These days bikes are starting to look increasingly similar. Full suspension cross-country bikes in particular have mostly converged on a similar design, with a single pivot just above the BB, a flexible seat stay pivot, and usually a shock nestled under the top tube driven by a short rocker link. Australia-based Tim Southall, director of Vasttech designs, decided to do things a bit differently.
The Veli full-suspension bike uses his Vasttech suspension system, which is a bit of an outlier. With the main pivot far behind the BB, it retains the basic double-diamond structure of a hardtail, with a short suspension link connecting this to the rear axle, developing 112 mm of travel.
Vasttech Veli Details
• 112 mm travel (120 mm fork), mixed wheels
• Reach: 445 mm (one size)
• Chainstay length: 414 mm
• 68° head angle
• Claimed frame weight: 1800g with shock, axle & hardware
• Claimed bike weight: 9.59kg (excl. pedals and saddle)
• Price: $13,700 AUD (complete bike with XTR)
According to Tim, this allows for a lighter frame (just 1800g with shock, axle & hardware) and some interesting suspension characteristics too.Vasttech suspension system
As a quick refresher, the reason modern bikes don't bob and "squat" into their travel too much when you pedal is that they have something called anti-squat
. When you pedal, the bike accelerates a tiny bit, and this acceleration puts more load on the rear wheel which acts to compress the suspension. This happens with every downward pedal stroke, which can cause "pedal-bob" as the suspension oscillates up and down, wasting energy. Anti-squat works because as the suspension compresses the cassette moves away from the chainring so the chain tension is acting to pull the swingarm back down and extend
the suspension. Usually, suspension designers try to make this anti-squat force cancel out the squat force caused by acceleration, so in theory, the suspension stays level in its travel, with no bob, no matter how hard you pedal.
The Vasttech suspension system has a pivot that's high above the axle at the start of the travel. This means the axle starts moving rapidly away from the chainring, creating a strong anti-squat force. So much so, that according to Vasttech's website, their suspension "extends from the 25% recommended sag on flat ground, to approximately 10% when climbing with power". The idea is to raise the BB and steepen the geometry when sprinting or climbing while having more relaxed geometry when coasting or descending. But according to conventional suspension theory, this may cause the suspension to oscillate up and down as the suspension extends
with each power stroke, so wasting energy.
At the same time, the short link and high pivot location mean the brake torque acts to compress the suspension when the brake is applied (this is known as anti-rise or brake squat) far more than a conventional single pivot. This lowers the bottom bracket and slackens the head angle when braking on a descent. According to Vasttech, "It's an automatic geometry adjustment system that requires no electronic sensors, buttons, levers or chips." But again, there's a reason not everyone is doing this. High levels of anti-rise are associated with suspension packing down and becoming harsh during heavy braking, which is why many manufacturers use Horst-link or Split-Pivot designs that reduce
the anti-rise compared to a conventional single pivot. That's not to say Vasttech's is a bad idea, but it will be interesting to see how the suspension tracks the ground while braking.
The short suspension link means the axle path arcs quickly from very rearward at the start of the travel to forwards by the end. This should help it absorb square-edge bumps in the first part of the travel, but without the chain growth (that's the increase in the distance between the axle and swingarm) getting too extreme. According to Vasttech, the total chain growth (and associated pedal kickback
) is less than a comparable conventional design with its main pivot 66mm above the bottom bracket.What about those wheels?
You might think the three-spoke monocoque carbon wheels are unusual, but they're even weirder than you think. For starters, the thru-axle isn't your standard 12 mm aluminum bolt; it's an extension of the left-hand swingarm where the carbon fibers flow from the swingarm into the axle in one piece. The axle tapers down from 40 mm diameter where it joins the swingarm. Vastech says it takes an extra minute to remove the wheel but stiffness and unsprung mass are "off the chart".
The ratchet mechanism is custom too. It allows the drive side hub bearing to sit 3.7 mm further outboard, which apparently results in "a marked strength and stiffness gain along with improved bearing life." There's no word on the engagement angle, but the press release says it's designed to allow the cassette to rotate forwards just enough to eliminate pedal kickback with the Vasttech suspension system. It's probably fair to assume there will be a larger engagement angle (slower pickup) than most modern hubs.
While Vasttech tried making wheels with conventional spokes, Southall says, "I could never escape the fact that monocoque wheels offer huge advantages, especially in the realm of lateral stiffness". But it's not just about the wheels in isolation.
Tim says the monocoque wheel offers superior stiffness without the need for wide hub spacing, so it uses a 49 mm chain line like a non-Boost hub. This means the drivetrain is brought inboard, reducing weight and flex in the frame, narrowing the Q-factor, and reducing the chances of damaging the derailleur.
Tim claims the three-spoke design allows the wheels to transfer forces evenly throughout the wheel. As an analogy, he points to a three-legged stool that always rests evenly on all three legs, whereas a stool with four or more legs may have one or more legs off the ground if the surface is uneven.
The patent-pending rim design is thickest at the points of most stress - at the intersection of the rim and spoke and at the mid-point between the spokes - just like a beam bridge. The carbon fibers run continuously from the rim to spoke to the hub shell and back again. There's no word yet on how much they weigh or cost - they're only available as part of the bike for now.
That said, this bike is obviously whack (for me). But I applaud the effort!
LONG LIVE ANYTHING BUT HEADSET ROUTING!!!!!!!!!!!!!
This explanation is bullshit.
Agreed— I love the axle design, wish they’d made a short-link fork to match the rear (oriented so the brake torque is anti-dive — make the whole thing ride very differently). Buuut- yes monocoque wheel is useless, and the stool analogy is just absurd.
Would love to see the AS curve for this, likely goes below 0% for most of the second half of travel. Which means this will squat sooooo much if you pedal hard directly out of a compression that uses more than like 50% travel.
Maybe he used to race BMX?
The comment of "Anti-squat works because as the suspension compresses the cassette moves away from the chainring so the chain tension is acting to pull the swingarm back down and extend the suspension" is a very inaccurate statement. With regards to the effect of chain tension it is 100% dependent on the location of pivot point the axle is rotating around. This can either cause the suspension to compress or lengthen. It also has a lot more to do with mass transfer when accelerating or decelerating then chain tention. Any type of suspension system from single pivot to VPP can have vastly different anti rise or anti squat characteristics depending on how they are designed. it is not inherent to the system. The amount of tune ability is though.
I haven’t been on pinkbike in a while but it has gone downhill. it seams like it is now just what is the weirdest products we can inaccurately write about while still hitting the right marketing buzz words.
There is merit to the short single pivot for pedalling, though it sounds like Southall went way overboard with the anti-squat, but his philosophy on anti-rise is horribly misguided. This thing will pack up and brake like a brick over anything rough. Also, the claim about a "three-legged stool" of the wheel is asinine - we don't ride our wheels flat and sideways.
I think there's some good ideas here. With some tweaking for less anti-squat, the rear suspension could offer great aborption over square edge hits, good pedaling characteristics, and low chain growth. That should also lower the anti-rise and make the braking salvageable, but still not on par with a good 4 bar. The rear axle is intriguing. The wheels look cool. But to function well, this badly needs a consulting engineer who truly understands kinematics.
I am wondering what that crazy short swingarm rides like! Despite the 3 points the author brought up on how 'conventional theory' says it wont work, I'm curious if that unusual pivot location might create unusual behavior.
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