944 Use of Wheel Spacers

[Gordon Fogarty]

I have recently bought a 1991 944S2. Car is beautiful with a fully documented total mileage of 35K. I was however thinking of lowering the suspension on the car and was advised that to make the wheels properly fill the arches I should use wheel spacers. I went to local motor race meeting on Saturday past where there were a number of 944S2's and a 968 competing and noticed that all I saw (road + race) were running spacers up to about 20mm.
Do spacers not upset the handling/steering & damage the wheelbearings?

 

[TTM]

Theoretically spacers do increase the load on the wheel bearings but in practice it is pretty difficult to measure the effects, of course if the size of spacers remains "reasonable". I have had 15 mm spacers at the four corners on my S2 and wheel bearings are still fine. Look-wise it is perfect.

Handling-wise, widening the rear track will increase understeer, while widening the front track will increase oversteer.

While rear spacers help stabilise the rear but increase understeer, and if you do not wish to alter the steering feel by fitting front spacers, then fitting a bigger rear ARB (18, 19 adjustable, 20 or 21 mm adjustable ) will help compensate understeer.

 

[mik_ok]

sending you mail Gordon. []

 

[John Sims]

I've been told that, when running 911 or Poxster wheels on a 944, 7mm spacers should be employed at the front.

This worries me as they are only shims and therefor reduce your thread length by 7mm. I was going to cut the back off a redundant wheel nut to see how much thread is available before I go this route myself. Taking the reduction in thread into account one might be better going with a full spacer with offset fixings rather than a small shim.

 

[berg944]

I fitted 34mm spacers to the rear and handling improved, I think it probably depends on how the geometry was set before fitting.
Just put new tyres on the rear, I did not realise the difference it makes to the steering.
The car turns quicker but with less over steer and I can let the turbo in earlier and feel the rear moving out. A lot more controllable as before It would step out too quickly without warning. Got to try them in the wet, not that I will have any choice today.

Conclusion - Best upgrade is good tyres and I should have done this first instead of being a tight arse and running the tread down to the blocks.

Must now fit the 968 castor mounts that have been on a shelf for 6 months, people keep putting me off with stories of broken internal threads.

Mike[:'(]

 

[944Turbo]

Tyre pressures can also make a difference to over/understeer behaviour as well as tyre type.
Tony

 

[Guest]

I have 6mm "shims" on the rear of mine to get the spacing right on my 18" 911 twists. I wouldn't go any further than that as you'll lose the cenrtal locating hub completely and be relying on the studs to centre the wheel. Not good (at all!)

IMHO, wheel spacers aren't bad at all. the weight of the wheel is designed to overhang in one position for the bearing to take more load. if the wheels fitted are set too inboard, then that will actually be worse than not fitting spacers to get them in the right place.

 

[Gordon Fogarty]

Fitted 7mm shims to front, and 15mm spacers to rear. Good job!
Now on the hunt for lowering springs for front to finish job off.

Thanks to all.

Gordon[]

 

[mik_ok]

Top choice that man [8D]

 

[A5DSR]

Can I ask a daft question? is the shim just a plate that fits over the bolts, so reducing the bolt thread by 7mm, or is it a plate with new bolts that fixes to the existing hub?
Where did you get them? I've been thinking of adding a pair to the front of my 2.7.

Cheers
Daz

 

[paulf968]

usually the 7mm items are just shims and you lose some of the length of your bolts.

I seem to remember from my engineering studies (3x years ago!)that to obtain full performance of a nut on a stud -- there must be at least a length of one stud diameter protruding beyond the nut. Any proper engineers out there? please confirm.

I did try 9mm shims on my 968, even with the slightly smaller steel nuts I was not getting enough stud protruding for my safety. (If anyone wants a set of 4 -- 9mm shims just pm me -- I moved up to 18" rims so do not now need them)

paul f

 

[Guest]

ORIGINAL: legaleagleboy
I seem to remember from my engineering studies (3x years ago!)that to obtain full performance of a nut on a stud -- there must be at least a length of half the stud diameter protruding beyond the nut. Any proper engineers out there? please confirm.

the amount of exposed thread depends on the load rating, diameter and pitch of the bolt, depth of the nut, and whether locking agent is to be added. It all gets very complicated!

I usually work on 1.5D of exposed thread to be safe, then work backwards when things don't fit (or some bean counter wants to save a millionth of a penny!)

 

[Guest]

If you're fitting shims, you should really replace the wheel studs with longer ones in order to ensure that you have the correct amount of thread in contact. As a lot of people fit chims, there should be plenty of place who can supply a longer stud (if not, there's a sales opportunity here for somebody on this list[])

A good rule of thumb is that if you put a 7mm spacer in, it's a good idea to use a 7mm longer stud. I work on the assumption that Porsche did their calculations correctly when they designed the car, so if you stick with their numbers you don't need to know all the science behind it.

James

 

[Fen]

That's a good assumption, except that Porsche may just as easily have bought wheel studs in bulk and in a size ideal for one application and acceptable for another and used in both as that was cheaper than sourcing the ideal size for both applications. If the 944 was the one where they were acceptable then the calculations may reveal they are ideal with shims. That is based on nothing other than being Devil's Advocate. Has anyone got any real-world experience of this? I'd consider thin shims for my 17" track wheels but they would have to come off for my 18" road wheels (I had to take a lump hammer to the arch lip to make them fit at the new ride height as it is) and obviously changing wheel studs at the track side is a bit extreme so I need to find a length that is suitable for both shims and no shims.

 

[John Sims]

You also have the added excitement of breaking your hub when trying to remove the original studs. []

I have thought about this myself and may yet subcontract. I hate understeer, and anything that might reduce it must be a good thing - not that it is anything like as bad as is used to be. I could tighten up the rear end a bit ( you can do that with 968 M030 ARB's []) but with the state of the roads, and the approach of winter, this is perhaps best avoided.

 

[Diver944]

ORIGINAL: Fen
Has anyone got any real-world experience of this?

Paul (Legaleagleboy) tried some thin shims for use with his track wheels to widen the track and help handling at the circuit. Unfortunately he did find that there was very little stud left to tighten his nuts onto []

There is a post about it somewhere on the forum but I'm blowed if I can find it [&:]

 

[John Sims]

Yes, I remember that. But I can't remember what thread it was under.

 

[paulf968]

The thread is here -- including the realisation that 9mm shims was not such a good idea!! (anyone want a set of 4??)

http://www.porsche968uk.co.uk/phpbb/viewtopic.php?t=928&highlight=shims

paul f

 

[Fen]

I think I might want them Paul. If I get open ended steel nuts from Bert (which is a good idea anyway) it won't matter if I have a lot of stud poking through with the road wheels on and it might not be a bad idea to replace the studs anyway. Let me look into new studs and I'll get back to you.