It has been suggested by Lou LaPointe that increasing tire diameter by one size(185 70-14 instead of 175 70-14) can help increase mileage. Anyone have any thoughts on this?
[quote="diamondlarry"]It has been suggested by Lou LaPointe that increasing tire diameter by one size(185 70-14 instead of 175 70-14) can help increase mileage. Anyone have any thoughts on this?[/quote]
I can see where taller diameter will increase overall gearing and thus slow the engine down...like overdrive but not to the same extent. I'd be concerned about going wider and creating more drag though. It will also raise the vehicle ever so slightly which would also create a little more aero drag.
Don't forget to correct speedometer readings too. Otherwise you'd short change yourself.
[quote]Don't forget to correct speedometer readings too. Otherwise you'd short change yourself.[/quote]
I found that I have to add 5% to my mileage to make it accurate when I did that.
I haven't really tested this. Some claim is doesn't work and might reduce mpg.
* But after thinking about it...I HAVE tested it on one car. Got 37 mpg with tires that were 5% oversized and around 30 mpg same car but with tires that were 1 % undersized. Also might have something to do with the tire construction involved. That's a 23% difference. Will be retesting this agian soon.
If you do go for oversized tires...it's a good idea to stiffen the suspension also...due to the higher roll center.
It's possible that most cars are setup with overall gear ratios for best mpg...but considering the high HP craze...I'd say not so.
Might look at the overall gearing for the few cars that were setup for best mpg from the factory...Geo...Escort...etc.
I'm talking about the specific versions of these cars that were setup for highest mileage...might be a general clue there.
Larry...you should consider rear fender skirts...full moon wheel covers...remove mirrors...wipers...antenna... etc? Some newer cars have tabs in front of all 4 tires to deflect some air.
[quote="E=mc2"]I haven't really tested this. Some claim is doesn't work and might reduce mpg.
Larry...you should consider rear fender skirts...full moon wheel covers...remove mirrors...wipers...antenna... etc? Some newer cars have tabs in front of all 4 tires to deflect some air.[/quote]
Like everything else you're probably going to have to test on your own vehicle. I would think it should help in most vehicles,especially when engine is modified so that it makes more torque and power to pull taller gears with ease. I agree with the aero mods, for any vehicle. However, you best be carefull pulling off mirros, check your local laws. I've seen panaramic mirrors for rear view mirros and small bicycle style mirros mounted inside the cab and will be trying that option.
Once I get the head swap done I will be spending some time on the Yahoo group maxmpg. They seem to have quite a bit of aero mods to look at.
Say I do increase the tire diameter, because logic says that per revolution, the larger diameter will go more distance....
The question is, how do I adjust the speedometer and odometer to reflect this change so they are accurate?
There are 2 ways of dealing with this. First, go to one of those places that calibrate law enforcement vehicle speedometers and have them do it.
Second, drive for about 10 to 20 miles on the interstate and compare your odometer to the mile markers along side the road. Figure out how much your odometer is off, then use that as a multiplier when you figure your mileage. You would have to also figure out where the needle should be to do the speed limit (for example, when the needle reads 62 mph you are traveling at 65).
you can also use a gps to calibrate you speedometer and odometer
Thanks guys. What really should happen is an actual calibration based on tire size. That way, your odometer keeps an accurate count.
A word of caution:
If you are going to test the difference tire diameter has on fuel economy, then it is important that you eliminate as many variables as possible.
Specifically, a new tire will have more rolling resistance than a worn out tire - all other things being equal.
Also, differences in rolling resistance between tires - even those of the same size - can be HUGE!
But as a general rule, larger diameter tires will have ever so slightly better rolling resistance - all other things being equal.
It has been our experience that a taller tire and a narrow tire properly inflated or slightly above will give you some fuel economy improvement. We have always noticed that the taller tire will turn down your rpms. If you are really into things, you can also look into changing gear ratios.