Andre Santos analyses full suspension frame designs and describes their true axle path, leverage ratio, anti-squat numbers, anti-rise numbers and so on.

>>> How to set up mountain bike suspension

If you’re a mountain bike suspension geek you may have encountered Andre ‘XTR’ Santos before, probably on YouTube.

Armed with this info he then details how the bike should fundamentally perform on the trail. He also can make recommendations on suspension spec and set-up ie. how much sag to run, what sort of shock to run, volume spacer usage and so on.

Andre doesn’t really ‘review’ the bikes he analyses. He describes how they should theoretically behave on certain terrain or under certain rider inputs. He does all of this without ever seeing the bike in person.

Send him your bike details, €25-40 (depending which bike analysis you want) and then wait for the report to arrive in your inbox.

Whilst we’d be a bit wary of purely assessing a bike on paper, it is useful info that can really help with either drawing up a shortlist of potential bike purchases or for assisting in perfecting a set-up of an existing bike. It’s also good for countering certain assumptions that people have about certain suspension designs.

>>> Discussing mountain bike suspension theory with the experts

Me and my bike

With this latter aspect in mind (perfecting the set-up of an existing bike) I dropped Andre a message to see if he’d be up for analysing my own bike (2016 Vitus Escarpe 29 running a Fox Float X fitted with off-set bushings).

The full text of his report is below but the most significant take-aways for me were: the frame has a very linear leverage ratio and has high anti-squat values at sag point.

So what do I do armed with these nuggets of info?

• Run the biggest volume spacer I can find to help better deal with larger hits and bigger drops.
• Upgrade my rear shock’s air can to one with a larger negative chamber (ie. Fox Evol) to improve off-the-top sensitivity and increase mid-stroke support a bit.
• Run sag nearer to a third than a quarter to better sit at the point where falling rate becomes linear/progression.
• Don’t fear the rear brake.
• Treat the bike as trail bike and don’t be tempted to try and make it a burly enduro bike.

All in all, I’m happy with that and would feel it had been money well spent if I’d paid for the service.

What does Andre offer and why?

Andre explains: “Since I started making suspension and kinematics videos on YouTube, I started to receive requests from riders, bike manufacturers and also from bike shops. Thus I created the site to make it official. The services provided can include: bike analyses, online training for bike shops and consultation services.”

www.andrextr.com

Bike analyses: “The kinematics can differ a lot from bike to bike, and before buying an expensive bike it’s important to check if it will match with your riding style and trail preferences. For instance, a linear bike might not be the best option for an aggressive rider, and conversely a very progressive one might not be the best for a less aggressive trail rider or for smooth tracks. Also, there are bikes that are more, or less, optimized for pedaling. You might want to play with modifications, like air/coil shocks, offset bushings, different shock strokes, etc, so these analyses can also be adjusted to help you on that.”

Online training for shops: “This is mostly suited for bike shops and service centers employees. I have done full-day classroom trainings in the past to some companies, where the objective is to learn about the basics of kinematics and suspension theory / shock settings. This can be accompanied with analysis of bikes you sell. Trained employees can impress customers and bring value by offering better and informed guidance to them.”

Consulting services: “I can offer R&D consultancy services about suspension design and kinematics optimization for bike manufacturers, or I can make video analysis for promotional proposes. I also have done this in the past.”

Vitus Escarpe 29 VR

The full report

Vitus Escarpe 29 VR (2016)

• 135mm wheel travel
• 190x51mm shock

Escarpe 29 VR (2016) uses a Horst-link 4-bar linkage with the lower shock mount on the chainstay. The average leverage ratio is 2.6, with a falling rate curve until the SAG point, followed by a slightly progressive (almost linear) curve until the end of travel.

Progressivity analysis

Taking in consideration the magnitude and shape of leverage ratio curve the total progressivity of the Escarpe linkage is only 2%, meaning that it only takes 2% more force to bottom-out when comparing to a fully linear bike (eg: Orange Stage) with a similar shock and SAG. In other words, Vitus Escarpe is as linear as you can get.

Analyzing the leverage curve in more detail, we can observe that the leverage increases until the SAG point, this is called a falling rate. Usually a falling rate makes the initial travel stiffer, while in the other hand a progressive rate makes the initial travel softer. However, since the falling rate in the Vitus Escarpe only happens until the SAG point, the final effect is very small. So, comparing to a fully linear bike (eg: Orange Stage) equipped with the same shock and SAG, the Escarpe is about 5% stiffer in the initial part of travel, which is negligible for most riders out there. To increase initial suppleness I would suggest an air shock with big negative air chamber (eg: EVOL, Debonair). After the SAG point, Escarpe has an almost linear rate, contributing to the overall linearity of the suspension. Given the linearity of Vitus Escarpe, it is relatively easy to use all available travel with medium-size impacts and obstacles, and thus, Vitus Escarpe is most suitable for less aggressive trail riders or easy / flow tracks. For aggressive riders, or for more aggressive trails, it would be quite easy to get some harsh bottom-outs on jumps and drops. Of course you can partially solve this by adding air spacers / tokens to the main air chamber of the shock but still it would be relatively easy to bottom-out on harsh impacts. So, in my opinion, Vitus Escarpe is a more trail-oriented bike than enduro-oriented one.

Pedaling efficiency

In simple words, anti-squat is an intrinsic property of the linkage that counteracts the pedal-induced bob and determines the pedaling efficiency. Every time that shock compresses and extends due to pedaling (pedal bob) it means that your energy is being dissipated and wasted by the suspension and not to propel you forward. Vitus Escarpe has good pedaling efficiency given its relatively high Anti-Squat values. At 30% SAG point and for a 32T crankset the anti-squats reach 105%, 120%, and 160% for a 42T, 24T and 10T rear cog, respectively. Since the anti-squat curves start at very high values and decrease rapidly across the travel, this makes the initial part of the travel relatively stiffer under pedaling counteracting even more the pedal induced bob. The relatively high initial anti-squats will inevitably cause some pedal kickback which should be noticeable mostly on rocky and technical climbs, but in my opinion this is not a major issue at all.

Braking

The braking forces of rear wheel can slightly affect the suspension. This is called “anti-rise”. The higher the anti-rise the more the braking affects the suspension, but the less the bike will pitch forward under rear wheel braking. The Vitus Escarpe has an anti-rise of only 30%, which is a very low value compared to most bikes in the market. This is due to the configuration of the rocker pivots which result in a forward virtual instant center of rotation in front on front wheel axle. So, Vitus Escarpe should have a quite active suspension under braking, however it will slightly pitch forward when you apply the rear brake (you can easily test this on a parking lot, after applying the rear brake the rear shock will slightly extend).

Effect of offset bushings

By adding a pair of 2mm offset bushing on both shock eyelets (pointing inwards), you decrease eye-to-eye length by 4mm from 190mm to 186mm (the shock stroke is maintained at 51mm). This means that with these offset bushings the suspension travel will start now on what was the previous 10mm original wheel travel point. So, you basically skip the first 10mm of wheel travel. Since the offset bushings do not affect the amount of travel, the maximum wheel travel (135mm) will shift 10mm after the original maximum travel. In some bikes too much offset in bushings can cause clearance issues with the rear triangle hitting the main frame.

By adding 2 x 2mm offset bushings on Escarpe 29, you decrease the BB height by 6mm, and you decrease HA by 0.5°. The effect of offset bushings on geometry will depend a lot on the initial leverage rate. On bikes with high initial rates, like SantaCruz V10, which starts with a leverage rate of 4, a 4mm of total offset would cause a 16mm wheel travel skipping, and thus, a 10mm BB drop and a HA reduction of 0.8°.

Regarding kinematics, these bushings won’t affect the progressivity of Escarpe (because the leverage ratio remains constant at the end of travel). However, in bikes with a sharply decreasing or increasing final leverage rate the bushings could affect significantly the progressivity. Since anti-squats decrease across the travel, the bushings will decrease the average anti-squats by ~5% comparing to the original shock (unnoticeable effect).

CONCLUSION – Vitus Escarpe 29

Overall, Vitus Escarpe 29 has a linear suspension curve and it has a suspension linkage very neutral to braking forces and optimized for pedaling efficiency.