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Re: tire size and speedometer accuracy
On Tue, 10 Oct 2006 14:30:57 -0700, Dennis Leong wrote:
[color=blue]
> Okay, then my question now is if the circumference of tires are changed,
> will speedo recalibration be necessary?.[/color]
How much over- or undersized are you going?
I had a Toyota Tercel I put 185/60-13's on, when the standard was
155/80-13. I did a spreadsheet to calculate the difference. It was about 2
MPH at 65 MPH. I put 185/60-14's on a Tercel wagon that came with
175/70-13's, but with the lower profile the speedometer was the same.
Google Tire Sized Calculator Dodge Ram; there is an excellent one there,
there is also a very good one if you change Dodge Ram to Miata, and there
is another at 1010tires.com.
You enter the stock size for your vehicle, and the size you want to
replace it with, and it will give you the difference as a percentage and
in MPH.
[color=blue]
>
> "Ray O" <rokigawaATtristarassociatesDOTcom> wrote in message
> news:327f7$452be1f6$44a4a10d$22193@msgid.meganewsservers.com...[color=green]
>>
>> "Ray O" <rokigawaATtristarassociatesDOTcom> wrote in message news:...[color=darkred]
>>>
>>> "Dennis Leong" <spgdxl@berkeley.edu> wrote in message
>>> news:eggn1l$16rd$1@agate.berkeley.edu...
>>>> When I was hot rodding in the late '60s, I spent a lot of time
>>>> researching how tire size and different differential gear ratios
>>>> affected speedometer accuracy. I bought a lot of different speedo drive
>>>> gears for the tranny (this was on a GM TH400) to compensate for the
>>>> changes I made. All this just to keep my speedo as close accurate as
>>>> possible as I didn't want to speed and collect tickets. Now someone
>>>> tells me that after putting in larger diameter tires on his car (Honda
>>>> Element), the tire dealer said that his speedo would still be accurate.
>>>> I find this hard to believe. Are today's electronics intelligent enough
>>>> to automatically adjust for different diameter tires? I would think at
>>>> least something needs to be manually re-calibrated? This is a good
>>>> group to get information even though this is not a Toyota specific
>>>> issues. Thank you.
>>>
>>> If the circumference of the replacement tire's tread is the same as the
>>> circumference of the original tires, then the speedometer and odometer
>>> will still be accurate. 2 tires can have different diameters and have
>>> the same circumference if the aspect ratio is proportionally different.
>>> A tire's diameter is measured from the center of the "hole" to the bead,
>>> not the tread.
>>> --
>>>
>>> Ray O
>>> (correct punctuation to reply)[/color]
>>
>> Oops, brain fade... Correction: A tire's radius is measured from the
>> center of the hole to the bead...
>> Diameter is 2 times the radius.
>> --
>>
>> Ray O
>> (correct punctuation to reply)
>>[/color][/color]
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