Gas milage issues
I recently purchased a1985 Ford Bronco with the 300 I6 and Np 435. I was getting about 18-23 mpg at first. Now I get about 7-9 mpg. The only thing I changed was the tires. At first I had 235/75/15. Now I have 31x10.50/15. The tires are about a 1/2" taller than the factory tires. I have never been much on Ford but I fell for this one . Would the tires change the mpg that much? Is there anything I can do to get better gas mileage that won't cost over a few hundred dollars. I bought the truck for $700 and have invested $4000 in small repairs. Windshield, clutch, tires, wheel bearings, fluids, etc. Any info will be greatly appreciated. Thanks for your time.
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235 is 9.25 inches
6.9 inches high, 15 inch wheel 15+14=29 inches diameter So you went from 29 inches to 31 in the diameter and you went from 9.25 inches wide to 10.5 inches wide and your new tires might weigh significantly more than your old ones. 29 pie=91 inches, 63360/91=696 revolutions to go 1 mile 31 pie=97 inches, 63360/97=653 revolutions to go 1 mile odometer reads 1 mile at 696 revolutions Odometer with new tires reads 1 mile but actual mileage is 6 percent more |
Originally Posted by g_k50
(Post 14453413)
235 is 9.25 inches
6.9 inches high, 15 inch wheel 15+14=29 inches diameter So you went from 29 inches to 31 in the diameter and you went from 9.25 inches wide to 10.5 inches wide and your new tires might weigh significantly more than your old ones. 29 pie=91 inches, 63360/91=696 revolutions to go 1 mile 31 pie=97 inches, 63360/97=653 revolutions to go 1 mile odometer reads 1 mile at 696 revolutions Odometer with new tires reads 1 mile but actual mileage is 6 percent more |
what gear ratio do you have? I bet its 3.08's in which case you could probably swap over a later year bronco front/rear diff to get 3.55's and see a great boost in performance. anytime you increase the tire size though your going to loose mpg not just due to tire size but also the vehicle being taller.
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Originally Posted by Kemicalburns
(Post 14455697)
what gear ratio do you have? I bet its 3.08's in which case you could probably swap over a later year bronco front/rear diff to get 3.55's and see a great boost in performance. anytime you increase the tire size though your going to loose mpg not just due to tire size but also the vehicle being taller.
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I dont think you can attribute just the tire change to that drastic a drop in mpg. You say you smell fuel and carb looks wet sometimes. I am betting you have more problems than tire size.
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start researching
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Originally Posted by Kemicalburns
(Post 14463977)
start researching
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I have an 83 Bronco, 6 cyl, NP435, 3.55 gears (stock) and 31" tires. I'm still getting in the high teens on the freeway.
You have something wrong with your truck and its not the tires. Too large a drop in mileage to be from tires alone. If your truck is not running pig rich you must have a fuel leak somewhere. Brakes dragging? |
Originally Posted by dan240
(Post 14475921)
I have an 83 Bronco, 6 cyl, NP435, 3.55 gears (stock) and 31" tires. I'm still getting in the high teens on the freeway.
You have something wrong with your truck and its not the tires. Too large a drop in mileage to be from tires alone. If your truck is not running pig rich you must have a fuel leak somewhere. Brakes dragging? |
power valve
If you dont see a large leak on the exterior, check manifold vacuum for base gasket leak which may cause power valve to stay open. Check power valve anyway, depending upon age of carbs, replace power valves anyway.
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Originally Posted by benshere
(Post 14536705)
If you dont see a large leak on the exterior, check manifold vacuum for base gasket leak which may cause power valve to stay open. Check power valve anyway, depending upon age of carbs, replace power valves anyway.
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