Cobra max cornering capability
 

Took my ERA 427 Cobra to Road Atlanta yesterday for a track day. I also had a G-Tech accelerometer device in the car and was looking at the results on my PC. Was wondering what the max cornering capability is for this type of car. I know there are lots of variables, but would be interested to hear what experiences others have and how you can actually measure what the limit is for a car and set-up.

I guess my ultimate question is to understand how close to (or in my case how far from) the limit am I driving? As an example, I noted on some laps I took turn 1 at .8 lateral g's, and another lap up closer to .9 g's. If the car's limit is .95, then I feel I was pushing it pretty good. If it's 1.2, then it's clear I'm getting no where near the car's capability.

Also interested in any tips on how to properly assess the information from the G-Tech to determine which numbers equal the fastest times. And also, what would be the first things to look at from a car set-up perspective to improve handling. Of course, the first thing to improve is the driver's skills :)

FYI - car is an ERA with a 427 side-oiler, Tremec TKO 600, Goodyear big letter "stock car special" tires, front roll bar, Jag rear suspension, with dual coil-overs. Weight with me in it is 2930 lbs, and considerably less with me out of it ;)

Thanks!
Scott

I have a rather thick book that comes with my ERA. The history of the car, original documents, receipts, pictures etc. Well you made me 'drag out the book'. :D

I recalled a letter from BFGoodrich to ERA regarding testing of lateral G's. It's dated June 28, 1984. Running BFG Comp T/A's, 50 series, the ERA test car posted a 0.967 G on the skid pad. The letter noted this was signifcantly higher than similiar testing in the spring of 1983. BFG noted that this was a 'streetable' car and thus achieving such numbers was remarkable.

What I find even more interesting is that the BFG Comp T/A's are pretty well known for 'lacking traction'. In my opinion running Comp T/A's on a Cobra is just asking for trouble (spin out's, etc.). I am confident the test would have exceeded 1 G had they used "Bill Board" Goodyears! :D

When I first 'tracked' my ERA (Bill Board Goodyears and Side Oiler) I was absolutly blown away at how good it handled. The front stuck like glue, all the talk about Big Blocks being to heavy, blah blah blah, just didn't hold water. The cars handling was indeed 'remarkable'.

I agree with Excaliber. I was able to take an all cast 427 CSX out for a test drive last year. It cornered like it was on rails. Granted, I wasn't on a track and could not push it to the limit, but I could feel no difference in handling between it and my SB Classic Roadster. I had also been told all the BS about how the BB just don't handle!:LOL:

On a skidpad, the ultimate cornering power is highly dependant on the tire. Those '83 Comp T/As were more performance oriented than the current family. High-speed rated and a softer rubber. Your Stock Car Specials, if fresh, could probably be in the 1.1G range, but the suspension must be set up for optimum camber under cornering. In addition, race tires are notorious for hardening up over time.

The first thing to look at...tire temps.

In the end Lap times are what matter.

A couple of months ago I got to take my SPF around Lime Rock for a few laps. Since the opportunity came without warning I went out with the recommended street tire pressure of 18PSI all around. Take it from me, this is not nearly enough pressure for cornering.

I have driven a couple of Porches and a few race cars around LR and I can tell you that the street set up in my SPF was not nearly as capable. Next time the tire pressure will be a few pounds higher.

Bob

Bob

SPF manual recommends 25 PSI for racing, 18 PSI for street.

I personally use 20 PSI for street.

For what tires? I find those pressures are ok with Goodyear Eagle IIs, but not nearly enough for the Yoko Avids, which has become a very popular 15" tire for the SPFs. I run 28-30 lbs in the Avids, street and track. FWIW.

I'm running Avids in front, BFGs in the back. Next spring the BFGs will be replaced by Avids. I wonder if I can interest Paul Donleavy in some 275-60-15 T/As. They have tons of tread.

Bob

I was running 25 psi in my Goodyear's and it was pretty cold in the morning - ie high 30s. I don't have a tire temp gauge, but I did try to feel them after a couple of runs - they were warm and a bit soft, but I wouldn't say they were hot. Exactly how do you use a temp gauge to determine if you are cornering close to the limit? I think I understand how to use it for determining air pressure, but am not clear on using it to as an indicator for grip.

I certainly felt like I could have pushed it a bit more on some of the turns and never came close to feeling like it was slipping or going to spin. I've been really happy with the performance of the Goodyears from a traction perspective, but was getting a heck of a vibration through the wheel - like the tires were square - on the straights. I think they were probably completely out of balance as they'd been balanced the day before while cold and new. Any tips on best way to go about getting race tires balanced properly?

Another big issue this time out was that I found out the inside edge of the left rear was scraping the inside of the wheel well on hard right hand cornering. Same on left handers but not as bad since there aren't that many hard ones at RA. I was putting out a big cloud of smoke coming out of #1 and #7. These are 10" Goodyears on standard Trigo 6 pin knock-offs. After a few runs, the edge of the tire got worn down and it stopped. But, I guess I'm either going to have to change the offset of the wheels with a shim, or modify the wheel well. Any ERA owners have this issue?

I'd like to get the car out on a skid pad and see what it'll do, and then next track day just keep pushing it a little bit more each time till I feel it start to drift a little.

I know you racers probably have this down to a science, but I'm just starting to learn, so keep the advice coming.

BTW - All these guys out there driving their Corvettes and Porsches are wimps :p - those cars seem to make it too easy vs really having to physically drive something like a Cobra. Really makes you admire the likes of Miles, Bondurant and Gurney
Thanks!
Scott

Scott,
Just curious, do you have Yellow Spax shocks on your ERA and how many clicks (or 1/4 turns) are they set at for the front and the rear? Are they IBOC springs, and what weight/lb are they? Also, did you lower the rear at all? I ran those same tires on my ERA and only had rubbing problems on full turns on the front only. It would also be good to find out if ERA narrowed those control arms on your car or if the original builder/owner did it themselves. The rear may be a tad different width than spec'd. As I recall my track from hub to hub in the rear is about 53.5" wide. DC

Duane,
It does have the yellow Spax shocks on it, but I don't know what they're set at as I haven't touched them since I got the car. Also not sure on the springs, but assume they'd be whatever ERA was providing in 1995-96 time frame. Will check this out when I take the wheels and tires off to put the radials back on. I also have assumed the control arms were done by ERA as the guy I bought it from didn't put the car on the track. I'll have to do my homework on all this and maybe see what Bob Putnam has on record for #414.
Thanks!
Scott

Gentlemen and Gentlewomen,

On a "non-aero" chassis with modern racing tires on a perfect surface, the max that I have seen is 1.56G. (Note: this is steady state 200 ft radius skid pad numbers. You can always spike the numbers with rapid steering input but those numbers are bogus.)

These numbers are very hard to produce and you will need perfect conditions to get there.

What you can expect with normal conditions is around 1.1G with proper camber setup.

And any of the current "Cobras" can be set up to handle quite well.

It is all a matter of what you start with and what it takes to get there.

Scott and ERA
 

Scott Are cars are cousins. ERA has a kit for putting bigger tires on your car. I run 335-35-17 pilots on 6 pin drive wheels. You will add these 2 fiberglass panels behind the seat to give your rear tires more room to move. You may want to look at a roll cage if you are going to push your car this hard. Ask Bob P to send you a picture of mine. The main hoop is taller, added the FIA bar going to the passenger side and a loop around the drivers side to the floor just under the door down to the floor. You can't see it from the outside, Niether the door or the body was cut to fit. A road racing seat would be another thing to add to the car. I believe that the springs and shocks are for street use. You need to go to 600lbs front and 500 lbs rear for track racing Camber, caster and toe need to be changed. You will need to get a larger sway bar for the rear also, 7/8" instead of 3/4". After this it is roadtesting at the track and tire temp work as Scotty J said. Rick Lake

I think Richard is right on. The set up is the key to get the over 1 G number. You can't just slap on slicks and get there. Things like a stiffer chassis and shock valving have a big effect on tire temps, and hence traction.

Scott

Rick,
Would really like to see some pics of your car. I've been playing with the idea of a roll bar that I could bolt in for track days, but not have to cut into the body so I could remove it for the street look.

I'll check with Bob on that kit as well. I did rub a hole through the fiberglass in the wheel well. Interesting that the Goodyear's say they are a 10" tire, but at the corners of the tire it's closer to 12" wide. Also interesting in that these are the Goodyear's with the yellow lettering. The first set had the white lettering, but said they were the same size, and I didn't have the rubbing problems. I wonder if I've got a different profile tire this time?