square spring rates vs "traditional" stagger
May 6, 2014 | 07:31 PM
#1
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From: Big city, Bright lights
square spring rates vs "traditional" stagger
been meaning to try and spark a discussion on this for a while. i feel like lately i have seen more and more guys running square spring rates, but i havent been able to fully convince myself that i understand what characteristics this would have, or exactly how to go about setting it up.
currently im on ohlins 8k/10k with, whiteline f/r bars (rear set full soft), RCK, 255 rs3's/z2's. at times i feel as though the front still rolls quite a bit and it is leading to some high tire temps/sliding the front end (over powering the tire?). a spring rate change may not even be the answer for me...but id still like to discuss.
what would be the advantage/disadvantage/other required changes of going 10k/10k, 11k/11k maybe even 11k/10k?
are a lot of guys going back to a stock rear bar when getting up into the 11k range?
currently im on ohlins 8k/10k with, whiteline f/r bars (rear set full soft), RCK, 255 rs3's/z2's. at times i feel as though the front still rolls quite a bit and it is leading to some high tire temps/sliding the front end (over powering the tire?). a spring rate change may not even be the answer for me...but id still like to discuss.
what would be the advantage/disadvantage/other required changes of going 10k/10k, 11k/11k maybe even 11k/10k?
are a lot of guys going back to a stock rear bar when getting up into the 11k range?
May 6, 2014 | 08:17 PM
#2
My understanding is, lessen the rear rate & increase understeer
Currently 10k/12k w/my 24mm rear bar set at the middle hole setting (still is understeer prone)
Currently 10k/12k w/my 24mm rear bar set at the middle hole setting (still is understeer prone)
Last edited by MinusPrevious; May 6, 2014 at 08:20 PM.
May 6, 2014 | 09:01 PM
#3
When it comes down to it, you really need to know your weight distribution. Go to a truck scale and weigh the front then rear. At that point you need to know a little about your un-sprung weight (or assume around 100lbs-120lbs). Then the math is a quick calculation for know what to run for spring balance if you go a couple 1/10ths higher rear N.F.
Maybe a stock car works out with more rear spring, but since most weight reduction comes easily out of the rear of the car, the rear rates will eventually come down.
I think Ive said all I really want to say on defending square, or at least not significantly higher in the rear, in other threads. Gotta get on that math to check it cause one Evo =/= every evo.
Maybe a stock car works out with more rear spring, but since most weight reduction comes easily out of the rear of the car, the rear rates will eventually come down.
I think Ive said all I really want to say on defending square, or at least not significantly higher in the rear, in other threads. Gotta get on that math to check it cause one Evo =/= every evo.
May 6, 2014 | 09:10 PM
#4
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From: Big city, Bright lights
Dallas - I've seen some of your comments on the subject, and that's what has had me trying to figure it out for quite awhile. I'm a very scientific/analytical person so I want to be able to understand before I do anything. No need to defend the theory I'm on your side based on what I've been seeing lately.
My car is still relatively stock weight so I get why the current rates "work". Have any articles you could share? I know some people are reluctant to discuss ecaxt setup specs
My car is still relatively stock weight so I get why the current rates "work". Have any articles you could share? I know some people are reluctant to discuss ecaxt setup specs
May 6, 2014 | 09:52 PM
#5
A good place to start would be here for weights if you are close to stock weight.
http://www.vorshlag.com/tech_evoweights.php
You could go through the weight reduction threads to approximate the weight at each end if you cant get to a set of scales.
If you havent read this stuff, Its a great place to start. Not really the end all be all gospel on the subject but you could do a lot worse than following this guide.
http://farnorthracing.com/autocross_secrets5.html
I would say this gets you close but all cars are different and some further digging is definitely needed.
http://www.vorshlag.com/tech_evoweights.php
You could go through the weight reduction threads to approximate the weight at each end if you cant get to a set of scales.
If you havent read this stuff, Its a great place to start. Not really the end all be all gospel on the subject but you could do a lot worse than following this guide.
http://farnorthracing.com/autocross_secrets5.html
I would say this gets you close but all cars are different and some further digging is definitely needed.
May 6, 2014 | 10:39 PM
#6
Very important... the front suspension and rear suspension have spring placement in different places resulting in different wheel rates. What this means is if you compression the front wheel an inch, the spring compresses very close to an inch as well. If you compress the rear wheel an inch, the rear spring only compresses aprox. .6 inches.
This is a big reason why people put bigger rates in the rear (even if they don't know that's why they do it). To have equal rates front and rear, you need to know the exact wheel rates and then use that as a multiplier on the spring rates.
Generally this isn't advised due to large difference in weight distribution.
Long story short... math.
Regarding roll, let's say your going around a right turn, that puts a lot of stress on the front driver's side tire. You can add rear spring rate (and/or to a lesser degree increase roll bar) and this will actually help plant the passenger front tire... everything acts as a seesaw. You can also add front bar/spring rate to reduce roll, but more rate generally will also reduce grip (this is very dependent though).
The better solution is geometry in my opinion. When an Evo is lowered too much, the front control arms don't work as designed. Two issues happen. First is a decrease in roll center height (see here http://www.motoiq.com/MagazineArticl...ll-Center.aspx ). The farther the roll center from actual center of gravity, the greater the lever arm/torque arm, the easier it is for the car to roll in turns. Next, instead of increasing camber in the turns, the control arms are now pointing in such a way that decreases camber when rolling, which can stress the outside of your tire, causing it to overheat. If you fix the geometry, you can run less spring/bar, have more grip, less roll, less heat in the tires.
Dan
This is a big reason why people put bigger rates in the rear (even if they don't know that's why they do it). To have equal rates front and rear, you need to know the exact wheel rates and then use that as a multiplier on the spring rates.
Generally this isn't advised due to large difference in weight distribution.
Long story short... math.
Regarding roll, let's say your going around a right turn, that puts a lot of stress on the front driver's side tire. You can add rear spring rate (and/or to a lesser degree increase roll bar) and this will actually help plant the passenger front tire... everything acts as a seesaw. You can also add front bar/spring rate to reduce roll, but more rate generally will also reduce grip (this is very dependent though).
The better solution is geometry in my opinion. When an Evo is lowered too much, the front control arms don't work as designed. Two issues happen. First is a decrease in roll center height (see here http://www.motoiq.com/MagazineArticl...ll-Center.aspx ). The farther the roll center from actual center of gravity, the greater the lever arm/torque arm, the easier it is for the car to roll in turns. Next, instead of increasing camber in the turns, the control arms are now pointing in such a way that decreases camber when rolling, which can stress the outside of your tire, causing it to overheat. If you fix the geometry, you can run less spring/bar, have more grip, less roll, less heat in the tires.
Dan
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May 7, 2014 | 07:37 AM
#8
Very important... the front suspension and rear suspension have spring placement in different places resulting in different wheel rates. What this means is if you compression the front wheel an inch, the spring compresses very close to an inch as well. If you compress the rear wheel an inch, the rear spring only compresses aprox. .6 inches.
This is a big reason why people put bigger rates in the rear (even if they don't know that's why they do it). To have equal rates front and rear, you need to know the exact wheel rates and then use that as a multiplier on the spring rates.
Generally this isn't advised due to large difference in weight distribution.
Long story short... math.
Regarding roll, let's say your going around a right turn, that puts a lot of stress on the front driver's side tire. You can add rear spring rate (and/or to a lesser degree increase roll bar) and this will actually help plant the passenger front tire... everything acts as a seesaw. You can also add front bar/spring rate to reduce roll, but more rate generally will also reduce grip (this is very dependent though).
The better solution is geometry in my opinion. When an Evo is lowered too much, the front control arms don't work as designed. Two issues happen. First is a decrease in roll center height (see here http://www.motoiq.com/MagazineArticl...ll-Center.aspx ). The farther the roll center from actual center of gravity, the greater the lever arm/torque arm, the easier it is for the car to roll in turns. Next, instead of increasing camber in the turns, the control arms are now pointing in such a way that decreases camber when rolling, which can stress the outside of your tire, causing it to overheat. If you fix the geometry, you can run less spring/bar, have more grip, less roll, less heat in the tires.
Dan
This is a big reason why people put bigger rates in the rear (even if they don't know that's why they do it). To have equal rates front and rear, you need to know the exact wheel rates and then use that as a multiplier on the spring rates.
Generally this isn't advised due to large difference in weight distribution.
Long story short... math.
Regarding roll, let's say your going around a right turn, that puts a lot of stress on the front driver's side tire. You can add rear spring rate (and/or to a lesser degree increase roll bar) and this will actually help plant the passenger front tire... everything acts as a seesaw. You can also add front bar/spring rate to reduce roll, but more rate generally will also reduce grip (this is very dependent though).
The better solution is geometry in my opinion. When an Evo is lowered too much, the front control arms don't work as designed. Two issues happen. First is a decrease in roll center height (see here http://www.motoiq.com/MagazineArticl...ll-Center.aspx ). The farther the roll center from actual center of gravity, the greater the lever arm/torque arm, the easier it is for the car to roll in turns. Next, instead of increasing camber in the turns, the control arms are now pointing in such a way that decreases camber when rolling, which can stress the outside of your tire, causing it to overheat. If you fix the geometry, you can run less spring/bar, have more grip, less roll, less heat in the tires.
Dan
OP, as Dan@ProfessionalAwesome said, and I'm sure you know, it is because of the motion ratios that we increase the rear spring rate, to get it up to match. Andy@GTWorx should be able to chime in with this and should know more or less spot on what it is.
I don't think it has too much to do with weight, a lot of the SMF cars I've seen with almost no weight in the rear are running higher rear rates as well.
Also OP, you may want to consider upping your spring rates. 8/10k is what I have for my Ohlins as well, and I think it is too soft for racing, ESPECIALLY if you are on rcomps (dont know if you are or not). Your notice of increase square rates may have something to do with the Evo Xs? They run square spring rates, but I think that is because they're just a little heavier (Ohlins for them are "tradiationally" 10k/10k)
May 7, 2014 | 08:59 AM
#9
Do the math based on your cars weight. Evos have roughly 0.96 front and 0.73 rear motion ratio.
Square them and you get 0.92 and 0.53. Big difference right? Well look at the weight distribution of an Evo, mine for instance is 1980 front and 1100 rear (or was I should say). An interesting number to look at for each is the percentage of the sum of each. The ratios are pretty dang close between both weight dist and motion ratios.
To just say rear needs more because motion ratio is like saying I heard this one time some said this one thing so it must be true but I wasn't there and don't really know... VAGUE!
Square them and you get 0.92 and 0.53. Big difference right? Well look at the weight distribution of an Evo, mine for instance is 1980 front and 1100 rear (or was I should say). An interesting number to look at for each is the percentage of the sum of each. The ratios are pretty dang close between both weight dist and motion ratios.
To just say rear needs more because motion ratio is like saying I heard this one time some said this one thing so it must be true but I wasn't there and don't really know... VAGUE!
May 7, 2014 | 03:27 PM
#10
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From: Big city, Bright lights
front motion ratio=.96-.98 (.966)
rear motion ratio=.796 (.8)
i think in the thought process in my head there is a disconnect between the sway bars and the spring rates for some reason...probably some small detail i keep forgetting about that would complete the thought process.
right now i like the way the rear of the car works, it always grips and is predictable, so lets discuss fronts. i thought the general rule of thumb was more spring = more understeer but obviously its probably not that dead simple.
i gues i really need to get down and just do the math...i would suspect it will make me understand everything. i just thought maybe there were some generalizations that could be used to explain good/bad of the setup.
May 7, 2014 | 04:35 PM
#11
The big thing to wrap you head around is this, Don't worry about what the rear is doing. Since the front is the problem child, do what ever you need to get the grip up front since rear grip is overly abundant.
You are right that the swaybars have an important effect. Here is my thoughts and how I work the roll rates, Use more rear roll rate overall, but also a higher % contribution from swaybars in the rear. My numbers in a previous thread on swaybars were off. Stock an Evo runs about 1.35/1.55hz with 50% of overall roll stiffness coming from sway bars up front and 60% rear. Going with more bar just hikes up the tire even more.
My simplistic method, around 2.5-3hz front with 0.2hz more rear, ~35-40% roll coming from bar front and 40-50% in the rear. I don't like more spring because bumpy courses really seem to upset the car way too much, though others seem to love it. If I were to run larger rear rates, or something like the formerly common 12k/16k I would have 0.6hz stiffer rear. That is a huge difference and way too much IMO.
You are right that the swaybars have an important effect. Here is my thoughts and how I work the roll rates, Use more rear roll rate overall, but also a higher % contribution from swaybars in the rear. My numbers in a previous thread on swaybars were off. Stock an Evo runs about 1.35/1.55hz with 50% of overall roll stiffness coming from sway bars up front and 60% rear. Going with more bar just hikes up the tire even more.
My simplistic method, around 2.5-3hz front with 0.2hz more rear, ~35-40% roll coming from bar front and 40-50% in the rear. I don't like more spring because bumpy courses really seem to upset the car way too much, though others seem to love it. If I were to run larger rear rates, or something like the formerly common 12k/16k I would have 0.6hz stiffer rear. That is a huge difference and way too much IMO.
May 7, 2014 | 07:42 PM
#12
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yeah you stepped above my current knowledge base on that one.
have not tried to dip into the suspension frequencies, definitely gonna have to study that one.
also, isnt it difficult to calculate the true stiffness of the bars because they are not a perfect u shape?
have not tried to dip into the suspension frequencies, definitely gonna have to study that one.
also, isnt it difficult to calculate the true stiffness of the bars because they are not a perfect u shape?
May 8, 2014 | 09:14 AM
#15
Over the last few years, with the help of Dallas my evo has had a far about of changes. When I got my evo it had tein ss. It was set up with 7k front and 6k rear. I ran it like that for few autocross days to get a feel for the car. We then swapped springs to 6kf/7kr. The car felt better over all. More neutral. I later added a 26mm front bar and 22mm rear bar.
I finished the season with that setup. Then the next year, I upgraded to Ohlins. They came with 8kf/8kr installed and 10k/10k on the side. I ran it like that for one event, then went 8kf/10kr. The car felt good but I was having issue with the car pushing one min and mass over steer the next because of the factory rear diff.
So to try and help that Dallas and I made the call to do the 10k/10k set up, That fixed my under/over steer issue and the car was back to being more neutral. Soon after I went from a 255 to a 265 and upgraded the rear diff to a 12 plate. With the addition of the 12 plate and the 265 I felt I had a really good SM car that only runs on Street tires. Car always felt planted and never lose. coming out of corners the *** end up step out about a foot and just stay. It was a supper stable set up. This year I am stepping up to 11k/11k, new 18x10.5 and 275s. I stayed with the square set up because it feels the best to me. Dallas try's to explain all the suspension stuff to me but its just way over my head. So I let him figure out what he thinks will work best and I just drive the car. If it does not feel right we make a change tell it feels good.
I finished the season with that setup. Then the next year, I upgraded to Ohlins. They came with 8kf/8kr installed and 10k/10k on the side. I ran it like that for one event, then went 8kf/10kr. The car felt good but I was having issue with the car pushing one min and mass over steer the next because of the factory rear diff.
So to try and help that Dallas and I made the call to do the 10k/10k set up, That fixed my under/over steer issue and the car was back to being more neutral. Soon after I went from a 255 to a 265 and upgraded the rear diff to a 12 plate. With the addition of the 12 plate and the 265 I felt I had a really good SM car that only runs on Street tires. Car always felt planted and never lose. coming out of corners the *** end up step out about a foot and just stay. It was a supper stable set up. This year I am stepping up to 11k/11k, new 18x10.5 and 275s. I stayed with the square set up because it feels the best to me. Dallas try's to explain all the suspension stuff to me but its just way over my head. So I let him figure out what he thinks will work best and I just drive the car. If it does not feel right we make a change tell it feels good.