Hi guyz, recently i needed to have my rear tyres changed due to unrepairable puncture. I had stock 225/45/R18 front and 245/45/R18 rear, My fronts are fine so only the rear is replaced to 245/40/R18s. Does the 45 to 40 profile change the VDC in any way? the tyre shop says its fine. But after some driving I'm finding VDC kick in earlier and itz a lil annoying at times.

Btw, my fronts are still 225/45/R18 rears are currently 245/40/R18.
Should I change my fronts to 225/40/R18 to make it the same?
would that make the ride better?

all suggestion appreciated. Thanx

 

Obviously the tyre shop people don't know the intricacies of your 350z's VDC. Yeah, changing the fronts to 225/40/18 will make the vdc a bit better, but im pretty sure your speedo is already out.

Definitely worth 1) Sticking to stock sizes or 2) Carefully selecting your tyre / rim sizes with an online calculator to ensure the DIAMETER of the tyre remains within 2 or 3 percent of stock.

 

so what about those that go from 17' to 19" with no issues ??

 

With a bigger wheel they get a smaller profile tire so the overall size is inititally the same.

Why didn't you just get stock size tires? Saves a lot of headaches and money

 

The front tires are taller than the rear.

Speedometer error is +3.75 MPH@100 MPH.

 

for the vdc to work properly your tires have to be stagerd. the rears should be bigger than the fronts.

 

tYres eh?

 

Fronts>Rears is a sure recipe for VDC malfunction. Just return rears to stock sidewall height.

 

Would the correct change out for the tires be from stock:

Front: 225/45/R18
Rear: 245/45/R18

To modified

Front: 245/40/R18
Rear: 265/40/R18

or

Front: 245/40/R18
Rear: 275/40/R18

 

Front: 245/40/R18
Rear: 275/40/R18

 

The overall tire+wheel diameter is all that matters. So run factory size through any online calculator, figure out the F/R ratio and compare it with your planned size. If it isn't off by too much, you will be fine, otherwise not. But since no one knows what VDC's acceptable variance is, any assurance will always be just a best guess.

 

THanx everyone, couldnt get stock size as they werent available and i had a bad puncture at rear tyre so had to go for 40s...now i need to change the fronts to 40s too....
shouldve askd first...

so havvin 225/40/R18 front and 245/40/R18 would be ok+better?

 

I wouldn't do that. With this setup, you have 4 tires all sized wrong.

I know what you're thinking... but trying to maintain the same percentage difference when the sizes are wrong is risky. In this case, two wrongs don't make a right.

--Spike

 

+1, 225/45/18 and 245/45/18 should be used, there isn't a good reason to go with the 225/40/18 245/40/18 combo anyways

 

I have a brand new set of 245/45/18 tyres just fitted to my car, only a few hundred km's on them.

I want to change my fronts to 245/40/18 and my rears to 275/40/18 as I have just bought a set of aftermarket rims.

Depending on the cost of shipping from NZ to Australia and visa versa I would be willing to swop my tyres with you.

 

or assuming your wheels up front are 8" wide you could put the 245-40-18 up front and buy some new 245-45-18 for the rear

Improved handling, no VDC/TC issues. Only 1 small flaw, it becomes TAD harder to keep the car going straight at highway speeds. But its not BAD

 

I’m running 245/40-18” fronts and 245/45-18” rears (Goodyear Eagle F1 GS-D3) and this setup tracks just great on the highway. I can take my hands off the wheel, and the car continues going exactly in the intended direction.

Maybe I misunderstood your post.

--Spike

 

I have same setup as you then (Eagle F1 GS-D3), maybe its the *bad* roads where I am that makes it so it doesnt track as well as stock sizes. As I said though, its not that much worse.

 

Actually, you make a good point. When you mount wider tires on the front, you risk poorer straight-line tracking. I’m sure there are people who will argue this, but it’s a fact. 4WD enthusiasts are very familiar with the phenomenon. They usually mount the same sized tires all around, and notice that the wider the front tire (past “optimum” width), the worse the vehicle tracks.

The staggered setup (width wise) helps keeping the car going straight and feeling this way. If you go all square width wise, the front can move around a little more in relation to the rear. I never notice this with 245’s on the front of the Z, but would be concerned going much wider. I suppose the right suspension and tuning permits a wider front, but that is past the casual driver. Nissan recommends replacing the stock springs, shocks, and sway bars when mounting wider than 225 on the front.

--Spike

 

What I think the problem is for him (and I might be wrong here) is the Slip light comes on when cornering as because of the different size tires the car thinks it is skidding and the traction control comes on. Thats what happend with me when i had non standard tires on anyway.