New Tires Installed, MPG Suffers

[96RS Alex]

My set of BF Goodrich Excentia GT 235/60R/15 tires reached past its 50K treadlife warranty to 55K miles. I was extremely happy how much life I got out of them and the superb ride I had for 2 years on my finely tuned 1991 Firebird. Now the set of tires are discontinued in that particular size according to tire dealers and cant find them anywhere so I go to a local Walmart Tire and their stubborn system tells me my Bird can only accept a 215/60R/15 size. I tell them that the car is sitting outside with 235's and they couldnt believe it but agreed after inspection. Anyways to my point, it's been raining very much here and the Bird hydroplanes a lot and I could not risk it any much longer so I hastily bought the Douglas Performance GT-H set and had them installed. It's been a week now and I noticed my MPG/fuel consumption has been increased but these are 40K miles warranty. Am I to assume a lower mileage tire is stickier therefore the engine has to work harder to spin them or should I let it break in a little more??? The car went through a 4 wheel alignment after the install I will mention. I feel like taking it back to Walmart and sticking with what I felt was best for my Bird but my dilemma is with the discontinued tires plus my old tires were chucked. How do I approach these so called "tire mechanics" with my problem? Any opinions would be helpful!

[3.4 slow to go]

what is the warranty/return policy on your tires?

tirerack.com has 10 tires to choose from in the size you want.

[zlexiss]

What's the tire pressure? Low psi = worse mileage

[96RS Alex]

The full warranty states automotive service for 90 days or 3000 miles, whichever comes first. The existing new tires state 44 PSI max on the sidewalls. I know for a fact that the old BFG's also said 44 PSI but nearly every mechanic I spoke to said to inflate to what the inner door jamb states which is 30 PSI as the standard inflation measurement. The extreme humidity here in CT has been ridiculous even at 3am now so I'm guessing that also doesnt go well with six cylinder combustion and MPG. I will recheck the present PSI along with a drier air conditions most likely by this Thursday because I am missing my trusty air gauge and will post soon.

[Jerriko]

If you left those butchers at Wal-mart do an alignment to your car, I would take it back. The alignment will easily reduce mileage if the toe is wrong and that is common for fast food shops. Does it pull or handle differently? If you only got the tires change and had this problem, you could safely assume that its the tires. But since you had the tires and alignment changed, you have to look at both factors. Your alignment will have a larger impact on mileage than the tires.

[96RS Alex]

Well this morning I took the Bird back to the alignment shop and they forgot to mention that my bushings are worn and needs replacing after they took my money and told me that they can affect handling & mileage, is this true? Walmart never does 4 wheel alignments but they spun balanced the new set and my alignment shop did an excellent computer job on my '96 Camaro before hence the improved ride. The alignment shop also said I can run a higher PSI in my tires ( 5-10 PSI ) for a smoother/economical ride but the trade off is I'll get LESS max life out of these 4 Douglas GT-H tires in other words 35K on a 40K warranty and deflate them back to 30PSI for the winter. I'm still skeptical about all this advice from tire mechanics, I only know so much about making power out of these 3rd Gen vehicles and their capabilities but not tire/suspension science. I also need shocks & struts too by the way, the Bird does bounce loosely once if I exert enough force on each end so therefore is that another possible culprit compounding my MPG issue? Seems this problem shouldve been easy to figure out, looks like a full suspension upgrade pretty soon. Yes... I'm keeping the car, it flipped 260K very recently.

[Jerriko]

It is not possible to get an accurate alignment with KNOWN worn parts. Whoever did that, I would NEVER do business with them again. Which bushings did they say were worn? Running a higher tire pressure will get you better gas mileage but it will not be smoother. Harder tires will transfer more force to the body of the car giving you a very hard ride. Yes, you should get the shocks and struts changed before other parts become damaged but the shocks/struts will not affect mileage.

[3.4 slow to go]

^^ as said above, and read in HPP mag, worn control arm bushings will not let you get/keep an accurate alignment.

[96RS Alex]

True, I was reluctant about changing the alignment or even bothering to go get one at least since I try my best to avoid pothole-ridden roads here in CT. My thought is if I had decent wear & tear on the tires with the proper rotation schedules, then why align the car the 2nd time around? I have the Bird on ramps and yes the lower control arm bushings are looking pretty sad today. The bushings on the front sway bar look worn too, both are gritty with cracks evident. I will look into polyurethane bushing kits plus the all around strut & shock combo. I kinda like how the car sags to the rear when I floor it however I must fix my ongoing MPG issue.

[Rob Bell]

I thought the 30 PSI on the doorjamb was a ridiculously low tire pressure, especially since the stock tires on mine (02 Firebird) can handle 44 PSI. I have them inflated to 35 PSI instead. I think it works well. I tries 40 PSI but the ride was a little harsh.

[Phoenix]

Just remember that if you have wider tires you will need lower pressure to keep an even footprint and make your tires wear evenly across.

[3.4 slow to go]

I like to thin kthat the tire pressure reccomended on the door/owners manual is for the stock tires, brand new. For replacement/upgrades, see what the manufacturer has to say, also search for reviews. Tirerack has many reviews to read on shi*tloads of tires.

[96RS Alex]

UPDATE: It's been nearly a month with this increased fuel consumption issue and I just changed the cap, rotor, Bosch +4 plugs and wires ( stock '91 coil still retained ). The Firebird runs smoother than before. I also inflated the tires an extra 5psi and Im averaging better mileage now but the extreme humidity is still present here in the Northeast. I'm halfway convinced now that air quality does affect engine performance. Can't wait 'til Fall weather arrives.

[3.4 slow to go]

change the engine &tranny erl too. then if you feel bulky, change the diff fluid too.