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Question: increase tire diameter to fill wheel gap?

Discussion in 'Design' started by ModFather, May 28, 2017.

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  1. ModFather

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    Okay I have a question for all you tire gurus out there. I have a problem with the tire/fender gap on the 3s spotted so far. If what the Mad Magyar says is correct, the tire diameter of both the 18 and 19 rims is about 26.4". If I increase the tread width and hold the profile constant OR hold the tread width constant and increase the profile, I can achieve an overall increase in the tire diameter with either the 18 or 19 inch rim. This would help in filling some of that fender gap. What say you about this strategy for correcting fender gap? Conventional wisdom says that tire diameter should not be increased by more than 3% to avoid brake damage.

    Second question: running a larger diameter tire than 26.4" could affect speedometer readings. Does anyone know if the speedometer reading on the MS/X is electro-mechanical or is it based on GPS? If GPS, tire diameter has no affect on readings.

    Maybe this should be in a thread of its own.
     
  2. MelindaV

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    would not recommend it - potentially could end up with rubbing issues (on the front) and/or risk looking like this (unless that's the look you are going for, then by all means....)
     
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    • ModFather

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      Ha. ha, that's the "Pretty in Pink" version. That color doesn't match my purse, heels, and false eyelashes, but nice try.

      Rubbing issues on the front, not sure I want to go there. No I am talking about increasing wheel diameter about an inch or so. SAS on the MS doesn't have rubbing issues on the lowest setting which lowers an inch from "normal." I don't mind a little extra meat on my tires. I never did buy into the rubber band look.
       
    • SoFlaModel3

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      Changing the rolling diameter will impact your speedo and shouldn't be done. To be honest a taller tire to reduce wheel gap looks worse as you now have the look of SUV tires on a car.

      I am disappointed in the wheel gap as well (mostly the back).

      The only answer is to swap out the suspension aftermarket.

      I'm not sure that I want to do that...
       
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      • garsh

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        I did this with my Nissan Leaf (pic, and thread). The OEM tires were 205/55R16. I installed 235/50R17 tires. That's an increase in diameter from 24.88" to 26.25". The good news is that they fill in the wheel wells much better. But there are tradeoffs.
        • They raise the car too. My Nissan Leaf now sits higher than a Nissan Juke. If feels a lot like riding in a small SUV. You could fix this by lowering the suspension, but that's a whole other expense that I didn't want to take on. I'm just playing around with my Leaf on the cheap (got the wheels on craigslist for $110).
        • Stability control was not happy. The stability control would kick in when going around moderate curves at moderate (~40mph) speeds. It was quite disconcerting to have the car suddenly start braking. I had to remember to turn off the stability control every time I started driving the car.
        • Speedometer did change. But it always showed too high before. The larger tires meant it showed a speed 1-2mph low.
        I ended up replacing the front tires with 215/50R17 (25.46" diameter). That fixed most of the issues. Speedometer is now very close to correct. Stability control no longer kicks in, but I do get a "brake" warning light when making a tight turn - I'm not sure what that's about.
         
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        • Mad Hungarian

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          #6 Mad Hungarian, May 29, 2017
          Last edited: May 30, 2017
          Agree this should get it's own thread, gotta make this quick before I hit the road though, maybe Melinda can start/move for us later?
          Although the tire industry's general rule of thumb for OD variance on replacement sizing is +/- 3%, that's still enough to get you into trouble on a few tighter vehicles so I've set the default at our place at +/- 2%. The only exceptions allowed are if the OE range for a given model exceeds that, which happens often with pickups and sometimes the odd larger sedan. In those cases we use the smallest and largest OEM ODs as the limit. No way to know what the 3's fitment limits will be until we get our hands on one. But I'd still prefer to go with a mild set of lowering springs to get it looking right, I'm sure the aftermarket is gonna be all over that. One other thing I definitely think will help would be to fit slightly lower offset wheels to bring them out a little more flush with the fender edges.
          To be continued...
           
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          • ModFather

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            Thanks everyone, your opinions and experiences are most useful and helpful. Rather than investing in aftermarket rims to address wheel offset (I rather like the two OEM rim styles shown thus far), how about using wheel spacers to address offset? You do have to be careful about using spacers on the front rims because you can experience tire rub when turning if the spacers are too thick. The Prius modifiers have had good success with using wheel spacers and coil over springs to address fender gap, especially at the rear wheels. Experimentation by the Prius group found that 25mm spacers at the rear and 12mm at the front provided the desired "flush wheel" offset without any tire rub. That is only an example. Too early to tell what the exact specification on the 3 might be. But I'm bored so I have to do something to fill the time waiting for my 3.
             
          • SoFlaModel3

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            By the way one more thought... not just speedo but obviously your odometer as well. If you're going to change the rolling diameter you really should have the car calibrated or you will misrepresent the mileage on the car.

            Moreover you just shouldn't do it!
             
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            • garsh

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              That will result in a larger positive scrub radius. This might affect the handling characteristics of the car. On my Leaf, the larger, wider tires also resulted in a higher positive scrub radius. This resulted in noticeable torque steer, but that's a phenomenon of front-wheel drive cars, so it shouldn't be an issue on a Model 3. But you might notice some other issue.

              Depending on the size of the spacer, you may need to replace all of the lug bolts with longer ones.
               
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              • ModFather

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                #10 ModFather, May 29, 2017
                Last edited: May 29, 2017
                Everything you say is correct @garsh. Scrub radius applies primarily to the front wheels and is a particular problem for FWD. I know that a creative alignment shop can correct the scrub radius with camber adjustment. I am interested to hear what @Mad Hungarian has to say about this.

                There are different types of wheel spacers. Some bolt to the hub and the lug bolts thread into the spacer which allows the reuse of existing bolts or have the bolts in place on the spacers. The Prius group has had the best luck with Adaptec spacers for both safety and utility.
                 
              • JDTM3

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                Really bummed they are not offering the 20" option that were shown at launch.
                 
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                • ModFather

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                  True that,sfm3, BUT frequently the speedo/odometer calibration at the factory is not correct either! That means you should have your 3 re-calibrated after the fact whether you change settings or not......if you want to play strictly by the book.
                   
                • SoFlaModel3

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                  I can't worry about the factory screwing up, but if I modify the car out of OEM spec and I don't that's deceitful for sure.
                   
                • ModFather

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                  True, unless you re-calibrate, which is what I recommend - not necessarily to the factory spec but to the true spec. There were a lot of people who did have to worry about a factory screw up when the value of their car went down as a result of the Volkswagen Diesel debacle. ;)
                   
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                  • SoFlaModel3

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                    That's a good point. You know I could have sworn that I read something about an issue with Ferrari odometers or maybe it was service intentionally rolling back miles. Yikes!
                     
                  • UncleT

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                    And those may be the least of the concerns. With absolutely everything computer controlled based on that wheel/tire diameter I would be concerned about causing some kind of drivetrain damage (I could be off on this). Maybe different springs instead?
                     
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                    • JBsC6

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                      Today's cars often don't lose speedometer accuracy with changes in tire sizes.

                      The front to rear diameter traditionally needs to stay within 2 percent of the factory set up..

                      It's not the size but rather the differential of diameter between front and rear.

                      Just wait for the aftermarket to offer wheels.. I want the launch rims we saw last April 1st ...where the rear wheels were larger in diameter...than the front,,,

                      It's necessary because of the visual weight of the rear half of the tesla model 3...much like corvette c5s, c6 s and c7 s....all having larger diameter rims and tire sizes out back...
                       
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                      • MelindaV

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                        The front and rear alpha wheels were both 20"s, tires with a diameter of 26.5".
                        The rear tires were 275/30Z/20 and the fronts 235/35Z/20, looking like this:
                        Screen Shot 2017-05-29 at 6.11.41 PM.png
                         
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                        • Watts4me

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                          Dubz or go home!
                           
                        • JBsC6

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                          Thank you Melinda ...I'll be trying to get that exact size setup from the aftermarket as I believe it will probably cost about the same as teslas 19 inch setup and I'll just keep the standard 18 inch rims and tires for a winter setup...come spring time I'll just slap on the wheels and tire sizes you just posted because that looked really good at the press release...

                          I never believe in rotating tires anyway...not worth the hassle in my opinion and with staggered sizes impossible anyway..
                           
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