products to my favorite hubs. I'll never forget that first ride on a set of Berd TR27's. And I don't just mean how light and fast they felt -- though there was certainly a mind-bending degree of wow factor in that alone. But the overall ride quality was just different, and after all, my big goal was to be different.
Photo Credit: Nick_NoetheVisuals (IG)
When racing UCI sanctioned events, a wheel must withstand 40 joules of impact force to be deemed safe. Berd is dropping 116 joules of impact force onto these TR27's. The more capability that the rim has to compress without fracturing and/or ripping a nipple through the spoke bed, then the stronger the wheel will be.
The textile nature of the Berd spokes support this in several ways. It also took a lighter rim than what you'll find in most carbon wheelsets to maximize this bend-but-don't-break level of compliance. But in short, the wheel is stronger because it's lighter.
So how exactly are they different? As stated, the ease of spin-up is inevitably going to be the first thing that you'll notice. Flat ground, mild climbs, techy climbs, steep climbs....it doesn't matter, they just make it all easier. Techy climbs in particular stood out as I'm no stranger to stalling on bigger roots and square-edge rocks when climbing at slower speeds, so a wheel that can so easily spin back up to a reasonable speed in one good pedal stroke was good medicine on the occasional carcass day when my 210 pounds feels more like 260 pounds. But it isn't long before you begin to pinpoint the differences in the actual ride quality. The manner in which the textile nature of Berd spokes dampen vibration is, to me, their greatest attribute. Whether it's an hours-long ride, or even a shorter one with abundant small chatter and/or frequent rock gardens, you quickly come to appreciate the added comfort. But the light-bulb moment is when you realize how much that added comfort reduces fatigue and you're ultimately pedaling against less rotational mass with a bit more energy in your tank. Either of those qualities in isolation are welcomed -- if not subtle -- but in tandem they yield a sum much greater than their parts.
Suspension effect: The Midwest is hardtail and short travel 29er country, so the prospect of adding to a bike's suspension capability while simultaneously lightening it's rotational mass on our never-stop-pedaling terrain is enticing. That first set of wheels with Berd's in-house TR27 rim arrived about the same time Yeti had just introduced their new ARC hardtail, so as I began mounting them to a new ARC, I thought hey, why not toss a lightweight XC version of CushCore's tire insert in the rear tire? Yeti had touted a carbon layup aimed at excellent vertical compliance for the rear of their new hardtail, but, I mean, it's still a hardtail, right? And the added weight of the lighter XC version of CushCore in just one tire had always been imperceivable under my 210 pounds.
The 2021 Yeti ARC with Berd TR27's and XC CushCore in the rear tire.
Up first was manualing the rear wheel into a common 6" city street curb near the shop. I'm still convinced that I could feel my face go pale at impact as I'd thought for sure I'd either pinch flatted or even slightly taco'd the rim. It was the impact that quite literally wasn't an impact at all -- more of a hick-up instead. But I quickly found a tire and rim that were both perfectly in tact and a mind that was racing trying to process the confusion. Was it a fluke event that I'd never be able to reproduce, or something more? Again, then again, and yet again, I manualed into that section of concrete curb, daring to add a bit of speed each time. The results were the same each time. With my mind still racing, I hussled back into the shop curious to see if the rear tire still had the same 20 psi I'd started with, and it did. At that point, I couldn't get that ARC into the demo van fast enough to make my way over to some of our local trails that had some big roots and small drops. I had thought myself to be well past the hardtail phase in my own personal MTB life. Sure, I'd sell the heck out of them to new riders and to the hardtail enthusiast's, but I was a short travel 29er guy at this point. So what do you do when a hardtail rides like it has a little 50mm travel rear shock, but still pedals as crisp and efficiently as any other hardtail?
Fast forward more than a year later, and I still find myself pausing to decide which bike to grab between the ARC and a SB115 when loading the demo van to go chase a customer wanting to demo a bike at a public trail system (about the only time this shop owner has to actually ride during the busy season). I've got both bikes set up with Berd TR27's and XC CushCore in the rear, though I do have a Berd TR30 that I'll sometimes toss on the front of the SB115.
Traction: As with anything that calms a wheel down -- be it perfectly dialed suspension or a little lower tire pressure -- traction is then improved. While this might be the most subtle benefit stemming from the compliance offered by a Berd spoke and rim combination, it's a notable one, and a nuanced one. Naunced because I believe the inter-relational dynamic between what a tire insert does and what a Berd spoke does could possibly result in what I referred to in this article's sub heading as something that could change the way some MTB's are designed. It's no mystery that tire insert's allow you to more safely run lower tire pressure to improve traction without as much risk of pinch flatting, rim damage, burping, or even rolling the tire right off of the rim in high G turns. But with the Berd spoke's ability to fall out of tension so easily, and allow their rim to easily compress, there is also a bit of rebound effect when it returns to it's original shape. If you can dampen some of that rebound effect then you've effectively added a bit of very usable suspension capability to your bike. If you can do that while also significantly reducing rotational mass, then all the better, because in this case you're also reducing the ratio of unsprung mass to sprung mass (especially on these lighter bikes) and thereby improving your suspensions ability to react quickly to the terrain below it without disturbing the sprung mass (i.e. you) above it. And with this reduced rotational mass also comes a subtle reduction in gyrational pull when cornerning on 29" wheels, which, it seems, to allow this improved unsprung:sprung mass ratio to grab traction in corners in an unparalleled way. While entry speed carried into corners can no doubt be pushed just a touch faster with this wheel system, I think it's the acceleration coming out of corners that will ultimately grab the headlines in the mind's of most riders.
A Berd TR30 Wheel, a Pro CushCore Insert, and a Minion DHF 2.5 EXO weighed in at 1,950 grams.
A DT Swiss EXC 1501 carbon wheel, no CushCore, and a Minion DHF 2.5 EXO weighed in at 1,844 grams.
A Berd TR27 Wheel, a XC CushCore Insert, and a Minion DHR II 2.3 EXO weighed in at 1,630 grams.
The dynamic deepens: While intentionally adding weight with a tire insert to such a light wheel -- even if only the rear wheel -- might seem a little counter-intuative, the gains made when dialing in both the compression and rebound forces in this wheel system are probably something you're going to have to experience yourself before you're able to fully appreciate it. If the technology here does in fact become a "new law" of MTB physics and thereby change the way some bikes are designed, then I do believe it is likely to be a law of diminishing returns. I've not personally experienced the same wow factor when experimenting with the heavier Pro Cushcore inserts and 2.5" wide tires on the wider Berd TR30 wheelsets. For one, the combined weight of the heavier insert, the wider/heavier tire, and the wider rim all add up to a collective weight significantly higher than you'll find with the lighter XC CushCore insert, a narrower/lighter tire, and the lighter TR27 rim. In the pic above you can see a 320 gram difference in just one wheel. 320 grams would be a lot of rotational weight difference in two wheels, much less just one. And while the superior vibration damping, compliance, and traction is still there on the wider setup, there is so much wow factor in the quick spin-up of the lighter setup that folks on short and mid travel trail bikes might really want to consider whether industry trends in tire and rim width are still applicable when a key dynamic has been shifted as hard as Berd has managed to shift it. I'll add that in my experience an XC CushCore insert on a 27mm internal width rim with a 2.3" wide tire results in a slightly more stable side wall at lower tire pressures than you get with a pro CushCore insert in a 30mm internal width rim and a 2.5" wide tire. And yet a 2.3" Minion DHF side knob is the same size as a 2.5" Minion DHF side knob, so cornering traction is nearly identical at these lower pressures when the added compliance of Berd spokes is at play. The 2.3" wide tire also rolls faster and carries speed for longer between pedal strokes. The one sacrifice you will make with the narrower tire in a dynamically functioning system such as this is in braking traction, but it's still pretty dang good at the lower tire pressures that this system seems to work best at. And on the type and grade and terrain you're likely to ride a hardtail or shorter travel bike on, the available braking traction is more than sufficient with either a DHF or DHR II 2.3" tire.
So could this mean the industry may circle back around and embrace the "old tech" of a 2.3" Minion DHF or DHR II as a resurrected new tech? Not likely on long travel enduro rigs -- that's where those Berd TR30's and 2.5" tires really do shine. But short and mid travel bikes have been getting progressively heavier the past few years as the industry is trending toward making carbon frames stronger and less warranty-proned, while at the same time more and more riders are looking to the hardtail and short travel 29er to provide the most contrast to that new e-bike in their quiver. It stands to reason that making these "small bikes" easier to pedal and more capable will be something the majority of MTB enthusiasts who own multiple bikes are likely to embrace in increasing numbers over the next few years.
Lateral Stiffness: Modules of elasticity.... stress divided by strain.... and other engineering terms of endearment are the kind of things most of us don't want to try to wrap our minds around when we go about exchanging the complexities of life for the simplicity of rolling through nature on two wheels. But, inevitably, one of the first questions I often get from customers asking about a Berd wheel is, "won't they have more side flex in turns?" Given the limp nature of the unlaced spoke, it's certainly an understandable projection that most people cast onto this system at first glance, but a wheel's lateral stiffness is almost entirely dictated by the strength of the spokes in tension (think tug-of-war), the amount of set tension itself, and by the bracing angle between the hub flange and the rim's nipple bed -- followed then by the width and lateral rigidity of the rim itself.
A wider hub with more space between the spoke flanges and/or a larger diameter spoke flange increases the bracing angle and thereby increases potential to make the wheel laterally stiffer. And under tension, Berd spokes have been tested to be up to 4x stronger than rigid spokes. Granted, Berd spokes need to undergo a couple of overnight rest and re-tensioning periods during the wheel building process in order to achieve a strength under tension that is greater than steel spokes, but the product as delivered to the customer has been through that process, and (at most) the same basic spot true and minor re-tensioning procedure that is typically part of a Spring tune-up for any type of bike is all the attention you may ever need to give to these wheels to keep them on par with the lateral stiffness of a metal-spoked wheel. If you're a bigger and/or very aggressive rider, I always recommend out of due diligence to check tension at around 500 miles, but in the few instances I've needed to add some tension for such riders at that point, it's always been the end point of ever having to add tension again, be it at 1,000 miles or 1,500 miles, etc.
Implications: I think I could put this Berd TR27 system on any hardtail, short travel, or mid travel bike (carbon or alloy) and know it's going to pedal like a dream while improving comfort and reducing fatigue. But it had to be asked if there were any other bikes that this wheel technology might compliment particularly well? Bikes with a more rearward axle path seem to do truly magical things when climbing techy ledges and roots at slower speeds. When the rear wheel engages an obstacle in the early half of the bike's rear travel, it eases rearward a bit, allowing it to decelerate without the bike decelerating, and thereby gives the sensation of floating up over the obstacle -- almost as if something gave the rear wheel a little bit of help with a rotational surge of energy. Though this will also likely mean that the bike's rear shock is going to be a bit more active when pedaling, a couple of rear suspension designs have been brilliant in finding a good kinematic middle ground that balances a rearward axle path with some pretty dang good pedaling efficiency. When paired with the quick spin-up of this Berd TR27 system and just a bit of focus on a smooth/circular pedal cadence (which I've found soon becomes subconsciously embedded somewhere in one's muscle memory) the Canfield Balanced Formula (CBF), as implemented by Revel Bikes, quickly and convincingly proved itself to be a particularly excellent match with Berd wheel's witchy tendency to levitate and accelerate. Again, this wheel system can make any bike pedal like a dream, but you'll find with some bikes that it really brings them to life in an intangible way that is hard to describe, but when you know, you know. And when you mount this TR27 system to a CBF bike, you definitely know.
Conclusion: If there could only be one central starting point when I build my own personal bikes, then right now it's gotta be a Berd TR27 wheelset -- but that's assuming I'd also have access to a lightweight version of a tire insert [edit on 4/27/22: definitely add Tubolight inserts to this list -- more to come on that] and some Minion DHR II 2.3" tires. As I've began telling my customers who are contemplating a direction for their next bike, "buy Berd wheels and build a bike around that." No joke. If you feel like you couldn't go back to riding without a dropper post, then chances are you'll feel the same way after adapting to a Berd wheel system. I sure didn't see this coming back on October 31st, 2019, but I can't think of anything that I've been a part of in the MTB industry since starting as a service-only shop back in 2015 that has brought me more satisfaction than seeing this technology and this small company grow into what it is quickly becoming.
Clint @ Boone Cycles