Need help with some stock LNF/FE5 suspension data
 

Trying to find out the following data for the stock LNF/FE5 suspension for tuning calculations. If anyone have any info, I would very much appreciate it or point me to some sources where I can find these information.

Thanks ahead.

• Ride Frequency: front and rear
• Motion Ratio (or sometimes called "Installation Ratio"): the data on wheel and shock travel distances)
• Droop %
• Wheel & Shock Travel
• Sprung Mass: per corner
• Roll Gradient
• Anti-Roll Bar Stiffness: front and rear (if different)
• Spring Rate: front and rear (if different)
• Damping Rate: front and rear (if different)

I posted this in another thread you asked for this data in as well, but I wanted to point it out here since thats a sticky and not at the top suspension thread new post list.

Youre going to need to physically measure to obtain the data that you want. And use your measurements to get specs on the stock as a baseline.
I think that finding out the baselines is a wasted effort, and potentially money. Motion ratio and sprung weight are all you need to calculate what spring rate you should be using. Because you should have already chosen a ride frequency you wish to use as your baseline setup and you should be using the formula:
Spring rate=4pi²(ride freq in hz ²)(sprung mass)(motion ratio ²)

to determine the proper spring rate to achieve your desired ride frequency, based on the vehicles stock prung mass and motion ratio(since springs are a lot easier and cheaper to change dont you agree that this is the proper way to proceed?)

Once youve got your ride frequency dialed in, youll know your spring rates, and using the spring rate information and your chosen roll stiffness you can tstart the process of calculating what antisway bars youll need based on the other data you already now have, cheifly among them being your track width(as determined by your tire/wheel combo if different than stock), your indiviual wheel rates(as calculated from your chosen spring rates and the motion ratio), the vehicles race weight and its Cg distance from the roll axis.

As you can see we come into several issues here...... First is that you need to know how far away from the roll axis of the vehicle the center of gravity is, this is actually TWO problems in one(its really 3 once we add a an antisway in the equation) Problem one is that we dont know the roll axis of the car(do you?) and problem two is that we dont know where the center of gravity is(do you?) Without these pieces of data you cant even begin to solve for sway bar rate to achieve your desireed roll gradient..... The thrird problem I mentioned is that once you add a rear antisway bar......wait for it......YOU CHANGE THE REAR ROLL CENTER.......oh snap. Now with a changed rear roll center it means our roll axis is no longer where we though/calculated it to be......So our freshly designed and carefully chosen rear sway bar, doesnt do what we wanted it to do. SH!T.


My advice? pick a ride frequency, bu some springs to achieve it, and then buy yourself a quiver of rear sway bars. You should be able to get a selection of 3 different rear sway bars for about $500 with careful sourcing. The just go experiment with the bars on your tracks, bring all 3 with you when you race, its only 4 bolts to change and takes less time than changing tires. You may find that once of the 3 commercially available bars is spot on for you....you may use all three and be able to decide you need a larger or smaller one and at that point guess how much stiffer/softer and calculate its size based on the hard points from the bar you dont like(or like the most) at this point you should be able to get a solid rear bar made up for about $200 and a hollow for about $75-100 more, max.

Have fun on the track.

RIGHT and further unless you CHANGE the twisting beam pivot joint from what it is to what it should be all your calculations will be popcorn...with all due respect to your impressive list of questions and Maven's equally impressive suggestions, this sounds like an issue of pseudo science over common sense.

Mav, thanks for the great reply!

Yes, I am will be deriving the spring rate from a chosen RF. The reason I wanted to find out about the stock RF, is I wanted to know the handling of the the stock car at where it is at now is under that certain stock frequency. In terms of the CG and the sprung mass CG, there is some great info in the RCVD to calculate that, it won't be 100% but it will be very close. The roll center will prove to be a bit hard to calculate as the suspension is not open like in a formula car , getting the measurements from the suspension geometry while it is on the ground with wheels mounted will be tricky.

By the way, don't I need to factor in the tire spring rate to get the wheel center spring rate? or Will that be over doing it? The problem is unless I am using full racing tires (which I won't be using), those information are not usually available for even with the DOT semi slicks.

Great suggestions on the ARB, I think thats what I am going to do. Then from that, I can derive the Roll Rate back if I wanted to.

Thanks. :cssNET:

P.S. need to divide "Spring rate=4pi²(ride freq in hz ²)(sprung mass)(motion ratio ²)" by 386.4 for imperial units (lbs/in).

I havent had a copy of Millikens book in plain sight for several years now(probably since i got married, my wife cant stand me leaving random pieces of paper with calculations all over the house:lol:) Theres a lot of great stuff in there though, but I think its really overkill unless you intend to reengineer the suspension(move things around to adjust antidive, ackerman, etc...) or are running an all out race car with multiple adjustable damping, and have a large selection of springs at your convenience(we dont).

I am very happy that I have an understanding (probably cursory at best if I am honest with myself :) )of the concepts and principals set forth in the RCVD, and I think its great to be able to understand how all the parts and pieces interact and how they affect each other. But understanding your suspension and utilizing the math from the RCVD to improve it are two completely different things. Like I briefly touched on, with a stock type suspension your best bet imo is gonna be to just go with some good ole trial and error, using what data you have and some simple math to keep the errors and trials to a minimum;) There are precious few spring sets available for these cars, and spring rate data is just as hard to come by as virtually all the other numbers. Try getting on your local SSCA regions forum, and snoop around and see what others are runing, and then do some of the experiments and the relatively minimal shopping I recommended.

Yes I think taking tire spring rate into account might be overkill, but if you go to http://www.gsp9700.com/pub/search/findgsp9700.cfm you can find a local shop with equiptment to get you some fairly accurate tire data.




Yes of course you need to keep track of your units, otherwise your answers will be worthless. You also need to be careful with your calculations(you always should be anyway) from the RCVD as it has been pointed out that from formula to formula the Millikens can be found to change deifinitions of their variables from one formula/exercise to the next, this is not an issue if you always check your units and know the deifnitions of what your looking to solve for, but it can be annoying at best, and lead you to horribly errored conclusions if the err happens in early in a long calulation/string of calculations.


While it doesnt deal with the math/theory anywhere near as heavily as the RCVD youll probably find this book much better reading and it offers you some information that is likey to aid most people in being succesfull in their racing endeavours. ISBN Number: 978-0-7680-0898-2

Thanks for the suggestions Mav!

That "Hands-On Race Car Engineer" book is an SAE pub, I will have to check that out.

Yes, if youre not an SAE member, it sounds like youre probably interested in this stuff enough to become one....Its not that expensive, iirc its under $100, and only like $40 if your a student, it will pay for itself with just a few bookstore purchases. Plus you get a subscritption to the SAE journal of your choice.:twothumbs