Wheel circumerence: redux [Toyota]

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From: Tegger on 8 Nov 2009 18:11

"C. E. White" <cewhite3(a)mindspring.com> wrote in
news:pO2dnQ05H_unrWrXnZ2dnUVZ_s6dnZ2d(a)earthlink.com:

> As I tried to point out before, the rolling radius is more influenced
> by the diameter of the steel belts in the tire, not the actual outside
> diameter. What brand and tire size were you testing? If we know that
> we probably can find the manufacturers revolutions per mile
> specification. If you check these, they are not a function of the
> outside tire diameter times pi. They are different than that.
>
> For instance....
>
> From the chart I posted in the previous string...
>
> .......................Revolutions
> ............Overall....Per
> Tire Size...Diameter...Mile
> 245/40ZR17 24.7" 841

They claim a 3% reduction from unloaded diameter.

My calculations for a 60-series tire show 3.55% reduction.

> 235/50ZR18 27.2" 762

They claim a 2.9% reduction from unloaded diameter for a taller tire
than the aforementioned 40-series.

This is counter-intuitive unless one presumes the effects of some other
factor, such as (as you suggest) a different diameter for the steel
belts in the carcass. A different (larger) belt diameter here would
necessarily also presume thinner tread. My Hankook tires have a fairly
thick tread.

>
> Take the 285/40ZR18 as an example:
>
> Outside diameter = 26.9" This implies an outside circumfrence of
> 26.9*pi=84.51". This equates to 749.74 revs per mile versus the
> manufacturers specification of 771 (this impies a rolling diameter of
> 26.16") . Clearly, the outside diameter of the tire is not the cheif
> determining factor in the rolling diameter. Again, think tank tread,
> not hard wheel!

Tomorrow I should check this out with the Clark forklift in our shop.

>
> So if you know the size and type of tire you are experimenting with,
> we could find the revs per mile specification and compare that to you
> experimentally determined numbers.

Here you go: A visual rendering of my test stats, plus exactly what kind
of tire it is.
http://www.tegger.com/hondafaq/misc/tire-test.pdf

>
> On other thing you might try. Reduce the air pressure in your tires by
> 20% and rerun the test. The loaded diamter will change. There may be a
> slight difference in the results, but I'll wager it will be less than
> the difference in loaded diameter.

I've done quite a bit to help this experiment on. Maybe you could
contribute some empirical evidence of your own.

--
Tegger

From: badgolferman on 9 Nov 2009 07:49

Jeff Strickland wrote:

>Using the Camry example from the previoius thread, if the base model
>car is fitted with a 195/70x14 and the premium trim (XLE ?) gets a
>215/45x17, then BadGolfer can put the base model tire package on his
>XLE, and the speedo won't change in any significant way. I'd be
>inclined to put the XLE tire package on my base model Camry, but
>that's just me, I suppose.

I don't have an XLE, I have a 1997 Camry LE and my tire size is
195/60x14.

The reason I brought up the original question was because I saw one of
those Ford Crown Victorias with the big wheels and purple lights with
loud bumpitty music and compared it to the police cruisers with bubbly
tires and red lights with loud CB radio talk. The police cruisers used
to haved those tires with big sidewalls and small hubs. I didn't like
the looks of the police cruisers in my rear-view mirror but in general
I prefer their setup any day.

From: Jeff Strickland on 9 Nov 2009 11:22

From: Jeff Strickland on 9 Nov 2009 11:33

"badgolferman" <REMOVETHISbadgolferman(a)gmail.com> wrote in message
news:xn0ghfvhe1riqh001(a)reader.albasani.net...
> Jeff Strickland wrote:
>
>>Using the Camry example from the previoius thread, if the base model
>>car is fitted with a 195/70x14 and the premium trim (XLE ?) gets a
>>215/45x17, then BadGolfer can put the base model tire package on his
>>XLE, and the speedo won't change in any significant way. I'd be
>>inclined to put the XLE tire package on my base model Camry, but
>>that's just me, I suppose.
>
> I don't have an XLE, I have a 1997 Camry LE and my tire size is
> 195/60x14.
>
> The reason I brought up the original question was because I saw one of
> those Ford Crown Victorias with the big wheels and purple lights with
> loud bumpitty music and compared it to the police cruisers with bubbly
> tires and red lights with loud CB radio talk. The police cruisers used
> to haved those tires with big sidewalls and small hubs. I didn't like
> the looks of the police cruisers in my rear-view mirror but in general
> I prefer their setup any day.
>
>

The answer to your question about the affect on the speedo is, if the tire
swap results in new tires with a similar circumference as the originals,
then the affect is minimal, and can actually be desirable if the minimal
effect is in the right direction -- the new tires are _slightly_ larger. The
reason is that the factory error rate of the speedometer is built in as a
percent. Typically the error is a few percent, less than 5% error. If the
car is indicating 70, it might really be doing only 66, or so. If the new
tires are 3% larger than the original tires, then the error rate of the
speedo might become 2% instead of 5%, so at an indicated speed of 70, the
actual speed might be 69. If the new tires are too large, then the indicated
speed of 70 could be an actual speed of 75, with obvious potential problems.

So, one can create an absolutely lovely car, or a god-awful ugly car, with
giant rims or small ones, and have a perfeclty functioning speedometer.

From: C. E. White on 10 Nov 2009 08:34

I got the information on your tire from
http://www.hankooktireusa.com/Handler/RequestFileHandler.ashx?fileName=PRODUCT/CATALOG/H418_Catalog.pdf&siteCode=

According to the Hankook information, the revolutions per mile for a
Optimo H418 - 195/60-14 is 895. This implies a rolling diamter of
22.53" (radius = 11.27"). This is dead on with your left rear tie
measurement and very close to your front left tire measurement.

Ed

"Tegger" <invalid(a)invalid.inv> wrote in message
news:Xns9CBDB8D49D178tegger(a)208.90.168.18...
> "C. E. White" <cewhite3(a)mindspring.com> wrote in
> news:pO2dnQ05H_unrWrXnZ2dnUVZ_s6dnZ2d(a)earthlink.com:
>
>> As I tried to point out before, the rolling radius is more
>> influenced
>> by the diameter of the steel belts in the tire, not the actual
>> outside
>> diameter. What brand and tire size were you testing? If we know
>> that
>> we probably can find the manufacturers revolutions per mile
>> specification. If you check these, they are not a function of the
>> outside tire diameter times pi. They are different than that.
>>
>> For instance....
>>
>> From the chart I posted in the previous string...
>>
>> .......................Revolutions
>> ............Overall....Per
>> Tire Size...Diameter...Mile
>> 245/40ZR17 24.7" 841
>
>
>
> They claim a 3% reduction from unloaded diameter.
>
> My calculations for a 60-series tire show 3.55% reduction.
>
>
>
>> 235/50ZR18 27.2" 762
>
>
>
> They claim a 2.9% reduction from unloaded diameter for a taller tire
> than the aforementioned 40-series.
>
> This is counter-intuitive unless one presumes the effects of some
> other
> factor, such as (as you suggest) a different diameter for the steel
> belts in the carcass. A different (larger) belt diameter here would
> necessarily also presume thinner tread. My Hankook tires have a
> fairly
> thick tread.
>
>
>
>>
>> Take the 285/40ZR18 as an example:
>>
>> Outside diameter = 26.9" This implies an outside circumfrence of
>> 26.9*pi=84.51". This equates to 749.74 revs per mile versus the
>> manufacturers specification of 771 (this impies a rolling diameter
>> of
>> 26.16") . Clearly, the outside diameter of the tire is not the
>> cheif
>> determining factor in the rolling diameter. Again, think tank
>> tread,
>> not hard wheel!
>
>
>
> Tomorrow I should check this out with the Clark forklift in our
> shop.
>
>
>
>>
>> So if you know the size and type of tire you are experimenting
>> with,
>> we could find the revs per mile specification and compare that to
>> you
>> experimentally determined numbers.
>
>
>
> Here you go: A visual rendering of my test stats, plus exactly what
> kind
> of tire it is.
> http://www.tegger.com/hondafaq/misc/tire-test.pdf
>
>
>
>>
>> On other thing you might try. Reduce the air pressure in your tires
>> by
>> 20% and rerun the test. The loaded diamter will change. There may
>> be a
>> slight difference in the results, but I'll wager it will be less
>> than
>> the difference in loaded diameter.
>
>
>
> I've done quite a bit to help this experiment on. Maybe you could
> contribute some empirical evidence of your own.
>
>
> --
> Tegger
>

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