Wheel Offset / Tire size Gurus - Please put your thinking caps on!

[intrepidagent]

I just picked up a set of 17” BBS E26’s that I plan on refinishing and putting on my early offset 944 NA. They are currently configured as follows:




F – 17 x 9, ET 35
R – 17 x 11, ET 55

I will be converting the brakes on my NA to a 951 setup in the near future however since the struts, hubs, spindles etc. are from a 1986 951 it will remain early offset.
I’m considering the a few wheel / tire size setups and wanted to poll the members here to learn the relative advantages and disadvantages of each, fitment issues and along with tire size suggestions. issues etc. Will swap barrels / faces if need be and will need to in order to get the offsets correct for the rear.



1. Square setup – 17 x 10 at each corner
2. Square setup - 17 x 9 at each corner
3. Staggered – 17x10 rear, 17 x 9 front
4. Staggered – 17x11 rear, 17x 9 front
5. Staggered – 17x11 rear, 17x10 front

I know there are a good many members who are running 17” setups on early offset 944’s. Any input in regard to fitment and suggested tire size is appreciated.

[DannoXYZ]

Here's what I suggest for the least amount of work.

1. Stick with those wheels sizes and use 17x9" with 255/40-17 tyres in front.

2. Use the 17x11" in the back with 275/40-17 tyres. If you have an '86 NA, you'll need the 21mm spacer from the '83-85NA in the rear as it will rub the corner of the tyre-tread on the inside of the fender. Effective offset will be 34mm, similar to the front.


Both the '86 951 and NA are an oddball. They use the early 23.3mm offset, but left off the rear 21mm spacer. Strange.

[intrepidagent]

Danno: thanks for the input. Neglected to mention that my NA is a 85.5.

[9FF]

...Both the '86 951 and NA are an oddball. They use the early 23.3mm offset, but left off the rear 21mm spacer. Strange.

That's because of the rear aluminum arms. From 85.5 and on all the 44's 51's had the same arms, they incorporated the 21mm spacing on the rear hub on 85.5-86 models and just changed the rear hubs to give a late offset on 87+ models.

[DannoXYZ]

Originally Posted by 9FF

That's because of the rear aluminum arms. From 85.5 and on all the 44's 51's had the same arms, they incorporated the 21mm spacing on the rear hub on 85.5-86 models and just changed the rear hubs to give a late offset on 87+ models.

Huh? I was saying that the '85.5-86 models did not come with the rear 21mm spacer. The studs are short 45mm ones, not the 65mm ones from the '82-85 cars. This made the 23.3mm offset wheels sit too far inwards compared to the '82-86 cars. If you want the rear-wheels to sit in the same position as the '82-85 cars, you'd need to change to longer 65mm studs and add the 21mm spacer. Those did not come as stock on the '85.5-86 cars.

[DannoXYZ]

Originally Posted by intrepidagent

Danno: thanks for the input. Neglected to mention that my NA is a 85.5.

Yep, same suspension as '86 NA. Came with updated oval-dash and aluminium suspension-arms. You'll still need the 21mm spacer + 65mm studs on the rear. Otherwise the 275/40-17 tyre will rub on the inside. If you had an '82-85 model, that 17x11 ET55 rear-wheel will work just fine because those came with the longer-studs and 21mm spacer.

[DannoXYZ]

Originally Posted by DannoXYZ

Huh? I was saying that the '85.5-86 models did not come with the rear 21mm spacer. The studs are short 45mm ones, not the 65mm ones from the '82-85 cars. This made the 23.3mm offset wheels sit too far inwards compared to the '82-86 cars. If you want the rear-wheels to sit in the same position as the '82-85 cars, you'd need to change to longer 65mm studs and add the 21mm spacer. Those did not come as stock on the '85.5-86 cars.

I used to think that the 21mm spacer was incorporated into the new hub design on the '85.5-86 cars too. But found out that's not the case. Here's the process:

1. I got a set of wheels for my '86 951 for track-use with maximum width & tyre-size about 15-years ago:

After careful measuring, these came to the following specs:

F: 17x10.5" ET-35, 255/40-17 tyres
R: 17x11.5" ET-35, 275/40-17 tyres

The rear-tyre was about 20mm taller than stock, but was the only thing available at the time. At full suspension-compression, it would barely rub the outside sidewall on my rolled fenders and the corner of the tread on the inside. My measurements put the everything in the centre of the available space just perfectly.

2. One of my friends with an '85.5 NA asked to borrow my wheels & tyres for a track-day. I did make sure he had front coilovers to fit the front wheels. Everything fit and went just fine.

3. Another friend with an '85 NA borrowed them a couple months later. He ended up shredding the outside of the rear-tyre just a block away. Strange... appears to be plenty of room on the inside no marks on the inside of the wheelwell, but rubs on the outside with just barely any suspension-compression. Hmmm, what's going on? Pulled out the ruler and measured... the rear-wheel sits about 20mm further out on this car than mine, why? A-HAH!! The stock 21mm spacer! After removing the 21mm and using open-ended lug-nuts, the wheels that fit perfectly on my '86 951 now works just fine on an '85 NA.

4. After discovering the rear-spacer issue on the '82-85 944s, I wondered about the lack of the spacer on my '86 951. I saw what I was missing for years, the rear-wheels where inset further into the fender than the front! So I installed the longer studs and 21mm spacer from the earlier cars. The wheels now look much more balanced front & rear:



CONCLUSION
The lack of the 21mm rear-spacer on the '86 951 and '85.5-86 944 NA is what allowed me to use 17x10.5/11.5" ET-35 wheels. The rear-wheels on these cars actually are inset more into the fender compared to the '82-85 944 NA. That's why using the 17x11.5" ET-35 rear-wheels didn't work on the earlier '85 NA. Removing the 21mm spacer from the early cars changed their configuration to match the '86 951 & '85.5-86 NA and allowed them to use the 17x11.5" ET-35 rear-wheels. Therefore, the '86 951 and '85.5-86 NA do not have the same rear-suspension configuration as the earlier cars and do not have the 21mm spacer incorporated into the hub.

This is also why the wheels the OP bought has different front/rear offsets:

F – 17 x 9, ET 35
R – 17 x 11, ET 55

These are configured for the presence of the rear 21mm spacers on the rear-hub of the '82-85 944 NA. If you removed the spacer from the hub and welded it to the wheel, you'd end up with similar F/R ET of 35mm like I calculated for my '86 951. Therefore, to use these wheels on '86 951 or '85.5-86 NA like the OP's, you have to add the longer-studs and 21mm spacer.

[veleno]

Or, to get a staggered appearance without the use of the 21mm spacer and longer studs, change the inner barrels and outer lips of the 17x11 +55 to achieve a 17x11 +35. I'm guessing the inner barrels will be about 20mm narrower and the lips will be 20mm wider.

[9FF]

Quote de 9FF

That's because of the rear aluminum arms. From 85.5 and on all the 44's 51's had the same arms, they incorporated the 21mm spacing on the rear hub on 85.5-86 models and just changed the rear hubs to give a late offset on 87+ models.

Huh? I was saying that the '85.5-86 models did not come with the rear 21mm spacer. The studs are short 45mm ones, not the 65mm ones from the '82-85 cars. This made the 23.3mm offset wheels sit too far inwards compared to the '82-86 cars. If you want the rear-wheels to sit in the same position as the '82-85 cars, you'd need to change to longer 65mm studs and add the 21mm spacer. Those did not come as stock on the '85.5-86

I always though it was built into the hub on the 86 but just checked and you are right. Learn something new everyday.

[DannoXYZ]

Originally Posted by veleno

Or, to get a staggered appearance without the use of the 21mm spacer and longer studs, change the inner barrels and outer lips of the 17x11 +55 to achieve a 17x11 +35. I'm guessing the inner barrels will be about 20mm narrower and the lips will be 20mm wider.

Yes, that would work too. I was looking at the configuration of those wheels and the extra 5th wheel to see if they can be re-arranged. Nope.

Simple enough to get longer-studs & 21mm spacer from earlier car. About $20 from pick-n-pull places or $50 shipped.

[intrepidagent]

Thanks to all who replied. Always learn something new about my car every time I come to Pelican!

Any suggestions / recommendations for the vendor or manufacturer for the spacers?

Thanks

[intrepidagent]

Additionally you mentioned the friend with the 85.5 NA had front coil overs however you had 10.5 up front. Do you envision any "inner interference" issues with 9" front width?

[Rasta Monsta]

Great thread and thorough, thoughtful answers!

[DannoXYZ]

Originally Posted by intrepidagent

Thanks to all who replied. Always learn something new about my car every time I come to Pelican!

Any suggestions / recommendations for the vendor or manufacturer for the spacers?

A lot of the dismantlers will have the parts. Here's what you need:

477 501 701 - 21mm spacer
911 331 671 00 - 65mm wheel stud

The easy way to replace the studs is to disconnect the parking-brake cable from the hub. Then push/pull the cable out of the hole in the trailing-arm. This hole is where you push out the existing studs. Rotate the hub so the back of a stud lines up with the parking-brake cable hole. Then push out the stud and poke into that hole. Hang onto it so it doesn't fall in.

Then stick the new stud's butt into the hole, then the other end out through the hub. No need to disassemble the hub! Use a C-clamp to press in the new stud, or zip with nut & impact-wrench. Finally, re-connect the parking-brake cable.

Good luck!

[DannoXYZ]

Originally Posted by intrepidagent

Additionally you mentioned the friend with the 85.5 NA had front coil overs however you had 10.5 up front. Do you envision any "inner interference" issues with 9" front width?

Won't be a problem with 9". The wider wheels will rub the rim on the spring-perch.

[DannoXYZ]

Originally Posted by Rasta Monsta

Great thread and thorough, thoughtful answers!