How much does temperature effect handling?

[bmxrider154]

I will start with my setup: 92 Fwd, Kyb Agx (F-3)(R-7), Sportlines, Susp. Tech. Rear Anti-Sway bar, Falken Azenis RT-615 tires.

When I first installed the rear anti-sway bar and the new springs, the car felt great. It was still cool out, probably in the 40's-30's when I drove it most. I have the sway bar on the middle setting currently. Understeer wasn't an issue at all and the rear end would come around very nicely.

Today, I took the car out and noticed a huge change in handling. It was around 80*, definitely the hottest day i've driven the car. The car feels real sloppy, I can't tell if there's too much oversteer or understeer. It feels like the back end is way too sloppy.

I know the temperature will effect handling a decent amount but I didn't think it would be this drastic. It doesn't feel as tight as it did a few weeks ago.

I would like some experienced insight on the matter, and maybe some tips.

Thanks.
Bryan

 

[jtmcinder]

My car understeers much more when it's cold or rainy. It only becomes neutral when the tires get some heat in them. But Kumhos (other than V710s) are known to like warmth. Falkens, in contrast, used to get greasy when they overheated, which is why you see people spraying water on them between autocross runs. Now, the 615 isn't supposed to be as prone to overheating as the original Azenis, but -- please forgive in advance -- you might be over-driving them. Any chance of this?

- Jtoby

 

[bmxrider154]

My car understeers much more when it's cold or rainy. It only becomes neutral when the tires get some heat in them. But Kumhos (other than V710s) are known to like warmth. Falkens, in contrast, used to get greasy when they overheated, which is why you see people spraying water on them between autocross runs. Now, the 615 isn't supposed to be as prone to overheating as the original Azenis, but -- please forgive in advance -- you might be over-driving them. Any chance of this?

- Jtoby

Seems as if my car does the opposite of yours. I had way more oversteer when it was cold. The 615's are suppose to be alot better when warm, i'm pretty sure they fixed the problem with them. I can't really speak from experience, I only have a couple hundred miles on them...mostly cold. I don't think the tires has anything to do with the change of handling today, if anything they would stick much better than the other days of driving.

 

[eclipsh]

How long have you been running around with a 2" drop on AGX struts? I know from experience that they fail very quickly with that much lowering. Mine died in a year and with very few miles driven. They will feel stiff during the winter because it is cold out and the oil is sluggish but will drastically under perform once they are warm again. Your stiff springs could be fooling you into thinking the struts still work when they are actually dead.

Option two: check your ball joints, bushings etc.

 

[bmxrider154]

How long have you been running around with a 2" drop on AGX struts? I know from experience that they fail very quickly with that much lowering. Mine died in a year and with very few miles driven. They will feel stiff during the winter because it is cold out and the oil is sluggish but will drastically under perform once they are warm again. Your stiff springs could be fooling you into thinking the struts still work when they are actually dead.

Option two: check your ball joints, bushings etc.

I only have about 200 miles on the Sportlines and maybe 1k on the Agx's.

 

[eclipsh]

How much tire pressure are you running?

My only other thought before I back out of this is that you may be getting more traction out of the tires now when it is warm so they are sticking and causing the rest of your suspension or sidewalls to slop around instead of the tires just breaking loose and "feeling" tight.

IE. More grip from the rubber could be making weak points more obvious.

 

[bmxrider154]

How much tire pressure are you running?

My only other thought before I back out of this is that you may be getting more traction out of the tires now when it is warm so they are sticking and causing the rest of your suspension or sidewalls to slop around instead of the tires just breaking loose and "feeling" tight.

IE. More grip from the rubber could be making weak points more obvious.

Well, I actually checked my pressure while warm and front and rear were both around 45psi. I lowered the front to 40 and the rear to 42psi. Cold, i'm pretty sure they were all around 35/37psi.

I actually thought about what you just said above earlier. I asked a few buddies if they thought the extra grip would bring out some other weak points in the car. I'm going to do some testing in the next week or so and see how much the temperature actually effects the handling.

 

[eclipsh]

At the last AutoX event I went to I talked to some very experienced, and very fast, Evo guys who suggested running 38psi front, 33 rear hot for my 1g AWD with 245/45 tires on 17x8s. I did so with wonderful results. The car was much more responsive with less understeer and easy to swing into oversteer. I don't know how being FWD will effect those pressure settings but play around a bit.

I'll be interested to see what your tests show

 

[jtmcinder]

Ah, I didn't notice that the car was dropped.

Transition to undrsteer in a front-heavy car as it gets warmer is often a sign that you are running out of front travel. When it's cold, you don't have enough grip to transfer enough weight (side-to-side) to run out of travel for the outside front. So, the front is gripping. So, if you have the car set up to be loose (e.g., excessive rear roll resistance), it'll actually be loose when cold. Then, when the tires warm up, they have enough grip to slam the outside front, so the effective wheel rate in this corner shoots through the roof and you plough.

This can make the car unpredictable and nearly impossible to drive when you have enough heat to have grip. Until the outside front hits the bumpstops, the car is loose. Then it switches to pushing in an instant.

Short version: you need to run a zip-tie test on your fronts. You need to know if you are running out of outside-front travel when it's warm.

- Jtoby

 

[eclipsh]

Zip tie test (I had to look it up) = Pull a zip tie tight around the strut shaft right where it comes out of the strut body. Go corner hard and see how far the zip tie gets pushed up the strut shaft.

Pretty cool test. I might do it during my AutoX this Saturday just to see what the car is doing

Incidentally, I picked up this months issue of Sport Compact Car due to the pretty Evo 10 on the cover. It has a great article on drag race launching which goes into some tire dynamics when they get hot. You might want to go read it.