Recalibrate Speedometer for larger tires?

I'm going up from 175's to 185's on the Corolla -- seems like that will
make my speedometer be under some, which is a big deal. Should I get
my speedometer recalibrated after I swap the tires?

"Learning Richard" <learningrichard@gmail.com> wrote in message
news:1116967568.044766.67770@f14g2000cwb.googlegro ups.com...
> I'm going up from 175's to 185's on the Corolla -- seems like that will
> make my speedometer be under some, which is a big deal. Should I get
> my speedometer recalibrated after I swap the tires?
>
There are many tire size calculators that will tell you the difference
(about 2%). No, you should not change your speedometer. Remember that your
tire diameter also changes as your tire tread wears.

The numbers you gave us are not quite enough. the tires are sized as
175/nnX13 <or 14, whatever> The nn part is needed. But, I can tell you what
the math is, and you can work out the variables to fit your needs.

Let's say you have 175/80x13s. The 13 part is a fixed number, and you can
replace it with 14 or 15 as appropriate. The 175 and the 80 are the numbers
we need to know, and the numbers we will manipulate in this exercise. The 80
means 80% of the 175 number, so multiply 175 by .8, the result is 140mm.
Divide 140 by 24.7 to convert to inches, you get 5.67. This is the sidewall
height of the tire, there are two sidewalls, so double this number, yoiu get
11.34. Now, add the rim diameter <13, 14, or 15, as appropriate - I'll
assume 13> and you get an overall diameter of 24.34.

Now, if you go to a 185/75, you will find that you get 138.75mm. This will
be essentially the exact same size from the perspective of your speedometer,
and you won't need to do anything as far as correction of the calibration. I
haven't begun to address any issues you might have with the tires running
into stuff under the car, and there may be no issues at all, but you can
work through this.

As you can see, if you go from a 175/80 to a 185/75, then you will end up
with a lower sidewall profile and a wider footprint. Both should be an
improvement to handling. To work out other conversions, multiply the first
number <175> by the second number <.80> to find the overall sidewall of your
current tire. Then multiply the new size <185> by the various sidewall
ratios <.75, .70, etc.) to find an overall sidewall number that is as close
as possible to the current tire size.

In the numbers on the tire, the first number <175> is the width of the
tread*, and the second number <80, 75, 70, etc.) is the ratio of tread width
that is the sidewall. The second number is called the Aspect Ratio, and when
the aspect ratio is calculated and doubled, then you know what the height is
of two sidewalls, add this number to the rim size <13, 14, 15, etc.) and you
will find the total diameter of the tire. If your current tire is 175/80x13,
and you wanted new tires and rims to dress your car up, but didn't want to
run into gearing issues or speedometer troubles, you could go to a
195/55x16. This would be 0.3 inches larger than stock diameter. Assuming
they didn't run into the shock towers or the fenders, the gears and
speedometer would never know they were there.

Go to www.tires.com or www.tirerack.com and you can find the various Plus
Sizes that fit your car and do not affect the speedo or the transmission.






"Learning Richard" <learningrichard@gmail.com> wrote in message
news:1116967568.044766.67770@f14g2000cwb.googlegro ups.com...
> I'm going up from 175's to 185's on the Corolla -- seems like that will
> make my speedometer be under some, which is a big deal. Should I get
> my speedometer recalibrated after I swap the tires?
>

On Tue, 24 May 2005 14:31:22 -0700, Jeff Strickland wrote:

> The numbers you gave us are not quite enough. the tires are sized as
> 175/nnX13 <or 14, whatever> The nn part is needed. But, I can tell you what
> the math is, and you can work out the variables to fit your needs.


<Dissertation snipped for brevity>

Very good, Jeff! You get the "A" for today!!!


>
> "Learning Richard" <learningrichard@gmail.com> wrote in message
> news:1116967568.044766.67770@f14g2000cwb.googlegro ups.com...
>> I'm going up from 175's to 185's on the Corolla -- seems like that will
>> make my speedometer be under some, which is a big deal. Should I get
>> my speedometer recalibrated after I swap the tires?
>>

--
The Relentless Pursuit Of Conception...

On Tue, 24 May 2005 13:46:08 -0700, Learning Richard wrote:

> I'm going up from 175's to 185's on the Corolla -- seems like that will
> make my speedometer be under some, which is a big deal. Should I get
> my speedometer recalibrated after I swap the tires?


Nah. Going from a 175/70-14 to a 185/60-14 (which is what I would do...)
will result in an error so small that it certainly isn't worth spending
the $100 or so it will take to swap the gear in the tranny. On a Tercel I
went from 155/80-13 to a 185/60-13 and the difference in speed was
negligible. I once asked a cop I saw doing radar to clock me, and at 60MPH
I was doing 61.

However, the handling was excellent!

--
The Relentless Pursuit Of Conception...

"Jeff Strickland" <spamcatcher@yahoo.net> wrote in message
news:me6dnWS2ZaagAA7fRVn-iw@ez2.net...
> The numbers you gave us are not quite enough. the tires are sized as
> 175/nnX13 <or 14, whatever> The nn part is needed. But, I can tell you
what
> the math is, and you can work out the variables to fit your needs.
>
> Let's say you have 175/80x13s. The 13 part is a fixed number, and you can
> replace it with 14 or 15 as appropriate. The 175 and the 80 are the
numbers
> we need to know, and the numbers we will manipulate in this exercise. The
80
> means 80% of the 175 number, so multiply 175 by .8, the result is 140mm.
> Divide 140 by 24.7 to convert to inches, you get 5.67. This is the
sidewall
> height of the tire, there are two sidewalls, so double this number, yoiu
get
> 11.34. Now, add the rim diameter <13, 14, or 15, as appropriate - I'll
> assume 13> and you get an overall diameter of 24.34.
>
> Now, if you go to a 185/75, you will find that you get 138.75mm. This will
> be essentially the exact same size from the perspective of your
speedometer,
> and you won't need to do anything as far as correction of the calibration.
I
> haven't begun to address any issues you might have with the tires running
> into stuff under the car, and there may be no issues at all, but you can
> work through this.
>
> As you can see, if you go from a 175/80 to a 185/75, then you will end up
> with a lower sidewall profile and a wider footprint. Both should be an
> improvement to handling. To work out other conversions, multiply the first
> number <175> by the second number <.80> to find the overall sidewall of
your
> current tire. Then multiply the new size <185> by the various sidewall
> ratios <.75, .70, etc.) to find an overall sidewall number that is as
close
> as possible to the current tire size.
>
> In the numbers on the tire, the first number <175> is the width of the
> tread*, and the second number <80, 75, 70, etc.) is the ratio of tread
width
> that is the sidewall. The second number is called the Aspect Ratio, and
when
> the aspect ratio is calculated and doubled, then you know what the height
is
> of two sidewalls, add this number to the rim size <13, 14, 15, etc.) and
you
> will find the total diameter of the tire. If your current tire is
175/80x13,
> and you wanted new tires and rims to dress your car up, but didn't want to
> run into gearing issues or speedometer troubles, you could go to a
> 195/55x16. This would be 0.3 inches larger than stock diameter. Assuming
> they didn't run into the shock towers or the fenders, the gears and
> speedometer would never know they were there.
>
> Go to www.tires.com or www.tirerack.com and you can find the various Plus
> Sizes that fit your car and do not affect the speedo or the transmission.

Very good explanation, I couldnt have said it better myself (much)

=)

On Tue, 24 May 2005 19:35:58 -0400, "Josh"
<nobody@noplacenowhere.never> wrote:

>Very good explanation, I couldnt have said it better myself (much)

That I will agree with you on.....


--

Scott in Florida

"Scott in Florida" <JustAsk@Florida.com> wrote in message
news:u8k791d2pc846c0uvn3og6qahvd22uc9ij@4ax.com...
> On Tue, 24 May 2005 19:35:58 -0400, "Josh"
> <nobody@noplacenowhere.never> wrote:
>
> >Very good explanation, I couldnt have said it better myself (much)
>
> That I will agree with you on.....
>

Thanks, but what happens when the whole mess detonates?

you can self test your actual speed at what ever you normally cruise at.
Get real accurate timing thru a measured mile at a constant speed (I usually
average 3 miles or so)

Divide 1 mile avg in seconds into 3600 (3600/60= 60mph).

This is cheaper than a speedo job and you can do it for any car/tire (how do
you think they "clock" you from a plane?)

Ron

OR, you can calculate your current tire size, then calculate where you want
to go and select a new size that is essentially the same overall diameter as
you currently have, and not worry that the calibration of the speedo is
whacked.




"ron" <randus3remove@pacbell.net> wrote in message
news:8bRke.1306$rY6.374@newssvr13.news.prodigy.com ...
> you can self test your actual speed at what ever you normally cruise at.
> Get real accurate timing thru a measured mile at a constant speed (I
usually
> average 3 miles or so)
>
> Divide 1 mile avg in seconds into 3600 (3600/60= 60mph).
>
> This is cheaper than a speedo job and you can do it for any car/tire (how
do
> you think they "clock" you from a plane?)
>
> Ron
>
>

"Jeff Strickland" <spamcatcher@yahoo.net> wrote:

>
>"Scott in Florida" <JustAsk@Florida.com> wrote in message
>news:u8k791d2pc846c0uvn3og6qahvd22uc9ij@4ax.com...
>> On Tue, 24 May 2005 19:35:58 -0400, "Josh"
>> <nobody@noplacenowhere.never> wrote:
>>
>> >Very good explanation, I couldnt have said it better myself (much)
>>
>> That I will agree with you on.....
>>
>
>Thanks, but what happens when the whole mess detonates?
>
>
Detonates?...DETONATES!?!...Christ, don't use that word around
here, you'll start a conflagration...
--


-Gord.

"I'm trying to get as old as I can,
and it must be working 'cause I'm
the oldest now that I've ever been"

Jeff Strickland wrote:
> The numbers you gave us are not quite enough. the tires are sized as
> 175/nnX13 <or 14, whatever> The nn part is needed. But, I can tell you what
> the math is, and you can work out the variables to fit your needs.
>
> Let's say you have 175/80x13s. The 13 part is a fixed number, and you can
> replace it with 14 or 15 as appropriate. The 175 and the 80 are the numbers
> we need to know, and the numbers we will manipulate in this exercise. The 80
> means 80% of the 175 number, so multiply 175 by .8, the result is 140mm.
> Divide 140 by 24.7 to convert to inches, you get 5.67. This is the sidewall
> height of the tire, there are two sidewalls, so double this number, yoiu get
> 11.34. Now, add the rim diameter <13, 14, or 15, as appropriate - I'll
> assume 13> and you get an overall diameter of 24.34.
>
> Now, if you go to a 185/75, you will find that you get 138.75mm. This will
> be essentially the exact same size from the perspective of your speedometer,
> and you won't need to do anything as far as correction of the calibration. I
> haven't begun to address any issues you might have with the tires running
> into stuff under the car, and there may be no issues at all, but you can
> work through this.
>
> As you can see, if you go from a 175/80 to a 185/75, then you will end up
> with a lower sidewall profile and a wider footprint. Both should be an
> improvement to handling. To work out other conversions, multiply the first
> number <175> by the second number <.80> to find the overall sidewall of your
> current tire. Then multiply the new size <185> by the various sidewall
> ratios <.75, .70, etc.) to find an overall sidewall number that is as close
> as possible to the current tire size.
>
> In the numbers on the tire, the first number <175> is the width of the
> tread*, and the second number <80, 75, 70, etc.) is the ratio of tread width
> that is the sidewall. The second number is called the Aspect Ratio, and when
> the aspect ratio is calculated and doubled, then you know what the height is
> of two sidewalls, add this number to the rim size <13, 14, 15, etc.) and you
> will find the total diameter of the tire. If your current tire is 175/80x13,
> and you wanted new tires and rims to dress your car up, but didn't want to
> run into gearing issues or speedometer troubles, you could go to a
> 195/55x16. This would be 0.3 inches larger than stock diameter. Assuming
> they didn't run into the shock towers or the fenders, the gears and
> speedometer would never know they were there.
>
> Go to www.tires.com or www.tirerack.com and you can find the various Plus
> Sizes that fit your car and do not affect the speedo or the transmission.
>
>

see why I don't talk about cars on here?

On Wed, 25 May 2005 08:29:09 -0700, Learning Richard wrote:

>
>
> Jeff Strickland wrote:
>> The numbers you gave us are not quite enough. the tires are sized as
>> 175/nnX13 <or 14, whatever> The nn part is needed. But, I can tell you what
>> the math is, and you can work out the variables to fit your needs.
>>
>> Let's say you have 175/80x13s. The 13 part is a fixed number, and you can
>> replace it with 14 or 15 as appropriate. The 175 and the 80 are the numbers
>> we need to know, and the numbers we will manipulate in this exercise. The 80
>> means 80% of the 175 number, so multiply 175 by .8, the result is 140mm.
>> Divide 140 by 24.7 to convert to inches, you get 5.67. This is the sidewall
>> height of the tire, there are two sidewalls, so double this number, yoiu get
>> 11.34. Now, add the rim diameter <13, 14, or 15, as appropriate - I'll
>> assume 13> and you get an overall diameter of 24.34.
>>
>> Now, if you go to a 185/75, you will find that you get 138.75mm. This will
>> be essentially the exact same size from the perspective of your speedometer,
>> and you won't need to do anything as far as correction of the calibration. I
>> haven't begun to address any issues you might have with the tires running
>> into stuff under the car, and there may be no issues at all, but you can
>> work through this.
>>
>> As you can see, if you go from a 175/80 to a 185/75, then you will end up
>> with a lower sidewall profile and a wider footprint. Both should be an
>> improvement to handling. To work out other conversions, multiply the first
>> number <175> by the second number <.80> to find the overall sidewall of your
>> current tire. Then multiply the new size <185> by the various sidewall
>> ratios <.75, .70, etc.) to find an overall sidewall number that is as close
>> as possible to the current tire size.
>>
>> In the numbers on the tire, the first number <175> is the width of the
>> tread*, and the second number <80, 75, 70, etc.) is the ratio of tread width
>> that is the sidewall. The second number is called the Aspect Ratio, and when
>> the aspect ratio is calculated and doubled, then you know what the height is
>> of two sidewalls, add this number to the rim size <13, 14, 15, etc.) and you
>> will find the total diameter of the tire. If your current tire is 175/80x13,
>> and you wanted new tires and rims to dress your car up, but didn't want to
>> run into gearing issues or speedometer troubles, you could go to a
>> 195/55x16. This would be 0.3 inches larger than stock diameter. Assuming
>> they didn't run into the shock towers or the fenders, the gears and
>> speedometer would never know they were there.
>>
>> Go to www.tires.com or www.tirerack.com and you can find the various Plus
>> Sizes that fit your car and do not affect the speedo or the transmission.
>>
>>
>
> see why I don't talk about cars on here?


LOL!

--
The Relentless Pursuit Of Conception...