Autocross Sunday!

M

mmarshall

Member #053
Location
Florissant
First Name
Mike
Last Name
Marshall
Autocross Sunday May 8th family arena.

If you want to participate be there by 0730.

If you want a ride in the coupe or spectate I am running between 11:30 - 1:30. Both are free. It is also kind of like a car show as everyone on the lot is a car guy.

I just got my Hankook track tires so the times should be improved. I took my 7 year old along on the ride to scrub them in and heat cycle them. The lateral grip was so great that she bruised her leg on the sidewall from not being able to hold her legs still. If you turn the wheel fast enough it feels like you are in a paint shaker!
 
Uh Mike, You do realize tomorrow is Mother's day. I'd love to see you run and I got my car working now, but I'll have to miss. Good luck though and bring home another win.
 
I'm hoping to get out there to see you about 10am, for a couple hours.
My daughter is taking my wife to church & breakfast, I was told it's girls' morning out, no boys. (finally! kids are a good thing! ;))
 
Mike had some great times today. I took a couple of pics, I'm sure a video will show up soon on his run :D

Mark P took a ride with Mike's co-driver
P1010391.png


At the starting line
P1010392.png


And they're off
P1010394.png


Down the stretch they come
P1010397.png


P1010398.png


P1010401.png


A Ferrari 458 was there, not participating because it's not broke in yet. Look at the size of the pizza pans for front discs :eek: Those are 20" wheels!
P1010399.png


A Lotus was there
P1010396.png


Along with a few S2000's
P1010395.png


Mark P, Keith, Rich and I were there to push Mike to not hit any cones :D Mike cut off 3/4 of a second on his second run at 37.0025. Not sure he ran any faster after I left, but he thought the other cars in his class couldn't run any faster. Great job Mike!
 
Last edited:
Tim, good pictures. Mike thanks for the ride, wish I could have stayed a little longer.
 
It was great to have Tim, Keith, Mark P. and Rich come out to spectate. Thanks guys for coming out for the visit and thanks Tim for the pics. I enjoyed taking Rich and Mark for a ride at speed. It was nice having some Cobra brothers onsite. Would be cool sometime to fill an entire heat with Cobras.

I ran the new Hankooks for the 1st time and it was my 1st time driving on a R-compound. They are much stickier and provide for higher speeds everywhere on the track.

Here is my fastest run of the day:
http://www.youtube.com/watch?v=AtEvxwSdMDE

The next run was even faster until I spun the car at a fairly high speed. I was suprised by how fast it came around and my countersteer did nothing. Too bad because the time on this run would have been good:
http://www.youtube.com/watch?v=2VeMZplxcIw
 
Mike, did you get your steering (was it under-steering before?) and brakes sorted out this weekend of do you have additional tuning?
I thought I heard you say you tweaked the rear for as much bite as you could get, so you had to de-tune the front a bit(?) to balance it.
It looked like it was handling VERY well. I know the ride was a thrill! Thanks Again!
 
MPTech said:
Mike, did you get your steering (was it under-steering before?) and brakes sorted out this weekend of do you have additional tuning?
I thought I heard you say you tweaked the rear for as much bite as you could get, so you had to de-tune the front a bit(?) to balance it.
It looked like it was handling VERY well. I know the ride was a thrill! Thanks Again!
Click to expand...

The brakes are probably 80% of where I would like them to be. I changed the system from manual MC and PBR fronts and Cobra rears to GT mustang fronts and same rear. This made the 2 closer in power. I then added hydroboost and placed a proportioning valve in the front loop. I did some testing and ended up fully closed on the proportioning valve. This reduces the front brake pressure by 57%. The rear could still use some more power but the front is reduced down as much as it will go trying to balance the system. As you saw during your ride the car does not want to swap ends under braking, so until it does I will pursue more rear brake.

On the handling I reduced camber from -2 degrees to -1 degrees. This reduced the grip on the front to give the back a chance to keep up and reduce the oversteer. I now have an issue with the new tires. I am seeing some wear on the outside shoulders on the fronts. This tells me I need to add some camber to even out the wear....but this will cause even more oversteer problems. I am now thinking about adding some aerodynamics to the rear. Does anyone have a metal brake????? Time to bend up some aluminum!

Thanks for coming out! You guys are always welcome in my car.
 
Mike, regarding your brakes and tire wear, my .02 worth:

- I get what you are trying to do, however, millions of cars are on the road that big car companies have approved with more brake bias to the front. Whenever you are braking hard, it seems to me the weight bias advantage that these cars have (Mine for instance 54% rear to 46% front) is now shifted to the front of the car thus requiring you to have more bias to the front. The idea, to my understanding, is to provide more than 70% of braking to the front tires, and the rest to the rear. This way, the 'light' pressure to the rear prevents the rear from kicking out or locking up. I really think your other brakes that you swapped out may be the better option, but not knowing your car, maybe not. Also, how do you have the lines coming out of the master cylinder? Do you have one reservoir that is larger than the other? Have you looked at separate master cylinders for the rear and front?

- Tire wear - how much do you play around with tire pressures? I know it makes a huge difference in my tire wear on a road course. For instance, the first runs I could tell I wasn't wearing all the way to the edge of the tire, so I increased the tire pressure, got better, I increased some more and achieved full contact on the pavement. I started with 20-22 and ended up with 24-26 psi on cold tires. I'm not sure your tire wear is indicative of Camber adjustments. Maximum cornering force is achieved when the camber of the outside wheels relative to the ground is about -0.5 degrees. A slight negative camber in a turn maximizes the tire contact patch due to the way the tire deforms under lateral load. Hence, it is good to have some negative camber to increase cornering force.

Another reason why it is helpful to align your suspension with a slight negative camber is that camber will change with suspension travel and body roll. Most suspension systems are designed so that camber increases with more suspension travel. However, camber relative to the car's chassis is not the same thing as camber relative to the ground. It is camber relative to the ground that affects handling. Therefore, even though camber relative to the chassis is made to increase, camber relative to the ground may actually decrease on the outside wheels if there is substantial body roll. To counter this tendency, it is important to use negative camber and to control body roll.

The only drawback to negative camber is increased wear on the inside of each tire. Since the top of the wheel is leaned in, the car is riding on the inside of the tire while it is on straightaways. In a corner, suspension travel and lateral forces on the tire's rubber compound combine to straighten the tire relative to the ground. Therefore, the car rides evenly on the tire in turns, which improves cornering ability. However, extra time spent driving on the inside of the tire causes that part of the tire to heat up and wear. This effect is small if you avoid adding too much negative camber. So, wear on the outside of your tires would indicate you don't have enough negative camber.

Can you take a picture of your tires showing the wear indicators?
 
Purple Venom said:
Mike, regarding your brakes and tire wear, my .02 worth:

- I get what you are trying to do, however, millions of cars are on the road that big car companies have approved with more brake bias to the front. Whenever you are braking hard, it seems to me the weight bias advantage that these cars have (Mine for instance 54% rear to 46% front) is now shifted to the front of the car thus requiring you to have more bias to the front. The idea, to my understanding, is to provide more than 70% of braking to the front tires, and the rest to the rear. This way, the 'light' pressure to the rear prevents the rear from kicking out or locking up. I really think your other brakes that you swapped out may be the better option, but not knowing your car, maybe not. Also, how do you have the lines coming out of the master cylinder? Do you have one reservoir that is larger than the other? Have you looked at separate master cylinders for the rear and front?
/QUOTE]

Tim, I'm going to have to disagree with this line of thinking. These are not factory produced passenger cars, they are street legal race cars. If your weight bias is 54-46 then the brakes need to be the same. As these cars have a very low CG and stiff suspension, they have very little forward weight transfer. In fact the FFR cars front suspension has anti-dive built into the geometry. Your idea of 70% front 30% rear is great for a daily drive with 70-30 bias under braking, not good in a roadster with 55-45 under braking. Mikes rears arent locking up, so until they do he is getting the most out of his brakes. You should use all 4 brakes on the car, not just all the front and 1/2 the rear. :D
Click to expand...
 
So, from this picture:
P1010398.png


You are telling me there is no weight transfer to the front? Maybe if he had the 750# springs, but with the 500# springs? Hmmmm..... Anti-dive? Explain further, not aware of this. EDIT: I couldn't wait, did a little research, and it's complicated to explain that's for sure, but as I understand it, on our Roadsters (maybe the coupe too) the Upper Control Arm has a slight pitch to it - is this what you are referring to? See pic below of ERA's front suspension, notice the rear tilt to the upper control arm.

Maybe I should move these last few posts to a Tech area? Great explanation of it here - http://www.chassishelp.com/antiprodive.html
 
Last edited:
Tim there is some weight transfer but not as much as in most production cars. Even some really well sorted cars:
DSC_3410.png
 
Mark thanks for the warm welcome tonight. I thought of you when I saw this picture. Body roll is not all bad. This car does very well even with some roll. If you come out to one of the events you can see this car do his thing as he is a regular.

Rick_3_alt.png
 
Last edited:
So here is my take on Mikes brakes, over the last three autocrosses he has achieved a very balanced system, however not getting 100% braking from either the front or the back, the front reduced 57% and the backs not locking up yet, but the system works for now. So where does he go from here to improve it?
My thinking would be to remove the proportioning valve from the front line and put it in the rear along with 12-13 inch rear brakes, this would allow 100% front braking force and you would be able to dial down the rears to balance the system.
So heres the score
Mikes current system 57% front +say 95% rears = 152%
My proposed set up 100% fronts + say 80% rears = 180% Who wins!

Thoughts!!
 
Keith I agree with what you said but don't forget that with the hydroboost I have plenty of power to lock the fronts even with the 57% reduction. So here is where i think I am:

100% front (they lockup) + 80% rear (unable to lock without 1st locking the fronts) = 180%
I can lock all 4, but that gets expensive when race rubber is $1,000 a set.

where I would like to be:

100% front + 95% rear = 195%

I would like the rears to lock slightly after the fronts. If the fronts are already locked then there is no steering or turning so the back should not come around.

I agree that at this point I need more power to the rear and then dial it in with the PV. In a couple of hours I could replumb the PV to the rears if that is what it takes. I could even install an additional PV in the rear and have total control over the balance.
 
I think you may have missed my point, currently you are using 100% of the 57% available in the front, and 100% of the rears.If you went back to no PV in the front and were then using 100% and went to larger rears you are essentially improving braking by 43% in the front alone and depending how big you go in the back letting you balance it out.
Wouldn't this allow you to go deeper into turns without locking up having more overall braking thus improving times?
My feelings are you need as much brakes as you can get,I am thinking upgrade the rears rather than turning down the fronts.
I am not knocking your setup ,mine is nearly identical except for the PV being in the rear for the future rear upgrade,was just wondering what you would do next to upgrade and get everyone elses opinion if my thinking is right or wrong or otherwise.
 
Keith, get rid of the PV in the rear line. Even at full open there is a slight reduction in pressure.
Mike what kind of pads are you running on the rear. There are a lot of grippy ones out there. I know thats on my list, better rear pads!
 
You must log in or register to reply here.
Back
Top