Autocross Spring Rate

[joelidge]

SMF 1990 CRX w/ B16

I just picked up a set of Whitener Racing shocks and wondering about spring rates. There doesn't seem to be very much info on SMF 4th Gen / CRX cars and the STS guys seems to be in two camps: Stiff rear vs. natural frequency. I was speaking with an STS national champ on Sunday who has been in the stiff rear camp for 20 years and is now trying out a natural frequency setup. I understand why the stiff rear is wanted but it really isn't my driving style, it requires making the car function on razor thin margins and I don't believe it is untimely the fastest for SMF given the additional horsepower potential negating the need to 100% commit to a momentum setup.

I am currently running 450 front 550 rear and the car is doing OK on Progress coilovers with BFG Rivals 15x245 front and 15x225 rear (I do not recommend Rivals unless you have a codriver). Those shocks are too soft in both compression and rebound but really not a bad set of shocks for the street. I am running a stock DX front bar and a 22mm ST rear bar. The car is good when I am perfect but is incredibly unforgiving when I make mistake; the window between fast and out of control is extremely small.

I have a set of 600 and 500 springs I am going to start with in the same configuration as before with the rear sprung heavier. With three events left, I plan to run them for a two events that way before swapping them around to 600 Front and 500 Rear. I can use the old springs on the rear but not the front as they are too long. My thought was to move to a setup with 600 LF, 550 RF, 500 LR and 450 RR or some aspect of that; maybe a touch softer in the rear. I tried figuring out the natural frequency but I will need to spend some time to pull the suspension and measuring everything but based on my guess that seems about right. It may be a job for the winter to measure the suspension and calculate all of values.

Anyway, what are any of you running and why?

[raffaelli]

What did Whitener recommend?

[joelidge]

He said 500 / 600 was a good starting point being that I am on 450 / 550 now but I would have to put some time into testing to really iron it out. He didn't really have a specific answer but did offer his advice as to the setup in the future.

Another SMF CRX I run against runs 500 / 600 but he is on stiff rear the lock the rear wheels out theory. The other 2 STS civics are also locked into this thinking. Gerry in his STS civic is the only one who is breaking from this and at least exploring the natural frequency setup. That is the way I am leaning and I really don't want to start two foot driving so I can make the car dance the way I need it to to make the stiff rear setup work.

[daveb91]

When I ran my CRX and Type R both had stiff rear setup and disconnected front sway. GC on koni yellows 450/600 amoung some other rates...i was on Hoosier a6 and r6 don't know if they are still around have since ventured into the rwd field..

[jwharnish]

He said 500 / 600 was a good starting point being that I am on 450 / 550 now but I would have to put some time into testing to really iron it out. He didn't really have a specific answer but did offer his advice as to the setup in the future.

Another SMF CRX I run against runs 500 / 600 but he is on stiff rear the lock the rear wheels out theory. The other 2 STS civics are also locked into this thinking. Gerry in his STS civic is the only one who is breaking from this and at least exploring the natural frequency setup. That is the way I am leaning and I really don't want to start two foot driving so I can make the car dance the way I need it to to make the stiff rear setup work.

I'd go with what Whitener suggested. He has done more testing than anyone I know, and I've been doing this for quite some time.
I do think with the b16 motor and more tire up front than the STS cars use, you may need to go with a higher front spring weight, to compensate for the heavier motor, and the wider tire can handle a quicker load with the heavier rate, maybe 600/650, or a staggered setup you suggested to fine tune everything.
What is "Natural Frequency Setup"? I have been doing this as long as Gerry has, and never heard this term before.
As far as the stiff rear setup, that has been the standard setup for a long time. Front drivers need to induce some oversteer to help with the push that is found in FWD cars. You can always use toe, camber, spring rate, tire pressure to get the amount of oversteer you are comfortable with. Or dial it out completely using the same adjustments.
BFG Rival's were OK when they first came out, but the latest Rival S 1.5 are much better, Hoosier's much better, and will respond better to the above changes with a higher confidence level. Many SMF Crx guys do well with the 205 on the rear, if you use a great tire. A lot of combinations are used, you just have to find one that gives you the greatest confidence level.

Good Luck

[AttackCRX]

I've been talking to Chris at RedShift and he suggested running a 550/650 with the BC coilovers.

Lot of good info on here!
https://store.redshiftmotorsports.com/category-s/137.htm

[joelidge]

Thanks. I have run 2 events now with 500 front and 600 rear. I set the alignment back to what I had prior as to not change to many things at once. Thus far this seems to be pretty good. It seems I have increased lat Gs by about a 10th in both peek and steady state and the car is much more forgiving leading me to believe I am not pushing it hard enough. I haven't even spun once with the new setup I need a few more events to gather enough data to see where I need to go from here but sadly there is only one event left this season. I will be adding big aero this winter so no idea how that is going to change the balance. I still want to try out stiffer front springs but likely wont be until April or May when I have a baseline for the current setup feels like with all the off season changes.

As for natural frequency, it isn't so much a "setup" as a method to derive a setup starting point. To determine the NF, you take your corner weights and spring motion ratio and calculate the spring rate based on the frequency you wish to achieve; generally 2.2hz to 2.4hz for a race setup. This works out to a stiffer spring where there is more weight. It doesn't really factor in swaybars as they don't contribute that much but when you use a Hollis bar with very little flex, the swaybar does impact the steady state setup a bit. In our case, the front would be stiffer than the rear for an NF type setup like Andy outlines in his setup notes.

For me, when I put on the staggered tires, I had to decrease the stiffness of the rear bar. This made a noticeable difference in slaloms and sweepers as the car is less prone to oversteer and the speed in both increased significantly; the same distance slalom was 5mph faster with the wider tires. I expected the tight stuff to be impacted but the front still has plenty of grip and I can get the rear to rotate in a controlled manor when needed. However, even with the reduced stiffness of the rear bar, I was struggling with was snap oversteer. This has significantly been reduced with the Whitener shocks and stiffer springs. The car can still get loose but it give a little driver feedback when you get close to the edge.

As for tires, I am running Rival 1.5S. I will get a second set of wheels this winter and likely mount another set of Rivals to have as backups. Once I burn off my current set I will think about Hoosiers but it depends on the local SMF competition. I would rather have someone to compete against than win every event by 4 seconds simply due to tires. One guy is going to Federal FZ-201S 205/50R15 which is a 40TW tire. I don't know how this is going to compare to the wider Rivals so it should be a fun start to the season. Regardless, putting stickier tires on doesn't fix the driver errors and can cover them up so I will probably be sticking to Rivals for most if not all of next season unless I make it out to a national event.

As for the Redshift page, its a really good overview to get a good start in the right direction and is pretty close to what I have already done and my setup.

Locally, none of us in SMF are particularly fast and although we don't have fully preped cars, much of that is the driver. Looking at the data, based on my segment times, I am leaving a quarter to half a second at most events. Looking at others data I can generally find the same or more I left on course. A buddy had a phenom STS driver codrive his CRX in August and he was 4 seconds faster which was on par with the fastest STS cars; that data was enlightening and really helped me improve. I have slowly been closing the gap and I am now about a second behind the top STS guys.

My logical brain just wants to get the car to a confidence inducing state where I can continue to learn and get seat time. I think where the car is presently should good enough to allow for that. However, it is in my DNA to tinker on things; I can't help myself.

[jwharnish]

Thanks. I have run 2 events now with 500 front and 600 rear. I set the alignment back to what I had prior as to not change to many things at once. Thus far this seems to be pretty good. It seems I have increased lat Gs by about a 10th in both peek and steady state and the car is much more forgiving leading me to believe I am not pushing it hard enough. I haven't even spun once with the new setup I need a few more events to gather enough data to see where I need to go from here but sadly there is only one event left this season. I will be adding big aero this winter so no idea how that is going to change the balance. I still want to try out stiffer front springs but likely wont be until April or May when I have a baseline for the current setup feels like with all the off season changes.

As for natural frequency, it isn't so much a "setup" as a method to derive a setup starting point. To determine the NF, you take your corner weights and spring motion ratio and calculate the spring rate based on the frequency you wish to achieve; generally 2.2hz to 2.4hz for a race setup. This works out to a stiffer spring where there is more weight. It doesn't really factor in swaybars as they don't contribute that much but when you use a Hollis bar with very little flex, the swaybar does impact the steady state setup a bit. In our case, the front would be stiffer than the rear for an NF type setup like Andy outlines in his setup notes.

"Thanks for explaining "NF" Sounds too complicated for an "old school" guy, but I understand what you are saying. I understand the more spring for more weight approach, but there are limits on what the tire can support as far as load applied to it. That's why spring weight are adjusted to achieve a load that will not overload the tire to quickly. Sway bars come into play here as well, and a reason many STS CRX's run without front bar, plus you achieve the stiffness you want with a spring change. And no front bar will allow a non LSD car to have more suspension travel to allow inside wheel to maintain contact longer in a sweeper.
I also understand Andy's approach with regards to rear stiffness. I bought his STC car. Andy also had to consider his co-driver, who did not like a car that oversteers much. So he kept his STC car more neutral than others did. Worked well for him."

For me, when I put on the staggered tires, I had to decrease the stiffness of the rear bar. This made a noticeable difference in slaloms and sweepers as the car is less prone to oversteer and the speed in both increased significantly; the same distance slalom was 5mph faster with the wider tires. I expected the tight stuff to be impacted but the front still has plenty of grip and I can get the rear to rotate in a controlled manor when needed. However, even with the reduced stiffness of the rear bar, I was struggling with was snap oversteer. This has significantly been reduced with the Whitener shocks and stiffer springs. The car can still get loose but it give a little driver feedback when you get close to the edge.

"Snap oversteer can be the result of too high rear pressure, and a tire not up to temp. Some will run a higher rear pressure to induce oversteer, which will work, but can produce a snap oversteer. Oversteer can also be produced from lower rear pressures, usually without a snap oversteer. Again a condition from loading up a tire too quickly."

As for tires, I am running Rival 1.5S. I will get a second set of wheels this winter and likely mount another set of Rivals to have as backups. Once I burn off my current set I will think about Hoosiers but it depends on the local SMF competition. I would rather have someone to compete against than win every event by 4 seconds simply due to tires. One guy is going to Federal FZ-201S 205/50R15 which is a 40TW tire. I don't know how this is going to compare to the wider Rivals so it should be a fun start to the season. Regardless, putting stickier tires on doesn't fix the driver errors and can cover them up so I will probably be sticking to Rivals for most if not all of next season unless I make it out to a national event.

"Use a tire that works for your level of competition, and wallet. Hoosier are the best but are pricey. "

As for the Redshift page, its a really good overview to get a good start in the right direction and is pretty close to what I have already done and my setup.

Locally, none of us in SMF are particularly fast and although we don't have fully preped cars, much of that is the driver. Looking at the data, based on my segment times, I am leaving a quarter to half a second at most events. Looking at others data I can generally find the same or more I left on course. A buddy had a phenom STS driver codrive his CRX in August and he was 4 seconds faster which was on par with the fastest STS cars; that data was enlightening and really helped me improve. I have slowly been closing the gap and I am now about a second behind the top STS guys.

My logical brain just wants to get the car to a confidence inducing state where I can continue to learn and get seat time. I think where the car is presently should good enough to allow for that. However, it is in my DNA to tinker on things; I can't help myself.

"Looks like you are on the correct path, keep at it until you find a combination that works for you."