Why doesn't anyone run early offset wheels on late cars?

[TNT25169]

I just threw some (one front and one rear) early offset phonedials on my '88 summer car while it's sitting in my shop and there is clearance of the fenders both front and rear. I'm running a decent amount of negative camber but nothing compared to a dedicated track car (the specs are at my house right now so I'm not sure but front is between 1.5 and 2 degrees) and it fills out the fenders real nice. ALso there's the benefit of the 6cm wider of a track front and rear. I know my hoosiers stick out to the fender lips on late offsets (due to hoosiers crazy way of making tires) so I will keep those for my race tires but can anyone give me a good reason not to run early offset wheels for my summer wheels next year? It looks much better....

[Brando]

It's all about the backspacing.

On most all early cars, you can't run late wheels because of how much spacing is needed. The only exceptions being those adapted to use late offset wheels - due to changes in the suspension or use of spacers.

The best reason not to use early wheels on late cars is the wheel is set too far outboard of the body. In the rear you will most definitely get the wheel rubbing on the fender, if it even fits. The fronts you can sometimes get away with it... Sometimes...

[Dave L]

By increasing the track I would think it would put added stress on the wheel bearings and possibly more stress on some of the suspension.

[TibetanT]

Hello there:

I am very glad this topic has come up! I agree that there is a good valid reason for running the correct offset on both front and back which only a physics major could probably explain. And, I do believe safety comes in to play in view of the forces that have roles when it comes to machines with drive internals and how it all fits to provide momentum.

Brando explains the physical limitations and from experience the reasons why certain cars with certain brake calipers can pose problems. And, DaveL hit the nail on the head regarding the physics involved, and I agree that there may be some issues with parts breaking down due to stress.

My fuchs on my 87 944n/a are 52mm offset and it looks to me like the wheels mount very close to the outside edge with alot of space between the mounted area and the inside edge of the tire. Where the early offset, 23.3mm, Fuchs appear to mount up more toward the middle of the wheel, relatively speaking.

This is one area where I am a little weak, so as I said I am happy this topic came up since I need some help with this in fully understanding the big picture.

Good discussion.

[Dantilla]

Early offset wheels will fit a late car only if the tires are really skinny.

Giving up contact patch to gain a little bit of track width is a poor compromise. I'll stick with contact patch.

[TibetanT]

Ah haa! Wow! Like a bell went off.

Dantilla's post mentions "contact patch" so I looked it up on Wiki. This is beginning to make a lot of sense now. Thanks.

The more the "contact patch" the better the grip right? Better performance and less risky when going into a turn at 85 mph...well, guess what I mean is there is more tire there to help grip the road and provide better response in the turn. Thus, giving you a safer turn then if you were using the skinny tires which have a smaller area to grab with.

[Sterling Doc]

That much change in offset in the front will lead to bump steer and throw the scrub radius out of whack. The bearing loading is also a convern, though the '88's have larger bearings than the early offset cars to begin with.

[Dave L]

If you are looking to fill out the fenders I would recommend 225/245 tires on 7&8's. This was available on the 944 series and looks great.

[924Sman]

The change was made to fit the ABS system on the late cars. The deeper O/S accomodates that space needed.

Dal

[idesign635]

Not my car, but these were posted recently.

[baby shark]

i've had an extra set of cookie cutters with new VR tires that the previous owner of my '84 thru in for a hundred bucks. When the tires on my '87 944S got low on tread, I put them on. The fronts are 205/55/15 and they fit and fill out the wheel well without jutting out. Just right. Same can be said for the 215/60/15 in the back. I don't question what others have said about less contact surface at the point of contact with the road. Don't know either way.

[TNT25169]

Thanks for that input Baby Shark. As far as less contact patch due to a different offset on a wheel....nothing would be affected. Contact patch is affected by camber and tire size. The tires are 205 in the front and 225 in the rear and clear my fenders without rubbing. Putting the wheel farther from the hub due to offset should in no way affect ABS if my car were to be equipped with it but it is not. I was running Yokohama AVS ES 100's on a set of7/8inch dials, late offset with 225/245 respectively and then later switched to Cup I's. Looked like **** because as negative camber is increased for my auto-x needs, the top of the wheel moved farther from the fender. I had easy a 2 inch gap between my fender and the top of my tire (In, not up). I will take pictures at some point.

[Tam Lin]

Originally Posted by Sterling Doc

That much change in offset in the front will lead to bump steer and throw the scrub radius out of whack. The bearing loading is also a convern, though the '88's have larger bearings than the early offset cars to begin with.

My understanding of the bearing load is that it is actually less when cornering, more if you drive in a straight line, so it's beneficial if you're doing autocross etc.

It's what Porsche did with the 924Gt/GTS/GTR line, just have a look at those spacers for an offset/track change. I assume they did this because they had good reasons to, despite the increase in unsprung weight.

Me, I go half-way house: I leave the front well alone, a) because of the abovementioned undesirable stability effects, b) the front track on our cars is wider at the front for some reason lost in the mists of 924 development. But the rear benefits from the early offset wider track, so I run Fuchs ET 36s rather than the correct, late ET 52.3 on there.

[Dave L]

I have had a shop who races 944 recommend spacing the rears out as well.

[Dantilla]

My early 944 race car has late-offset rear suspension.

Since class rules limit wheel width to 7", I use 225/50/15 Hoosiers on 15x7 Cookies.

I had to roll the fenders slightly to eliminate the occasional rubbing I was getting on a couple places on the track.

If not for the 7" rule, I would use wider tires on wheels with the proper offset. But as long as tire width is limited, may as well have as wide of a track as possible.

I would not use this combonation on a street car.

[autoxr]

I am researching this issue presently for a BStock Autocrossing '87 944S and the offset, although originally changed to accomodate ABS brake systems, really needs to be correct. The reasons have to do something with the steering rack "centering" itself after a turn, , bump steer, suspension deflection, and related issues. I am going for 968 wheels 16"x7 front 16"x8 rears ET 52.3 (late) offset with 225 50/16 up front and 245 45/16 out back. This should be great for autocrossing, street, or track. It should be legal for all stock racing classes and known as the M030 wheel upgrade option from the factory. Do any of us claim to know more than Professor Porsche and the boys in the engineering lab? I think not!

Happy Motoring from Dirty Jersey!

[70SWT]

In the inverse of the primary topic: a cool concept I used was to install the early 951 suspension with Brembos onto 924S and compatible 924/931 chassis (compatability is another topic). This pretty much requires 16" wheels or bigger, and thus works great with late offset wheels, especially the Boxster 16" wheels, the kind on the first few years of the Boxster with 5 split spokes. This requires a thin spacer, you can make them out of stamped 1/8 or 1/16" sheetmetal, to get the wheel hub to fit properly onto the centering ring and to clear the big brakes. Looks great, and the way the wheel kind of sucks under the narrow bodywork lets you run wider tires than the 924 ordinarily can, so its a win-win.