Fuel Mileage Drop since Installing 225s on Cutlass Supreme

[chevelle3504speed]

I replaced my 215/60/16s with 225/60/16s this time on my '95 Cutlass Supreme 4-door 3800 supercharged and am not sure I can live with the fuel mileage drop. I am down 3 mpg on average since this tire change.  I prefer the appearance of the 225s but am strongly contemplating replacing them with 215s considering the drop in fuel efficiency.  Has anyone else encountered this?

 

Thanks,

 

Andy

[55trucker]

Not sure that makes any true sense,

 

the 225 is not just a wider tire but also a taller tire by 1/4",  that will throw off your speedo by a small fraction, you will be moving faster than what the speedo states you are moving at, 65 mph on the speedo is actually 66.

 

are you attempting to do this calculation in the middle of the winter?

[Imp558]

That's only 1/2" difference, not a substantial difference. Is this tire a lower pressure than your last ones? I picked up 2 MPG when I put my Yokohama tires on because they were a higher pressure.

[55trucker]

The 225 tire is 1/4" taller across the total dia with respect to the shorter 215, that's a 1/8" taller radius gain.

[Imp558]

According to 1010tires.com the 225/60/16 is 26.63" diameter and the 215/60/16 is 26.16" diameter, that's where I got the half inch difference.

 

82.12" and 83.66" are circumferences for the two sizes.

[55trucker]

No harm no foul, my chart reads as 26.2 vs 26.6.

[vipmiller803]

Are the tires the same make and model?  How old were the old ones? Old tires have stiffer rubber, which causes bad traction, blowouts, etc, but also has the side effect of decreasing rolling resistance. Also, the new tires may be a softer compound good for lots of dry traction. To make matters worse, you are increasing the section width and height of the tire - all working against mpg. 

 

Consider that putting a new 215 tire may not put you back at your original mpg.

[Galaxie500XL]

Not sure that makes any true sense,

 

the 225 is not just a wider tire but also a taller tire by 1/4",  that will throw off your speedo by a small fraction, you will be moving faster than what the speedo states you are moving at, 65 mph on the speedo is actually 66.

 

are you attempting to do this calculation in the middle of the winter?

Um...if your speedometer now reads less than your actual speed...so does your odometer...you may be driving farther than indicated by the odometer, which would be reflected in lower calculated fuel mileage.

 

How far off would the indicated speed/distance be with tires that have a larger circumference? Find that, and you’ll probably discover the source of your lower fuel mileage

[Galaxie500XL]

Did a little math.  The circumference change means an indicated 65 is actually 68.6 mph....in other words, your speed/distance is being underreported by 5.25%.

 

If you travel 300 actual miles on the taller tires, the odometer is only going to indicate you've traveled 284 miles.

 

300 INDICATED miles on the odometer is actually 315.75 miles travelled..in other words, for every 100 miles your odometer now reports, you actually travelled 105.25 miles.

 

You're going to end up with fuel mileage calculations that are lower, because you've travelled farther than you think.

 

The question then becomes, is the difference in the old mileage vs the new mileage around 5%?  If so, you've found the problem.

[chevelle3504speed]

RIghto, thank you guys for the feedback.  I have changed manufacturer of tire.  The 215s were Yokohama Avid Envigor, and the replacement 225s are Pirelli P4 Four Season Plus.  215s were put on in September of 2013 and were pretty well worn out when I pulled them off.  Fuel mileage with the 215s was right at 26 flat, while the 225s give me about 23.3 on average.  By my math, that's roughly a 10% difference.  So perhaps I'm losing 5% as a result of this tire change.  

[oldmangrimes]

I'm sorry, I just have to say that I misread the title of this thread as "Fuel Mileage Drop Since Installing 22s on Cutlass Supreme" and I came in here ready to see pics of a w-body donk rolling on 22 inch rims.  Darn!

 

But speaking to the ACTUAL original question, are you changing tire size but keeping everything else the same (tire manufacturer, tread pattern, psi, rubber compound, etc.)?   

 

I would also be suspicious of the pressure exerted by the drivers foot on the gas pedal.  The wider tire might encourage a few tests to see if launch traction increased, which would decrease mpg.   

[Imp558]

The Envigor is a very fuel efficient tire being that it's higher pressure. I have them on 2 different cars and love them.

Pirelli P4 have a max pressure of 44LBS which should still reduce rolling resistance.

 

We're supposed to run the tires at the car manufacturer's recommended pressure but I always go with what's on the tire so they wear and perform properly.

[chevelle3504speed]

Haha, no 22s here.  I have changed tire manufacturer and compound.  I am running 35 psi in these new tires.  I have not consciously adjusted my driving style since installing these tires.  In-town mileage has remained basically unchanged (19-20 on average); it's namely the highway mileage that has suffered.

 

Andy

[Imp558]

Try 45, they'll handle more but I like them there. The higher pressure will reduce them laying down on the sidewall on a deep turn. Mine took a corner like a basketball player.

[bluecalais79]

I second that one, my max press on my 225-60-16's is 44 and I run them at 41.5 cold. I have Uniroyal Tiger Paw Touring tires on mine, not the best but the price was right.

[55trucker]

At max pressure or near max I would have to believe that the tire would crown in the centre causing the tire to prematurely wear there unless the vehicle is continually loaded to capacity and also at that pressure the tire would cause the steering to go extremely light and also lose traction.

[Imp558]

Well, tires are engineered to be a certain pressure now and a lot has changed.

The Envigor has a max pressure of 55 LBS which was a little too much for me to be comfortable with but I run them at 45 and they're responsive and roll great.

These are also going into their 4th season which is crazy since they were only like a 40,000 mile tire so they've worn better than expected at that pressure.

[55trucker]

My last recent purchase was a replacement set of Radial T/A's for my truck, those tires still use *old* technology, I dare say that when the tires go on the GP something of a *new* technology tire will go on.

 

50lbs must ride like a rock.

[bluecalais79]

When I first bought those Uni's I was skeptical of going that high up the bar but the shop had them at 36 warmed up and the car flopped around like a carp out of the lake. I did make a typo above though, I run them at 40.5 cold not 41.5 and that does the job.

[Imp558]

50lbs must ride like a rock.

 

Yeah I wasn't willing to find out, or how violent a blowout would be, 45 was scary at first but no problems yet. I'll be replacing my Envigors with Envigors.

last year I nicked a curb with the sun in my eyes and took a little chunk out of the sidewall on both right tires, the left tires are worn slightly different so I'll end up replacing all 4 for the GS venture and then using the 2 used ones as spares for both cars.

I don't even know what I'm running for wheels on the GS, my X-laces won't clear the second gen stuff supposedly so I'll probably grab a set of steelies and save for something aftermarket.

[chevelle3504speed]

Thanks again for the feedback here.  I will try running a bit more pressure and see where that gets me, but previous experience has led to to a similar to conclusion as stated by 55trucker.   I'm currently running 35 psi and am hesitant to run much more than that for fear of premature wear. I've got a full-size conversion van that I ran 40 psi in (had 255/70/15s on it), and the centers of the tires wore excessively relative to the rest of the tire.  I have run subsequent sets of tires at 35 and the tires have worn much more evenly.

[Imp558]

It has more to do with what is proper for that individual series of tire. Running a lower pressure could wear the outsides of the tread more rapidly. We should follow the tire manufacturers recommendations for best handling and wear ability.

[bluecalais79]

As luck would have it the rain over the weekend cleared away the road salt and it looks like I'll get to drive the Cutlass for the next few days. This is the coldest weather yet that I've driven the car & the Uniroyals are hacking it just fine. All in all for a car with the soft ride package FE1 I don't think it will be worth the investment getting more aggressive tires when spring rolls around, I think I'll just keep what I have on the car. With the exception of the strut brace and the thicker sway bar I have on order, there really isn't all that much else I plan on doing, maybe some new KYB's in the front and a 4-wheel alignment and call it a day.

[Schurkey]

The Envigor is a very fuel efficient tire being that it's higher pressure. I have them on 2 different cars and love them.

Pirelli P4 have a max pressure of 44LBS which should still reduce rolling resistance.

 

We're supposed to run the tires at the car manufacturer's recommended pressure but I always go with what's on the tire so they wear and perform properly.

What's molded into the sidewall of the tire is the MAXIMUM inflation that the tire construction is rated to withstand.  It is not the pressure that provides even tread-wear and maximum traction given the specific weight and weight distribution of YOUR VEHICLE.

 

I'm surprised you're not burning the center of the tread off your tires.

[Imp558]

This year I put the snows on the SSEi, last year was so mild I didn't bother. These are run at 45 lbs.and to my untrained eye appear to be wearing evenly.