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What is the wheel offset for 4GS & its effects on handling?
I am looking at aftermarket wheels.
I notice that the 4GS is something like pitch circle diameter PCD of 114.3 mm; the diameter distance between the center of the studs.
How come the 4GS seems to be compatible with both offset from 38 to P45?
What does P38 to P45 mean anyway?
Does it mean "positive" offset from 38 to 45 mm, where the mounting face of the nuts is 38 to 45 mm away from the center axis of the wheels?
Does anyone know what the exact offset of the 4GS's alloy wheels are? For example, P40 or P45 etc???
On the F-Sport, it's....
Front: 19x8
Offset: +45
Backspacing: 6.3
Rear: 19x9
Offset: +60
Backspacing: 7.4
But offset can vary.There's plenty of room for them to stick out at least an extra 15mm
And keep in mind, offset changes with width. So if you get a really wide wheel, you'd have to get a higher offset to compensate, which is why cars with wider wheels in the rear have a different offset on the rear wheels. The F-Sport being one example.
If the OEM is 8" wide and has a positive 45 mm offset, then an aftermarket 8" wide positive 40 mm offset will mount each wheel outboard by 5 mm per side, to widen the track by 10 mm.
1) Does this theoretically make a small change to the suspension geometry?
2) Is it a significant change in practical terms?
3) How is the handling affected?
4) How is the ride affected? Will mounting the wheels outboard by 5 mm per side give a slight deterioration in the ride?
Apparently, using a smaller positive offset than the original positive offset of 45 mm mounts the wheels outboard to widen the track as noted above.
However, this does affect the geometry.
Normally, the steering's king pin angle coincides with the tire's center axis to give what is known as zero scrub radius for the lightest steering, and the least kickback below.
Below is a wider wheel rim which will fill the arches out more, but with the same positive offset, to maintain zero scrub radius steering geometry.
When we commonly use a smaller positive offset, the new wheel's mounting face is positioned closer to the new wheel's central rolling axis, such that the new wheels are mounted more outboard for a wider track than the original wheels.
This improves the appearance as the wheels are mounted more outboard, and the track is wider.
This also improves the terminal grip as the same center of gravity on a wider track reduces weight transfer to the outer wheel.
On the downside, it creates a steering geometry scrub radius which makes the steering heavier because the new wheel is no longer turning on its central axis, but "translating" bodily, and the steering is also more prone to kickback vibrations.
The scrub radius also tends to promote more understeer balance, rather than oversteer.
Another point, widening the rear track more than the front track also promotes more understeer balance, rather than oversteer, because a wider rear track promotes greater rear end grip and rear end stability.
08-18-15, 03:58 PM
What is the wheel offset for 4GS & its effects on handling?
