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Discussion Starter #1
Just completed a two day Evolution Performance Driving School and can't express how much fun I had but also how much it opened my eyes and I learned a ton!

https://www.facebook.com/evoschool/

Completed two autox last year with the stock koni's and Nitto 555's. Car pushed / under steered like crazy even though I had the front spring collars cranked down about as far as possible while still maintaining any resemblance of a comfortable ride. I still like to drive it on Sundays! :)

So this year decided to get an extra set of rims and put on the Potenza 71R at 32 psi all the way around. What a difference, the car sticks like glue and love the feel/feedback of the tires (once warm). I am not running any type of sway bars front or rear but the car didn't push through the corners anymore but did have a huge tendency for the back end to come around during heavy deceleration and turn in. Although the driver, me, was the culprit the instructors mentioned reducing tire pressure in the rear by 4-5 psi. Also mentioned that I need to adjust my brake bias to allow the engine compression (2nd gen coyote) to take care of some of the braking. Currently too much rear bias. I am running an individual master cylinder for the rear but the brake bias bar is kicking my butt. If I adjust to get more bias bar onto the fronts, I am running out of pedal travel (I have all the threads extended already on the front cylinder). Any suggestions!

Have also been reading posts for hours and see a lot of information about front bars keeping the car flat and rear bars helping with the back end coming around. But I also see posts where rear bars are unhooked completely. I like the 'frito' VMP rear bar but again, am I trying to solve problems by throwing parts on the car when really I could fix it with better foot modulation. So looking for any feedback from those of you running sway bars.

So getting long winded but just wanted to post about how beneficial the school was. Started with times in the 37 second range and by the end of the school, turning consistent 31's, even when the course was reversed. Can't say enough about how knowledgeable and professional these types of schools are!! Can't wait to get more seat time.

Couple videos
https://youtu.be/ng0fRvJt6n4

Slow motion of a small tail slide at the 45 second mark.
https://youtu.be/yjTGeFYMOdY
 

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Unconventional Builder
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Thats great, good improvement. I would stick to just driving this season with out any new parts. You can fine tune your car with tire pressure and go fast pedal pressure.

What brake pads?

What size Potenza 71R tires are you running?

What pressure you noted 32 in post most of us run mid to low 20's in a variety of tires.

Unfortunately the back end coming around is not mechanical its driver, I still do it almost every event. Last one full 360 and kept going. You need to go slow to go fast, you are entering that section tooo fast.
 

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Discussion Starter #3
What brake pads?
Running the Forte's Wilwood package front and rear and not exactly sure which pads, will have to do some digging.

What size Potenza 71R tires are you running?

What pressure you noted 32 in post most of us run mid to low 20's in a variety of tires.
Running 255/40-18 in the front and 275/35-18 in the rear. Was concerned too low of a pressure would cause the sidewall to roll over too bad. One of the instructors mentioned the same thing, low to mid 20's. Still learning. I have signed up for another autocross on the 23rd so will drop the pressure and see how that feels.

I appreciate the feedback. Can't wait to get back in the car!
 

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Unconventional Builder
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A good tire pressure to start would be 24 in all four. Once you are driving hot tire pressure is what you monitor. As soon as you get back to grid check tire pressure it should be at least 3 lbs higher if you are getting heat in tires. Let air out til they all read 24 lbs. On your next run see what is going on if you feel like the car is pushing, understeer, increase rear pressure. If the rear is too loose reduce rear pressure. Make adjustments in 1 lb increments. This is very time consuming and experimental, makes notes. You may also find as the outside temp rises your pressures need to change.
 

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With the factory spring rate these cars naturally understeer. Driving style can exacerbate this condition.

Cranking the spring collars only changes ride height, not spring rate.

Adding a bar to the front without a corresponding change to the rear (more spring or bar) will make it push worse.

Alignment settings and ride height play into the over/understeer equation. More negative camber=more front bite. More positive caster=additional camber gain when turning.

I've not run the RE71s but the Kumho XS and Nitto NT-01 that I have used like 18-22 PSI depending on ambient temp and the track surface. I often wind up with a 1, maybe 2# split front to rear. Again depending on temp and surface 1# can make the difference between neutral and loose or push.

FYI, with my setup mine is neutral to a bit loose; 3 link rear, 750# front and 500# rear springs, 1.5 to 1.75 negative camber, 8 degrees positive caster, 3/32" toe in, 3.75" front and 4.25" rear ride height, tire pressures as above.

Have fun with it!

Jeff
 

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Sounds like a valuable and fun event. I've done an autocross at that location in Salina before. It's a neat space with plenty of run off. It was in my 88 4cyl mustang, but I do remember the car being particularly tail happy there. I would blame the surface since your experience was similar, but it was likely the nut behind the wheel. :eek:

I am signed up for an autoX school with the KC area SCCA on April 29, an an event the following day. Definitely looking forward to the school to get some tips and feel out the car a bit more. I did an autocross with the newly registered FFR last fall, but it was in a very tight space and I don't think we even broke 35mph. The cobra was out of it's element on that course with the gearing and width of the car, but I saw an old mini that got around great.
 

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Discussion Starter #7
Appreciate all the feedback everyone!! Will drop down to 24psi and see how it feels.

Jeff, running 1.5 degrees negative camber, 7 degrees caster and a 1/4 toe in the front with about an 1/8 in the rear with the old IRS. Converted from manual to power steering (Fast Freddies) over the winter which made autoX'ing much more enjoyable.
 

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...Jeff, running 1.5 degrees negative camber, 7 degrees caster and a 1/4 toe in the front...
Are you sure about that toe?

That's awfully heavy and will will be really hard on tires...AND...can promote understeer on initial turn in (hmmmm???).

Jeff
 

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FFCobra Craftsman
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Which dual MC do you have Wilwood or CNC? I would change that front toe to very close to zero. Get an old school bottle of white shoe polish w/ a sponge on the top. Put a glob at the edge of the tread 2-3 spots around the circumference. This will allow you to see exactly how far it rolls over as you drop pressures. I would expect to see it go to at least the tip of my red arrow, maybe a little further.

BTW, new polish every time you change pressure.
 

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...Put a glob at the edge of the tread 2-3 spots around the circumference. This will allow you to see exactly how far it rolls over as you drop pressures. I would expect to see it go to at least the tip of my red arrow, maybe a little further.
I just stepped into the garage and snapped this photo. No chalk or shoe polish but you can clearly see where the heat has been showing the roll over:



This would have been after running with 20-21 PSI. The little triangles are actually to show where the wear indicators are across the tread but are often used as a guide for roll, which isn't a bad rule of thumb for a starting point.

Cheers,
Jeff
 

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Discussion Starter #11
Looks like I need to take a little toe out of it.

Craig, I have the CNC triple, also running Forte's hydraulic clutch setup.

This is the rear, looks like too much pressure based on what you guys are stating.


Front looks a little better.
 

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FFCobra Craftsman
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RE: CNC. I have had one since about 2008 and am quite happy w/ it. Here are few thoughts from my experiences. I adjust the pedal pushrod for nearly zero free play to that aluminum Tee shaped piece. At rest that big aluminum Tee should be fully to the rear, against the main housing. I adjust the individual MC pushrods for the same near zero freeplay. These are the biggest pain in the a$$ in existence. The rubber bellows are very difficult to work with. Hard to move out of your way and impossible to work back onto the MC after you are done. There must be freeplay in all these pushrods but every little bit gives you more slop in the pedal before something happens. Since the Tee is now at a fixed position, The MC pushrods can be adjusted individually to get rid of all freeplay as the bias bar rocks in the tee. Usually you want the bias bar, at rest, to be a little closer to the front MC. This is because the rear MC, being smaller diameter, will move more on brake application. So, if you start out w/ the bias bar closer to the front MC, it will move closer to the rear MC upon brake application. One thing to watch for, since your bias cross shaft will not be at an exact 90 degree angle to the MCs, if you move it much, more than maybe 2-3-4 turns, you will affect the free play in the MC pushrods. So, as you are making adjustments to the bias, check the MC push rods to see if they need to be adjusted again.
 
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