Orjan

Inside my forged 928 dish rims, I have a strange rubber puck. This has some sort of a membrane in the center. Anyone knows what this is for? Is it bad?
My closest guess would be that it's some sort of a pressure self-adjusting system, but I have never seen this.

Will post a picture later.

/Orjan

A930Rocket

A GPS bug planted by your jealous G/F to see where you go on your night out with the guys? LOL

Or maybe a tire pressure reading system?

Orjan

AHA!!!! Good thing they are sitting in the garage then!

I thought about that, but it doesn't look like having any sending facilities though (looks like a very dumb membrane and rubber lump).
Possibly it could be an automatic pressure normalizing system if such exist??

John Veninger

Tire pressure sensors.
Are they Design 90's? If so they are cast, not forged.

Orjan

I think the forged flat dish rim was the stock rim for the 928S4? I don't think they are pressure sensors (how on earth could anything be transferred wirelessly from a rubber puck? :-)

/ØRjan

John Veninger

Those are forged. More than likely from a 1990 928S4.
Do you have a picture of the puck? The stock wheels from 1990+ had two of the sensors per wheel. These sensors were a simple on/off switch with preset pressures. There were "pickup" sensors mounted to each corner of the suspension. The spinning of the wheel past the pickup sensor created a field that could be read by tire pressure computer (system called RDK).

Orjan

Hi John. If they were not forged, I would not have bothered buying them

The rims are at a local shop to have tires mounted, so I haven't been able to take a picture of the "puck". I was not aware of this "puck" when I bought them for our tracked 944, and we are now moving to willwood brakes - I'm afraid this will limit us in terms of rotor size.

If these were stock on the -90 S4, they should give enough room for the 304x32mm rotor and the Porsche/Brembo big black (928S4/944TurboS) calipers. These rotors and calipers would be a great option for us, if they weren't so heavy. The willwood superlites will acommodate our near-stock 2.5 8v NA engine better, and I hope and believe that they are a little more low profile than the brembo caliper - giving room for a little more rotor.

Are you certain though, that the 928 only had 7" fronts and 8" rears for the 1990 model?

Thanks in advance,

/Ørjan

John Veninger

I'm sure.

90-91S4 7x16 / 8x16 225/50-16 245/45-16 Flat "Disc"(RDK) F-65/R-52.3

90-91S4 (M400) 7.5x16 / 9x16 225/50-16 245/45-16 Design 90 (RDK) F-65/R-52.3

90-91GT 7.5x16 / 9x16 225/50-16 245/45-16 Design 90 (RDK) F-65/R-52.3


www.928gt.com tips section

Orjan

Does "(RDK)" mean forged? The rims on the M400 or the GT are the forged design 90 from the 944 Turbo S... beauuuuutiful rims in my book, but I havent dared trying our 205's on 9" yet :-).
Thanks for your insight so far John.

/Ørjan

John Veninger

RDK is the pressure sensor setup on the 928.
The M400 was the option for the S4 to get the D90 cast GT wheels on the car in 90-91.
The forged club sport wheels (looks like the D90) was on the 89 928GT w/ 8" front and 9" rear w/ a 60mm offset, no pressure sensor.

Orjan

I'm getting totally off track here, but I'm quite certain that the d90 wasn't cast in 7.5 and 9" wide. I have cast d90 7 and 8", but no 7.5"? I thought this was a special size for the forged "d90" only.

John Veninger

All Design 90's are cast. My 928GT has 7.5" and 9" D90 cast wheels, std. equipment in 1990 and 1991

The 7" D90 is from a 944.

The forged "D90" (known as club sport) were in 8" on the 928 and I think 7" on the 944.

vpk944

The 944 turbo s forged wheels (look very similar to D90's) are 7" and 9". The 7" is actually closer to 7 3/8". This is helpful in PCA Club Racing were you can go up 1 inch in width in the stock classes. I run the same wheels you are talking about for a 928S4 on my 924S for Club Racing. I actually had the pucks (pressure sensors) removed and sold them on ebay for around $250. The wheel shop welded and smoothed the area where the sensor was. Most D90's (cast) are 6" and 8" for the 911's, 7" and 8" for the 944's, and 7.5" and 8.5" (IIRC) for the 928's. Don't know if any of this helps, but hope so.

John Veninger

Don't know what IRRC is, but they are 9" not 8.5 on the 928.