Video: Can Skinnier Tires Increase Fuel Economy?
 

I remember back when I used to ride a bicycle (man that was YEARS ago; that's got to change) I noticed that the mountain bikes felt like they had more rolling resistance than the cruisning bikes with their skinny tires. This made me wonder if getting skinny 'donut' tires on my car would increase fuel economy.

I purposefully put the smaller tires on the rear so that my speedometer and gearing would remain the same as with the larger tires.

These are the documented results:
http://www.youtube.com/watch?v=b2K4j037TyY

I should add that I don't use these tires on a regular basis because of their lack of traction, ride quality, and quietness.

Feel free to discuss.

I'm surprised this hasn't been discussed here yet. I've thought of going with a more narrow lighter rim/tire combo for the rear. Impressive gains with a small change shown in the video.

I don't know if a thread has been put up on the topic yet, but I know people have recommended them before. I don't remember if it was on GS or here, but someone put extremely skinny tires on their vx. 155/85/13 if I remember correctly.

Ofcourse you lose traction/stopping ability, though. I think a bigger question is what is a better choice: a wider LRR tire or a skinnier normal tire?

Good work, though. :)

- LostCause

a timely topic - i was just looking for other wheels and tires for the rear of the altima as well. Equipt with 205/60 -15's. pondering going to a 175/55 - 17's so in can fit them under a cover in the rear and moon disks up front ( although i have only seen up to 16 for moon disks .

Would love to see data on LRR vs skinny tire. anyone have comparison?

steve

?"Your Guess is as Good as Mine"?

I would believe that rolling resistance plays a part in the reduction factor,
BUT,
Don't discount the aerodynamics of the two tire styles.
OEM = taller, wider, more contact patch
Donut = shorter [slightly], narrower, less contact patch, and they present a round face to the wind.
OEM tires present a large flat face to the wind.
many variables in one component.
changing all those variables at once = big difference.
I have found a source fro 145 80R 13 tires.
when my current tires are worn out I will replace them with the 13's
Your video just pushed me over my decision hump. I was waffling because this change requires the purchase of new rims also.
But I haven't been to the bone yard in a while, they probly miss me.
Schultz

SPOILER ALERT:

Peakster'll probably be mad at me for posting the results here in the thread, but here's what he observed in an A-B-A test, with a pair of donuts (on the rear) for the B test:

A - 55.9 mpg (US) average (regular tires)
B - 60.9 mpg (US) average (donut tires)

I'm looking at narrower but heavier and taller tires.

Current tires are 235/70R16s which are 29.1" tall and 32 pounds rated at 44 psi and driven at 55 psi.

I'm looking at replacing them with 215/85R16s. They tend to run around 30.4", 0.7" taller and about 4½% more gearing which should nullify the speedo error. Nearly all models are heavier. Some as much 47-48 pounds. The weight wouldn't help in the city stuff. Rotational mass is the bane of all cyclists.

The D rated tires in this size are rated to 65 psi and the E rated tires 80 psi. It would be nice to get rolling resistance and noise specs...

Think they'd help? The aero could get worse from the vehicle being even taller. The gearing change should be minimal but help on the hwy unless lost to aero. They take mega PSI...

No opinions?

Who - re. tire size change.

Take a step back - you mentioned speedo error. Do you have an error now and the taller tire should correct it? That would be nice.

Some thoughts re the tradeoffs with the larger tire:

It's taller so raises car so aero gets worse.
But remember, .7 inch bigger diam. means the car will be .35 inch higher. Yes, .35 inch raise is not ideal but maybe not as significant as the other gains you'll get.

Tire is heavier:

I think the large weight increase will hurt you. But read on, I think there's hope...
A larger tire will be heavier but if tire is taller and also skinnier I don't think it has to be that much heavier than your stock tire, and maybe not heavier at all.

What I'm getting at is I think the tire(s) you've found are rated for a much higher load capacity and so are built with a lot more beef. Probably pricier too. If you find tires with similar load rating and spec'd for 44 psi they'll likely weigh similar to what you have now. You can still run the 44 psi tires at 50-55. If you want more, maybe go to a tire rated at 52 to 55 psi and I'd think you can run it at 60-65-70 psi without worry, if you can stand the hard ride.

Oops - I just noticed you're driving a Santa Fe. Anyway, do look up the orig spec tire and its load rating. No need to get a tire built to carry 50% more weight than OEM spec unless that's how you load up your vehicle.

This is probably a totally dangerous/unfeasable option, but I was at the Lowes the other day and walked past their trailer tires. 12" just like the metro, but skinny, and a VERY high psi rating. ??? ummm...to bad they were a 5 lug.

There's a Uniroyal that is actually quite a bit lighter and is only 29.9" tall instead of 30.4 or so. The Δ for the radius / axle will be 0.65" for most and 0.4" for this tire. Too bad it is a Uniroyal.

The mass of the tires is gonna hurt. I can't drive across the city at a time where I won't need brakes. Short drives on short sections of roads in cold weather... yahoo. BTW, I got even worse mileage with my Aerostar before this and I drove it very mildly in the winter - no snows, I had to. :p Few people ever check their mileage except on long trips with summer gas. They end up thinking their overal mileage is way better than it is, especially in the winter. My wife's car and MetroMum's Corolla are proof. I finally realized this winter that axle bearings alone have a big impact on short drives.

The taller tires could help with cold rolling... a bit better gearing too although it puts my 4th 5th shift speed up from 62 KPH to 65 KPH. My speedo error is just less. All cars with analog speedo error on the side of no tickets and shortens the warranty. Honda lost a class action suit for this a couple of years ago. Anyway, same deal here. If I am driving at 100 KPH, the speedometer says 103 KPH plus or minus 1 and is GPS and mile marker verified. Funny how the ODBII port is bang on right from the factory. Anyway, I'd go 3% in their favour to 1.5% in my favour with 30.4" tall tires, and just about neutral for the Uniroyals.

I thought the increase was pretty significant.

It could be due to less tire touching the ground (sort of like how a bike with skinny tires is easier to pedal compared to one with fatter tires), but also possibly because of the lowered rear-end reduced the aerodynamic wake of the rear?

How much lower would you say it was? Do you remember?

I don't believe the rear drop will be significant.
I just put my donut against one of the OEM tires[I keep some around just in case]
They are the same diameter,
however,
If Peakster has 13's they may be smaller.
but not much.
S.

I'd say it was about an inch. Here's some photos of how much they lower my front end:

http://memimage.cardomain.net/member...2458435_31.jpg
http://memimage.cardomain.net/member...2458435_32.jpg

If you have low gearing, taller AND skinnier tires are better than smaller skinnier ones. if you run 3k at 60, smaller and skinnier won't help as much. it's bandaid for low gearing. If you lower (or have lowered) your vehicle, it will be good to compensate for the taller-ness, then taller would be the way to go I'm thinking.

Ah, OK. That's a good illustration.

Contact patch doesn't change ;)

The only things that will change contact patch is a change in vehicle weight or a change in tire pressure.

Wider tires will have a wider patch (left-right) but will be thinner (front-back).

Skinnier tires will have a skinnier patch (left-right) but will be thicker (front-back)

Hi! this is my first post! :)

I found an article about how tire type can affect gas mileage (Honda Civic VX '95)
Link to the original article

Absolutely.

My Ford Aspire has 165/80/13" wheels and I recently put 195/55/15" on the car and there was a _noticeable_ increase in drag. I have a 1.1 stretch of road that I coast down and I wasn't able to make it all the way with the wider tires.

I took them off, and now I'm back to the 165/83-13", and she coasts as smooth as ever.

To be fair, I should mention that the larger wheels (aluminum rims) were actually heavier than the factory steel 13" wheels by about 8 pounds each.

Also, I found this calculator that will tell you how your speedo will misreport based on wheel size changes:
http://www.miata.net/garage/tirecalc.html
or:
http://www.miata.net/garage/tirecalcold.html

When I put had the larger 195 wheels on my car, my speedometer was slow by .02% (which I consider acceptable).

Hi, xtiago -

Good link. One of our Prius driving members documented a similar situation just this spring: http://forum.ecomodder.com/showthrea...ires#post11668

At first he saw a 10% decrease, which "improved" to just a 5% loss after a few 1000 miles.

Anyway, welcome to the site. If you're not shy, post a note in the "introductions" forum & tell us a bit about yourself.

-Darin

so when are you going to do a 4 donut setup for further testing..

You know your curious! ;)

Ha, funny you should mention it...!

I was actually thinking about it this morning on my way in to work. My local junkyard just got another Aspire in stock today, so I'm going to head over there this weekend and get some. I think they're $10 each at my local yard, so this will be a $40 experiment, but it's for the greater good. ;)

I'm a little hesitant about putting small wheels on the front, but I'll probably try it out anyway (at least one fill up) to see what happens.

I'll post my results as I make them happen...

I've been looking at that same thing - but my truck wears 5-lug, so it's feasible. They're cheaper than a set of Ranchos, look about the same, and come with a tire already on them! And a taller tire would correct my speedo, too. The VIN code says I've got the 3.73 rearend, but I think the speedo gear is for the 3.35.

Rather than replace the speedo gear for $10, I want to replace the rearend gear and slow the engine down at cruise. How's that for dedication?

Safety first - but that sounds like a great research idea. I looked at some trailer websites, but all of the wheels seem to be 5 lug.

Most of the wheels that I'd be interested in using are made overseas (so the shipping would be too expensive).
:(

Aren't do-nuts rated at 70-psi? Would that make the patch reduced?

RH77

I think tires should also be rated to include Total Air Capacity in addition to Pounds per Square Inch.

I tend to think that the more air in the tire at high temperatures and on a smaller hub yields higher MPGs when everything else is equivalent. I don't [yet] have any empirical evidence to base it on (other than my own experiments and observations).

any aftermarket lightweight wheels available in a 15x4? or 16x4 or so?

I want some skinnys.. I've be willing to run a 185-75-16 on my truck all around (if they make em)..

stock they were 205-75-15's

but I cant get anything narrower than that for mine.. :(

5" is the lowest rim width I've seen unless you start looking at dead axle drag wheels, but those are just as inherently dangerous as donuts.

new tires = lots of tread depth = worse mpg VERY TRUE I've witnessed it my self.

Maybe us EcoModders should buy used tires?

I know nothing of the subject, but my car has HTR200s with only 7000 on them and they are a vast improvement over the aged Nittos that were on them previously. But to be fair I wasn't driving full out hypermiler status then. Still got like 45 mpg.

But if you want little or no tread, you could go with slicks but then you're going to have insane amounts of grip and short lifespan. Buying used could be a viable solution and ecofriendly for a period of time, but you've got to be cautious of buying tires with less than 6/32 of tread left depending on where you live.

if i find a set of 15" steel wheels to re rubber I'll run my stock tire size (205-75-15)

but I'd like to go with a skinnier tire, but they dont really cater to my perposed sizes, so i'm somewhat stuck with that being as narrow as I can go..

I've added 115's to my car:
http://aspire.dashpc.com/pictures/DSC01118.JPG
http://aspire.dashpc.com/pictures/DSC01010.JPG

They're clearly much narrower than the stock Aspire wheels (and our Bimmers thick 245's)

The wheels on the side are the Civic SI 195's that are seen in my avatar picture.

alot of this is in another link, and they list skinny tires also. The bad part is the other link starts talking about square contact patches like they are required. I guess those skinny tires dont work lol maybe bike racers will go to fatter tires

Well, I guess I get to bump this thread yet again by reporting that, on my '05 F-250 HD 4x4 (reg. cab, longbed, 8200# GVW) 5.4L automatic, with 4.10:1 ratios, going from a 245/70R-17D to a 285/70R-17D did not cause a drop in MPG. In fact, it gained a skosh (though it not really outside a reasonable margin for error). Yes, I recalibrated the speedo to match the exact loaded circumference of both tires (the factory calibration was within a few millimeters for the stock tires) and am using the PID feature of my Edge Programmer to monitor instant and average FE. Oddly enough, I also lifted the front end about 2.5 inches to clear the tires and that had no measurable effect on economy by itself ( I guess going from a garage door to a 2.5 inch higher garage door...). Combined with the tires, which had approximately 1.1 inch more radius, dropped my rpms by 200 and my effective gear ratio to about 3.84:1. The engine seemed to like it. No loss and perhaps up to a 0.25 mpg gain. Seems counter-intuitive... but I'm not complaining.

Bear in mind that my ultimate goal is not the highest mpg. What I seek is to make my truck more efficient configured as I need it (as a work/farm truck that takes an occasional trip).

OK, instead of a donut, what about a motorcycle tyre? They have a varity for sizes and compouds, and speed ratings.
Also I have thought about using a vaccum guage or manifold pressure guage to measure thsi sort of thing. Higher vaccum at the same speed should mean more efficiency, no?

I'm wondering about the rolling resistance with a motorcycle tire. Aren't they softer than automobile tires to help traction?

Depends on the compound, touring compounds can be had with hard material to limit wear. Motorcycles tyres have a round tread pattern so the ebike can maintain a contact point on the tread when it leans over. this would mean less drag, although it also means they wouls wera more in the centre on a non-leaning vehicle. There also are sidecar tyres that have a flat tread pattern.

Trailer tires are going to be a lot tougher than passenger car tires. They have a very stiff sidewall to handle a lot of weight. Typical 5 lug trailer axle is rated for 3500 lbs. Thatd be like a 7000 lb car. Plus trailers typically dont have shocks so the tires are made to really take a beating. My 900 lb (empty) utility trailer had almost no air pressure in its 14" tires for quite some time, and I never knew it because the sidewalls retained their shape anyway.