dannobre

iTrader: (3)

The Koni's adjust the compression and rebound together.......

shaunv74

I'll have to try the 50%. Either way I have a baseline with the OEM springs so now I'm excited to see what happens with the Swifts. Although if I'm getting too much travel with the OEM I don't know what's going to happen with the shorter Swifts...

dannobre

iTrader: (3)

stiffer springs = less travel for same bump...so you will need less

What is the springrate on those?

swoope

iTrader: (5)

well tighten up the shocks. see what happens! shorter springs does not mean the same travel as oem.. if it were that simple everyone would have a good spring out!

the swifts have a good rep. i am a bit jealous, but i changed my setup to make it do what is needed..

btw, dan. thanks for the fender heights! i am at 26" all the way around..

beers

shaunv74

I guess what I meant is if I'm bottoming out taller springs what will happen with shorter.

The Swifts are 0.8" less front and rear. the front rates are 207 lbs/inch and the rear rates are progressive 90-129 lbs/inch.

compared to stock 156lbs/inch and 113 lbs/inch respectively. 33% increase in the front and -25% to +14% in the rear. I am concerned about the reduction in the rear rates as the total increase isn't that much to make up for the reduction in ride height. And if the fronts and rears are matched on the OEMs then I'll probably end up bottoming them out as well.

dannobre

iTrader: (3)

Is that .8" less length...or .8" less ride height? The higher spring rate and the shorter springs won't necessarily relate to .8" less ride height if the spring is that much shorter.

With the rears set that much stiffer than the front did you notice that you got more rotation in the rear?

shaunv74

It's 0.8" less right height, not spring length. But that should add up to the same reduction in suspension travel correct?

Not sure I understood the second question. do you mean the shocks at 25% in the rear and full soft in the front? It rotated well. Although on the skid pad it was harder to get it to oversteer with throttle. It would generally understeer first.

swoope

iTrader: (5)

you will loose .8" ride height.. and really.. turn the adjusters up on the fronts. it is easy..

just drive it on the street and it is that obvious..

in the rear, less is more. the front more is more.


beers

dannobre

iTrader: (3)

Shorter springs with the same spring rate will result in no change in the suspension travel...until it bottoms out Then the effective spring rate gets really high

Stiffer springs result in less suspension travel...so you might not end up bottoming out even with shorter springs

Make sense

LionZoo

They adjust rebound only. There are dyno plots for the Konis in my Bilstein thread.

EricMeyer

The cart is getting ahead of the horse. Drive the car. Collect the data.

shaunv74

Hi Eric.

Are my conclusions on the OEM springs with my Konis correct? Just looking for some feedback.

QUOTE=shaunv74;2689915]Nice log sheet Kris. I'll use that at the next event when I get the temp probe.

I have some data from this weekend:

1)My total front shock travel is 7.5" and rear is 7"
-I figured this out by measuring the jacked up extended length of each shock rod from the shock body to the bump rubber.

2)At rest I have 4.5" of compression travel in the front and 4" of compression travel in the rear.
-I figured this out by measuring the height from the top of the shock body to the bump rubbers at rest and subtracting it from the extended length. Note: the rears at rest have the shock body almost up in the shock tower so I measured the shock body top to the spring perch and then measured the shock tower height to the inside bump rubber and added it to the length from the spring perch to the bottom of the shock tower at rest to get a full height with the spring perch as my datum. I then subtracted the length from the shock body to the spring perch to get the remaining shock rod travel.

So it looks like the Konis are a good length match for the OEM springs. Since we have 7 and 7.5" of total travel respectively and have 4 and 4.5" of travel remaining at rest. This also tells me we could potentially take 1" off the overall ride height and still have 3" and 3.5" of travel and still be in the 45-50% ratio range.

Eric would this be correct?

Zip Tie experiment:
Well I had a problem with this one. I could only put a zip tie on the front shocks because the rears are up in the shock tower and I was unable to reach inside and tie them on let alone measure them. So I only have front shock data.

The front zip ties were pushed all the way up to the bump rubbers.

The exercises performed were skid pad spins/skids, emergency stops and maneuvers and slalom courses. So I definitely gave the suspension a good workout.

So Eric this tells me at the current spring length I should use a higher spring rate. Is that correct? And if I go to a shorter spring It should be stiffer still.

Please let me know if my conclusions are on the right track.

Next steps. I'll have to install the swift springs and run this test again.[/QUOTE]

EricMeyer

MY NOTES IN BOLD BELOW

I have some data from this weekend:

1)My total front shock travel is 7.5" and rear is 7"
-I figured this out by measuring the jacked up extended length of each shock rod from the shock body to the bump rubber.

2)At rest I have 4.5" of compression travel in the front and 4" of compression travel in the rear.
-I figured this out by measuring the height from the top of the shock body to the bump rubbers at rest and subtracting it from the extended length. Note: the rears at rest have the shock body almost up in the shock tower so I measured the shock body top to the spring perch and then measured the shock tower height to the inside bump rubber and added it to the length from the spring perch to the bottom of the shock tower at rest to get a full height with the spring perch as my datum. I then subtracted the length from the shock body to the spring perch to get the remaining shock rod travel.

So it looks like the Konis are a good length match for the OEM springs. Since we have 7 and 7.5" of total travel respectively and have 4 and 4.5" of travel remaining at rest. This also tells me we could potentially take 1" off the overall ride height and still have 3" and 3.5" of travel and still be in the 45-50% ratio range.

HERE IS WHAT I HEARD:

TOTAL DROOP FRONT IS 7.5". THIS IS THE LENGTH OF ROD AT FULL EXTENSION. AT CURRENT RIDE HEIGHT, THE CAR USES 3" OF THIS TRAVEL AND THEREFORE HAS 4.5 INCHES OF COMPRESSION TRAVEL REMAINING BEFORE WE HIT THE BUMP STOP. YES?

Eric would this be correct?

Zip Tie experiment:
Well I had a problem with this one. I could only put a zip tie on the front shocks because the rears are up in the shock tower and I was unable to reach inside and tie them on let alone measure them. So I only have front shock data.

The front zip ties were pushed all the way up to the bump rubbers.

SOUNDS TO ME LIKE LOWERING THE CAR AN INCH WITH THE CURRENT SPRINGS IS GOING TO MAKE THE PROBLEM WORSE.

The exercises performed were skid pad spins/skids, emergency stops and maneuvers and slalom courses. So I definitely gave the suspension a good workout.

So Eric this tells me at the current spring length I should use a higher spring rate. Is that correct? And if I go to a shorter spring It should be stiffer still.

THIS IS CORRECT. YOU'LL HAVE TO WATCH OUT HERE BECAUSE YOU CAN INDUCE OVERSTEER AND UNDERSTEER WITH YOUR SPRING CHOICE. HERE IS HOW THIS WORKS: A LIGHTER SPRING IN THE REAR (RELATIVE TO THE FRONT) ALLOWS THE REAR TO "ROLL OVER" MORE IN A CORNER. FOR EXAMPLE, A 500 FRONT AND 350 REAR SPRING. THE CAR GOES INTO A RIGHT HANDER. THE CAR LEANS TO THE LEFT SIDE. THE FRONT SPRING IS STRONGER AND THEREFORE DOES NOT COMPRESS AS MUCH AS THE REAR SPRING. THE REAR "ROLLS OVER" MORE BECAUSE IT IS A LIGHTER RATE. AS A RESULT THE CAR WANTS TO OVERSTEER A LITTLE. THIS IS A BASIC PREMISE.

SO.......IF YOU ARE GOING TO INCREASE YOUR SPRING RATE AT EITHER CURRENT RIDE HEIGHT OR A SLIGHTLY LOWERED RIDE HEIGHT, KEEP IN MIND YOUR CURRENT SPRING RATE SPREAD. FOR EXAMPLE, THE FRONT'S MIGHT BE 30 OR 40% STIFFER THAN THE REARS.

Please let me know if my conclusions are on the right track.

YOU ARE RIGHT ON TRACK. TEST. TEST. TEST.

Next steps. I'll have to install the swift springs and run this test again.[/QUOTE][/QUOTE]

shaunv74

Thanks Eric!

You're understanding of my post is dead on. The next set I have to put on are 30% stiffer in the front and progressive up to 14% stiffer in the rear with a 0.8" drop both front and rear.

I'm curious why the softer springs in the rear would cause more oversteer? I would think the opposite. If I get more body roll in the rear wouldn't that put more weight over that wheel relative to the front and provide more grip?

thanks and I appreciate the help.

EricMeyer

This is where very good driving comes in. BTW, what's your name anyway? The ability to drive a car on it's edge allows you feel what it's doing. This is a difficult skill set to acquire when you're looking for very small vehicle dynamic signals. It's easy for huge issues, i.e., GIANT oversteer, but more difficult when your fine tuning.

For me, I've found that driving a road course line spot on at a very fast click does the trick. Keep in mind that some people just can't do this. Put two guys in the same car and one driver is 3 seconds a lap faster than fast another---why? Because he/she is really that good. Step 1 (for my style) is driving the crap out of the car and searching for the car's tendancies under breaking, corner entry, mid corner and exit. Same for going to full power. I have met a couple of guys in my short racing career that are excellent at this diagnostic. Some have even found issues when I thought the car was spot on. It's a skill. Some guys don't change their set up at all. Back in my Spec Miata days, all you had at the track to tune your car was suspension. For those of us Mazda guys on this forum that are NOT familiar with Spec Miata, you should know that this is the very best entry level closed wheel car series you can run. Period. Inexpensive. High speed cornering cars. Well balanced. I digress.

So back to the softer springs issue that is normally hard to get on the first pass. Most people think like you do about softer = better grip. Here's how the concept was first taught to me a few year's ago.

You have a car. It has 4 equal shocks and springs that are mounted to all four corners like a regular car. It's 3,000 lbs with driver. 1,500 lbs front. 1,500 rear. 750 on each corner. 50/50 weight distribution. Get it so far? Let's pretend that the springs are all equal on the car. 500's, 600's, whatever. It doesn't matter. All that is important for this example is the spring rates are the same for all 4 corners. Let's say they are all 400.

Now let's roll into a corner. For simplicity's sake we have some weight transfer to the loaded side. For a right hand corner the car rolls left. For a left hander it rolls right.

Let's say that the 750 lbs on the front left (for a right hander) and 750 rear (again we are turning right in this example) are now higher because the car is rolling. Let's say that it's more than 750. Let's car it 1,000 per corner or 2,000 for the left side . What is the rest of the car? 1,000 right?

OK. Now let's decrease our spring rates in the rear a bunch. Let's pretend we go from the 400 to something less. Let's make a big change. The rear springs decrease from 400 to 250. We go into the same corner. Now this is your opportunity to think and learn:

How does the car now behave? Think about it. Don't read the next paragraph until you have thought about it please. Don't deny your opportunity to examine your current belief system. Page down when ready. What is the car doing???









Answer: Because the car is stiffer IN THE FRONT than the rear, the car wants to roll over more in the back. The same right hander example has a stiffer foundation on the front left due to a stronger spring. The rear is more weak so to speak. All that 2,000 lb weight transfer to the left and the new rear spring rate. Where does the weight go? It rolls over more in the rear---right. The front end is more solid because it has higher spring rates (think of stronger men carrying a casket or a fridgerator or something horizontal). The guys in the back carrying the same object are weaker. They are carrying the object lower, with less rigidity. Time out for a second. If you're following this concept thus far, you are in the minority. The first time I heard this I didn't get it for a while. If you don't get it you're probably normal and/or I suck at explaining things (or both).

In our example the rear of the car has less spring than the front. Rolling to the left side has the front left offering more strength or foundation than the left rear. The front left becomes more of a pivot point than the left rear. Therefore, the left rear spins or rotates around it so to speak. This is how I learned it. Conceptual but you get the idea. The rear has less ability to hold it's 1,000 lb weight and attempts to roll over more inducing oversteer tendancies. This is a simplistic story. I beleive the rear engineering reason is more complex however I never got the engineering version and since most people on these forums aren't engineer's, I'm going with my version--the salesman turned business owner turned race car driver version.

I beleive the reason why the front springs on most cars are higher in the front is to help them turn. We run higher front's and lower rears. Our share this info along with some other goodies in the next thread.

Happy motoring. You're doing great. Keep it up! Remember to test! test! test! Even if it's wrong, you'll learn something valuable.

EricMeyer

I'd probably run about a 300 front and 250 rear spring. A really stiff roll bar in front and invest in some solid coilovers with very good shocks to lessen the higher spring rates.

DEFINITELY a strong front bar. I'd remove the rear bar. Absolutely higher spring rates (these cars reaaaaaalllly like to roll over). Lower it a bit (you can lower more without issues when you have plenty of shock travel and run a higher spring rate). And perhaps something like this give or take or have some custom shocks made: http://www.koni-na.com/1150.cfm

Now that I think about it I'm going to look into having some made and marketing them. Perhaps I can get the cost really low and end up with an attractive price point.

So many things to do. So little time.

shaunv74

Since more weight is being transferred back to that corner of the car the centrifugal forces on the rear of the car will be greater than the increased grip you get? Causing a net tendency to oversteer?

I'll have to see that one in action to fully understand it. Based on that I think I should see an increase in the tendency to oversteer with the next set of springs then since the rear rate increase is less than the front rate increase. My current setup has a tendency to understeer at the edge so that should be good to try and get it a little more neutral.

Thanks,
-Shaun

LionZoo

Funny enough Eric, you came to close to the conclusions that I came to in my Bilstein development, which is still in progress.

A couple corrections if I may; while I can see a softer rear providing more steady state oversteer, I would think it would lead to turn-in understeer as it takes longer for the rear to respond to inputs and so the car initially still wants to go straight. At steady state though, the car is all leaned over and the extra roll in the rear means there's more weight transfer to the outside wheels. Since weight transfer results in a net grip loss (the extra grip gained from the weight on the outside wheels isn't enough to offset the end to steer that extra weight), the rears lose traction first, causing steady state oversteer.

In my opinion, this is why F1 cars are set up with rates that are so counter-intuitive at first glance; their front rates are much higher than their rear rates even though their weight distribution is something like 43/57. Since their cars are already so nimble, the extra turn-in understeer isn't a huge issue and is more than offset by the steady state "pointability" of the car. Also, a softer rear would allow them to more effectively put power down coming out of corners, but I digress...

Now here's a monkey wrench: what is tricky here is that the balance of the car might have changed; if the cornering loads were even between front and rear this would definitely be the case. However, changing the grip conditions will change the balance; the end of the car with more grip does more of the turning, so the cornering loads in this case would shift more to the front. This load is akin to weight transfer in a way and so in this case will decrease oversteer. Therefore, you have two dynamics fighting each other.

Shaun, I don't want to be pimping my thread, but I don't know if you've read through my Bilstein thread: https://www.rx8club.com/series-i-wheels-tires-brakes-suspension-55/custom-bilstein-build-up-thread-148914/ It has some interesting findings in regard to the factory dynamics of the RX-8 and what Shaikh and I believe to be some deficiencies in the aftermarket offerings. Take a look if you haven't already.

EricMeyer

Springs are just one part of the suspension SYSTEM. I wouldn't jump to any conclusions so early in your testing efforts.

WRT your understeer. What are your camber, toe, and corner weights?

EricMeyer

LZ,

Just trying to keep it simple and easy to read. I've found that many a person who wants to know can easily be scared off and/or will steer away from any mods as people can make it difficult for a "newbee" to understand.

We run about a 100 lb spread from front to rear with a huge front bar and very low rear roll center. Also the torsen diff. The Cusco is only good if you like understeering pigs.

I will read your thread at the next chance. Thanks for supporting a good thread.

Eric

shaunv74

Camber is -.9 in the front and -1.3 in the rear. I have 0.5mm toe in, in the rear. That is the most camber I was able to get in the front. I should be able to get more with the new springs. Provided I need it once I know where my tire temps sit.

I can't adjust the ride height of the spring perches on the shocks so I can't corner balance the car. The alignment was done with my weight in the drivers seat.

Thanks,
-Shaun

swoope

iTrader: (5)

eric,

this is a very simple wondering question. btw, lots of great info above..

knowing that the koni st cars run stock suspention links and locations.

what is the tire dia that is being run, and the corresponding fender height? and yes i know it is not perfect, but it is close enough to check.

btw, what happened with the header?

note i find twist ties safer that zip ties.

beer

EricMeyer

http://www.hoosiertire.com/grandamc.htm RX8's run 225/45/17 as required by the rules. For ride height at the fender, consider that the lowest point on the car has to be no lower than 3.5" above the ground. I'll measure these heights and get back to you. Keep in mind that our fenders get hit ALL the time and therefore we don't use this as a reference (as it can change and/or is not consistant).

swoope

iTrader: (5)

wow,

tire dia is much closer than i would have thought.. and i would love to know your ~ fender height.

beers

shaunv74

Alrighty I have an update!

I installed the Swift springs this weekend and took some interesting measurements.

The front Swift Springs are 3" shorter than the OEM front springs but drop the car 1". The OEMs were 15" long and then Swifts are 12" long.




The Rear Springs are the same length as the OEM,14", and drop the rear 1". I guess that the initial softer rate of the Swifts creates the drop.




The install went without mishap and everything went in and out fine. I measured the effective compression travel with the new springs and here is what I have found:

The fronts still have the same 7" of full extension and at rest on the ground I have 4" remaining. Sounds good.

The rears have the same 7.5" of full extension as well (since there the same shocks as before it should) and 3.5" remaining at rest.

The car fenders sit at 26.5" above the ground all the way around so I've lowered the car about 1" and still have 4" of suspension compression in the front and 3.5" of suspension compression in the rear. Most importantly the coils aren't resting on each other at rest like the Espelir's were.

It looks like the Swift springs are designed well at this point and they have done a good job with sizing them relative to the spring rate.

We'll have to see how they do under heavy compression once I get the alignment done and get a chance to work it a little. i've reseated the zip tie resting on the shock body on the front shock. I'll take a look at it after I get a chance to work the car out.

Initial driving impressions are the new springs definitely control the body roll more. There is not nearly as much squat and dive as there was with the OEM springs and turns are flatter which is more confidence inspiring. We'll have to see what the data tells me.

Front Swift springs installed car resting on the ground


Rear Swift springs installed car resting on the ground