HELP problem installing 17 in boxster wheels on 951

[porschengineer]

I tried to install the wheels on my 89 951 and as the rears fit perfect the fronts would not fit because the bearing cap will not allow the wheel to sit flush with the hub. Even with the bearing cap off they still will not fit flush. I see pictures of 944s with these wheels, so is a spacer needed?
The fronts are 7x17 ET55 (Part Number 986.362.124.00)
The rears are 8.5x17 ET50 (Part Number 986.362.126.05)

The gap is approximately 11.5 mm when all the lug nuts are tightened.

If a spacer is required, what is the maximum spacer I can use that will be safe to secure the wheel to the hub?

[smudo]

I myself was thinking about boxster wheels but did not know about such issue. One solution might be bore bigger diameter opening for the for the hub. But you will not be able to use those wheels on boxster without hub-centring rings (if at all) and you should look out that you do not make it to big as otherwise it will be hard to center the wheels and it will vibrate at higher speeds. If you use spacer, you should look that you get at least around 7 full turns for the bolts. If less, you should get longer ones. It seems that you need 12 mm spacer to make them fit. 15 - 20 mm spacer should be still fine, but not sure if the length of the bolts will be sufficient.

[flash968]

yup - you either have to use a spacer (dangerous if too large) or counterbore the backside of the wheel for clearance.

keep in mind that you can only use a maximum of a 7mm spacer without either lengthening studs or using a spacer with its own additional stud set. the rule is that you must have a minimum of the same amount of threads of engagement as the diameter of the stud. it is not a "number of turns". 14mm diameter stud means 14mm of engagement. this is with steel lug nuts. with aluminum it is 1.5 times the diameter, which means that spacers would not be safe at all without longer studs.

[veleno]

Did you try the rear on the front? If it clears, another option might be to purchase a pair of rears and run a "square" setup instead of a staggered setup.

[Paul Waterloo]

For my track wheels, I use a 5mm spacer, works perfect.







Got the spacers on ebay for cheap, only need them in the front, lug nuts still have plenty of thread engagement.

[flash968]

yup - while i hate spacers, and most sanctioning bodies do not allow them, as long as you are using steel lug nuts, 5mm is fine.

however, if you are using aluminum lug nuts, no spacer is safe. the engineering rule for aluminum is 1.5 times the diameter in thread engagement. that means 21mm of threads needed. the studs are 31mm long. the wheel thickness at the bottom of the taper is 10mm. that leaves exactly what is needed for torque retention. i don't think that was an accident. porsche is pretty good about that kind of thing.

[porschengineer]

thanks for all the feedback. I am going to make some 1/4 inch spacers to test (machine shop). I will feedback the results. I will also test rears on the front.

recommendations on steel lugs?

[flash968]

i'd contact wheel enhancement

[porschengineer]

thanks for all the feedback. I am going to make some 1/4 inch spacers to test (machine shop). I will feedback the results. I will also test rears on the front.

recommendations on steel lugs?

[porschengineer]

would 17 inch turbo twists be the same - requiring spacers?

[zedsn]

I ran 18" twists on my 89 951 and the fronts are 7.5 wide and the rears are 11 wide and had no issues what so ever.

[flash968]

it's all about the tire size, offset, camber angles, ride height, and in the rear also the toe set

[mytrplseven]

I don't know if the front spacer requirement on a turbo is different than the base model ('87) but I installed 17" Cayman wheels on my car and I used 7mm (1/4") HRE spacers and it worked perfect.

[porschengineer]

zedsn how does it drive with the 18s

[flash968]

that's another one that is very specific to choices. a car on heavy 18s with stiff tires won't ride at all like a car on light ones with soft tires. similarly, a car with a lot of camber won't ride like a car with none. toe will also make a huge difference on how it works. you can go from horrible to excellent, depending on what you do. mine is on 18s and rides great. a buddy of mine is also on 18s, but rode like crap, and it was all in the wheels, because at the time, our setups were nearly identical, but his wheels were a lot heavier than mine.

there isn't any magic answer that's "one size fits all".

that being said, there is a memo out there from porsche warning against using 18s. it makes sense, as it negatively alters the geometry of the load, and you really need to beef things up to handle it.

also, just because somebody (including me) hasn't had any issues, it doesn't mean that there won't be any. physics is physics. the loads are what the are, and parts will wear out and fail as a result. it's just a matter of time. while it's largely been ok, i've had to replace caster blocks twice, and need to look at my wheel bearings again. so even i have not been immune.

do a lot of homework first. drive some cars with what you are looking at. talk to the owners about their experiences. see if it's what you want and can afford. the real cost goes way past the wheels.

[333pg333]

If it's just a matter of the wheel not sitting snuggly on the stub axle it would only be by .5mm or thereabouts. What about getting the inside of the wheel milled to fit?

[flash968]

that's what i suggested first off. a simple counterbore would do it. i've seen it done for this very reason, with success

[porschengineer]

UPDATE - I hate to admit it, but i made a mistake. if you look in the pictures i originally posted, something is missing... you guessed it - the rotor. After initially trying to install on the 89 951 and seeing it wouldn't fit, i pulled a spare 951 hub off of my shelf and used that to get the measurement. Although i still need a spacer, the spacer requirement may only be 3/16 inch. I used your suggestion and installed a 1/4 inch spacer and the wheel installed with no problems. I am going to try some 3/16 inch aluminum and 10 gauge stainless (0.1406) to see how thin i can go. Thank you everyone for your feedback and help.

[djnolan]

Are you using the original OEM lugnut?

[porschengineer]

I was using a steel lugnut, but I decided to use the C2 Turbo wheels without spacer and use stock lugnuts