Race track set up - great suspension discussion by the masters

[warp9.9]

All this bike talk makes me hungry!!!

 

[Speedy]

This video I linked, watch his videos when you have some free time. He knows more about racing suspensions that still work well on the street than anyone I'm aware of. He learned the trade working on motorcycle suspension and applied his knowledge to cars. Fatcat suspension is equiped on nearly every SCCA champion car these days, many of which are street driven with the exact same setup. I've ridden in one, and I thought it was the stock suspension because it is so comfortable. There is nothing special about motorcycle suspension theory vs cars.

I'd suggest viewing, in particular, his discussion about Konis (which will apply to Ikons). They're far from bad, but also far from optimized (so are Wilbers).

Starting effort on all these nitrogen gas shocks is going to be too high. Fatcat may be willing to do a one off set of motorcycle shocks, I haven't inquired as the Wilbers are fine for me and I don't want/need a plush ride.

65/130 spring rates aren't all that high to be honest for a Rocket 3. Only slightly higher than the Progressive 444s, what will make them feel stiff is the gas pressure being (too) high.

If you're after drag specific shocks, contact Penske. Skip all others, go directly to Penske (with a big budget). For the right money they'll build a custom setup.

The brilliance of them is only realized in certain scenarios, on seriously bad roads where most suspension will bottom out, the Wilbers will not and cornering where they don't collapse under cornering forces. It's a compromise for sure and one not for everyone.

When you get to the point where you're riding beyond the spring rates established for your weight, and have to start springing for speed instead of weight, the Wilbers are perfection in motion. Weight use to determine spring rates is only ever a starting point for suspension design.

The separate nitrogen chamber in monotube shocks is a gas spring. It is necessary to accommodate the rod's displaced volume. The weight it takes to depress the rod is spring pre-load. Take a coil spring and put preload into it and it will act the same. It will not deflect until the load is greater than the amount of preload. The amount of dampening force is NOT changed regardless of the gas pressure, but the effective spring rate is. A gas spring is progressive unlike a constant rate spring so the rate of increase is not linear.

A major problem of gas charged shocks is that they are extremely heat sensitive, (think ideal gas law relationship between temp, volume and pressure) compared to low pressure twin tube designs, so the pressure always builds as the shock is used. Secondly, the gas pressure must always be higher than the maximum compression dampening (pressure). If it is not, the oil below the piston on the moving rod will compress the gas charge. When and if this happens, the rebound side of the shock cavitates (negative pressure explosion resulting in foam) resulting in a loss of rebound dampening on the return stroke. If you want more compression dampening, you have to deal with more spring rate.

I don't disagree with the idea of ride harmony, but the gent in the video's explanations of the physics and theory behind suspension dynamics leave much to be desired. Perhaps intentionally so.

Jacking down is very real and is a huge problem when it happens. Take that BMW drag bike in the other link down a rough road and you will quickly learn what the term means.

Very few "suspension experts" delve into the effects of geometry on how shocks and springs work. How much anti-roll? How much anti-dive? How much anti-squat? Of these; how much impact when? Roll center calculations are good tools but they are called "instant centers" for a reason: they are only at the calculated point for an instant during actual use. Where are they the rest of the time? Where and how far they go can be more important than where they started. How does rim offset impact anti-roll? Does anti-roll change with steering angle? Which part of a vehicle actually moves: the wheels, the chassis, both? Why does it matter? What is the actual weight of a vehicle at rest and then at 150mph? Clue: they are the same but inertia at 150mph adds a new dynamic. Inertia acts upon the chassis differently than static weight and both are different than aero down force. How does an anti-roll bar actually work? What happens to the roll center when it is twisted? The Fat Cat video is, to put it gently, not quite right. Okay, not even close.

Also, beware of shock dyno readouts: they can be very misleading if you don't know how to interpret what you see. How accurate is the dyno? How constant is the pre-set speed? Can it really instantaneously change directions and not change velocity doing so? Does the software "clip out" those data points that are not at the pre-set velocity? Does it emulate real shock travel frequencies and velocities found on real surfaces at real speeds? The actual offsets needed to cancel gas pressure effects on the total "load" are not as simple as adding one uniform value. What is the spring and damping rate of the tire of choice? How can you get them when those values are not published?

Ever see an entire coil-over unit tested on a dyno and the forces documented? How about a performance tire running at speed on a glass drum photo'd from underneath with high speed equipment while loading and slip angle changes are made? Ever hear one of the suspension gurus telling you to remove several inches from your contact patch to roll center width calculations at 1g lateral acceleration because of carcass deflection? Bet not.

One of the reasons active suspension systems are slow to be developed is that almost all the old assumptions about vehicle suspension dynamics were inaccurate and based on the limitations of spring and shock systems and not as much on the limitations of actual geometries. Suspension geometries that were assumed necessary aren't if you can control wheel positions and travel speeds accurately. Is anti-squat really necessary if you can go from static ride height to lifting the rear wheel, stopping it and then accelerating it back to static height fast enough to traverse a bump at 60mph under full throttle without changing the vehicle height or roll angle? Are roll angles beneficial?

Motorcycle suspension dynamics are not special but they are different from four wheel vehicles (and the three wheelers are in a world of their own.) The greatest difference is that as a bike is leaned over, the lean angle is not in-line with road irregularities so at 45 degree lean the wheel moves 1.4" to traverse a 1 inch high bump (given that the lean angle and CG remain constant.) It doesn't of course because the fork or the swing arm or the chassis, or a combination thereof, twists some and the suspension travels some. So cycles are much more sensitive to frame and suspension torsional strength variations than a four wheeled vehicle. In this respect they are similar to un-sprung racing karts where the frame is engineered to be the suspension. The center of gravity in a cycle moves along with the rider where as in a car, the CG moves very little.

Disclaimer: I am not an expert, but I do know a little about the subject and have some experience to make it real.

 

[Claviger]

Excellent post my friend. He does, as you suggest, dumb down a lot of his videos to make them easier to consume. He's posted some very technical ones however, that show exactly what you mention regarding different Dyno rates, loads, etc between some top Brand shocks vs his modified billsteins and explains how the charts impact actual vehicle Dynamics.

Having ridden in one of the 2017 SCCA national champion cars equipped with his top level product vs 25 years toying with performance suspensions of all kinds, I will say his billsteins hands down out perform (comfort and control) every setup I've experienced. That includes some custom spec, triple adjustable Konis, Tein's race their products, Ohlins, etc.

As an idea of the difference for others interested, an otherwise BONE stock ND Miata with his suspension out paced a NISMO 370Z, C7, C6, an unlimited class NC Miata turbo, 2017 Porsche Cayman S, same track same day etc etc. Most were on the same RE-71 tire, most were very experienced.

I'll have to link you one of his worksheets he does for customers, quite in depth with measurements, dimensions, and forces.

I only link his stuff because it's a great starting point to learn the how's/why's of suspension for layman IMHO.

The second video I linked to demonstrate for others just how different a dedicated drag suspension is to a street suspension, and why I wouldn't trust a historically street and road racing specialist company to build a drag suspension.

All that said I do not see dedicated drag suspension as a good cost/performance value when the same cash can net you more ET reduction by adding power. For a little over the cost of 642 nightlines you can make 200whp+.

 

[Kevin frazier]

In

The separate nitrogen chamber in monotube shocks is a gas spring. It is necessary to accommodate the rod's displaced volume. The weight it takes to depress the rod is spring pre-load. Take a coil spring and put preload into it and it will act the same. It will not deflect until the load is greater than the amount of preload. The amount of dampening force is NOT changed regardless of the gas pressure, but the effective spring rate is. A gas spring is progressive unlike a constant rate spring so the rate of increase is not linear.

A major problem of gas charged shocks is that they are extremely heat sensitive, (think ideal gas law relationship between temp, volume and pressure) compared to low pressure twin tube designs, so the pressure always builds as the shock is used. Secondly, the gas pressure must always be higher than the maximum compression dampening (pressure). If it is not, the oil below the piston on the moving rod will compress the gas charge. When and if this happens, the rebound side of the shock cavitates (negative pressure explosion resulting in foam) resulting in a loss of rebound dampening on the return stroke. If you want more compression dampening, you have to deal with more spring rate.

I don't disagree with the idea of ride harmony, but the gent in the video's explanations of the physics and theory behind suspension dynamics leave much to be desired. Perhaps intentionally so.

Jacking down is very real and is a huge problem when it happens. Take that BMW drag bike in the other link down a rough road and you will quickly learn what the term means.

Very few "suspension experts" delve into the effects of geometry on how shocks and springs work. How much anti-roll? How much anti-dive? How much anti-squat? Of these; how much impact when? Roll center calculations are good tools but they are called "instant centers" for a reason: they are only at the calculated point for an instant during actual use. Where are they the rest of the time? Where and how far they go can be more important than where they started. How does rim offset impact anti-roll? Does anti-roll change with steering angle? Which part of a vehicle actually moves: the wheels, the chassis, both? Why does it matter? What is the actual weight of a vehicle at rest and then at 150mph? Clue: they are the same but inertia at 150mph adds a new dynamic. Inertia acts upon the chassis differently than static weight and both are different than aero down force. How does an anti-roll bar actually work? What happens to the roll center when it is twisted? The Fat Cat video is, to put it gently, not quite right. Okay, not even close.

Also, beware of shock dyno readouts: they can be very misleading if you don't know how to interpret what you see. How accurate is the dyno? How constant is the pre-set speed? Can it really instantaneously change directions and not change velocity doing so? Does the software "clip out" those data points that are not at the pre-set velocity? Does it emulate real shock travel frequencies and velocities found on real surfaces at real speeds? The actual offsets needed to cancel gas pressure effects on the total "load" are not as simple as adding one uniform value. What is the spring and damping rate of the tire of choice? How can you get them when those values are not published?

Ever see an entire coil-over unit tested on a dyno and the forces documented? How about a performance tire running at speed on a glass drum photo'd from underneath with high speed equipment while loading and slip angle changes are made? Ever here one of the suspension gurus telling you to remove several inches from your contact patch to roll center width calculations at 1g lateral acceleration because of carcass deflection? Bet not.

One of the reasons active suspension systems are slow to be developed is that almost all the old assumptions about vehicle suspension dynamics were inaccurate and based on the limitations of spring and shock systems and not as much on the limitations of actual geometries. Suspension geometries that were assumed necessary aren't if you can control wheel positions and travel speeds accurately. Is anti-squat really necessary if you can go from static ride height to lifting the rear wheel, stopping it and then accelerating it back to static height fast enough to traverse a bump at 60mph under full throttle without changing the vehicle height or roll angle? Are roll angles beneficial?

Motorcycle suspension dynamics are not special but they are different that four wheel vehicles (and the three wheelers are in a world of their own.) The greatest difference is that as a bike is leaned over, the lean angle is not in-line with road irregularities so at 45 degree lean the wheel moves 1.4" to traverse a 1 inch high bump (given that the lean angle and CG remain constant.) It doesn't of course because the fork or the swing arm or the chassis, or a combination thereof, twists some and the suspension travels some. So cycles are much more sensitive to frame and suspension torsional strength variations than a four wheeled vehicle. In this respect they are similar to un-sprung racing karts where the frame is engineered to be the suspension. The center of gravity in a cycle moves along with the rider where as in a car, the CG moves very little.

Disclaimer: I am not an expert, but I do know a little about the subject and have some experience to make it real.

is there anyone else that goes wow I can’t believe I have access to some of the greatest minds in the world post knowledge on our beloved bikes, I feel like they’re should be a place to insert card, (mind blowing knowledge) free, crazy, I’d put our great minds up against any forum on the net #solucky, I’m just amazed daily, and I save 1000s at the shop and 1000s on unneeded parts and pieces, thanks speedy and the rest of the brain trust that gives so freely

 

[barbagris]

If you don't want springs on your bike then you better go with air shocks too.

You've not ridden with proper Air Shocks at a guess. I run on Fournales rears.

 

[barbagris]

I am a LONG way from wishing to pursue a learning curve that will get me even close to Messrs @Claviger and @Speedy . I do love reading their interpretations on technical stuff though. There was a time -------------------

I was a bit flummoxed at some of the replies - until I realised that you referred to STRAIGHT tracks - rather than the lovely curvy ones we associate with the same word over here.

I do have a wee bit of info to impart however: having ridden shaft drive bikes most of my riding life.

Do not underestimate the torque effect on the bevel box which usually exhibits a climbing effect and most certainly do not underestimate the often massive increase in rear un-sprung weight.

ime of 40 years riding OLD Guzzis - just about no "off the shelf" hydraulics will cope "well" with the mass once it starts to move. Compression or Rebound.

I have NO IDEA if it is really the case - But I inferred from stuff I read ages ago that Fournales not only have infinitely variable spring rates - but the damping also varies dynamically as a product of internal pressures. I'd suggest however they are NOT suitable for Drag-Tracks.

Frankly as long as the guy designing the shocks/forks has a decent knowledge base - they'll be close - the rest is down to fiddling about until it suits the rider on the day.

I'm lucky - these guys are just down the road from me. DMX SUSPENSION|Especialistas en Suspensiones.Fabricación,Reparación y preparación|. For their off road customers they have a test track.

 

[barbagris]

Motorcycle suspension dynamics are not special but they are different that four wheel vehicles (and the three wheelers are in a world of their own.) The greatest difference is that as a bike is leaned over, the lean angle is not in-line with road irregularities so at 45 degree lean the wheel moves 1.4" to traverse a 1 inch high bump (given that the lean angle and CG remain constant.) It doesn't of course because the fork or the swing arm or the chassis, or a combination thereof, twists some and the suspension travels some. So cycles are much more sensitive to frame and suspension torsional strength variations than a four wheeled vehicle.

This is a major issue on many Highways intersections here - Whether it's ground settlement post surfacing or a simple lack of interest. Not bumps but dips - the effect is almost akin to a change in lean angle. Can be "exciting"

 

[Speedy]

@Claviger I don't doubt that his set-ups work well. "Ride Harmony," if I understand his idea, is that the entire system must act in concert. No one piece can be changed without an impact elsewhere. Additionally, suspensions need be no stiffer than needed to manage the loads imposed. If wheel travel has to be severely limited for a car to respond well, the loads are extreme (think Formula One) or the suspension geometry is not up to the task (think C7 with its severe anti-squat.)

Part of my rant was that poorly communicated ideas are worse than saying nothing. They leave the listener or reader with doubt or misunderstanding. Of course they must then go to the "guru" who is more than happy to sort out their problem, for a fee of course. This may not be the intent of the linked videos but the man did a lot of talking and posturing without saying much. And some of his explanations were poor at best and misleading at the worst. Sort of what I expect from a pitchman.

It is not possible to communicate detailed technical information about a dynamic system to a neophyte in 25 minutes, so the performances are aimed at more than teaching. If the intent is to teach, then start with basics communicated accurately. The pyramid of knowledge must be broadest at the base.

@barbagris Chain drive cycles experience torque induced squat, the opposite effect. The need to control chain tension imposes geometries where it is inherent to some degree. Shaft drives give designers more freedom in swing arm length but as they make them shorter the anti-squat, or jacking up, effect gets worse. However, put the front shaft joint ahead of the CG and the jacking induces squat.

Our Rockets have fairly severe jacking. The normal 1/2" or so of set in makes it hard to feel during straight line acceleration but it is obvious when the suspension is loaded as Claviger noted in his missive several weeks ago about his experience riding a stock R3. If the bike wallows mid-corner, just get on the throttle and the torque lifts the chassis to full suspension extension. No more wallow (but don't pass over dip in the road or you will have a pucker moment as the suspension can't extend further and inertia limits the chassis from following the road surface so the tire unloads and grip disappears just when you need it most.)

Both squat and anti-squat are throttle controlled where as suspension spring support of imposed loads is not. Thus each has its own challenges and both type of systems are compromises of handling, ride quality, and rider perception.

 

[Kevin frazier]

@Claviger I don't doubt that his set-ups work well. "Ride Harmony," if I understand his idea, is that the entire system must act in concert. No one piece can be changed without an impact elsewhere. Additionally, suspensions need be no stiffer than needed to manage the loads imposed. If wheel travel has to be severely limited for a car to respond well, the loads are extreme (think Formula One) or the suspension geometry is not up to the task (think C7 with its severe anti-squat.)

Part of my rant was that poorly communicated ideas are worse than saying nothing. They leave the listener or reader with doubt or misunderstanding. Of course they must then go to the "guru" who is more than happy to sort out their problem, for a fee of course. This may not be the intent of the linked videos but the man did a lot of talking and posturing without saying much. And some of his explanations were poor at best and misleading at the worst. Sort of what I expect from a pitchman.

It is not possible to communicate detailed technical information about a dynamic system to a neophyte in 25 minutes, so the performances are aimed at more than teaching. If the intent is to teach, then start with basics communicated accurately. The pyramid of knowledge must be broadest at the base.

@barbagris Chain drive cycles experience torque induced squat, the opposite effect. The need to control chain tension imposes geometries where it is inherent to some degree. Shaft drives give designers more freedom in swing arm length but as they make them shorter the anti-squat, or jacking up, effect gets worse. However, put the front shaft joint ahead of the CG and the jacking induces squat.

Our Rockets have fairly severe jacking. The normal 1/2" or so of set in makes it hard to feel during straight line acceleration but it is obvious when the suspension is loaded as Claviger noted in his missive several weeks ago about his experience riding a stock R3. If the bike wallows mid-corner, just get on the throttle and the torque lifts the chassis to full suspension extension. No more wallow (but don't pass over dip in the road or you will have a pucker moment as the suspension can't extend further and inertia limits the chassis from following the road surface so the tire unloads and grip disappears just when you need it most.)

Both squat and anti-squat are throttle controlled where as suspension spring support of imposed loads is not. Thus each has its own challenges and both type of systems are compromises of handling, ride quality, and rider perception.

Speedy is there hope for a Neanderthal to catch on?

 

[Kevin frazier]

@Claviger I don't doubt that his set-ups work well. "Ride Harmony," if I understand his idea, is that the entire system must act in concert. No one piece can be changed without an impact elsewhere. Additionally, suspensions need be no stiffer than needed to manage the loads imposed. If wheel travel has to be severely limited for a car to respond well, the loads are extreme (think Formula One) or the suspension geometry is not up to the task (think C7 with its severe anti-squat.)

Part of my rant was that poorly communicated ideas are worse than saying nothing. They leave the listener or reader with doubt or misunderstanding. Of course they must then go to the "guru" who is more than happy to sort out their problem, for a fee of course. This may not be the intent of the linked videos but the man did a lot of talking and posturing without saying much. And some of his explanations were poor at best and misleading at the worst. Sort of what I expect from a pitchman.

It is not possible to communicate detailed technical information about a dynamic system to a neophyte in 25 minutes, so the performances are aimed at more than teaching. If the intent is to teach, then start with basics communicated accurately. The pyramid of knowledge must be broadest at the base.

@barbagris Chain drive cycles experience torque induced squat, the opposite effect. The need to control chain tension imposes geometries where it is inherent to some degree. Shaft drives give designers more freedom in swing arm length but as they make them shorter the anti-squat, or jacking up, effect gets worse. However, put the front shaft joint ahead of the CG and the jacking induces squat.

Our Rockets have fairly severe jacking. The normal 1/2" or so of set in makes it hard to feel during straight line acceleration but it is obvious when the suspension is loaded as Claviger noted in his missive several weeks ago about his experience riding a stock R3. If the bike wallows mid-corner, just get on the throttle and the torque lifts the chassis to full suspension extension. No more wallow (but don't pass over dip in the road or you will have a pucker moment as the suspension can't extend further and inertia limits the chassis from following the road surface so the tire unloads and grip disappears just when you need it most.)

Both squat and anti-squat are throttle controlled where as suspension spring support of imposed loads is not. Thus each has its own challenges and both type of systems are compromises of handling, ride quality, and rider perception.

Mid corner wallow twist it, I like that