F50 steering/handling questions for Q45tech

[StarPD]

Dennis, I know you are well versed on handling problems and solutions for G50s, but I've seen little from you on F50s. Maybe for myself and other F50 owners, you could do some research and study of F50s to ameliorate some of their inherent shortcomings.

One is the exaggerated understeer. Usually, that is improved by going to a thicker rear sway bar, and firming up the sway bar bushings with replacement bushings or shims to tighten the linkage. I understand however that there are no alternate sway bars for F50s, and that the method of attachment doesn't use bushings at the ends which can be firmed up to improve handling response. It seems that only having a new thicker sway bar made by a spring shop would answer this. That's a bushel of snakes itself though, not only for the expense, but I understand that all new attachments would be required, both for the bar mounting and for the ends. Getting everything right might be a challenge. If that is the ONLY solution, how should we determine how thick a new sway bar should be?

I have found that turning the VDC off reduces the understeer, but not enough to make the car dig into the turns like my '94 "t" model with "HICAS. That car handled like a sports car, and had just the right amount of slight oversteer to allow excellent control going into and through a curve. Still, turning off the VDC every time one goes into a curve, or even every time starting the car is a PITA, and I'd like to make handling more neutral at least.

The second is steering. My '05 Q45 doesn't track well, even though it wears 245/45Z18 Bridgestone RE050A "Pole Position" tires on 18" x 8" aluminum wheels with the correct offset. I run 34.5 psi tire pressure, as it seems to be the best compromise between ride and handling. As you know, the F50 has no provisions for adjusting caster. That would probably help tracking at least, but alas, there's no no way to do that that I can find.

Further, steering is vague, perhaps overboosted, and with little feedback.I investigated tightening up the rack mounting and perhaps steering linkage connections, but am told there is no way to do either. I suspect that steering boost is controlled electronically, so it appears that some sort of mods to one or more of the computers might be necessary. That would be complicated I think though, as so many of the computers are interdependent on each other, and affect each other.

Dennis, I know that you are THE Q45 guru, and know more about them than anyone. I am also aware that there are a lot more G50s around, and a lot more G50 owners in this forum than F50s, but we F50 owners are Q45 guys too, and we need help. What might I do to persuade you to get an F50 on a lift and examine the rear suspension and steering systems to find a way to improve them as you've done for the G50?

I dearly love my '05 Q45, and would like to improve these deficiencies so I can enjoy it more fully.

Will you help?

Thanks.

[Q45tech]

Besides sway bars you use spring stiffness to control the stiffness ratio between front and rear. [set the under/oversteer ratio]

The rear being adjustable [Camber, toe] allows you some compensation for front.

Look to the newest M45 for clues and possibly components that could be adapted to fit?

[maxnix]

Look to the newest M45 for clues and possibly components that could be adapted to fit?

Since the FY33, Y34 and F50 are basically the same platform when it comes to suspension, I would investigate the FY33 rear bars in particular. There is a very interesting post on those. Even the G50 rear is a similar design.

Doesn't someone here have access to the Espelir springs?
Modified by maxnix at 12:48 PM 11/30/2007

[Q45tech]

Forgot to ask when you last changed shocks/struts as the car is over 4 years old? Probably just poor rear rebound stiffness allowing massive rear sway under transistions.

[StarPD]

Forgot to ask when you last changed shocks/struts as the car is over 4 years old? Probably just poor rear rebound stiffness allowing massive rear sway under transistions.

Car is only 2 years old with 30k miles, too soon I'd think for that. Ride and handling are fine, in fact, a little stiff, but bearable. Except for the understeer, and the wandering/overboosted and slightly vague steering, I find nothing that might indicate worn springs or shocks/struts. My '94 didn't understeer like this even when it needed new rear shocks.

Any other F50 owners notice too much understeer in curves?

[maxnix]

Do tire brand, size and wear match at all four wheels?

[StarPD]

Do tire brand, size and wear match at all four wheels?

Yes, new 18" x 8" TSW "Kyalami" wheels and 245/45Z18 Bridgestone RE050A "Pole Position" tires. 4 wheel alignment done at dealer, tires @ 34.5 PSI, set exactly using racing digital gauge that measure in 1/10th pound increments. Suspension checked at dealer for worn or damaged bushings, all suspension connections verified tightened to specs, steering rack adjusted for zero lash but no binding at all at dealer by pretty sharp technician w/ over 10 years Infiniti experience. No excess weight in the car anywhere (I weigh 160 pounds, wife weighs 120), nothing in trunk. Car rarely driven with less than 3/4 tank, I keep it topped off.

[Q45tech]

Is the 34.5 psi cold not driven psi?

Are these not 51 psi max tires so wouldn't 40-41 psi cold be more appropriate? At least on front to reduce contact patch area and thus understeer.

[xerexabante]

Any other F50 owners notice too much understeer in curves?

I purchased 06 M45 Sport 19"rims with oe tires. It handes like a BMW, than a Cadillac before. It corners surefooted, but for the understeer question you have I totaly forgot the bad handling of my stock 18" rims. They were so so unlike the 19's

[StarPD]

Is the 34.5 psi cold not driven psi?

Are these not 51 psi max tires so wouldn't 40-41 psi cold be more appropriate? At least on front to reduce contact patch area and thus understeer.

Worth trying I suppose, but my tires are pretty stiff already, being 100W.And it's already a little sharp on manhole covers and bridge expansion joints. I'll give it a try anyway.

[StarPD]

I purchased 06 M45 Sport 19"rims with oe tires. It handes like a BMW, than a Cadillac before. It corners surefooted, but for the understeer question you have I totaly forgot the bad handling of my stock 18" rims. They were so so unlike the 19's

I believe your M45 Sport has "Active steering", much like the "HICAS" on my '94 Q45t. That makes a considerable difference in steering and handling, so you wouldn't "enjoy" the front end pushing I do. Alas, not available on the '05 Q45, which is what I have.

Anyone with an F50?

[maxnix]

Worth trying I suppose, but my tires are pretty stiff already, being 100W.

Load rating has little to do with sidewall stiffness, but tire pressure does affect spring rate and determines true load carrying capacity.

Considering your front tires are carrying ~54% of the wieght, try 38 psi in the front and 33 - 35 psi in the rear unloaded. More in the rear if loaded as balance and total axle rate cahnges.

[elwesso]

Heres what I would do...

Since the car has a mcpherson setup, you will need to run more static camber to get the contact patch optimal. I would see if you could get some camber plates from another car to work... maybe a Z or G35?

Second, getting custom sway bars arent a big deal. Ive heard people talk about having them made for $200 or around there.. Just take your stock one in, they bend in a new one of whatever you want, and slap it on the car...

Unfortunately, I dont think theres any way to adjust caster... The G50s and Y33s used tension rods, and I dont see one on the F50s... So your only prayer is to find camber plates to increase static camber and then play with the toe so that hopefully your caster comes in somewhere decent...

What are your current alignment specs? We need something to play with to get started.

[xerexabante]

I have an F50 I just bought the M45 rims for my F50

[mhoepfin]

I believe your M45 Sport has "Active steering", much like the "HICAS" on my '94 Q45t. That makes a considerable difference in steering and handling, so you wouldn't "enjoy" the front end pushing I do. Alas, not available on the '05 Q45, which is what I have.

Anyone with an F50?

I have a 2002 F50 with 65k and the Sport package which has the adjustable suspension (not sure if this was standard on the '05's). I've got the Infiniti 18 inch wheels and have new Nitto 555's on them.

I think the car handles incredibly well. I don't have any steering issues. I'm not sure if this is because of the sport suspension. The only comment on ride concerns some road noise from the tires and being able to feel the bumps on rough roads.

[rickymartinakasgk]

it seems like the '05 Q would be quite similar to the LS 430 in it's handling.

[qship96]

Ls is a superior car all around to the F50 series,especially the drivetrain/suspension-really not in the same league at all

[elwesso]

Ls is a superior car all around to the F50 series,especially the drivetrain/suspension-really not in the same league at all

On paper anyway.. I am not sure if would actually be more fun to drive or as fun to be in... Thats at least how most lexus are compared to Q.. Id probably rather be in a Y33 than a 97 LS400, despite the LS being faster.

driver enjoyment is relative, qualitative and hard to compare.. Just food for thought.

[StarPD]

Load rating has little to do with sidewall stiffness, but tire pressure does affect spring rate and determines true load carrying capacity.

Considering your front tires are carrying ~54% of the wieght, try 38 psi in the front and 33 - 35 psi in the rear unloaded. More in the rear if loaded as balance and total axle rate cahnges.

JACKPOT!Thanks, Brian.To recap. I have 18 x 8" TSW "Kyalami" chrome wheels with 245/45/18ZR 100W Bridgestone RE 050A "Pole Position" tires. I was running 34.5 PSI all around.

I tried 34.5 PSI front/36.5 rear (I have a digital gauge that measures in 1/10 increments). It gave a considerable improvement. Tracking is much improved, tramlining is reduced, and understeer is greatly reduced.

I then changed it again to 34 front and 37 rear. That got a slight further improvement, but ride is harsher over manholes and expansion joints.

I'm going to drive it this way for a while, then try 33.5 front and 37.5 rear to see how much further change I can get, and how much harsher the ride becomes.

F50 owners, you may want to try adjusting tire pressures as I did if you are not happy with steering/handling as I was.

I still want to pursue a thicker rear sway bar, but the tire pressure trick helped a lot. The car is now a pleasure to drive.

Thanks again, Brian.

[Q45tech]

In a shoter sidewall tire the stiffness is greater say 2000 pounds per inch, most of this comes from inflation pressure, so 2000/51= ~~~40 pounds per psi. Bur max load might be less than 2,000 pounds at any pressure.

Support might be 30 pounds and stiffness 40 pounds per psi. You must measure the bottom deflection loaded and unloaded to get a more exacting number for the brand, model, and size at a constant temperature.

Remember the tire spring is in series with the vehicle coil spring which is in series with any rubber above spring and the flexible body.

A good rule of thumb is the real stiffness is 15% less than published coil spring stiffness.

[widebodyq]

I read some where that in heigher speeds, the power steering is turned off. I will look online for the article for you.