DavidM

Hi guys,
I'm trying to make my 350Z handle more to my liking. Part of it involves putting same width/height tyres on the front and back. Though my 350Z has the VDC, and I've read this in a 'Sports Compact Car' article:

"It should be mentioned that our tire selection will most likely disable or at least really **** off the Vehicle Dynamic Control system if you have one. VDC observes the world through wheel speed sensors and assumes the rears are slightly taller than the fronts. With all four the same size, it will always think the rear tires are spinning slightly."

Last thing I want is to be driving with the VDC cutting in all the time (ie. permanently). So I'm wondering if there is anyone with VDC, who is running same width/height tyres on their 350Z? If so, do you find the VDC to be a problem? Is it still a problem when you have he VDC in the OFF possition?

Also, is there a way to either calibrate VDC to 'behave' with equal tyre width/height front and back? Or is there a way to dissable it totally (as I don't really care much for it)?

Any help/suggestions will be greatly appreciated. Thanks.

2003z

iTrader: (7)

it doesn't really **** it off that much, but if you want to maintiain the stagger, you can go 245.40-18 front and 245.45-18 rear, and lessen the understeer while keeping the vdc happy.
fwiw, I run 275/40-17 all around for autocross, and sometimes for street without any problems.

DavidM

Thanks 2003z. Can you also tell me if you are talking about the VDC when it's in the OFF or ON state (or both)?

...you can go 245.40-18 front and 245.45-18 rear, and lessen the understeer while keeping the vdc happy.

If I could, I would. Though, the tyres I'm picking up ASAP are for my spare set of wheels (ie. R-spec) and I can't get those in those sizes ... just 245/40/18". Once it comes to my road tyres, then I should be able to find a set that will give me both 40 and 45 profile.

it doesn't really **** it off that much...

Can you also elaborate on this? Can you define 'too much'? Me, I would ideally have it not interferring at all. Not sure if this will be the case even with the VDC in the OFF state.

ares

iTrader: (2)

Id venture to say 245/40 is farther from stock stagger than equal all around. but I havent dont the math.

either way, as he said, it wont **** it off that much.

meaning for normal driving it might step in a bit easier. as the article pointed out it thinks the car is in a continuous burnout, but only slightly. if you really do spin the tires a little bit it will be quicker to step in as your closer to the line.

normally this shouldnt be a problem,might even be good.

on the track this might be a nuisance, which is why youd wanna turn it off.

2003z

iTrader: (7)

Specification Sidewall Radius Diameter Circumference Revs/Mile Difference
225/45-18 4.0in 13.0in 26.0in 81.6in 777 0.0%
245/40-18 3.9in 12.9in 25.7in 80.8in 784 -1.0%

I drive to and from events on my race tires and haven't noticed any problems with VDC on or off

ether

per the question on the other thread, when VDC is turned off.. its off period... it will not kick in again, there are no residuals functions that remain

ether

one more thing, i hate this TCS auto reset to on, if I needed help in driving a sports car I wouldn't have bought a sports car, the situations that this kicks in is exactly when i want 100% control of the car..

oh well.. must wait until somebody creates an auto TCS solution..

back to topic.. same size tires all the way around will just decrease the amount of slippage detected before this VDC/TCS kicks in.. take note that nissan did allow for some margin or error in sizes.. for example my base came with only a 1.6% (i hope i calc that correctly) difference.. something that is not that hard to partially wear away or to arise from differences in tire pressures

DiRN

There was a thread of this nature. Someone had developed something for his G that should work in the Z too. I don't know if anyone tried it. If only the search worked...

DavidM

Specification Sidewall Radius Diameter Circumference Revs/Mile Difference
225/45-18 4.0in 13.0in 26.0in 81.6in 777 0.0%
245/40-18 3.9in 12.9in 25.7in 80.8in 784 -1.0%
I drive to and from events on my race tires and haven't noticed any problems with VDC on or off

Thanks 2003z. Have you used the same tyre height/width on the track as well? As that is what I'm getting the new set of tyres for. I'm wondering how it is when you're pushing hard and close to the limit, or your back steps out?

per the question on the other thread, when VDC is turned off.. its off period... it will not kick in again, there are no residuals functions that remain

Sorry, IU wish that was the case (in whichcase I'd be extatic), but that is not the case. I have experienced the VDC (or some kind of driver aid) when I had the VDC off. When I was on the skid pan (ie. 'cone dodging'), this is when the car would 'intervene' even with the VDC in the OFF state:

a) Get the car sliding and touch the brakes. This will make the car
straighten itself. ie. it'll stop it from sliding ... which is not what you want on the skid-pan, but never really bothers me on the road or even track as you don't do that there. You only hit the brakes if you're really out of control ... not to slide the back around even more.

b) The other way is a bit harder to observe. Though, I think there's some intervention if you kick the back out. Anytime I get the back sliding out (ie. under powered, out of corners), it feels like the brakes are grabbing the rear wheels (or just one of them ie. the inside one). It seems like the car wants to correct the slide even though you have it under control. Though, this is very subtle so hard to put my finger on.

Also watch the Best Motorring International v6 (as well as 7) and it shows you how the VDC (or whatever 'aid' it is) kicks in when trying to slide the car.

btw, I'm not 'trying' to slide the car at all, but as you mentioned above, when I'm on the track and on the limit, last think I want is the car fighting me for control and upsetting the balance as well as my driver inputs. So I'm looking at it from mostly drivinng on the track ... or just at 8/10th or above.

2003z

iTrader: (7)

Yeah, what you are describing is called the 'ice mode', I believe. Doesn't matter if its on or off, it still kicks in. As for the same size on the track, yes I have run that way, and I like it a lot. The car has a little less understeer, but is still very controllable, even at the limit.

ether

what you describe is TCS kicking in.. luckly I have an off button for that.. VDC is off.. TCS works by cutting fuel to one or two cylinders to correct in an oversteer situation..

VDC utilizes TCS and the ABS system to manage fuel(engine power) and brakes to correct the travel path (using sensors (yaw, pitch, etc..) to figure out what the car is doing and is supposed to be doing)

So when i said VDC s off its off.. what you see kicking in IS not VDC but TCS.. a technical point that probably did not answer the original question

ether

ignore my above post... VDC does use more sensors and then tries to correct by using TCS and ABS systems.. but the correction to my above post is that when you hit the VDC off button it should also turn off TCS (amazing things happen once you read the service manual)

can't really explain what you are experincing.. i have the base model with just TCS which i can turn off. On the track with it off i do not experience what you have seen, especially b) i have complete control over oversteer

Jason@Performance

iTrader: (11)

you would need to do something like...

245/40/18 front
245/45/18 rear...

275/35/18 front
275/40/18 rear...

etc etc...

for it to work with VDC

igor@af

I just came back from Mid-Ohio running this setup:
245/40/18 F
255/40/18 R
and the VDC was working great.

DavidM

Ether, you are probably right - what I'm describing might not be directly related to the VDC but to other 'gizmos' in the 350Z. I think that the (b) situation comes about due to the LSD used in the 350Z .... ie. it applies the brake to the spinning wheel (from what I gather). The (a) situation may be VDC related, but it might be BA (ie. Brake Assist) related .... not sure. Still, would be good to find out for sure as if it's related to something else but VDC, then the same width/height tyres should not cause a problem wn it is in the OFF position.

shimz350z

hmmm i have a touring and you can see what i've done below(not much but relative)

thank God for tcs(chicago weather) but when i push that button and it turns off.......those tires can spin pretty well if I push the metal to the pedal. when it's on...it sure protects me.

i'm assuming that once you turn it off you have pretty much all the control you want....only because I tend to do donuts in the rain (assuming it'll save rubber and i'll get the same enjoyment)
-feel no resistance whatsoever.

once again all in layman's understanding.

p.s
I don't feel a difference...possibly the set up maybe making my ends loose...but i think it's the gradual break in power of the car that is doing it.(need to track it)

ps.II
at 5,000 miles prior to my rim/tire change my end had already started loosing it so...the difference...doesn't seem much except for a stiffer bounce.

tcz

just to clarify , your wheel can be any width but the height of the tire (if thats what you call it) has to be 5 apart ... fr instance 40 and 45? 35 and 40?? then the same size wheel (18) and my wheels could be 245 front and 275 back no problem? this would keep the ratio the same?
Tyler

Syentifiq

You've pulled the brake light fuse right?

jreiter

iTrader: (6)

This is exactly what I was thinking the other day. However, this results in the front being an entire 1.1 inches shorter than the rear. Seems like that might make the VDC unhappy, too, since the stock difference is only .7".

But anyway, I'd probably just go with 275/40/18 all the way around. The Z is a heavy car, so the 275 width all the way around should make a noticable difference over 245 width all the way around. More width the better. The VDC might become more sensitive when having no stagger, but that should only be noticable during heavy cornering where you are pushing at the limit. At that point, you'll probably have your VDC turned off anyway, so it shouldn't matter.

digerydingo

One more thing to consider, if you plan on getting suspension most, if not all, will not work with VDC anyways. If that's the case then you don't have to worry about driving with VDC off.

For the VDC off discussion, Nissan builds the VDC like all other manufacturers in the sence that even when VDC button is turned off the system will engage 100% when the brakes are activated. Reason why Nissan refuses to admit this is confusing because all other manufacturer Mercedes, BMW, Audi, Volvo all freely admit that their systems reactivate every time the driver steps on the brakes as they beleive it would help recover the vehicle if necessary, and then the system shuts off once the brake is released.

VDC on the gas is still unproven though. DavidM: I know what your talking about with the sliding but I think it has more to do with bad dampening rates. I find when I slide the car about on rough, cracked, bumpy tarmac I feel what you do however I've been on some very smooth tracks and the car slides effortlessly and predictably when pushed?? Don't know if I'm missing something, mind you when my car heats up a good deal it seems to shut off VDC, TCS and ABS. I'm getting the dealer to check that out.