Why such a big size difference for 16 vs. 17 in oem tire sizes?



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Thread: Why such a big size difference for 16 vs. 17 in oem tire sizes?

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    Why such a big size difference for 16 vs. 17 in oem tire sizes?

    Does anyone know why there is a difference in tire size between the 2009 caravan se for 16 in and 17 in tire sizes.

    The oem tire size for 16 in steels are 225/65/16 but the oem tire size for the optional 17 in rims ( which I have ) are 225/65/17.

    According to the tire size calculator the the size is off by 3.51 percent. Same van same motor both oem tire sizes. Which one is correct? I can't figure out why chrysler would use two different tire sizes that are off by so much.

    I am looking to buy winter tires and trying to figure this out.

    thanks
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    You want tires that will match the diameter of your stock tires. If your stock tires are 225/65R17, they're about 28.5" tall. A 225/70R16 will be about the same diameter (well, within 0.5% anyway). That'd be a good winter tire size for you, and there's a good selection of tires in that size.

    Why Dodge used the different sizes, it's hard to tell. But you can bet that the speedometer is programmed for the size, so if you put the 225/65R16s on, the speedometer would be reading faster than your true road speed.
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    225/70R16 was the tire size I was planning on going with. I was sarting to wonder though becasue even on tire rack it says recommened tire size is 225/65R16 or alternate size os 215/70R16 which are not as close the oem tire size as 225/70R16
    MY GARAGE
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    Picking nits, even the 225/70R16 is just a HAIR shorter than your stock tires, 225/65R17, though measured in tenths of an inch. The difference in circumference is extremely small. It's as close of an equivalent 16" size as you'll get.
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    Quote Originally Posted by Jason View Post
    You want tires that will match the diameter of your stock tires. If your stock tires are 225/65R17, they're about 28.5" tall. A 225/70R16 will be about the same diameter (well, within 0.5% anyway). That'd be a good winter tire size for you, and there's a good selection of tires in that size.

    Why Dodge used the different sizes, it's hard to tell. But you can bet that the speedometer is programmed for the size, so if you put the 225/65R16s on, the speedometer would be reading faster than your true road speed.
    Tire size is programmable. The transmission shop, when they were diagnosing a problem I had once, discovered that the tire size on my 95 was set incorrectly, and changed it. I'm sure it's a PCM setting, and you might be able to do it yourself if you have a high-end scan tool.
    Michael
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    Quote Originally Posted by thumper1 View Post
    225/70R16 was the tire size I was planning on going with. I was sarting to wonder though becasue even on tire rack it says recommened tire size is 225/65R16 or alternate size os 215/70R16 which are not as close the oem tire size as 225/70R16
    You're absolutely correct - Tire Rack has the alternate size listed based on the previous generation vans (2001-2007) which did not offer a 17" rim. This alternate size is listed in 4th gen the manual/sticker. Interestingly enough, the 5 gen vans don't have an alternate size listed on the sticker inside the door or in the manual.

    However, the alternate size listed by Tire Rack would work if you had a 16" rim (215 70 R16 tire would cause speedo will be off by 1.17%).

    For a 16" rim, 215 70 R16 is the closest size to the stock tire (225 65 R16).

    A great tire size/speed calculator is here: http://www.miata.net/garage/tirecalc.html

    I recently installed winter tires on my van, but I have 16" rims. I did a write up here:
    http://forum.chryslerminivan.net/showthread.php?t=14913

    As mmahamm said, the wheel size is programmed into the PCM at the factory in order to ensure the speedometer is accurate for both 16" and 17" wheels. You could not re-program the PCM to compensate for an alternate wheel size.
    Last edited by JOEMAMA; 12-08-2009 at 08:36 AM.
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    Tire size is programmable at the dealer with the scan tool, options are 225/65/17 or 225/65/16. I removed my 17's and installed 225/65/16 on steels, then programmed the tire size in the TIPM, (Total Integrated Power Module). I'm a Chrysler tech.

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    I don't really think that size difference is that great, TBQH. If you look at some other vehicles (not just Chrysler) they may offer several tires size differences depending on the trim level. Like Audi Q7 will offer a standard 19 inch rim, go with the sport package and you get a 20 inch, if you opt for the S-Line it jumps up to 21 inch...
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    Quote Originally Posted by lxman View Post
    Tire size is programmable at the dealer with the scan tool, options are 225/65/17 or 225/65/16. I removed my 17's and installed 225/65/16 on steels, then programmed the tire size in the TIPM, (Total Integrated Power Module). I'm a Chrysler tech.
    Good to know that the dealer can program different sizes - I know that some options cannot be programmed by the dealer later on.

    Although - it would suck having to pay the dealer twice a year to program the PCM to compensate for wheel size! Fortunately you can do it for free!
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    If you put bigger tires on and don't reprogram the pcm for them, the speedo might be wrong, but you will also accumulate miles on the odometer slower. with 3% longer rolling circumference, a mile on the bigger tire as shown on the odo will be 3% longer than an odo mile on the smaller tire, if you measured both miles with a tape measure. Your formerly 30 mile commute to work will now use only 29.1 miles on the odo. This will help down the road with resale or warranty coverage.
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