Suspension tuning - brake dive

[Sieg]

Originally Posted by gerno

Thanks for the guidance. I'll be swapping the MC this week to the smaller bore. I had forgotten I had an extra one sitting around. I'll also swap my smal block (600lb) Hotchkis springs in this week for the QA1 coilovers. I figured since many other people were using them they would be ok but apparently not so much. For now I'll use the shocks alone with the other springs but will eventually sell the coilovers and get some good shocks

Call Tobin at Kore3.com for a brake system recommendation. I went with a 7/8" Wilwood manual from factory '69 power and couldn't be more satisfied with the modulation and pedal effort.

[JRouche]

Hmmm? Ok Ill go off a lil. Ok wait? Ill stay on track for a second. The 350lbs springs are a lil light for your car. I like the advice with the 450lbs springs. And like smoker said, 700lbs (I think yer 600lbs are too tight) is not needed.

I dont mind too much load transfer (front end dip). It loads the front end up so it can really work. Too light up front and the car will be loose. And YES!! Loose in racing can translate to fast track times. But ONLY if its a track only car. Race cars are NOT street cars.

I personally like a loose car for the track if I know the car. But I never want a loose (read light on the rear and basically a level feeling car) for the street.

For you I would stiffen up the front springs some and focus on the rear shocks a lil. If they are adjustable I would tighten them up for rebound. Make them hold the rear end compressed for just a second while the car is turning and braking. Something as simple as the shocks will help with an apparent dive issue.

And I say apparent dive issue (with braking). I dont have a problem with it. And Im talking about a STREET car that likes to see the track sometimes.

I have driven front heavy street cars to their maximum adhesion on a closed track. Big heavy (on the front cars). Driven them to the point of major understeer, basically trying to rip the front tires off the rims with turns and braking. LOL Tires never came off but Im sure alot of rubber did.

At first during this training session I was slow. But after a few more laps and understanding the car I was able to increase the lap speeds and bring the times down.

My point? Even supposed heavy front end cars can dig their way around the track. Dont worry to much about how it seems to dig in cause you might be actually hitting the track at a decent speed.

A car can feel out of shape and look out of shape but the clock will ALWAYS tell the true story. JR

[gerno]

I agree Tobin is the brake expert. Since I have the other MC already I'll give it a shot first. I used it before with the same brakes but not the hydroboost so I know it matches well with the calipers so it should work. I only have the current large bore becuase it came with the hydroboost.

I'll work on adjusting the rear shocks a little. They are only single adjustables but I'll play with them a click at a time and see what happens. The 600lbs springs I have are not coilovers, they are standard full sized springs. Since I already have them I was thinking to give them a shot but I just noticed the cost of new QA1 springs is not too bad.

At this point I am actually waiting on my new trans to be delivered and the car is inoperable for a while. I'll focus on the brakes and the shock adjustments first then after the new trans is installed will decide if I'll use the 600lbs or purchase some new coil over springs.

[Chassisworks]

Gerno,
A couple of us from Chassisworks were out at Mather the same day as you. We noticed your car porpoising around the course and commented that you definiately needed either a better set of shocks or some serious adjustment. I agree that the 350# front springs are too light, assuming they are 9"-10" free length.

Also, most of the time on a car like yours we would recommend either a 1" or the 7/8" master so you're going in the right direction.

If we see you out there next time we'll make sure to introduce ourselves and maybe we can help you out a little.

[gerno]

Chassisworks - I've never heard a car referred to as porpoising but I would have to agree that's what it felt like. Can you explain a little more about what you saw for my reference? I assume my driving skills also had something so do with it since it was my first autocross. Do you have any quick tips on areas I could possibly improve my driving skills?

Both my front and rear shocks are single adjustable QA1's and were set on setting 7 of 12. In addition to the stiffer spring, do you think simply adjusting them to a stiffer setting would help from what you saw?

I'll be around more often, feel free to come say anytime or let me know what car is yours and I'll come by.

[Sieg]

Gerno - One way to help you better understand the valving is to adjust the shocks full soft and make a run, then adjust to full firm and make a run. Then you'll know the extremes and could do another at 75% firm and you'll have a first hand idea of what your shocks are capable of and if your springs are in the ballpark.

The spring and shock work in harmony so if one isn't complimenting the other you're in a compromise situation. If the spring isn't holding up it's end of the deal, that little shock is working overtime.

[Chassisworks]

Porpoising is a term we use all the time with the drag race guys but it applies in autocross too. In simple terms what happens is the car hooks then loses traction in quick succession. The most common reason is because the shocks do not have enough extension/rebound dampening. The suspension extends too quickly so it's not applying the power smoothly in the rear which upsets the front. The opposite holds true under braking in regard to the front. That's an oversimplification but hopefully it makes a little bit of sense.

Lino (Psydwaze) will probably be at the 6/9 event in Stockton. I'll have him keep an eye out for you. I have to go to a birthday in SoCal.

Feel free to swing by the factory m-f if you have questions. I know you don't have our parts but we're always happy to help out a local guy.

~Carl

[gerno]

Sieg - good point with the adjustment. Funny how I forget the simple things first. I just wish the front shocks were a little easier to adjsut. The rear can be adjusted with ease but the front know is stuck deep in the spring pocket. Either way I'll get it figured out.

Chassisworks - I can't make the 6/9 event but will aim for the next one. I sold the trans from the car this weekend and am waiting on the new one to arrive. The car will most likely not be ready until the mid to end of the month. I might take you up on the offer to stop by when it's back together. I talked to some of your guys at Autorama and wanted to come see the shop.

This first time out I figured I needed to focus on the driving aspect first since even with a completely wrong setup the car is still better than me. Considering I knocked 6 seconds off my time I think I did ok learning. With a little intellegence behind the setup I'm excited to see how much better I can do.

[gerno]

I took some advice from the comments here and made some changes to the car. I changed the front spring rate from 350lbs to 500lbs. I also fixed an issue I had with the plumbing and pedal ratio of the brakes. Yesterday I went and did some testing at T-Hill. The car feels much better with the stiffer springs and corrected brakes. I'm amazed that the car is actually smoother with the springs when the shocks are on a light setting. I expected a harsher ride

That said, I also had my shocks on a mid range setting and decided to go full stiff to see how the car would react. The car was incredibly stiff but did handle well. I noted much less noise from the tires. Only issues I felt was a harsh feel under braking, ouside tire wear on the driver side front and the rear feeling loose in the turn.

I decided to take 2 clicks of adjsutment out of the front shocks and to increase the tire pressure from 38 to 41. After these adjustments the car was more stable and the rear felt more solid. I can't tell about the tire wear but there was much less tire noise in the corners. The car was still a bit harsh (for lack of better words) under braking but seemed better.

Hard to say if I was faster or not becasue I am too much of a novice for timing with NCRC but compared to my first time at T-Hill the car was 100% better. The car was not diving near as much under braking and seemed to be pushing much less in turn 11. I'm very interested to see how the car reacts with these settings on a tighted autocross course.