Taller tires = better MPG?

[BeoWolfe]

Greetings,

I had a question for you MPG folks. I have a manual transmission car that runs over 3k RPM when I am going 75mph (I drive 180 miles a day on the highway). Would changing to a taller tire lower my RMPs and give me better MPG?

[diamondlarry]

Greetings,

I had a question for you MPG folks. I have a manual transmission car that runs over 3k RPM when I am going 75mph (I drive 180 miles a day on the highway). Would changing to a taller tire lower my RMPs and give me better MPG?

It could give slightly better mileage. The only drawback would be that your odometer/speedometer would be off.

[Hockey4mnhs]

i would think not because there is probly more tire hiting the ground

[thisisntjared]

The only drawback would be that your odometer/speedometer would be off.exactly, so you wouldnt really know if you were getting better mpg. narrower (lower rolling resistance) tires are better for fuel economy.

[LxMike]

They would lower your rpm's somewhat and that in theory shoudl help with milega ebut would be a small change. unless you get tires 2-3" taller

[MetroMPG]

unless you get tires 2-3" taller
Which would of course make aerodynamics worse, possibly cancelling the benefit of lower engine RPM :) (Of course you could try to go taller, but narrower...)

Dropping my engine RPM by 25% with the transmission swap (http://www.metrompg.com/posts/tranny-swap.htm), I got a 5% increase in MPG in top gear.

[SVOboy]

Tell us more about the car and we can prolly give you better suggestions. I vote for aero mods at this point.

[thisisntjared]

I vote for aero mods at this point.i agree but i think it depends more on the type of driving done than the car...

[SVOboy]

i agree but i think it depends more on the type of driving done than the car...
He said 75mph 180 miles a day.

[Sludgy]

Narrower tires of the same height would provide a definite aero improvement. Go with a low rolling resistance brand, and inflate to the maximum sidewall rating. Did he say what size tire he's running?

[BeoWolfe]

I drive a 2000 Escort ZX2. I used to have a Geo Metro and I still get emails from MetroMPGs site on what he is up to :P.

Anyways, I ... (takes a deep breath) can admit to being a bit of a fuel economy geek. The current tires on my car are 205/55/15's . And slowing my commute from 75 mph to 55 would help my fuel economy but add alot of time to my work commute.

My tires are wearing low and its time for some replacements so I wanted to see if I could get some better fuel economy by getting taller tires. I thought of getting thinner tires but does thinner tires mean that I need to buy rims or can a go a few sizes smaller on my current rims?

Thanks for all the replies

[LxMike]

those tires are already taller than stock size on the zx-2 i have a 99 and my tire size is 185-65-14.

[Ryland]

185/65-15 would be the exact same hight, and would leave your speedo working exactly as it is now as well, the 185/65-15 would simply be 20mm narrower section width (not tred width, tred width varries, altho narrow section width makes narrower tred more practical) and they look like they will fit 5-6.5" wide rims, so dependong on what you have, they could work.

[Spule 4]

Thirteen odd years of Metro driving showed me bigger tires than 145R12 hurt mileage....

[Silveredwings]

Which would of course make aerodynamics worse, possibly cancelling the benefit of lower engine RPM :) (Of course you could try to go taller, but narrower...)
Even if you don't go taller but do go narrower, you'd likely see a benefit...I've tried it and believe this to be true.

[BeoWolfe]

those tires are already taller than stock size on the zx-2 i have a 99 and my tire size is 185-65-14.


I have one of the rare Escort S/R's. Ford only made 2,000 of them between 1999 and 2000. The S/R escort is lowered 1'in and has some engine/exhaust enhancements and also came with the larger rims. I love the car but being a former Geo owner I would like to squeeze some efficency out where I can.

[LxMike]

what kind of mileage are you getting now??

[thisisntjared]

He said 75mph 180 miles a day.ah yes, then i vote aero mods whole heartedly. especially at 75mph. aero mods will give the greatest benefit!

[BeoWolfe]

My current MPG is 33 to 35 MPG.

Mrs.Clause got me a Pro-Scan OBDII scanner for Christmas too :). Can't wait to start screwing around with things to see what improves my MPG

[CO ZX2]

I drive a 2000 Escort ZX2. I used to have a Geo Metro and I still get emails from MetroMPGs site on what he is up to :P.

Anyways, I ... (takes a deep breath) can admit to being a bit of a fuel economy geek. The current tires on my car are 205/55/15's . And slowing my commute from 75 mph to 55 would help my fuel economy but add alot of time to my work commute.

My tires are wearing low and its time for some replacements so I wanted to see if I could get some better fuel economy by getting taller tires. I thought of getting thinner tires but does thinner tires mean that I need to buy rims or can a go a few sizes smaller on my current rims?

Thanks for all the replies

Beo, I have a 99 ZX2. If I were you I would put 205/75/15 on your car. There is no doubt in my mind that this would improve your FE at the speed you drive. Your speedo would register 65 when you were going near 74.

If your RPM at 74 is 3200 this would lower to 2800 at 74mph. Your engine has enough torque to handle this OK and it definitely will help mileage. Look at DiscountTire.com. CO ZX2

[badgett]

I tried the taller tire thing. My neon had factory 185 65 R14 tires. When it came time to replace I put on 185 70 R14's. I noticed an instant decrease in power. Which will end up being worse FE. But once I maxed out the tire pressure my FE was right back where it was before. So I guess I'm saying it doesn't help any. Not for my ride anyway.

[MetroMPG]

Did you correct for introduced odometer error when calculating your MPG with the bigger tires? Bigger tires would cause the odo to under-report distance travelled, which would make it appear you're getting worse fuel economy in your calculations.

If your calcs (uncorreted) show the same MPG as before the swap, you're actually doing better.

[badgett]

Cool , I did use a tire calculator on the net to see the speedo difference but I had forgotten about the difference. It says I am going 67.5 mph when the speedo says 65 mph. So I guess bigger is better.

[koinos]

I agree with badgett. The tire size 185-65-R14 means, the width is 185 mm, 65 means the height of the tire is 65% of 185 mm, R14 means wheel size is 14 inches. Therefore if you have such a tire, you can only change it to 185-70-R14 or 185-75-R14 depends on the clearance between the tire and body unless you want to change wheels. The rpm is engine rpm, odometer and speed meter are programmed with the rpm meter, therefore you cannot notice before you take out your calculator. If you changed your tire from 65 to 70, the actual tire diameter will be (185x0.70+14x25.4)/(185x0.65+14x25/4)=1.02 or just 2 % increase.

So if you see 65 mph and 3,000 rpm in your meter, you are actually 66.3 mph. If you travelled 100 miles, it is actually 102 miles. Some auto dealers may void your warranty if you have done so. If you want actual 65 mph, you should drive 2,942 rpm and/or 63.7 mph. Running lower rpm usually gives better mileage. Anyway the change will be small.

I'm waiting for my tires worn out, I'll post my own result when it comes.

[95_corolla]

has anyone tried putting taller tires on the rear to improve Cd.... example 165/55/14 on the front and 165/70/14 on rear to give your car a more forward cant.

[cfg83]

Hello -

I guess this isn't really a question, just where I am in tire shopping. My car's original tires were :

185/65-15

According to Tire-Rack, here are my original OEM tires (rated at a measly 35 PSI :mad: ) :

http://www.tirerack.com/tires/tires.jsp?tireMake=Firestone&tireModel=Affinity+Touring&vehicleSearch=true&partnum=865TR5AFT&fromCompare1=yes&minSpeedRating=S

I read (in the Green Seal tire article?) that the OEM tires are usually good for MPG because the manufacturers pick them to increase the car's FE.

I thought that I would increase my next tire size to :

195/65-15

But according to what you are saying, I should increase to :

185/70-15 or
185/75-15

.... But, these sizes don't exist on Tire Rack.

.... Soooo, maybe I am back to 195's or maybe the stock tire :( .

I am using the Miata tire calculator to figure out the new size :

http://www.miata.net/garage/tirecalc.html

The longer I look, the harder it is to decide.

CarloSW2

[Lug_Nut]

I've thought about regearing the fifth for a higher ratio (lower RPM).
I've also over-diametered the tires to lower revs per mile and have come to the conclusion that this change (lower revolutions per mile) is not a benefit to me. Here's why:
I tend to do a lot of suburban and rural secondary road travel. My speed is infrequently above 50 mph. My trip meter display of average speed is closer to 35 mph. With the factory gearing and factory size tires I can travel at that speed at idle rpm in 5th. With the larger tires, or if I swapped for a taller 5th, I'd have to drive faster (traffic conditions don't permit that) or drive in 4th at some rpm faster than my present. Either of these will hurt, not help, my fuel economy.
If I were to drive at the original poster's 75 mph it'd be obvious that I wasn't truly interested in reducing fuel consumption. Driving 75 instead of 55 saves just over 36% of the travel time but increases air drag by 85%!

[bzipitidoo]

I put on taller tires and a differential with a taller ratio. It didn't have much effect on FE unfortunately. At least FE didn't get worse. It did have some nice effects I hadn't anticipated. I could go 70 with ease (which didn't help FE!) where before the engine was revved up a little high at those speeds. Most of all, the engine noise was considerably reduced. And finally, the engine ought to last a bit longer.

Where taller really helps is if the car has power to spare. Being British, my car was already underpowered, so that worked against the idea. (Britian had an engine tax that encouraged manufacturers to put in the smallest engine that could move the car. And the engines were aways 1 or 2 cc less than some round number.) If you improve your power with a few simple techniques like changing to lighter oil, LRR tires inflated to the max, and perhaps an aero mod, then you're in a better position to reap benefits from taller tires. How does your car handle hills? If it can maintain speed without straining while going uphill, then probably taller will help. My engine otoh is currently in bad shape, and as it was already underpowered when up to snuff, the taller ratio hurts more now that it's putting out something like (wild guess) 80% of the power it ought.

Also, taller magnifies your gas consumption both directions. That is, a driver who burns excessive gas thanks to hard driving with lots of acceleration, jack rabbit starts and such, will do even worse with taller ratios. Drive easy, letting the car lose a little speed on the ups and getting speed back on the downs, and taller will aid you.

[caprice]

Hi people I just joined and this is my first post! Want fuel effecient tires? 185/70 r14 http://web.archive.org/web/20060503174638/http://www.greenseal.org/recommendations/CGR_tire_rollingresistance.pdf :thumbup:

where to buy: http://www.tirerack.com/tires/tires.jsp?tireMake=Bridgestone&tireModel=B381
:cool:
David

[MetroMPG]

Hi David. Welcome to the site.

Feel free to post a brief "hello" message in the Introduce Yourself (http://www.gassavers.org/forumdisplay.php?f=2) forum. Tell us a bit about yourself, your car & how you came to be interested in fuel efficiency.

[brucepick]

...Driving 75 instead of 55 saves just over 36% of the travel time but increases air drag by 85%!

Actually it increases the drag by 2.535% compared to the 55 mph drag amount. Drag increases with the cube of the speed, so even a 10-20% speed change adds a lot of drag. Speed KILLS your fuel economy. (20% speed increase = 1.95 x drag increase)

[brucepick]

As for the ?, will taller tires help, I'm pretty much with bzipitidoo. If you have power to spare, you can drop the engine rpms by changing the gearing or different tire diameter, that should definitely help with FE.

Definitely get used to using a tire calculator like http://www.miata.net/garage/tirecalc.html
or
http://www.wickedbodies.net/Tire-Size-Calculator.htm

Of course getting a larger diameter tire turns your speedometer into a liar, and could help you get a speeding ticket too.

Getting a skinnier tire of same diameter will also help FE for two reasons. One, a smaller front profile pushing against the air. Two, the narrower tire will have less "squirm" which just wastes the energy you're trying to conserve.

The specs on TireRack.com show the range of flange width(s) you can use with any given tire. Obviously that should match the width of your rims. Sometimes it's stamped on the rim so you can see it even with tire mounted on rim.

As for traction, wider tires don't have more rubber on the road so you lose nothing with a skinnier tire. The weight of car vs. air pressure in tire gets you x square inches of rubber flattened onto the road. The wider tire on wider flanges with shorter sidewalls does give less sidewall flexing and more overall control, but you pay for it with FE lost to the rubber squirming and air drag issues.

At fast highway speeds, you really need aerodynamic improvements, or you need to slow down. Air drag goes up with the cube of the speed change so it gets huge quickly. I found it in wikipedia, http://en.wikipedia.org/wiki/Drag_%28physics%29#Drag_at_high_velocity

[VetteOwner]

that and skinnier tires help traction on the snow (sliding, fishtailing especially) because theres more concentrated weight to sink in the snow down to pavement. but if your in sand, you dont want to sink thus wider tires (also depends on the car)

kinda like a road bicycle (the ones with the 1" width tires) vs mountain bike tires (2-3")

oh and if u think having the4 RPM's at 3K going 75 try 3K when your only going 60...liek my chevette. man do i need some taller tires on that. geared obviously designed as a city car cuz i hit 4th gear at 35mph.

[rvanengen]

I tried the taller tire thing. My neon had factory 185 65 R14 tires. When it came time to replace I put on 185 70 R14's. I noticed an instant decrease in power. Which will end up being worse FE. But once I maxed out the tire pressure my FE was right back where it was before. So I guess I'm saying it doesn't help any. Not for my ride anyway.

According to all my truck driver / racer friends...if you run taller tires, you have worse performance at slower speeds but better performance at higher speeds. That is why you see shorter tires on "city" trucks and really tall tires on flatland highway trucks.