How has tire size effected your gas mileage on the sc430?
09-09-08, 08:11 AM
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How has tire size effected your gas mileage on the sc430?
What kind of gas mileage should I expect in everyday driving with the sc?
Has putting on big wheels and wider tires changed the gas mileage? If so, how much?
Has putting on big wheels and wider tires changed the gas mileage? If so, how much?
09-09-08, 04:47 PM
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Well this question can get quite technical, but quick answer is both yes or no. Contrary to popular belief, not all low profile tires hurt MPG, though the majority do.
Technical Answer (I'll try and be breif):
Alot of people have misconceptions about the effects of sprung and unsprung weight. Going back to the basics, its quite obvious to understand why sprung weight (weight which is supported by the suspension) affects MPG, and why that affect is linear. Most estimates by the EPA say that for every 10% reduction in your sprung weight, fuel efficiency increases by roughly 7%.
Unsprung weight (not supported by suspension, i.e. tires and wheels) is much different. If you read up on the properties of rotational mass, you'd find alot of technical and mathamatical equations, but 2 basic things to understand are:
1) Unsprung weight when moving causes a rotational force and so therefore affects your performance/MPG exponentially the faster you go.
2) The distance unsprung weight is from the center affects your performance/MPG porportional more so than weight closer to the center.
Basically all this means the tires affect the most, because they are at the furthest point from the center. A rough example to compare it to sprung weight would be that the rims affect with twice the force, while the mass of the tire affects with ten times. Under this example a 1lbs increase on the rim is like having 2 lbs in your trunk, and 1 lbs on the tire is like having 10 lbs in your trunk. So, even if you put ultralight magnesium wheels on your SC400 that weigh 10 lbs less than stock rims, if you end up adding 2 lbs to your tires, you wont see any improvement. Another thing to remember is that if you go for low profile tires which weigh they same as stock, even though they might weigh the same, that lower profile tire has its weight pushed out further away from center, so it will still hurt performance and MPG.
This is why most drag racing cars and muscle cars have thick tires and small rims (often 15" or less). The weight gets dispersed away from the edges, improving performance, and thus improving MPG. If your real serious about improving MPG, then go onto tirerack and compare different tire brands and sizes. you'd also be surprised at how different brands can weigh significantly different.
Technical Answer (I'll try and be breif):
Alot of people have misconceptions about the effects of sprung and unsprung weight. Going back to the basics, its quite obvious to understand why sprung weight (weight which is supported by the suspension) affects MPG, and why that affect is linear. Most estimates by the EPA say that for every 10% reduction in your sprung weight, fuel efficiency increases by roughly 7%.
Unsprung weight (not supported by suspension, i.e. tires and wheels) is much different. If you read up on the properties of rotational mass, you'd find alot of technical and mathamatical equations, but 2 basic things to understand are:
1) Unsprung weight when moving causes a rotational force and so therefore affects your performance/MPG exponentially the faster you go.
2) The distance unsprung weight is from the center affects your performance/MPG porportional more so than weight closer to the center.
Basically all this means the tires affect the most, because they are at the furthest point from the center. A rough example to compare it to sprung weight would be that the rims affect with twice the force, while the mass of the tire affects with ten times. Under this example a 1lbs increase on the rim is like having 2 lbs in your trunk, and 1 lbs on the tire is like having 10 lbs in your trunk. So, even if you put ultralight magnesium wheels on your SC400 that weigh 10 lbs less than stock rims, if you end up adding 2 lbs to your tires, you wont see any improvement. Another thing to remember is that if you go for low profile tires which weigh they same as stock, even though they might weigh the same, that lower profile tire has its weight pushed out further away from center, so it will still hurt performance and MPG.
This is why most drag racing cars and muscle cars have thick tires and small rims (often 15" or less). The weight gets dispersed away from the edges, improving performance, and thus improving MPG. If your real serious about improving MPG, then go onto tirerack and compare different tire brands and sizes. you'd also be surprised at how different brands can weigh significantly different.
09-09-08, 07:57 PM
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I know that on my GS4, when I put on my 275/30/20 combo my "indicated" mileage dropped approximately 10%....24mpg down to 22 mpg with 70% hwy mileage. I say "indicated" because my 20" combo is 1+ inches taller than my stock 17" combo, which throws the odometer off by roughly 5%...my car travels FARTHER than the indicated odometer reading because of the taller tire/wheel combo. If I take that into account, the net-net is that my heavy 20" combo takes roughly 5-6% off my fuel economy, or said another way, 20 miles less on a tank of gas.
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