Öhlins TTX GP Shock: Make Haste Slowly

Ohlins TTX GP shock studio

Öhlins TTX GP shock is becoming commonplace in the MotoAmerica paddock. New-style compression and rebound adjusters can be rotated by hand or with a hex tool.

One day at Öhlins R&D, someone walked in waving a thumb drive, saying, “I have here a lap of Mugello as suspension damper movement taken from race-bike data acquisition.”

Soon the drive’s snout was poked into one of the inputs on a shock dyno with a rear suspension unit in position. Nothing much happened. The damper hardly moved.

“Is it running? Is there power?”

Everything was working. The fascinating fact is that dampers on road racers don’t move all that much.

Histograms made from race-bike data show that 70 percent of the time damper velocity is under 5mm per second and not much higher than that 80 percent of the time. At the front, the fork compresses at the beginning of braking, but all the work that goes into balancing the complex squat/anti-squat forces at the rear has intentionally resulted in very little movement there.

Suspension does compress and extend as a bike enters and leaves corners, but the rate is gradual (if the suspension compresses one inch (25mm) in one second as the bike rolls over, at the damper, the rate is between one-third and half of that, or 8-12mm per second). There are bumps and rough pavement, but riders often choose a “line of minimum disturbance” in preference to a geometrically ideal line.

These truths being established, what did they imply about how damper performance could be improved? At very low velocities, the washer stacks are not involved, just the low-speed orifices that are adjusted by the clickers.

Some light was thrown on this back in 1992 when Grand Prix racer Luca Cadalora put some miles on a prototype Öhlins “CES” computer-controlled damper. He complained that much of the time the bike felt “dead.” This was because, in the absence of sufficient disturbance, the damper locked up. This showed how important the feeling of connected suppleness that can come from good low-speed damping is to riders.

Ohlins TTX GP internal

New adjustment needle is said to provide more precise damping. Arch-shaped orifice becomes smaller as the clicker draws inner tube into the sleeve.

Conventional tapered-needle-in-an-orifice low-speed damping is not linear; a click at one end of the range makes a much bigger difference than one click at the other end. The new “GP” adjuster on the latest TTX damper consists of a tube, capped at the end, closely fitting into a sleeve, and moved inward or outward by the clicker. There is an angled cut in the inner tube, forming an arch-shaped orifice, which becomes smaller as the clicker draws the tube (some are calling it a “blade”) into the sleeve.

Another feature of the new TTX GP damper is a new solid damper piston and piston seal. In former times, piston seals have been either split metal, plastic piston rings, or some kind of elastomer seal in a groove (O-ring, X-ring, etc.).

The problem with a piston ring is that to expand and seal against the cylinder it must be free in its groove. When the piston changes direction in its bore, that groove clearance results in a short undamped motion—a “clunk”—which at the axle is multiplied times the leverage ratio (leverage ratio is the ratio of axle movement to damper movement).

One manufacturer back in the 1980s actually used the piston rings of its front dampers as one-way valves, resulting in a lot of clunky undamped motion that you could easily feel. An elastomer seal in a groove deforms under pressure, giving a similar short undamped motion as the seal is driven to the low-pressure side of the groove.

Some riders feel undamped motion as loss of tire grip, just as they can feel the sideways “take up” of soft-sidewall tires entering a corner as a loss of grip. It unsettles them. These are the reasons why a modern damper-piston seal fills its groove completely and is not split. Because it can neither move nor compress, it is instantly able to seal in either direction, with zero lost motion.

Veteran Öhlins technician Jon Cornwell views the suspension as a “filter,” which delivers the information the rider needs to know about what the tires are doing. Riders can go quite fast on a wide range of suspension settings, but near the limit, small things become important. In this region there is no right or wrong, just information that the rider either can or cannot use.

If Dani Pedrosa or Valentino Rossi rejects a certain technology, it’s not because the technology isn’t good. It’s because he can’t read its signals as well as he can those of another system. Mick Doohan wanted to feel that his bars were extensions of the front axle, directly connected to the tire, but Cadalora needed to feel large-scale movements of the suspension to gauge what his tires were doing.

Think of a rider on the track as being like a person enjoying an exciting book, alone in a dark house. Everything is calm until there’s a noise. What’s that? Is someone there? This is what happens when a rider gets an unexpected message from the suspension. The rider can no longer focus completely on riding because the message could mean many things, some of them threatening.

This is why Cornwell has for years said, “What we do here is not engineering. It’s building rider confidence.”

Ohlins TTX GP shock studio

Öhlins TTX GP shock is becoming commonplace in the MotoAmerica paddock. New-style compression and rebound adjusters can be rotated by hand or with a hex tool.

One day at Öhlins R&D, someone walked in waving a thumb drive, saying, “I have here a lap of Mugello as suspension damper movement taken from race-bike data acquisition.”

Soon the drive’s snout was poked into one of the inputs on a shock dyno with a rear suspension unit in position. Nothing much happened. The damper hardly moved.

“Is it running? Is there power?”

Everything was working. The fascinating fact is that dampers on road racers don’t move all that much.

Histograms made from race-bike data show that 70 percent of the time damper velocity is under 5mm per second and not much higher than that 80 percent of the time. At the front, the fork compresses at the beginning of braking, but all the work that goes into balancing the complex squat/anti-squat forces at the rear has intentionally resulted in very little movement there.

Suspension does compress and extend as a bike enters and leaves corners, but the rate is gradual (if the suspension compresses one inch (25mm) in one second as the bike rolls over, at the damper, the rate is between one-third and half of that, or 8-12mm per second). There are bumps and rough pavement, but riders often choose a “line of minimum disturbance” in preference to a geometrically ideal line.

These truths being established, what did they imply about how damper performance could be improved? At very low velocities, the washer stacks are not involved, just the low-speed orifices that are adjusted by the clickers.

Some light was thrown on this back in 1992 when Grand Prix racer Luca Cadalora put some miles on a prototype Öhlins “CES” computer-controlled damper. He complained that much of the time the bike felt “dead.” This was because, in the absence of sufficient disturbance, the damper locked up. This showed how important the feeling of connected suppleness that can come from good low-speed damping is to riders.

Ohlins TTX GP internal

New adjustment needle is said to provide more precise damping. Arch-shaped orifice becomes smaller as the clicker draws inner tube into the sleeve.

Conventional tapered-needle-in-an-orifice low-speed damping is not linear; a click at one end of the range makes a much bigger difference than one click at the other end. The new “GP” adjuster on the latest TTX damper consists of a tube, capped at the end, closely fitting into a sleeve, and moved inward or outward by the clicker. There is an angled cut in the inner tube, forming an arch-shaped orifice, which becomes smaller as the clicker draws the tube (some are calling it a “blade”) into the sleeve.

Another feature of the new TTX GP damper is a new solid damper piston and piston seal. In former times, piston seals have been either split metal, plastic piston rings, or some kind of elastomer seal in a groove (O-ring, X-ring, etc.).

The problem with a piston ring is that to expand and seal against the cylinder it must be free in its groove. When the piston changes direction in its bore, that groove clearance results in a short undamped motion—a “clunk”—which at the axle is multiplied times the leverage ratio (leverage ratio is the ratio of axle movement to damper movement).

One manufacturer back in the 1980s actually used the piston rings of its front dampers as one-way valves, resulting in a lot of clunky undamped motion that you could easily feel. An elastomer seal in a groove deforms under pressure, giving a similar short undamped motion as the seal is driven to the low-pressure side of the groove.

Some riders feel undamped motion as loss of tire grip, just as they can feel the sideways “take up” of soft-sidewall tires entering a corner as a loss of grip. It unsettles them. These are the reasons why a modern damper-piston seal fills its groove completely and is not split. Because it can neither move nor compress, it is instantly able to seal in either direction, with zero lost motion.

Veteran Öhlins technician Jon Cornwell views the suspension as a “filter,” which delivers the information the rider needs to know about what the tires are doing. Riders can go quite fast on a wide range of suspension settings, but near the limit, small things become important. In this region there is no right or wrong, just information that the rider either can or cannot use.

If Dani Pedrosa or Valentino Rossi rejects a certain technology, it’s not because the technology isn’t good. It’s because he can’t read its signals as well as he can those of another system. Mick Doohan wanted to feel that his bars were extensions of the front axle, directly connected to the tire, but Cadalora needed to feel large-scale movements of the suspension to gauge what his tires were doing.

Think of a rider on the track as being like a person enjoying an exciting book, alone in a dark house. Everything is calm until there’s a noise. What’s that? Is someone there? This is what happens when a rider gets an unexpected message from the suspension. The rider can no longer focus completely on riding because the message could mean many things, some of them threatening.

This is why Cornwell has for years said, “What we do here is not engineering. It’s building rider confidence.”