2014 Event #4

[STLMARSHALL]

I ran event #4 today and continued to be amazed by how much better the car is. It understeers in some places and gets loose in others, but remains controllable no matter what. My raw time today tied my best finish ever back when I was on fresh R-comps. Not too bad for my 100 TW street tires. What is cool is that there is even more time left in it. I have no doubt there is another second left in it. I was the 6th fastest car on raw times and all the other 5 were some really fast cars on Hoosier bias or A6's. One of them was a EM national champion Sam Platt. I was only .2 sec behind a really fast CP car on Hoosier Bias tires. What a blast it is to finally have a car that I can push really hard everywhere on the course. The NT-01's are also holding up very well.

Here is my best run of the day. I did get a bad cone call which I was told only moved 1/4" and was still in the box. Even so it was a very fast run.

https://www.youtube.com/watch?v=NjT8VyvBVpo

[skullandbones]

Congrats! Looks like you are in full control. Enjoy these videos. Thank you, WEK.

[CraigS]

Now you have it working. If it pushes in some spots and is loose in others that is about perfect. Be sure that the push isn't from coming into the turn too hot. And read up on trail braking which I can't always get right but really helps when I do.

[STLMARSHALL]

Thanks WEK! Glad you enjoy them.

I agree Craig. After observing my front tire wear I can see that 1 degree of camber is not nearly enough. I am going to jump to 2 degrees for the next event and see how it goes. I will then bracket from there. Also my front tires are overinflated and is also probably causing some understeer. Now that I am able to catch the rear when it steps out I am ok with slowly dialing out some of the understeer.

Currently the only oversteer I have had is under trail braking (I run a lot of rear brake bias), exiting tight turns under power, and during slaloms. Understeer comes during steady state sweepers and increases as I accelerate. I actually try to run into a corner too deep because that gives me an opportunity to trail brake the car which gives you full control of the rotation of the car. I have begun to master the transition from a trail braking slide right into controlling the slide exiting the corner with power. When it is done right it is awesome!

[Jeff Kleiner]

Really nice smooth run Mike!


Also my front tires are overinflated and is also probably causing some understeer. Now that I am able to catch the rear when it steps out I am ok with slowly dialing out some of the understeer.



You mention that your fronts are overinflated which leads me to believe that you would like to lower their pressure...doing so without a corresponding change to the rear pressure will increase understeer. To "dial out some of the understeer" via pressure changes would require raising the fronts &/or lowering the rears, right?

BTW, since we've conversed regarding your experiences with the NT-01s following some experimentation I feel like I hit their "sweet spot" with my 3rd. event on them last week. Going with 20# in front and 22.5# in back gives me just a touch of oversteer. A couple of pounds more in front or less in the rear and it gets a little too loose. Ambient temp was around 80; we'll have to see if these pressures continue to work well on hotter days.

Cheers,
Jeff

[skullandbones]

I didn't see your rear end setup in your signature. It must be a 3 link or an IRS but which is it? I'm looking at some sort of watts link with a 3 link so I'm interested in hearing anything about rear suspension experiences and ideas. Thanks, WEK.

[STLMARSHALL]

Thanks Jeff.

I would answer with a definite maybe. For a given day any tire has a optimum pressure for grip. Any change higher or lower will move away from the best grip. If my fronts are already above optimum pressure then raising it even more would just make matters worse. If raising pressure always provided more grip then we would end up running 50+ psi always chasing more grip each run. I tend to manage my pressures via tire rollover. I run the lowest pressure I can without the tire rolling over and wearing past the tips of the diamonds. On a cold day that will be less pressure as the tire has less grip and will not rollover much at all. On a warm day though the grip is high and the tire rolls over more easily and requires more pressure.

The REAR: I started out at 25 psi (NT-01) on the rear last year and it seemed to work ok. Now my car is performing better and seems to be generating more grip thus is rolling the rear tires over even more. Last event I started out at 27 psi cold and the rollover was perfect all day long as was the grip. I ran 25 psi the previous event and they were rolling over way too far ( towards the bottom of the diamonds).

The FRONT: I ran 28 psi the first event to induce some understeer via over inflation. It worked and the tires did not rollover at all. This event I stayed with it and am now seeing a little more rollover but am also seeing some strange wear in the middle of the tire. This leads me to believe that they are over inflated. Also I am not seeing any wear on the inside shoulder which tells me that I need more camber to use more of the tire. Next event I will try 2 degrees camber and 27 psi front and rear and see how it goes. Some day I will get around to buying a proper probe style tire pyrometer and doing this the right way.

BTW here is the same run from the outside. You can see the slight cone wobble near the start that cost me a great index position.

https://www.youtube.com/watch?v=-VrGjVASlyo

[Greg23]

Would an infra-red pyrometer work? They are pretty cheap and all over the place. You can also use them for exhaust temps and checking heat loss from your doors and windows at home!

[STLMARSHALL]

Greg not very well. The temps you are looking for on the tires are deeper into the rubber. The surface cools quickly after pulling into the pits and throws off the readings.

This is what you need:
http://www.speedwaymotors.com/Longacre-50635-Rebco-Electronic-Pyrometer,893.html

[Jeff Kleiner]

Yeah, kinda like a meat thermometer stuck in the Thanksgiving Butterball. Hey....wait a minute....my wife has one of those in the kitchen drawer...hmmmmm...I wonder???? ;)

Jeff

[CHOTIS BILL]

Here is a link to Loneacre pyrometers. http://www.longacreracing.com/products.aspx?itemid=1721&pagetitle=Tire+Pyrometers. I purchased one many years ago and even though expensive was invaluable in adding to my data base. For me half the fun of racing is gathering data, analyzing what is going on and then figuring out how to optimize every adjustable part on the car. One really cool feature it had was it calculated the rate the probe was heating up and would predict the finial temperature which saved time waiting for the temp to stop going up. I did take part in a test using both a probe pyrometer and an infrared pyrometer and the temperatures with the infrared one was lower but the spread across the tire was about the same which showed the infrared pyrometer might work OK for setting camber and tire pressures but not for getting accurate temperatures. One point that is often overlooked when using a probe type pyrometer is the first time you insert the probe it takes heat out of the tire to heat up the probe so to get more accurate readings you should insert the probe and get a maximum reading and then rotate to a new position to get the first real temperature to record. I found the second reading would be around 5 degrees higher that the first.

Bill Lomenick

[STLMARSHALL]

Bill thanks for the info, good to know.

WEK I am running a 3-link with FFR Konis. I have modified the lower shock and panhard bar mount points. I lowered the shock mount points to recover some of the travel I lost by running a 3.5" ride height.

Jeff I am trying to figure out how you are running those low pressures without the tire rolling over too much. I am wondering if you will end up cording a outside shoulder down the road.

[CraigS]

I don't know what Jeffs front is aligned to but you will find that more negative camber allows lower pressures. Realizing my A6s are completely different, I am at 2 3/4 camber and run as low as 16 in the front on colder days. Then up to 18 now that it is warmer.

[Jeff Kleiner]

Mike,
I have 2 degrees negative camber but with 8 degrees of positive caster there is a ton of dynamic camber gain when turning. On the Nittos the line is right on the point of the triangle indicators in back and ~ 1/8 off in front. I ran the Kumhos a couple of pounds lower and showed the same rollover. Because I keep the car a little loose I always show more rollover in back than the front. Keep in mind that the courses I run are fast and flowing; if they were real tight parking lot style layouts it might well be a different story and indicate working the outside of the fronts harder.

BTW, watched the video---you got robbed on that cone call. If that was out of the box it must have been part way out before you wiggled it.

Jeff

[STLMARSHALL]

Thanks Jeff. I am now running the same alignment specs as you so we will see how the front does. As for the back it was rolling over pretty far at 25 psi. I am now on my second season with these tires(rear only) so maybe they are getting better with some age causing them to roll over further. The fronts are new so maybe they will get better also.

I agree on the cone call. Oh well stuff happens.