How much of an increase might be expected by increasing the tire size?
I'm looking at something to fit on PYOs - maybe 255 or 265/75 R16, maybe H2s if I can find a cheap set with tires.


Tire suggestions also taken.
I will be towing ~8000+ lb travel trailer often. I do a little 2 tracking, but don't drive the truck in the snow if possible. I also like tires that last and are quiet on the freeway.

Thanks :)

daurand-

i've been waiting to hear what someone smart might have to say to this thread. not sure why they haven't spoken up yet.

i'm not going to have any real insight, but i would say from experience that you should not consider going bigger than 265's. for a couple reasons... the first being that you tow a good size load (long too). i have the h2 takeoffs, and sometimes the truck needs encouragement to take the shot from 4th to 5th.

more importantly... any bigger than 265, you will need to start messing with t-bars, cutting air dam, tying back fender liners, etc. then... the side effects.... rough over potholes or bumps, leaking cv joints, and torn up fender liners. as you can tell, i kind of wish i stuck to stock geometry on the front end. the h2's hum pretty loud on the highway too. but they look friggin great! but... you already have pyo's... those are really nice. don't put anything bigger than 285 (? i think ? smart people chime in here), as the pyo rim is only rated up to a certain size because of rim width.

as far as mileage... i think the argument above is worth a lot more than going up or down a couple mpg's. i have heard of improvements of a couple highway mpg's going to 265's when empty. but... mpg's really count when towing... and i got crushed by having 315/70/17 while towing 9k#. if the argument were purely mpg... to me... 265's seem like a good comprimise between towing, not towing, city, and highway.

good luck.

The more meat on the road the more friction created

Friction=resistance, means lower MPG's

I run 315s and dropped about 3MPG....

My experience has been that the city mileage will decrease as it take more gusto get them spinning. Highway mileage may increase as it will take less RPM to run the same speed as with the smaller tires, but for the most part bigger tires = less MPG.

Bill

with a large tune or stack i have seen better mileage with 285, over stock on hiway pulling or not, the 400lower rpm at higher speeds makes the mileage better, on a stock hp tune smaller tires are better

I have 285's and have seen a good 2mpg drop from the stock 245's. This is mostly city driving and short trips though not too much highway driving mixed in.

I am still running the factory pizza cutters on my '05 -:t . I can say that i picked up 1-1.5 mpg ini my old '02 by gooing to 265's. As soon as In can see the air in my current 245's I will be going to 265's on the '05.

I too have been looking into the 255/85/16 , same resistance as 265 , same height as 285 , and ok for rim size . Currantly have 265's , last summer towed camper ('76 25' airstream , 5000# ) 2600 miles , aver 14 mpg . From what I've read it seems like taller and wider kill milage + speed of course . Will need rubber by end of summer so still reading. Have tried the H2 route , too many minuses ..

I'm with Redapple, I switched to 265's a few months ago and lost a solid 1.5 mpg. I think it is mostly due to the stop and go part of my driving. After some time in town it takes alot of hiway driving to get the average back up. With 245's I was usually around 17.5 now it is rare to average 16mpg.(2004 LLY)

I'm with Redapple, I switched to 265's a few months ago and lost a solid 1.5 mpg. I think it is mostly due to the stop and go part of my driving. After some time in town it takes alot of hiway driving to get the average back up. With 245's I was usually around 17.5 now it is rare to average 16mpg.(2004 LLY)

I lost about 3mpg when I switched to 265's

The factory size is usually optimized for best performance and fuel economy for what its worth

The more meat on the road the more friction created

Friction=resistance, means lower MPG's

I run 315s and dropped about 3MPG....

Unfortunately, that is not correct. The amount/coefficient of friction does not change with larger, wider...tires. There are many other factors that do however. Wind resistance, unsprung weight, and effectively lowered gear ratio. You could run your kids bicycle tires, theoretically, and you would not "decrease" the amount of friction. Your engine now has to overcome all these things. In stop and go driving, the engine mainly is fighting the inertia of the extra mass of the tires and lowered gear ratio due to larger diameter. Normally, this does not affect diesels as much as gassers due to our tq numbers. I moved up to 265 and gained mpg and will be going to 315's soon. IMHO, driving habits are what lower mpg not a small increase in tire diameter. Stock to 265 is not a significant jump.

My .02 ran out.

I moved up to 265 and gained mpg and will be going to 315's soon. IMHO, driving habits are what lower mpg not a small increase in tire diameter. Stock to 265 is not a significant jump.

My .02 ran out.

I am glad it worked out for you. Still, most of us lose mileage, and my "meager" 265 swap DID LOSE mileage. I was quite pissed for the first month. ;)

I am glad it worked out for you. Still, most of us lose mileage, and my "meager" 265 swap DID LOSE mileage. I was quite pissed for the first month. ;)

Maybe it's cause I have a manual too. Yeah, I would be pretty upset too. However, I do expect a slight decrease when I move to 315's, but who knows, maybe I'll be surprised.:o:

Dan

I lost mpg's not sure exactly how much. I try not to pay attention to that
(kind of dissapointing) I think wider and taller =less MPG's.

I,m currently running 285's and have lost considerable mileage around town. My mechanic told me recently that he had attended a GM training class and the instructor told him that they have seen an increase in transmission failures due to large tires. I would like some feedback from others on this potential problem.
My main problem is a speedometer that reads 6-7% low that I have not been able to reset at a reasonable cost. I bought a Super Chips tuner, but it has no capability to adjust for tire size.

I,m currently running 285's and have lost considerable mileage around town. My mechanic told me recently that he had attended a GM training class and the instructor told him that they have seen an increase in transmission failures due to large tires. I would like some feedback from others on this potential problem.
My main problem is a speedometer that reads 6-7% low that I have not been able to reset at a reasonable cost. I bought a Super Chips tuner, but it has no capability to adjust for tire size.I would be they think it is tires, but it's tuners that are causing the increased failures. Most guys with tuners have upsized tires too. Most guys satisified with the original sized tires are more likely to leave the truck stock.

Predator will reset for tire size

Unfortunately, that is not correct. The amount/coefficient of friction does not change with larger, wider...tires. There are many other factors that do however. Wind resistance, unsprung weight, and effectively lowered gear ratio. You could run your kids bicycle tires, theoretically, and you would not "decrease" the amount of friction. Your engine now has to overcome all these things. In stop and go driving, the engine mainly is fighting the inertia of the extra mass of the tires and lowered gear ratio due to larger diameter. Normally, this does not affect diesels as much as gassers due to our tq numbers. I moved up to 265 and gained mpg and will be going to 315's soon. IMHO, driving habits are what lower mpg not a small increase in tire diameter. Stock to 265 is not a significant jump.

My .02 ran out.

I stand corrected.... ;)

I put 265's on stock rims and it hasn't affected my milage (highway) one Ioda (FWIW).

I put 265's on stock rims and it hasn't affected my milage (highway) one Ioda (FWIW).

You be a lucky a SOB or fibbing. ;)

You be a lucky a SOB or fibbing. ;)

I have to agree with SIDEBITE252 - Check some of my previous posts on the subject. When I went from the stockers to 265's there was little or no change - no reduction in MPH and little if no gains either.

Our sigs are a little different than yours though - therein may lie the difference.

like most problems, this change is not due to just one variable. If you are not starting and stopping a lot (the starting requires more power/fuel) but are running at an efficient rpm and gear (mine is a 6 spd) with a bigger tire you will get slightly higher mpg. if you are driving around town, mostly, it will lower your mpg. I don't do much towing but I would expect that the impacts would be more.

keep in mind dic and odometer will be off with larger tires

i lost 2 - 3 mpg with the 315s, that is after i gained 1+ mpg with a pre OEM filter and the juice. on the highway though, i typically run at 80+ so not sure how much it would be at 70 or below, more important to get there than save a tiny bit of fuel.

towing my 5er with 315s, I notice a bit of lag on the 4 to 5 shift but the juice takes care of it most times unless on steep grades. my cruise speed on the highway is raised at the 1800 rpm range, which is nice for towing.

if 285s were cheaper than H2 takeoffs (315s) I would run those.

I would guess I'm just lucky there cdhd2001 - I have no motivation to lie (LOL) - after all, a 265 is not that much larger than the 245 that I replaced and I didn't increase the width of the tire so........Sure, it's put the speedo off just a bit but with correction calculated for the size difference and calculate fuel used vs. milage I'm still getting about 19 mpg on highway use. I do see the theory that you guys are shooting at. Seems logical.

i have tons of data on fuel mileage while towing with 315 h2's. 10 tanks of fuel empty and 10 tanks full.

i'm going to do the same trip with 265's next month. i'll be able to share some observations between 315's and 265's.

any guesses? btw... i'm guessing that by switching the tires before a 4,000 mile towing trip, i'll save about $250 in fuel. nice chunk of change applied to the tires.

Tire 315 265
Miles 4,000 4,000
MPG 10 13
Gallagons 400 308
Price $2.75 $2.75
Cost $1,100 $846
Savings $254

Tire 315 265
Miles 4,000 4,000
MPG 10 13
Gallagons 400 308
Price $2.75 $2.75
Cost $1,100 $846
Savings $254


I can see that as being accurate. Big jump from 265's to 315's.

the 245 to 265 jump is minimal.

with some stretches into the wind (15-20mph winds), towing a very tall and very wide trailer loaded at 9k pounds, going 75 mph with boost reading 19-21, i was getting mpg in the 7's! empty with zero wind was 10 mpg, and empty while driving 40 mph through yellowstone, it was 12 mpg. with edge set at 2, power was NEVER a problem. but i suppose i'll really be able to charge the hills with 265's.

i'm hoping for 3 mpg accross the board improvement while towing.

with 315's... empty, no trailer on the highway, i was 17-18 mpg, so it was only towing > 70 mph that caused problems.

I would guess I'm just lucky there cdhd2001 - I have no motivation to lie (LOL) - after all, a 265 is not that much larger than the 245 that I replaced and I didn't increase the width of the tire so........Sure, it's put the speedo off just a bit but with correction calculated for the size difference and calculate fuel used vs. milage I'm still getting about 19 mpg on highway use. I do see the theory that you guys are shooting at. Seems logical.

Lie is a harsh word.
:eek:

Fib however goes with exagerate.

Anyway, I said either you were fibbing or lucky, and it seems that compared to my results you are lucky.

P.S. Adding +1,500 lbs. hurt my mileage less (only 0.5 mpg) than the 245>265 swap. Anyway, I NEED the extra 800 lbs of capacity.

Also, I drive about 75% city and 25% highway, so I see a lot of start and stop driving. However, my best mileage to date with the 265's is 18 mpg, and my best with 245's was 22 mpg.

and my best with 245's was 22 mpg.

not trying to start anything... just an observation... :o:

while you think it required either luck or exageration (sp?) for someone to experience no mpg change from 245 -> 265, there are a lot of people on this forum that would say it requires more than luck or exageration in order to get to 22 mpg....

my only point being that of all the reading i've done on this forum, i think 22 mpg on 245's is more surprising than no change from 245 to 265. actually.... with the motley crew that hangs out at dp.... i've learned that anything is possible! ):h

cheers...

not trying to start anything... just an observation... :o:

while you think it required either luck or exageration (sp?) for someone to experience no mpg change from 245 -> 265, there are a lot of people on this forum that would say it requires more than luck or exageration in order to get to 22 mpg....

my only point being that of all the reading i've done on this forum, i think 22 mpg on 245's is more surprising than no change from 245 to 265. actually.... with the motley crew that hangs out at dp.... i've learned that anything is possible! ):h

cheers...

Interstate (NM, AZ, TX) at 65 mpg solo 22 mpg was pretty regular. Non Interstate highway driving would yield 20 mpg easily.

With 265's on Interstate (same conditions) best has been 18 mpg. Non Interstate highway driving is a best of 16.5 to 17.0 mpg.

Mixed driving went from 17 to 15 mpg.

P.S. My reason for replying. I originally went to 265's because of members stating that their mileage increased (last year). I was extremely frustrated and let down when I lost 2-3 mpg from switching tires. The percentage difference between my 245's and 265's is 3.8%. I am fudging my numbers with 4% and still show the loss.

Others should understand that not everyone will gain mileage. Kind of like the thread where the guy got better mileage running in J/A level 3 and boost 1. Tried it and lost 4 mpg compared the J/A level 2 boost 5 setting.

65 mph helps, that's for certain!

you have a cool flat bed set up. do you have any pics of your exhaust smoking? (that is a stack isn't it? - pic is small). the video of the 10.77 ctd was cool because the exhaust is farting straight up during spool, then when it spews out the back of a speeding truck, i think it looks like a cat that puts his ears back.

65 mph helps, that's for certain!

you have a cool flat bed set up. do you have any pics of your exhaust smoking? (that is a stack isn't it? - pic is small). the video of the 10.77 ctd was cool because the exhaust is farting straight up during spool, then when it spews out the back of a speeding truck, i think it looks like a cat that puts his ears back.

The stacks are photo shopped at the moment. I just had too see what it would look like. :ro) Funny thing, wife likes the look. :eek: I currently finishing paint and running light setup on bed. Next will be the stacks (two 5" tip outs). Hopefully before summer ends.

Ok - Fib - by god that's funny, I don't care who you are:lol:

Nice truck cd

I wonder if the tread design has anything to do with mileage? The General AT's I have look just like BFG AT KO's and whine on the highway. Maybe more of a "road tire" tread helps?

Just curious.

I wonder if the tread design has anything to do with mileage? The General AT's I have look just like BFG AT KO's and whine on the highway. Maybe more of a "road tire" tread helps?

Just curious.

well, i think so... and i just placed my bets. i just ordered about the most boring looking tire you can imagine, but i did it because they are quiet and long lasting (which i'm thinking means better mileage). i could have ordered the bfg rugged trail's in the size i need, which would have looked light years better, but i really need to put function first right now, and i'll spend most my time on the interstate.

Tread design may have some influence but I put on Michelin LTX m/s 265's and they have what I would consider a road design tread. I lost 1.5 to 2mpg compared to stock 245's. Maybe it would have been worse with a more aggressive tread design.

i couldnt get 22 mpg driving at 55 with a tail wind, windows rolled up on summer fuel if I had to. 18+ all day.

Just my .02 but I don't think anybody has mentioned tire weight yet. I just recently went from a 315-70-17 to a 35-12.5-20. I went up in size only 1/2 an inch but went from a D rated tire to E rated tire and believe me they weighed a ton more. Speaking from just my experience the taller and wider the tire the lower the gas mileage. It's based on alot of factors ie, more rotational mass, more tire weight, more wind resistance to do increased frontal surface area, higher gear ratio for starting, and several other factors I can't think of.

BTW, when stock I couldn't get 22 mpg if you dropped the truck out of plane.

Rich.

I would think the increased rolling resistance of the bigger, wider, heavier tyre would be a big factor in the lower MPG as well. The engine will be working harder to accellorate to a given speed, then also working harder to maintain a given speed. All-round (no pun intended), it should mean worse fuel mileage.

Just my .02 but I don't think anybody has mentioned tire weight yet. ...... more rotational mass, more tire weight.....

bingo.... i think that is a very big part of it. i'm kind of a cycling nut, and the absolute worst possible spot to have any incremental weight is on the wheel, and it just gets exponentially worse as you move out toward the edge of the tire (more plys). the further out it goes, and the more weight there is... the tougher acceleration is. i just don't have a clue if that relative variable is as big for a diesel truck as it is for a pair of legs. i put the word relative in italics because i was afraid someone would compare our trucks vs a pair of legs on an absolute basis.

how many rpms will my truck drop if I went with 265's cruising at 70. Right now I'm at 2,000 or a hair over.

Unfortunately, that is not correct. The amount/coefficient of friction does not change with larger, wider...tires. There are many other factors that do however. Wind resistance, unsprung weight, and effectively lowered gear ratio. You could run your kids bicycle tires, theoretically, and you would not "decrease" the amount of friction. Your engine now has to overcome all these things. In stop and go driving, the engine mainly is fighting the inertia of the extra mass of the tires and lowered gear ratio due to larger diameter. Normally, this does not affect diesels as much as gassers due to our tq numbers. I moved up to 265 and gained mpg and will be going to 315's soon. IMHO, driving habits are what lower mpg not a small increase in tire diameter. Stock to 265 is not a significant jump.

My .02 ran out.
What kind of wisdom is that? The friction INCREASES when the contact surface of the tire on the road increases. Wider tire = more contact surface on the road = more friction. THATS THE REASON WHY VERY VERY FAST CARS LIKE FORMULA ONE ARE USING VERY WIDE TIRES TO CREATE A MUCH HIGHER FRICTION SO THAT THEY ARE NOT FLYING OFF THE ROAD DRIVING THAT FAST!

Try to slide a standing quarter over a table. Than lay the quarter flat on the table and slide it again - bet the standing quarter slides easier........
:lol:

Actually dkubek was correct. The size of the tire has nothing to do with friction. Friction is proportional to the normal force applied. Therefore, if larger tires were added and were heavier, they would in fact add more friction; however, if the weight remains the same the friction would not increase. As for the reason race car tires are wider, the wider tire actually provides a better probability that the tire will contact the road when considering the fact that the asphalt is not smooth. If the surface were perfectly smooth, a skinny tire would hook just as well as a wide tire provided the tires were made from the same composition.Larger tires do however cause more wind resistance and also add more mass further out from the center of the wheel. By adding more mass further from the center of the wheel, the inertia is increased dramatically. Inertia for a round object can be defined by Inertia = mass * radius^2.I had to jump in on this one, being a mechanical engineer, I had already questioned these theories on many occassions.

Went from 245's to 265's, mileage dropped 1-2mpg. Borrowed a GPS, tracked mileage and speed, turns out the speedo/odo must have been overreading with the stock 245 tires, it's correct for 265's w/o any speedo/odo adjustment (for my truck). I also went from highway tread 245's to AT tread 265's FWIW.

Tim

when i had 265's (highway tread) the speedo & odo were right on the nuts.

when i had 265's (highway tread) the speedo & odo were right on the nuts.

How did you come to that conclusion?

...anyone concluding lower milegage off the DIC, any tire diameter increase is going to reflect in lower mpg off the DIC. There is a lot of bad information in this thread.

I have 315's (H2) and my hiway mileage is almost exactly as it was with the stockers. Hand calculated under similar conditions, it is about 1 mpg lower in-town. The single best thing you can do is inflate tires to rated pressure, if you don't mind the crappy ride. For me, in H2's, I run 28/40 psi (32/45 on long hiway trips) empty.

How did you come to that conclusion?

100 miles on the road markers was within a quarter mile on the odometer.

i used the same method on my h2 setup. 100 miles on the road was 89 miles on the odometer.

as a rule of thumb, i think stock tire setups err a bit on the conservative side so that consumers think they are going a couple mph than they actually are. of course, that's just my own rule of thumb, and in this case, 265's fit right in.

100 miles on the road markers was within a quarter mile on the odometer.

i used the same method on my h2 setup. 100 miles on the road was 89 miles on the odometer.

as a rule of thumb, i think stock tire setups err a bit on the conservative side so that consumers think they are going a couple mph than they actually are. of course, that's just my own rule of thumb, and in this case, 265's fit right in.


Okay.

To counter Killer, my calcs are all done by hand (and calculator) in my mileage book which contains every fuel up since I bought the truck. Plus, I always write down what the DIC says for gallons and mileage, just to see how far off it is. Running 265's and J/A lvl 2 the DIC averages about 1.5 mpg higher than the hand calcs.

I'm running some off-brand 265's , came with the truck.They run small 30" dia. , half way between 245 and 265 . When i have checked odometer against road markers it comes very close , usually 40 or 50 mile runs . What throws off the DIC for me is the gals used . The DIC always reads 1 to 2 gals less than actual . Has anyone figured out if the sending unit or sensor can be recalibrated , are most of yours acurate or not

i don't have a DIC

What kind of wisdom is that? The friction INCREASES when the contact surface of the tire on the road increases. Wider tire = more contact surface on the road = more friction. THATS THE REASON WHY VERY VERY FAST CARS LIKE FORMULA ONE ARE USING VERY WIDE TIRES TO CREATE A MUCH HIGHER FRICTION SO THAT THEY ARE NOT FLYING OFF THE ROAD DRIVING THAT FAST!




wider tires (low profile) do NOT necessarily have a larger contact patch. Contact patch is mostly determined by tire PRESSURE, nothing else. (neglectiing sidewalls stiffness) Can't violate the basic laws of physics. Example if you have 2000 lbs on a tire and the pressure is 50lbs/sq in. the contact area will be 40 sq inches independent of tire profile. (wider etc). (Again this negelects sidewall stiffness which first order doesn't have much affect.) Drop the pressure to 25lbs/sq in and the contact area will double. It is a very linear relationship as long as you are within the recomended inflation recomendations and don't run such low inflation that sidewall stiffness comes into play.

I remember a Road and Track article years ago comparing all kinds of tires narrow and wide on one vehicle. The tire contact patch area didn't vary more than a few % from the narrowest to widest. There was a big difference in traction, especially cornering but it wasn't due to the contact patch area being different.

So why do race cars have wide tires? it has to do with contact patch shape and other dynamics of adhesion. wide tires have a wide narrow patch and with a short sidewall have less rollover of the sidewall and better control. Tire dynamics play into it also. There are traction advantages of wide and short vs. narrow and long contact patch based on physics. But it is a big myth that wide tires have a bigger contact patch.

Mileage is affected by change in tire diameter in many ways, but the largest loss will come from leverage:

It takes "effort" to move a lever and a wheel is just one continuous lever with the force being applied at the hub (the folcrum[sp]) and the action taking place where the tire hits the road. If you increase the length of the lever from the folcrum, leverage is lost, requiring an increase in effort to aquire the same results. To increase the effort the engine must work harder, using more fuel.

Try this to feel what I am talking about -
Hook a one gallon water jug on the end of a four foot board and lift it by the other end. Now try the same from the end of an eight foot board, there is a good chance you can not lift it at all.

The engine of your truck will work less if you regear, this will remedy the force needed to be applied, through the gearing.

But you will always have the lesser losses due to increased weight and possibly rolling resistence derived by a different tred pattern. Additionally there will be some minimal loss in raising your vehicle, due to "wind" resistence, to fit those new tires, unless you raise it enough to get sufficient airflow beneeth you truck, but then you loose stability.

Summarily... you will loose some going to a larger tire, never gain.