I'm fairly blown away by the generosity being shown here. What a great forum!
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I'm fairly blown away by the generosity being shown here. What a great forum!
Had some down time while away and an internet connection, so I logged in to reread the instructions so they would start to sink in more. I believe I'm starting to get the idea better and better all the time.
My main concern is how I'm going to get the measurements when things are in the way...but I'm sure I'll figure them out.
Thanks again for all of the knowledge sharing Ron and thanks to David for stickying the thread. Hopefully many of us can help blueprint our cars better with the info in this thread.
If you need more clarity or guidance, don't be afraid to ask. The first time is always intimidating. After measuring a car or 2, it becomes just another car thing. Once you get the #'s, I'll work out your front end geometry & we will know where you are. Then I can work out ways to achieve your handling goals.
Take care!
As far as measuring shock travel, you want the measurement from the moved zip tie on the shock shaft back to the shock body when the car is sitting at ride height in between runs correct?
I'm back home and planning out my shop time before Sunday and need to get the car on the lift to make sure I'll be able to get to all of the shocks to record this measurement in the grid between runs.
It looks like it is going to be super hot this weekend and I haven't had time to scrub in my new street tires yet, so I think I'll just run the slicks on all 4 runs Sunday.
Uh, this might be an issue...
https://static1.pt-content.com/image...0530_876-1.jpg
That is the right front shock, zip tie installed and car let down to sit at ride height, then raised back up for the picture.
This is the left front
https://static1.pt-content.com/image...0348_890-1.jpg
Here's the backs same scenario
https://static1.pt-content.com/image...0315_232-1.jpg
https://static1.pt-content.com/image...0302_652-1.jpg
Shock travel measurements...
Was a busy day as I had to get the car ready for a co-driver to drive it first heat, then I was to drive it in heat 2, both of us were to get 5 runs each. I didn't do any measuring during Dan's runs in heat 1 as I was busy trying to get him used to the car then I took the opportunity to videotape his runs as I wanted some footage of the car on the track from the sidelines.
Here's a taste of that
http://youtu.be/Ya8ZOd5O76Q
Getting measurements on my front shock travel was next to impossible between runs as I could not only not see the bottom of the shock, much less measure in there...I was able to get my cell phone in there and get a pic of the ziptie after a run though. And it was as I figured, the zip tie was pushed down to the base of the shock.
https://static1.pt-content.com/image...3233_202-1.jpg
I verified this when I got it back home and on the lift, both zipties on the front shocks were bottomed out but not broken off or crushed. The front suspension pretty much lives on the stock bump stops, and I think the bump stops and the shocks bottom out at about the same point. The rubber cushion of the stock bump stop keeps it from being a hard stop though which makes it un-noticeable when driving, but it is clearly happening.
https://static1.pt-content.com/image...0435_708-1.jpg
The rear shocks work as intended from what I can tell. First off I had to take the backs loose to get the boots off of them and put the zip ties on. This let me feel the dampening on them when loose. I had to put my shoulder onto the bottom of the shock to push it back up and onto the shock mount when reinstalling...I was actually surprised at just how much pressure it took to push the shock back in.
I forgot my tape measure on the grid during my runs, but I did grab my phone and take pics of the rear shocks after each run, then pushed the zip tie back up again.
Left rear shock after run 2
https://static1.pt-content.com/image...0314_031-1.jpg
Left rear shock after run 3
https://static1.pt-content.com/image...1824_599-1.jpg
Left rear shock after run 4
https://static1.pt-content.com/image...3121_653-1.jpg
Right rear shock after run 2
https://static1.pt-content.com/image...4824_077-1.jpg
Right rear shock after run 3
https://static1.pt-content.com/image...1848_102-1.jpg
Right rear shock after run 4
https://static1.pt-content.com/image...3140_845-1.jpg
I know it's not exactly scientific, and I'll do better next time I promise.
I was having a few other issues at the same time that I was dealing with, one being this...
https://static1.pt-content.com/image...3702_102-1.jpg
This course design was heavy on fast left hand turns and fast long straights with lefthanders at the ends of them and it not only abused my brakes but also my right front tire...cutting my day a bit short. I decided to not try my fifth run and I wouldn't have bettered my time anyway as it was sliding the front pretty bad on my 4th run.
I HAVE to do something about my brake setup, it was a true weakness that this course design exposed big time. Several times under hard braking it wheel hopped the rears real bad...you just couldn't drive the car to it's potential because you had to back up the corners at the end of the straights so much.
Here is my best run from the side mount view.
http://youtu.be/8YhTlaVJOV4
If you watch in the carousel, you can tell it is sliding the fronts almost all the way through. Still a fun drive though.
Hi Lance,
*To keep anyone that is following along on the same page with us, Lance has not made any tuning changes yet. I asked him to get shock travel numbers to help us calculate suspension travels. Lance's next step is to measure all of the geometry points in his front suspension, so I can calculate his camber gain, roll centers, etc. Suspension travel numbers are helpful to figure out actual camber gain/loss & other things.
Shock travel measurements...
Was a busy day as I had to get the car ready for a co-driver to drive it first heat, then I was to drive it in heat 2, both of us were to get 5 runs each. I didn't do any measuring during Dan's runs in heat 1 as I was busy trying to get him used to the car then I took the opportunity to videotape his runs as I wanted some footage of the car on the track from the sidelines.
Here's a taste of that
At the 1:25 mark, you can clearly see the rear tire hop on corner entry under braking.
Getting measurements on my front shock travel was next to impossible between runs as I could not only not see the bottom of the shock, much less measure in there...I was able to get my cell phone in there and get a pic of the ziptie after a run though. And it was as I figured, the zip tie was pushed down to the base of the shock.
Even though we know the shocks are basically bottoming out, we still need the travel #. When you're back in the shop ... and push the zip ties up against the shock body ... and compare that to pushed all the way down ... you'll know the shock travel dimension for us.
I verified this when I got it back home and on the lift, both zipties on the front shocks were bottomed out but not broken off or crushed. The front suspension pretty much lives on the stock bump stops, and I think the bump stops and the shocks bottom out at about the same point. The rubber cushion of the stock bump stop keeps it from being a hard stop though which makes it un-noticeable when driving, but it is clearly happening.
Agreed, and not acceptable for your goals ... I think. I mean, using tunable bump stops on the shocks is the best cutting edge suspension set-up. But most people don't understand them & don't want to run bump stop style suspension set-ups.
You accidentally happen to have the A-arm bump stops touching at the right spot to not upset the car. So I am assuming you will want to correct this so we're not relying on the A-arm bump stops.
If we can get the front end to travel more, transferring more load & grip onto the front tires ... that will improve your cornering speeds. But ... and this is key ... you will need a bigger sway bar to control the roll. Right now, the bump stops are reducing the roll. :seizure:
The rear shocks work as intended from what I can tell. First off I had to take the backs loose to get the boots off of them and put the zip ties on. This let me feel the dampening on them when loose. I had to put my shoulder onto the bottom of the shock to push it back up and onto the shock mount when reinstalling...I was actually surprised at just how much pressure it took to push the shock back in.
Sounds a little stiff on compression valving. Good for turning ... not good for traction on corner exit. When you increase the spring rate in the rear, we may want to soften this valving.
I forgot my tape measure on the grid during my runs, but I did grab my phone and take pics of the rear shocks after each run, then pushed the zip tie back up again.
LOL. Rookie mistake, but I like photos.
Left rear shock after run 2
Left rear shock after run 3
Left rear shock after run 4
We can see the travels are not the same, which is unfortunately typical. The higher travel on different runs can be caused by either hitting a bump, or simply driven harder with more body roll. Only you can provide us with that feedback.
Right rear shock after run 2
Right rear shock after run 3
Right rear shock after run 4
Run 3 shows the most travel on the RR shock. Run 4 shows less, which is a good indicator the RF front tire was giving up. Anytime a tire .. or both tires ... are not gripping, body roll & pitch will be less. Other than hitting a bump ... it takes grip to produce body roll & suspension travel.
I know it's not exactly scientific, and I'll do better next time I promise.
Oh sure. Everyone says that. JK. :poke:
I was having a few other issues at the same time that I was dealing with, one being this...
That is a big ol' piece of proof that you car is over working the outside edge of the front tires, due to the KPI/Caster Split favoring the KPI so much.
This course design was heavy on fast left hand turns and fast long straights with lefthanders at the ends of them and it not only abused my brakes but also my right front tire...cutting my day a bit short. I decided to not try my fifth run and I wouldn't have bettered my time anyway as it was sliding the front pretty bad on my 4th run.
Good call. If you continued running hard ... the only thing you might have learned is how to get grass & cones off the under carriage.
I HAVE to do something about my brake setup, it was a true weakness that this course design exposed big time. Several times under hard braking it wheel hopped the rears real bad...you just couldn't drive the car to it's potential because you had to back up the corners at the end of the straights so much.
The "hopping" isn't a brake issue. You have too soft of a spring back there, and the shock can't control it.
*Lance sent me his brake system specs & I calculated his front, rear & total braking force. Which will be an upcoming topic for us.
Yes, you do need more front braking force & less rear braking bias. But the rear springs being so soft ... is the main culprit to the hop ... and also contributes to your mid corner push. More on this later.
Here is my best run from the side mount view.
A few observations & tips:
0:24 Keep the late apex, but increase your degree of turning to end up with a lower, straighter exit.*
0:36 Use more of the track. Let the car "eat" by running a larger, gentler, wider radius to the outside of the track on exit to carry more speed.
0:38 Straighten out this section ... to be closer when you clip by the inside edge ... then wider when you get to corner entry.
Cone Esses: You're a tick behind in your steering making you have to turn more.
1:03 Use more of the track. Let the car "eat" by running a larger, gentler, wider radius to the outside of the track on exit to carry more speed.
1:14 Keep the late apex, but increase your degree of turning to end up with a lower, straighter exit.*
*If the handling will let you.
If you watch in the carousel, you can tell it is sliding the fronts almost all the way through. Still a fun drive though.
Cool !
Was it really 75 degrees there? It was 108 here!
Ron,
I've got planned to get the car on the lift here at the shop Wednesday morning after a car show tomorrow afternoon. I've got the part numbers of upper ball joints and hope to get them measured at the parts house on the way home tonight.
Thanks for the tips Ron. What I was really concentrating on was to find the line that got me through the tightest sections of the course with the least amount of steering input (knowing now how much more camber loss there is with the increased steering input).
For instance, during the pace lap I figured out that the large carousel near the beginning was just about the exact same radius the whole way around, so I found the line that got me through it all basically without moving the steering wheel at all once in the turn. I tried to control how it came out onto the next straight with the throttle not the steering wheel.
The run before was better in that section, but I really struggled with that next section finding the right braking spot to not leave too much time on the table while at the same time not wheel hopping under braking. I left some time leaving the carousel because I was thinking about how to set myself up for the end of the next straight.
I know I was behind every time in the esses, again I think it was because I'd upset the car before that first gate getting into them. In fact, I got scored with a DNF my first run (erroneously which they fixed after) because I went right at the first cone instead of left. I was about halfway thru the esses when I discovered that I was coming out pointed the wrong direction for the entry into the Chicago box (another rookie mistake).
#1 dealing with the hard braking zones and then #2 dealing with a going away right front tire really made for some less than satisfying runs for me. It was fun still the same, but I just wasn't getting the results I wanted.
And yes, it really was 75 degrees... Was a beautiful day for an autocross.
Lance,
I suggest you figure out what your scrub radius with your current set-up ... to help guide us on decisions about possible spindle KPI changes. If we see your current scrub radius in under an inch, it may be ok to change from your current spindles with 8.75 degrees KPI to a spindle with slightly smaller KPI .. like 8.0 degrees. On the other hand, if we see it is a couple inches or more ... and there are no plans to put wider wheels with more back spacing on ... we should stick with the 8.75 degrees.
As you know, I measure everything & work it out in a suspension software. But for the average car guy in his garage ... do this:
a. Determine the EXACT centerline height of your front spindle (Pick one ... left or right ... doesn't matter) ... with all 4 wheels & tires on the ground ... suspension loaded. It is going to be around 12-13". Let's say it is 12-3/4".
b. Remove that tire & wheel. Put a good, non-leaking jack under the the ball joint (or other secure point on the lower A-arm) & jack the spindle back to that exact same height ... in this example 12-3/4". (you are simulating ride height ... with 3 tires on the ground & a jack under one front corner.
c. Using a string, laser, straight edges or whatever works for you ... make a true line through the CENTERS of the upper & lower ball joints ... projecting onto the floor. Mark it. (I use blue 3M masking tape, so I'm not marking up my floor permanently.)
d. Ideally ... you want the mark on the shop floor to be more than a dot. What works best is a line 8-12" long TRULY PARALLEL with the car.
e. Put your tire & wheel back on ... and set the car on the ground.
f. Find the true centerline of your tire tread ... and measure the distance to the line you put on the floor. Whatever that measurement is ... in inches ... is your scrub radius. This method may not be dead on accurate ... but it'll be close enough to know what you're working with.
Attachment 78317
Please post the Scrub Radius dimension, so I also know what we're working with.
That shouldn't be that hard to do, can do it with the rest of the measuring when the time comes.
To figure the true centerline of the tire tread, maybe put a straight edge on the floor on the inside and outside of the tire, measure the distance front and back to make sure they are parallel then measure to find the center between them?
I have two drive on lifts at work, one is pretty dern level both directions, the other is level side to side but the back of it is 3.5" lower than the front. This lift is MUCH easier for me to get access to. I have to move 2 cars and quite a bit of stuff to get access to the level lift.
I'm thinking about cutting 4 pieces of 4x4 posts and putting them under the back legs of the lift to get it much closer to level. Obviously if I didn't have to do this, it would save me more time for more accurate measuring.
Ron, what do you think I'll have trouble getting accurate measurements on if the back of the car is sitting 3.5" lower than the front but otherwise level side to side? Is that an issue that I would be better off dealing with?
The lift ramps are somewhat dirty, my plan is to cover the majority of the areas that will need reference marks made on them with duct tape as it's stickier and stronger. I plan to use strings with weights on each end to replicate the centerline of the car and the front tire centerline. This too should give me more time to concentrate on the rest of the measurements.
I'll spend the next couple of days getting everything in place and probably hit the actual measuring part on Saturday.