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Old 08-17-2008, 09:37 PM   #1
Mil
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Default weight difference between 17'' and 18'' wheels

Did anybody compared the weight difference between oem 17'' and 18'' wheels?
Does it make a big difference on fuel efficiency?
Is there a big difference on 0-60 mph (or 0-100 km/h)?
How about handling, is there a really big difference?

I do have oem 17'' on my 3 door XR, but i may plan to go bigger, i have to consider fuel efficiency as i drive about 110 km/day.

Thank you for your comments

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Old 08-18-2008, 08:46 AM   #2
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Default Re: weight difference between 17'' and 18'' wheels

I do not know the weights of these wheels, but I think that lookin over what some folks are getting in the MPG area that the 16 and 17 inch wheels are doing better than the 18 inchers. Someone might want to do a poll on this.

My running average is in the 31-32 range in commute duty with 65-70 Highway travel.

After living with this XR with the 18 inch wheels for almost 3 months, I'll hate putting on either All-Seasons or Snow Tires on 16 or 17 inch wheels. This car is so good with the 18's!

Chris

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Old 08-18-2008, 09:01 AM   #3
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Default Re: weight difference between 17'' and 18'' wheels

Interesting question about unsprung weight affecting fuel economy. My uneducated guess is its very minor and more important to know if you're likely to have speedometer/odometer errors deliberately introduced by oversize wheels not calibrated to the electronics. Given that a large diameter wheel turns less total revolutions per mile compared to stock wheels, it can be presumed that errors are automatically introduced in the speedometer and odometer leading to incorrect mileage calculations that may appear to look better on paper than in reality. Some food for thought.

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Old 08-18-2008, 11:15 AM   #4
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Default Re: weight difference between 17'' and 18'' wheels

if u measure the circumference of the tires both 17" and 18", u will probably find that they are almost the same because of the different aspect ratio.
the computer cannot compensate for wheel/tire size. it would have to be programmed. on older cars, u would have to change the plastic speedo gears at the tranmission.

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Old 08-18-2008, 11:44 AM   #5
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Default Re: weight difference between 17'' and 18'' wheels

I had a '78 Chevy Malibu Classic wagon which recorded only 9 out of every 10 miles traveled. It confused me for a while until I compared the tires on the car to the recommended tire size in the manual. The previous owner had put on larger diameter tires.

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Old 08-18-2008, 01:43 PM   #6
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Default Re: weight difference between 17'' and 18'' wheels

Mil - the biggest hit to the F.E. will be the tire contribution. Generally, size really does not matter (). What matters is the rolling resistance of the tire. Usually, smaller tires are made with a harder "batch" compound in order to decrease rolling resistance and therfore improve FE. As you go larger and get to a more "performance" oriented tire, rolling resistance goes up and your FE will go down. Unfortunatly, the average consumer will not be able to get rolling resistance numbers for any spec-ed tires unless you work for a tire manufacture. In our world, we HAVE to get that information in order to spec out tires for upcoming programs and models. As you would expect, we are focuasing heavily on RR #'s now.

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Old 08-19-2008, 08:28 PM   #7
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Information Re: weight difference between 17'' and 18'' wheels


I have the 18' wheels and it doesn't effect my MPG. I still get the estimated MPG like everyone else. (approx. 24/city 32/interstate) Like GM Sky Man said, it is all about the tires and not the wheels. If you get the right size tire you won't effect your MPG.
The 18's tire size is 215/45/18. It is overall a smooth ride and the handling is incrediable. Do know that the wider the tire the better handling. I do enjoy the 18's.

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Old 08-26-2008, 10:43 AM   #8
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Default Re: weight difference between 17'' and 18'' wheels

On my previous car (a 2006 Jetta TDI) when I went from the skinny hi-efficiency 16" rims to a set of performance 18" rims (lightest available 18" wheels by the way) I lost about 3-5 mpg. As a % that was not as bad as the car went from around 46 mpg to 42 mpg of so. The 18s did handle dramatically better, they also made more road noise.

PS. My Astra has the 18's.

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Old 08-26-2008, 04:19 PM   #9
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Default Re: weight difference between 17'' and 18'' wheels

Lets look at a couple things that might go a long way to solve the question.

1. Unsprung weight: This is any weight that is not supported by the springs. Examples include wheels, tires, brake assemblies, lower control arms, front spindles and struts, and the rear axle assembly. This weight moves as the car does. When you go over a bump, it has to go up, then down again. Inertia is a large factor. The less unsprung weight, the more responsive the car will be to inputs.
2. Gyroscopic effect. When a wheel is spun, then asked to change axis (yaw) it will resist the attempt to change direction, like a gyroscope. The bigger the wheel in diameter, the greater the resistance. There's a reason why F1 runs 13-15" wheels.
3. Rolling resistance: Directly related to the "grip" of the tire, and also the size of the contact patch. In some situations, it also adds aerodynamic drag.

Having said this, you will notice differences in many things by going from 17 to 18" wheels. Your fuel economy may suffer because of extra rolling resistance; you may discover that your struts wear out sooner, trying to control the inertia of the bigger wheels. Your ride "feel" will be different. To keep the same rolling diameter (so the speedo is accurate) you'll go to a smaller section tire. Instead of 225-45-17's you may find yourself with 235-35-18's. Less sidewall section=stiffer sidewalls and less shock absorption when going across road imperfections.

My advice: If you feel the need to upsize from 17 to 18s, find THE LIGHTEST ONES POSSIBLE. A lightweight 18 should come in between 16-18 lbs, and will probably cost you ~$300-$500 each.

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Old 08-26-2008, 08:59 PM   #10
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Default Re: weight difference between 17'' and 18'' wheels

Thanks for the answers.
By the way, i will soon be able to confirm any differences as i bought oem 18'' wheels and tires from elias799.
Oem wheels are sold as an option on the astra, so it can't be wrong to put thme on.
I will keep my oem 17'' wheels for winter, winter tires may cost a little more but at least i will still enjoy my car's handling even during winter.
And most of all, i will make sure to get my winter tires on before i got stuck in a snowstorm.
By having two sets of wheels, i won't have to get an appointment at the garage to get those winter tires on.(I mean during winter tires install rush)
This year may be a problem in quebec as a new law force every car owner to get winter tires on before december 15th.
I always used winter tires, but it's a good thing to have them mounted on different wheels, this way, you decide when you put them on, you don't depend on garages business hours and availability.

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Old 08-27-2008, 06:57 AM   #11
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Default Re: weight difference between 17'' and 18'' wheels

for winter snows on 17 or 18" rims will probably be a very expensive issue compared to 14 and 15". in quebec, ar mandated to run snows on all 4 wheels?

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Old 08-27-2008, 10:49 AM   #12
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Default Re: weight difference between 17'' and 18'' wheels

Quote:
Originally Posted by 72gssaturn View Post
for winter snows on 17 or 18" rims will probably be a very expensive issue compared to 14 and 15". in quebec, ar mandated to run snows on all 4 wheels?
Since the smallest wheels offered on Astras are 16 (on the XE), it hazard a guess that 15's won't fit. Having said that, 17's are significantly more expensive than 16's, and you can run a narrower, taller tire (great for cutting through snow).

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Old 08-27-2008, 10:56 AM   #13
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Default Re: weight difference between 17'' and 18'' wheels

You could mount any size tire and wheel combo you would like on the Astra...provided you do not want brakes. Ultimately, the size of the wheel is determined by how far the brake caliper sticks off the rotor in free space. This car is designed with a 16" brake system. Therefore, the smallest size wheel you could run is a 16" wheel.

Here's a tip for all you fellow snow folks. If you are thinking about mounting snow tires on your Astra's and you do not want to pull the tires off your current rims, best thing to do (and probably the cheapest) is to buy a set of teh 16" steel wheels from Saturn and mount your own snow tires. Then just swap them out in the Spring. I know cause that is EXACTLY what I am going to do. And by far the 16" steel wheel is lighter that any 17+ approved GM wheel.

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Old 08-28-2008, 04:37 PM   #14
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Default Re: weight difference between 17'' and 18'' wheels

Yes i can confirm that 17'' winter tires cost more than 16'' and also it's true to say that a narrower tire will be better in snow conditions, but since 90% of my driving is done on highways, i may see a lot more ice than snow.
On ice, a larger tire is better, so 17'' may be a good compromise.
We'll wait to see.
And by switching for other oem wheels and tires +tpms, i won't have tho buy another set of wheels and tpms sensors.
At the dealer, 16'' steel rims sell for 225$ each, and that's without any tpms sensor.
At that price, i prefer spending a little more on tires, but still have a nice handling on higways and ice.
Not to mention that the car will still look cool in winter.
I'll have to be a little more carefull in snowstorms.

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