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Discussion Starter #881
Jay,

Changes to the swaybar stiffness at either end of the car make relative changes in the handling. If you double the front swaybar stiffness, the car is going to understeer more, relative to what it did before. It could still be oversteering, but just much less than it was. My comment about the Eibach front swaybar and stock IRS rear swaybar handling balance has a number of other assumptions. Weight distribution of the car, front/rear wheel rate ratio, etc. If any of these are different, the car could oversteer or understeer absolutely with that swaybar combination.

Without understanding slip angles, it really isn't possible to understanding handling or really drive a car fast.

Slip angle is the difference in angle between the direction the tire is pointing and the direction that the tire is rolling on the ground. Anytime the car is cornering at all, there is an angle developed. The harder the cornering force, the greater the angle. The two links below provide a good description with one exception. When the slip angles gets too high, the maximum amount of cornering grip that the tire can develop reaches a peak and then starts decreasing past this peak. The graphs at both show the grip staying constant.



It is the driver's job to drive the car such that the slip angles of the tires are at the maximum grip point. If the slip angle is higher than that, there is less grip and car goes slower. It is important to understand that anytime the slip angle is lower than the angle for peak grip, the tire is not sliding in the conventional sense. In other words, it isn't leaving black marks on the ground.

How does the driver feel the slip angle? A couple of different ways. The primary way is through the self aligning torque. See graph below.


Slip angle versus grip is the red curve. The blue curve is the self aligning torque. This the torque required to turn the tire to keep the car on its current heading. This torque develops because the rubber at the contact patch is being deformed as it touches the ground and then rebounds in a different direction the instant it is picked up at the back of the contact patch. Stretching the rubber requires work to be done, thus the torque. The higher the slip angle, the more that the rubber is deformed and the greater the torque, up to a point. If you drive the car to the right of the peak in the blue curve, then the steering starts to get lighter, because more and more of the rubber is actually sliding on the ground, so even though the slip angle goes up, which requires more torque, the total amount of rubber being deformed is dropping at a higher rate, so the total steering torque is decreasing. When you get to the slip angle where maximum grip occurs, more or less the entire tire is sliding and the steering gets much lighter. This change in self aligning torque and the grip changes is how the driver can feel what the front tires are doing. Every driver, with any cornering experience whatsoever knows this through experience. This doesn't mean that they can describe it. It how a good racecar driver can jump into a car they have never driven and get 99% of its speed out of it in a few laps. They don't have to spin the car 10-20 times to find out where the grip limit is. They can feel it, even below the limit.

How does this affect handling balance?

Oversteer is when the slip angle of the rear tires is higher than that of the front tires. Understeer is when the slip angle of the front tires is higher than that of the rear tires. See the image linked below.


The above image doesn't really make sense until you add some more lines to it. See below.


In the above image there are two pairs of lines added. The two dotted lines are drawn at right angles to the direction that the tires are pointing. The intersection of these two lines on the left is at what is called the turn center. This is the point is space around which the car is turning. This part of the drawing is inaccurate for deformable tires. This is because any deformable tire will develop a slip angle whenever it also develops a cornering force.

The two solid lines in the sketch are drawn at right angles to the direction that the tread at the ground is rolling. Thus they are affected by the slip angle. The intersection of them generates another turn center, which is an accurate one. You can see that if the rear slip angle is much higher than the front slip angles, the turn center will be located further forward. If the opposite is true, the turn center will be located more rearward. If one looks at a 4WD car doing donuts, you can see that they oversteer so much so that the turn center is way in front of the car. In some cases, the car is actually pointing at it!

Different types of racecars operate at different slip angles. This is mostly a function of the tire construction. F1 cars operate at low slip angles, so they more or less seem to be going the direction that the front tires are pointed. When one gets overdriven in a corner and the slip angle goes past the optimal angle, you can then see the car get a lot more sideways. NASCAR cars with tall, soft sidewall tires have a much larger slip angle. On a road course, the slip angle in some corners is nearly 10 degrees and is very visible.

This should explain how you can determine the handling balance of the car, even when it is driven at significantly less than than its maximum cornering potential.
Thanks Jack for the great information. Do you have books you would recommend reading about suspension setup and handling?
 

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I would read "How to make your car handle" by Fred Puhn first. It is out of print, but you can still find used copies of it. Wait until you have mastered this book before going on. I would get "Fundamentals of vehicle dynamics" by Thomas Gillespie next. It is a lot more technical. It is used for basic college level vehicle dynamics classes. None of the math is complex, but there is quite a bit of it. It is really important that you don't skip over sections when reading these books. I know that the tendency is to want to skip to chapter 7 where it tells you what the magic swaybar combination to run on your car is, but don't do that because you will be disappointed. There is no such answer in any of these books. For the most part, they only explain the physics going on. It is up to the reader to figure out how this applies to their particular car and use.

Books such as Herb Adams, "Chassis Engineering" have a lot less math and physics, and a lot more "do this, don't do that" without a lot of reasoning behind it. Read this type of book after you understand the physics involved, so that you can decide if the recommendations make sense or not.
 

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Jay,

Changes to the swaybar stiffness at either end of the car make relative changes in the handling. If you double the front swaybar stiffness, the car is going to understeer more, relative to what it did before. It could still be oversteering, but just much less than it was. My comment about the Eibach front swaybar and stock IRS rear swaybar handling balance has a number of other assumptions. Weight distribution of the car, front/rear wheel rate ratio, etc. If any of these are different, the car could oversteer or understeer absolutely with that swaybar combination.
I actually do understand these parameters fairly well, I was just wondering why I seemed to be getting feedback from other parties thinking the 1.375" Eibach bar would cause significant understeer in my car. Upon further review, I realize how much difference there is between spring rates between Peters car and my own. He has 400/750 front/rear spring rates in conjunction with previously mentioned swaybars, I currently have 375/550 springs in my car also with the same bars. Assuming (I know) similar weight bias it would appear I need to either reduce front bar rate or increase rear spring rate.

Thank you very much for the detailed information regarding slip angles, I always learn a lot tapping into your vast reservoir of information.

Jay
 

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Discussion Starter #884
During my inspection of the car after the first test drive I realized the my old T5 is leaking allot more fluid then I had anticipated. I also found plenty of trans fluid on the rear bumper. I picked up a lightly used T5Z over a month ado I hadn't planned on swapping in the new trans until the end of the year but decided it was time to swap it in and get the old one out.



I had blocked out the whole week to get it done turns out I was able to swap it in about 8 hours with me moving at a slow pace. I'm glad to have that done if I make the chuckwalla event I will feel much better running a trans that isn't leaking fluid. Now I just need to get some fluid for the trans so I can take it for a test drive next weekend. I'm also going to have a driveshaft shop make sure the driveshaft is balanced and fine. I've been getting a vibration that starts around 3500 rpm and continues to redline. I can rev the engine when its in neutral and I don't get it but it happens when its in gear. I've checked the driveline angles and everything is in spec but can't seem to get it to go away. Its happened with both the live axle and the IRS.
 

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Discussion Starter #885
I would read "How to make your car handle" by Fred Puhn first. It is out of print, but you can still find used copies of it. Wait until you have mastered this book before going on. I would get "Fundamentals of vehicle dynamics" by Thomas Gillespie next. It is a lot more technical. It is used for basic college level vehicle dynamics classes. None of the math is complex, but there is quite a bit of it. It is really important that you don't skip over sections when reading these books. I know that the tendency is to want to skip to chapter 7 where it tells you what the magic swaybar combination to run on your car is, but don't do that because you will be disappointed. There is no such answer in any of these books. For the most part, they only explain the physics going on. It is up to the reader to figure out how this applies to their particular car and use.

Books such as Herb Adams, "Chassis Engineering" have a lot less math and physics, and a lot more "do this, don't do that" without a lot of reasoning behind it. Read this type of book after you understand the physics involved, so that you can decide if the recommendations make sense or not.
Thanks Jack for the book recommendations I was able to find "How to make your car handle" they had it at pegasus racing so I picked up a copy. The second one was easy to find a really good used one for cheap. I actually have the third book which I will go back over once I understand the other books.
 

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During my inspection of the car after the first test drive I realized the my old T5 is leaking allot more fluid then I had anticipated. I also found plenty of trans fluid on the rear bumper. I picked up a lightly used T5Z over a month ado I hadn't planned on swapping in the new trans until the end of the year but decided it was time to swap it in and get the old one out.
A good upgrade to these T5 is the counter gear stabilizer sold by Paul Cangialosi. Cheap insurance. Im not sure if hes been able to restock these. Send him an email. Buy his only, other ones out there are made of aluminum, his is steel, and the copy cats dont fit properly either.
 

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Discussion Starter #887
A good upgrade to these T5 is the counter gear stabilizer sold by Paul Cangialosi. Cheap insurance. Im not sure if hes been able to restock these. Send him an email. Buy his only, other ones out there are made of aluminum, his is steel, and the copy cats dont fit properly either.
Thanks for the link. I've watched all his videos on rebulding T5 transmissions I even bought his book. The plan right now is to take the old T5 apart and replace the gears with the Astro A5 gear set. Then the T5Z will be my back up if for some reason I have issues with the Astro A5.
 

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The Astro kit includes a steel counter gear bearing support, I also used their 3-4 gear billet keys when I did my A5. The A5 gear set is massive compared to the stock gears. I retained the stock output shaft for my build, Tony thought it would be fine for my application. Astro stuff is very nice, you will definitely not be disappointed!

Jay
 

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Discussion Starter #889
The hammer finally dropped on the stadium.


This the place in 1997 I caught the autocross bug with the car I'm rebuilding now. I'm glad I was able to get a some events in last year with the car at stadium. I'm going to miss having such a big lot to run in. I'm hoping we can find some place to go locally but what ever we do it won't compare.
 

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Discussion Starter #891
Went over the car and did a nut and bolt over the suspension and the steering rack. I'm also going some work on the front of the car. I got a grill bar eliminator kit a while back that I'm starting to install now on the car.



Getting the front cut out wasn't back didn't take much. It took a bit of trimming to get it to sit in place right.





This should help the air flow into the radiator. I've also been looking at boxing in the radiator or at least filling in the gaps around the radiator. The passenger side of the car has a really big gap around the side of the radiator.



The driver side isn't to bad.



There isn't much of a gap under the radiator.



The top will be a bit harder to fill in but I have a plan or at least I think I have a plan.



I haven't decided if I'm going to just fill in around the radiator or build a box that will extend to the front bumper channeling the air towards the radiator. My only concern about fully boxing in the radiator is the fan shroud on the radiator will become a restriction at speed since it doesn't have a flaps to allow more air through when the car is moving. I use to run just a fan with no shroud and really the fan was only there to keep it cool when sitting still at the autocross with the engine running getting ready for my run.
 

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My fox body cars have all had a black rubber like flexible panel , that filled the gaps between the radiator and core support .
 

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Discussion Starter #893
My fox body cars have all had a black rubber like flexible panel , that filled the gaps between the radiator and core support .
I took a look at them they will help around the sides of the radiator but won't help channel the air into the radiator.
 

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Discussion Starter #894
Got more work done on the car. I got the front opened up even more should have some good airflow.



I also got the angle brackets mounted. Now I need to cut out the sheet metal to extend to the bumper to make a wall to the radiator.



I also made this to keep the air from going behind the bumper I think this will help force the air into the radiator and coolers. I'm going to tie the side panels to it so it will help seal everything up.



I haven't mounted the oil cooler yet since I'm still debating the placement. I could run it up high so it has airflow through the top center of the car the only drawback is the lock and hook for the hood will block airflow.



Now I could switch to hood pins and ditch the lock and hook but not really sure I want to go that route. I'm not worried about it from a security stand point since this isn't a car I'm going to leave in a parking lot or at the mall or something unless its a car show or autocross in which the hood will be up any way. Now I don't want to mount it up to high since I want it to get air follow from the bottom.
 

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Discussion Starter #895
I got a bit more work done on the car this weekend. Not much has been happening right now to much work and other things going on and a bit of idea block happened so its been slow going. I'm hoping to get some more passes to drive the car on the street on Thursday or Friday so I can take it out again.

I started the box around the lower part of the air dam.



The gaps I'm going to fill in with this edge sealer that will make it possible to remove the air dam from the car. The piece above will have another flat piece connecting it to the bottom of the radiator.



Then I will create the sides to finish boxing it in. Then I just need to work on mounting the coolers for the power steering and oil.
 

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Discussion Starter #896
Made some progress on the car. I got the sides made for the boxing of the radiator. Wasn't to hard to do I made up some templates fitted them to the car then cut them out of some aluminum I had in my garage.





Where the clicos are I'm going to replace with some rivnuts so I can use screws to hold the panels together. This way I can remove them if I need to without having to drill out a bunch of rivets. I also have a water temp gauge coming in that I'm going to add to the car so I can keep an eye on the temps. I'm going to build a lower panel to seal off the bottom that I can remove. I want to see how the cooling is affected when you leave the bottom open with the lower air deflector installed or what happens if the car is a front feed only with the air deflector removed and the bottom of the box closed.
 

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Peter, did you resolve the driveline vibration issue?

Have you had a chance to test the difference between front only air feed versus the addition of bottom feed air?

Jay
 

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Discussion Starter #898
Peter, did you resolve the driveline vibration issue?

Have you had a chance to test the difference between front only air feed versus the addition of bottom feed air?

Jay
The vibration is gone for the most part there is still a bit of one. I'm going to check the drive line angle one more time to make sure its set properly. I also have to remember that my motor is solid mounted the trans has a poly mount and the diff is hard mounted so I'm going to feel something no matter how perfect I get it.

I haven't had a chance to drive the car since August. Getting moving permits is difficult right now it used to only take me about 15-20min since I could make an appointment. Now it takes around 2-3 hours to get one since they are not taking appointments right now. I'm planning on trying to get some this week so I can test drive it this weekend. I'm going to run it out of gas then fill it up run it again and data log the car in normal driving so I can send it off to Decipha to have him look it over and let me know if everything looks good. If its good I'm going to take it to get the car smog tested to see what happens. If it passes great I will get it registered if it doesn't then I will fix what needs to be fixed. If they decide to not pass it due to visual failure then depending on what they say I will decided from there.

Right now at this point there isn't going to be any autocross events in San Diego for the rest of the year or the foreseeable future. All the events on the calendar right now are track days and road rallies with the talk of hill climbs. They are still trying to get some autocross events for next year but the place we would be running is about a 70 mile drive one way. I won't end up doing the road rally but the track days and hill climb I would like to run. No matter what I'm going to have to tow the car. I'm working on a truck and trailer right now. I'm looking at getting an ATC or Intech trailer it's just hard to find one I don't have to travel 500+ miles to get. I'm at a crossroads with the car right now. If its easy to smog the car and I don't have to make huge changes to make it pass smog then great I will register it. If they make it really difficult and costly to get to pass smog then I won't bother with it. I'm still going to have insurance on it so I could get moving permits if I ever wanted to drive it on the street. I originally wanted it to be street legal so I could drive to the events that were a few miles from my house now that its gone I'm not that worried about it anymore.

Here's a bit of an update on the car right now. I finished up the boxing on the radiator. there is still few places I want to fill in but for the most part its done. I got the oil cooler mounted and the new power steering cooler mounted since I couldn't use my old power steering cooler.







I also added a water temp gauge to the car to be able to monitor the water temps better. I used an adapter in the upper radiator hose to mount the sensor.



Then added a two gauge panel to the car and moved the fuel pressure gauge to the new panel and put the water temp gauge in better view. I also added another temp gauge that I'm going to run to the rear diff to monitor its temps. I'm not planning on hooking that up until the end of the year.



The fuse panels have come in handy making it really easy to wire up gauges. If I run track days more I might look at putting a cooler on the diff since I've been reading allot out problems with the IRS diff over heating. I do have some header wrap that I'm going to put on the exhaust where it gets close to the diff but I'm also going to do that later. I want to get the car back on the ground right so I can get some more test driving on it and maybe make it street legal so I don't need moving permits anymore.
 
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