Thread: Limitations of offset with coilovers on a S14

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  1. #1 Limitations of offset with coilovers on a S14 
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    So I guess the point of this thread is to help dispel some of the questions that people have about what offset will fit with coilovers and what won't.

    First off we have to define what offset is and how it affects the car:

    Wheels

    Offset

    Offset is the relativity of the mounting surface of the rim to the center of the wheel.

    Zero Offset ***8211; When the hub mounting surface is even with the centerline of the wheel.

    Positive ***8211; The hub mounting surface is toward the front or wheel side of the wheel. Positive offset wheels are generally found on front wheel drive cars and newer rear drive cars.
    Negative ***8211; The hub mounting surface is toward the back or brake side of the wheels centerline. "Deep dish" wheels are typically a negative offset.

    +15 Offset Green = Zero offset




    -20 Offset Green = Zero Offset



    With this being said the lower the offset DOES NOT mean the better. Different cars require different offsets. Cars with wishbone or double wishbone suspensions handling can be severly affected by low offset wheels. Cars like Porsche 911, Toyota Supra, Mazda RX-7, Lotus Elise, Honda S2000, Mazda Miata, Subaru WRX, Mitsubishi Evo and others are cars that require relatively high offsets.
    Cars like Nissan 240sx, Toyota Corrolla, Nissan 350z, Nissan Silvia S15, Nissan Skyline and others do not require low offsets or benefit from them greatly but it will not harm them.

    Brake Clearance
    To popular belief brake clearance is NOT determined by offset but by spoke design. Larger calipers require more space horizontally and the spoke needs to bend the right way for it to clear.

    Fits



    Doesn***8217;t fit


    Now that we have defined offset and its affects we will move on to the S14 in particular. PS this whole 15 images per post thing sucks lol.
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  2. #2  
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    As all widths of wheels and tires will vary by person the easiest way to judge is by looking at the backspacing of the wheel. This is the distance between the hub of the wheel and the innermost edge going towards the suspension. Essentially this is the "inside" dish.

    For example purposes we will be using the wheel that I have pictures of and the front suspension since that is the most common area where people will run into fitment issues with the suspension. The wheel of choice will be a 17x9.5 Volk wheel with a +22 mm offset.

    The following image will show how to calculate your own backspacing.




    Remember offset is not the only thing that will determine if you will clear your suspension. It is just a means of being able to determine how wide of tires on that wheel. On some wider wheels, you may not be able to fully utilize all of that wheels width. Tires are the parts of the setup that will contact with the suspension and lower offset wheels are a means to be able to mount a wider tire with more clearance.

    In the example of the 9.5 inch wide rim with +22 offset, you can see the clearance that it has on the coilover suspension in the front of a S14 (this is with the widest tire that is available and still fits properly on this wheel with this offset, a 255/40/17):



    You can see that even though the rim has no contact with the coilovers, there could be a clearance issue with any larger tire (the sidewall has only millimeters of clearance). Seen above you can see part of the rim's width is not being used and the sidewall of the tire is slightly angled in, indicating that this tire is being stretched to fill up the space that it is. "Stretching" a tire is pretty common in street modified cars. People use it as a means to fit smaller tires on larger wheels and it can have many benefits.

    In drifting stretched sideways will cause the breaking point of traction to be very concise and controllable. It provides them with more sliding control as they are losing and regaining traction constantly. In time attack and grip racing this is not the case, but this is not a thread where we will discuss that.

    On the street people will often stretch tires not only for coilover clearance but for fender clearance as well.

    Moving on... Since not everyone is using the same wheel width or offsets or tires and to avoid getting 1000 threads asking "will these wheels/tires fit with coilovers" it's best to establish a minimum backspacing at which you can use a tire equal to the size of your wheel width. Conservatively I would say any wheel with backspacing of 5.5" or less should with no issues be able to run a unstretched tire (full rim width). Beyond that is a danger zone due to the fact that coilover manufactuers do not all use the same size sleeves and the diameter or "thickness" of the coilovers can vary slightly. In the 5.5"-5.75" backspacing range expect to have to run a tire 10-20 mm below the width of the rim (i.e. 255 tire on a 9.5 inch rim). Anything greater than 5.75" backspacing I would imagine that you will be required to use severely stretched tires (20mm+ below the width of the rim) and even if the tire clears you may still have clearance troubles with the actual rim hitting the inside outside of the coil threads (see picture above).

    Hope this helps some people out
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  3. #3  
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    very nice this is actually the first thread i have seen where it is easy to clean and still figure out what you want vs askin people what you should run ... this needs to be a sticky.
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  4. #4  
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    lotsa factors play when you're talking clearances with a certain set of coilovers and a car.

    of course, the coilovers themselves, depending on how they're designed.
    tire size, self-explanatory.

    BTW.. looks like this site is getting alot of good technical articles already!
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  5. #5  
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    yeap thats what this thread was supposed to help some of the less technically inclined ppl to realize and understand.
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  6. #6  
    flip's Avatar
    flip is offline What is power without control? 240Atlanta.com
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    Awesome writeup! Great stuff to know when choosing wheels, tires and suspension components...

    +10
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  7. #7  
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    ahmonrah is offline The Watcher..... Men with guts attack those corners...
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    great contribution!! maybe now i wont have to bug yousef.....
    r.i.p jason"jsmoov" robinson
    7/22/79 8/6/06
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    "Misses don't count, I don't give a shit what you think of the .45. if it doesn't hit vitals, its not going to do jack....unless you get lucky and hit a sissy."
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  8. #8  
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    this is the most helpful offset thread I've ever seen. There are countless threads on NICO that try to explain this, but it doesn't come out as nice. +1
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  9. #9  
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    Lonnie D is offline I cut a bitch once Men with guts attack those corners...
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    I am glad I did a search and found this, very helpful and I agree this should be a sticky.
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  10. #10  
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    I have 18x9.5 +12 on the front, there is less than a fingertip width between the rim and the coilover. No spacers. 18x9.5+15 is prolly the max offset in that size with no spacers. (for the front).

    I had some 9.5 sportmax on there at one point. Not sure the offset but the tire was rubbing the coilover enough to wear off the anodizing on the collars.
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