Hi, after I read the post- "Will these tires work with my VDC enabled car??? Read HERE! ". I did a calculation about my friend setup, and seem to have problem.

My friend has F265/30/19 and R285/35/19.
His new front is actually smaller than the stock by -2.7% (Compare to 225/45/18)
and his new rear is bigger than stock rear by 0.6%. (Compare to 245/45/18)
So far he didn't break the 3% rules here I guess?

However, with his setup, his rears is bigger than the fronts now by 6.3%. This is change of 3.6% (2.7-6.3)
So he break the 3% rules, isnt he?

But how come he tell me he was able to drive the car without problem? Or is my calculation goes wrong?

Thanks

 

the VDC isn't that concerned about the tires. The rim width, section width, rim diameter and section height are more important issues.

just saying.

 

That thread can tend to be a tad confusing.

But you shouldn't be comparing your friends setup to the stock setup, you need to compare it to his actual front and rear and how he was able to maintain the proper stagger to keep VDC happy.

This redirect in that thread helps explain it better:

https://my350z.com/forum/4936171-post42.html

 

Tad? so no one also suggests he adds brake fluid. I want to know what is wrong with his Z.

 

lol

At least is has the correct redirect

 

Tell the truth. You don't have any friends do you.

 

so we only need to make sure the front/rear pairs that maintain the stagger of at least ½" and less than 1". And of course, the rears has to be bigger than fronts.

 

lol, what are you trying to say?

 

Front tire difference from stock "Diameter Difference: 0.2%"
Rear tire difference from stock "Diameter Difference: 3.57%"

OEM tire diameter difference between the front and rear tire "Diameter Difference: 2.67%" with the rear taller than the front.
His new setup is has a 1.12% difference, in the wrong direction. The rear need to be taller than the front.

Simple solution 285/35-19 rear tires. http://www.1010tires.com/TireSizeCal...?action=submit play around on this site

 

osp, just found out i type it wrong, its F265/30/19, R285/35/19

 

You've got it totally backwards. VDC ONLY cares about the OD of the tires. It looks at the rotation rates of all 4 wheels which is determined by OD.

That's why we tell everybody to try and match the ODs of the OEM tires. As you wheels get bigger or smaller, the choice of profile height varies to adjust the tire height to keep the OD the same as an OEM setup.

just clarifying

 

My thread isn't that confusing...is it?

I got your PM aRYip. So here we go.

The essence of the thread is this:

The difference in the rolling circumference of the stock wheels is 2.7% (rears are bigger). As long as you move to a configuration that stays within roughly 3% of this difference, you should be fine. In other words, as long as the difference between front and rear stays between roughly 0% (front and rear same size) and 6% (rear circumference 6% larger than fronts) you should be ok. So aRYip, let's look at your friend's setup:

He's using a 285/35-19 in the rear. This tire has a circumference of 84.35 inches which is roughly 1% larger than the stock tire that came on the Ray's track wheels (which I used in my example). So if he changed ONLY the rears and left the fronts stock, it would bump the difference between front and rear up to about 3.7% because he's adding 1% to the rear circumference (2.7 + 1.0 = 3.7%)

Now let's look at the fronts:

He's using a 265/30-19, which has a rolling circumference of 79.32 inches. This is 1% SMALLER than the stock 225/45/18 on a Rays wheel.

So he made the rear tire 1% bigger and the front tire 1% smaller. He started with a 2.7% difference on the stock tires. That became 3.7% because of the larger rear tire. Now it's 4.7% because of the smaller front tire. But 4.7% is still less than the 6% that the computer will allow, which is why your friend is not having any problems.

Make sense?

 

Yup...Dave's right. The computer could care less about the rim section/width or diameter. It's using the ABS wheel speed sensors to determine the rolling speed of each tire. It wouldn't matter if you were using a 21" rim with a 10 profile tire or a 16" rim with an 80 profile tire (or whatever). It's all about the rolling circumference/speed of the tires in relation to each other.

 

This is generally why I do not do "my friend" threads:

Friend does not have a problem. Little point in solving a nonexistent problem.
Cannot verify sizes with driver.
Cannot verify IF car is VDC equipped.
Cannot verify IF driver operates car with VDC ON or OFF.

VDC threads can be confusing enough communicating with the driver much less a friend.

 

True, but at least it provides one more example that the math is sound.

 

OMG - somebody woke Kelly up.

 

Zzzzz....huh, what? Did you say something? I was sleeping.

 

I hadn't seen you on the forum in a long long time. I see you updated your sig too. No more Viper but replaced it with another big displacement monster.

 

Yeah, I drove the Viper something like 4 times last year and finally went "Well this is stupid." So I sold it and bought something I can drive to work every day and not feel guilty about packing the miles on it. The Camaro is a bit of a pig with a God-awful clutch, but it's fast and comfortable for a guy who's 6'4, 260 lbs.