Taller rear tires on RWD vehicle

[Diesel_Dave]

I've been thinking over this potential mod for a while and wanted to get other's opinions. Would there be an advantage to running taller rear tires on a rear wheel drive vehicle (such as my pickup)?

The advantage of a taller tire is supposed to be lower engine RPM's becuase the powertrain has effectively been re-geared lower. Typically, however, people who go to taller tires (all around) see FE decrease. The thinking hear is that the taller tires hurt the aero because the effective frontal area has increased. Some people also cite the higher rotational mass. Another factor is that many taller tires, tend to generally have higher rolling resistances.

So here's my thinking. If you went to taller tires, but only on the rear of a RWD pickup, you'd get the gearing benefit without the aero penealty, right?

Anybody tried it?

[BackroadBomber]

I got slightly. Bigger tires on my ford ranger and I see a decent mpg increase, like 2 mpg. Also, the reason people think they get worse mileage is because people don't re-calibrate theirs speedo and odometer. A bigger tire will make your speedo read slower, so your odometer will show less miles than actual miles driven. If you put bigger tires on, make sure you get your speedo recalibrated, or if your trucks older like mine figure out the percentage it's off and factor that In to figure out your true mileage. Oh by the way the tires that are supposed to be on my truck are 225-70-14 and I put on 225-75-15 so they're around 2 inches taller and they throw my speedometer off by 7.11% (when I'm doing 60 my speedo will read 56). So whenever I fill up and want to figure out my mileage, I multiply the distance on the odo by 1.0711 and find out my actual miles travelled.

[royanddoreen]

well put!!! I am thinking of going 1" taller, good to hear you got 2 mpg better, I'm sure I will do as good. Thanks for the info!

[Rick323]

I went from 235/85/16 to 255/85/16 on the rear of my F250. I don't know if my fuel mileage went up or down (I don't think it went down). The only thing I think it will affect is the abs. My Ford only had rear abs (4 wheel abs was an option in 99).

[slowmover]

It's an expensive way to barely increase one performance parameter while being detrimental to others, IMO. But I would start by searching commercial operators: Hotshot, LTL, etc, for other than anecdotal on 8,000-lb pickup trucks under 24,000-lb trailers one direction, and deadheading others. Kind of like a GV O-D. I don't recall having "seen" a benefit in my reading in those forums on this, and long ago shelved the idea. Maybe something newer has come along. A place to start is a large-area search on a contributor to many forums -- RV & commercial -- JIMNLIN, as he made a living going back 30-years with pickup trucks in service. Also owns a Dodge. A good source of what works well for tires on these trucks.

[brucepick]

I've seen VW beetle people call this a "rubber overdrive". But I suspect they're resizing all four wheels.

The increased rotating mass of the bigger tire will be negative for city stop and go driving - due to you have to accelerate that mass all the time. On the highway the increased rotating mass doesn't hurt you nearly as much.

[ex-x-fire]

Everybody did that in high school, usually included air shocks & cragars.

[mcrews]

Originally Posted by BackroadBomber

I got slightly. Bigger tires on my ford ranger and I see a decent mpg increase, like 2 mpg. Also, the reason people think they get worse mileage is because people don't re-calibrate theirs speedo and odometer. A bigger tire will make your speedo read slower, so your odometer will show less miles than actual miles driven. If you put bigger tires on, make sure you get your speedo recalibrated, or if your trucks older like mine figure out the percentage it's off and factor that In to figure out your true mileage. Oh by the way the tires that are supposed to be on my truck are 225-70-14 and I put on 225-75-15 so they're around 2 inches taller and they throw my speedometer off by 7.11% (when I'm doing 60 my speedo will read 56). So whenever I fill up and want to figure out my mileage, I multiply the distance on the odo by 1.0711 and find out my actual miles travelled.

exactly!

[Diesel_Dave]

Originally Posted by BackroadBomber

I got slightly. Bigger tires on my ford ranger and I see a decent mpg increase, like 2 mpg. Also, the reason people think they get worse mileage is because people don't re-calibrate theirs speedo and odometer. A bigger tire will make your speedo read slower, so your odometer will show less miles than actual miles driven. If you put bigger tires on, make sure you get your speedo recalibrated, or if your trucks older like mine figure out the percentage it's off and factor that In to figure out your true mileage. Oh by the way the tires that are supposed to be on my truck are 225-70-14 and I put on 225-75-15 so they're around 2 inches taller and they throw my speedometer off by 7.11% (when I'm doing 60 my speedo will read 56). So whenever I fill up and want to figure out my mileage, I multiply the distance on the odo by 1.0711 and find out my actual miles travelled.

Glad to hear that you've seen a benefit. I've looked into it and you are one of the few that's seen FE go up. Certainly the speedo needs recalibrated for different tire sizes. From what I've heard, I'd say fewer than 1 in 10 people report better FE with taller tires (after speedo re-calibration).

[mcrews]

actually dave, quite a few have.
As a general note, frank lee commented that trucks doent see a benift.
But the trick to the equation is how much highway miles you are driving vs city driving.
Also you cant be going from 15 rims to 17 rims, because then the issue is the extra wieght. But a 4-7% increase in diameter (given hwy driving) absolutely will result in betterr mpg.

Just common sense alone would have to question your 1 in 10 statement.