This question should be straightforward for the more tech oriented guys/girls on this forum. If you don't know the answer, please do not guess, as I have already tried that.....and failed.

I recently ordered a set of Enkei RPF1 17" track wheels, stepping down 1" from my stock 18" RAYS. I wanted to save some weight, and money by purchasing smaller tires for the track.

Tire Rack had a massive blowout on Bridgestone RE01R's, yet the only size available was 245/45/17. I decided to try running a square setup, and purchased the set for only $380.

I drove on them all week to break them in, and then ran them yesterday on a very fast autocross course. I finally got them gripping well halfway through the day, and they were feeling great.

The problem came at the end of an 80mph straight, when I quickly found out I had lost my ABS. Sliding through a cloud of tire smoke, I noticed the infamous VDC, ABS, and Slip lights were all brightly glaring at me. I finished the runs without any ABS, which is a great exercise in threshold braking a flying 3200 lb monster.

I turned the car off, and on again, and within 2 minutes, the lights went off, and I drove it home.

My theory is the rear tire is not taller than the front with the 245/45/17 setup, and after I activated the ABS a couple of times, the computer took over, and shut the whole damn thing down. It reset itself when I restarted the car, but I'm willing to bet if I activated the system a few times quickly, the computer will turn the VDC/ABS system off again.

If I go to a staggered setup of 225/45/17 front, and 245/45/17 rear, there is a overall diameter difference of 3.9% front, and 3.75% rear....compared to the stock 225/45/18(F), and 245/45/18(R) sizes. From what I have been reading, the computer would like to see no more than a 3% overall difference in size.

The overall percentage difference is fairly equal front to rear (3.9%(F) and 3.75%(R)), but is the difference enough to make the ECU shut down the VDC/ABS when I get hard on the brakes???? The rear will be taller than the front, and I know the computer likes that.

I'd like to run a staggered setup of 225/45/17 front, and 245/45/17 rear without any unnecessary ABS drama. Is this going to be possible with the overall difference in size???

Thanks.

 

You run 245/45/17 all around? VDC might not like this.

 

I only tried running them all around because of the great deal on the RE01R's. And no, I don't think VDC likes it. The question is, once I add a 225/45/17 up front, will this problem indeed go away?

 

Maybe this site can help you.

1010Tires

 

Was VDC turned off ?

Also remember and a lot of people don't, ABS also works off our tire stagger.

 

Thanks for the link. According to the calculator, it recommended staying within 3% of the original size tire. I'm up to 3.86% off size right now.

Yes, I was running VDC off. Do you think running a 225/45/17 up front will solve the problem, even if it's over a 3% variation from the OEM size?

 

I believe what you saw was ICE mode. It's a condition where the ABS/TCS/VDC system gets so confused that it disables everything. The only times I recall it happening to people is when the car spins or gets totally out of control, i.e. doing donuts.

I assume when you're autocrossing, you have VDC turned off, correct? I've been autocrossing for years now and have never experienced ICE mode but I always run with VDC off. I'm using 265/35/18's which are probably close to the 245/45/17 in OD so I really doubt it's your tire size.

 

I always autocross with VDC off. I've only had this particular setup for one week, and the very first time I tried autocrossing with it......the ABS went out.

The only thing I can think of, is the non-staggered setup had something to do with it. The rear tire is not taller than the front now, and I read it needed to be, for what it's worth.

 

Why do people thing its a 3% thing with stock size, its a 3% thing with front to rear. you could run a 35 in truck tire in the front and a slightly larger (withing 3%) in the rear and VDC willnot care. Same goes if you were to put 13 inch reverse offset daytons on your car. 175/70-13 and some 195/70-13's and your good to go.


Yes a lot of people run square setups without problem (with VDC/TCS off)

 

I was running it off and had problems.

This is what I saw when I typed some info into the Tire1010 calculator:

 

I'm running a 2.63% difference between front (1.12%), and rear (3.75%) right now, and VDC doesn't seem to like it. The largest Dunlop Direzza Star Spec I can run in the rear is a 255/40/17, which will bump the difference to over 5%.

The main problem is, the tires I run (Star Specs/Bridgestone RE Series) don't come in a hell of a lot of sizes. If I could get them in a 50 series, or a wider 45 series, then the problem could be solved easily.

From what you've said, I should be able to run a 225/45/17 front, and 245/45/17 rear with no problem, since it's only a .11% difference between front and rear???

 

That's your answer.

 

Running 275/40/17s all around myself with VDC off. ABS was a little sensitive with the big grip (V710s), but has never led to the ICE mode.

 

Well I read it from a guys' post on here. He could be a nutter.

 

With VDC/TCS turned off, the front/rear stagger is meaningless. The 3% or 0.25 - 0.75" rules only come into play for TCS/VDC. A lot of us are running square setup, both for autocross and on the track with no problem.

I drive mine on the street occasionally as well as to/from events and have only had VDC kick in once or twice and that came from pushing the car too hard.

My setup is 0.4" shorter than yours so I doubt your tire size is too small for VDC/TCS.

Although it would be odd and rare, maybe one of your wheel sensors is damaged and that is causing the whole system to screw up now. Or, the computer is wacked.

 

Hi ZRated67,

I read your thread and the responses, and I notice the replies are from members who have been here for awhile and maybe have older Z’s than your car (Your join date is fairly recent, so I wonder if you have a more recent model-year Z).

Question: What year is your Z? If it’s a newer model, perhaps its version of ABS behaves differently.

I’m guessing (something that you asked responders to refrain from ), but other than that, the only explanation is a defect (which I doubt is the case).

--Spike

 

Spike - one thing that I have observed over the years is that VDC/TCS seems to have gotten more tolerant over the years. I base that on less and less complaints about it kicking in unexpectedly. It's either that VDC/TCS is more tolerant or more people are finding out the rules on tire sizes BEFORE they buy new ones and aren't making the same mistakes as were common back in 2003/2004.

 

Dave, I agree. It seems that the 2003 to 2004.5 VDC-equipped models apparently had the fussiest function/activation. I certainly noticed this on my 2003 Performance model when trying different tire setups (sizing, mixing different brands front-to-rear, etc.).

One thing I’ve never experienced is ABS “shut-down,” which seems to be ZRated67’s problem report.

ZRated67 states that his VDC was off when ABS failed. I’ve read postings from members here who state that turning VDC off does not completely disable the device (they same some features of VDC remain active). But, I have no idea why ABS would shutdown under any circumstance. Isn’t ABS supposed to operate even with VDC off?

I suppose if the “system” senses total failure, it would appropriately turn off everything (including ABS?) since it is no longer capable of providing its inherent safety features (that are tightly integrated and are probably not designed to work safely as independent functions).

But, I’m guessing… and that’s exactly what the OP asks that we not do answering his question.

--Spike

 

Spike

I drive an 03 Track Model. I track the car with VDC off, and yes, the ABS is fully functional during that time....as you suspected. Pushing the VDC OFF button doesn't affect the ABS system in the least.

My only complaint is the ABS turned itself off, and then apparently reset itself when I restarted the car.

I'm convinced there is a delay in the system, as to when the computer tells the functions to shut down. The new wheels don't have the TPMS sensors installed, and it takes the ECU a good 30 miles before the annoying orange warning light comes on. I think that once I activated the ABS system on the track, the ECU said "Nope. We don't like what we're seeing here" and shut itself down. Not a good safety feature if you ask me.

I'm hoping that getting a 225/45/17 front will fix the ECU's discrepancy. What is your opinion??

 

Here's part of the problem with VDC - hence the threads about "fully" disabling it. When you turn it off, it's not really 100% off. You can beat it hard and never have it kick in, but there is some point where you really upset the car and the ICE mode kicks in.

There's a note in the FSM under the system descriptions that states:

The ABS warning lamp, VDC OFF indicator lamp, and SLIP indicator lamp might turn on when the vehicle is subject to strong shaking or large vibration, such as when the vehicle is on a turn table or a ship while the engine is running. In this case, restart the engine on a normal road, and if the ABS warning lamp, VDC OFF indicator lamp, and SLIP indicator lamp turn off, there is no problem.

While it sounds like the mode can be triggered by subtle movements, in reality it is triggered by violent movements. I've spun my Z in a couple autocrosses and while VDC was off, it appeared to kick in anyway. I didn't trigger the ICE mode though.