I know this is a highly contested subject and people have different opinions but i thought maybe i could get a straight answer in regards to a 2007 Acura RDX AWD. I want to reduce under-steer in this vehicle around tight curvy roads. I understand that in FWD you should go in slow and exit fast. Also in tuning you would increase the front tire pressure and reduce the rear. i have 37PSI F and 32PSI R on my TL and this works well. However since my RDX is AWD i can't find the right PSI for the front and the rear. Has someone experimented with this and found the perfect pressure? thanks in advance.

 

You are correct that lower tire psi = greater slip angle. To some extent you can modify a front driver's handling with tire pressure, although adding a stiffer rear anti-roll bar is a better choice to reduce understeer in FWD.

In the case of the RDX though, it is detrimental to the SH-AWD to reduce rear tire psi. The RDX understeers because like most cars, it has a front weight bias. Enter a corner off throttle and the heavier end of the car is less willing to change direction -- it plows toward the outside of the curve.

This is where SH-AWD comes in with corrective oversteer -- but you have to drive it correctly to use SH-AWD and some of that feels counter-intuitive, especially to a driver of hot hatches or sport compacts with FWD.

To activate SH-AWD you must have the turbo spooled and ready for boost as you enter the corner then apply throttle before the apex. In a sport compact this would put you off the side as the front tires lose traction. In the RDX the rear tires gain authority and the outside rear is apportioned more than the inside rear. The outside rear tire yaws the nose into the turn, adding corrective oversteer. You can really feel it. More throttle = more yaw.

This initially feels scary and you have to learn to trust it. Start with easy curves and wait until the apex or later, then start throttle earlier and earlier.

So how do you keep the turbo spooled? Honda's got that covered. Though they didn't give us a manual they did provide paddle shifters. Use Sport mode and click into the appropriate exit gear before entering the corner. Keep the rpm above 4000 for immediate power. Start adding throttle and feel the force Luke.

 

It is freaky the first time your REALLY feel the SH-AWD. I came off of a WRX wagon with sway bars, etc., so I am used to mashing the gas before the apex. The difference is the WRX was pretty neutral on or off throttle (never did get that last bit of lift throttle over steer tuned out, though). The RDX rapidly goes from medium understeer to slight oversteer when you mash it. Not enough to send you spinning, but you need to be ready for it, i.e. have the steering angle set for it.

 

thanks for the response so im guessing i should be keeping all the tire psi the same with perhaps a bit more bias towards the rear tires? im thinking 35psi all or 35f/36r. also about the front end being heavier, my 2003 TL which is fwd with 40psi front 33psi rear does an amazing job in corners. i can get the rear end to really swing around and have cause some big oversteers, the only problem being that it loses a lot of speed when this happens. the rdx though i go around the same corner about 40km/h faster and i don't feel any oversteer or loss of control?! but i kind of feel if i push it more i will understeer really bad and go off the track, im not sure why i feel this way...also the steering doesnt have much feedback in corners it just feels stiff as hell.

 

I try to run the fronts on my RDX about 1 PSI higher than the rears and it seems to work out well for the SH-AWD. I like it's feel. Of course, the pressures must be monitored year-round with season changes. The TPMS works well to keep me informed.

 

I see, what's your cold tire psi?