Wilder

I have 18" turbo twists on my cab and was thinking about putting spacers on it to fill the fenders using the car on the attached image (not my car) as a reference. I lifted the car and tried various sizes. 7mm in the rear and 14mm in the front looked perfect and I was ready to order them until I read another post regarding spacers where concerns were raised about the use of spacers in the front.

I searched other posts but found no conclusive answers to my questions so I'm calling on the experts. Can a 14mm spacer in the front with 8" ET52 turbo twists have adverse effects on handling? If so can the issues be addressed with alignment? If not, what is the largest size spacer I can get away with in the front without problems? Thanks in advance.

roebedo

LJ,

I've never heard of using spacers in the front of the car, just in the rear with the wide body cars. Do you have an odd off-set with your wheels?

I would definitely assume that spacers in the front wouldn’t be a good idea. Can you lower the car more in the front to fill the gap?

Bill Verburg

From my wheel page


A 14mm spacer in the front will push the wheel/tire assembly way to far outboard

More wheel info here

Wilder

offset is OEM: 8" turbo twists with ET52. My car is already lowered to a ride height slightly above the car on the pic. What I mean by filling the fenders at this point is changing the offset so that the wheels are more flush with the body as referenced in the picture above. That car BTW, has replica 18" cup wheels sold in Europe that have odd offsets. I'm not sure what they are but I belive the rears are ET57 vs ET65 for OEM NB twists. Don't know about the fronts but it seems to me that the offset would be a few mil off from the OEM 18s.

Bill Verburg

W/o the o/s and width of the wheels that you are dealing w/ it is impossible to answer your question.

If you don't know the o/s it's easy enough to measure, if you are carefull.

1)Put 2 stiff slats across the front and rear wheel edges, be sure to not touch the tires. Measure the perpendicular distance between the slats.

2)measure the perpendicular distance from the mounting face to either of the slats

3)let us know

Wilder

Thanks Bill. That link is very helpful. Would you be concerned about rubbing issues with 14mm spacers or would there be other issues to be concerned about? When I put the 14mm in the front, they seemed fine. Maybe it's because I'm running camber at about -1.6 front?

Looking at other wheel offsets on your list, it seems to me that I should be able to go up to 9mm in the rear and up to 11mm in the front with what I asume would be OEM spec camber and therefore slightly larger with more agressive camber. Would you agree?

Wilder

You beat my post. Offset is ET52 8x18 front and ET65 10x18 rear.

Bill Verburg

Take a look at the charts
if you use, say a14mm spacer, everything shifts left, this means you add 14 to the #s to the left of the mounting face and subtract 14 from the #s to the right. As I said they will stick out too far

Wilder

Thanks for the help with the newbie questions.I know you know your subject well.

I did add the numbers and the 14mm + 58mm that the wheel extends out from the mounting face would be 72mm, which is only 1mm beyond the 71mm that the 9" wide wheels would come out to. Maybe I'm missing something? If I am, what is the largest spacer that you suggest I run?

Bill Verburg

You are right, but keep in mind that the 9 is right at the ragged edge and the chart is base on hypothetical flange widths. The flanges can be up to .5" on each side. I have the 9's on the front of my car and wouldn't want to have them come out any further. My car is extremely low, so maybe at a regular ride height it would be ok, but it is certainly right at the edge.

Garth S

You may be missing a basic point .... that ET values for Porsche wheels are invariably negative numbers, and are referenced from the wheels centerline to the inner bead flanges. When any spacer is added, the result is a lesser numerical ET. The resulting question of fitting within the bodywork must include the total external rim width and tire section dimension -as Bill mentioned.
The front ET, in consideration of wheel rim width and tire size, places the center of the tires contact patch a specific offset from the steering axis, or scrub radius as previously mentioned. It is generally of greater significance to respect this than be concerned about filling the front wheel well.
The rear is generally less sensitive in this regard.

Wilder

These are exactly the issues that I'm concerned about and that I need to weigh. Obviously I want to achive a specific easthetic goal by adding the spacers but not at the expense of performance. Ultimately that is far more important and this is why I appreciate the input. Thanks.

Wilder

True enough and I also understand that every car will be slightly different depending upon various factors. To this end, I guess it's a matter of fitting various sizes to determine what works best. However, Garth's comments are valid and I need to weigh them also. Ultimately, I think spacers in the front are okay, so long as I use a smaller size, 5-7mm maybe. However, I do hope that others step in and put in their .02c.

Bill Verburg

That is not true, Porsche uses the same system as most of the rest of the world. On a Porsche o/s or ET is always positive. O/s or ET is the distance from the mounting face to the plane of the wheel centerline, As shown here

That is why you subtract the width of a spacer from the o/s to get the new o/s.

You are correct that when discussing fitment in the wheel wells the total width including the flanges needs to be discussed as well as the total width of the tire, which generally has a wider section width than the bead width or even the overall width. Part of the confusion comes from the fact that when discussing wheels the bead width is used. When the flange width is added 2x you have the overall width. In the charts I posted I assumed a falange width of .35" which would make an 8" wheel = 8.7" overall. Some wheels have up to .5" of flange. For instance Speedlines, where n 8" wheel is 9" overall and a 10" wheel is 11" overall. Forged Porsche Fuchs from 911s have a flange width of .35" there a 9" is 9.7" overall.








Here I agree, Scrub radius is the distance between where the steering axis inclination intersects the ground and the center of the tire. This distance must be exactly the same from side to side or the vehicle will pull strongly at all speeds. While included angle problems(usually cmber issues) will affect the scrub radius, it is not the only thing that will affect it. Different wheels or tires from side to side will cause differences in scrub radius as well as a tire that is low on air. Positive scrub radius is when the tire contact patch is outside of the SAI pivot, while negative scrub radius is when the contact patch is inboard of the SAI pivot (front wheel drive vehicles usually have negative scrub radius).

If the brake on one front wheel is not working, with positive scrub radius, stepping on the brake will cause the steering wheel to try to rip out of your hand. Negative scrub radius will minimize that effect.

Scrub radius is designed at the factory and is not adjustable, unless you change the effective o/s of the wheel, as woulkd happen if a spacer is used. A pacer will always add to the scrub radius and will generally negatively impact steering, brake and handling. The larger the increase in scrub radius the more so.

Garth S

[QUOTE=Bill Verburg]That is not true, Porsche uses the same system as most of the rest of the world. On a Porsche o/s or ET is always positive. O/s or ET is the distance from the mounting face to the plane of the wheel centerline, As shown here ....

In reality, I suspect that we are in agreement on all results .... as the end result is the same - but not entirely in agreement on automotive convention/terminology; from my time in tire design, pilot runs for chassis development, track testing, blah - de blah , the convention used with vehicle manufacturers was that all wheels with more than half of their width to the outboard side of a vehicle were termed to have positive offset. For porsche, all wheels that I can recall are the reverse ... namely, having negative offset ... sic, the ET quoted is a negative number: when a (positive) spacer is added to a negative number ( +ve ET value), the result is the difference of the two, or a subtraction: regardless, that's the convention as applied in the Industries I associated with .... but the result is identical.