Posted: 7/19/2010 11:52:53 AM EDT
|
Here's the situation.
I need new tires for my truck. The current tires are P245/70R17. However, while looking around, I saw that P265/70R17 would also fit on my truck. Going with 265 instead of 245 would mean a larger tire circumference, which would mean more ground covered per wheel rotation. Now, I'm going to stick with the 245 since I don't want to have to buy a replacement spare, but this got me wondering: If you put a tire with a larger circumference on a vehicle, would it have better gas mileage because each wheel rotation would cover more ground, or would it have worse/unchanged gas mileage because each tire would weigh more? Just curious. _MaH |
| Yes. Less rolling resistance and weight. The downside is that your engine will run at a higher RPM for a given wheelspeed, although going up or down a size or two isn't really that noticeable. I went from 265s to 285s on my truck and didn't lose hardly any fuel mileage. |
|
here is a tire size comparison calculator that may provide some info.
http://www.miata.net/garage/tirecalc.html |
|
Quoted:
The "265" is not the tire circumference. Its the section width, or how wide the tires are from sidewall to sidewall. The middle number is the aspect ratio, which is sidewall hieght, all in metric Thank you for that. I saw some 245's next to 265's in a store and the 265's were larger - I suppose I missed the other part with the larger number. _MaH |
|
Quoted:
Quoted:
Worse because of the increased gearing and more rolling friction. Then would switching to a smaller tire circumference improve gas mileage (to a point)? _MaH I've never seen factory mileage improved from a smaller, but bigger will damn sure hurt it. I worked 7.5 years at Wal-Mart TLE, and 10 times a day a redneck would come in and want the absolute most rubber possible crammed in his fenders. It used to make my head explode. I told them engineers with college degrees are paid to design these things, so my advice was to go by the tire placard. Then I got lectured on how their daddy used to own a tire shop and how he has to pull a trailer, derp, derp, derp... I don't miss that job... |
|
Quoted:
Quoted:
The "265" is not the tire circumference. Its the section width, or how wide the tires are from sidewall to sidewall. The middle number is the aspect ratio, which is sidewall hieght, all in metric Thank you for that. I saw some 245's next to 265's in a store and the 265's were larger - I suppose I missed the other part with the larger number. _MaH And to expand on that, the aspect ratio is the percentage of the section width. So the 265/70 will be wider and taller than the 245/70 because 70% of 265 is more than 70% of 245. |
|
Quoted:
Quoted:
Quoted:
Worse because of the increased gearing and more rolling friction. Then would switching to a smaller tire circumference improve gas mileage (to a point)? _MaH I've never seen factory mileage improved from a smaller, but bigger will damn sure hurt it. I worked 7.5 years at Wal-Mart TLE, and 10 times a day a redneck would come in and want the absolute most rubber possible crammed in his fenders. It used to make my head explode. I told them engineers with college degrees are paid to design these things, so my advice was to go by the tire placard. Then I got lectured on how their daddy used to own a tire shop and how he has to pull a trailer, derp, derp, derp... I don't miss that job... I'll take a man with 7.5 years of experience on a subject at his word. Thanks! _MaH |
|
I'll add to all that, if your truck specs are ok with the 265, they might work better if you see some offroading. Wider will always be better than pizza cutters in the mud.
The gas mileage trade-off shouldn't be that bad for that size difference. Truck might also look better. Secondly, LT tires will generally be rougher riding compared to P tires, since they're rated for heavier loads and will have thicker sidewalls. If you do a lot of highway miles and value a quiet, cushy car like ride, then you might want to keep P type tires on your truck. |
|
Quoted:
Quoted:
Quoted:
The "265" is not the tire circumference. Its the section width, or how wide the tires are from sidewall to sidewall. The middle number is the aspect ratio, which is sidewall hieght, all in metric Thank you for that. I saw some 245's next to 265's in a store and the 265's were larger - I suppose I missed the other part with the larger number. _MaH And to expand on that, the aspect ratio is the percentage of the section width. So the 265/70 will be wider and taller than the 245/70 because 70% of 265 is more than 70% of 245. exactly. |
|
I went from P245/70R17 to LT285/70R17 and lost ~3mpg. Going from passenger tires to light truck tires will do it without the size increase because the rotating mass increases but going up in size makes it even worse. Of course I also went from a street tire to an all terrain tire which I assume made a difference as well.
I don't regret it though. The extra ground clearance has been nice and the wider footprint has really helped traction. Any bigger and I would need to lift which makes it a lot more expensive for little gain so I doubt I will ever go bigger. |
|
Quoted:
I went from P245/70R17 to LT285/70R17 and lost ~3mpg. Going from passenger tires to light truck tires will do it without the size increase because the rotating mass increases but going up in size makes it even worse. Of course I also went from a street tire to an all terrain tire which I assume made a difference as well. I don't regret it though. The extra ground clearance has been nice and the wider footprint has really helped traction. Any bigger and I would need to lift which makes it a lot more expensive for little gain so I doubt I will ever go bigger. Got a Dodge, huh? At least tell me it's 4wD. If it's not, and it's an automatic, good luck getting 100K out of your tranny... |
|
Quoted:
Quoted:
I went from P245/70R17 to LT285/70R17 and lost ~3mpg. Going from passenger tires to light truck tires will do it without the size increase because the rotating mass increases but going up in size makes it even worse. Of course I also went from a street tire to an all terrain tire which I assume made a difference as well. I don't regret it though. The extra ground clearance has been nice and the wider footprint has really helped traction. Any bigger and I would need to lift which makes it a lot more expensive for little gain so I doubt I will ever go bigger. Got a Dodge, huh? At least tell me it's 4wD. If it's not, and it's an automatic, good luck getting 100K out of your tranny... 2004 Dodge Ram 1500 Quad-cab SLT 4WD here. Odometer currently at 108k. That truck is a beast. Went 20k miles once over a year without an oil change because I was retarded and completely forgot to do it. Never gave me a problem during that time or after. It's taken me from DC to Toronto and back, and across the country from DC to Colorado Springs with a back seat fully loaded with ammo and firearms, a bed filled to the top with furniture, while towing a Ford Explorer packed with more stuff. I've driven it up Pikes Peak numerous times, through Rocky Mountain National Park twice, up secluded dirt roads to obscure 14er trail-heads, and through the fierce Wyoming wind on I-80 outside Cheyenne. I have driven this truck into the ground and back, and so far the only major maintenance it's needed was to replace a broken water pump. That aside, it's been oil changes, spark plug replacements, and now new tires (to replace the ones that covered all the aforementioned terrain). People talk about Dodge trucks falling apart and especially about the transmission being worthless. I just haven't seen it. My Dodge is one cannon short of being a tank. If it doesn't make it to 250k, I'll be livid. If it falls apart into every individual nut and bolt after 300k, I'll have considered myself to have had a damn good run with it while it lasted! _MaH |
|
Quoted:
I think what kills Dodge trannies is having it in O/D while towing or driving in the mountains, or driving at extended high speeds, like I-95 in FL in the summer, causing the transmission to constantly shift back and forth from O/D. Causes it to overheat. Huh... I do (or have done) all those things but never put it into O/D. Interesting to know and will be remembered... _MaH |
|
Quoted:
Quoted:
I think what kills Dodge trannies is having it in O/D while towing or driving in the mountains, or driving at extended high speeds, like I-95 in FL in the summer, causing the transmission to constantly shift back and forth from O/D. Causes it to overheat. Huh... I do (or have done) all those things but never put it into O/D. Interesting to know and will be remembered... _MaH The fact you did all that without O/D engaged might be why you still have a good transmission. It's not just the Dodges too. |
|
My overall fuel mileage went up by a good 2-3mpg (diesel) when I went from a 245 to a 295 tire. I dont know that id do that in a lower torque gas engine and get the same results.
Also keep in mind that ive got a 4:10 rear end so it brought up my final ratio to somewhere between 3.73 and 3.55. On the highway it was much more enjoyable as at 70mph my RPM's had dropped by about 3-400 (thats alot when your redline is 3000) |
|
http://www.dickcepek.com/DickCepekTireGuide.pdf http://clubs.hemmings.com/clubsites/chevylist/tech/tire_size_conversion.htm  245/70/17 section width 9.6" Section Height 6.7" tire diameter 30.5" 265/70/17 section width 10.4" Section Height 7.3" tire diameter 31.6 Wider tires also burn more fuel |
|
Quoted: 2004 Dodge Ram 1500 Quad-cab SLT 4WD here. You can go to a 285/70/17 without needing spacers or a lift no problem. Many people swear you can get a 305/70/17 done... But I suspect you will be rubbing with it. -02 Dodge Ram 1500 QC SLT 4WD owner Edit: Mine came with 265/70/17. Upgraded to 285/70/17. |
|
Quoted:
Quoted:
I went from P245/70R17 to LT285/70R17 and lost ~3mpg. Going from passenger tires to light truck tires will do it without the size increase because the rotating mass increases but going up in size makes it even worse. Of course I also went from a street tire to an all terrain tire which I assume made a difference as well. I don't regret it though. The extra ground clearance has been nice and the wider footprint has really helped traction. Any bigger and I would need to lift which makes it a lot more expensive for little gain so I doubt I will ever go bigger. Got a Dodge, huh? At least tell me it's 4wD. If it's not, and it's an automatic, good luck getting 100K out of your tranny... 4WD Dodge yes. Shouldn't be a problem considering one of the 4WD models comes with 285/70/17s. IIRC the 20s on the 2WD models are about the same size. |
|
Quoted:
Quoted:
I think what kills Dodge trannies is having it in O/D while towing or driving in the mountains, or driving at extended high speeds, like I-95 in FL in the summer, causing the transmission to constantly shift back and forth from O/D. Causes it to overheat. Huh... I do (or have done) all those things but never put it into O/D. Interesting to know and will be remembered... _MaH You sure about that? OD is automatic on my 05. You have to turn on the tow/haul mode to disable it. |
|
Quoted:
Quoted:
Quoted:
I think what kills Dodge trannies is having it in O/D while towing or driving in the mountains, or driving at extended high speeds, like I-95 in FL in the summer, causing the transmission to constantly shift back and forth from O/D. Causes it to overheat. Huh... I do (or have done) all those things but never put it into O/D. Interesting to know and will be remembered... _MaH You sure about that? OD is automatic on my 05. You have to turn on the tow/haul mode to disable it. Hmmm, now that you mention that... There's a button on the end of my gear shift that does something. Now that you've mentioned it, I don't know if that turns on O/D, or Tow/Haul mode. Whatever that button is, I never press it. Regardless, I haven't had any transmission problems with my Dodge. I shall now go knock on wood. _MaH |
|
Quoted:
Quoted:
2004 Dodge Ram 1500 Quad-cab SLT 4WD here. You can go to a 285/70/17 without needing spacers or a lift no problem. Many people swear you can get a 305/70/17 done... But I suspect you will be rubbing with it. -02 Dodge Ram 1500 QC SLT 4WD owner Edit: Mine came with 265/70/17. Upgraded to 285/70/17. People say a lot of weird things on the Dodge truck forums. The way they constantly recommend cranking the torsion bars to people that do not realize the consequences of doing so amazes me. |
|
Quoted:
Quoted:
2004 Dodge Ram 1500 Quad-cab SLT 4WD here. You can go to a 285/70/17 without needing spacers or a lift no problem. Many people swear you can get a 305/70/17 done... But I suspect you will be rubbing with it. -02 Dodge Ram 1500 QC SLT 4WD owner Edit: Mine came with 265/70/17. Upgraded to 285/70/17. Hope your prepared to rotate every 5,000 miles. Maybe it's the heat down here, the abrasive roads, but I never saw anyone get more than 30,000 out of a set of tires when they made a 2-3 size jump. Not to mention the redneck logic of "well, I got bigger tars, now I need to put 80psi in them, derp, derp..." I'll argue all day that there is ZERO to be gained from upping the tire size from a 245/265 to a 285/305 besides it "looking cool" and the ill-perceived notion your truck will now haul/tow more or handle better. It's all untrue but if it makes you happy... BTW: I'm not trying to shit on anyone's truck or tires they like, but 7.5 years at Wal-Mart trying to tell the hillbillies that 285's on their 1/2 ton, 2wD Dodge is bad idea, only to have them give you a 100 bullshit reasons why your wrong, ultimately have them come back 20,000 miles later cussing you about their accelerated-wear tires, and how I sold them defective tires and their going to sue Wal-Mart...makes you a bit of a cynic 
|
|
Quoted:
Quoted:
Quoted:
2004 Dodge Ram 1500 Quad-cab SLT 4WD here. You can go to a 285/70/17 without needing spacers or a lift no problem. Many people swear you can get a 305/70/17 done... But I suspect you will be rubbing with it. -02 Dodge Ram 1500 QC SLT 4WD owner Edit: Mine came with 265/70/17. Upgraded to 285/70/17. Hope your prepared to rotate every 5,000 miles. Maybe it's the heat down here, the abrasive roads, but I never saw anyone get more than 30,000 out of a set of tires when they made a 2-3 size jump. Not to mention the redneck logic of "well, I got bigger tars, now I need to put 80psi in them, derp, derp..." I'll argue all day that there is ZERO to be gained from upping the tire size from a 245/265 to a 285/305 besides it "looking cool" and the ill-perceived notion your truck will now haul/tow more or handle better. It's all untrue but if it makes you happy... BTW: I'm not trying to shit on anyone's truck or tires they like, but 7.5 years at Wal-Mart trying to tell the hillbillies that 285's on their 1/2 ton, 2wD Dodge is bad idea, only to have them give you a 100 bullshit reasons why your wrong, and ultimately have them come back 20,000 miles later cussing you about their accelerated-wear tires, and how I sold them defective tires and their going to sue Wal-Mart...make you a bit of a cynic Well, one could argue that some bigger tires would help you tow more––Many LT tires aren't 8-ply until 31"-33" (depending on wheel), but thats' just me being nitpicky. 
What tires were giving out in 20k? The only ones I've seen do that consistently where those damned Mud Grapplers that Nitto makes, and assorted Interco pieces of shit. |
|
Quoted:
Quoted:
Quoted:
Quoted:
2004 Dodge Ram 1500 Quad-cab SLT 4WD here. You can go to a 285/70/17 without needing spacers or a lift no problem. Many people swear you can get a 305/70/17 done... But I suspect you will be rubbing with it. -02 Dodge Ram 1500 QC SLT 4WD owner Edit: Mine came with 265/70/17. Upgraded to 285/70/17. Hope your prepared to rotate every 5,000 miles. Maybe it's the heat down here, the abrasive roads, but I never saw anyone get more than 30,000 out of a set of tires when they made a 2-3 size jump. Not to mention the redneck logic of "well, I got bigger tars, now I need to put 80psi in them, derp, derp..." I'll argue all day that there is ZERO to be gained from upping the tire size from a 245/265 to a 285/305 besides it "looking cool" and the ill-perceived notion your truck will now haul/tow more or handle better. It's all untrue but if it makes you happy... BTW: I'm not trying to shit on anyone's truck or tires they like, but 7.5 years at Wal-Mart trying to tell the hillbillies that 285's on their 1/2 ton, 2wD Dodge is bad idea, only to have them give you a 100 bullshit reasons why your wrong, and ultimately have them come back 20,000 miles later cussing you about their accelerated-wear tires, and how I sold them defective tires and their going to sue Wal-Mart...make you a bit of a cynic Well, one could argue that some bigger tires would help you tow more––Many LT tires aren't 8-ply until 31"-33" (depending on wheel), but thats' just me being nitpicky.
What tires were giving out in 20k? The only ones I've seen do that consistently where those damned Mud Grapplers that Nitto makes, and assorted Interco pieces of shit. By tow more, I mean a 1/2 ton pickup will never tow/haul more than the C load range tires that come on them would allow. But man those idiots think putting on those E load range tires on their 4.3 litre chevy automatically turn it into a Duramax with an Allison... Any tire that's 2-3 sizes above recommended, never rotated, and ran way over PSI will be smooth (in the middle anyway) by 20,000 no matter who makes them...and this is what I dealt with nearly every damn day... |
|
Quoted:
Quoted:
Quoted:
2004 Dodge Ram 1500 Quad-cab SLT 4WD here. You can go to a 285/70/17 without needing spacers or a lift no problem. Many people swear you can get a 305/70/17 done... But I suspect you will be rubbing with it. -02 Dodge Ram 1500 QC SLT 4WD owner Edit: Mine came with 265/70/17. Upgraded to 285/70/17. Hope your prepared to rotate every 5,000 miles. Maybe it's the heat down here, the abrasive roads, but I never saw anyone get more than 30,000 out of a set of tires when they made a 2-3 size jump. Not to mention the redneck logic of "well, I got bigger tars, now I need to put 80psi in them, derp, derp..." I'll argue all day that there is ZERO to be gained from upping the tire size from a 245/265 to a 285/305 besides it "looking cool" and the ill-perceived notion your truck will now haul/tow more or handle better. It's all untrue but if it makes you happy... BTW: I'm not trying to shit on anyone's truck or tires they like, but 7.5 years at Wal-Mart trying to tell the hillbillies that 285's on their 1/2 ton, 2wD Dodge is bad idea, only to have them give you a 100 bullshit reasons why your wrong, ultimately have them come back 20,000 miles later cussing you about their accelerated-wear tires, and how I sold them defective tires and their going to sue Wal-Mart...makes you a bit of a cynic I haven't been stuck in soft sand since upgrading. The 1.1" of height I gained and 1.6" of width per tire helps a ton. The tires I have will wear faster but I knew that going in just like I knew my gas mileage would drop. IIRC I should get around 40000-45000 miles out of them. I would have gotten 60k out of the BFGs but they costed a lot more. |