tire size change - will this affect on board computer - Page 2
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Thread: tire size change - will this affect on board computer

  1. #11
    crv|oc Rank: Junior
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    Quote Originally Posted by crv383 View Post
    To the OP (and someone else whom I won't name to protect the innocent), here's how you calculate metric tire dimensions:

    235 X .60 X 2 / 25.4 + 18 = 29.1" diameter
    235 / 25.4 = 9.25" total width

    255 X .55 X 2 ?25.4 + 18 = 29.04" diameter
    255 / 25.4 = 10.04" wide

    245 X .60 X 2 / 25.4 + 18 = 28.61" diameter
    9.65" wide

    Actual total tire width will vary slightly depending on rim width.
    That's a nice, simple method for rough calculation, but if fails to take in manufacturing variations such as mold construction, bead design, seam dimensions, etc., all of which vary depending on tire type, design, style, etc., and which also vary from one tire maker to the next. All these things make precise math impossible. There are variations in even the same tire by the same maker in different size classes. So simple math is not accurate, and neither is what is published precisely accurate. But I generally go with what is published. The information used to generate that data is more comprehensive and probably closer to reality and closer to mfr. specs.

    Heck, when I buy a new set of tires, I want a set from the same batch, with matching dates.
    Larry


    Now that I've learned my lesson, I'm supremely confident that next time I'll make a different mistake.


    2007 CR-V EX-L AWD Green Tea Metallic
    1991 Ford F250 Lariat Supercab LWB 4X4, 460 AT

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  3. #12
    crv|oc Rank: Member
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    Quote Originally Posted by crv383 View Post
    Mathematically, the 245/55/18 is slightly shorter (about 1/2") than the stock 235/60/18 and will skew the speedo slightly. A 255/55/18 is virtually identical in height to stock but slightly wider. It's the tire overall height/diameter that affects the speedo, width will not affect the speedo. A taller tire will place more load on the drivetrain. Kinda like riding a 10 speed bike, your legs feel the increased load of a higher (taller) gear.
    than you for the kind feedback.
    255/55/18 tires maybe in my future.

  4. #13
    crv|oc Rank: Member
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    Quote Originally Posted by kloker View Post
    Your stock 235/60/R18 tire shows to have a 30" diameter on the Discount Tire website. The 245/55/R18 has a diameter of 29". The 245/60/R18 would keep the 30" diameter (same as stock) and not cause any changes, though they would be slightly heavier as well as wider. Going with the smaller diameter tires would cause your speedometer to read slightly higher than actual, and give your engine a slight advantage in leverage/power, but only by a very small amount, and you would have an equally small percentage drop in fuel mileage. The smaller tires would likely be slightly lighter in weight, which could help offset the drop in fuel mileage. Any visual or appearance change would likely be unnoticeable. I see no advantage, so I'd go with the 30" diameter tires to keep all other aspects stock, and likely have no effect on the computer.
    thank you for the kind feedback.

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  6. #14
    crv|oc Rank: Senior
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    Class......it's simple, 2+2 always equals 4, and mathematics is very precise, even when some try to tell you otherwise.

    We are talking passenger car/light truck tires..........not tires for tractor/trailer big rigs with 18 wheels/tires.

    Doing the simple, but accurate math, to determine passenger car tire height and width is a lot easier, or should I say simpler, than running around various tire stores with a tape measurer and measuring various metric size tires.

    My Stanley carpenter's tape just verified the 235/60/18 tires on our CRV are 29" tall, not 30". Mathematically close enough for me.
    Last edited by crv383; 03-31-2019 at 09:23 AM.
    2017 stripped EX-L - unmolested by the dealership
    Built July 2017, Indiana USA

    MAN LAW - raise your hood once a week and have a look

  7. #15
    crv|oc Rank: Sophomore
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    Quote Originally Posted by esportzman View Post
    2017 CR-V EX-L FWD


    Current tire size 235/60R18 BTW- OEM HANKOOK KINERGY GT - SIZE: 235/60R18 ... ( DO NOT BUY! )

    TIRES AT 18000 MILES ( 4/32 tread left - tires rotated and balanced every 6 months )- JUST TERRIBLE WEAR - NEED TO REPLACE THESE PIECE O' ****!

    Would like to try 245/55R18

    any feedback is welcome.

    thank you
    curious, why do you balance your tires twice a year?
    I was planning to change my hankooks (when its worn out) to a 235/70/18 tires, have not decided what brand yet but my priority will be "quite". This will add .46 inch to the total height of the CRV, width is the same. At 17K miles, the Hankooks are still pretty new. No problem, we don't drive it hard though. (EX 2017 fwd)Name:  tires.jpg
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    Last edited by BBLee; 04-01-2019 at 03:50 PM.

  8. #16
    crv|oc Rank: Member
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    esportzman
    Agree with bobinpa that tire manufacturer's revolutions per mile is the way to compare tires. We significantly changed the tire sizes (all six) on our motorhome. Using the software on the truck shop's laptop plugged into the engine port just like on all cars. The speedometer/odometer was re-calibrated to the revolutions per mile of the nearly 4" taller tires. Of course we did research first with Cummins and Allison for their OK, and mounted the tires to ensure there was no problem. I am guessing the same could be accomplished for your CRV. Good luck!
    flynnwalter

  9. #17
    crv|oc Rank: Junior
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    Quote Originally Posted by crv383 View Post
    Class......it's simple, 2+2 always equals 4, and mathematics is very precise, even when some try to tell you otherwise.

    We are talking passenger car/light truck tires..........not tires for tractor/trailer big rigs with 18 wheels/tires.

    Doing the simple, but accurate math, to determine passenger car tire height and width is a lot easier, or should I say simpler, than running around various tire stores with a tape measurer and measuring various metric size tires.

    My Stanley carpenter's tape just verified the 235/60/18 tires on our CRV are 29" tall, not 30". Mathematically close enough for me.
    I did make an error - that tire was 29" and not 30" - so I went back and corrected the post - thanks, Rocky and crv383!
    Larry


    Now that I've learned my lesson, I'm supremely confident that next time I'll make a different mistake.


    2007 CR-V EX-L AWD Green Tea Metallic
    1991 Ford F250 Lariat Supercab LWB 4X4, 460 AT

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  11. #18
    crv|oc Rank: Member
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    Quote Originally Posted by gnosisdog View Post
    I dropped down a size to 235/55/18 when I switched to high performance summer tires. (The Firestone Indy Hawk 500's weren't available in 60) The speedo is slightly off which is the only downside. Nothing else was affected. I find the CVT to be slightly under-geared anyway - so the tiny change in gear ratio feels like a plus. …..
    For my Tow Vehicle, I installed smaller size rubber (on same rims) as well. Went from 225/65/17 down to 225/60/17 - which is a 3.2% change. A few "arm chair" auto mechanics experts got their nylons in a knot over my findings. But from my view, using a smaller size tire worked great on my tow vehicle. And even when NOT towing, my vehicle gets better MPGs - due to less lugging and down shifting.

    Glad you found this same hidden secret as well. re: Going with smaller size rubber is sometimes better. Especially when the vehicle is geared too high at the factory. And, when one is forced to use diluted ethanol gas and its winter weaker formula mixture as well.... But, that's a topic for a different thread....
    Last edited by newbie99; 04-02-2019 at 08:16 AM.

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  13. #19
    crv|oc Rank: Senior Tigris99's Avatar
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    Quote Originally Posted by newbie99 View Post
    For my Tow Vehicle, I installed smaller size rubber (on same rims) as well. Went from 225/65/17 down to 225/60/17 - which is a 3.2% change. A few "arm chair" auto mechanics experts got their nylons in a knot over my findings. But from my view, using a smaller size tire worked great on my tow vehicle. And even when NOT towing, my vehicle gets better MPGs - due to less lugging and down shifting.

    Glad you found this same hidden secret as well. re: Going with smaller size rubber is sometimes better. Especially when the vehicle is geared too high at the factory. And, when one is forced to use diluted ethanol gas and its winter weaker formula mixture as well.... But, that's a topic for a different thread....
    I love your report on this

    The armchair guys don't get each vehicle.is different. It's not the downsizing in tires overall that mattered. It's that you downsized on a vehicle that was in need of it. And it's not just tire size. Brand, weight, rolling resistance and so on all play a part. Guessing you likely upgraded tires as well as went down a size, which your V likes better of course.

    Your right in it's also a gearing issue. You run down the highway for a long distance that benefit will likely decrease, but head wind versus tail wind will matter more than a little tire size change.

    Really want to give it a boost. Get nice and light weight aftermarket rims. Gains will go up even more especially in the MPG department.

    Sent from my SM-G950U using Tapatalk

  14. #20
    crv|oc Rank: Member
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    Glad to hear they only lasted 18,000 miles although with my driving that will still be 4 more years. I will be happy to see the end of them too.

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