Crosswinds (don't?) suck

[BlueSkyJaunte]

I bemoaned the crosswind-handling capabilities of my fully-laden Targa in this thread: Crosswinds suck

Well, I finally have some experimental data to provide.

I adjusted my tire pressures to 34psi rear, 30psi front. "Bounce" test indicates that my shocks are OK. Side-to-side push test results in very little movement. I believe the Dunlops are ZR rated.

The so-called "monsoon" season is in full swing here in the 'burbs of PHX, so I now have nice handy crosswinds to deal with. Finally, my mother-in-law is in town, so I've got extra mass in the car (ha-ha).

Drive 1: "westbound" (really heading dead north) on I10 at 65-80mph towards downtown Phoenix, sporadic crosswinds (sometimes sustained for up to 1 minute) at maybe 20mph from the west. 3/4 tank of gas indicated (eventually down to 1/2). Mother-in-law in the passenger seat, wife relegated to the rear passenger seat. In the crosswinds I did notice some tendency to be blown off course, easily corrected by a few degrees of input from the steering wheel--not like the last time where I was all over the lane. DEFINITE improvement.

Drive 2: Same direction and wind conditions. No passengers. Couldn't detect the crosswind impact to vehicle direction.

Conclusions:

Correct tire pressures and slightly greater mass in front (more gas--never went below 1/2 tank) significantly improved handling in crosswinds. Granted I don't have a whole lot of datapoints here, but I'm happy with my results.

Thanks to all who provided suggestions and guidance on how to correct this!

[Jim Sims]

You mean you couldn't fit the Mother in law in the front trunk? Now, that would have moved the center of mass forward of the center of pressure! Jim

[pbs911]

"Bounce" test indicates that my shocks are OK.

I am glad to see you worked out some bugs. However, I have heard on this board that the bounce test doesn't work on the 911. After this weekend I am convinced this is true.

My 78SC passed the bounce test. Nonetheless, I replaced my Koni rear shocks with Bilsein Sports this weekend looking for a little added performance. To my surprise the Konis could be completly compressed and extended using no more than a couple of fingers. The shocks were GONE even through they passed the bounce test!

The ride quality is now incredibly different with new shocks. Just thought I'd share my .02.

[jkeyzer]

Same here Paul. My rear Konis passed the bounce test but were in sad, sad shape once I got them off the car.

[BlueSkyJaunte]

Really?! I'm sure it must have something to do with the weight distribution, blah blah but I'm not a MechE.

I do hit a really big bump on the way to/from work every day (monster cattle grate). The car does seem pretty settled over it.

However, for the sake of science I will pull the shocks next chance I get. (One more thing to add to the list )

[masraum]

What changes did you make? front and rear spoiler? alignment?

[BlueSkyJaunte]

I just adjusted the tire pressures. For some reason (laziness being the most likely candidate) when I had crosswind problems my pressures were 29lbs all-round (according to my after-the-fact pressure check). At 30f/34r I'd say over 90% of the crosswind sensitivity was eliminated.

At 29lbs f/r it was truly a white-knuckled, cold-sweat ride.

[porsche74]

Blue Sky:

Remember, the further away the center of gravity gets from the aerodynamic center of pressure, the more sensitive a 911 will be to crosswinds.

LOL,..Done a LOT of aero testing on these cars,....