quick question if you wanna help =]

[Rockstarenergy]

Right now my tires are bald from burnouts so im looking into new tires , the ones i have on now are 265/70/R15 but i google'd and explorers are supposed to have 225/75/r15 or 235/70/r15 would this be giving me worse gas milage or a worse ride?

 

[zecolleman]

Specification Sidewall Radius Diameter Circumference Revs/km Difference
265/70-15 186mm 376mm 752mm 2362mm 423 0.0%


225/75-15 169mm 359mm 718mm 2257mm 443 -4.5%

the tire that you got on now are 4.5% larger so I would think you get worse milage and a wrong speedometer but not worse ride ..I think

 

[Carguy3J]

Specification Sidewall Radius Diameter Circumference Revs/km Difference
265/70-15 186mm 376mm 752mm 2362mm 423 0.0%


225/75-15 169mm 359mm 718mm 2257mm 443 -4.5%

the tire that you got on now are 4.5% larger so I would think you get worse milage and a wrong speedometer but not worse ride ..I think

Not only is your math off, but you've got the results backwards.

265/70/R15 has a tread width of 265mm. The sidewall height is 70% of that, so:
sidewall height is 185.5mm X 2 sidewalls= 371mm+rim/inside diameter of 15inches
15" x 25.4= 381mm for the rim + 371mm= total diameter of 752mm * 3.1416= 2362.4832mm circumference

225/75/R15: Tread width=225mm*0.75=168.75mm*2=337.5mm
337.5mm+381mm(rim)=718.5mm total diameter*3.1416=2257.2396mm circumference

So: 265/70/R15 has a circumference of 2362.4832mm
225/75/R15 has a circumference of 2257.2396mm

2362.4832 is 104.66249% of 2257.2396.
In other words, the 265/70/R15 tire is 4.66% bigger (in circumference) than the 225/70/R15

The "bigger" tire will have a similar effect as installing slightly taller gears. For example, it would the same as going from 3.73 gears to 3.55 gears. This will sacrifice a bit of bottom end acceleration, for more top end capability, or a lower engine rpm at a given speed. This SHOULD result in an improvement in highway fuel economy.

As for the speedo, assuming the truck/speedo is configured for 225/75/15 tires, and you have the 265/70/15's, then the speedo will indicate a speed 4.66% lower then what you are actually traveling. In other words, when the speedo indicates 70mph, you are actually travelling at 73.26mph. At an indicated 25mph, you are really going 26.165mph This can be corrected easily, on a 2nd gen Explorer, with a tuner, such as an xcal3. Just tell the person writing your tunes about the different tires sizes.

As for handling, there is no question. The 265's have a MUCH larger footprint then the 225's and will drastically improve lateral stability and cornering ability. On the highway, the 225's would make the vehicle feel very "floaty" and just "sloppy", compared to the 265's. Given the much wider contact patch, the 265's will also get much better traction, wet and dry. The only POSSIBLE exception would be deep snow. In deep snow, a narrower tire is better, because it allows the tire to sink, and "cut through" the snow, instead of "floating" on top. But, we are talking a very limited situation here. It really only applies to deep, unplowed snow.

Also, as far as the 2nd gens, I thought they all started at 235/75/R15's, and went up from there. I now the 1st gens had stock 225/70/15s, but those would be awfully small for a 2nd gen. Double check your door sticker. You may even find that those 265's are the stock size. I have a '93 Ranger right know, that came stock with 265/70/15's.

 

[zecolleman]

Not only is your math off, but you've got the results backwards.

265/70/R15 has a tread width of 265mm. The sidewall height is 70% of that, so:
sidewall height is 185.5mm X 2 sidewalls= 371mm+rim/inside diameter of 15inches
15" x 25.4= 381mm for the rim + 371mm= total diameter of 752mm * 3.1416= 2362.4832mm circumference

225/75/R15: Tread width=225mm*0.75=168.75mm*2=337.5mm
337.5mm+381mm(rim)=718.5mm total diameter*3.1416=2257.2396mm circumference

So: 265/70/R15 has a circumference of 2362.4832mm
225/75/R15 has a circumference of 2257.2396mm

2362.4832 is 104.66249% of 2257.2396.
In other words, the 265/70/R15 tire is 4.66% bigger (in circumference) than the 225/70/R15

The "bigger" tire will have a similar effect as installing slightly taller gears. For example, it would the same as going from 3.73 gears to 3.55 gears. This will sacrifice a bit of bottom end acceleration, for more top end capability, or a lower engine rpm at a given speed. This SHOULD result in an improvement in highway fuel economy.

As for the speedo, assuming the truck/speedo is configured for 225/75/15 tires, and you have the 265/70/15's, then the speedo will indicate a speed 4.66% lower then what you are actually traveling. In other words, when the speedo indicates 70mph, you are actually travelling at 73.26mph. At an indicated 25mph, you are really going 26.165mph This can be corrected easily, on a 2nd gen Explorer, with a tuner, such as an xcal3. Just tell the person writing your tunes about the different tires sizes.

As for handling, there is no question. The 265's have a MUCH larger footprint then the 225's and will drastically improve lateral stability and cornering ability. On the highway, the 225's would make the vehicle feel very "floaty" and just "sloppy", compared to the 265's. Given the much wider contact patch, the 265's will also get much better traction, wet and dry. The only POSSIBLE exception would be deep snow. In deep snow, a narrower tire is better, because it allows the tire to sink, and "cut through" the snow, instead of "floating" on top. But, we are talking a very limited situation here. It really only applies to deep, unplowed snow.

Also, as far as the 2nd gens, I thought they all started at 235/75/R15's, and went up from there. I now the 1st gens had stock 225/70/15s, but those would be awfully small for a 2nd gen. Double check your door sticker. You may even find that those 265's are the stock size. I have a '93 Ranger right know, that came stock with 265/70/15's.

The tire that you got on now are 4.5% LARGER that what I said. If you improve your milage with larger tires were are the limit? if you put larger then 265/70-15 put on 35" tires.

 

[weh87]

i would keep the larger tires. it handles much better with those than the smaller ones.

 

[KPSquared]

If you're tires are bald from doing burnouts, why are you asking mileage questions? If you bag your truck, your mileage is gonna suck either way...

 

[OneLever]

If you're tires are bald from doing burnouts, why are you asking mileage questions?

Now there you go using that logic stuff on us...

 

[Carguy3J]

The tire that you got on now are 4.5% LARGER that what I said. If you improve your milage with larger tires were are the limit? if you put larger then 265/70-15 put on 35" tires.

It's really a pretty complicated answer, with no real clear definite answer. That's why I included the phrase "all else being equal".

Of course, it's very easy for alot of things to not be equal.

Weight is a big factor. You have to "weigh" the increased weight of the larger tire, vs. the gearing advantage of it. Again, as all makes/models of tire are different, I couldn't give you an exact "break point" of when a larger tire loses it'as possible mileage advantage. However, it is safe to say a 35" tire is only going to cause you to lose mpg. Why?

Well, there are a number of other factors to consider:
Tread pattern, tread compound and tire construction methods and materials, all of which affect rolling resistance, as well as handling. There a very few, if any 35" tires that have anything approaching a reasonable, all-season tread pattern. They are nearly all "lug" type tires with relatively soft compounds, and very heavy duty construction. These factors all combine to create a very high rolling resistance, and a heavy tire. Additionally, most tires that large are bias ply construction, which only further hurts fuel economy. Additionally, using 35" tires requires a number of other vehicle mods, to use that size tire safely, that further impact fuel economy. One of the most important complimentary upgrades to go with tires that large are bigger brakes. Bigger brakes weigh more, and to make it worse, they constitute rotating weight, which takes even more energy to accelerate to speed then "static" weight.

As far as handling, again, whatever a 35" tire might gain from increased tread width, is more then lost in increased sidewall flex, and from the typical tread pattern. A lug-type tread pattern is noisy, and has very poor traction on pavement (especially wet, but even on dry); particularly when compared to an equivalent contact patch size of a less "aggressive" tread pattern. Remember, all that empty space between the lugs is just that "empty space". As in, there is no rubber there connecting the vehicle to the road surface.

Again, it's a complicated question with many factors to consider, when comparing different tires. However, within reason, when comparing otherwise identical tires, a larger (greater circumference) tire will tend to have greater highway fuel economy. Of course, if you spend most of your time driving in the city, in frequent stop and go, that "taller" effective gearing may be a bad thing and hurt economy, as the engine now has to work harder to get you moving.

As for your math, no it wasn't a HUGE error, but an error nonetheless. You rounded 185.5 to 186,etc... and then used those rounded figures for further computations, thereby compounding the error with each calculation. 4.5% is not the same as 4.66%. We are talking about mm here, so small numbers matter.

 

[Carguy3J]

If you're tires are bald from doing burnouts, why are you asking mileage questions? If you bag your truck, your mileage is gonna suck either way...

Not to mention, his transfer case will be toast pretty soon. .....assuming he has one. I'm not sure if he ever managed to find it.
http://www.explorerforum.com/forums/search.php?searchid=4925818

Now there you go using that logic stuff on us...

Based on the Op's other posts, he isn't really a fan of logic anyway. I'm guessing he'll either ignore, or not understand the answers posted here, and continue to ask the question over and over, maybe even starting another thread or two. But... It seemed like an easy enough answer so I gave it a shot. We'll see what happens.

 

[IZwack]

You know that you guys dont have to look at the circumference. The circumference is derived by a constant multiplier (pi). So If you are comparing two things, the ratio will always cancel them out once you get to the division. In addition, by multiplying by pi, you've introduced a slight error since pi is not finitely defined - not that it matters too much in this application, but a shorter equation with less elements is easier to understand. So you dont need to look so much at the circumference, but just the radius/diameter - the resulting percentage will be the same.

 

[zecolleman]

It's really a pretty complicated answer, with no real clear definite answer. That's why I included the phrase "all else being equal".

Of course, it's very easy for alot of things to not be equal.

Weight is a big factor. You have to "weigh" the increased weight of the larger tire, vs. the gearing advantage of it. Again, as all makes/models of tire are different, I couldn't give you an exact "break point" of when a larger tire loses it'as possible mileage advantage. However, it is safe to say a 35" tire is only going to cause you to lose mpg. Why?

Well, there are a number of other factors to consider:
Tread pattern, tread compound and tire construction methods and materials, all of which affect rolling resistance, as well as handling. There a very few, if any 35" tires that have anything approaching a reasonable, all-season tread pattern. They are nearly all "lug" type tires with relatively soft compounds, and very heavy duty construction. These factors all combine to create a very high rolling resistance, and a heavy tire. Additionally, most tires that large are bias ply construction, which only further hurts fuel economy. Additionally, using 35" tires requires a number of other vehicle mods, to use that size tire safely, that further impact fuel economy. One of the most important complimentary upgrades to go with tires that large are bigger brakes. Bigger brakes weigh more, and to make it worse, they constitute rotating weight, which takes even more energy to accelerate to speed then "static" weight.

As far as handling, again, whatever a 35" tire might gain from increased tread width, is more then lost in increased sidewall flex, and from the typical tread pattern. A lug-type tread pattern is noisy, and has very poor traction on pavement (especially wet, but even on dry); particularly when compared to an equivalent contact patch size of a less "aggressive" tread pattern. Remember, all that empty space between the lugs is just that "empty space". As in, there is no rubber there connecting the vehicle to the road surface.

Again, it's a complicated question with many factors to consider, when comparing different tires. However, within reason, when comparing otherwise identical tires, a larger (greater circumference) tire will tend to have greater highway fuel economy. Of course, if you spend most of your time driving in the city, in frequent stop and go, that "taller" effective gearing may be a bad thing and hurt economy, as the engine now has to work harder to get you moving.

As for your math, no it wasn't a HUGE error, but an error nonetheless. You rounded 185.5 to 186,etc... and then used those rounded figures for further computations, thereby compounding the error with each calculation. 4.5% is not the same as 4.66%. We are talking about mm here, so small numbers matter.

Ok I just used tire calculator on the web. and I am not so good writing english so my answer might have been better. but that was very good answer you gave. and that is what this site is al about.

 

[Carguy3J]

You know that you guys dont have to look at the circumference. The circumference is derived by a constant multiplier (pi). So If you are comparing two things, the ratio will always cancel them out once you get to the division. In addition, by multiplying by pi, you've introduced a slight error since pi is not finitely defined - not that it matters too much in this application, but a shorter equation with less elements is easier to understand. So you dont need to look so much at the circumference, but just the radius/diameter - the resulting percentage will be the same.

You're kind of right, if we're just talking about hypothetical numbers, then yes, just looking at the radius would be sufficient, and eliminate the minute error introduced by truncating pi to only 2 decimals points. In fact, tires of the same "theoretical"/advertised radius can in fact have different rolling circumferences,due to design/manufacturing differences/tread pattern/etc.. Of course, wear will also affect rolling circumference, reducing it as the tread depth is reduced. Bias ply tires will tend to have a greater variation between tires, and between advertised measurements and actual; compared to radial tires. This is why you need to look at the "revs-per-mile" when comparing tires. Go to tirerack.com, and look at the detailed specs of several different brands/models of the "same size" tires, you'll see a difference in some of the revs-per-mile. Sometimes, it is a significant difference. Enough to throw off the speedo , the ABS, or damage the drivetrain, if you mixed them on the vehicle.
I recall, from my dirt stock car racing, that brand new tires off the tire truck, with the same advertised size, could vary as much as 4" in the rolling circumference, when mounted and aired up. When the rules mandate using 1 size, this is the only way to get stagger; by sorting through a bunch of new tires and measuring until you find the ones you want. Of course these were bias ply tires, intended for racing, but it illustrates the point.

 

[IZwack]

You're kind of right, if we're just talking about hypothetical numbers, then yes, just looking at the radius would be sufficient

Which is what we're doing here - which is why we're talking about the numbers on the sidewall. If we werent talking about hypothetical numbers, then we'd be talking about empirical numbers and would be using a ruler or tape measure instead of reading the label.

 

[OneLever]

Go to tirerack.com, and look at the detailed specs of several different brands/models

Thanks for the reference. Is that the best online source for specs in your opinion? Looks like Michelin has a mail in rebate special going on till November 15th. Too bad I don't need new tires right now.

 

[Rockstarenergy]

thanks everyone for the answers except the guy that said something about bagging my truck and the guy who said i cant find my trasfer case lol