kazx9r

I rarely post but I thought some of you might find this interesting. I'm studying up on suspension geometry just for fun and wanted to see what the 350z engineers were thinking when they designed the front suspension. I jacked my totally bone stock car with stock Enthusiast trim 18" wheels 225/45/18's, then got the front suspension to factory ride height. I put a pencil on the center of the wheel on the outside wall right where the contact patch would be, then in the center and then inside. After turning the wheel 10 or so times, I got enough clean lines to determine the arc of the steering.

Here's what I found.





DISCLAIMER-I'm not saying this is the correct way to do this or what I found is correct, all I know is that I got consistent results. I'm just a car junky.

So what this shows is the inside wheel has less turn-in than the outside wheel during a left turn. So obviously with a two ball joint (or however you want to call it) the 350z designers created what they were after, a virtual moving steering axis. From what I know, this should have a massive effect on scrub radius.

So when the wheel is straight, the scrub radius is on outside tire patch (outside being if you cut the tire width in half of the left wheel
engine side will be inside patch, outside patch obviously on the outside).
So from above you'll get two circles. One with a 6" diameter and the other with a 17.38" diameter. You then find the distance to the center of the tire axis. So using the center of the steering arc above the scrub radius is -1.5". As you turn right the scrub radius stays negative, neglecting camber change, it stays -1.5" (will talk about camber change in a second).




However, things change when you start to turn left due to the virtual pivot steering axis of the 350z. As you start to turn left, the steering axis moves closer to the engine. Scrub radius goes massively positive. At the end of the left turn the scrub is +4.5" (which is the width of the 8.9" tire, probably not a coincidence). So the steering axis ends up on the inside tire patch.




As for camber, the suspension raises 3/4" from complete left lock to right lock. So a bit of camber gain going on as it should. So since the arc above is drawn on an angled plane, if you project the arc on a flat plane, the arcs above would have a slightly smaller in diameter. Not much to discuss on this. I'm more concerned about Ackerman and scrub. So those that want to put spacers in have a little wiggle room before it the scrub starts to go positive.

I honestly believe this is okay if you want to take tight turns. I don't think it improved handling even though they had good intentions when they designed it and I believe the 370z addresses this issue and goes back to a more conventional single axis steering. So retrofitting a 370z knuckle with its subframe or create your own suspension pickup points matching the 370z would benefit the 350z.

So was this a good experiment or did it show absolutely nothing?

venture210

Interesting display of steering geometry. If that anti-ack line corresponds to our cars stock angle in relation to turning, then it could be said that we are slightly toed in under full lock. Not ideal for drifting. Other than intvesting in an angle kit, I wonder what could be modified to go for a parallel full lock angle relation...

canadarob

iTrader: (1)

Great experiment! Thank you for the data.

I hope to try this at different ride heights as well

kazx9r

No problem, lowering it more would reduce the camber gain and make the lower arm parallel instead of slightly angled like the stock one is.

I don't see any real way to fix this without getting new knuckles, too risky changing the tie rod hole. And the 370z may have the same ackerman design but the steering axis is probably fixed.

Just can't do much with it.

jg021v

Well camber correction kits were only 105.00 free shipping...just like to post this right here. After a year of proven, lengthened front tires wear; I recommend them. They have positions for zero camber!




This may clear up steering for drifting purposes. 800.00 gets you this Max Super angle kit, assembly required.

venture210

Last time I checked, those angle kits are out of stock who knows when there will be more available. I've outgrown the extended tie rod mod and plan to get some real angle with that kit when the time is right

SLId3W4YS 89

iTrader: (2)

well, I have got the PBM kit and I will say it is great for the price, but my suggestion when you buy it, buy two of them or at the very least replacements for all of the ball joints on the kit, it does not take much contact from another car or anything for them to bend and if you are using this kit, I kind of hope you are pushing to be drifting that close to someone, or maybe that's just me. Anyways, honestly, if you can foot the money I would suggest going wisefab before you go PBM but if you are ballin on a budget then go PBM but make sure you pick up some extra heim joints or ball joints or whatever the hell you call them.