Cornering Problems

StreetSnake · #1 (**permalink**) 03-21-2009, 02:30 PM

Lets see if you guys can fix this problem too. Under exceleration while turning/turns the car wants to drift quite a bit. In other words the car wants to go straight versus turns, not a good scenerio. Any thoughts?

Apex Rider · #2 (**permalink**) 03-21-2009, 02:39 PM

Get better tires and/or quit accelerating in corners.

bobcowan · #3 (**permalink**) 03-21-2009, 02:46 PM

That's called a Push, or Tight. It's probably a fairly simple matter of suspension tuning. If you do a web search, you'll learn why that happens, and what to do about.

vector1 · #4 (**permalink**) 03-21-2009, 02:57 PM

rear end locked?

Ron61 · #5 (**permalink**) 03-21-2009, 03:21 PM

Quote:

Originally Posted by bobcowan

That's called a Push, or Tight. It's probably a fairly simple matter of suspension tuning. If you do a web search, you'll learn why that happens, and what to do about.

What Bob said is most likely your biggest problem. I did all of my suspension over and wound up with 12 way adjustable QA-1 shocks and spring packages and by the time I got through I could make my car turn with no tight or loose. Also tires as mentioned are a huge help. The reason I went the way I did was I had to change my settings for the different tracks and roads around here and the QA-1s were very easy to adjust the rebound on and when fitted with the proper spring rates they worked great.

Ron

StreetSnake · #6 (**permalink**) 03-21-2009, 03:44 PM

The rearend is not locked and I'm running michelin ps2 335/17s on the rear and 245/17 on the front. I will look into the adjustablity to fix the push. I have afco's on the rear and aldan on the front. I should have just put afcos or QA1 all around.

Tommy · #7 (**permalink**) 03-21-2009, 04:03 PM

Thinking of it this way may help. Each tire has a limited amount of force that the driver can tap to either accelerate, deccelerate or turn. The amount of force available is determined largely by the road surface, the type of tire and the amount of weight pressing down on the tire. When you accelerate, there is an effective weight shift off the front tires and on to the rear tires. The harder you accelerate, the less weight you have on the front tires and the less force they can generate to help you turn. Hence, the push described above. The most common ways to put more weight on the front tires are to delay the point in the turn where you start accelerating, or alter your suspension to reduce the weight transfer during acceleration.

Cobra #3170 · #8 (**permalink**) 03-21-2009, 05:31 PM

There is really not enough information to offer sound advice, for example, how is the car under steady state cornering, is it balanced, does it immediately under
steer as soon as throttle is applied? What are the front and rear wheel rates and what are the anti roll bar diameters and link ratios? What are the front and rear ride heights or better yet, roll center locations? If it were my car with this limited information I would first increase the front tire size to a 285 or 295 as a starting point then possibly increase the rear wheel rate by about 50# per inch. You could also lower the front if clearance and geometry permit and increase the front shock rebound settings. You will get much better braking performance with a larger front tire. Your rears will easily overpower such small fronts and although you could achieve the balance you want with increased rear roll stiffness you would compromise acceleration and maximum cornering force by taking that route.

StreetSnake · #9 (**permalink**) 03-21-2009, 05:33 PM

Thanks for the explanation Tommy. After reading a little bit so far on it, I obviously have an understeering problem, I think that is.

Do you run a higher # coilover in the rear to help prevent weight transfer from front to back, or am I thinking all wrong again. I'm just looking to optimize the car when I drive it. I'll probally never regularly take it to track events, but when I do and when I'm on the backroads, I don't want to end up it the trees. LOL!

Silverback51 · #10 (**permalink**) 03-21-2009, 05:45 PM

Just Google "Understeer" and you will find a bunch of information.

There are a number of things you can do to address it.

vector1 · #11 (**permalink**) 03-21-2009, 05:48 PM

soften the front end or stiffen the rear with springs might help.

wtm442 · #12 (**permalink**) 03-21-2009, 06:11 PM

There are at least 20 different parts and/or settings that affect handling.

Therefore, it is a COMBINATION of the right parts AND having them all adjusted properly. Of course, the driver is the most important part of the equation, so attendance at a road racing course is very important in many respects.

Second ... you should contact the manufacturer and find out what you have in the car now for spring rates, shocks, sway bars, brake pads, etc. Can you do a 4 corner weight measurement?

Then get suggestions for the manufacturer on what upgrades they recommend.

Then come back to this thread and do a technical dump of all the information and ask the same question.

Then you will get a really good cross section of answers, because there is tons of expertise lurking on this forum. Some of the answer here are very good, but even the experts cannot give too much useful suggestions without knowing what you have now.

For now, the best thing you can do is try the things that cost no (or little) money.

First is the driver. Slow down your entry speed and then get back on the gas earlier on exit.

Second is the front tires. Play around with the air pressure and see what happens. Do you have a pyrometer to measure tire temps? Try to get consistent temps across the front tires from bead to bead.

Play with the front end hight. This will affect under-steer.

Cheap changes - new set of good sway bar bushings.

Tommy · #13 (**permalink**) 03-21-2009, 06:20 PM

Quote:

Originally Posted by StreetSnake

Thanks for the explanation Tommy. After reading a little bit so far on it, I obviously have an understeering problem, I think that is.

Do you run a higher # coilover in the rear to help prevent weight transfer from front to back, or am I thinking all wrong again. I'm just looking to optimize the car when I drive it. I'll probally never regularly take it to track events, but when I do and when I'm on the backroads, I don't want to end up it the trees. LOL!

You won't be able to use my experience to help with your problem. My car has C5 Corvette suspension and I run wide racing slicks when I'm driving it hard. Understeer has never been my problem. ... As was noted in an earlier post, there are lots of things to consider when optimizing a car's suspension for performance. Given that you don't plan to run it on the track and you've got a lot to learn about suspension tuning, I suggest you simply let it get further out of the turns before you get hard on the gas. BTW, I suggest that anyone who wants to drive a Cobra hard learn to do so on the track. It's much safer than finding the limits of your car on a public road.

StreetSnake · #14 (**permalink**) 03-21-2009, 06:54 PM

Agreed. Thats why i'm trying to get this somewhat set up before i go to mid ohio in june and learn how to drive it safely.

john chesnut · #15 (**permalink**) 03-21-2009, 08:30 PM

Tommy, I am interested in knowing more about your suspension. I didn't know that E-M ever put C5 into their cars. Is this something that you did on your own? I know that they used C4 in some of them. But, there is a pretty big difference between the C4 and C5, both front and rear. Just wondering. John

Tommy · #16 (**permalink**) 03-21-2009, 08:44 PM

John,
I don't know if I got the C number right. The suspension is from a 1987.

john chesnut · #17 (**permalink**) 03-21-2009, 09:06 PM

Tommy, That is a really nice set up. It is C4. The C4 is from 1984 - 96, The C5 and C6 run the same geometry and independent rear transaxle and began in 97. It is the same that GM is using today. I have C4 in some of my Dragons and it works great. See you at the track someday. Here is a picture of the C5/6 stuff in my Dragon chassis. I use it in my Cobra chassis too.
I don't know what type of rear end we are talking about in this thread. But, if it is an independent rear a partially broken or bad ujoint in an independent rear can make the car jump side ways under acceleration.

juansofla · #18 (**permalink**) 01-17-2011, 09:26 PM

CMC build manual... on my CMC (StreetBeast) Cobra... "The recomended tires are P205/70hr-14 for the front and P255/60HR-15 for the rear. The mounted tires should not extend past the outside rim of the fenders" ... (which the rear does at this size)... but the whole manual is full of errors, the parts they sent with the kits have all the instructions from the manufactuerer removed... it is like StreetBeasts does not want you to finish building their fine cars.
Mine does not seem to over-streer or under-steer... but I have not driven it at over 40mph yet... going to go slow for first 1000 miles... car feels normal and very solid/quiet

strictlypersonl · #19 (**permalink**) 01-18-2011, 06:15 AM

Has the bump-steer been measured?

Curt C. · #20 (**permalink**) 01-18-2011, 09:48 AM

Is your car a solid axle or IRS? If you are running a solid, you can tighten the rear end up via a larger sway bar too. Its a lot easier to tune via sway bar changes than springs and may give you and indication you are going in the right / wrong direction before buying more expensive pieces.