Motion Control Single adjustables installed
09-17-2015, 03:15 PM
#141
<p></p><p> </p><p>You've basically just completely validated his argument and his point: The Miata is cheaper, and has great bang for the buck, but carping about a bit of minor hysteresis on a car of this caliber is a little silly. It's not a GT3 cup car, it's a Miata.</p>
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09-17-2015, 05:40 PM
#143
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i was mostly responding to the "shitty" references. But, for the sake of argument, if my miata is as fast or faster than a track prepped Porsche... and a Porsche racer feels that its an advantage to install a Penske or JRZ shock,... and the t-miata can generally outperform the Porsche, then why wouldnt I also consider a high end shock race shock for my miata? I think that if AR racing can get thier MC shocks in the ballpark, then i could fine tune them and be really happy.
als
als
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09-17-2015, 06:17 PM
#144
I was just reading Grassroots motorsports and they pitted a NC with Penske shocks against a ND Miata with twin tube shocks and the ND pretty much beat the NC in every handling category. I'd be a bit pissed if I was the owner of the NC who dumped 5K into Penske shocks.
Shock can't really fix a compromise street suspension.
Shock can't really fix a compromise street suspension.
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09-18-2015, 09:46 AM
#146
I was just reading Grassroots motorsports and they pitted a NC with Penske shocks against a ND Miata with twin tube shocks and the ND pretty much beat the NC in every handling category. I'd be a bit pissed if I was the owner of the NC who dumped 5K into Penske shocks.
Shock can't really fix a compromise street suspension.
Shock can't really fix a compromise street suspension.
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09-18-2015, 10:58 AM
#149
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That being said, this chassis is going to get used for non spec racing series as well (continential challenge, pwc etc)... and the suspension setup will be part of that package i'm sure. So performance has to be up there in terms of a consideration. Those series pit the miata against the cayman s.
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09-18-2015, 11:00 AM
#150
Just playing devil's advocate here..
Given that they are supposedly benchmarking two dampers against each other I'm sure that along with price, mfg support and durability their conclusion will likely also take into consideration some measure of performance. Otherwise, with that reasoning, they would just use an OTS Bilstein, no?
Great reading in here. In to learn more about valving and stoked to drive on my MCS 1wnr again next week. Hell yeah!
Given that they are supposedly benchmarking two dampers against each other I'm sure that along with price, mfg support and durability their conclusion will likely also take into consideration some measure of performance. Otherwise, with that reasoning, they would just use an OTS Bilstein, no?
Great reading in here. In to learn more about valving and stoked to drive on my MCS 1wnr again next week. Hell yeah!
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09-18-2015, 11:46 AM
#151
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<p>Just playing devil's advocate here...</p><p>If all you are taking into consideration is price, availability, why not just use showas?</p>
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09-18-2015, 02:02 PM
#155
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I don't think HVT makes an offering for the ND yet, and NASA American Iron just switched from HVT to MCS, listing performance and rumblings about HVT going out of business as some of the reasons. A lot of the guys were not happy with the HVTs at all.
And back to the whole spec thing, just because it is a spec series doesn't mean the shocks need to be terrible. Look at Spec E46, MCS 1 ways as the spec shock, bigger dollar spec series get better shocks, this isn't your typical spec Miata series, ND spec series will be $$$
And back to the whole spec thing, just because it is a spec series doesn't mean the shocks need to be terrible. Look at Spec E46, MCS 1 ways as the spec shock, bigger dollar spec series get better shocks, this isn't your typical spec Miata series, ND spec series will be $$$
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09-18-2015, 04:00 PM
#157
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Emilio, any comment on my previous question about why you run a relatively large sway bar in your big grip kit? I am genuinely curious as to your logic there.
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09-18-2015, 05:55 PM
#158
WRT to hysteresis, I'll reply Monday. Been busy this week and it's just not high on my to do list.
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09-22-2015, 11:37 PM
#159
Hysteresis and you
Re: smack talk
The narrative in this thread seems to be “why xida hysteresis?” We are able to run very high wheel rates (stiff springs) and roll stiffness with Xidas yet maintain compliance over any surface. Outstanding ride quality, grip and predictability. How? Digressive valving and optimized damper length are key ingredients.
Damper length
Years ago, when we first began the search for a pro level OTS coilover (that did not yet exist), we already knew that bump /droop travel at the rear of the NA/NB platform was critical to grip levels over kerbing and your typical less than glassy smooth club race track or autocross course. We came up with what was the maximum possible bump travel with the damper tech available from AST at the time. It was too little droop travel however. So we investigated a new main piston, separation piston and cylinder design to give us those precious extra mm of droop travel. The resultant lower half design became standard across the AST line when space was at a premium. Our 5100 was the first with the new design and it was pushed forward because I’m stubborn when it comes to these suspension things.
Fast forward a few years where we transferred the dimensions and basic dyno plot across to the Tractive made Xida we now offer. We were able to maintain the bump/droop range while gaining adjustment range, adding useful digression and increasing damper service life with the larger 46mm piston.
Shocking words
First off, a quick primer on damper terminology. When discussing dampers (shocks), “high speed” and “low speed” will usually refer to damper shaft speed, not vehicle road speed. Damper shaft and road speed are completely unrelated for purposes of this discussion. Every damper, regardless of usage, vehicle type or tuning, has a range of damping force (resistance) from near zero shaft speed to very high shaft speeds . The art and science of making high performance dampers is consistently getting the forces you want at each shaft speed and shaft position within the packaging and cost constraints of the application.
Low speed in damper speak is 0-4 in/sec (0-.1m/s) shaft speed. This is basically driver induced pitch (squat/dive) and roll.
High speed is 4-12 in/sec (.1-.3m/s) is road induced damper movements. From coarse pavement to big sharp hits. These are generalizations and have exceptions but are widely accepted tuning principles.
All dampers have measurable hysteresis.
Nitrogen volume and pressure
An N2 (nitrogen) charged monotube damper is filled with oil for the valving, heat dissipation and lubrication. The N2 chamber is opposite the end the shafts pokes out of, on the other side of a floating Separation Piston. The primary job of the N2 pressure is to maintain pressure on the oil and eliminate the formation of air bubbles which really mess up damper performance. When the damper is compressed, internal N2 pressure increases. The smaller the N2 chamber, the greater the increase in N2 pressure rise. The greater the N2 pressure delta between fully bump/droop, the greater the chance of hysteresis increase.
By reducing the length of the rear Xida body for the NA/NB to get our desired bump/droop ratio, we were accepting a steeper nitrogen pressure ramp at full compression. Xidas are filled to about 15 bar (217psi) of N2 The rears will increase to as high as 25 bar (362psi) at full bump. This increase in pressure effectively changes the compression damping towards full bump the same way a remote reservoir does. A longer, higher volume body (front NA/NB Xida) still increases nitrogen pressure from 15 to about 17bar. A damper filled with only say, 6 bar will have a lot less hysteresis potential. MCS appear to be 12 bar (175psi).
Digressive Valving
Any damper with a distinct “nose” or steep increase in damping force at very low piston speeds builds internal pressure much more quickly than a damper with a smaller increase “nose” and far more than a damper with no nose whatsoever like the damper mentioned elsewhere in this thread. Straight forward tradeoff, improved nose shape for some hysteresis. Decreasing low speed rebound damping in particular reduces responsiveness to driver inputs and allows what I call overshoot. That’s where a driver input allows the car to pitch (dive/squat) or roll beyond the point where it would otherwise settle to in steady state. At this point, the one thing the suspension needs then is greater low speed damping to control the rebound, precisely the one thing it’s lacking and the cause for the condition in the first place. It wallows a bit, or oscillates quickly, depending on bounce frequency (spring rate). Without changing the damping, the fix for lack of enough low speed damping is to simply drive the car smoother. This is what you experience every time you try to whip a stock street tuned suspension into a turn too quickly for the damper to control. The issue is that a standard linear valving with a useful nose will often continue to increase damping to a level far beyond what is needed in a Miata with such relatively high sprung to unspring mass ratio and low wheel rates. IOW, you always want strong low speed rebound in a performance application, provided you can bleed off enough for high speed impacts and small undulations. This is where digressive valving comes in. A digressive valved damper costs more to build than a linear rate so you don’t see them much at the OEM level until you get into some pretty expensive cars. For offroad use, linear valving tends to work well because grip is low. You are actually trying not to plant the tire quickly but let it float a bit. Motocross, rally and desert racing vehicles tend to use position sensitive damping instead of digressive. That’s a whole different animal but the point is that digressive valving is largely a high performance cars on pavement technology.
Vacuum filling
Minor detail but Xidas are vacuum filled with oil. This eliminates any air in the oil. Since air is very compressible, it reduces the N2 pressure increase at full bump which in turn reduces hysteresis. Air in the damper oil is bad thing though as it reduces damping precision, responsiveness to small shaft movements and leads to early damper fluid degradation. So one by product of the fancy vaccum filling is a tiny increase in the potential for hysteresis. Again, an intentional engineering tradeoff for the greater benefits of uncontaminated oil.
Engineering choices based on testing validation
Much like the way a lowered Miata has really messed up roll centers but somehow manages to go over bumps, steer, grip, stop and put down power faster than one that sits 2” higher, the Xidas manage to excel in their intended environment despite the intentional hysteresis difference front to rear. The new ND Xida has no such space constraints so we ended with up huge bump/droop range and no hysteresis anywhere. Big tubes, lotsa N2.
In a perfect world, every high performance damper has virtually no hysteresis. In the real world however, there are a host of design constraints that work against this goal. Every remote reservoir damper in existence has greater hysteresis on the compression side that it’s non-remote version. The fluid moving back and forth through the hoses is responsible for this. The longer the hoses, the worse it gets. I’m guessing no one here has ever looked but our doubles/triples have always had two hose length options. The shorter hose makes locating the reservoirs more of a PITA but measurably reduce hysteresis. I ran the shortest hoses I could on my car. The doubles still ended up being a bit more versatile than the singles despite the additional hysteresis.
While some might question the Xida plots in comparison to the other brand, the proof of concept is how they actually work. Our Xida has become the gold standard for OTS NA/NB coilovers and the product that many compare other OTS coilover options to first. Beyond the countless positive reviews there continues a steady flow of national championships, race wins and track records for the Xidas. We are happy with our design and engineering choices and we’re not the only ones.
The narrative in this thread seems to be “why xida hysteresis?” We are able to run very high wheel rates (stiff springs) and roll stiffness with Xidas yet maintain compliance over any surface. Outstanding ride quality, grip and predictability. How? Digressive valving and optimized damper length are key ingredients.
Damper length
Years ago, when we first began the search for a pro level OTS coilover (that did not yet exist), we already knew that bump /droop travel at the rear of the NA/NB platform was critical to grip levels over kerbing and your typical less than glassy smooth club race track or autocross course. We came up with what was the maximum possible bump travel with the damper tech available from AST at the time. It was too little droop travel however. So we investigated a new main piston, separation piston and cylinder design to give us those precious extra mm of droop travel. The resultant lower half design became standard across the AST line when space was at a premium. Our 5100 was the first with the new design and it was pushed forward because I’m stubborn when it comes to these suspension things.
Fast forward a few years where we transferred the dimensions and basic dyno plot across to the Tractive made Xida we now offer. We were able to maintain the bump/droop range while gaining adjustment range, adding useful digression and increasing damper service life with the larger 46mm piston.
Shocking words
First off, a quick primer on damper terminology. When discussing dampers (shocks), “high speed” and “low speed” will usually refer to damper shaft speed, not vehicle road speed. Damper shaft and road speed are completely unrelated for purposes of this discussion. Every damper, regardless of usage, vehicle type or tuning, has a range of damping force (resistance) from near zero shaft speed to very high shaft speeds . The art and science of making high performance dampers is consistently getting the forces you want at each shaft speed and shaft position within the packaging and cost constraints of the application.
Low speed in damper speak is 0-4 in/sec (0-.1m/s) shaft speed. This is basically driver induced pitch (squat/dive) and roll.
High speed is 4-12 in/sec (.1-.3m/s) is road induced damper movements. From coarse pavement to big sharp hits. These are generalizations and have exceptions but are widely accepted tuning principles.
All dampers have measurable hysteresis.
Nitrogen volume and pressure
An N2 (nitrogen) charged monotube damper is filled with oil for the valving, heat dissipation and lubrication. The N2 chamber is opposite the end the shafts pokes out of, on the other side of a floating Separation Piston. The primary job of the N2 pressure is to maintain pressure on the oil and eliminate the formation of air bubbles which really mess up damper performance. When the damper is compressed, internal N2 pressure increases. The smaller the N2 chamber, the greater the increase in N2 pressure rise. The greater the N2 pressure delta between fully bump/droop, the greater the chance of hysteresis increase.
By reducing the length of the rear Xida body for the NA/NB to get our desired bump/droop ratio, we were accepting a steeper nitrogen pressure ramp at full compression. Xidas are filled to about 15 bar (217psi) of N2 The rears will increase to as high as 25 bar (362psi) at full bump. This increase in pressure effectively changes the compression damping towards full bump the same way a remote reservoir does. A longer, higher volume body (front NA/NB Xida) still increases nitrogen pressure from 15 to about 17bar. A damper filled with only say, 6 bar will have a lot less hysteresis potential. MCS appear to be 12 bar (175psi).
Digressive Valving
Any damper with a distinct “nose” or steep increase in damping force at very low piston speeds builds internal pressure much more quickly than a damper with a smaller increase “nose” and far more than a damper with no nose whatsoever like the damper mentioned elsewhere in this thread. Straight forward tradeoff, improved nose shape for some hysteresis. Decreasing low speed rebound damping in particular reduces responsiveness to driver inputs and allows what I call overshoot. That’s where a driver input allows the car to pitch (dive/squat) or roll beyond the point where it would otherwise settle to in steady state. At this point, the one thing the suspension needs then is greater low speed damping to control the rebound, precisely the one thing it’s lacking and the cause for the condition in the first place. It wallows a bit, or oscillates quickly, depending on bounce frequency (spring rate). Without changing the damping, the fix for lack of enough low speed damping is to simply drive the car smoother. This is what you experience every time you try to whip a stock street tuned suspension into a turn too quickly for the damper to control. The issue is that a standard linear valving with a useful nose will often continue to increase damping to a level far beyond what is needed in a Miata with such relatively high sprung to unspring mass ratio and low wheel rates. IOW, you always want strong low speed rebound in a performance application, provided you can bleed off enough for high speed impacts and small undulations. This is where digressive valving comes in. A digressive valved damper costs more to build than a linear rate so you don’t see them much at the OEM level until you get into some pretty expensive cars. For offroad use, linear valving tends to work well because grip is low. You are actually trying not to plant the tire quickly but let it float a bit. Motocross, rally and desert racing vehicles tend to use position sensitive damping instead of digressive. That’s a whole different animal but the point is that digressive valving is largely a high performance cars on pavement technology.
Vacuum filling
Minor detail but Xidas are vacuum filled with oil. This eliminates any air in the oil. Since air is very compressible, it reduces the N2 pressure increase at full bump which in turn reduces hysteresis. Air in the damper oil is bad thing though as it reduces damping precision, responsiveness to small shaft movements and leads to early damper fluid degradation. So one by product of the fancy vaccum filling is a tiny increase in the potential for hysteresis. Again, an intentional engineering tradeoff for the greater benefits of uncontaminated oil.
Engineering choices based on testing validation
Much like the way a lowered Miata has really messed up roll centers but somehow manages to go over bumps, steer, grip, stop and put down power faster than one that sits 2” higher, the Xidas manage to excel in their intended environment despite the intentional hysteresis difference front to rear. The new ND Xida has no such space constraints so we ended with up huge bump/droop range and no hysteresis anywhere. Big tubes, lotsa N2.
In a perfect world, every high performance damper has virtually no hysteresis. In the real world however, there are a host of design constraints that work against this goal. Every remote reservoir damper in existence has greater hysteresis on the compression side that it’s non-remote version. The fluid moving back and forth through the hoses is responsible for this. The longer the hoses, the worse it gets. I’m guessing no one here has ever looked but our doubles/triples have always had two hose length options. The shorter hose makes locating the reservoirs more of a PITA but measurably reduce hysteresis. I ran the shortest hoses I could on my car. The doubles still ended up being a bit more versatile than the singles despite the additional hysteresis.
While some might question the Xida plots in comparison to the other brand, the proof of concept is how they actually work. Our Xida has become the gold standard for OTS NA/NB coilovers and the product that many compare other OTS coilover options to first. Beyond the countless positive reviews there continues a steady flow of national championships, race wins and track records for the Xidas. We are happy with our design and engineering choices and we’re not the only ones.
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