Taller tires for better MPG ?

Peter,

You bring up an interesting idea, and I'm curious to see if anyone has concrete info from experience.

So the engine turns 8.5% slower with the new set up, right? Let's go with what I think is an optimistic increase in mileage of 5% -- over

40K miles (arbitrary lifetime of work truck tire), that's burning 3077 gal of fuel stock, 2930 with bigger tires. 146 gal. @ $2.50 (ya right) is $365 bucks.

My point is that if you're trying to be ecologically sensitive, then ok, give it a try. If you're trying to save money, then maybe there's an alternative.

I don't know what you're looking to pay, but stock truck tires are practically given away by the tire shops around here....$70-90 for med. duty set of 4 mounted and balanced, like new condition. You get name-brand quality in construction and name brand ride.

Taller tires are also harder on your brakes and will work your tc or clutch more....

Of course I did the same thing I'm recommending, going with a set of

17" take-offs -- a little taller, yes more rim but less tire. Tough to beat OE Michelins IMO for 5 on rims at $100. Sorry if that's too off-topic or off in the wrong direction.

Jon

snipped-for-privacy@yahoo.com wrote:

Theoretically, it would seem that having a taller tire would change the "gearing" very slightly and give you better mpg on the highway...

Our Ram had 245/16 on it when we got it... the door sticker called for 255... We went to 265/16 and didn't see a mileage difference, but didn't really track it before the new tires..

NOTE: changing tire size WILL throw your speedometer and such off... ours reads

60 when we're doing 63 mph... I'm guessing that it was off by the same amount in the other direction before... If so, the odometer would tell you that the mileage was better with smaller tires because it registered 4% faster/further than you actually went???

Mac

Your idea is sound, but will be harder on equipment, because of the gearing change. Another way to save gas is to buy Load Range E tires. These tires can be inflated to 80 psi, and then you will have less rolling resistance, with the same gearing.

Remember the difference on a 10 speed bike between 60 psi tires and 100 psi tires, if not, go test a bike at a local bike shop - and really save some gas!

I believe the 80 pounds is when the truck is loaded to it's max. Operating at 80 pounds m/t isn't going to put much rubber on the road and the truck will ride hard as hell imo.

Roy

I can't tell the difference in ride at 40 psi or 80 psi. on my 98 Ram 1500 SLT Larime. Of course, it ain't the best ridin' truck, anyway! But I do get another mpg or so (depends on how much highway crusin' you do.)

I guess my ass is more sensitive than yours.

Of greater concern is the stopping ability of your truck with the 80 pounds in the tires and m/t. You have a much smaller patch of rubber in contact with the road.

Roy

You bet it is!!!!

Stopping???? what's that????

While it is true that 80 PSI is required for max load capacity, there is benifits from increase average presure from reduced rolling resistance which can improve MPG. The only real draw back is a stiffer ride on a bumpy road. Tread design and profile plays a roll here too. A 83 series tires (like a 235/83/R16 E) will have less drag and rolling resistance than a 70 or 75 seris. It is also about 1 inch taller than a 245/75/16 too. Finailly, the tread design itself plays a roll too. A smooth tire with little or no cleats will consume less power than one with a "meaty" tread. (look at a semi tire sometimes) Genrally unless you are carry enough weight to need it, there is little or no gain in MPG with pressure over 55 to 60 PSI so even a D range tire running at or near max pressue will roll nicely with a smooth tread.

----------------- TheSnoMan.com

And it's cute too! There's a gimmie for wide ride

Roy

Where do you find a tire with an 83% aspect ratio??? or 83 series as you call it?

oh and while I'm asking questions.....you find that knock sensor yet?

just wondering.

Well, well, look what crawled under the door. Tired of spreading false info at the other group and decided to drag your ass back here? First you have a few questions to answer from the last time you were here. You remember them don't ya? Or are you here for another reason, I figure there is another reason.

Your sig looks good.

Oh, you didn't address the stopping issue with over inflated tires. Care to take a shot?

The key is 'overinflated'. The tires are not 'over-inflated'; they are inflated to spec.

Really? So it is your position that filling your tires to max air pressure and running the truck with no load does not present a over inflated condition with regard to braking and handling? Am I correct in my understanding?

Roy

Phil:

That ain't necessarily the case. The max pressure stamped on the sidewall is the max pressure at the max load. If your load is less than max, you should run a lower pressure for better road contact, handling and braking. While running the max pressure on the sidewall will not harm the tire it will compromise the ride quality, increase NVH and will also impair the traction, especially under wet or slick conditions.

The ideal thing is to weigh the truck at each axle and using an inflation/pressure chart use the appropriate pressure for the load the tire sees. Hope this helps

Mike

own a set. I know what they do.

In every single case I have ever put larger tires on the result was lower mpg. While the effective ratio should improve it, the engine has to work harder to turn the larger tires. I've yet to see a case where it improved mpg.

Miles makes an excellent case here. Some years ago we had a great e-mail list, it was called the RTML, or Ram truck mailing list. Some current newsgroup members were on it. One of the members ran an experiment with his overdrive. He ran back to back tanks of gas, one using overdrive as normal, one with it locked out. He got one MPG less with it locked out. Overdrive on a Dodge is .69, about a 30% reduction in RPM for given road speed and MUCH more than you'll get with a larger tire.

One of the other caveats is rolling resistance, one of the major considerations of the factory selection is rolling resistance, and most aftermarket tires don't give this much thought. I've seen people lose two MPG with aggressive off road tread tires. If you use a larger diameter and usually wider tire, you may gain some rolling resistance.

Lastly I've seen discussions of axle ratios and fuel economy, too low a ratio and fuel economy suffers, too high a ratio and it suffers again. The discussion I'm referencing took place before automatic overdrives were offered. The synopsis at that time was about a 2.9 final drive was about optimal for fuel economy. This obviously was also well before fuel injection was commonly available. But consider this, most half ton trucks today come with 3.42 to 3.55 ratios standard and automatic overdrives offer a 30% reduction of RPM's and now we're down into the 2.5 range. IMHO, this is mostly for emission control to reduce amounts of pollutants per mile, NOT to increase fuel economy. Maybe with the better atomization of fuel with injection this is the new optimal ratio, it's hard to say, I could be wrong. But if we're already this high in axle ratios, how much could a little taller tire help?

Now if you want taller tires because they look better, I'm with you there. Just don't want you to do something expecting one thing and not getting it.

I went from 215/75-15s to 235/75-15s on my Dakota and lost a couple of mpg.

Ken