My 2007 TL, from day 1, has had terrible understeer. Is this the tires? The suspension? Is there anything that can be done to fix this?

 

I assume your TL is stock.

Check your tire pressure cold.
Set the pressures to 37F/33R (which is higher than the recommended pressure, but pressures up to 40 psi on stock size 17"s should be fine) and see if that reduces understeer.

If you're experiencing understeer in autocross or track events, play with the psi front and rear, starting at 40 psi up to 46 psi.

Otherwise, welcome to the world of FWD.

You can mod with a stiffer rear anti-sway bar.

 

Won't raising pressures cause the tires to loose traction sooner, thus meaning more understeer?

I suggest you reduce the pressures up front and increase the ones in the rear so the rear will loose traction sooner swinging the car around, mimicking some of the effects of "drifting" and helping you oversteer.

As well get yourself a RSB. Comptech and Progress make them and they are nice and solid and help with the car's handling greatly. New tires may help out, but it's not guaranteed.

This is the common issue with FWD, welcome to understeer.

 

I've been arguing this for a couple of years, but no one ever agrees.

It's why I run ~33F/36R.

Here's an interesting link i found this week (go down about 2/3rds of the page to "Suspension Adjustments":
http://www.pca.org/Activities/Autocr...spx#Techniques


OP: Progress Rear Sway Bar (24mm adjustable) is just the ticket. Best help you can get for understeer and only $150.

Depending on your tires, that can make a huge difference too.

 

Not on the street tires we're running at "recommended" pressures-- there is a lot of sidewall flex in them which accentuates understeer or "push." Additional pressure will decrease sidewall rollover and flex.

Tire pressure is different with FWD cars than RWD too, so increasing front psi and lowering back psi (relatively) should decrease understeer, or make the car handle a bit more neutrally.
For a quick & dirty rundown, see Tire Rack's summary at: http://www.tirerack.com/tires/tirete...jsp?techid=58&
Try running 40F/36R on a couple of fast twisty drives and see if that feels better.

 

WTF the autocross article is contradicting the tire rack article. Which tires pressures do what now?

 

I "like" the autocross article.

 

The autocross article is by the Porsche Club of America-- RWD, wider rear tires than front, rear engine (unless one is running a 924, 944, 968 [or 928 ]).

We've got a FWD, front-engine configuration: the reverse of the Porsche 2-seaters.

When in doubt, try a fast drive/autocross run or two with highF/lowR psi, then lowF/highR psi on your car and see which you prefer. Check each tire sidewall after each run, too.