[mschubb]

Still driving my 1999 Forester with barely $1000 spent on repairs in almost 15 years! (Excluding reg maintenance, brakes, tires, etc.) But it finally needs major engine work, so thinking about a 2014 Forester.

What's the deal with wheels and size? What are the benefits -- other than esthetics -- of 5-spoke aluminum alloy over base model steel? And what do you get when you upgrade 17 x 7.0-inch to 18 x 7.0-inch wheels?

Mileage? Handling? Ride?

Thanks in advance for help with such a basic question... seems like something I should already know, but don't.

 

[YoGeorge]

Auminum wheels look better and are usually a bit lighter than steel wheels, making for slightly better acceleration, deceleration, and better damping by a given set of shocks.

As for moving from 17" to 18" wheels, it is all about looks IMO. And the cost is a LOT, the tire/wheel combo will weigh more in the larger size. With a given tire diameter, the 18" wheels will have a shorter tire sidewall which will make for a harder ride at a given pressure, cause wheel damage more often if you hit a chuckhole hard, etc.

One of the auto magazines (Car and Driver or Grassroots Motorsports) did a test of a given small car with 15", 16", 17", and 18" wheels. I believe the "sweet spot" for performance was with the 16" wheels and tires. I believe they tested acceleration and timed the car around an autocross course.

The stock 15" tires had a smaller tread, whereas the wheels larger than 16" caused a net weight increase that reduced performance. The 2014 Foz is larger than the car they tested (something like a Civic or Golf) and especially with the turbo, the larger wheels won't present as much of a burden. But spending money to go from 17" to 18" wheels will not generally get you a performance increase of any kind.

For off-roading, you are almost always better off with a smaller diameter wheel and a taller tire sidewall that will take to lower tire pressures better and "wrap" around rocks, etc.

George

 

[RiffleKing]

I agree with all of what was written above and wanted to add that an indirect performance upgrade of larger wheels is that you can fit larger brakes underneath them. This is usually why you see high performance and race cars with large wheels.

Also, correct me if I'm wrong but there may be an advantage on asphalt to having a low profile tire with a smaller sidewall. This car probably doesn't have the power or agility to really benefit from it though.

Finally, as far as mileage, I've heard different things about it regarding wheels size. I've heard people who think lighter improves mileage in every situation and I believe that I've also heard that a moderately heavier, larger diameter wheel helps highway mileage by carrying momentum as it turns at speed. I'd love to hear more about that myself.

 

[YoGeorge]

I agree with all of what was written above and wanted to add that an indirect performance upgrade of larger wheels is that you can fit larger brakes underneath them. This is usually why you see high performance and race cars with large wheels.

Also, correct me if I'm wrong but there may be an advantage on asphalt to having a low profile tire with a smaller sidewall. This car probably doesn't have the power or agility to really benefit from it though.

Finally, as far as mileage, I've heard different things about it regarding wheels size. I've heard people who think lighter improves mileage in every situation and I believe that I've also heard that a moderately heavier, larger diameter wheel helps highway mileage by carrying momentum as it turns at speed. I'd love to hear more about that myself.

As a bicyclist, wheel weight has long been a discussion in this sport. With equal rolling resistance and aerodynamics, on a totally flat straightaway at a steady speed, a heavier wheel does not hurt performance but does not increase it it either. Consider the momentum of the bike and rider, and in a car, consider the momentum of the vehicle itself as well as flywheels, engine and drivetrain momentum. So on a car, gas mileage would not really suffer on a flat straight road with heavier wheels but I see no reason why it would ever increase.

Once you get into accel/decel, going up hills, etc, the heavier wheel/tire combo will always be slower and use more energy/gasoline.

In theory, a shorter sidewall with "flop around" less in cornering, but with adequate tire pressure, I don't think a 17" wheel/tire combo will really flop around more than an 18" wheel/tire combo and the latter will always weigh more with equivalent wheels and tires. (The weight of the wheel rim will offset the weight of a half inch taller sidewall.)

There has been some increase in wheel size to fit larger brakes--for example, big American "half ton" pickup trucks used to use 15" wheels universally. Now, they have larger brakes and generally need 17" wheels. (But they also offer up to 20" wheels as an option for people who enjoy breaking wheels and tires in chuckholes and who enjoy the harsher ride and reduced payload that the larger wheels dictate. A Ford pickup with 20" wheels can have a total payload under 1000 lbs--you lose a few hundred lbs of payload for the looks.)

The large wheels of today are a fashion statement meant to look like concept car drawings coming out of auto design schools. Beyond a point, they reduce performance in many ways in favor of looks. Like a woman wearing spike heels, they look good, but if you take a 5 mile walk with the woman in heels, you will generally hear a lot of complaining.

George

 

[RiffleKing]

As a bicyclist, wheel weight has long been a discussion in this sport. With equal rolling resistance and aerodynamics, on a totally flat straightaway at a steady speed, a heavier wheel does not hurt performance but does not increase it it either. Consider the momentum of the bike and rider, and in a car, consider the momentum of the vehicle itself as well as flywheels, engine and drivetrain momentum. So on a car, gas mileage would not really suffer on a flat straight road with heavier wheels but I see no reason why it would ever increase.

Thats interesting. When I was shopping around for mountain bikes about 10 years ago, 29ers were becoming fashionable. One of the benefits proclaimed was easier pedaling for road use. I guess that was more of an advertising gimmick than fact.

There has been some increase in wheel size to fit larger brakes--for example, big American "half ton" pickup trucks used to use 15" wheels universally. Now, they have larger brakes and generally need 17" wheels. (But they also offer up to 20" wheels as an option for people who enjoy breaking wheels and tires in chuckholes and who enjoy the harsher ride and reduced payload that the larger wheels dictate. A Ford pickup with 20" wheels can have a total payload under 1000 lbs--you lose a few hundred lbs of payload for the looks.)

I agree with all of what you said except for this. There has been a lot of increase in the brake size of today's vehicles. 16" wheels on typical roadgoing cars (probably not pure offroad oriented stuff) will almost certainly be extinct soon and I don't think there are many new performance cars out there that can take less than a 17" wheel. Even a car like the new XT which isn't a road burner by any means cannot handle less than a 17" wheel due to brake size. As cars get more powerful and heavier, brakes will get bigger. All of the big wheels or I would even say most of the big wheels out there are not just for show. I remember when I used to think 18" wheels were ridiculous and made no sense on a sports car, now I don't think you could fit anything less on a Corvette. But yeah, it has become a cliche to roll around on dubs to look cool.

 

[YoGeorge]

29ers are better for rolling over bumps and rocks, not on a level and smooth road. In general, that's where MTB's are ridden and raced (my son was a Cat 2 road racer and an Expert MTB racer, as well as a collegiate racer road and MTB). The larger tires is an extension of a skateboard going over a 4" curb kind of concept.

For a while, time trial bikes actually used 650 mm tires instead of 700 mm more for aero reasons, but the larger wheels made more sense for stability and frame geometry. And I will note that the carbon disk rear wheels and tri-spoke carbon front wheels favored for time trial bicycles ARE heavier than spoked designs with deep V rims--the aero advantage makes for a net speed gain on a flattish course--and TT bikes don't have to repeatedly slow down and accelerate. But when there is a lot of climbing involved, most TT riders will choose lighter and less aero wheels. It's always a tradeoff, bikes and cars both.

Note that now, 29" mountain bikes are being challenged by 650B, which are about 27.5" outer diameter. Kind of an "in between" and bike frame geometry especially in smaller sizes can be made more logical--the 29ers end up with weird geometry for small riders. 29ers are 700C wheels, so using that size was logical because it was the same as a road bike rim size. The 650's accelerate faster because they are lighter.

I'm with you on the brake thing--I did not mean to imply that every brake can fit in a 17" wheel, just that there are compromises as wheel diameters get unnecessarily larger. Again, a gigantic F150 pickup with 20" wheels is limited to a payload under 1000 lbs because of wheel capacity (leverage on a larger wheel is greater). So 4 big guys in the truck and they can't even bring a cooler of beer... And I find it funny to see a little 9" drum brake on the back of a small car thru the spokes of an 18" wheel...

I would say that many big wheels are still for show--so many cars have a base size wheel which fits around the brakes and optionally upsize the wheels by 1-3" for people who want to "wear" their wheels. Bigger wheels are often wider as well, and it makes me cringe to see big dollar wheels that have been curbed, or someone on the side of the freeway with a tire like a large rubber band that caught a chuckhole and trashed a huge chrome POS Chinese wheel... Rotating weight means a lot for accel/decel. So for a tire with a fixed width and outer diameter, let's assume that the tire belts will be the same on a 17" and a 20" tire. But then consider where the mass of the rim will be--the 20" rim is not only heavier, but it is closer to the outermost point of the wheel/tire combo.

Good discussion,
George

 

[RiffleKing]

29ers are better for rolling over bumps and rocks, not on a level and smooth road. In general, that's where MTB's are ridden and raced (my son was a Cat 2 road racer and an Expert MTB racer, as well as a collegiate racer road and MTB). The larger tires is an extension of a skateboard going over a 4" curb kind of concept.

I remember those selling points as well. I think that; like so many misguided consumers, I wanted something that did everything and what really stood out to me was the statement that it made a better road bike as well. It sounds like I would have been disappointed with its road going ability. In the end, I went with a used Trek off of craigslist to save money. It ended up throwing me off and separating my shoulder. :frown: Bigger wheels might have saved me from a couple shoulder surgeries.

I was all about performance when I was younger. I thought big wheels (anything over 18") were a bad idea. Over the years, I've seen how cars have changed and realized there is no magic number like 18" or 20" that is too excessive. The kicker for me is seeing production based race cars today, like those at the 24 hours of Le Mans with gigantic wheels. I was just watching the WRC Rally of Spain last week and they miraculously swapped out all of the drivetrain (overnight!), including moving to a larger wheel when going from gravel to asphalt. I know those guys wouldn't compromise performance for an inch or two of wheel. Now its mind blowing to see what has become of showroom cars.

Again, a gigantic F150 pickup with 20" wheels is limited to a payload under 1000 lbs because of wheel capacity (leverage on a larger wheel is greater). So 4 big guys in the truck and they can't even bring a cooler of beer... And I find it funny to see a little 9" drum brake on the back of a small car thru the spokes of an 18" wheel...

I'm one of those big guys with a gigantic F150. I didn't realize the wheel size had such an effect on payload. I've probably exceeded that payload # many times. Mine is a 2010 with what I believe are 18" wheels. Its too bad about the lower payload but I still would take a lower payload as opposed to the rear drum brakes that were on my '97.

Well, I hope I didn't get too off topic. This is a good discussion.

 

[YoGeorge]

What is the payload of your F150 from the door sticker, Riffle? I have been a Ford Truck Enthusiasts forum member for years (bought a 1978 F100 brand new, have had a full size truck of van since then, and still have my '02 E150 that I bought new as "weekend motorhome").

There was a long thread on payloads of F150's, and many are at 1200-1300 lbs, but those with 20" wheels were often under 1000 lbs, barely more than a Forester's. (And remember that this includes trailer tongue weight, so if you are towing 10k lbs with 1k of tongue weight, your remaining payload is basically the driver.) Of course trucks are overloaded, but the 20" wheels make for a silly low payload, all for appearance sake.

All of my points on tire and wheel size and weight are relative. In the world of small cars (I have a '91 BMW 318is with 14" wheels--the M3 that year got 15's with 205/55 tires) the weight is more critical. On stuff like new Corvettes and 5 liter Mustangs with 450 horsepower (and WRC cars), the larger brakes (and wheels/tires to accommodate them) are certainly more important, and there is plenty of power to offset the additional rotating mass.

By the way, I'm president of a large bicycle club in Michigan, and know what the racers use/have used. 29ers are still the way to go for most larger mountain bike riders (my son was racing at 220 lbs at 6'3" and winning regional collegiate short track MTB races, and top 5 in regional crits--helluva sprinter). The equation that sticks in my mind is that a pound removed from the wheels of a bike is like 3 lbs removed from the frame or other components because of the leveraged force it takes to accelerate the "flywheel" of wheels and tires.

Enjoying the discussion as well--I don't think we have any fundamental disagreements at all. The way to judge whether larger wheels will make your car faster is to see how larger wheels affect your quarter mile times and your autocross or lap times on a fixed course. But I do believe in the concept of "physics--it's the law"

Take care,
George