Height of tires ver's MPG

[mjgord51]

Ha guys I think this has been addressed before, I'll be short. Not knowing whats in the 3rd member (ratio) "if that makes a difference" does the height of the tires have an affect on gas millage or not? Thanks Marvin aka mjgord51

[Stocker]

It depends -- maybe yes, maybe no, but probably not enough to notice or matter either way. If you are geared fairly low, taller tires might help just a bit. But if you are geared fairly high, taller tires might cause the engine to struggle and could actually hurt fuel mileage a little. Your driving style makes a difference too. Too many variables at play for a quick accurate answer.

[mjgord51]

Having stock rims & tires and driving with a raw egg between gas peddle & foot will makes all the difference in MPG, I guess its not Rocket Science, thought there would be more to the question than that much of a little difference.

If any more input please go on, Thanks, Marvin

[swamp rat]

depends on how extreme of a change, a really tall tire will take a heavier throttle to get the truck moving as there is more torque needed, a smaller tire will require less gas pedal and less torque to get the truck moving.

On the other hand once your up to speed a taller tire will drop the engine rpm's and in effect get better mileage unless the tire is so tall it drops the rpm's too much then your pushing that pedal more to compensate.

so if you need better freeway manners a size or two larger diameter will help by raising the mph per a given rpm.

[summitflier]

I don't know about MPG. According to a few tire calculators I've found on the internet
my rear wheels are 1.7 inches taller and rotate 21 times less per mile. With my TH400 that equated from about 2650rpm on the freeway to about 2500rpm. Not really very noticeable.
If anything maybe less than 1/2 mile per gallon increase. Switching to the 700R4 with lockup overdrive dropped me down to about 1900rpm. Also between 5-6mpg increase.

One thing I have noticed, that it seems many people don't think about is how wheel size affects your overall gearing. For example they'll switch from a 3.73 to a 4.11 so they can do burn outs and accelerate better, but then they go from 15 to 22 inch wheels which raises the effective gear ratio back up. I don't this affects gas mileage all that much, but 3 times in the last five years I've seen people with jacked up monster trucks on (approx) 36 inch tires trying to tow things like 30foot RV camping trailers up fairly steep hills broken down beside the road. All 3 trans went out (none were late 60's chevys) but I think the principle still applies.

[Stocker]

Originally Posted by mjgord51

Having stock rims & tires and driving with a raw egg between gas peddle & foot will makes all the difference in MPG, I guess its not Rocket Science, thought there would be more to the question than that much of a little difference.

If any more input please go on, Thanks, Marvin

Well, if you'd like more specific answers (or guesses! ), start by giving us more specific information. Tell us about your truck, its engine & drivetrain, gear ratio (yes, it's important to know this), and your current tire size.

Also what type of driving you usually do -- mostly city, lower speeds with lots of stop & go traffic, secondary highways, flat or mountainous, long freeway trips?

[motorcritter]

Summitflier has a point- I did good business rebuilding transmissions for just such truck owners. The strain created by poor gearing/tire choices ends up in the drivetrain, and the transmission usually gets beat to death. But they look cool, except for that ride on the flatbed to the shop! Matching all the alterations up to equal a reasonable final drive ratio is just mathematic work.
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