What's the performance difference between 15 inch, 16 inch and 17 inch tires (all else equal)?

[Mad Roger]

It seems that Ed Pawlowski, Frank, and I are the only ones who are trying to quote from real articles.

Here's a quote from the LA Times on the subject which backs up the Cooper Tire assertion that there are too many variables involved but in most instances of larger tires, you lose fuel economy.

"all else being equal, bigger rims and wider tires are heavier, are less aerodynamic and create more rolling resistance."

But notice they talk about wider tires, which I was trying to keep out of the equation.

They do say that every tire in and of itself has a different fuel economy, which backs up what Cooper Tire said, which is that most cars won't get better gas mileage mainly because of the complexities involved (including the torque curve and resistance of each tire itself). "Others who upgrade to oversize rims and low-profile tires -- which are known to increase fuel consumption -- may not realize what a price they're paying".

[trader_4]

You keep saying "our intuition" when it's clear that both Bob F and I don't agree with your intuition.

That's not belief, it's fact. Assuming of course that you do change the gearing.

People generally

Maybe they do, but it's not correct. Following that logic, you could bog an engine down into the low RPM range and with it struggling, it would use less fuel, even with the throttle wide open.

While

But you're the one making the incorrect and simplistic assumption that less torque means less fuel used.

I didn't misinterpret anything. I gave you an example of where you can ride a bike up a hill at two different gear ratios and with the lower gear ratio, it will take less torque at the pedals, but the energy used is exactly the same. You then proceeded to throw another variable in, going up the hill at different speeds and the effect of wind resistance. The car example you keep bringing up, you're talking about different diameter tires, but driving at the same speed and how much energy is used. Changing the speed is just obfuscation.

versus what was quoted but that doesn't

"our" intuition again.

Wow, imagine that.

[rbowman]

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 look kewl.

[Mad Roger]

I completely misquoted the article.

I agree with you that they lost about 25% in torque going up in four inches, not one inch.

That's what the Cooper Tire article said.

"the vehicles which stand to benefit from a larger diameter tire are those that produce more torque than they need to in order to maintain speed...[but] There are just too many factors to consider to make general statements that larger or smaller tires are more fuel efficient."

This Consumer Reports report says that the OEM tires are designed for fuel efficiency where the replacement tires can have a few mpg impact, so, that seems to back up the claim that too many things change even if all you do is change the tire diameter.

"Consumer Reports recently tested a few all-season tire models with low rolling resistance and found that those tires can improve fuel economy by an additional one or two mpg."

[Stormin' Norman]

Trader, why do you feel the need to insult and pick fights with everyone you encounter on Usenet?

Are you unusually short? Did your parents not allow you to attend kindergarten? Never play team sports? Never served your country? Flunk out of kindergarten? Were you raised by howler monkeys?

Not every discussion has to result in a fight and insults. You need to learn how to play in the sandbox with others. I wouldn't be surprised if this has been a problem your entire life.

[rbowman]

Even worse news... Drag is a square, horsepower is a cube of velocity.

[rbowman]

Bling and performance have no correlation. Race cars generally have to meet specifications. For example NASCAR calls for 15" steel wheels. F1 is even more restrictive. The wheels RE 13" and all tires are supplied by Pirelli. Pirelli has several different models based on stiffness, wet/ dry, and so forth but they're all Pirelli. At one time Bridgestone was in but they were dropped. I don't know why. IndyCars run Firestone on 15" wheels.

I'm curious what race cars run 17/18/19" wheels.

[rbowman]

I would assume so. I run 14" wheels in the winter, 15" in the summer. The OEM size was 15". I had a set of wheels left over from the same model car when OEM was 14. The indicated speed is off with the 14" wheel/studs but I go by the GPS indicated speed anyway.

[trader_4]

I don't. But after a few back and forth's with some posters, enough is enough. And you do worse, getting nasty with them on the first retort, typically because they dared to do something you say isn't allowed, like mention Hillary negatively. You hit them with a sharp retort. Calling people "trumptard" is an example.

Go f*ck yourself hypocrite. How's that?

[trader_4]

You really think a reporter at the LA Times is an authority on tires and their effect on fuel economy?

[trader_4]

Note that you're going from 15" OEM to 14". I'm not sure it's safe to assume that you can almost always go up 1" in effective diameter, which is what he's claiming.

[Stormin' Norman]

You have a condition son, Hillary this, Hillary that. Tell the truth, have you ever gotten laid without paying for it? Don't respond, I know the answer......

I am crushed, your opinion matters so much to me.

[trader_4]

Stifle yourself! I made one sarcastic remark to the poster, after about

6 exchanges where he's going in circles, and I was accused of being nasty to everyone on the internet!

[Stormin' Norman]

Not the Internet son, "Usenet". Do you not know the difference?

[clare]

OK - first you need toclarifynwhatyou meen by larger, and all else being equal. Rim size larger, all else being equal means no change in speedo reading, ride hight, etc, and the only "performance" difference will be tighter handling due to shorter sidewalls, and possibly a bit of accelleration advantage if the tire/rim combination is lighter than the original, due to less rotational inertia.

Oversize tires, regardless of rim size, will change the effective gear ratio which, unless corrected for in the ECU or speed sensor (speedo gear) will make the speedo read wrong, and will also reduce accelleration because it will reduce the tractive force delivered to where the rubber hits the road. Conversely, smaller diameter TIRES will make a car accellerate more quickly from a stop because it increases the effective gear ratio. Oversized tires will also raise the center of gravity of the car, which can affect handling in corners and turns.

Oversized tires will also decrease braking power, because the "torque arm" is longer, increasing the number of "ft lbs"applied to the brake.

[clare]

Not necessarily less gasoline if it makes the engine work harder (which it will) by enough to counteract those savings (which it often will, under some cercumstances of speed and driving conditions)

[Mad Roger]

I'm not looking to argue what he said and she said so I won't say what you said. I'll just keep looking for the answer but it seems pretty universal what the answer turned out to be (which wasn't what I originally thought).

This article "The Drawbacks to Bigger Wheels"

concludes by saying "there's undoubtedly a negative correlation between [larger] wheel size and fuel economy."

[Stormin' Norman]

ROFL - "Stifle", who dug up Carroll O'Connor and gave him access to Usenet?

"Stifle yourself Edith, dummy up"

- Carroll O'Connor as Archie Bunker, All in the Family, 1971 - 1979

[clare]

If the tire diameter is increased by one inch to cause the reduction in tractive force, the suspension hight CAN NOT remain unchainged If the tire hight /diameter is increased, there is MORE cushioning if the rim size does not change, and the same if the rim and tire diameters change. The unsprung weight can go up or down, depending on the weight of the tire and the rim.

In other words, you can't take points from 2 different articles discussing 2 different things and put them together and draw these kinds of conclusions.

[clare]

You need to define "all else being equal"

IF it is only the rim size changing, all else being equal, the rolling diameter of the tire , by definition, has not changed.

Smart people USUALLY try to keep the rolling diameter the same, but nobody said the "tuner kids" were smart.

That said, I replaced the stock 14 inch tires and rims on my 1996 Ford Ranger with the 16 inch tires and rims from a later model Ranger-based Ford Explorer. They are "significantly" larger and required changing the speedo gear ( making the speedo more accurate than it was with the stock tire/gear combination) and I also had to install larger diameter front brake rotors to maintain stopping performance. With a 4 liter V6 it had more than adequate power with the 3.55:1 final drive ratio, the larger tires make it behave more like it has 3.23:1 gears with the small tires. Still adequate power, and if driven right, I CAN get better mileage, and running lower RPMs on the highway DOES make it a bit quiter. The ride is a bit stiffer on bumps, but I don't feel all the little lines and cracks in the pavement, due to a combination of more unsprung weight and more cushioning from the tires.The truck does not acellerate as quickly from a dead stop as it did with the small tires, but then again, it doesn't spin them as easily either - - -