Ugly MPG surprises after tire / wheel upgrades?

I'm contemplating upgrading wheels and tires on a new LX 4cyl 5M, and
the Tirerack surveys really don't offer much info regarding fuel
economy of tires.

I'd rather not give up more than 1-2 MPG in the search for better
handling, ride or other performance aspects, so I'd like to hear from
people about their MPG after changing OE tires.

Does MPG typically fall when changing to a 16, 17, 18, etc., wheel or
is it more a function of the specific tire chosen?

What combination of larger wheel / tires produced a relatively small
drop in fuel economy?

At the same OE size, do any tires perform better than the stock
Michelins for fuel economy?

Thanks in advance.

-- CL.

+-----------------------------------------+
| Charles Lasitter | Mailing / Shipping |
| 401/728-1987 | 14 Cooke St |
| cl+at+ncdm+dot+com | Pawtucket RI 02860 |
+-----------------------------------------+

 

On my 2003 Civic Hybrid, I bought "normal" tires, instead of the low
rolling resistance tires that were on it originally. My mileage seems to
have dropped from 46 to 44 overall.
I think part of this is due to the different rolling resistance, but it
must also be attributed to higher driving speed on windy roads, now
that I have better traction and handling.

 

wrote in

Now this is an excellent point. It's really hard to make 'all other
things being equal' as if the car was being driven (before and after)
like a robot, not changing the driving habits (lead foot) in response
to a more fun car ...

OK. I may have to make a bit larger allowance in fuel consumption so
as to take the "fun factor" into account.

Still need to hear about _particularly_ unfortunate surprises ...

-- CL.

+-----------------------------------------+
| Charles Lasitter | Mailing / Shipping |
| 401/728-1987 | 14 Cooke St |
| cl+at+ncdm+dot+com | Pawtucket RI 02860 |
+-----------------------------------------+

 

this is of related interest, its not specific to your honda, but as a
comparison its useful information
http://www.teknett.com/pwp/drmayf/cobra.htm

basically it has some data on wind resistance and rolling resistance vs
speed

cheers.

 

All I've done is switch from my stock Turanzas to stickier Azenis.
Can't say I've noticed a clear difference in mpg.

And even with really heavy tires/wheels, physics says the added
inertia is just not big compared to that of the vehicle. So, I
wouldn't sweat it.

But if you are in search of better handling, I'd stick with your
stock size and concentrate on the rubber.

 

I've found that the biggest impact on the car's consumption rating is the
seasonal additives in the fuel. The winter fuel seems to have about 7%
impact on fuel consumption. In the winter, I used to get about 600km/tank
and now it's up to 650km/tank. My 185/65/14 winter tires return about the
same amount of consumption as my 205/50/15 summer tires. If most of my
driving was in the city, the summer tires (mated to light weight rims) would
return about 2% improvement over the heavier/rougher winter wheel. But,
since most of my driving is highway, there isn't much of a difference in
fuel consumption between the different wheels. I'm fairly positive it's the
gas that's causing the biggest variant on fuel consumption, but it's tuff to
prove. I can understand a 3% decline in fuel consumption from the winterized
gas, but 7% is too much.

Pars
98 Civic Hatch (230,000km)

 

(Dave) wrote in @twister.nyroc.rr.com:

What car were the Turanzas stock on? Your tire / wheel size, and
were they LS-V, T or whatever?

One guy at the 'Rack said that tires made little if any difference in
fuel economy, and that lighter wheels would be more likely to
influence fuel economy.

This is why I'm a bit confused about just how to persue better
handling or ride. One way might be to conserve $$ by sticking with
steel wheels and dumping it all into the best tire in the OE size.

Other people go upsize in wheels with a shorter sidewall, and they
say it gives them better responsiveness, even if the type of tire
(all-season, high performance grand touring) stays the same.

Others still favor changing wheels AND going to a max / ultra high
performance tire, which would have the lower profile AND a type of
tire built for maximum cornering.

One thing I'm really interested in figuring out is where the law of
diminishing returns kicks in when in persuit of handling or ride.

Some people at the Tire Rack have suggested that with wheel size it's
both linear and incremental. You get a very modest handling
improvement for every inch increase wheel size, versus, say, a large
change from 15" to 16", and much less from 16" to 17", or 17" to 18".

-- CL.

+-----------------------------------------+
| Charles Lasitter | Mailing / Shipping |
| 401/728-1987 | 14 Cooke St |
| cl+at+ncdm+dot+com | Pawtucket RI 02860 |
+-----------------------------------------+

 

i went that route. from 185/65-14 OEM firestone FR680s to 195/60-14 BFG
tourings. big difference in handling and comfort. havent crunched the
MPG numbers, but i dont think they changed noticeably. definately worth it.

 

Another significant factor is air temperature. Colder winter air
means lower mpg for numerous reasons:
Higher air density -> greater air drag
Higher air density -> reduced throttle setting for a given power
-> greater (air) pumping losses.
Usually longer idling time -> more excess fuel consumption
Slower to warm up -> higher oil viscosity -> more oil windage,
friction, pumping losses

But it also means more power

 

205/45-16 stock size of '01 SE. I went for the same size Azeni's.
Well actually I think they are 10mm wider. Don't recall the stock
Turanza model number but they are very expensive 3-season tires
that are about the only ones rated "grand touring". They are
almost universally panned by the Miata community.

Both contribute. And both to a pretty small extent. My wheels
weigh about 20 lbs, my tires about 20 lbs. So, why would the
wheels contribute but the tires not? Frankly, there's a lot of
conventional wisdom, and not all of it is right.

There is no simple answer. Though all the above is at least
generally correct.

It is true that a shorter sidewall will generally be stiffer,
result in less squirm, and thus be more responsive. And usually
harsher.

A wider tire allows for a greater contact patch which gives
greater ultimate grip. And you may need a wider wheel for that
wider tire.

Some talk about a greater wheel OD giving a greater contact patch
(picture an infinite sized tire and the contact patch becomes a
straight long line). But I think (no prood) this effect is very
minor. First of all, most of the time when you +1 or +2, you stay
with basically the same tire OD trading off short sidewall for the
increased wheel OD.

Many in the Miata community swear by small wheels which, all else
constant, are lighter. And they attest to great gains in
performance. I think a lot of it is power of suggestion (at
least for accel). Though the reduction in moving mass will be
beneficial and I honestly do not know the magnitude of this
effect. Plus, small wheels lead to much cheaper tires!

It all depends on what tradeoff you want, how much you want to
spend, and the tires available play a major factor in that.
There is no clear cut rule to go by. Best to ask for experiences
as you did. Go to miata.net and read through the "Tires & Wheels"
forum. If you have steel wheels, I assume you have an older Miata
with 14"? Then you are fortunate in that these tires are
super-cheap (though performance types are limited). I'd consider
14" alloys for looks and a bit lighter weight. And perhaps Azenis
for very high 3-season performance. Another very popular tire is
the Toyo TS-1. But again, check size availability. I might
consider +1 to 15" for better looks and a shorter sidewall.
Certainly no more than 16". UHP tires are a lot more expensive,
though they vary. But a UHP Azeni in 14" is dirt-cheap!

We have a general industry trend to bigger and bigger. It's 99.9%
driven by looks.

But check miata.net and you'll find more info, and opinion, than
you probably could want!

 

FWIW, I remember reading a Road & Track article ~10 yrs ago or so when
the big wheel thing was getting popular. They did a study IIRC with a
BMW M3 and compared handling, ride quality, noise, etc. with stock, +1,
+2, and +3 sizes wheels and tires. They pretty much confirmed your
theory of incremental tradeoffs with +2 being about the highest they'd
go in that little experiment.

Wish I could provide more info about that issue.

 

(Dave) wrote in @twister.nyroc.rr.com:

My searches have taken me to Miata groups entirely by accident, and
they are a fanatical bunch -- with lots of info, as you suggest.

-- CL.

+-----------------------------------------+
| Charles Lasitter | Mailing / Shipping |
| 401/728-1987 | 14 Cooke St |
| cl+at+ncdm+dot+com | Pawtucket RI 02860 |
+-----------------------------------------+

 

wrote in

This +2 is what I'm getting a feel for myself. At the moment I'm
looking real hard at this combination:

Ultra High Performance All-Season
215/50WR17 Avon Tech M550 A/S

The tire is gaining a dedicated following from the comments. And
while the scores represent composites for all sizes of the tire as
tried on all vehicles, it's a VERY affordable #2 in it's category:

http://tinyurl.com/4eknl

And purely for economy, this 17" wheel looks pretty good to me:

http://tinyurl.com/6wq5a

Thanks for your thoughts.

-- CL.

+-----------------------------------------+
| Charles Lasitter | Mailing / Shipping |
| 401/728-1987 | 14 Cooke St |
| cl+at+ncdm+dot+com | Pawtucket RI 02860 |
+-----------------------------------------+

 

The factors you mention about additives for winter fuel and winter
blending of fuel are well know for their impact on winter fuel
economy. Thank you.

I was doing more searches last night and got into what is a pretty
important area of "rolling resistance", which apparently more of a
factor in city MPG (where wind load is low) versus highway speeds
where wind loading becomes the 900 pound gorilla.

Once you get past the skinny/tall/hard OE CAFE tires, rolling
resistance for tires seems to be a function of sidewall flex, tread
flex, contact area, and wind resistance of the tire itself. And more
stuff I can't remember ...

Rolling resistance isn't that hard to measure in theory. I just wish
Tire Rack had the numbers for what they carry. But that info might
tend to depress wide wheel and tire upgrades ...

-- CL.

+-----------------------------------------+
| Charles Lasitter | Mailing / Shipping |
| 401/728-1987 | 14 Cooke St |
| cl+at+ncdm+dot+com | Pawtucket RI 02860 |
+-----------------------------------------+

 

True, especially for those cars that only undergo short trips. In my case,
the car is constantly running/moving and I'll go through a tank of gas in
couple days, so the impact from cold startup isn't as drastic.

Pars
98 Civic Hatch

 

My 195/50/15 Toyo Proxes FZ4 seems to have very good rolling resistance for
performance oriented tires. They also last forever, but tend to get noisy
when hey get old (frequent rotation would be important on this tire). Also,
they have very solid side wall (at least the 50 series does), which is
useful on a tight suspension. The solid sidewalls also help during a blow
out...it almost act like run flat tires. One time, a nail blew-out one of
the rear tires while I was doing some radical driving at 150km/hr. I felt a
tugging on my steering wheel and thought something happened to the
suspension/alignment. So, I reduced my speed to 100km/hr and continued along
my merry way. After I exited the highway (5 km later), I decided to pull
over and inspect the car. I was shocked to find that I was driving on a
completely flat tire. When it comes to tires, I'd put rolling resistance way
down the list, especially when you consider steering feel, road noise and
safety.

Pars
98 Civic Hatch



CL.

 

Charles, of course you have to let us know what package you upgrade to.
I just bought OEM hubcaps for my "new" '92 Civic EX and will put the $
into parts. Sigh.