After a bit of a hiatus, we're back.
If you'd like to know more about the Behind the Numbers series, aren't familiar with the terms being used, or want to know why we're doing it then check out our Introduction article
for all the information.
Next up in the series is the Santa Cruz Megatower, and our final bike of the enduro category.
But first, let's explain that hiatus.
Among the plethora of suspension designs out there we can somewhat simplify them into two categories: long link designs and short link designs. Long link designs, such as the Specialized Stumpjumper Evo that we’ve previously looked at, have relatively big distances between the pivot points - take the main pivot to Horst pivot as an example.
Bikes like the Santa Cruz Megatower have much shorter distances between the pivots, meaning their links often rotate through larger angles in a shorter space of time. Given that it’s these links that are defining the instant center position a small change in the pivot points can result in a big difference in the suspension curves, far more so than longer link designs.
It’s then up to the designer to balance the pivot point placement along with all the other inputs and requirements and arrive at their desired characteristics. There’s no more or less priority for short or long linked designs, just that a poorly timed sneeze when placing a pivot would have a drastic effect on the bike's character.
Up until the Megatower we had been analyzing relatively long linked bikes, and so our degree of accuracy when taking the measurements was more than enough for those layouts. But for short linked bikes we needed to find a more accurate way to capture the data to ensure this same level of accuracy with these more sensitive layouts.
3D scanning is a method of data collection of real-world parts and objects. The data can then be used to construct digital 3D models for product development, quality control and analyzing bike suspension.
Creaform is a Canadian company that develops and makes portable 3D measuring instruments
, and it is with Creaform that we have partnered to capture the data for the Behind the Numbers series.
Creaform's HandySCAN 3D in action producing the live mesh of the Megatower. And right, the entire scan of the bike once completed.
Using their HandySCAN 3D
handheld scanner they generated a 3D mesh file of the Megatower that is accurate to 0.025mm. That’s an accuracy as small as a human hair, and a good magnitude finer than the manufacturing tolerances achievable in the bike industry. This 3D mesh file is then imported into CAD software to generate the CAD model.
The scan itself is comprised of millions of small triangular surfaces that build up to create the bigger surfaces of the bike. The scan of the bike is pretty data heavy, and for post-processing a decimated version is used to speed up the proceedings, decimation being the process of reducing the number of triangles while still keeping track of the actual geometry of what you’re scanning. From this decimated model the necessary surfaces and points are grabbed, like the pivot points, axles and tubes of the fork and seat post. And from these extracted points we can get the geometry and kinematic of the bike.
It sounds like a lot of effort to get just a 2D sketch of a bike, but it’s remarkably fast and the accuracy is so damn good that we monitor the tolerances of individual parts of the bike. Even the fork and tires have tolerances that mean in the real world they sometimes don’t follow their designed dimensions. The scan itself took a time of about 15 minutes and the whole process went from set up to final 3D model in under an hour.
So, what does this mean for you? Confidence in the series and the information that you can take away. The same can still be said of our previous bikes, but now we’ve just taken a step forward to ensure accuracy and confidence for all bikes and layouts.
A huge thank you to Creaform 3D scanning experts and mountain bike enthusiasts Simon Côté and Louis-Philippe Turgeon, for their willingness to collaborate and their invaluable help and efforts. Also, a thank you to Santa Cruz for being open and up for discussion and for being one of the catalysts in us hunting for higher accuracy. A long distance thank you to Québec local bike shop Mathieu Performance who lent us a bike for the scan. Last but not least, thank you to Bastien and Thibaut at The Factory Bike Shop in Fribourg, Switzerland, for letting me loose on one of their test bikes with a measuring tape.
Let’s get on with the analysis.
Almost all of the Santa Cruz bikes have now moved over to a lower link driven shock layout. Maybe they now focus more on having a progressive and smoother changing leverage ratio? Maybe they like water bottles? Either way, it's a good move.
The construction needed to achieve this layout is decidedly more complex than some of the more traditional double diamond layouts of the other bikes in the enduro category. Complexity in most cases leads to some extra weight. The complexity needs repeatable quality in manufacturing, and if the form of the frame naturally twists, turns and splits then more material is added to ensure that the expanse of edges and corners won’t provide a strength problem. That being said, at least all of the complexity of the bike is low and centered, and the quality of the Santa Cruz frames and attention to detail is impressive.
Santa Cruz Megatower Analysis Details
Travel Rear: 159.5mm to 163.6mm
Travel Front: 160mm
Wheel Size: 29
Frame Size: L
COM Height: 1150mm
Chainring Size: 30T
Cassette Cog Sizes: 50T, 24T and 10T
Added to all this are the adjustability options. A small chip on the lower link and rear axle allow four different bike setup possibilities. Adjustability is good, as long as it's in a useable range, allowing the rider to nip and tuck the bike to their riding needs and terrain demands. The downside of this adjustability is the added curves on the graphs, but stick with it and you'll start to see the characteristic changes that each adjustment option brings. While the changes to geometry that the shock chip adjustment gain might be small (a measured 0.26˚ on the head angle and 3.58mm in BB height) the differences in suspension characteristics are far more pronounced. The 10mm chainstay adjustment has a bigger effect on the geometry, balance, and weight distribution, while also having a noticeable change on the suspension.
Long CST / Low Chip – 31.5% progression with an average ratio of 2.85.
Long CST / High Chip – 27.54% progression with an average ratio of 2.82.
Short CST / Low Chip – 30.57% progression with an average ratio of 2.81.
Short CST / High Chip – 26.78% progression with an average ratio of 2.78.
The Megatower has a good chunk of progression in every setting, with around 31% in the low chip position and around 27% in the high setting. The chip adjustment has more of an effect than the chainstay adjustment.
While not at a truly extreme amount of progression it is a little on the higher side of the fence when compared to a lot of other bikes in this category.
What is high are the average leverage ratios. Lots of bikes at the moment, with metric stroke shocks and 160mm travel, are hovering around a 2.76 average ratio. They’re doing this by using 60mm stroke shocks. The Megatower has a 57.5mm stroke shock as standard, and so the ratios take a jump up. Higher ratios are going to transmit more force into the shock, and so need higher spring rates or air pressure to support them. Higher ratios will also be moving the shock shaft at slower speeds, generating less damping force that would need to be accounted for in the shock tune.
Bikes with more progression and high ratios tend to ride dynamically deeper in the travel, which is why Mike Kazimer in his review
probably preferred the high chip setting to not only raise the BB a smidge, but reduce the amount of overall progression and have the bike dynamically higher in its travel when riding.
The further towards the extremes we go the more the setup compromises rear their head. We witnessed this with the very linear Orange Stage 6 and Specialized Stumpjumper EVO.
For the Megatower the extremeness is not as severe, but there will be a swing to either two scenarios. Setting up with a normal amount of sag would then mean spring rates that would perhaps deprive the bike from using the available travel, whereas setting it up to use the available travel would result in increased sag. This lower sag in combination with the progression could lead to riding with more time spent in a harder sprung and lower leveraged portion of the suspension, potentially coming across as harshness.
In these situations, it could be beneficial to side with less sag; this would cause the bike to ride higher in the travel and in a zone of lighter spring rate and higher leverage.
The leverage ratio curves are quite constant in their change. Only right at the end of travel in the low chip position do we have a bit of a shoulder of increased progression. Depending on shock setup this extra shoulder, coupled with an air spring's natural ramp, could provide a small wall of overall progression at the end to hit.
Suggestions of tricky shock setup from Mike perhaps come from these higher leverage ratios in all settings. The high leverage ratios with high progression define the character of the squish and there are going to be less perceivable ride feel changes when fiddling with the adjusters on the shock, due to this high amount of force going into the shock and its slow movement.
The full range of the Megatower anti-squat.
A zoomed-in look at the anti-squat to show more detail for the lighter gears.Anti-Squat
First off, apologies for the overload of curves, but 4 bike setups and 3 different gear sizes result in a busy graph.
The first anti-squat graph shows the entirety of the range of figures, which is big. The second graph zooms in to +160% / -100% anti-squat to give a bit more detail for the gears more relevant to climbing.
For the easiest gear (30T chainring and 50T cassette) there’s nearly always above 100% anti-squat, so in that gear the bike should do an OK job of combatting the weight transfer. As the gears get harder the amount of anti-squat increases, but so does the exponential shape of the curve, so much so that in the hardest gear the asymptote drops the anti-squat down to just shy of -360%. Luckily, this trend is towards the higher gears and so perhaps further away from the climbing gears. The increased anti-squat at the beginning of travel in these gears could go some way to stabilizing out of the saddle sprinting.
This trend in rapidly decreasing anti-squat is also going to lead to a drop off in the pedal kickback towards the end of travel. The most extreme drop offs come in the low chip position, so running the bike in high could also smooth out the anti-squat while still keeping that flavor of high weight transfer support to end of travel drop in pedal kickback. It does, of course, depend on the riding scenario, component choice and impact speed as to whether the theoretical pedal kickback will actually be felt.
Coupled with the leverage ratio, which would lead to a somewhat active supple feel, this healthy dose of anti-squat is a positive, and as it seems from Mike’s review the bike does indeed pedal well and have the feel of moving forward with pedal power rather than bogging down into the suspension with lackluster anti-squat there to support you.
The familiar VPP style curve resides in the anti-rise graph, too, although at least this time there aren’t 12 curves to try and absorb. The overall range of the anti-rise, however, is much less, going between around 85% and -25%.
The higher figures at the beginning of travel will equate to a degree of squatting to combat weight transfer from braking. As the bike goes further into the travel this effect will diminish, and in the last 20mm the bike will actually extend a touch and slightly accentuate this weight transfer, rather than combat it.
To do this combatting, or accentuating, the suspension system needs to give up something else, and in the case of anti-rise, and the Megatower, it’s perhaps some sensitivity in the suspension at the beginning of travel. Some designers would prefer the opposite and have low transitioning to high figures, giving perhaps more traction in the first portion of travel and increased weight transfer support deeper in the travel, when the riding scenario might be of a higher energy level.
Again, it’s not fully clear if this was intentionally designed in or if it’s a resultant of optimizing other characteristics. But there’s maybe a sneaking suspicion that Santa Cruz focussed on some other suspension factors, like leverage ratio and overall frame layout and packaging, and other characteristics had to follow.
Yes, the scale on the graph is different, but don’t worry, we’ll do a comparison with all the bikes on the same graph so you have a good overview of the whole enduro segment of bikes. Zooming in does allow us to see the details and nuances of the individual bikes.
What we see is that the Megatower does have around 2mm of rearwards axle path. But in reality, this will only be of use when landing from absolute zero travel. As from the sag point onwards (25% shock stroke equates to about 45mm of rear-wheel travel) there is only a forward trajectory on the rear axle.
While this is commonly thought of as bad, it depends on if you’re looking at the compression stroke or rebound stroke. A high pivot bike will, of course, move its axle out of the way with more ease as the axle path is more in line with vector created by the bump. But on the rebound stroke the axle will be travelling straight into, imagine head on, into the next bump. It then has to decelerate, pass zero velocity and accelerate away again.
So, a benefit in one direction can be a deficit in the opposite. A more forwards axle path will require more energy to move out of the way, but will not be firing itself directly back at the next impact.
Like all the factors involved in a bike, there’s a point of balance in there somewhere. It’s a hard job balancing 100 spinning plates on your own, and Santa Cruz has done a good job of taking their older generation layout and improving a lot of characteristics, not just in the suspension department.
One thing we can see is that the high chip position looks to be the more favorable position with slightly more rearward travel up to the sag point and then around 3mm less forwards travel.Final Thoughts Previous Behind the Numbers Articles:GT Force Suspension AnalysisOrange Stage Six Suspension AnalysisMarin Mount Vision Suspension AnalysisSpecialized Stumpjumper EVO Suspension AnalysisIntroducing Behind the Numbers - A New Suspension Analysis Series