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245 to 265 gas mileage ?

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Wingnut Senior Enthusiast

Wingnut

Posted
Posted

245/265...Those numbers are referring the width of the tire.

 

You would have to post the entire tire (say that three times fast) size to be sure, as the second number is the height/width ratio.

 

But if you are talking about going to a taller tire, it will hurt your torque, therefore your towing.

 

You mileage may be slightly better on long haul, but the motor would lug at lower RPMs. This would negatively affect gas mileage in town, and when towing. Basically, it's raising your final drive ratio...Just like putting taller gears in would do.

 

Nothing too bad, because you aren't talking about a HUGE change, but you will be able to notice the difference.

 

This can be remedied by changing out the gears (optimal, but expensive)...Or by getting your PCM re-tuned, which is a lot cheaper, but not quite as effective.

 

Keep in mind that your speedometer/odometer will be off a bit as well.

 

 

Welcome to the forums, by the way :wtf:

chadlyt Enthusiast

chadlyt

Posted
Posted
my BAD  245/75/16    Thanks

 

 

 

 

 

I went from 245 75 r16 to 265 75 r 16. the taller the tire, the less low end you have. If you have the 4.10 rear end , it will not really be 4.10 after you go to 265. You wont gain anything other than a fuller wheel well and about and half andinch to and inch in ride height.

97K2500 Enthusiast

97K2500

Posted
Posted

While we are on this topic (and some knowledge is speaking) I want to switch tires and wheels.

Stock is LT 245/75 R 16.

The new wheels I want are 17". The only tires in the load range "E" that I can find are LT 265/75 R 17 and 265/70 R 17. I don't want to switch to a taller tire, so would the 265/70 R 17 suit me better? Or is it a taller tire?

 

Thanks,

Ben

 

Oh, and how much mileage would I lose going to the wider tires?

Shawn T Enthusiast

Shawn T

Posted
Posted
While we are on this topic (and some knowledge is speaking) I want to switch tires and wheels.

Stock is LT 245/75 R 16.

The new wheels I want are 17". The only tires in the load range "E" that I can find are LT 265/75 R 17 and 265/70 R 17. I don't want to switch to a taller tire, so would the 265/70 R 17 suit me better? Or is it a taller tire?

 

Thanks,

Ben

 

Oh, and how much mileage would I lose going to the wider tires?

 

 

 

 

 

Here is a little formula to convert from metric size to english:

 

The first number is your width, the second number is the % of the width measured from the edge of the rim to the outside perimeter(tire radius-wheel radius) of the tire. Example:

 

1. convert from mm to cm 265/10=26.5

2. convert from cm to inches 26.5/(2.54)=10.43 This number is you width.

3. multiply the percentage by the width: 10.43*.70=7.30

4. multiply that result by 2(converts radius to diameter): 7.30*2=14.6

5. add the diameter of the wheel to this number: 14.6+17=31.6

 

So, if you are running 265/70 R17, your approximate tire size in inches is:

31.6 X 10.43. Use this formula for 245/75 R16's and your tire size is:30.47 X 9.65

 

You are gaining about 1 inch in heighth and about 7/8 in width. Hope this helps.

97K2500 Enthusiast

97K2500

Posted
Posted

Holy crap, that is very useful! :wtf: Tab's on me! Nice truck, too #9.

That will help quite a bit in my search for the perfect tire/wheel combo.

Btw, I am looking at the Cragar Black Soft wheels (pc'd black steel) with A/T tires that carry the E load range, so it is kinda hard to find the appropriate sizes. It seems as if there are zero 245/75R17's out there. Oh well, the search continues.

Edit: Actually, I overlooked something. The tires I just mentioned un 32.65" tall according to your excel file. The stockers are 31.65". I didn't take into consideration the proportional ratio of wheel diameter to tire diameter. An additional inch of diameter (about 3.14" greater in circumference) shouldn't make that big of a difference, should it?----Just found a way to figure this out.

 

This should work:

(New Tire Diameter / Original Tire Diameter) X Indicated Speed = Actual Speed with new tires

 

Example:

(32.5" / 27") X 55MPH = 66.2 MPH Actual Speed with new tires

 

My change from a 31.65" to a 32.65" tire increases the speed from 55mph to 56.737mph. I can probably live with a difference as little as 2mph. I can just factor that into my usual speeding habits.

 

 

Thanks,

Ben

mhraracing Enthusiast

mhraracing

Posted
Posted
I f I put 265 on will my mileage go up or down?

04 2500HD with a 6.0  truck is a stock

Will it help me with pulling my race car?

 

 

 

 

1Bad - I have the 265's on my truck and didnt notice much of a gas change - if any at all. As for pulling yuor race car - if you have 4.10's - you will barely notice the difference. My truck revs about 200 rpms lower at 75 now.

Remember - if you change your size - you will need to reprogram your speedo - so it reads correctly (if you want) - This is a perfect time to convince yourself to get a Westers tune....not only will you fix your speedo - but you will get more HP/TQ and gas milage to boot !!!!

 

Sorry for the plug !!! I love my Westers !!!

SilverCrew Enthusiast

SilverCrew

Posted
Posted
I f I put 265 on will my mileage go up or down?

04 2500HD with a 6.0  truck is a stock

Will it help me with pulling my race car?

 

 

 

 

1Bad - I have the 265's on my truck and didnt notice much of a gas change - if any at all. As for pulling yuor race car - if you have 4.10's - you will barely notice the difference. My truck revs about 200 rpms lower at 75 now.

Remember - if you change your size - you will need to reprogram your speedo - so it reads correctly (if you want) - This is a perfect time to convince yourself to get a Westers tune....not only will you fix your speedo - but you will get more HP/TQ and gas milage to boot !!!!

 

Sorry for the plug !!! I love my Westers !!!

 

 

 

 

 

Yup yup....I agree.

 

I went from 265/75/r16 to 315/70/r17's and it definitely impacted gas mileage and low end torque/speed. My new PCM is on the way (mainly for the speedo calibration) but hey, while you're doing it you may as well get some extra ponies too right?

 

Anywho...I'm headed to the outerbanks this weekend so I'm hoping to have my new PCM in by then so I can see how it does.

2004GMC2500HD Enthusiast

2004GMC2500HD

Posted
Posted

If you are worried about gas mileage, buy a car. My 8.1 / Allison sucks gas like no other, but its a big engine in a truck. I have 285/70/17's on it and didn't notice a difference probably because it was so bad to begin with. Oh well. I average about 9.5 normally and around 5 pulling my 12,300 pound boat. Thats why you always take customers (and/or your friends) out on the boat so the gas bill goes to your business and comes right off your corporate taxes!!

 

Good luck with the tires. Bigger tires will make it look much better. :cheers:

Beaux Duke Enthusiast

Beaux Duke

Posted
Posted

Getting a little info from the Tire Rack on tire diameters we can assume the following.

 

According to Tirerack.com the BF Goodrick Radial Long Trail 245 has a diameter of 30.5 inches and the 285 has a diameter of 32.8 or a 7.5% increase in diameter. That means your "effective" rear gear ratio has been decreased by 7.5% and is now the equivalent of 3.79 approximately. That would net you an increase in fuel efficency.

 

However your odometer and speedometer are now also off by 7.5%. Each revolution of your larger tire now carries you 7.5% further but your speedometer and odometer are registering less by 7.5% When you attempt to calculate your mpg after driving 100 miles per your odometer your will actually have driven 107.5 miles.

 

For simplicity's sake lets say you used exactly 10 gallons and using the mileage as indicated by the odometer you will calculate your mpg at 10. In reality your mpg is 10.75 because you really drove 107.5 miles instead of 100 on the 10 gallons of fuel.

 

Nothing to it.

 

Get your speedometer re-calibrated after you get new tires and calculating your mpg will once again be simple.

 

Just noticed we were supposed to be talking about 245's versus 265's not 285's. The difference between those two sizes is only about 1.6% so if you want to see the difference just replace 7.5% with 1.6%. Sorry for the confusion!

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