Sevs2k

Would it affect the traction control or VDC?

I ask because I will be buying some winters soon and I want tp put 225/45-18 all around to save cash and also because a thinner tire is better to cut snow...

The ratio of front tire to rear tire rotations will change since the fronts remain the same size and the rears get smaller... Will this affect anything?

Thank you.

Blue Liquid

Yes Holmes, this will affect the rate at which you put miles on your car. It may also negatively affect ABS (very bad) traction control and VDC. If the rear wheels are a smaller diameter, they will spin faster at any given speed, and your car will show more miles on the odomoeter than are actually on the car. This is bad as well.

Sevs2k

I am aware of the miles thing and so on. I am not going to be doing much driving in winter anyway...

Just worried about the effects of the ratio difference on the elecronics ability to do their job... VDC, ABS and TC...

Sevs2k

I've been told by my tire shop to run 225/45/18s all around since its better not to have a stagger set-up in winter.

However I am unsure of the effects it will have on the VDC systems ability to keep the car under control in a skid.

I need help.

Blue Liquid

Sevs2k, here's the real problem: Nobody really nows what effect will occur, in terms of the electronics. Nissan recommends that one does not go more than 0.5-0.75 inches from the stock diameter. That's all they mentioned to me when I asked. However, others on this board will quickly tell you that they run the same size tire all around and they have 'no problems'. However, the problem with that kind of subjective opinion is that these people really have no idea what is going on with their systems. Their opinion is based purely on their seat-of-the-pants driving. As far as they can tell, the TC, VDC, and ABS is still working, and they still slow down quickly as they did before. The real test would be to test a car both before the stagger and then after, same tire brand and type, same day, etc. Then see how/if their stopping distances are affected. Until something like this is done, every answer you get will be someone's opinion and not based on fact. That's why I worded my original post as I did. We already know that the speedometer and odometer will be affected, because we can do the math. The rest, so far only Nissan knows.

Sevs2k

Yes, thats what I fear. I thought someone had some official statements from Nissan or some kind of definitive answer, like the 0.5-0.75 inch rule... Thanks.

The tire shop I go to are real tire experts and unlike most delears I trust what they say. However with the new electronic gismo era, things are a little different and I wouldn't expect them to know much about how TC or VDC gets affected.

They told me that they have already installed 225-45-18s all around on 350Zs and G35s with no problem reported. What I told him is almost the same thing you wrote to me. How do these people know that their VDC and ABS are still performing properly? Yes, teh car should be still ok in a straight line but what if it gets sideways, is the VDC going to misjudge and possibly overcompensate and cause a crash... I don't know...

I am probably going to go with the stock stagger setup 225-45\245-45.... I am just worried about the ability of the rear tires to cut snow... I believe this setup is might end up being safer though since there aren't any unknowns.

Jason Bourne

I'm running 235/40-17s all around (track tires) right now and it does seem like my traction control is getting confused occasionally. I have an enthusiast model (no VDC) and occasionally while accelerating, the slip light flashes and it cuts back power. This tends to happen when I am also turning but the car is definitely not losing traction (this happens even in the higher gears, at art throttle, on dry roads with very grippy rubber so there's no way I'm really spinning the tires). I'm guessing what's happening is that it is measuring the wheel rotation rate of the outer rear wheel and comparing to one of the front wheels and not seeing the difference that it expects to see (rear wheels spinning faster than usual).

It doesn't bother me much, I've just gotten into the habit of turning off TC whenever I drive the car and all is good again.

ABS is unaffected.

Jason

NCZMAN

Correct me if I am wrong, but Mileage is not determined by the rear end, but by the transmission, so him going smaller will not accumalate more miles, but only throw off the speedometer? .

Blue Liquid

C'mon man, how can you say this? The truth is you have absolutely no idea if your ABS is affected or not. You would need to run the same width and compound tire, but in the two different heights to simulate 1.) the correct stagger, and 2.) your current stagger, and then do 60-0 or 70-0 stops or what have you, to really test whether or not the ABS is affected. I believe your claim about TC being thrown off because you have the proof (SLIP light while no obvious loss of traction and car losing power temporarily). The ABS thing tough, as I've said before, is pure conjecture.

Sevs2k

That's kind of what I suspect will happen, I believe the VDC will especially get confused with this change as it will see what it believes is the rear wheels going at a faster rate than the front wheels and possibly compensate for it by applying brakes to the rear. Braking only in the rear in the snow = big no no.

Jason Bourne

No actually, I have a really good idea. I was able to push my brake points by a full brake marker deeper at both of the threshold braking zones at Watkins Glen this weekend relative to last time. That is very consistent with my previous experience of going from street tires to these same (exact) tires on my BMW where there was no size mismatch. If ABS was affected, this wouldn't be the case.

Furthermore, ABS does not modulate based on small differences such as the 1.5% overall diameter difference that exists between a 225/50-17 and a 235/50-17 tire. If that were the case, being down by about 3-4 psi in one tire would screw up your ABS right away.

Finally, as an instructor with many thousands (10,000+) track miles under my belt, there's no way I couldn't feel a difference like early ABS activation.

Jason

Blue Liquid

Hey, are you Treadstone? Look at what they make you give... But anyway, what I'm postulating here is that it's going to be nearly impossible to tell if your car is now taking an extra 5-10 feet to stop, on average. I understand you have a good feel for your car under these specific conditions. Also, the whole thing about going a full marker deeper than before...well, that just doesn't hold up to scientific rigor, my friend. Who knows, you could have extra heat in the tires that day, feeling more confident, etc. There are just too many other variables involved.

As for this quote "Furthermore, ABS does not modulate based on small differences such as the 1.5% overall diameter difference that exists between a 225/50-17 and a 235/50-17 tire.", I'm curious as to how yo know this. I'm not saying you're wrong, I just want to know how you know this.

And now this quote, "If that were the case, being down by about 3-4 psi in one tire would screw up your ABS right away.", this really makes me wonder. If this is true, then are we to assume that people's ABS is not working properly until they get their tires up to the recommended operating temp (and therefore pressure) or what? You follow what I'm saying? If my tire manufacturer recommends 35 psi cold, does that mean that after filling to 35 psi cold, that when my tires heat up on the highway and get to 38 psi that my ABS is off? I smell liability isses there.

So i'm going to stick with my view that it is really only a guessing game, and until actual, controlled testing is done, nobody except Nissan's engineers are going to really know the answers.

Jason Bourne

Hey Blue Liquid, I like the Ludlum reference!

Two things:
First, I was comparing going from street tires on the z to R compounds on the Z to doing the same thing in my BMW on the same track (actually they are the same exact tires too, I just moved them from the bimmer to the Z). In both cases I was able to brake deeper by one full marker. On the BMW the tire sizes were the same as stock while on the Z they were not and yet the result was the same.

Second, the way ABS works is by measuring individual wheel rotation rates and comparing them against each other. If it detects a difference while braking it will pulse the brakes on the wheel that is going slower (sometimes a whole axle rather than an individual brake). My example of a low pressure tire was to show that brake engineers need to allow for some minor variation between the wheels before ABS kicks in to account for one tire being low on pressure or being in a corner. If all of your tires are lower than they usually are, it would not matter since they are still turning at the same rate until they all heat up (more or less equally) so this is really a seperate issue. But utlimately my point is that the engineers have to build in some tolerance before ABS kicks in or it would engage in many situations where there is no reall lockup. I'm not sure what the difference has to be for ABS to engage but I can't imagine it would be any less than 5%.

And one more point, if ABS were thrown off by my tire sizes it would show up pretty noticeably on the track, it wouldn't just prolong my brake distances by a few feet (which I could potentially not notice). Believe me, given the amount of driving and brake testing that I have done (tried at least 10 different track pads over the years) I am very in-tune with my brake system and I wouldn't miss something like that.

Of course you may still think that I'm BSing you in which case I would encourage you to attend a driving school where I am instructing and I'll give you a ride. I'm actually going to be at Pocono this weekend, which isn't far from you and I would be glad to give you a ride and show you that the brakes are working just fine with my tire sizes.

Jason

Gendo Ikari

This is what would happen:

https://my350z.com/forum/showthread....threadid=44129

Blue Liquid

Well Jason, it's obvious you are very experienced, and very knowledgeable about the subject. I think it's my scientific traning that makes me look for evidence of some effect. As a result, I tend to cast doubt on those who say they think they can feel a difference, etc. I just like to see proof, but by no means do I think you're just some random user on this board trying to BS me.

As for meeting you at the track, I'd love to at some point in the future. I'm always ready to listen and learn from someone who knows. With my Type R I've been to Pocono North, Summit point, and Lime Rock Park. It's only a matter of time before I'm back on the track for the first time in the Z. I either go with the Schattenbaum Porsche Club or NASA. I'll be sure to post on the board here when I schedule my next outing. And as for a ride..well, I went with my instructor at Lime Rock, first ride with an instructor ever, and I really thought he was going to kill us both. He had his supercharged NSX (shod with 295 Kumho's)drifting around that track, he in his 5 point harness, me in the standard lap belt. I almost asked him to pit and let me out!

Sevs2k

so basically, it's what I thought when I first posted this thread.

You want to maintain a setup close to the 26.0:26.7 inch which is the front to rear ratio.

If I put 225-45s all around, I will be within the borderline limit as I will be at 26.0:26.0 ... Almost 3/4 inches less in the rear while staying stock in the front...

This would explain why Jason Bourne is not having any problems, he is at 1:1 ratio front to back which is borderline acceptable.
While someone like the guy in the link who has gone with smaller tires in the rear, upsets the ratio and has VDC problems.

I think I am going to stick with stock sizes then.

Now, the only problem is that the rear 245-45-18s are back ordered... Hopefully they will make it in on time.

Thanks all for your help.

D'oh

Not anything definitive, but some general impressions, again from race tires.

I'm running 265/35-18 all around for race tires, which is a whopping 5% smaller on the rear than stock (and 2% smaller than the stock fronts). Your tires would only be 2.7% smaller than the stockers.

I have not yet had any problems with TCS/VDC/ABS activating when I don't want them too. On the other hand, I haven't had TCS/VDC activate at all either (turned them off on the track, and I'm not trying to get race tires spinning on the street). ABS I have experience with.

The ABS has not been affected enough make a significant difference (again based on subjective things like "feel" and so forth). Also though, there is no way a car manufacturer would be able to release an ABS system that was not tolerant to differences in tire size. Remember, we only have one spare tire, and the car will need to work with that tire on either the front or back of the car. Also remember that the tire pressures can change by +/- 5 PSI easily given different weather conditions. Even though Nissan recommends one thing, they will need to make the car tolerant of small deviations. Therefore, I would not be concerned about the ABS system (again, no scientific proof of this, just experience and common sense - plus maybe some...um...lets just say "courageousness").

The traction control shouldn't activate if your tires are all the same size, but it will probably be much more sensitive. The computer will think you are on the edge of "slipping" any time you are moving, even though you have perfect traction. Therefore, you may be more likely to set off the TCS (maybe due to pressure/temperature changes, bumps, corners, etc). TCS is pretty simple since all it does is cut power, so it will still work but it will just be more sensitive.

The VDC I do not understand well enough to know if and how badly it might be affected. I would however be very surprised if a change of tire size less than 3% was enough to mess things up. Your stock tires will change by a similar % just from tread wear. So, if you look at it that way, your 225's will be larger than a worn set of stock tires anyway. Although I did see some indications of SLIP when I had my bald stock rear tires and new 245/40-18 front tires. It only happened twice though, in about 4000 miles.

Either way, up to you.

I admit, it would be ironic to be running snow tires that caused VDC to fail which in turn allowed you to crash when you otherwise wouldn't have.

-D'oh!

Sevs2k

Nicely summed up. Thank you.

The way I see it, I have two scenarios:

1. Keep stock stagger = Larger footprint in the rear which isn't good for driving through snow since the fronts will plow through more easily... In this situation, I know what will happen.

2. Go with equal tires all around = Unknown results, could drive fine in a straight line for 4 months and one day, because of a slight sideways skid, the VDC might overcompensate and apply too much brakes etc... It's unknown so it's a gamble...


I am still undecided on what I am going to do, as it stands now, looks like I am going to go with the stock stagger setup but since th 245-45s are back ordered, if they don't make it for snow season which is in 1 month, I will be forced to go with setup # 2.