Well last Friday after work I was tipping a cool one, talking Cadillacs with my good buddy. We decided to check the door tags on his 94 sts and my 98 sts...As it turned out his 94 sts has a z rated door tag, mine is the h rated 98 sts. If anybody can shed some light on how many z rated 94 sts's and how many were h rated for the 98 sts? And were all sts's h rated? just a few z rated? Any other describtions of these two cars?
Thanks
Guy

The Z-rated option was special order. I don't know if there are any production figures, GM doesn't like to break them down that far!

It was an inexpensive option (~$250), that was not very popular because of a couple of things:

1-What are the odds of someone "needing it" in the US? It was mainly for Export cars.

2-Firmer ride, not what most consumers would want.

Were Z-rated tires and higher govenor ( or lack of govenor? ) the ONLY changes to a Z-rated STS as opposed to a H-rated STS?

Were Z-rated tires and higher govenor ( or lack of govenor? ) the ONLY changes to a Z-rated STS as opposed to a H-rated STS?

Yes. The only difference should be the software version in the PCM and the tires.

Z rated tires wear faster and ride harder. It's not the smooth Cadillac ride that traditional owners like, so they put softer-riding S rated and H rated tires on instead. The manufacturer has a legal responsibility to prevent you from killing yourself by not allowing the car to go faster than the equipment it comes with can handle (aka the tire speed rating), so the "governor" comes in. S rated Cadillacs (Deville, DHS, Seville SLS, Eldo base, etc) are limited to 110 and the STS, DTS, ETC are H rated and limit is at 130. Z tires are good for speeds 150 and higher so, no governor.

Pre OBD II may be able to get an aftermarket chip to override this limitation but I am not sure. (and I wouldn't do it b/c I don't know if there are other differences other than just the speed limit)

It is rumored that if you have a good relationship with your dealer, and you show up with Z rated tires... they may be kind enonugh to reflash your PCM.

They would have to figure out how to do it because I think this is a rare request. They may also choose not to do it for liability or whatever.

Pre OBD II may be able to get an aftermarket chip to override this limitation but I am not sure. (and I wouldn't do it b/c I don't know if there are other differences other than just the speed limit)

Yes, most aftermarket OBD I chips remove the speed limiter. The Superchip I had in my old 1994 Deville Concours did as well.

It was an inexpensive option (~$250), that was not very popular because of a couple of things:

1-What are the odds of someone "needing it" in the US? It was mainly for Export cars.

2-Firmer ride, not what most consumers would want.

So a Z-rated STS rides firmer than an S-rated? Cool. Mine is Z-rated, we love the ride!

I have H rated and I've hit 140 in my ETC....

So a Z-rated STS rides firmer than an S-rated? Cool. Mine is Z-rated, we love the ride!

It does ride firmer. I have noticed a big difference in the ride in my 99 with H rated tires compared to my 96 with Z rated tires. My grandparents noticed it as well.

Well, you can't compare the ride in a '96 STS vs. a '99 STS. They are two different cars!
And besides the tires, I really don't think there is anything in the STS suspension that makes it ride firmer.

Well, you can't compare the ride in a '96 STS vs. a '99 STS. They are two different cars!
And besides the tires, I really don't think there is anything in the STS suspension that makes it ride firmer.

I agree with this statement. The only difference is the harder tires. Perhaps there are other factors from model to model because of different usage patterns wear/tear, (shocks worn, etc).

There is a difference between an SLS and an STS in terms of handling and feel, but not between an H STS and a Z STS.

I have H rated and I've hit 140 in my ETC....

If the door jamb says H, then the odometer may be miscalibrated. The needle tends to be off a little. If you mod your analog IPC to have digital MPH on the DIC, you will see a normal discrepancy between the readout and the needle < 5 MPH.

Did you get a "TOP SPEED, Fuel Cutoff EXP 111" message, or you just ran out of road?

I have noticed that there is a variation on the actual cutoff of a few MPHs. Not sure why that is.

So a Z-rated STS rides firmer than an S-rated? Cool. Mine is Z-rated, we love the ride!

Yes there are spring rate differences as well as damping calibration differences on the shock absorbers. The CVRSS is supposed to have the best of both worlds, and be smooth on flat and firm cornering, but in reality it's firmer all the time vs. an S-rated base model that does not have CVRSS.

On caddyinfo.com I read Extreme Motorsport is maybe putting a map together for the OBDII cars??? Not that I would do 155....well I might air it out on the way to BIR to watch my kid do alittle roadracing....there are some nice open streches you can see everything for a long way.
Maybe a MAS sensor, air box mod, exhaust and a map for the OBDII....thats all I think it would take to wake her up on the bottom all the way to top....will this stuff be available?

If the door jamb says H, then the odometer may be miscalibrated. The needle tends to be off a little. If you mod your analog IPC to have digital MPH on the DIC, you will see a normal discrepancy between the readout and the needle < 5 MPH.

Did you get a "TOP SPEED, Fuel Cutoff EXP 111" message, or you just ran out of road?

I have noticed that there is a variation on the actual cutoff of a few MPHs. Not sure why that is.


No cutoff, the bridge was ending soon so I slowed down and I knew H was rated 135 so I didn't want to risk it. And yea I have done the code to show a digital speedo, actually it was 139 not 140.