shaunv74

Hi Eric! First let me say I'm honored to have you post this excellent and educational writeup in my thread and sincerely appreciate your interest in my problem.

Second let me appologize for not reading and recognizing your posts right away. For some reason I didn't get notified about your updates to my thread and when I checked back to answer the one question I didn't take the time to read your information before responding.

Third: I see your point and now understand the relationship between not only sring rate but spring length and shock travel length. It makes sense that a spring designed to work with the OEM tokico shocks may not be designed to properly work with the Koni shocks.

although I would think that Koni would want to replicate the travel and length of the OEM shocks with their shock in order to avoid incompatibility with the OEM springs and other springs that would be OEM replacement.

I have a question in my next post for you.

shaunv74

I have the Swift Sport Mach springs I want to swap in to the car and currently the OEMs are on the car with the Koni shocks.

A good test today would be to measure the front and rear exposed shock rod length with the car on the ground, then jack up one side until the wheels are fully off the ground and measure the exposed shock rod length. If the exposed length in the air is 2x the exposed length on the ground then I have a proper shock to spring travel ratio and they are a properly matched set. If it is more or less then I am not using the full travel of the shock and not getting it's full benefit or bottoming out the suspension.

Is that correct?

So if that's the case would any shock that is made to replace the OEM shock work properly with a spring that offers a lower ride height?

Can I assume that the Swifts with a 1.25" drop will have the same problem not because of bad design but because of incompatibility in length?

EricMeyer

YOU COULD. I THINK YOU WANT TO SEE HOW MUCH CURRENTLY AVAILABLE SHOCK TRAVEL YOU HAVE AND SUBTRACT THE LOWERED SPRINGS OF 1.25 INCHES. IF YOU HAVE NOT VERY MUCH, YOU COULD BOTTOM OUT YOUR "NORMAL LENGTH" SHOCKS. YOUR CURRENT MEASUREMENT EFFORTS SHOULD TELL YOU THIS. ONE MORE THING YOU CAN TRY.

STEP 1: PUT A TINY PLASTIC ZIP TIME AROUND YOUR EXISTING SHOCK ROD (THE CHROME PART). DO THIS TO ALL 4 SHOCKS.

STEP 2: DRIVE YOU CAR LIKE YOU WANT TO DRIVE IT---HARD CORNERING IF YOU HARD CORNER. RALLY DRIVING IF YOU RALLY DRIVE. STREET DRIVING IF YOU STREET DRIVE. BASICALLY DUPLICATE HOW YOU DRIVE. YOU NEED ONLY DO THIS FOR A FEW MINUTES. A PARKING LOT IS GREAT IF YOU WANT TO SIMULATE AUTOCROSS OR SHARP TURNS. MAKE SURE YOU SIMULATE BODY ROLL. MAKE SURE YOU ARE USING DESIRED WHEEL HEIGHT (18" OR 17" WHEELS OR WHATEVER). NOTE: THIS IS A GOOD TIME TO CHECK YOUR TIRE PRESSURES PRIOR TO THIS EXERCISE. LOWER WINTER TEMPS OFTEN MEAN YOU NEED TO ADD MORE AIR.

STEP 3: JACK UP THE CAR AND LOOK TO SEE WHERE THE ZIP TIES ARE. BY THE WAY, THIS IS A GENERALLY ACCEPTED RULE OF THUMB BY THOSE PEOPLE EXPERIMENTING WITH RIDE HEIGHT AND SHOCK TRAVEL. IF YOUR ZIP TIE IS WEDGED WAY UP INTO THE BOTTOM OF THE SHOCK BODY, THEN YOU HAVE DETERMINED THAT YOU RAN OUT OF SHOCK TRAVEL-----SHOCK TRAVEL NOT LONG ENOUGH----SHOCKS TOO LONG OR CAR TOO LOW OR SHOCK BODY VS. ROD LENGTH IS INCORRECT. MAKE SENSE? STOCK CARS MAY FIND THAT THE LEFT SIDE OF THE CAR HAS LESS TRAVEL---BECAUSE THE DRIVER'S WEIGHT MAY MAKE THE LEFT SIDE LEAN MORE THAN THE RIGHT (WHICH CAN EXPLAIN WHY YOUR CAR MAY HANDLE BETTER IN LEFT TURNS AT YOUR NASA HPDE EVENT WHEN YOUR BUDDY IS IN THE PASSENGER SEAT). WOW YOU SAY. ARE YOU GUYS GETTING IT YET?

THIS WOULD BE A GOOD EXERCISE FOR SOMEONE WITH STOCK SUSPENSION TO PERFORM AND REPORT BACK TO THIS THREAD. SAME FOR SOMEONE WITH AFTERMARKET SHOCKS AND/OR SHOCKS AND SPRINGS. IF YOU ARE INTERESTED IN DOING THIS EXERCISE, PLEASE OFFER A COUPLE OF THINGS:

1. SPRINGS (STOCK OR OTHER). USE THIER "FREE LENGTH" WHICH IS WHEN THEY ARE NOT COMPRESSED AND ALSO WHEN THEY ARE COMPRESSED. THIS GIVES THE THREAD LOTS OF GOOD INFO AND PREVENTS QUESTIONS OR GOING BACK AND JACKING UP THE CAR TO PROVIDE THIS THREAD WITH THIS INFO.
2. TYPE OF SHOCK (STOCK OR OTHER). SAME LENGTH ISSUES---FREE LENGTH OF THE TOTAL. LENGTH OF THE BODY AND LENGTH OF THE ROD.
3. STOCK OR LOWERED RIDE HEIGHT (IT MAY BE EASY TO MEASURE FROM THE BOTTOM OF THE FRONT FENDER JUST ABOVE THE MIDDLE OF THE WHEEL). THIS WOULD BE THE SPACE ABOVE THE TIRE TO THE BOTTOM OF THE FENDER.
4. USE INCHES AS A UNIT OF MEASURE TO MAKE IT EASY FOR EVERYONE TO COMPARE
5. INCLUDE YOUR DROOP HEIGHT, COMPRESSION HEIGHT AND THE DISTANCE OF THE ZIP TIE FROM BOTH FROM THE TOP OF THE EXPOSED ROD TO THE BOTTOM OF THE EXPOSED ROD.
6. WHEEL SIZE

THIS WOULD SHOW YOU AVAILABLE SHOCK TRAVEL AND HOW MUCH YOU ARE USING OF THIS AVAILABLE TRAVEL.

I WILL DO THE SAME AND REPORT BACK.

I RECALL THE LAST TIME I DID THIS WE HAD 6.5" OF DROOP AND WE HAD SHOCKS DESIGNED TO GIVE US 1/2 OF THAT (REAR SHOCKS) SO WE ENDED UP WITH 3.125 INCHES OF TRAVEL UNTIL WE HIT THE BUMP STOPS. THIS IS WITH A REALLY STIFF SPRING SO IT WILL BE TOO LOW FOR STREET GUYS---I THINK WE DID THIS WITH 500 SPRING RATE REARS BUT THIS WAS A YEAR AGO OR SO.

HERE IS A GREAT EXAMPLE OF A RECENT DEVELOPMENT. WE SWITCHED DIFFERENTIALS BACK TO THE STOCK RX8 TORSEN STYLE DIFF AND ON SOME CORNERS WE EXPERIENCED A LITTLE INSIDE WHEEL SPIN. THIS MEANS THAT THE CAR IS NOT TAKING ADVANTAGE (AND THIS IS ERIC TALKING HERE) OF THE CAR'S FULL ABILITY TO MORE FORWARD. TO COMPENSATE FOR THIS WE LOWERED THE REAR OF THE CAR A BIT. WHEN DOING THIS YOU ARE LOWERING YOUR REAR ROLL CENTER AND THIS ALLOWS THE REAR END TO "HOOK UP" MORE AND IT SHOULD OF DECREASED OUR INSIDE WHEEL SPIN A LITTLE. IT DID. GUESS WHAT HAPPENED---WE DECREASED OUR AVAILABLE TRAVEL. HARD HIGH SPEED CORNERING (MID OHIO TURN 1 TO BE SPECIFIC). THIS IS A LEFT TURN BY THE WAY. WE FOUND THAT WE WERE JUST BARELY TOUCHING THE RIGHT REAR REAR BUMP STOP (THE FRONTS WERE FINE). THIS CAUSED THE CAR TO OVERSTEER IN AROUND MID-CORNER (WHEN LOTS OF THE SIDE LOAD/ROLL IS OCCURING). OUR ZIP TIE METHOD DETERMINED THAT WE WERE BOTTOMING OUT. WE RAISED THE CAR A BIT, WENT TO A HIGHER SPRING RATE AND GOT RID OF THIS TEMPORARY ISSUE. LONG TERM FIX IS TO HAVE THE SHOCKS REBUILT SO WE HAVE MORE TRAVEL SO WE CAN RUN THE CAR LOWER IN THE REAR AND MAKE IT "HOOK UP" BETTER TO AVOID WHEEL SPIN. THIS WOULD INVOLVE MEASURING EXACTLY WHERE WE NEED RIDE HEIGHT AND TRAVEL. THIS IS A CURRENT LATE FALL/EARLY WINTER PROJECT THAT WILL MOST LIKELY DECREASE THE SHOCK BODY'S AND ADD A LITTLE MORE ROD LENGTH. PROBABLY ABOUT 1/2" TO 3/4" TO EACH---NOT SURE YET. PROJECT SUMMARY: REDUCING OUR REAR ROLL CENTER/LOWERING THE REAR MADE US RUN OUT OF TRAVEL AND WE WILL NEED TO REDUCE THE SHOCK BODY'S BY 1/2" OR SO AND ADD 1/2" OR SO OF ROD LENGTH. THIS WILL PROBABLY RUN US $200 BUCKS OR SO A SHOCK (TOTAL GUESS). WE WILL USE OUR EXISTING SHOCKS FOR THIS (THE SPEC KONI CHALLENGE 2812 SHOCKS REQUIRED IN KONI CHALLENGE).

TIME TO GO TO THE SHOP. HOPE THIS HELPS. HAPPY MOTORING.

ERIC

EricMeyer

Just thought of something. When using larger diameter front springs, we've found that you can run into some interference with the upper control arm. On some of these control arms there is a more pronounced nub on the inside portion of the casting next to the spring. To put this another way---inside the middle of the "A". I believe the nub is on the back side of where a bracket is located to hold the brake lines. SOME times our spring hits/rubs against this little nub. We run 2.25" springs. Just thought I'd share this with you guys since we're on the subject. This is the FRONT UPPER control A arm. Either side.

shaunv74

Thanks Eric! I actually have a great way to try this this weekend. I'm going to a PCA driving class so I can really test this out.

One question to make sure I'm clear on the zip tie method. The street Koni shocks are set up with the shock body on the bottom attached to the spindle and the shock rod on the top attached to the body (opposite of yours). In that case I am thinking I want to start with the zip ties attached to the shock rod resting on top of the shock body and see how far up the shock rod they travel to see how much compression I am getting. If it travels up to the end of the shock rod then I know I am running out of shock length correct?

Please let me know if that makes sense or I'm missing something.

If not I will take the measurements on my Koni shocks with OEM springs, try the zip tie method and measure it's height after Saturday's event and report back with data!

HeavyMetal699

I will contribute as soon as my tires come in. I will edit this post at that time.

I just installed racingbeat springs with koni yellow sport shocks. I'm curious to how close of the 50%/50% shock travel I have.

Also, I'm guessing how sticky the tires are could cause more body roll in turns. So some sticky rubber might cause alot more roll.

Edit: Getting tires installed/balanced/aligned by hopefully next weekend. I believe the next AutoX in my area is on the 2nd, but I should be able to get a good write up before then. Also I was interested in the sprint springs as well, but ran into the racingbeat springs for a price I could not pass up. They are definitely stiffer than stock if effort turning the spring compressor is any indication. I don't want to discuss handling until my new tires come in because my rear tires are about useless.

shaunv74

Eric,

For the benefit of the community would you be willing to start a thread on suspension setup or spring/shock matching in the Suspension forum and copy your writeup over? I'll be the first one to vote for a sticky! Then we could have folks like HM and I post up our data for review and discussion.

I think this would be a huge help since most of us see suspension tuning as a bit of a black art and would be really excited to get some clarity and feedback on how to do it right.

Thanks again!

swoope

iTrader: (5)

WOW,

LOTS OF GREAT INFO.. CAP LOCKS REALLY, REALLY HURT MY HEAD..


beers

EricMeyer

You don't need exactly 50/50 to make your car work properly--you need compression travel and rebound travel (which is saying that you need a shock that is not bottoming out). I haven't spent much time on this forum to know if bottoming out is a big problem or not. I do know that the RX8 has a strong ability to corner and therefore has the ability to put roll forces on the car and therefore tax the springs and shocks. Whether or not this has several aftermarket suspension owners bottoming out is something I'm unaware of.

So 50/50 is not a super magic number that makes your car handle better (this is rear shocks). It's just a percentage that suggests you have an equal amount of compression and rebound. You would want to take this 50/50 number, factor in the actual length of travel (for comp. and rebound), use the zip ties to see if you have some travel left over (typically the key zip tie info you're looking for is the compression number) and you can confirm you have enough travel. If it looks like a lot of travel (distance from the zip tie during maximum compression while Auto-X or open track), you have room to lower the car a bit. These cars like to be lowered in the rear I've found (using the stock diff).

EricMeyer

Sure

EricMeyer

You are correct. Remember to check your tire pressures frequently. Tire pressures often. Preferably AS SOON AS YOU COME OFF THE TRACK. Hop out of the car in pit lane or have a buddy who is waiting there for you do this. If you want to do it right, get a tire pyrometer. Here is an inexpensive one: http://www.longacreracing.com/catalo...id=200&catid=7

I don't like the Laser technique and would suggest NOT using it. Tire pyro will help you discover general camber issues (as in too much or not enough). This is determined by taking 3 temperature readings across the face of the tire----inside, middle and outside. The metal probe that comes with the pyrometer is inserted into the tire and provides a temperature reading. For a stock suspension car, you generally find that the outside front left temps are much higher than the rest of that tire. This would indicate..............stop reading this and think about this question please..................lack of camber in the front left. Conversely, some one that has too much camber would see higher temps on the INSIDES of their tires. There is more to this than I've offered but as a general rule, you can validate a need for more camber and/or see how your current camber choice is performing. Our race car target is to get the tires within a 15 degree F spread from Inside (hotter) to outside. For example, we might see on a particular track on a particular day on the front left (200F inside, 193 middle and 185 outside). These numbers would make me very happy. Sometimes you don't achieve this, other times you do. Depends on the track. If our outside numbers were the same as the inside after some robust practice sessions during afternoon sessions (when the track has heated up), we would add a little camber----perhaps .2, .3 or .4 and then go try it again. As a general rule, once you figure out your car's operating zone, you're pretty close in using that camber number everytime. Keep in mind that as you become better at driving, you push the car harder and will see higher tire temps and pressures due to the fact that.....tada.......you're going faster! This is why a tire pyro is a great tool to have. It can give you hard data. The majority of drivers in DE events have (no offense) no clue about how thier car feels under spirited driving. This is an acquired skill set honed after lots and lots of seat time in a well prepared car. This is one reason why I'm against 82 way adjustable shocks. People make changes to something and this generally covers up the real issue. For example, someone might make a shock adjustment when the tire temps show that there is too much (or not enough) camber. The real issue is the camber! You only have a few square inches of potential tire contact patch to use. Not using one tire can reduce your potential grip by 25%! HUGE!. You need to start with a good foundation and work from there. Here comes the broken record...........do yourself a favor (everyone on this thread and in this forum) buy a good tire pressure guage and an inexpensive pyrometer. Trust me that you'll learn a ton.

Meyer out.

ZumnRx8

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shaunv74

Thanks Eric. (edit meant to say ERIC)

I drew up a diagram based on what you're saying. It makes a lot of sense. Thanks for the lesson.

Is this correct?



I have question on tire pressure. You mention checking tire pressures often but I'm not sure how to tell which pressure my tires perform best at.

Should I be using the temperature gauge to monitor this? EG the lowest temp spread across the tire for a given camber setting should be the best tire pressure?

Thanks again!

kristopher_d

For pressures and alignment, Shaun, you're looking to have the tire temps even across the width of a single tire. Of course, hot pressures are different from cold pressures, and the same trick used in auto-corss will work on the circuit. Chalk the shoulders and see where you're rubbing the tire clean. If you're getting onto the shoulder you'll need to increase pressure. If there's still chalk on the circumference, air the tires out a bit. For car balance, your indicator is the balance of temps across all 4 tires relative to the cornering forces you see. Unfortunately that varies a lot from track to track. At Pacific we should see the passenger side front quite a bit warmer than the driver side rear since there's really only 2 corners that put any significant load on the left side of the car, and both of them are low speed bends.

dannobre

iTrader: (3)

I usually run 2 lbs less in the right front to start in Seattle. Works out pretty good most of the time....

Pressures will vary depending on the tire, ambient temp, setup and a whole lot of variables. The thing to do is keep detailed records at your track days and then you have data to back up decisions at later dates.

shaunv74

Thanks guys.

I'll have to play around with pressures this weekend a bit with the chalk trick as well as the zip tie.

Yeah I should start keeping a notebook on pressures and shock adjustments along with comments. The trick with the notes is being able to tell better from worse and make sure I know whether it's the car or the driver.

dannobre

iTrader: (3)

Some of the data is driver independent........so don't be so hard on yourself

The more data you have the better chance you have of it meaning something later.

shaunv74

Good point. Either way time to start up a notebook.

EricMeyer

Agree 100%! Your learning curve is about to go through the roof. Take as much info as you can. Time of day. Ambient outdoor temp. Use your new pyrometer toy and stick the asphalt to capture the temp. Cloudy? Hot and sunny? Starting and ending tire pressures.

Here is what Eric's ole' crystal ball is telling him: You're going to see the chalk mark on the outside of your front left tire get used up. Your right rear will look near new. Your tire pressure on the front left will gain more than the others (as Danno stated). To give you an idea: I run the FL in our GAm Hoosiers at about 1/2 psi less than both the FR and LR and 1 psi less than the RR. My target (for those particular tires) is to come in hot at 39 psi after a long session in the hot afternoon. You want your tires to be at their best at the END of the session. For racing this allows your car to be strong when other car's tires may be fading. Experiment. Don't be afraid to try something. Make 1 big change and 1 change only and drive the crap out of the car. Danno is right on the money about his driver variation comment. As you get more laps you will become much faster very quickly. You become a large variable in your suspension equation.

Have fun.

Eric

kristopher_d

Here's the session log I use
Instructions - http://www.turnfast.com/tech_practice/practice_notes
The form - http://www.turnfast.com/downloads/session_log.pdf

shaunv74

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.

swoope

iTrader: (5)

you keep saying that. get them on! you will be surprised.

beers

HeavyMetal699

Wow, great data!

A quick question though, what are your konis set at?
Mine are set at 50%(5.5 half turns) on the rears and about 65%(4 half turns) on the fronts.

The car is so stiff that there is almost zero roll in any direction and I doubt its because of the racingbeat springs.

shaunv74

Yeah yeah. Well I need a weekend where I haven't been driving or taking the wife to a wine country getaway in Oregon to get them on. I think this coming weekend is a good opportunity.

Heavy Metal: Mine were on full soft in the front and 25% from full soft in the rear. I figure I didn't want to mess with the shock settings until I was able to take some data.

Since the Konis are rebound adjustable only I didn't think it would affect the total compression since we should see the most compression on first cycle and damp out from there.

swoope

iTrader: (5)

do i have to come out an help you? btw, i would turn the fronts down to 50% and learn. i had them on a car that would shock you.. and the 25% rear is fine. but you will be shocked what happens when you get the front to at least that level..

my only change to all the above info would be twist ties vs zip ties.. dont crush into the bump stops!

beers