NZ951

If so, what size on the front and rear would you reccomend? I am talking about the thick metal insert not not the bolt on type of spacer with new studs attached...

GeorgeNZ

NZ951 - the LTSA has just changed the rules for using wheel spacers - they now must be mechanically fixed to the hub or wheel other than being bolted up using wheel studs/nuts and over a certain limit will require Low Volume Vehicle Certification.

Jerad

http://members.rennlist.org/951_race...Q-spacers.html

daniel951

1/4" spacers on the front

MitchB

Well, here's where I'm at - my plan anyway. Guys, feel free to correct my logic.

I recently bought a set of 16 inch Fuchs (early offset) to run on the street so I can put track rubber on my fone dials.
When I went to bolt them up, they just barely hit the (stock) calipers. So I called Wheel Enhancement to get some advice and ended up ordering only two 7mm (their thinnest) spacers to see how they worked - since they said that may not be enough. They also said any thicker would require longer wheel studs. I thought 7mm would be plenty.
It isn't.
Using two, i.e., 14mm is plenty but there isn't nearly enough stud left. A quick check of spacing showed it to be the same as the fone dials. The design of the Fuchs just hits the edge of the caliper. I even filed a bit of the caliper to clear the wheel - then it just hits the fins of the caliper... just barely.

Sooo...
I'm going to go with 10mm (the next size up) up front, and abt 20mm in back to "fill the fenders". Since I'll have to replace all the studs, might as well do it right.
Since track work will be with the fone dials and steel lug nuts, clearance, longer studs and spacers shouldn't be an issue.
I am a little concerned abt alignment issues with the spacers installed, I may have to find a comprimise between the two wheel sets...
We'll just have to see...


M

Jerad

Mitch, check to make sure those Fuchs have a 951 part number.

Danno

Mitch, you got the 911 Fuchs then. The only 911 Fuchs that fit without hitting the brake-calipers is the 16x9" one. Perfect for a rear 245/45-16 tire.

Even with my stock wheels on my '86, I noticed that the rear wheels were set deeper into the wheelwells than the front. So I converted it to be the same as the earlier '82-85 944NA using the same longer studs and 21mm spacers. Here's the final result:


This way, I was able to use the same 16x10.25" HRE wheels all around.

TonyG

Bolting the spacers to the rotors/hubs is trivial.

You simply counter bore a hole in the spacer with the same bolt pattern as the pan head screws that hold the rotor to the hub. Then use longer pan head screws.

TonyG

NZ951

So how many mm front and how many mm rear? Also, if I update my wheels on my 86 ti a later style wheel with the bigger offest, will these spacers become unnecessary? Is it easy to change the studs?

TonyG

Also... adding spacers will affect the handling as the track of the car changes as does weight transfer to the tire. Further, the load on the wheel bearings increases.

Know what you are doing when you add spacers.

TonyG

NZ951

So how do you do it in a scientific way, or a smart way Tony?

Danno

First some background....
"So how do you do it in a scientific way, or a smart way Tony?"

You compute the lateral torque at the wheel-bearings. Imagine looking at a bare mounted wheel (no tire) on the car from the front or the rear. There are two rim-edges that take the load. Load pushing up on the outside rim-edge tends to rotate the entire wheel/hub assembly inwards. Load pushing up on the inside rim-edge tends to rotate the rim outwards. You add these two torques together and this is the resultant torque on the wheel-bearings. Ideally, you would have the bearings positioned exactly between the rim-edges to carry a straight vertical load and all rotating torques cancel out. The bearings only face a radial load from the weight of the car. But due to brake-calipers and ABS-sensors, you need to move the mounting surface outwards a little to make room. Also, due to cornering forces and bumps not centered between the rim-edges, you end up with rotating motion and add an axial load on the bearings. The outside wheel bearing bears () the brunt of the load from cornering.

This offset created by moving the mounting surface and spokes outward creates a certain amount of axial torque on the bearings. Note that the curvature of the spokes and their displacement from the mounting surface only affects the load-path through the wheel itself. However, once that load arrives at the hub, only the effective offset determines the torque. THat is, the offset of the mounting-surface away from the centerline exactly in the middle of the rim-halves. So when changing wheels you want the offset to be as close to stock as possible to maintain the stock torque on the bearings.

In the front, steering geometry and scrub-radius is also affected by the offset. By sticking close to stock offsets, you preserve the steering geometry. The '86 cars had positive scrub-radius which makes for sensitive steering and good response, but a little jittery in the bumps. Th e later '87+ cars had negative scrub-radius for more stability (but lazier response). When hitting single-tire bumps under braking, the direction the car darts is also in opposite directions depending upon the scrub-radius. Ideally, you want zero scrub-radius; in which case, hitting single-tire bumps under brake results in zero darting (this is especially important entering corners).

So the idea with using spacers is to restore the effective offset close to stock. Using later '87+ 52.3mm offset wheels on an '86 car will actually work, but the wheels will be inset into the wheelwells by an extra inch. The extra offset also affects the load on the bearings and changes your steering geometry. However, it's better to have the wheels more inward than stock rather than more outwards than stock; the increase in loads on the bearings aren't as detrimental By using spacers to restore effective offset back to stock, or closer to it, you reduce the effects of different offsets. Remember that's there no torque or bending at the wheel studs at all, they only serve to generate friction on the mounting surface; so they're loaded only in tension. This friction clamps the entire wheel, spacer and hub into one assembly; the forces are transferred to the hub and bearings as if the wheel itself is welded solid to the hub. Check out this site for some basic info on forces in a bolted assembly: Bolt Sciences.

Now the uneasiness I have comes in when spacers are used on wheels with proper effective stock offset, be it early 23.3mm or later 52.3mm offsets on the same vintage car, are used to space the wheels outwards. This increases the loads on the already overloaded outside bearing. In the case of using 911 23.3mm offset wheels on a 951 with 23.3mm offset and using 1/4" spacers to clear the calipers, you're reducing offset down to 17mm, not that different. You'll still need 8mm longer studs to get 9 full turns on the lugnuts (1.5x diameter of stud in engaged threads).

Ok, now to the specific application at hand...
"So how many mm front and how many mm rear? Also, if I update my wheels on my 86 ti a later style wheel with the bigger offest, will these spacers become unnecessary? Is it easy to change the studs?"

With those 911 Fuchs, you only need 4mm of extra clearance. So a set of 5mm spacers and 5mm longer studs are all you need.

If you want to use the later '87+ 52.3mm offset wheels, then you'll need to get much larger spacers to make up for the difference. Complete parts list with Porsche part# and step-by-step procedure is documented on my RacerX website in the link above...

NZ951

Danno, you are an animal. I have phone dial wheels, 16" with 245/45 and 225/50... So do I need the 21mm rear and what on the front?

NZ951

Danno, would you like to sell me the necessary parts to space out correctly my wheels? I feel emotionally compelled to by from you.

Songzzz

NZ951, I have a pair of 28mm spacers for the rear complete with 10 x 72mm studs. P/N 930.331.611.04 + 901.331.671.01 for sale.

Send me a PM if you are interested.