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> Tire Size And Offset?
flyin_spider
post Feb 14 2008, 10:34 PM
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i'm looking for a set of rims for my eclipse 2003... but i don't know from wut offset to?? size?? bolt pattern?? i'm looking for 18"s, Please help!!
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post Feb 15 2008, 02:42 PM
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Lug Pattern
On the 3G Eclipse, you must use wheels that have a 5x114.3 (5x4.5") bolt pattern. For wheels that have two bolt patterns (like 5x100/5x114.3 or 5x114.3/5x120), one of those bolt patterns must be 5x114.3 in order for that wheel to fit.

Wheel Width
Width of the wheels can be anywhere from 6" to 8.5". WIDTH ALONE MEANS NOTHING. It must be combined with offset to determine if and how a wheel will fit on the car. For example, a 17x7.5" +42 offset will sit on the car in almost the same way as a 17x6.5" +46 offset wheel.

Lug Nut Size

12 x 1.5mm

Offset
Factory GT wheel spec: 17x6.5" ; +46 offset ; 5x114.3 ; 67.1mm centerbore (applies to all 2000+ Eclipse models)

Offset is the measured distance in millimeters between the centerline of the wheel and the hub mounting surface (where the wheel hub mounts up against the brake rotor/drum hub).

The basic principal behind offset is that all things being equal, the higher the offset the wheel is, the more tucked the wheel will be. The lower the offset, the farther the wheel will protrude.

Example: a 17x7" wheel with a +40 offset will protrude out an extra 15mm when compared to a 17x7" +55 offset wheel. In retrospect, the +55 offset 17x7 will be pushed 15mm closer into the wheel well when compared to the +40 offset 17x7".

Given the many sizes of wheels that are designed for the 3G (and similar platforms) offset should be between +35 and +48.

While offset is SOLELY a measurement of rim parameters, offset does play a role in determining if a certain size tire will fit.

Hubcentric Rings

The principle of hubcentric rings is as follows:

You have 3 spinning circular objects (the axle hub, the brake rotor, and the wheel/tire combo). So just imagine a small circle (axle hub), a bigger circle (brake rotor), and the biggest circle (wheel/tire combo). The ideal situation is to have the center most SINGLE POINT of all three circles to be exactly the same. If one circle isn't spinning on the same axis as the other two, the total motion of all three circles combined won't make a circle, but instead will combine to make an oval. Imagine if your wheels and tires were shaped like ovals, you'd get vibrations at speed.

The hubcentric ring compensates for differences between the centerbore of the brake rotor and axle hub, and between the centerbore of the wheel and axle hub. It allows the brake rotor and/or the wheel/tire combo to be better positioned on the hub so that the center most point of all three parts are the same. In the case with my current SSR wheels, the centerbores are bigger than the centerbores of the axle hubs so the center most point of the wheels isn't the same as the center most point of the axle hubs.

Here's what a hub centric ring looks like: (the top part of the picture is what would be placed into the wheel; the bottom part would fit snug over our 67.1mm axle centerbore)

(IMG:http://img.villagephotos.com/p/2002-10/61578/BBShubcentric002.jpg)

Here's what a centerbore looks like without a hubcentric ring:

(IMG:http://img.villagephotos.com/p/2002-10/61578/BBShubcentric003.jpg)

Here's what the centerbore looks like with a hubcentric ring:

(IMG:http://img.villagephotos.com/p/2002-10/61578/hubrings002.jpg)

So lets say that you order a set of wheels that have a 73.1mm centerbore, you'd have to order centering rings that have a 73.1mm outer diameter and a 67.1mm inner diameter. If the wheels have a 75mm centerbore, you'd need rings that have a 75mm outer diameter with a 67.1mm inner diameter.

Recommended Tire Sizes
15" - 195/65-15 (Stock RS size)
16" - 205/55-16 (Stock GS size) ; 225/50-16
17" - 215/50-17 (Stock GT size) ; 225/45-17 ; 235/45-17
18" - 215/45-18 ; 225/40-18 ; 235/40-18
19" - 225/35-19 ; 235/35-19

Lets look at the tires listed in the 18" size.

In the tire size 225/40-18, 225 is the section width of the tire in millimeters. 40 is the aspect ratio (percentage) of the sidewall compared to the section width of the tire.

Example: the sidewall of a 40 series tire is 40% of the section width of the tire, which is equal to 90 millimeters for a 225/40-18 tire. The sidewall of a 45 series, 215mm tire is 96.75 millimeters. The 40 series tire will have a smaller sidewall (lower profile) than the 45 series tire. The sidewall of a 75 series 265mm tire (truck tire) is 198.75mm. The last number in the tire size is the required rim diameter needed to mount a specific tire.

This link will give you a good idea about changing your tire size and the effects it'll have on your speedo/odometer:

http://www.miata.net/garage/tirecalc.html

The tire sizes listed above are the ones that will keep your speedometer/odometer pretty accurate. Any other tire that has a smaller overall diameter will make you think your going faster than you actually are. This will put MORE miles onto your car faster than if you had tires with a similar overall diameter compared to stock.

Here's a really cool calculator that calculates BOTH changes in offset and tire size!

http://www.geocities.com/xtremephoenix/tire.htm

If you decide to use ANY tire size that's not listed in the aforementioned size list, you WILL experience noticeable negative effects in the accuracy of your speedometer, odometer, ABS (Anti-lock Braking System), and (TCS) Traction Control System, which can and more than likely will decrease passenger safety... Take this statement close to heart.

Tire Fitment on Different Width Wheels
The following will give you a GENERAL idea of how different width tires will fit on different width wheels. These are purely generalizations and you should confirm tire to wheel fitment by looking up an individual tires rim width range in its specifications. What everyone needs to realize in this section is that as a tires sidewall gets smaller and smaller, it'll need wider and wider wheels to ensure proper & SAFE contact patches between the tire and the ground. For example, the rim width range for a 215/40-17 tire is 7.0" - 8.5" whearas the rim width range for a 215/50-17 is 6.0" - 7.5" because the 215/50-17 has a larger sidewall than the 215/40-17. Another example, a the minimum rim width for a 235/45-17 tire is 7.5", whereas the minimum rim width for a 235/40-18 tire is 8". The 235/40-18 needs a wider rim because of the decreased sidewall. The Acura MDX comes with 235/75-17"s and they're mounted on 6.5" wide wheels. That is possible and safe because the sidewall on that tire is HUGE! For this listing I will only compare the tire sizes that I recommend for the 3G.

15" Tires

195/65-15 ; Rim Width Range = 5.5" - 7.0"

16" Tires

205/55-16 ; Rim Width Range = 5.5" - 7.5"
225/50-16 ; Rim Width Range = 6.0" - 8.0"

17" Tires

215/50-17 ; Rim Width Range = 6.0" - 7.5"
225/45-17 ; Rim Width Range = 7.0" - 8.5"
235/45-17 ; Rim Width Range = 7.5" - 9.0"

18" Tires

215/45-18 ; Rim Width Range = 7.0" - 8.0"
225/40-18 ; Rim Width Range = 7.5" - 9.0"
235/40-18 ; Rim Width Range = 8.0" - 9.5" (I did run these on 18x7.5"s without problems)

19" Tires

225/35-19 ; Rim Width Range = 7.5" - 9.0"
235/35-19 ; Rim Width Range = 8.0" - 9.5"

Lowered Suspensions & Different Wheels
Now that you hopefully understand what offset is and the parameters surrounding tire sizes, it's time to combine the two.

A common question on this board is "Will I rub?" Offset plays very little a role in determining if your FRONT TIRES will rub on something inside the wheel well. Offset plays a large role in determing if your wheel/tire combo will rub the REAR vertical control arms. To reitterate, offset is very important in determining if a wheel/tire combo will rub in the rear, but not nearly as important in the front.

When lowered ANY AMOUNT, a 225mm width tire, on 7" - 7.5" wide rims with an offset between +38 and +43 or +42 and +48, respectively, will not be prone to rubbing ANYTHING inside the front or rear wheel wells. Don't EVER mount 235 width tires on ANY rim with an offset of +48 or higher.

When lowered more than 1.2" a 235mm width tire on any wheel will be very prone to rubbing this black box in your FRONT wheel wells:
(IMG:http://img.villagephotos.com/p/2002-10/61578/CIMG0377.JPG)

Unlowered OR lowered, a 235mm width tire on a 7.5" wide wheel with an offset up to +45 will come VERY CLOSE to wedging up against the REAR vertical control arms. If you have 7.5" wide +42 ~ +45 offset 18" wheels, stick with either 225/40-18's or 215/45-18's.

(IMG:http://img.villagephotos.com/p/2002-10/61578/thewheelandtyrebible.gif)



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post Feb 15 2008, 02:45 PM
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and one more thing, they're called WHEELS - not RIMS. :)

A wheel is comprised of a hub, spokes, and a rim. I seriously doubt you only want to buy a rim unless you're trying to replace out a damaged "rim" ona 3-piece wheel. ;)
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flyin_spider
post Feb 15 2008, 05:17 PM
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do u guys think this will fit
18"x8" 18"x8.5"
5/114.3 5/114.3
offset 38 or 48 45
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post Feb 15 2008, 09:47 PM
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QUOTE(flyin_spider @ Feb 15 2008, 05:17 PM)
do u guys think this will fit
18"x8"                                  18"x8.5"
5/114.3                                5/114.3
offset 38 or 48                      45
[right][snapback]142627[/snapback][/right]


I jsut granted you an open book test and now you want me to fill in the answers for you?? *** - I'm faily certain you can figure it out given what I said above. You figure it out.

You have to eventually learn this stuff.

Hint - USE THE OFFSET CALCULATOR LINK.
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