STS4 05 Tires 1sg - Page 3

jamesbalzer · #31 (**permalink**) 10-31-09, 10:56 PM

Quote:

Originally Posted by EChas3

They would make her speed read 0.84% too fast. (said affectionately, of course)!

EChas3: You know this but for the benefit of all others; Speedometers are not accurate enough to care about .84%. It is likely at least that far off now. Colorado State Trooper had me at 86mph but I had the cruise set on a very level stretch of road at 84. Almost a 2.5% variation! Ran the STS against my Garmin GPS for the remainder of the trip and it showed that the cop was right; my car is over 2% off. There used to be a listing of this in Motor Trend or Car and Driver or one of those mags, that showed actual speed vs. 60 on the speedo. Pretty much none of them were dead on. You would think that these cars, for the price, would be darn near perfect but......Point is, I say go for the 255's and have fun!

EChas3 · #32 (**permalink**) 11-01-09, 12:31 AM

Different make & model tires vary. New tires have larger diameters than old ones. While my wife uses a 'Watch your speed because we are.' RADAR sign to see how high she can get it before passing, I use it to test the accuracy of my speedometer. Measured miles are even better. Mile markers are placed within 10 yards, use longer runs with them to average-out any errors.

While speedometers may be inaccurate, the ones in these cars are extremely consistent. If your car was reading 2.5% slow, I'd bet you're not on OEM rubber. My wife's and my cars have different rear-end gear ratios and different sized wheels & tires but both read within 1% true speed. Your car should very slowly grow more accurate as your tires wear. The electronics won't change much, if any at all.

jamesbalzer · #33 (**permalink**) 11-01-09, 11:53 AM

OEM tire size, but brand new (less than 1500 miles on them when I was stopped) Bridgestone tires. I thought of trying to explain that to the cop but I did think I was going 84 in a 75. Seemed like a losing argument to dispute his 86 claim. So, I was REALLY nice. Told him I had left late, traffic was light, visibility was good, car was as capable as any of safely going that fast and despite what I knew was right decided to try to make up some time. Got off with a verbal warning.

Totti808 · #34 (**permalink**) 11-01-09, 04:40 PM

I immediately changed all the four tires when I bought my used 2006 STS.

The original tires were P235/50ZR18 and 255/45ZR18 (Michelin)

I changed all the tires to P245/45R18 96W (bridgestone turanza)

Can I expect better ride quality and handling if I changed back to the original tire sizes?

jamesbalzer · #35 (**permalink**) 11-02-09, 10:08 AM

Generally, the bigger the sidewall the better the ride quality. The Bridgestones I picked up have "Serenity" technology which I think is a carbon cord specifically to help with ride quality on a low profile tire. These aren't your Grandpa's Cadillacs anymore with 75 series sidewalls and road-boat suspensions......

Angus Young · #36 (**permalink**) 11-02-09, 09:17 PM

My moonstone 05 had 275 50 17 Rear and 255 50 17 front just changed them out with 255 45 18 Toyo Versado LX on all wheels with 9 spoke 1sg rims that I just had chrome plated, very nice inprovement in both looks and ride.

My Black 05 1sg I just put 255 55 18 Vredestein Ultra Sessanta all the way around on the same 9 spoke cadillac rims that also just came back from getting chromed.

What a difference side by side from the 7 spoke aluminum to the 18 inch 9 spoke chrome.

As far as the speedo issue... "You'll get that!!"

EChas3 · #37 (**permalink**) 11-03-09, 11:39 PM

Tires are very much a personal preference. Like most technical decisions, design trade-off's produce many different opportunities. Ride quality and handling can be opposites. Road noise vs. poor-weather traction is another design dicotomy. GM tried for the middle of the road. Like in politics, trying to please everyone ends up offending most serious enthusiasts (of any bent).

Oh, and by the way, tire pressures can affect speedometer accuracy, too. Think of the radius; axle to road.

stevenriz · #38 (**permalink**) 11-05-09, 02:13 PM

I may have mentioned this in another post but I went with SUNNY tires a couple months back and completely hated them. I have the 18" stagerred sizes as well. My car sounded like a truck and I even think I felt a vibration coming from the front. I exchanged them for the Michelin AS Sport. Love em... so far...