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Old 05-15-2015, 09:41 AM   #225 (permalink)
victorofhavoc
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Join Date: Oct 2011
Location: Kansas City
Posts: 229
Drives: 2014 370z
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Quote:
Originally Posted by kdochert View Post
Just done the tire height calcs myself and there is almost no difference in balance as follows:

OEM tires

Front 245 / 40 = 98mm, Rear = 275 / 35 = 96.25mm

The front tire height is therefore 1.75mm higher than rear on OEM tires and this is balanced as per car design.

Oversized tires

Front = 265 / 35 = 92.75mm, Rear = 91.5mm

The front tire height is therefore 1.25mm higher than rear which is only 0.5mm different to OEM tires?

I'm now unsure again on why the car feels so vague and floaty at high speed?
245/45/19 = 27.7" diameter
265/35/19 = 26.3" diameter

305/30/19 = 26.3" diameter
275/35/19 = 26.7" diameter

front = 1.4" smaller
rear = .4" smaller

0.5" total pitch difference. Although small, can be noticeable.

Other things to consider in your setup:
Did you get an alignment? any toe out in front?
Have you hit any potholes recently?
Any vibration in the steering wheel?

There are really a lot of considerations when it comes to a car's suspension/tire setup and for the most part shops get you to what's "close enough" or "good enough" because you won't ever notice it in daily driving. It may be that what they consider "good enough" you don't. I race my car, so I strive for my alignment to be as dead on as possible...I take it to a race shop and pay double to triple what most pay to have someone sit there and get it just right. 1/16" toe out in front will make a car handle significantly better, but it will also make a car more shifty at high speeds in a straight line.
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Had a 2010 WRX- boy was it quick in a straight line, got a 2014 Z- man is she grippy in the corners-- then left the Z and later got a GTI, now back in an 09 racecar Z!
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