1. Join the Community!

    DSMtuners is a massive archive of DSM information - but more importantly, it's a COMMUNITY! Join in and participate with other DSMers, and invite all of your DSM friends to make this place their home. Chat with others, create a build thread, post questions and answers. Get involved! Logging in will also remove many of the advertisements, along with this notice. ;)

Newbie 2g DSM Wheel and Tire Fitment / Selection Guide

Posted by wret, Jan 16, 2004

Please Support Morrison Fabrications
Please Support STM Tuned
  1. wret

    wret Proven Member

    2,693
    65
    Joined Jul 3, 2003
    Bel Air, Maryland
    Ok, so you want to put some cool new wheels on you DSM. The decision process usually starts with three or four primary considerations:
    · Size. You want bigger right? To a certain extent wider is better and likewise bigger is better.
    · Weight: Possible justification for spending 1 to 2+ Gs. They have a name for people that attach things to their cars just for looks.
    · Appearance. Looking good is pretty important.
    · Price. If this is not a consideration, you probably don’t own a DSM

    Selecting the size

    Diameter: Most likely you will choose 17, 18 or 19 inch diameter. Most of us started with 16’s and you gotta go bigger right? I can tell you from experience that 18” wheels start to become a tradeoff for practicality issues vs. function and looks. Bigger wheels will NOT normally help you with your “wheel gap” as the overall diameter of your wheel/tire combination will stay close to stock (see Tire Profile Height below).

    Width: The wheel width you want is somewhat dependent on the tire width you want to run. Wider is better right? 225’s will be a pretty easy fit. 235’s are starting to push the clearance envelope. 245’s are possible and at least one DSMtuners member reports successfully using 255’s. The rule of thumb is that the wheel width should be somewhere in the neighborhood of 70 to 100% of the tire section width, closer to 100% being ideal. The stock 205/55/16’s on six inch wheels are pretty close to the 70% minimum. 8.5” is the widest wheel I’ve heard of any members using.

    Below is simple chart using the 70%-100% rule to calculate wheel and tire min and max widths. Don’t say I said it would or wouldn’t work though; this is only a guideline. Many dsm’ers swear by 225’s on 6” stock wheels.

    Tire Wheel Min Wheel Max
    195 5.5 7.7
    205 5.7 8.1
    225 6.2 8.9
    235 6.5 9.3
    245 6.8 9.7

    Wheel Tire Min Tire Max
    6 152 218
    7 178 254
    8 203 290
    8.5 216 308

    Excessive tire width results in tire sidewalls that are not well supported and flex more in turning.


    Tire Profile height: Many newbies do not understand this size attribute. This is the middle number of the tire size. It’s a proportion of the tire section width. As a “proportion” it is variable. A 50 series on one size tire is not the same height as a 50 on another. After you decide on your tire width, use a tool like this one, to help you choose a tire with a similar overall diameter as your stock tire:
    http://www.miata.net/garage/tirecalc.html

    Try to stay within a couple percent or so or you could have significant speedo errors.

    Offset: Another difficult thing for some to understand. Offset is typically stated in millimeters. Simply put, it is how far the wheel is pushed in from the centerline. The greater the offset the farther your wheels are pushed under your fenders (and towards suspension members). Stock offset is 46mm.

    According to vfaq.com, 225 tires with stock offset leave a minimal clearance of 4mm. Thus a 235 tire which is 5mm wider on each side, would require maximum of 41mm offset. Extrapolating using these numbers gives these values:

    Tire Width Max Offset
    225mm 46mm
    235mm 41mm
    245mm 36mm
    255mm 31mm

    I’ve read that going below 30mm offset is likely to result in accelerated bearing wear.

    Here’s a link for everything you want to know about offset:
    http://www.vfaq.com/mods/macross/offsetFAQ.html

    Center Bore: Depending on whom you believe, this is either a critical concern or not even worth worrying about. Most aftermarket wheels have a center bore that is at least as big as the hub of any car it is likely to be used for. This means that any aftermarket wheel you buy will likely have a larger center bore than your DSM hub. Some “experts” claim that it is highly important that this gap be filled with something called a hubcentric ring, keeping all the stresses on the hub and not the wheel mounting studs. Others will say that this is ridiculous and that the studs are up to it. You decide for yourself. You can get rings for around $20. DSM’s have 67mm center bore. Get rings 67 mm ID and “x” OD, “x” being the center bore of the wheels you have chosen. I orederd them and after seeing them, I have a hard time believing that a thin plastic ring is critical to supporting the weight of my 3000+ lb vehicle.

    Bolt Pattern: DSMs have a 5x114.3mm (4.5") bolt pattern.


    Selecting the style

    You probably have a good idea what look you are going for before you start. A couple of the major tire dealers have online features that show different wheels on your car. I’ve heard of other guys cutting out pictures of wheels and taping them on their computer screen over a properly sized image of their ride. When I started looking, I went through an issue of Compact Sport Car magazine and dog-eared every page that had a wheel that caught my eye. After looking at them over and over again I found that I was drawn to a completely different look than what I started with. Pick the look YOU like. If you post it for opinions you are guaranteed to draw criticism from members whose selection criteria and taste differ from your own.

    Once you have a style in mind, compare all the similar designs from different manufacturers. Check prices on line. When you get down to one or two brands you can search for just the specific model and search for best price.

    What’s left? Oh yeah, weight. You probably started out thinking you were going to get some really lightweight wheels to put that raw power to the road instead wasting it rotating all that metal mass. But once your eyes locked onto those really cool, bling-bling wheels, weight became less of a concern right? You likely found that almost none of the wheels you looked at had any weight information available. Guess why. Cause they’re heavy. Stock aluminum wheels are pretty heavy. I believe the GST wheels are around 22 lbs each. Since the mass of the wheel must be rotated and not simply accelerated in a straight line, variation in wheel weight has a much greater impact on acceleration than non-rotational or static mass. Opinions vary on the effect of increased rotational mass but most put it in between 1.5x to 3x static mass. Let’s say 2x is the right number. This means that if you use a wheel that is 5 lbs. lighter than stock, it would be like taking 40 lbs. off weight off your car. That’s significant.

    Increased unsprung weight also forces your shocks and springs to work harder so, although bigger/wider wheels may handle better on a skid pad, there may be a tradeoff in diminished handling characteristics.

    Here’s a site with weights many popular wheel types:
    http://www.wheelweights.net/

    Installation

    If you are unsure of your fitment selections, it is highly advised to make your purchases through a local installer who will be responsible for the proper fit. If you buy your wheels and tires online and then have a local guy mount them for you, YOU are responsible, you may have difficulty trying to return anything if it doesn’t fit. Do your homework and don’t be afraid to post your size selections and ask for advice.

    Do not use this as your only source of information. I am not an expert. I’m just another noob who’s been through the wheel and tire selection process a couple of times. Consult other sources including tire sellers and other DSM’ers that have the size combination you are considering.

    Ron Tew
     

    Attached Files:

    DGajre777 likes this.
  2. wret

    wret Proven Member

    2,693
    65
    Joined Jul 3, 2003
    Bel Air, Maryland
    Some helpful DSMtuners members brought some additional issues regarding offset to my attention.

    The chart I posted for maximum offset is very basic and fails to emphasize the effect of changing overall tire diameters. I was inspired to work out an offset formula to take both width and diameter variables into consideration. Unfortunately I don’t think there is a way for this site to perform mathematical equations or it would be possible to set up a set of entry boxes for tire size and get the maximum offset calculated as a result. Instead I posted the results in a table, which should be broad enough to include most possible tire size combinations. For now the table can be found in the suspension forum. I won’t link to it directly so it will not become a permanent part of this tech article until I can prove a few more reference points. When I have more clearance data I will be able to post it here.

    It should also be mentioned that there is no guarantee of size consistency from one tire brand or type to another. My calculations for maximum offset leave no margin of error. They allow for a 4mm clearance, which is thought by some to be the minimum without risk of rubbing. If you cut it too close and your particular brand of tire is a couple millimeters wider or taller you will likely have a rubbing problem.
     

Share This Page

Support Vendors who Support the DSM Community
ECM Tuning ExtremePSI Feal Suspension Fuel Injector Clinic Jacks Transmissions JNZ Tuning Kiggly Racing Morrison Fabrications OHM Racing RixRacing RockAuto SouthBay Fuel Injectors STM Tuned Track Decals Track Sculptures VR Speed Factory