These guys just use the " wings " for advertising .. :-)
I remember the super-modified races at Flamborough in the early 1970's .. their brakes were glowing red at the end of the feature ! I don't know how they avoided fires ? The cars were akin to go-carts - but with big modified V8 engines.
Maybe MadRoger could scientifically analyse the wheels - - different sizes - IIRC -
- left vs right due to the banked corners ! :-)
John T.
Depends on the rims. The 16 inch torque thrust rims on my ranger weigh less than either the 14 inch "deerfoot" alloys from the factory OR the stock steel wheels.Yess, the 235/70 LT tires DO weigh more than the
205/75 passenger tires that came on the truckThat depends ENTIRELY on the particular vehicle (some will get better mileage, some worse - generally the higher powered cars gain, the lower powered loose) and how the car is driven (usually an improvement in "sane" steady speed generally level driving, and generally worse in city or stop/start driving, or "leadfooting" on the highway)
I'll admit putting the 16 inch torque thrusts on my Ranger was "mostly" for looks - the 14 inchers didn't look like they belonged in the large wheel openings, particularly with the higher 4700 gvwr suspension the truck came with ( it sits about the same as a 4X4), and the rather rare 16 inchers became available at a good price - - -
In many cases yes, but also in some cases, NO. There are vehicles where a half inch change in tire radius will put the edge of the tire in contact with the strut spring seat. Particularly when the larger tire is also wider (and when going for looks OR performance, it almost always is) Then when they put the bigger wider tires on and also lower the suspension, they often use a different offset rim to fix the strut interference problem - and then the tires hit the wheel openings - so they stiffen the suspension or pot suspension stop blocks in - and sometimes the tires still smoke on the wheelwells if they don't slow down enough for a bump.
It takes some "engineering" to do a proper job of modifying suspension components - including something as "simple" as putting on bigger wheels - - - .
When it has 1000 plus horsepower to the rear wheels, that decrease in torque CAN mean he doesn't burn the tires off as easily - and on a drag car, the tire diameter can be adjusted to get the car to launch better, and to top out it's speed at the right point on the track
It CAN be true though at certain speeds, with certain engines, because you drop the RPM of the engine, and if that drop gets the engine "off the cam" the torque output of the engine suffers , in some cases a WHOLE LOT.
"tuner kids"
Cheap old farts notwithstanding .. When I can't avoid visiting the city - I enjoy watching the Kids with their lowered cars trying to go into/out of a driveway ... duh. Really ? At what point does reality kick in ? John T.
see
I REALLY doubt it was "uncorrected" data, and the shiftpoints need to be reprogrammed (if it is an automatic) or shift points changed by the driver to optimize either mileage or accelleration. It is NOT a simple calculation to determine which way mileage will go, or how to drive the modified vehicle for best results.
When I first asked the question, oh so long ago (this morning), there was so much I didn't know that I *assumed* I could factor out the rubber, the gear ratios, the change in torque curve points, etc but it turns out that the best summary seems to be the Cooper Tire summary.
When you factor in all the variables (seemingly random unless you design them in), there's almost no performance gain to larger overall diameters, and in fact, there is plenty of ways to get decreased performance.
To get to the answer to the question was really all I had wanted, where I naively assumed we could easily factor out the variables.
When I first asked, oh so long ago, I had not considered that the "right" way to upsize wheels is to "downsize" the aspect ratio such that the overall diameter remains similar.
Whether someone does that or doesn't do that greatly affects the end result, it seems.
So the end diameter is a factor that must be taken into account.
Yes. It turns out that, in the case of actually increasing the overall diameter, the motorhead would be very hard pressed to gain anything in performance. It's apparently possible (mostly due to torque curve realities) but if left to randomness, the reliable articles said that "most cars" would see no performance gain of any form.
The number of variables change everything depending on how you tweak the variables - which is why I was trying to keep the change only to the overall diameter alone.
I don't know how Car & Driver compensated for the things you guys talk about, but what I find interesting is that they were not in the least surprised that they had a relatively huge decrease in MPG when they ran their tests.
Seems like they were not expecting an increase in MPG, that's for sure.
Even worse, it could be argued that "standard methods" of calculating mpg are off by a factor of about a mile per gallon either way, which means that, say, 20mph is anywhere from 19mpg to 21mpg.
Certainly anyone who calculates mpg with decimal places is ignoring sig figs in their measurement capabilities in that nobody does a reliable test loop (and even those who do, in Austin Texas for example, get sig figs not much better than that).
WARNING: I have to look up if challenged the actual reliability but I "assume" that most people think their measurements are infinitely more accurate and repeatable than they really are. If it's not as big as +1 and
-1 mpg accuracy, it's not that far off. Certainly there is no decimal place in typical mpg calculations by a consumer.
Originally, the main reason for trying to limit the number of variables was to figure out what the performance benefit was po only changing the diameter of the assembly.
Turns out there is no performance benefit, and, worse, the other facts that I was hoping to not cloud the issue play a LARGER role than does the one inch change in overall diameter.
So, it turns out, you can't eliminate the other factors, but, if you could, the only factor that plays a major role appears to be the torque curve.
However, everything depends on whether you compensate for the extra inch by lowering the rubber, where the original question didn't take that into account (because it didn't occur to me since I didn't know the problem set then as well as I know it now).
It seems that the Cooper Tire article is the most accurate and most in line with what the rest of the reliable references said, which is that if you change the overall diameter, you'd be lucky to get a performance boost, and you'd only get that (realistically) if the torque curve was affected in your favor - but - other factors play as big a role, at least combined - such that it would be a crap shoot - unless - you *changed* a bunch of other things (such as gear ratios).
Shooting down one reference that says what the others said (particularly the tire manufacturers' article and consumer reports and the cartalk guys), doesn't shoot down them all.
I referenced in this thread all the reasonably reliable articles I can find.
Every one said essentially the same thing.
If you want to say the opposite of what the quoted references said, that's fine - all you need to do is find a reliable reference that supports the alternative view that you intimate is "more better".
I've read basically a dozen seemingly reliable articles where you are correct that it's hard to impossible to cross reference their claims.
However, almost every article maintained three key concepts, which are the takewaways.
Of course you can put carbon fiber rims on to replace oem steel rims and then one can argue that the "larger" carbon-fiber rims weigh less - but apples to apples - if you change the diameter upward using the same material rims, the weight should always go up.
However, in the articles I read, I wasn't sure if the weight would always go up if you kept the diameter the same, and only increased the rim diameter, since you're essentially replacing rubber with steel.
Does anyone know if, apples to apples, you increase a rim by one inch, whether the decrease in sidewall rubber compensates enough to counteract the gain in rim weight?
Apparently this is an age-old argument sort of like the "what oil" or "blue or green coolant" arguments that shadetree mechanics always seem to have an opinion on that isn't based in any science.
It seems from most of the referenced articles that, realistically, there's no change in gas mileage for an inch change in diameter simply because of all the other factors involved in the real world.
However, if it was truly an apples to apples comparison, with only the one inch diameter gain, and the tire not compensated for in overall size, then the torque factor kicks in as the most important, with only cars with spare torque faring well - the rest faring poorly.
That's what the references said anyway.
It seems that the torque curve is almost everything when it comes to adding inches to the diameter of the tire and wheel assembly.
Without knowing the torque curve, there's no way to predict the result, but most accounts I referenced said that your chances are greater that you'll lose mileage than you'll gain it.
But, everything depends on the variables, which I tried to remove in the original question - but - they return with a vengeance because the variables determine whether or not you gain mileage - not the diameter of the end result.
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).
I searched for that thread.
Is it this one? Why 20" wheels, by Micky, May 8, 2017
If so, I'll read it to see if there was more accurate information there than here.
HomeOwnersHub website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.