Wheel ET calculation confusion

CarreraRSR · Aug 16, 2011

Sorry for the dumb question, and for the hard of learning (me) let me give you this brain teaser.

I have on my 924 turbo 6x15 wheels with an ET23 front and rear. However the rears have a stock 21mm spacer. To maintain the exact wheel position without the 21mm spacer do I need a new deeper dish wheel of ET44 or ET2?

If I read online ET descriptions I feel I need ET2. But I have been told ET44. In my head that means the wheel will sit too far inboard?

Ultimately I want an 8'' rear wheel, deeper dish and therefore trying to calculate the correct ET required. The 21mm spacer is confusing me and others in this calculation.

Help my head hurts!![

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bmnelsc · Aug 17, 2011

Here is a wheel offset calculator http://www.1010tires.com/WheelOffsetCalculator.asp but more importantly - it has a picture outlining offset. Based on this info - I would say you would want ET44 to keep your wheel rims in the same location relative to rear wing. Actually would be 1 mm less clearance than you have now.

I ran across a very good page discussing all this including negative offset vs positive offset. I'll keep looking for it and post a link if I find it.

Also - ET44 is valid if you are using a wheel of the same width as your current wheels without the spacers. If you are looking for wider wheels, then you must take the width of the wheel into consideration also. The above calculator will help with this but you need to know what your clearance measurements are on each side of the wheel.

edh · Aug 17, 2011

I would have thought you need to reduce ET - the lower the number, the more the wheel sticks out.

on that link, 7J ET13 (or lower) would be about right, and then reducing the ET as you go wider than 7J

8J ET44 works if you keep the spacers - but that won't give you a deep dish wheel

as an aside, I thought the 924 turbo used the same offset as 924S - 6J 52.3?

944 man · Aug 17, 2011

ET44 Steve, but surely a 931 uses 52mm offset wheels?

CarreraRSR · Aug 17, 2011

See, more confusion!! [

]

924 turbos are ET23.3mm front and rear with the rear having a 21mm spacer.

924S are 52mm!? The rear trailing arms are the wider alloy 944 ones.

Now I'm confused again!!

944 man · Aug 17, 2011

I havent ever owned a 931, but Ive had several 924s and 924Ss; and presumed that all 924s were 52mm......

Think of offset as 'inset' and itll be clearer. The higher the number the more of the rim is inset and the less rim you see.

BTW: Ive just bought a Safety Devices cage and I have been trying to find some pictures of your interior. Im trading up from RollCentre and Id like to see how it looks and where it fits.

Simon

944 man · Aug 17, 2011

Are you certain about 924 Turbos offset? Imagine a 924T with 23mm offset 7" ATS Cookie Cutters on - they only fit in a wide bodied car, but if their offset was correct then theyd only be 1" wider.

CarreraRSR · Aug 17, 2011

I understand 7 x 15 ET23 Cookies fit a 931 rear end only with the rear spacer removed. The rear looks to inboard and the front looks too outboard of the arches in pictures I have seen.

My current wheel short list include

Fuchs in gunmetal grey! I'm not sure that these actual wheels will fit but looking into alternatives in 15 or 16''. These are 7 and 8 x16 ET23 front and ET10 rear. Costs are £600 for reps or £600-£1200 for genuine wheels depending on condition.

BBS E50 style (these are magnesium, hens teeth, and expensive. not ideal for road use) Similar to the Image or Compomotives split rims. Image wheels made to measure will cost £1200-1500 new.

Here's a race car with 7 and 8 x 16'' BBS E50's

Good old Minilites and should only be £650 and made to measure. Again I quite like gun metal grey

On a 911 with staggered fitment

As I said I'd like to remove the rear 20mm spacer which would allow a deeper dish. It seems despite comments that say they don't fit, 7'' front and 8'' rears should fit in 15 or 16'' diameter, I've seen them on a few cars. As my car is running lowered suspension with a fair bit of negative camber this should give me more top of wheel clearance. I may modify or roll the inner lip to accommodate as well.

Heres the SD cage as is now Simon. Let me know if you need more pics or advice.

Rear view before the door bars went in. The bars foul the rear quarter card slightly and will leave a small dent in the card if/when removed.

The cage fits well and clears all the interior. Only needed to leave the door pockets off with the door bars installed.

bennyboy · Aug 17, 2011

Loving this Mr RSR (what is your name?!). Saw the mag feature too - doing the front-engined world proud mate! Are you on Edition 38 or Stanceworks forums? Lovely 924 posted on there recently which has wheels similar to the BBS's above. Let me know if you haven't seen it and I'll post a link. Would have to be BBS or Fucks for me - think the BBS with gold centres would look superb on yours and would probably get my final vote!

CarreraRSR · Aug 17, 2011

ORIGINAL: bennyboy

Loving this Mr RSR (what is your name?!). Saw the mag feature too - doing the front-engined world proud mate! Are you on Edition 38 or Stanceworks forums? Lovely 924 posted on there recently which has wheels similar to the BBS's above. Let me know if you haven't seen it and I'll post a link. Would have to be BBS or Fucks for me - think the BBS with gold centres would look superb on yours and would probably get my final vote!

Hi Ben, its Steve!

I guess you may mean this 924? A very clean ex concours now with 8'' front and 10'' rear Compomotives

Here's mine with BBS RS photoshopped in

Just need to do the Fuchs and Minilites now.

Hilux · Aug 17, 2011

When using a roll cage as harness bar ensure you stop lateral movement regarding the harness on the bar with a welded hoop the harness straps fit into when they looparound the bar or use zip ties each side to stop it moving laterally

bennyboy · Aug 17, 2011

Yeah that's the one but, ooh, now I'm not so sure on yours? Although I think the cross-spokes you posted originally would look better than the RS's. What about having white centres? Get photochopping Steve!

CarreraRSR · Aug 17, 2011

ORIGINAL: bennyboy

Yeah that's the one but, ooh, now I'm not so sure on yours? Although I think the cross-spokes you posted originally would look better than the RS's. What about having white centres? Get photochopping Steve!

bennyboy · Aug 17, 2011

Better I think?!

Mike_Pollock · Aug 17, 2011

Am also curious about the offset on your car at the moment.
My 2.7 (ie wide body with wide track, alloy arms) came to me with 924 Turbo wheels on it 6Jx x 15 52mm offset with no spacers -

Which would suggest that yours are 52 not 23mm and that the geometry is that of the steel wishbone/early alloy 944s , rather than the 86 wide track cars?

These are 7J x 16 65mm offset (928) wheels

And with 7J x 16 52mm front and 8J x 16 52mm offset (944) wheels

I think that similar sizes will fit your narrower body in a similar way, ie the way they fill the arches.

Go for the white centred multispoke!!!

944 man · Aug 18, 2011

Steve: 7" and 8" Fuchs are going to need a wide body, unfortunately (and theyre the wrong offset in the way that cant be corrected with spacers too, unlike 52.3mm wheels on a 23mm car where you can add 30mm spacers. They arent out far enough, but here the wheel are out too far) and I think that your car is now far too nice for that.

On the positive side: 6" and 7" Fuchs off an SC or a Carrera should fit.

944 man · Aug 18, 2011

You appear to have two extra bars over me Steve. Were they (second 'LHD' diagonal and the harness bar) an option?

CarreraRSR · Aug 18, 2011

ORIGINAL: 944 man

You appear to have two extra bars over me Steve. Were they (second 'LHD' diagonal and the harness bar) an option?

Yep, when ordered they were available to our desired specification and price and built to order. SD offered a menu of options and directional pricing for multiples. Ideally you need 5+ to get the best pricing. The diagonals can be specified for LHD/RHD.

PORSCHE 924 / 944 '83-'85 (pre dash change)
P 000 Light-weight 6 point bolt-in cage. Clears normal trim and dashboard. All tubing 45mm CDS. MSA/FIA homologated

RBP0003XSU Front cage £189.33

RBP0005XSU Rear cage, single fixed diagonal £220.98
RBP0005XSU Rear cage, cross diagonal £280.98
RBP0005XSU Rear cage, cross diagonal & harness bar £320.98

RBP0003DXUN Door bar N/S (left) £54.49
RBP0003DXUO Door bar O/S (right) £54.49

Prices +VAT

944 man · Aug 18, 2011

Was that a 924 owners club group buy? Id noticed that one of the other GB cages was for sale at cost (a lower spec than yours, at a shade under £500), but the fellow was in the other end of the country in that London.

Ive only had a RollCentre cage before, which isnt brilliant, especially around the A-post feet (which mount on the floor rather than the sill!) so I have high hopes for this SD kit.

Simon

CarreraRSR · Aug 18, 2011

It was that group buy. Went really well with enough people to get a good price versus the very few second hand cages that have been for sale on flea bay at prices close to SRP!

The SD weld in cages mount on top of the sill via a weld in mount. The bolt in cages mount on the floor but the weld in mount is L shape and welds to the floor and up the sill.

One of the group buy guys went to Roll centre first but for some reason I preferred the SD way of doing things. The only criticism for me as the cage is in a road car is the prep pre powdercoat could have been better.