Yes, and the fastest guy out there is on 225/17's. 2nd fastest on 265s'...hmmm.

 

guitman32 give us an update mang! How you likin the new rubber?

 

+1

I run a 245/40 in the front and a 275/40 in the rear and I would say the 275 is just a tad too big. You end up getting noticable sidewall flex that makes for a pretty bumpy ride. On the next set I will be going with a 265/40 and I suspect it will be just about perfect. This is with the BFG TA\KD by the way...

 

The difference is barely noticeable to the eye.

 

Remember the rims are not the same. Just a heads up.

 

Unsprung weight is definately a huge factor with regards to the performance of the suspension, but on the track model the car has 18 inch rims stock and the OEM Volks are actually pretty light. With that in mind using the stock track rims with a proper tire should be great for most track aplications. The problem is what is the best set up for the rims.

There are two schools it seems:
Wide rim narrow tire for sidewall strength.
Like 225 tires on an 8 inch rim

Wide rubber equals more traction, but sidewall strength is sacrificed.
245 tires on 8 inch rim

Does anyone know if going with a 245 30 profile tire instead of 40 would enhance the sidewall strength to get the best of both worlds? Also this would make the overall tire hight lower so I have no idea what the implications would be on the Speedometer although I guess you would get a fraction better accelaration out of it?

Does the 350z speedometer react to different tire sizes or does it adjust?

 

The Z speedometer does not adjust. There were a few guys who tested things out side-by-side and the speedo was different with 20's than it was with 18's.

 

Well that pretty much kills that experiment

 

Ah yers, well I have had the pleasure to attend an AutoX event this last weekend and really put the new tires (Falken Azenis RT615) through their paces...my thoughts:

To reiterate, my sizes are 245/40/18 in the front and 255/40/18 in the rear on factory 03-05 track Rays (8in front, 8.5in rear). Pics are on page 1. The balance of the new setup coming from 225 fronts and 255 rears is more neutral (obviously). The sidewalls, however, are a bit less responsive than the Potenzas in 225 (Front) and the Pilot Sports in 255 (rear). I think this is a result of two things:

1. The increase in sidewall flex under hard cornering due to more sidewall bulge of wider tires
2. The Azenis sidewalls aren’t the stiffest

That being said, I think this has an almost negligible effect on the handling of the car. To elaborate, the reduction in responsiveness due to the above reasons is more than offset by the increase in grip (attributed to the tires - these Azenis grip like crazy...really night and day from any other street tire ive driven) and the improved balance from the wider front track.

For the event, I left my sway settings unchanged and only played with tire pressures as I ran throughout the day. I noticed that I can take slaloms a bit faster (car rotates better) and also in long sweepers (there was a wide U designed into the course - really comparable to a track turn - almost) the front end really turns better.

In summary, I think the net effect of the wider front tires is a slight decrease in responsiveness and a greater increase in positive handling characteristics (realized in the form of less understeer and more car rotation).

Cheers.

 

Guitman32 thanks for sharing your experience. I think I might try a simmilar setup for my stock rims before buying wider wheels.

 

that is the exact setup i am going to do at my tyre change good to read a review on it!

 

I run 255/35/18 and 265/35/18. This low of an aspect ratio makes the car feel every little road imperfection and the car is noisier. The car feels very rough with the 03 hard suspension and this small aspect ratio. However, the grip in the twisty roads is definitely increased by a good margin. You feel the car letting go when the rear begins to slide a little. The turn in is way more sharp and the understeering characteristics of the vehicle are diminished. The cars also has better dive in braking and it sits lower to the ground. Is like it has sport springs. I don’t like that the wheel gap is increased between the tire and the fender. It makes the car look toyish and wheels look disproportionate relative to the car. The overall diameter is decreased by about half an inch. So acceleration is noticeable faster although traction is an issue. First gear looses traction even if the clutch is rolled. At 4000 RPM if you go WOT, traction is lost. Second gear has to be pressed gently to keep traction and as RPM fly by open it up completely. There is no noticeable difference in the reading of gauges, but I have noticed that the car revs faster due to smaller wheels.

 

Hmm that is interesting. That way you can go witha wider tire but still keep your sidewall strength, at least I assume you get more sidewall stiffness with a lower profile tire.

 

Yes. But you'll need sport springs to compensate for the increased wheel gap. If the streets were you live are ok, then I say do it. If they are f*uked up, don't.

 

Thanks Guitman32, very helpful review.

However, don't the RT615s have stiffer sidewalls than your average high performance summer tire?

Also, what do you have you sways set at currently?

 

so the tread pattern on those rt615 on left wheel and right wheel are reversed to each other? i wonder if its gonna affect anything..

 

guitman32:

Do you run that setup on the street too or is that strictly an autocross setup?

If autocross only - why not run the same size on all four?

 

guitman32 - what was your autox times with the new setup? Did your times improve? Also, it looks like you have about 2 lbs. of weights on one of those rims. Were the other tires that far off as well?

 

I do think the Azenis sidewall is certainly very stiff, but I have read that it is not as stiff as say a Bridgestone RE050 or the old Potenza S03. I think that the reason I notice a slight decrease in responsiveness is more attributed to the wider tires/beefier sidewalls.

I have the Hotckis sways set at 3 (3rd hole from full soft in the front (I have the newer 4-way) and at medium in the rear (middle hole - 3-way). I might be able to get away with full stiff in the rear, but right now the car is balanced nicely and is somewhat forgiving to brutish inputs.

 

I run my current setup on both street and autox/occasional track event. I do agree that going 255 on all four would be ideal in terms of balance, but I didn’t want to push that width on the 8in fronts. I know it would fit sans problem, but I thought 245 would be a good tradeoff between contact patch and sidewall bulge/responsiveness. So far, I think the benefit of improved balance going identical on all four can be offset with a sway adjustment. I will say that I am considering the purchase of dedicated race wheels, in which case I will undoubtedly go identical sizes on all four corners – probably 265/275 on a 9.5 wheel.