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08/2012 ROTM
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1,622 Posts
Discussion Starter #1 (Edited)
As many people do when they get new cars a lot of us are swapping out the stock wheels for aftermarket setups. I have noticed a lot of people don't understand the numbers when it comes to wheel/tire purchases so here are some knowledge bombs. Feel free to add to this.

Wheels

Wheels come with 5 important measurements
Diameter
Width
Offset (Sometimes they give you backspacing and you have to calculate offset or find a table)
PCD
Hube Bore

These 5 numbers will help you decide what will fit on your new car and not rub on the fenders, suspension components, the brake calipers or if they will even mount.

For our cars the PCD should always be 5x4.5(inches) or 5x114.3(mm) if you get something different you will need an adapter/spacer to run them
Also for our cars the hub bore should be 67.1mm or larger. If it is larger you will want to get hub centric rings with an inner diameter of 67.1 and an outer diameter that matches the wheel.

Now for the other three:
Diameter: The measure across the center of the wheel face from one rim edge to the other (this plays a role in tire sizing)
Width: The measurement across the barrel from the inner rim to the outer rim (this plays a role in tire size and offset)
Offset: The measurement from the center line of the wheel to the mounting surface. (the center line is the line down the middle of the barrel, it occurs at half the width, the mounting surface is where the wheel connects with the hub of the car when mounted)

The lower the offset the more pushed away from the vehicle the wheel becomes. Spacers are used to help lower the offset by pushing the wheels away from the vehicle as well.

Now depending on your suspension setup (Stock, Lowered, Slammed, Bagged) and where you want the wheel face to sit (Poked, Tucked, or Flush) some of these measurements will have to change from stock. There are few people on the forums who have created setups that are very flush with the fender, one option is to either copy their width and offsets for your setup or use and offset calculator to see how yours may vary from it. I use Online Wheel & Tyre Fitment calculator. Offset and Tyre Stretch

Wheel weight is also important. Increased wheel weight will reduce gas mileage, and power to the ground and braking ability. Increasing wheel diameter will often cause wheel weight to go up while also moving the weight further from the hub thus making the aforementioned faults even worse. Lighter wheels will increase the power put down, mileage and braking ability but can come at the cost of strength. Forged wheels which are generally the strongest and lightest also come at a higher cost. Finding a good balance for your budget and local roads is the best route.

Tires

Tires comes with 3 measurements as well
Width (usually in mm)
Sidewall Ratio
Wheel Diameter (usually in inches)
Which is shown like this W\SwR\WD

Width: The measure of the tread width of the tire, while the number is the same the actual width will vary slightly between manufacturers
Sidewall Ratio: Take this number put a decimal in front of it and multiply it by the width to get the sidewall height
Wheel Diameter: This number needs to match the diameter of the wheel you want to use the tire on.

When buying tires the wheel width will come into play because a tire that isn't wide enough will cause the sidewalls to stretch, this has become popular in many enthusiast crowds as it allows the owner to lower the vehicle more without rubbing the tires on the fenders. If the tire is too big it will hang out over the wheel too much and risk bubbling and bursting. There are suggested wheel width ranges for each tread width.

Also with the sidewall height being related to the width of the tire it also needs to be considered. The overall diameter of a tire should never be more than 3% different than stock. If it is the ECU will need to be adjusted to calculate for the change. Going 3% larger may also call for upgraded braking systems to account for the added rotational mass. So as your wheel diameter goes up your sidewall ratio should go down, generally by 5 for every inch increase in the wheel diameter. Now if you plan to go with a wider tire you may need to lower the sidewall ratio another 5 to account for it. For example on our cars if you go to a 245 width tire or greater the sidewall ratio would need to be lowered so that its height does not become too tall. I use Tire Size Calculator - tire & wheel plus sizing for tire sizing as it will let you know when the tire is too far off.

Good luck with finding your new wheel setup!

A good site I forgot I had bookmarked https://www.rsracing.com/tech-wheel.html
Site to see tire stretch, find your wheel width (the first number in the listings) then the first two numbers from your tire size to see how it will look Tyrestretch.com - Image Library

Spacers/Offset Cont.
How to figure out what size spacer to use to make the wheel face flush with the outer or inner fender. This can also be used to figure out the perfect offset your new wheels will need as well and will be explained at the end.

You will need tape, string, a metal washer, and a measuring device preferably with millimeters.
  1. Take the string and tie the washer to the end of it
  2. Hang the string down the center of the wheel so that the washer is below the centercap. Preferably closer to the tire than the centercap.
  3. Cut the string so that the is about an inch extra at the top, you will use this inch to tape the string to the fender.
  4. Tape the string to the inside or the outside of the fender depending on where you want the wheel to be flush. The string should bisect the wheel/tire.
  5. Once the string has stopped swinging, measure from the string to the rim of the wheel at the top of the wheel.
  6. This distance will tell you what size spacer is needed to make the wheel sit where the string currently is.
To use this to find the right offset for wheels with a different width: (We are going to use the stock SX wheels and a measurement of 15mm for this example)
  1. Using the dimensions of the stock wheel width 7.5in and et46mm we can calculate what offset we would need for the wheel to be flush using our flush measurement at 15mm.
  2. This will be done by subtracting the measurement from the wheels offset. 46-15=31mm
  3. Go to a website like the before mentioned http://www.willtheyfit.com/index.php and enter in your stock wheel flush information 18x7.5et31
  4. Now enter the wheel diameter and width that you want to purchase.
  5. Finally adjust the offset until the "Poke" measurements are as close as you can get them. This will tell you what offset your new wheels will need to be. Getting wheels that vary by 1-3mm wont make too much of a difference.
Factory Wheel Information
Optima LX
Wheel Size:
16"x6.5"
Offset: ET41
Wheel weight
: ~25 lbs?
OEM tire size: 205/65R16
Wheel and tire: ~42 lbs?

________________________________________
Optima EX and EX Turbo
Wheel Size: 17"x6.5"

Offset: ET44
Wheel weight
: ~24 lbs?
OEM tire size: 215/55R17
Wheel and tire: ~43 lbs?

________________________________________
Optima Luxury Wheels
Wheel Size: 18"x7.5"
Offset: ET46
Wheel weight: 23.5 lbs
OEM tire size: 225/45R18
Wheel and tire weight: 48 lbs


________________________________________
Optima SX
Wheel Size: 18"x7.5"
Offset: ET46
Wheel weight: 23.5 lbs
OEM tire size: 225/45R18
Wheel and tire weight: 48 lbs


________________________________________
Optima Hybrid
Wheel Size: 16"x6.5"
Offset: ET?
Wheel weight: 25 lbs?
OEM tire size: 205/65R16
Wheel and tire weight: 42 lbs?



Stock Tire Pressures
 

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2019 Mercedes-Benz Sprinter 170
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2,115 Posts
When buying tires the wheel width will come into play because I tire that isn't wide enough will cause the sidewalls to stretch, this has become popular in many enthusiast crowds as it allows the owner to lower the vehicle more without rubbing the tires on the fenders.
 

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itscoldoutdog
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1,825 Posts
Ahemmm "Borrowed" from other forum, old thread...

16"x6.5
" Optima LX: ~25 lbs?
et?
Wheel and tire:
~42 lbs?
OEM tire size: 205/65R16


______________________________________
17"x6.5" Optima EX and EX Turbo: ~24 lbs?
et?
Wheel and tire:
~43 lbs?
OEM tire size: 215/55R17


__________________________________________________ _____________________________________________

18"x7.5" Optima Luxury Wheels: 23.5 lbs
et 46
Wheel and tire: 48 lbs
OEM tire size: 225/45R18


__________________________________________________ _________________________________________
18"x7.5" Optima SX: 23.5 lbs
et 46
Wheel and tire: 48 lbs
OEM tire size: 225/45R18


______________________________________
16"x6.5" Optima Hybrid: 25 lbs?
et?
Wheel and tire:
42 lbs?
OEM tire size: 205/65R16
 

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144 Posts
Unsprung weight is the enemy of handling and ride quality. Lighter is better in almost very case, up to the point that the rim is easily bent. Wider usually = heavier, so it's a balancing act between s-t-y-l-e and ride/handling.

If you drive where the roads are smooth, no big deal, but in bumpy country, watch out for the weight.

Here's the best source I ever found on wheel weight. You might want to bookmark it: WheelWeights.net - Database of Wheel Weights
 

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668 Posts
Can we add the manufacturers recommended tire pressure? I only ask because I have sx wheels but don't know what Kia recommends as tire pressure those wheels...I can find it online anywhere either.
 

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08/2012 ROTM
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1,622 Posts
Discussion Starter #8 (Edited)
Check the driver side door sill its often on a sticker in there for most cars plus its in your manual. Generally for stock wheels and tires its 30-34PSI.

Im going to do some stuff today and come up with offsets to sit flush with the widths of 6.5, 7, 7.5, 8, 8.5 and 9in. The only thing is that they will vary a little bit with lowering but should still be close.

Edit: confirmed its in the driverside door sill.
 

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08/2012 ROTM
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1,622 Posts
Discussion Starter #9 (Edited)
Check your manual then, as its in there on 8-4 all the stock wheel and tire setups are. I'm actually surprised the sticker didnt list them all my last VW did.

Took a pic of the page and put it up top. Stuff like that will always be in the manual. They wont print a different one for each trim because it would be too costly.

On another note, check your tire pressure if you havent since you bought the car. I normally do but didnt until just now and all my tires had 10PSI TOO MUCH in them and were 5PSI from the max. This tells me they never deflated them after transport as they are supposed to. Gas mileage should get a little better now.
 

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2012 SX
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So I'm new around here - but I found a great deal on some TSW Vortex's and could use some advice on fit and what the "look" might be when it comes to being flush. The wheels are 20x8.5, +20 offset, 73.1mm center bore. I have a variety of tire sizes I can choose from and different brands. I've read some posts on here that 245's would be a bit wide and rub the wheelwells - true? Also, it seems like an 8.5" wheel is about the max the Optima SX can take, so should I stick with a 225 tire to be as close to stock as possible? A 245-45-20 tire from hankook would be a nice sidewall, but I want to be careful about the rubbing issue. My car is not lowered or anything, totally stock.
 

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08/2012 ROTM
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1,622 Posts
Discussion Starter #11
That offset is going to be too low and you are going to poke out of the fender. Did you read any of the first post? There are links ot sites that you can compare widths and offsets. You need to take the info about your stock wheels and plug that in followed by your new wheels. Then find the difference in "POKE." With that number in mind (convert to inches if need be) go out to your car with a tape measure. Put it on the the top rim of the wheel (not the tire) and see how much farther out the wheel will be sticking out. Most people who have 8.5in wide wheels are running them at 35mm offset so your wheels would stick out 15mm more than theirs do which is over a half an inch. You will 100% not want to run a tire larger than 225 and I would even say look into a 215/45 or even a 205/50 so you dont rub on the outer fender. Also plenty of people are running 9in wide wheels at all four corners as I will be doing when they arrive.
 

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2019 Mercedes-Benz Sprinter 170
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The +20 offset is going to stick way too far out. You need a +45 to +35 offset with an 8.5" wheel. Even the +35 is pushing it if you want to use a 245 tire. I would look for a +40 offset. As far as bore goes, just make sure it's larger than 67.1mm and then use centering rings in the center bore. You can use 245s as long as you stick with and offset of +40 or greater, but no way you should be using a 45 series with the 20" tires.

You need to re-read the fist post here as you are way off with almost everything you have in mind. Tire size is way too big, offset is way too low, max rim width, etc. You may also find it helpful to read through the aftermarket wheel and tire thread to get a better idea of the acceptable size tires and wheels that will work on our car.
 

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Can anyone confirm that any Kia 17" rim from any Kia car will be the same specs as the Optima's 17 inch wheel (i.e., 5x114.3)?

I want to buy winter tires and mount them on OEM alloy rims if I can find the latter at a low price. I've seen ads for Forte 17 inch rims but no specs.
 

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itscoldoutdog
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1,825 Posts
we should probably talk about a wheels load rating. (and tires) It was hinted on once or twice, talking about "light weight is good until a certain point where the rim can be easily bent"...

On the driver door sill of every car is a tag mentioning tire psi, and next to it is a tag with weights...looks like this:



That is from my car, which is the heaveast trim (loaded-SX) besides the Hybrids (think they are more?)

GVWR = Gross Vechile Weight Rating ..thats max weight "allowed" including cargo/towing

FYI, On my tire sticker it list max cargo at 906 lbs..so my 4497 GVWR is coming from my 3591 lb loaded SX, plus 906 lbs of potential "allowed cargo"

GAWR = Gross Axle Weight Rating... thats the max weight allowed on the front axle/wheels and rear axle/wheels.

This is more important than GVWR when looking and wheels and tires since the total weight is not distributed evenly b/c our cars (less Hybrids probably) are front heavy...so pay attention to the front rating.

2425 lbs "allowed" on front axle means my wheels and tires ought to be rated for 1212.5 lbs EA , which is 550 kg.


Most wheels come from plants overseas, and also since metric rules, wheels typically have their load rating on the rim face in KG..if not, it has to be there in LBs.

A lot of standard casted aftermarket wheels are rated at like 500kg..no problem for civics and many other cars, but watch out on our cars whenever its full of cargo or taking hard turns on a street course etc.

You may be thinking, "I never have 906 lbs of cargo, etc, so i can use a 500 kg rated wheel." Thats probably true if you aren't driving spirited or around potholes. Just realize taking those wheels on a street-track and you'll be pushing their limits. You can't go wrong by assuming the worse and making sure your car's shoes will able to handle it.
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Lots of aftermarket, cheaper cast wheels are heavier to allow for the higher load ratings. So very often you have the trade off of weight vs strength rating.

You can still go light and strong, and thats typically where higher cost comes into play..Its not always just "looks better, add $100+ per wheel", lol

That said you can get good light AND strong enough wheels for a decent cost. My 18x8 $210 (incl shipping) per wheels that are only 20.5 lbs are rated 700 KG ea, thanks to spin-casting/flow forming wheel creating process. Same process and rating as almost all Forgestars, some TSW's like Nurburgring, lots of BBS's...and many others.

When shopping if you cant find the wheels rating listed, don't be afraid to ask a vendor.

As for tires, on Tire Rack each tire's load rating for that exact size, brand, and model, is shown on the specs.
 

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I'm really not sure what you ar asking. The offset is related to the wheel not the car. You can get stock sized wheels and run an offset lower than stock, closer to 30 would give you a more flush with the fenders/sport look.

I want to get 18's for my SX to give it a different look. What offset do I need so I don't rub claipers or anything of that nature. Stock SX offset is 46, so 45mm would work correct? I'm going to lower it with eibach because I don't want to drop it like ark's do.
 

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08/2012 ROTM
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1,622 Posts
Discussion Starter #20
Offset will depend on the width of a wheel you go with. You really should read the first post. Offset needs to be paired with the width or else its arbitrary. I'm running a 9in wide will with a 42mm offset and my wheels sit flush with the fenders. A narrower wheel will need a lower offset to accomplish the same look.
 
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