Getting rid of understeer
02-14-17, 12:05 PM
#1
Instructor
Thread Starter
Getting rid of understeer
Our cars are the ultimate understeer machines. A whole lot for the front wheel drive RXs, a little less for the AWD RX and "variable" for the hybrid AWD. The car's chassis is pretty much FWD and front engine. So there isn't much we can do except to have strong hands to keep on turning the wheel as we get closer to the apex of the turn (or brake in the middle of the turn like Mrs. MellonC and get yelled at by me about how to drive safely in rain or bad traction)
I thought of a couple of ideas. Let me know how viable these are:
1. run 2 psi higher tire pressure up front and 2psi lower pressure in the back than factory recommendation - autocross guys do this all the time....
2. (when my tires get worn) replace rear tires with 10mm thinner widths - it will be reverse staggered sizes
3. Carry 2 or 3 sand bags in the very rear part of the trunk.
I thought of a couple of ideas. Let me know how viable these are:
1. run 2 psi higher tire pressure up front and 2psi lower pressure in the back than factory recommendation - autocross guys do this all the time....
2. (when my tires get worn) replace rear tires with 10mm thinner widths - it will be reverse staggered sizes
3. Carry 2 or 3 sand bags in the very rear part of the trunk.
02-15-17, 06:37 AM
#3
Add spacers in the front to widen the track. Question is how thick do you go in order to get the results you want? Too thick and you risk putting unnecessary stress on the wheel bearings. Too little and you might as well not add spacers.
Stiffer rear sway bar. Don't see any aftermarket bars available for the RX so that's probably off the list. Perhaps change the rear sway bar bushing to polyurethane to reduce deflection. The results may not be as noticeable as replacing the sway bar, but every bit helps! It's quite possible aftermarket bushings can be used with some modifications.
Stiffer rear sway bar. Don't see any aftermarket bars available for the RX so that's probably off the list. Perhaps change the rear sway bar bushing to polyurethane to reduce deflection. The results may not be as noticeable as replacing the sway bar, but every bit helps! It's quite possible aftermarket bushings can be used with some modifications.
02-15-17, 06:52 AM
#4
Moderator
There is another thread on handling and one on the spacers.
https://www.clublexus.com/forums/rx-...for-rx350.html
https://www.clublexus.com/forums/rx-...spacers-2.html
Get the spacers from H&R Springs. I have the 20mm ones part no. 4065600 and they are a simple bolt on. The do improve handling and reduce body roll.
http://www.trakplus.com/results I found them for less $ elsewhere than the price from TrakPlus.
https://www.ecstuning.com/Search/SiteSearch/4065600/ This is where I got mine.
http://www.autoanything.com/wheels-r...3A4219152.aspx
There are no aftermarket rear sway bars as I and others have looked. Also no aftermarket polyurethane rear bushings that will fit. I have bought and test fitted a couple and although they sort of fit, but were too narrow width wise, I did not see any difference and they moved around due to being too narrow.
https://www.clublexus.com/forums/rx-...for-rx350.html
https://www.clublexus.com/forums/rx-...spacers-2.html
Get the spacers from H&R Springs. I have the 20mm ones part no. 4065600 and they are a simple bolt on. The do improve handling and reduce body roll.
http://www.trakplus.com/results I found them for less $ elsewhere than the price from TrakPlus.
https://www.ecstuning.com/Search/SiteSearch/4065600/ This is where I got mine.
http://www.autoanything.com/wheels-r...3A4219152.aspx
There are no aftermarket rear sway bars as I and others have looked. Also no aftermarket polyurethane rear bushings that will fit. I have bought and test fitted a couple and although they sort of fit, but were too narrow width wise, I did not see any difference and they moved around due to being too narrow.
Last edited by Clutchless; 02-15-17 at 07:02 AM.
02-15-17, 07:59 AM
#5
Moderator
Some have installed the F-sport lateral dampers and claimed they helped with body roll etc. They are expensive. There are a few threads you can find that discuss this part, including the first one in my post above.
Regarding the rear bushings, read the first link in my post above, then do some more searching on your own and let us know what you find now that it is a few years later. Maybe the market has changed and maybe something new is available that may fit.
Regarding the rear bushings, read the first link in my post above, then do some more searching on your own and let us know what you find now that it is a few years later. Maybe the market has changed and maybe something new is available that may fit.
02-15-17, 09:48 AM
#7
Moderator
If you are successful with making urethane bushings, I am interested in buying a set.
The thread on handling to which I posted a link above contains discussion of my bushing test fit experiments for both front and rear.
The thread on handling to which I posted a link above contains discussion of my bushing test fit experiments for both front and rear.
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02-15-17, 02:48 PM
#9
No, I don't play soccer!
Clutchless, Henry would have to be a vendor to sell here. It's in the rules.
This is one of the reasons I went with the sport package. The steering was nice and tight.
This is one of the reasons I went with the sport package. The steering was nice and tight.
02-16-17, 06:25 AM
#12
Intermediate
I'd interpret that there's a distinct difference between selling an item for profit (Vendor) and selling an item for its approximate parts value (not a Vendor) in order to get opinions from multiple users on how the design performs under a variety of conditions. Including a DiY further differentiates this, because it clearly indicates that you're not attempting to sell a proprietary item and gain a market share. That's just me, though...
At any rate, good luck with the design and keep us posted!
To the OP:
Are you sure this is actually a problem? I mean, how often are you finding that you're cornering this SUV to the point of chirping understeer? You mentioned AutoX, but obviously, you're not literally doing that, right?
I've encountered zero instances of literal understeer in this vehicle (ice & snow don't count).
At any rate, good luck with the design and keep us posted!
To the OP:
Are you sure this is actually a problem? I mean, how often are you finding that you're cornering this SUV to the point of chirping understeer? You mentioned AutoX, but obviously, you're not literally doing that, right?
I've encountered zero instances of literal understeer in this vehicle (ice & snow don't count).
02-16-17, 07:33 AM
#13
Lexus Champion
Upgrade to the Lexus GX460. That's how I plan to fix that very same issue.
There's very little you can do with the FWD platform - it will inherently understeer. The h is a little better in this regard than the 350. 350 will fully release the rear axle in the turn, while h will send power to mask some understeering tendencies.
No need for sandbags in the boot either. It will only make the things worse. We already have a battery sitting under the rear seats, which helps with weight distribution.
And please don't yell at Mrs. MellonC. She does exactly the right thing - transfer weight to the front in the middle of the turn to get more traction for the steering and less in the rear to rotate the vehicle.
https://en.wikipedia.org/wiki/Lift-off_oversteer
The WRX STi I had refused to turn. The only way to really rotate it was to go into a turn hot and then slam on the brakes.
There's very little you can do with the FWD platform - it will inherently understeer. The h is a little better in this regard than the 350. 350 will fully release the rear axle in the turn, while h will send power to mask some understeering tendencies.
No need for sandbags in the boot either. It will only make the things worse. We already have a battery sitting under the rear seats, which helps with weight distribution.
And please don't yell at Mrs. MellonC. She does exactly the right thing - transfer weight to the front in the middle of the turn to get more traction for the steering and less in the rear to rotate the vehicle.
https://en.wikipedia.org/wiki/Lift-off_oversteer
The WRX STi I had refused to turn. The only way to really rotate it was to go into a turn hot and then slam on the brakes.
02-16-17, 07:44 AM
#14
I used to have this fight with my dad every time I wanted to change something on my car (usually the exhaust system). I completely understand your point. With a manufacturer it's all about compromises, and sometimes my priorities are a little different than what others look for in their car, I have no doubt that Lexus designers and engineers are a lot smarter than me, but understeer scares the #%^$@ outta me. Especially in the snow! Therefore, I would happily sacrifice a little of the ride quality to help our RX turn, which is a compromise that Lexus clearly chose not to make.
02-16-17, 07:49 AM
#15
Lexus Champion
On a second thought, the absolute best thing one can do to a car is to get a set of really good tires. That will push boundaries of when the oversteer or understeer starts. Snow tires will make understeer less pronounced and far less scarier.
Oversteer is what all manufacturers try to avoid, as most drivers will not know how to deal with it. That why almost all cars out of the factory are tuned to understeer.
There are some exceptions to modern vehicles, as electronics take car dynamics over, so it is possible to tune the vehicle to oversteer as long as the computer catches it before the car ends up in the bush.
Oversteer is what all manufacturers try to avoid, as most drivers will not know how to deal with it. That why almost all cars out of the factory are tuned to understeer.
There are some exceptions to modern vehicles, as electronics take car dynamics over, so it is possible to tune the vehicle to oversteer as long as the computer catches it before the car ends up in the bush.