Porsche Wheels

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In my quest for good, cheap wheels that will work on the P6, I've been thinking about Porsche rims, especially after seeing a set of 17" Boxster rims for £150 on ebay.

Now the P6 PCD is 5 * 127mm and the Porsche PCD is 5 * 130mm, so effectively only 1.5mm per wheel stud.

I'm wondering whether the bolt holes could be offset-drilled to correct them for 127mm and then just use nuts with adequate taper washers. (most alloy nuts are like this anyway).

I wonder if anybody has an opinion on this (Chris ?)

Of course I haven't even considered offset or centre bore yet, but hey ho !
 
Webmaster,

I dont know what stud size you will drill but I assume its like for like so you will end up with slots unless you open them up to a larger size, then you have the problem of nut location.

Martin P
 
I know JC suggested the weld up with TiG and redrill route on another thread recently - perhaps he could elaborate and / or suggest someone who could do this?

Personally I go with Dave; I think this is a seriously risky route if you intend using the wheels for anything beyond posing for photos. With a spoked wheel it will be necessary to redrill exactly where you have welded up the original holes. The welding operation is very fraught because of the possibility of introducing heat distortions and because of the difficulty of getting exactly simliar materials in the weld to the wheel. The latter can really screw up the redrilling as well. Whilst overdrilling - drilling much larger holes at the slightly smaller new centres and then making bespoke wheel nuts to suit - is theoritically possible, it is again fraught with many hazards. Not least among these the probability of cutting tool run off due to the unequal material cuts.

All these add up to likely weakness around the stud holes and or run out and or distortion, none of which ought to be contemplated unless you are going to fit a 20mph speed limiter.

Of course, I remain to be pleasantly surprised by news of a reliable technique of achieving this! I learnt my engineering a long time ago and a lot has happened since!

Chris
 
One other thought on this. I don't know what the offset on Porsche wheels is like, but say you actually needed to spacer them out from the hubs, which visually looks possible. If you could get enough material into the spacer you could bolt the spacer to the hubs using the Rover centres and then have a second set of studs offset into the spacers alone to fix the wheels. Or weld up and redrill the hubs - much easier cos they are steel.

Chris
 
Hmm, they're a bit too 80's for me, not to mention the £300 price tag !

Adapter / spacers are a possibility, I've seen them used before. Also modified hubs are an option, if your doing this then might as well pick the most common PCD available.

I think I looked at modified hubs before, but the problem was with the rears. I seem to remember fronts are full circles, which means you can just drill for extra studs further round, you could even go 4-stud if you wanted. But rears are star shaped, so you would need to look at welding, or, drill out and fit studs with a bigger head.

The yanks have a system of wheels called "uni-lug" which appear to have oval shaped bolt holes, you then have various oval shaped inserts with the hole drilled offset to give the PCD you want.

In terms of centralisation, you simply make the central hole the correct size for the hub, either by machining it out, or by making a sleave to fill any gap.
 
I've just been thinking about this some more, based on the fact that the PCD is only 1.5mm diferent for each stud. This means you only need to open the bolt hole up by 3mm to move the centre 1.5mm.

If you've got a 12mm stud for instance, you only need to go up to 15mm, which isn't massive and would I suspect easily be taken up by some decent tapered seat alloy wheel nuts.

I have also seen on 800's some nuts which have a sleeve as part of the seat too.

I've done a couple of "drawings" to illustrate :)

bolts.jpg
 
Those adaptors are spot on what I was thinking of - the $64k question is whether there's enough offset in the wheel to stand adaptors inside it. I suspect you might finish up having a fairly major D post modifying and wing flairing sketch anyway if you like that sort of wheel. At least you won't have to worry about the rubber seal for the back door!!

The wheelnut you've sketched is completely routine and not a million miles away from a standard SD1 wheel nut. The problem is trying to remove the material between your green and red circles. If you use a cutting tool (drill or miller) anywhere near the same diameter as the hole you get all the load on one side of the tool and even with the stiffest machine and tool set up that will cause you to run off the desired line. The only way I can think of to do it would be to use a very tiny milling tool, perhaps no more than 1mm diameter and treat it as milling a new shape that just happens to be a circle. The problem is that the tool is going to be very long in relation to its diameter in order to get all the way through the wheel. So its going to be a special tool and it will be very fragile. This approach will also make it quite a challenge to achieve the relative positioning of the new holes. All possible but a very specialist machine shop required.

Chris
 
Ok then, so the adaptors are a possible, next question is what is the standard offset on P6 wheels, I know you've answered this before but I couldn't find it in a search.
 
OK, here comes the quote from the previous posts:

I've now done the trial fitting of my modified SD1 Vitesse 15" wheels to the car and so can report on offsets!

And the news is that they are comfortably clear of both the unmodified D post double skin section and of the boot side portion of the wheel arch. !!!!~~HOORAY~~!!!!

I'm afraid there will be quite a long wait before I can report on whether cornering loads shift the suspension around enough to give any rubbing problems! Bearing in mind that Denovo's were 205 section and the amount of clearance, I don't expect any issues though.

These wheels are fitted with 205/65 X 15 94V Pirelli P6000 Powergy tyres. These tyres are correct for rolling radius but you should note that they have a marginally narrower tread than many tyres of this section.

I have measured up the modified wheels and get a dimension across the outside of the wheel of 190mm and a depth from the inner rim edge of the wheel to the contact face to the hub of 148mm. By my calculation that gives an offset of 53mm into the car. The figure for the offset is unaffected by the rim size (it is relative to the centre line of the rim) so this dimension could be quoted when buying any width rim to give an exact central location within the wheel arch.

I don't reckon it would be wise to try going above 205 section. You might just get away with 215, but it would need a trial fitting first and for the wheels to be absolutely exact to this offset.

The wheels were produced by first carefully measuring the exact offset of the unmodified wheels. Each wheel was then individually machined to give the quoted offset by skimming the raised "boss" that seats against the hub. Between the five wheels we had (three from a car set of five, and two odd individuals which replaced wheels from the set which had damaged stud holes - looked like they had been run with the nuts loose and the whole wheel had been moving on the hub - that's V8 power for you!) THREE DIFFERENT OFFSETS!! Clearly Leyland quality control left something to be desired! Hence the individual machining which took off around 3.5mm.

For comparison I have also measured the Jensen Interceptor alloys originally intended for the car and sometimes seen fitted to P6's. Their offset came out at 30mm - so they would need around an INCH taking off to achieve the same offset. I really couldn't contemplate that much strength loss! Equally it illustrates the level of butchery required to the D post to allow them clearance when unmodified.

If you were really committed to the Jensen's, I reckon you could lose 5mm from the wheel, perhaps 5 mm by skimming the face of the hub, leaving around 15mm to gain by single skinning the double skin section of the D post. That sounds just feasible, but rather a lot of effort! Another possible dodge would be to shorten the half shafts very slightly to pull the De Dion tube in slightly narrower - best to try on a scrap one first though as I'm not sure how much tolerence there is inside the tube slider.

I don't have an offset figure for the standard steel wheels, but note that they probably don't run exactly central in the wheel arch. Nor do I have one for either the P5 (15") or P6 (14") Rostyles. Anyone out there with any minus their tyres - could you measure them up and post please.

I do know that the P5 Rostyle was a bit too far out for 205's, 195's are really about the limit. In any case the rim width is really too narrow for 205's. One possible solution if someone really wanted the P5 Rostyles would be to have different rims fitted to the wheel centres. This would be quite easy to do at time of rechroming and I know of at least one firm that does this sort of thing (albeit for lorry wheels).

I hope that adds to the fund of knowledge! Lets see some more data for the various types of steel wheel and also for those Jeep Cherokee wheels?


So what does that mean in these circumstances? The spacers are going to push the wheels out from the car by 34mm. So we need to ADD that to the 53mm to get the actual offset you are looking for. IE 87mm. Any less offset than that and you are into varying levels of butchery of the D post and or wing flairing variety. Don't worry about how wide the wheels are for now - width and offset are independent of each other. We do know that maximum tyre size in an unmodied wheelarch is 205. Any bigger and they will foul on the side of the boot as well as on the D post. If you want to use a bigger tyre size than this then you are committing to D post etc mods. Say you wanted to use 245 section. That's 40mm bigger than 205, so you need to ADD a further 20mm from the wheel offset to get the same clearance to the boot wall. And of course roughly 40mm interference with the D post etc.

Once you've decided how much pain you want to endure on the D post etc, you can choose your tyre width. Then I'd use the rolling diameter calculator mentioned above to arrive at the exact tyre size you're planning to use. Next a trip down the tyre shop to acquire some scrap ones of the correct size and lay them up in your wheel arches. Review the D post pain decision and make sure your'e happy with the amount of butchery. Then you can choose your rim width based on the chosen tyre width and profile and procede to buy tyres, wheels and spacers!

Chris



Edited By chrisyork on 1202756093
 
Coming back to this again...
I was looking at the hubs the other day, thinking of re-drilling, and I noticed something interesting, at the front the wheel fits tightly around onto the hub centre, which is as it should be, the hub centre takes the load rather than the wheel studs.
But.. at the rear there is no hub centre as such, just the hub nut, so the wheels are secured purely by the studs, which apparently is bad.
 
Hmmm, all a bit theoretical that. If your'e planning on running up to 200mph then a register by the hub centre to the wheel centre will help to keep wheel and hub running concentric better than location solely by the studs, so there is a potential improvement in wheel/hub balancing.

In our world the only real issue is whether there is enough mating surface friction to withstand traction and braking loads without the wheel rotating relative to the hub; that ultimately leads to fretting between the wheel and hub and loose wheels.

Note that braking loads are much greater than traction loads, so this comment is really applicable mainly to the front where most of the braking is done.

Chris



Edited By chrisyork on 1204359400
 
Rick - just an idea - but if you look at Midland Wheel Ltd website http://www.midlandwheels.com/kolist....20Spoke

they have MWS EMPI 5 wheels for volkswagen vans. They have one in a 5.5 x 15 wheel with 205 pcd. I havn't given it a lot of thought but could you get these and redrill with the Rover PCD I think the new holes should fit comfortably within the originals. you could then reshape the hubs to "loose" the original holes? Alternatively you could fill the unused holes with filler and respray them? I don't know the offset but they look like they might be suitable.

Cheers

Barry
 
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