What's the *performance* difference between 15 inch, 16 inch and 17 inch
tires (all else being equal)?
Let's say that the stock wheel is 16 inch and let's ignore sheer looks, and
the fact the speedometer will read differently, and let's ignore obvious
non-performance wheel-well fitment issue since they're obviously not
What *performance* changes will the one inch larger or smaller tire cause?
Basically, I'm wondering why people almost universally want larger wheels,
where all I'm asking about are what the performance tradeoffs are.
Thank you for that article, where the 3 main takeaways are...
"If the wheel diameter increases by one inch, the height of the tire
should decrease accordingly to compensate, in order to keep the overall
diameter the same."
"With larger wheels and lower profile tires ?X and the resultant shorter
sidewalls ?X they??re stiffer and there??s less of an air and rubber cushion
than before, increasing the chances that hitting a large pothole could
damage the tire, wheel or both."
"An 18-inch tire, for example, will probably weigh at least a couple of
pounds more than a 16- or 17-inch tire. That could also be true of a larger
To summarize what the article said for moving to larger-diameter wheels...
+ The overall vehicle suspension remains at the same ride height
+ Tire air "cushioning" is greatly reduced
+ Unsprung weight goes up appreciably
I agree that people do things for looks alone, but what is strange is that
there doesn't seem to be a single beneficial performance impact of an
overall larger diameter "tire-and-wheel assembly".
I wasn't expecting huge performance gains, but I would have expected at
least one or two benefits - and not all negatives based on the two articles
If the diameter of the wheel and tire assembly increases by one inch
overall due to the one-inch increase in rim size - and assuming everything
else is kept equal in materials and aspect ratio and tread width - then the
two articles stated...
+ The engine delivers ~25% less driving force to the wheel contact patch
+ Which results in a decrease in acceleration
+ And which decrease in fuel economy (presumably at all times)
+ And unsprung weight goes up by a few pounds
The main astounding number is the fact the torque felt at the wheels is
astoundingly less for a single inch in overall diameter change.
Presumably that torque loss happens at all speeds (why would it not?) so
that denies us the one intuitive performance advantage of highway MPG.
On Wed, 19 Jul 2017 13:36:23 -0400,
I'm having a hard time fathoming that there are zero performance benefits
from putting a one-inch larger diameter tire-and-wheel assembly.
Most things done for "looks" have a semblance in reality, I thought.
For example, low-profile tires give better steering response, so, that's
why (I presume) I see SUVs with super low profile tires (because they want
to look like a better steering vehicle).
Likewise a wing in the rear has a genesis in actual aeordynamic theory so I
understand that people want the look of a fast car (although at 60mph, a
wing is probably just for looks).
Same with dual exhaust, or a hood scoop, both of which allow the engine to
bring in and shove air out easily (which is essentially what an engine
So the whole performance-look thing is a bit confusing to me.
Unlike the examples above where the look is to replicate situations where
there is actually a performance gain, if there are no performance gains to
larger wheels, then how does the *look* of larger wheels look like you get
There are little to no performance gains for any of the above. It is
all about looks. Duel exhausts? Ever look at the pipes underneath?
They may end up with two termination points but that is after it all
goes through the same single pipe. Duals go back to the V-8s in the
A car manufacturer sends me (and many others) an occasional survey.
They may ask what I think looks better. Two pipes on opposing sides
versus two pipes next to each other on one side versus two pipes in the
center. They never ask what I think of performance, mostly style once
in a while ergonomics on control location but that is for style of the
Its all about style. If people don't like the looks they won't go to
On Wed, 19 Jul 2017 11:38:24 -0700 (PDT),
Maybe I'm wrong that people try to replicate an image of speed and handling
(e.g., why do people put M3 badges on a non-M3 bimmer then?).
Anyway, I just want to know what the performance impact is of a larger
diameter change of one inch.
This Car and Driver article tries to answer the question:
Effects of Upsized Wheels and Tires Tested
"What?s immediately apparent from the results is that as the wheel-and-tire
packages get larger and heavier, acceleration and fuel economy suffer.
Neither is a huge surprise, but we measured a 10-percent drop in fuel
economy and a four-percent degradation in 0-to-60-mph acceleration from the
15s to the 19s"
Taking this a little further even in the same size aftermarket alloy
wheels are often heavier than OEM pressed steel wheels with the
resulting increase in unsprung mass and rotational inertia. But they
On Wed, 19 Jul 2017 18:56:18 -0000 (UTC), Mad Roger
http://www.therangerstation.com/forums/photoplog/index.php?n !83 for
what my Ranger looks like with the "big boots" on.
If I drive very conservatively I CAN get a bit better mileage than
with the original small tires, but generally speaking, in normal
driving there is little if any improvement -and around town, it is
slightly worse. The truck works harder every time it starts from a
stop or accellerates at low speed. I'm willing to put up with that on
a 21 year old truck with about 350000km on it, to have the "look" I
wanted. It is not a "performance" look - - -
On Wed, 19 Jul 2017 19:20:49 -0400,
I'm just curious how close do you think you can get to "accurate" gas
mileage calculations using the classic odometer plus fill it up to guess at
the gallons used method?
I've read that nobody can accurately get the sig figs closer than +- 1 mpg,
despite the fact that most people I've seen do it try to calculate it down
to the tenth or even hundredth of a gallon, which, even for computers, is
impossible given there are no controls.
So 20mpg is really from 19mpg to 21mpg, which makes calculation difficult
(when I was looking up the wheel size stuff earlier today, Consumer Reports
said as much so that's why I'm curious how close you think you can get to a
repeatably precise figure (yes, both repeatable, and precise).
On Thu, 20 Jul 2017 01:45:19 -0000 (UTC), Mad Roger
With my scanguage calibrated to my GPS, over a 2 or 3 tank run I can
be accurate to tenths
I used to have a gas milage tester that could be accurate to way less
than a tenth - fuel consumption measured to within less than a cc.
With the fuel mileage rig I had (for carbureted vehicles) you could
see the differnce made by changing tire pressure by a few PSI if the
wind didn.t change. You could see the difference from winding down a
On Wed, 19 Jul 2017 22:59:45 -0400,
Take everything I say with a grain of salt because I'd have to dig up the
references of where I got this idea that even the EPA can't get better than
4% (as I recall), and they don't measure volume (since that's inaccurate).
They measure weight. And they used, as I recall, plastic bags filled with a
known *weight* of fuel.
In addition, they ran on test course, and they repeated the tests.
And even then, they couldn't get better than 4% as I recall.
Unless I dig up the reference, that's all hearsay, but, as I recall, nobody
is going to get accuracies and repeatabilities anywhere near decimal places
at home if they're not repeating the tests under extremely well controlled
circumstances and weighing the fuel consumed.
On Thu, 20 Jul 2017 08:50:37 -0400,
Being the progeny of two PhD chemists, I'm well aware of density, but are
you sure every mom and pop who "claims" their spectacularly "accurate" 22.9
mile-per-gallon numbers understands what you and I both know?
Do they realize that you have to keep the *entire* test at the same
atmospheric conditions, and where the typical mom and pop doesn't do that
for an entire tank of gas (which might take a week to use up during which
time the atmospheric conditions change greatly).
Do they even know what "test conditions" they're testing and do they run
Point is, my assertion (as yet unproven) is that the mpg figures with a
decimal point in them that people "say", are an indication of their
ignorance of what they measured.
As for what accuracy "can" people measure with the typical tripmeter
divided by pumpmeter test, I opened a separate thread on that topic because
it's a valid question (where I added the science & car guys).
What is the realistic accuracy & precision of typical consumer MPG
calculations (tripmeter miles/pump gallons)
While I question pop's back of an old receipt calculations, the question
isn't what the mpg would be for a known quantity of fuel at STP, but how
many real world miles were traveled with that quantity.
For example, when I was driving a truck I would often get close to 7 mpg
going east on I94 in North Dakota. Going west with the same load I would
be lucky to get 6. If you don't know why you've never been to North
Dakota. However, as far as planning my fuel stops, standard atmospheric
conditions didn't count.
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