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Joined: Dec 2001
Posts: 31
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Joined: Dec 2001
Posts: 31 |
Hello all. I travel the I-5 regularly at 70-80 mph, and for the likes cant do better than 21 mpg. My 91 SHO used to get 24+ mpg all day, with the motor turning about 3100rpm. My best guess is that my SVT is turning around 3700rpm at this speed and the secondaries are open, dogging the mileage. So, to sum up my question: I am ready for new tires. Lowered 98 EO (K&N) on stock wheels. I currently have the 225x50-16, and want to go to a taller tire to gain some gearing and lower the rpm for freeway cruising. I was thinking of going to 205x60-16 or 215x55-16. The SHO had 215x60-16... what about those... too tall? Please comment, and if anyone has fitted these sizes. Thank you very much, Pat.
98 EO Silver Frost SVT, K&N, Eibach springs, 225x50-16, tinted.
#3867 of 6535
Replacement for my 91 SHO.
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Joined: Dec 2001
Posts: 304
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Joined: Dec 2001
Posts: 304 |
It would probably be easiest to go to TireRack.com and use their tire chart dealie that shows the different tire sizes, the differences in their diameters and the differences in the revs per mile they do. The chart is in the SPECS section after you make your tire choices. You'll need to spend some time searching there because some manufacturers don't make some sizes. Your 225x50's are 25" in diameter although I saw that depending on manufacturer, diameters changed even if sizes didn't. Good luck.
Karl
*** It's all about consistency! ***
98 SVT Contour
86 Ranger GT
69 Fiat 850 Sport Spider
67 Formula-S Barracuda
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Joined: Sep 2001
Posts: 132
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Posts: 132 |
Different tires are going to have a minimal effect on gearing, so little that you probably won't even be able to tell. If you get a 60 series tire, I don't think you'll like the sidewall flex very much. I'd stick with a 215, 50 series tire if I were you. You won't see a MPG change with taller tires.
95 T-Red SE MTX
Eibach springs, Custom cat-back exhaust, Cross-drilled front rotors, Momo air race leather shift-knob, Kenwood head unit, Kenwood 600w amp, 2 12" Infinty's, 18" Tantrums w/ Yoko Paradas, SCA CAI
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Joined: Sep 2000
Posts: 7,329
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Joined: Sep 2000
Posts: 7,329 |
The 225/50's you are running are the best compromise already.
If you are only getting 21mpg on the highway I would look for problems.
I get 23-25mpg in mixed driving with a lead foot and ~30mpg in straight highway driving.
BTW - you wouldn't want to go to 60 series because you would lose a ton of performance.
Also go too tall and you may start rubbing the fender liner.
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Joined: Sep 2001
Posts: 586
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Posts: 586 |
My best guess is that my SVT is turning around 3700rpm at this speed and the secondaries are open, dogging the mileage This doesn't sound correct. At 70, my SVT is at 3000 RPM's, at 75 about 3250 RPM's and at 80 about 3500 RPM's. The secondaries are not open at this point. They kick in at about 3900 unless you are at WOT, then at 3400. It sounds like you have other problems with your gas mileage. Check the normal stuff, plugs/wires, fuel/air filter and tire pressure. 
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