J30 suspension

[Q45tech]

In honor of all the J30 here I have spent some time analysing the following:front springs std....... 112 lb/infront springs hicas.... 123 lb/infront sway bar std.... 25mmfront sway bar hicas.. 24mmrear springs std......... 112 lb/inrear springs hicas...... 123 lb/inrear sway bar std ..... 19.1mmrear sway bar hicas... 17.3mm

front shock ................139-192 lb/in in expansionfront shock...................44---71 lb/in in compressionrear shock..................159-216 lb/in in expansionrear shock....................57---88 lb/in in compression

Since the front is coil over without an upper link to control camber the sway bar attaches to the shock housing with an arm length of 16" [so 6/16= 0.375 x [(xfactor)25/29^4~~~] too complicated to explain some where around 110-120 lb/in is the stock front bar stiffness.and 95-105 with HICASThe rear bar is around 33 lb/in and 24 lb/in with HICAS.

Kind of wierd 225-230 lb/in front and 145 lb/in rear Standard and 225-230 lb/in front and 147 [145] lb/in rear with HICAS..

The springs are 11 pounds stiffer on Hicas but the sway bars are proportionally less stiff with HICAS.

The front roll stiffness is roughly 61% vs 39% rear so in theory there is less unsteer than the Q but I don't have the expertise to evaluate the camber change [and its effect] with the roll of the McPearson strut. Generally this would result in more understeer as the tires camber towards positive.

If you want to improve handling [reduce understeer] of the standard J30, you could use the rear HICAS springs [leaving the bigger bar in place] and reduce the front 25 mm bar to the 24 mm HICAS bar....the new numbers would be 210/156 or 57% front 43% rear.

If you have a J30t you would just find a 19.1 mm rear bar fom a stock J30 and exchange it......you could also change to the softer 112 lb/in stock front springs but see what the bar does first!

10-20 lb/in of wheel rate change won't do much to affect the roll just change the at limit balance away from understeer more towards neutral.

[SR20 Infiniti]

your a smart guy

[PalmerWMD]

your a smart guy

That's why he is a NICO-Super Moderator!And we're proud to have him too.:patriot

Fred....:blue

[Q45tech]

Still looking for someone to actually measure the stiffness of front sway bars [impossible to use formulas because of all the convolutions and bends flat areas, etc] because all my rear numbers are extrapolated from measuring the 15.9 mm rear bar on a Q45t and correcting with a ratio formula which cannot correct for the thin wall diameter changes in hollow bars.

Nissan helped with the actual stiffness of the front 29mm Q bar but I lost my engineering contact [a few years ago].......so everything forward has been based on that one number with ratio adjustments.

I'm sure errors on the order of 5% have crept in but hopefully they apply to both front and rear so the ratios would be pretty correct.

If you think about it 10-20% stiffness increases are quite noticeable on the street due to road bumps and irregularities.

If you design suspensions for a living there must be dozens of secret rules of thumb you develop and fine tune after seeing the as built track data.

Notice I added the shock parameters to the intro post and that they generally follow the rule about the compression being half the spring stiffness and the expansion being 1.5 times the spring stiffness. And the rule that the rear shocks are always stiffer than the front by 20% on compression.

The above is a function of tuning speed [the mph on smooth highway] where the ride is optimized to protect against seam pitching in concrete roads.

The major variable is the trunk and amount of gasoline as this is rear of the rear springs and doesn't get more equally divided as the driver and passengers do nearer the center of gravity.The front mass never changes in front of the front springs vs a potential of 200-300 pounds on the rear.

If a car is just optimized for a driver and gasoline what happens when 700 more pounds - almost 20% is added?The understeer is set with what load?

Anyway the 10% stiffer springs on the J30t move the optimum tuning speed up by roughly double the amount.....say from 55mph to 66 mph. {guess t car drivers are expected to drive faster}Race cars have extremely stiff suspensions so that they are tuned to be smooth at 150-200 mph and are horrible and unusable on the highways/city streets at slow speeds.

[Q451990]

Why all of the research in to the J? Thinking of a project car?

Heath

[VimyJ]

Excellent research, Q45tech. Now I wonder what the sway bar stiffness is on the post 94 nonHICAS J30t (if there is any difference at all). Would the thinner sway bar on HICAS equipped Js be there to enhance 4 wheel steering?

[maxnix]

Since Dennis is doing this dissection of the J suspension, I wonder if he will complete his inquiry into swapping the J's rear vented discs (and presumably calipers) to a first generation Q?

I remember this conjecture in one of the previous boards, but I don't remember it reaching a definitive conclusion.

[Q45tech]

Other than changing the rear rotors and rear calipers and using J30 rear pads it should work fine as it is just a thickness increase from 9mm to 14 mm...............whether this helps any is still to be determined.Never thought the rears were a problem if the wheel bearings and hubs are kept within spec.

I always get at least 45,000 miles out of the rear stock pads and rotors seems fine on a 4,000 RWD car.........guess it would be worse with TCS doing its thing.

[maxnix]

Thanks Dennis. Just a thought since the cooling coefficients would be more similar if both ends were vented. Not a big deal, but the symmetry is appealing.

I wonder why Infiniti thought they were required on the lighter J?

Big mountains out here.

[Eswift]

ANSYS Finite Element Analysis could be used to determine all the stiffnesses if we had either

1) 3d solid-model CAD file of the partsor 2)complete dimensions of the bar and material properties so i could draw up the parts myself and do the analysis

then with the model, the optimal thicknesses could be calculated for various load situations in the car.

[Eswift]

i guess i could pull out the digital calipers and just make some pretty good estimates....

[Q45tech]

I just used a sway bar and disconnected one end and pulled it down /pushed it up with a screw jack and a 200 lb scale to get the basic 15.9 mm numbers [160# per inch]. All bars have similar convolutions to clear exhaust pipes but there is a 1.5" width difference between J/Q/97Q.............errors creep in but since we have only finite oem choices on each model.......without designing and building new bars the relative stiffness is sufficient for a decision.

After all the various oem rear bars of all models only go from 12 lb/in to 40 lb/in [actual wheel rate] in all configurations adding from 10% - 33% in rear roll resistance.

An optimum configuration would only apply to a single car since too many othe variables.

If a std J likes a 21% extra stiffness from a rear bar, the 33% should be ample to add a more controlled feeling especially with the Q's extra rear weight. Against the Q choices of none, 10%, 33% or 100% [stillen 24 mm bar].

[macitt]

Hey Guru...I am not worthy!!Can you help me with my posted thread regarding the replacement of my front and rear struts anfd timing belt for my J30? This Kentucky boy is headed on a relocation to Georgia and needs the car in shape.Thanks,[email protected]