Last post on Apr 08, 2009 at 8:01 AM
You are in the Cadillac STS/STS-V
What is this discussion about?
Cadillac STS, Cadillac STS-V, Sedan
#796 of 1325 derrelhgreen
Oct 08, 2004 (8:07 am)
As far as I can find, the only thing we know for sure is that the 1SG (premium luxury performance) package has the 3.42:1 axle. This axle ratio give 30 MPH per 1000 RPMs. So at 75 the engine will run at 2500 RPMs with torque converter locked up. The 2.73:1 would reduce this to 2000 RPMs but the base/luxury V8s have 17 inch wheels, so probably 2000 would be around 70. The 3.23:1 is also a RWD ratio:
Oct 08, 2004 (1:33 pm)
Using the TireRack charts for Michelin 255/45-17s, that tire turns 794 revs per mile times the 2.73 ratio times .76, or 72.84 mph at 2000 rpms.
I'm not sure whether this is the exact tire that comes with the 1SE RPO or not, but I tried!
The difference for the 17 inch tire and the 255/45-18s that are supplied with the 1SG RPO package makes for 762 revs per mile. 762 X 3.42 X .76, or 1980 rpms at 60 mph.
This means that the regular sedan with 1SE that has 2.73s will be going 12 mph faster at the same (2000) rpm.
No way that the performance axle equipped 1SG (3.42) will deliver the same highway fuel economy even with the slightly larger wheel and tire combination.
Maybe mount the 255/55-18s that are available on the SRX if they'll fit?
To bad it's not possible to order a fully equipped 1SG with the 2.73s, or the 2.93s that come standard with the XLR 2-seater.
#798 of 1325 Re: Got my STS last night [nbfc260]
Oct 08, 2004 (10:45 pm)
Congrats are in order!
Do you know for sure what your rear-end ratio is?
Or, what exact rpm are you turning at exactly 60 mph in overdrive fifth gear with the T/C engaged or locked up? Knowing that, one should be able to determine the exact rearend ratio.
Anyone know where the SPID is located? It will show all the RPO codes for your car including the gear ratio.
G80 is the RPO code for the limited slip differential, and the ratio codes will be one of these:
GU2 - 2.73 - 1SE
GU5 - 3.23 - All-wheel drive models and maybe the 1SF
GU6 - 3.42 - 1SG
Done any fuel economy testing yet?
Was wondering what you are getting in your real world conditions?
For Ray . . how do you know that the 1SF you test drove had 3.23s?
If the 1SF has 3.23s and 17 inch wheels and tires, that will work out to be almost the same overall ratios (rpms) as the 1SG package with the 18 inch wheels and tires, right?
Oct 10, 2004 (9:33 am)
The 17 inch wheels with 255/45 tires are about 26 inches in diameter while the 18's are 27 inches in diameter. So the 17's will run about 4% faster. The 3.23:1 axle will run about 6% slower than the 3.42:1 axle. The net results of both 17 inch wheels and the 3.23:1 axle is that it should run about 98% as fast so:
if the 3.42:1 axle with 18 inch wheels is 2000 RPMs at 60 MPH
then the 3.23:1 axle with 17 inch wheels should be 1960 RPMs at 60 MPH
The 2.73:1 axle would give 1655 RPMs at 60 MPH. This axle would permit 1st gear to reach 50 MPH, 2nd to hit 80 MPH and 3rd to reach 110 MPH. The quarter mile with the 3.42:1 gears is reached in 4th gear in the magazine tests.
#800 of 1325 No 1SFs around here!
Oct 10, 2004 (9:43 pm)
nbfc260 . . Looks like it's up to you, as none of the four dealers that I visited had vehicles in stock with the 1SF option, although the GM BuyPower site showed all of them to have one or more of these vehicles in stock. All said that the vehicles were enroute. Yeh right!
So nbfc260 . . IF you would be so kind as to open your trunk, lift that floor compartment cover and inspect your SPID label for the RPO that starts with GU - and tell us what that number is on
your car. I can't find one at a dealer to verify what is the correct rear-end ratio for the 1SF option. Thanks in advance.
Checked out a 1SE and it did have the correct RPO (GU2) for the 2.73s.
sls002 . .
Don't know how you got 1655 rpms when I calculate only 1629 but we are close enough for debating to be sure.
It depends on which tires we're using for the revs per mile.
The one I'm using is a Michelin 235/50-17 that shows 785 revs per mile (26.3".) Your calculation is based on another Michelin tire, a 26.0"(?) that turns 797 revs per mile?
BTW, the standard tire for the 1SE isn't 255/45-17, but 235/50-17. Maybe that's where we differ?
TireRack isn't up to date on most of the tires that are listed as OEM for these cars.
Neither is the Michelin site!
We do know for sure that whatever it turns out to be exactly, it is 300 plus rpm lower than the 2000 rpm figure that is agreed upon for the 1SG option that has 3.42 with 255/45-18 drivers.
#801 of 1325 Re: Got my STS last night [derrelhgreen]
Oct 11, 2004 (5:58 am)
“For Ray . . how do you know that the 1SF you test drove had 3.23s?”
Someone with access to GMVIS did a vehicle build and said the 1SF is 3.23.
Impressed with the difference in ‘liveliness’ between 2.73 and 3.23 . . .
#802 of 1325 derrelhgreen
Oct 11, 2004 (7:39 am)
I did assume 255/45's in back. But you are right, the GM site for dealer online orders say that the V8 gets 235/50's all around on base/luxury orders. So that would slow the engine even more. The 255/45 tire is about 26 inchs in diameter with 17 inch wheels. The 235/50 is about 1% larger diameter with 17 inch wheels.
I think that the 17 inch wheels with 3.23 axle and the 18 inch wheels with the 3.42 axle should result in very similar performance. The 1SG should give the best performance (since it costs more), but the differences should be small. The 2.73 axle should result in less performance, but it may be only a half second on 0-60.
#803 of 1325 Re: derrelhgreen [sls002]
Oct 11, 2004 (9:08 am)
"The 2.73 axle should result in less performance, but it may be only a half second on 0-60. "
Well - my (un)calibrated "butt dyno" suggests more like a full second.
(My current Lincoln LS V8 has been independently established as capable of a mid-6 second 0-60 and 14.7-ish quarter.)
My guess is that the 1SE is a 7+ sec 0-60 and the 1SF is roughly equal to the 1SG times I have seen published (less than 6 sec.)
Wondering if 1SE buyers will feel shortchanged . . .
#804 of 1325 rayainsw
Oct 11, 2004 (9:28 am)
I was guessing a half second because the STS with 2.73:1 gears is geared like the FWD Seville with the 275 hp engine (3.11:1), while the 3.42:1 gears are very similar to the FWD STS gearing (3.71:1). Cadillac rated the 0-60 performance difference at a half second for the FWD STS vs SLS. Cadillac rates the STS 1SG package at 6 seconds or less for 0-60, while the V6 is said to do it in 7 seconds. I would think that the base V8 STS could do better than the V6.
Oct 11, 2004 (11:50 am)
Got a call this morning from a very helpful salesman in Alhambra that went to the trouble of calling GM, and verifing that the "F" package, as he called it (that's the 1SF option package) does have 3.23s (GU5.)
So the 1SE has 2.73s, the 1SF has 3.23s, and the 1SG has 3.42s.
Because of the slight differences in the 1SF and 1SG equipment, I doubt if there will be even 50 rpms differnce at 60 mph. Still, the Premimum Luxury Performance (1SG) should have the edge because of its slightly my powerful overall gearing.
If you want your STS to be a real highway cruiser and get better fuel economy, I think you'll need the 2.73 gears that are supplied with RPO 1SE.
Wonder if Caddy would allow a person to order the 1SF or 1SG option with the higher GU2 (2.73) gears? I'll bet it'll be impossible with the lower gears (3.23s or 3.42s) to get 22 mpg on the highway, and at the speeds I like to cruise, probably only 19 or 20 mpg. Oh well!
The EPA figures of 15/21 for the SRX with its 3.23s and RWD back this up, and with AWD, those figures are only 15/20 mpg. 'Course, the SRX is heavier, and with its 37+ C/D, what would one expect?
Waiting for nbfc260 to pick up on this, and lay the 'real' fuel economy truth on us!