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Custom order wheels - this is a geeky, nerdy, technical post

82DVY

82DVY

Monza
Joined
5 Sep 2013
Messages
168
Hi, this is a geeky, nerdy, technical post, I warn you now!

I'm looking to order some wheels for my 1999 Porsche 996 C2 and wanted to canvass some opinion.

I've been researching into the best setup for my requirements - my driving will be mostly road with perhaps some limited track/driving tuition time.

I'm going through the details of the standard wheel options that came with the car, width, offsets, spacers and tyre choices, learning about scrub radius etc...

I'm looking for a
1. balance that increases fun - more over than understeer
2. relative lightweight
3. cornering ability/ good geometry setup running approx. 30mm lower than standard

To caveat I'm not at either extreme of the spectrum e.g I'm not looking for outright lap times and going racing and I'm not looking for scene points down the local Halfords cruise either!

Just a fun predominantly fast road driven toy.

I did have GT3 996.2 wheels on my car and it drove well – but I feel they were excessive for the cars 296 horses. Spec of those are:
FR: 18 8.5J ET40. 235/40/18
RR: 18 11J ET63. 295/30/18

As standard my car would have come with these (and permitted to use 5mm spacers I understand)
FR: 18 7.5J ET50. 225/40/18
RR: 18 10J ET65. 265/35/18

A lot less tyre and a very different scrub radius, by 11.3mm without spacers to the GT3 fronts if my math is right?!

What I don't know is the standard OE scrub radius – positive, negative or otherwise

So for my purpose I'm now thinking would an 8J + 235 section fronts 10J + 275 section rear setup be more fun / entertaining.... But what offset... increasing track is attractive but not at the risk of ruining the cars handling...
 
If I were you I'd visit Center Gravity and have a chat, talk through how you want your car to drive. They've made my 4S feel like a different car, yet all the components are standard.

Much of what you ask could be achieved with geo changes eg over- vs understeer, cornering ability, more 'fun'.

Unless you live in an area with billiard-table smooth roads I'd have thought M030 ride height eg 10mm lower would sharpen things up without making it too harsh... seeing as you are nr Cookham then you aren't a million miles from South Oxon where I live and the roads are laugh-out-loud/cry appalling.
 
Below is the CG fast road/minimal understeer setup that Chris put on my car which is standard with the M030 sports suspension option (10mm drop) and using 225/275 PS4 tyres on standard wheels

as said above, get the car to CG and they will discuss your requirements and an advise on what any changes will mean for your car
 

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If you're looking for the best handling/most engaging drive, then smaller wheels are a must. Check out ELA's thread on his super-lightweight build. He went with custom made Fuchs replicas in 17" with 215 on the front and 255 on the rear. I have a lighter than stock (but not nearly as light as ELA's car) car and run 225/45/17 good tyres on the front and 255 ditchfinders on the rear. The car is brilliant, no understeer and oversteer whenever I want it. When I had 265 or bigger on the back then the car wasn't anywhere near as much fun.
 
Ive had about 6-7 sets of wheels on my car all with varying offsets and widths / tyres. Also weights have varied quite a bit as well. Basically they have made very little difference to the way the car felt. Small changes but nothing really noticeable. Therefore I would pick ones that you like the most and sit reasonably well on the car.
As your not tracking it or chasing laptimes then as long as there not mega heavy then as said above the geometry will make the biggest difference.
 
Robertb - yes, I intend to visit Center Gravity just need the wheels first as it's currently sat on axle stands!

peterg1955 - Thank you that's really useful

Martin996RSR - i hear you, i'm intending to stay at 18 but following similar logic
 
I'm waiting on my wheels but I've ordered 9" ET50 fronts and 11" ET56 rears.

I need to work out what tyres to put on these, they're 18" BBS LM's.

I've got Carrera five spokes at the moment- 8" ET50 front and 10" ET65 rear with Michelin PS2's.
 
If you're staying on 18's I don't think you'll find tyre sizes make much difference to grip levels... I'm on 265 PS4's, and mine has pretty much unbreakable traction in the dry.... only way it will oversteer is by loading thee suspension up mid corner and then lifting... or by giving it 'a bung' on the way in, and that's not really sensible on the road IMO.

Looks wise, you want at least et50 off set on a 10" wheel - stock et65 is too tucked, particularly on a lowered car. You can use spacers to fine tune the fit. Et 40 should be OK without needing to get the arches rolled.

On the front, stock 7.5 et50 are massively tucked... this is what I have on mine, and even with a 7mm spacer the track looks too narrow. I'd be looking for an 8 or 8.5 around et 40... depending if you want to run a 225 or 235 tyre.

Overall, I don't think you'll find your car drives significantly differently by just changing the wheels and dropping 20mm off the rear section.

Only real way you can make them handle differently (assuming no change to shocks/spring/ARBs) is to reduce the amount of rear toe.
 
Re: Custom order wheels - this is a geeky, nerdy, technical

82DVY said:
Hi, this is a geeky, nerdy, technical post, I warn you now!

I'm looking to order some wheels for my 1999 Porsche 996 C2 and wanted to canvass some opinion.

I've been researching into the best setup for my requirements - my driving will be mostly road with perhaps some limited track/driving tuition time.

I'm going through the details of the standard wheel options that came with the car, width, offsets, spacers and tyre choices, learning about scrub radius etc...

I'm looking for a
1. balance that increases fun - more over than understeer
2. relative lightweight
3. cornering ability/ good geometry setup running approx. 30mm lower than standard

To caveat I'm not at either extreme of the spectrum e.g I'm not looking for outright lap times and going racing and I'm not looking for scene points down the local Halfords cruise either!

Just a fun predominantly fast road driven toy.

I did have GT3 996.2 wheels on my car and it drove well – but I feel they were excessive for the cars 296 horses. Spec of those are:
FR: 18 8.5J ET40. 235/40/18
RR: 18 11J ET63. 295/30/18

As standard my car would have come with these (and permitted to use 5mm spacers I understand)
FR: 18 7.5J ET50. 225/40/18
RR: 18 10J ET65. 265/35/18

A lot less tyre and a very different scrub radius, by 11.3mm without spacers to the GT3 fronts if my math is right?!

What I don't know is the standard OE scrub radius – positive, negative or otherwise

So for my purpose I'm now thinking would an 8J + 235 section fronts 10J + 275 section rear setup be more fun / entertaining.... But what offset... increasing track is attractive but not at the risk of ruining the cars handling...
Click to expand...

I can understand the concern about scrub radius. It's a key part of the handling geometry that chassis designers use and it's a concern I share! Have a play with willtheyfit.com if you haven't already disappeared down this rabbit hole:

https://www.willtheyfit.com/

Personally I reckon that the car is overtyred with the OE 18s so in an ideal world and with much more money I would go with the 17" wheel widths (7j/9j) and tyre widths (205 and 255) but with the lightest 18" wheels I could afford and 17" offsets (55 F&R).

You can safely go up to 215 on 7J rims for a bit more front end bite. And other than that you can obviously play with geometry and pressures.

You could try 18" Boxster 986 wheels front and rear which are:

Front 7.5J x 18 225/40 ET50
Rear 9J x 18 265/35 ET52

Which are cheap and would keep things 'in the family' from a cosmetic POV.

I'm running 235/40 18's on the front of my C2 with 265/35 18's on the back which seems to work well. The OE Carrera III wheels are heavy though and I'd love a lighter set, that makes a huge difference to handling and steering feel...
 
Thank you for so many constructive replies! It's really helping to shape my thoughts.

My current thinking is:
- Dial back from the 'poke' of my GT3 rim face approx 5mm
- Reduce to 8j / 10j setup (from 8.5 / 11)
- Run 235 / 275 (maybe 285) tyres
- leading to offset Front ET38 / Rear ET55

That would be equivalent to running spacers on stock 8j 10j rims as:
- 15mm front / 10mm Rear

Anyone have anything approaching this setup?

Some pics of the GT3 wheels for reference
 

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I run 981 Cayman wheels on mine
Front: 8 J x 18 ET 57 with 9mm spacers
Rear: 9 J x 18 ET 47

Tyre sizes are stock early model, 225 / 265. No need for any more rear grip, handles great imo

Oz alleggerita do 18's very close to your front specs 8x18 ET40, 10" rears are only available ET65 so you'll need a 10mm spacer. They will be lightweight (and look awesome too)
 
I would have stuck with 8" front and 10" rear if I was sticking to the stock power, but with the engine update I thought it might be an idea to go a little wider.
 
I second the suggestions to look at Boxster/Cayman rims. The 8"/9" fronts/rears are a much better choice of rim width if you're looking to fit tyres that will give the best fun/grip compromise. You can also fit stock Panamera rims, which another forumite has already done. If you're really looking for oversteer and a fun car, then you need to be looking to bias toward narrow rears and no more than 225 section fronts. Once you have the right tyres on you can dial out rear camber and toe to get the handling balance right. The wider the rear tyre, the more grip you'll have to dial out with suspension tuning.
 
Just about to hit 'go' on the wheel order - final spec to be

2x Front
- 8J x 18"
- et42
- PCD130
- Centre Bore 71.6
- tyres 225/40/18 PS2

2x Rear
- 10J x 18"
- et55
- PCD130
- Centre Bore 71.6
- tyres 265/35/18 PS2

Essentially 'stock' offset plus 10mm - so when compared against my GT3 setup 8.3mm less aggressive on the front and 4.7mm less aggressive on the rear with added fun of skinny tyres!
 
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