rawky

I'm constantly looking for wheels that have et65 at the front, but it seems alot of people on Rennlist just go with et55 anyway, what do you lose out on when you get et55 wheels? Does 10mm make a difference? Do I really need to get et65s?

John Veninger

RyanPerrella

i have 55 on the front of my car but now you have to look at wheel width, the width of my fronts are 8.5" (The other 8" 997 wheels use a 57mm offset)

the original 65mm offset could very well be for a 7" front wheel. Use Andrew O's wheel calculator to see just how far the wheels stick out.

rawky

How about handling wise?

RyanPerrella

the car has 235 tires and its great, i previously had 245's but the car did noticeably tramline. a simple switch of 10mm section width made a huge difference honestly.

245's (and larger) may work but i would want them on wheels with a higher offset.

Brett928S2

Hi

I have 18 inch wheels by 7 inch on the front of my S2 with a 52 offset AND 3 mm spacers which make a 49 offset.....

They work fine and if you look straight down from above the wing the tyre (225/40/18) is dead level with the arch, so it doesn't stick out at all...

Now the THEORY on offsets says that 52 is too low and with the 3 mm spacers it SHOULD give worse handling.....in my case it was good handling with 52 and even better with 49...and I have absolutely NO IDEA why lol

All the best Brett

Slantnose!

I have some Cup 1's with the 55 offsets.
Looks and handles fine...

SeanR

Had ET55's on the front of both of ours and was fine.

jcorenman

We've got ET65 on the S4 and ET55 on the GT, both work just fine. Different tires, both tramline a fair bit, the GT might be a bit worse but also has larger tires (235/45 vs. 225/45, both on 7.5" rims) and also worn kind of funny (from previously-crappy alignment). Hardly the basis of good science.

My understanding of this stuff is that you want the center of the tire tread a bit inboard of the steering-axis, that makes the handling a little more friendly if one wheel gets into lousy pavement or soft stuff. As the ET gets smaller the tire moves outboard, and the steering axis is nominally 55mm inboard of the wheel hub.

Here's a picture from the WSM which I dug out to try to get my head wrapped around this when we were looking for wheels. The red line is the tire centerline, the yellow line is the plane of the wheel hub, the difference is the offset (ET). As ET gets smaller the tire moves outboard, left in this picture. The green line marks the steering axis, and Franz wanted the tire centerline 10.2 mm inboard.

The theory is that if the right tire (for example) runs into goo, e.g. dirt at the edge of the road, drag goes up and the offset betwen centerline and steering-axis tends to rotate the tire to steer the car away from trouble. It's a relatively small effect I think, but if the ET were less than 55 then the tire-center would be outboard of the steering-axis and the effect would reverse-- the car would tend to steer towards softer ground. That is considered bad.

I think you can make a pretty good argument that having the tire-centerline exactly on the steering axis puts everything into perfect balance, so ET55 s good. On the other hand Franz wanted ET65 (except for Club Sports which got ET60), so ET65 is good also.

That's my theory and I'm sticking to it...

toofast928

I think the tramline is exaggerated by the type and grade of tire used when the offset gets less than 65.
Also consider any steering play (rack bushings for example) and how good was the guy that did the wheel alignment.

doktor-t

I Also use 55´s (225/45-17 continental) in the front and I´m happy with it.

/Tobias

dr bob

The issue is where the center of the wheel patch sits relative to where the center line of the steering axis sits. The original offset puts the middle of the wheel inside of the steering axis. When something happens to try to slow the tire down, it exerts an offsetting amount of input to the steering so that car does not turn towards the side whwre there's more drag. To illustrate, think about how your little red wagon steers, the Radio Flyer you have for your kids. Put a pebble on the sidewalk in front of one of the front wheels, and push. As the wheel hits the pebble, it tries to slow down. The steering axis center is right in the middle of the wagon, so there's an extreme pull towards the side that hit the pebble as you try to move forward. On your 928 with high offsets, the wheel is actually inside the steering axis, so that wheel would push that wheel towards the other rather than away from it. When the offset is just right, you can suffer a flat tire on the front and barely feel any change in steering. Hit something small in the road, same thing-- the effect on car direction is exactly opposed by the effect on the steering. Back to the little red wagon example, this is where you are headed as you decrease the offset. How much can you 'get away with' without adverse effects? Depends on your tolerance for steering upsets, the tires you choose, and the roads you drive. Certain tires seem more prone to tramlining. Wider tires are more prone to tramlining. Lower wheel offset numbers make the car more prone to tramlining no matter what tires you use.

All that said, there are certainly plenty of folks running 55 offset fronts and happy with the results. Willing to trade the high-speed stability for prettier wheels? Most in the US are, because we drive slow relative to the stated capability of the car. So the effect isn't so apparent. Like many other things, the effect changes with the square of the increase in speed, so what's "fine" at 55 would be "fine" divided by four at 110. As others mention, when you add in the typically sad state of most 928 front suspension and steering components, maybe 110 is too fast. Your rack, rack bushings, tie rods and tie rod ends, ball joints, wheel bearings, inner control arm bushings all play a part in how the car tolerates offset changes. Suspension wears slowly so many don't realize how tired a lot of these components are when they drive. Higher offsets accelerate wear on steering parts for sure, as do saging springs and tired shocks. Invest in steering parts then see if the car will tolerate lower offset wheels. That's my conservative advice.