Hi, I'm wondering if the tires size have some matter with the VDC and slip function

I'm now running my 350Z HR 2007 model with 19x9.5&10.5 and my tires are 245x35x19 and 275x30x19

Yesterday while I was driving the VDC off and slip light came on my dashboard. I stopped driving and let it idle for a while (I was on the phone to my mechanic) Then I decided to drive to him. I have an automatic transmission and I found out that the gear shift at very high rpm so I selected the manual shift mode and drive to the garage. All the way to the garage the car ran normally except that I have to shift the gear myself.

When I arrived at the garage I turned the car off and guess what when my mechanic arrived he turned the car on and BAM!!! The lights were gone!!

I used to be like this once last 3 months.

Today I went to check my tires pressure it showed that I only got 31psi each. Is that the cause? Or the tires size?

Thanks for helpping me and sorry for my grammar.

 

To answer your question, yes. Your rear tire needs to be a small percentage taller than your front tire to keep VDC happy and your current rear tires are actually marginally shorter than your fronts so I would assume if you do any spirited driving with the VDC active then your lights will come on. Additionally, tire height is not the ONLY reason the lights will illuminate but in your situation I would guess it's your tires.

 

275/35-19 is the common and proper rear tire, for some odd reason people can't seem to figure that out

 

Search the "3% rule".

 

i thought a 295/30 works too?

 

Depends on your front tire. It's the ratio front front to rear that matters , not the ratio from stock.

Quick example 175/50-13 and 195/50-13 would work just fine as far as the computer is concerned. Everything else will be very off

 

Well it happened again

While I was driving home this morning, I dropped by a store near my place for about 10-15 mins. When I got back to my car I turn the key to ON position and guess what, lights illuminated normally it will show only ses, airbag, seatbelts and some signs except VDC and SLIP light. This morning it did. I tried to start the car but seems not working. I noticed that when the key is in the ON position, I can hear my car's fan running (the radiator and engine fan) and I don't know why. I took the key off and let it sit for about 5 mins then tried to start again and it worked!!

Any idea?

 

You seem to be describing two separate problems. For sure you need to correct your rear tire size. I’m not sure if that will fix the additional problem you describe.

But... I think there is more to your car's problem...

 

I just went to the garage today for code check. OBD II threw me a lot of codes like C1132, U1000, U1001, P1212, P1610, P1612, P1721. So I decided to remove the HKS SLD which I believe it lead to the problem of U1000, U1001. Found out that after removed the SLD and tried the super fast driving and get back to the garage. Ran the code check again and got no code left.


Could the bad SLD (5-6 years old I think) or the wiring cause all the symptom that I had? Cause I noticed that the problem occurred when I have a passenger with me and SLD wiring are a bit exposed to passenger feet if they put their feet up a bit.

 

You very likely hit out of the 3% range for the VDC due to your tire size.

I have the same wheel size as you and I run 245/35/19 and 275/35/19 without any issues. (Granted I do feel like my VDC kicks in a lot easier than necessary while my car still gets adequate grip with VDC OFF due to my not perfectly ideal tire sizes)

I think best match would actually be 265/35/19 in the rear in your situation if you like how the front wheel+tires fit.

If you look at OEM tire specs, the stock 18 is actually running on 225/45/18 and 245/45/18, so the front and rear have a 20mm difference.

So some ideal possibilities you could run with are below:
245/35/19 + 265/35/19
255/35/19 + 275/35/19

Running the 245/35/19 + 265/35/19 actually keeps your car at a minimal variance compared to OEM (not increasing the wheel+tire diameter) so your speedo will be accurate as well.

The 255/35/19 + 275/35/19 will give your car a slightly beefier tire look, but you will raise the diameter of your wheel+tire, so your speedo will likely read a tiny bit slow if I'm not mistaken.

 

I'm actually doing some research in tire sizing to remind myself again on what to pick for sizes. According to the calculator, a decrease in tire diameter will also make the speedo read as if you're going slower than you really are.

My current setup is 245/40/18 for the front and 275/40/18 for the rear. I'm thinking of replacing the rears with 295/35/18 but I'm still calculating stuff out.

 

I think you will make the variance way more if you don't up the fronts to 265-275.

I'm not sure which way to calc. Either divide the rear diameter by front or reverse and see what % difference you get. I'm currently using 245/35/19 with 275/35/19 and my diameter variance is either 3.01% or 3.10% depending on which way you divide by.

 

Here ya go guys, diameter chart to keep your VDC happy.

18" Sizes

Tire Size Diameter Notes

225 45% 18 25.97 Stock Reference Size
245 45% 18 26.68 Stock Reference Size
245 40% 18 25.72 Stock NISMO Front
265 35% 19 26.30 Stock NISMO Rear

245 40% 18 25.72 Front-Best Alternate
255 35% 18 25.03
255 40% 18 26.03 Front-2nd Best Alternate
255 45% 18 27.04
265 35% 18 25.30
265 40% 18 26.35
275 30% 18 24.50
275 35% 18 25.58
275 40% 18 26.66 Rear-Best Alternate
285 30% 18 24.73
285 35% 18 25.85
285 40% 18 26.98 Rear-2nd Best Alternate
295 30% 18 24.97
295 35% 18 26.13
295 40% 18 27.29
305 30% 18 25.20
305 35% 18 26.41
305 40% 18 27.61

19" Sizes

225 45% 18 25.97 Stock Reference Size
245 45% 18 26.68 Stock Reference Size

235 35% 19 25.48
245 35% 19 25.75 Front-Best Alternate
245 40% 19 26.72
245 45% 19 27.68
255 35% 19 26.03 Front-2nd Best Alternate
255 40% 19 27.03
265 30% 19 25.26
265 35% 19 26.30 Stock Nismo-Rear
275 30% 19 25.50
275 35% 19 26.58 Rear-Best Alternate
275 40% 19 27.66
285 40% 19 27.98
285 35% 19 26.85 Rear-2nd Best Alternate
285 30% 19 25.73
295 30% 19 25.97
295 35% 19 27.13
305 30% 19 26.20
305 35% 19 27.41

 

Dave, shorter tire will cause speedo to read higher and shorten gearing (numerically higher) due to higher wheel speed (tire rpm).

Conversely, taller tire will do the opposite. Speedo will read slower, gearing will get taller (numerically lower). "But officer, my speed showed I was going 65 exactly!"

Here's the science for fellow geargeeks: https://tiresize.com/speedometer-calibration/

 

My vdc-slip light comes on and stays on occasionally, I have stock wheels and tire size... It seems to do it when the weather is cold, or if I spin the tires. (Consequently whenever it's cold outside my summer tires get no traction) also seems to show up after I do some sort of work on the car where I jack it up etc. It hasnt happened in like 2 month's or so. Knock on wood

 

I might be reviving a dead thread but it popped up along my search for my SLIP/VDC issue so I am currently running a 2005 Infiniti G35 Coupe recently got work on her and upon getting my car back i still seem to have this weird VDC/SLIP light issue I’m told it was either because my car was sitting suspended or that it’s my wheels so I just ended up grabbing my new pair of wheels I had for my car but I noticed after putting on that the tire diameters we’re 275/40(19x9.5) on rear and 245/40 (19x8.5) on fronts could this be the problem as to why I’m still seeing my VDC/SLIP light on it only seems to pop on when I start driving it’s never on when I first start the car up

 

Your tire size could be the problem. Your 40 series side walls are too tall. The correct sizing is 275/35-19" on rear and 245/35-19".

 

90% probability this. ^^^

With the 40 aspect tires, there's a 3.5-3.6% delta.

With the proper 35 aspect tires, delta is just above 3%, which is exactly what the ECU is expecting to see. Too much above or too much below (~ +/-0.5%) is a red flag and triggers VDC.

Has NOTHING to do with your suspension. You could be aired down into the weeds (if you had air) or jacked up 4x4 style and that wouldn't give any readings to the ECU that would trigger slip controls. It's all about wheel speed.

 

A bit off topic but im also in the process on new wheels and my car happens to have vdc. I want to go with 18x9.5 22+ 255/40/18 squared. Do you think this would cause any problems with vdc just daily driving?

 

Most likely, VDC doesn't like squared setups.