BrettFF205D
Member
Tire size: engineering
"http://messenger.yahoo.com/messenger/mboards.html"?"http://me
ssenger.yahoo.com/messenger/mboards.html""http://profiles.yahoo.com/ro
ger_scotty"
(M/Colorado) 4/25/01 9:14 pm
"The math works out the same. The compared ratio of the circumference
of the two tires in question will be equal to the ratio of the radii
of the same two tires."
Whoa...I'm not as sure about that. But I am sure that having an
engineer's perspective would be useful. Suppose that the tire is on
soft ground - As most ag tires are used. What radius do you use to
calculate the circumference...The radius from center to outer end of
the lug? Or the one to the ground surface? What if a tire is loaded
or low on air? what happens to the measurement then? And if anything
does happen which is more important: a full bucket in the front or a
heavy implement in the rear?
I've a feeling that these are pretty tricky questions, and it sure
would help to know the answers.
To get a Firestone engineer I just typed in a question where they
said to ask technical questions (at the Firestone web site) and
several of them answered me.... But I didn't ask the questions above.
After all, why let them have all the fun?
Re: Tire size: engineering
"http://messenger.yahoo.com/messenger/mboards.html"?"http://me
ssenger.yahoo.com/messenger/mboards.html""http://profiles.yahoo.com/so
undguy34421"
4/26/01 12:53 pm
"The math works out the same. The compared ratio of the circumference
of the two tires in question will be equal to the ratio of the radii
of the same two tires."
'Whoa...I'm not as sure about that. But I am sure that having an
engineer's perspective would be useful.'
Mathematically, it has to be, under set circumstances. For the
following, lets assume that the tires in question are circles, and do
not deform, or that they at least deform equally to a similar
degree.Ok, you have two circles, one larger than the other. Measur
ethe circumference of both circles. measur ethe diameter, and the
radi of both circles. Using C=piXd ( for all those non-geometrically
inclined, c= circumference, d= diameter, r=radious ( which is .5 d ),
and pie can be represented as 3.14 ) At comparison ( ratio )of the
circumferencs of both circles must equal a comparison ( ratoi ) of
the radi of both circles. Assuming the following: equal load between
front and rear,proper inflation of tires, zero, or similar rate of
deformation of both tires being measured including load and inflation
variables, and true measured depth of the tire from it's center, not
just where the tire penetrates the ground's surface. It is also
helpfull if the front and rear tires are of hte same design, both
knobby ag, or flattend turf. For the ag tires, circumference from
middle to the end of a knob can be used, if both front and rear are
ag tires. Even though real circumference will differ due to soil, and
other conditions.
Suppose that the tire is on soft ground - As most ag tires are used.
What radius do you use to calculate the circumference...The radius
from center to outer end of the lug? Or the one to the ground
surface? What if a tire is loaded or low on air? what happens to the
measurement then? And if anything does happen which is more
important: a full bucket in the front or a heavy implement in the
rear?
Equal load is assumed for the purpose of the above calculation, but
unequal load, uneven ground and other variables including tire
pressure and amount of tread wear will have some effect of the
compaired ratios. This is a static comparison, but should yeild a
ratio that is within an acceptable error range for choosing tire/rim
sizes.
Re: Tire size: engineering
"http://messenger.yahoo.com/messenger/mboards.html"?"http://me
ssenger.yahoo.com/messenger/mboards.html""http://profiles.yahoo.com/ro
ger_scotty"
(M/Colorado) 4/26/01 7:13 pm
Soundguy, I see where you are starting from when you say:
"Mathematically, it has to be, under set circumstances. For the
following, lets assume that the tires in question are circles, and do
not deform, or that they at least deform equally to a similar degree".
Well, that's the whole problem with selecting tires in a nutshell. I
wish we could too, but we don't get to use those nifty assumptions
and simple formulas. It turns out that the radius is not constant
because the tires do deform. They also do so unequally front to rear.
We gotta get more sophisticated with the math.
Re: Tire size: engineering
"http://messenger.yahoo.com/messenger/mboards.html"?"http://me
ssenger.yahoo.com/messenger/mboards.html""http://profiles.yahoo.com/bw
c3647"
(54/M/Mpls MN suburbs) 4/26/01 4:33 pm
It seems to me it is easier and a hell of a lot less controversial to
mark the tires, mark the floor, roll the tractor forward one
revolution of the tires, mark the floor again and measure. I am an
engineer too, but pragmatism has it's place.
Bruce
Re: Tire size: engineering
"http://messenger.yahoo.com/messenger/mboards.html"?"http://me
ssenger.yahoo.com/messenger/mboards.html""http://profiles.yahoo.com/so
undguy34421"
4/30/01 9:08 am
Actually, in all honesty, I was just trying to come up with a 'quick
estimate' way to calculate trie ratio's. Other variables aside, it is
alot faster to measure the radii on the tires, than start up the
machine, mark, roll and mark, then measure. ( albiet less acurate ).
And as a spin, and proof, on pargmatism, 'the more you over tic the
plumbing, the easier it is to stop up the drain'...
Re: Tire size: engineering
"http://messenger.yahoo.com/messenger/mboards.html"?"http://me
ssenger.yahoo.com/messenger/mboards.html""http://profiles.yahoo.com/ro
ger_scotty"
(M/Colorado) 4/26/01 7:40 pm
Marking the tire and then rolling the tractor is the method I've been
playing with for the past year (it is harder than it appears) - this
after I finally ran into an impasse with mathematical methods. There
are two big problems with the tire marking method. The first one is
that it only works AFTER you have bought and mounted the tires...So
it isn't much help in figuring out what tires to order. And secondly,
it doesn't tell you anything about what the ratio is between the
front and rear drive shafts - and after all, you are trying to buy
tires to match the existing drive shaft ratio. Not vice-versa.
Geeze! this is fun! Isn't it dandy problem! It makes me pity all
those new tractor owners who simply go to their dealer and buy
tires....I'll bet they don't even know what they're missing.
Re: Tire size: engineering
"http://messenger.yahoo.com/messenger/mboards.html"?"http://me
ssenger.yahoo.com/messenger/mboards.html""http://profiles.yahoo.com/so
undguy34421"
4/30/01 9:49 am
"Geeze! this is fun! Isn't it dandy problem! It makes me pity all
those new tractor owners who simply go to their dealer and buy
tires....I'll bet they don't even know what they're missing. "
A friend of mine once said that reverse engineering was akin to
forensic science.
Re: Tire size: engineering
"http://messenger.yahoo.com/messenger/mboards.html"?"http://me
ssenger.yahoo.com/messenger/mboards.html""http://profiles.yahoo.com/ro
d_ym240d"
4/27/01 1:02 am
Jack up one side of the tractor so both left or both right tires are
off the ground. Start up the tractor, put it in gear, 4WD and let it
idle with the raised wheels turning. Count revolutions of the front
and rear tires for a given time (say 2 minutes, doesnt matter as long
as you count both front and rear for equal times). The Front-to-Rear
driveline ratio is # of revolutions of front wheel divided by # of
revolutions of rear wheel. Then buy tires such that the Front-to-Rear
tire size ratio is the inverse of the Front-to-Rear driveline ratio.
For example: Assume the front tire turns 60 times and the rear tire
turns 20 times. The front-to-rear ratio is 60:20 or 3:1. Your tire
size ratio would then be the inverse, i.e. a front-to-rear ratio of
1:3.
Use standard safety precautions while performing this dangerous
experiment.
Rod
Re: Tire size: engineering
"http://messenger.yahoo.com/messenger/mboards.html"?"http://me
ssenger.yahoo.com/messenger/mboards.html""http://profiles.yahoo.com/tr
actorlaird"
4/26/01 10:39 pm
After a person has determined the ratio is between the front and rear
drive shafts........
True or false?
The circumference of the tire is nearly the same unloaded or loaded,
even throught the radius to the ground can be much different.
From Firestone: "The desired amount of lead is 2 percent, which means
the front wheels are 2 percent faster than the rear wheels. Anywhere
from 0 to 5 percent lead is considered acceptable. But no amount of
lag is acceptable"
Then after you have purchased your tires:
Here is the link to that Firestone article about tire Lead/Lag.
"http://www.firestoneag.com/tiredata/info/info%5Flead.asp"
Re: Tire size: engineering
"http://messenger.yahoo.com/messenger/mboards.html"?"http://me
ssenger.yahoo.com/messenger/mboards.html""http://profiles.yahoo.com/mt
wap"
(36/M/monroe, va) 4/26/01 7:52 pm
So in the end it comes down to a guess...because there are
differences in the deformation between the front and rear tires due
to side wall high's tire loading and just plane old differences in
tire construction so there is no constant so no mathematical equation
to figure the correct tire sizing so you make your marks and make
your guess....
Re: Tire size: engineering
"http://messenger.yahoo.com/messenger/mboards.html"?"http://me
ssenger.yahoo.com/messenger/mboards.html""http://profiles.yahoo.com/ro
ger_scotty"
(M/Colorado) 4/27/01 1:04 am
Excellent questions! And I'll be the first to confess that I don't
know the answers. As to the circumference question, I've heard good
arguments both ways. In my own experiments I varied tire pressure
instead of load and got results that I don't have much confidence in.
I don't have any answers on the lead/lag argument...although
Firestone's sounds confusing to me. They say that lag is more
destructive to tires (and hard on transfer cases)than lead. But they
don't explain why that would be so. Just off the top of my head they
would seem to be slipping the tire or winding up the shaft the same
amount but just in different directions. And why 2 to 5%? what is
magic about those numbers?
In cars I thought a front axle lead was so that the front wheels
would maintain steering control....and the 5% was so that it would
ALWAYS maintain steering control. I've personally built a 4wd vehicle
with the front lagging and have to say that it was a bear to steer.
Before you wonder, the axle ratio was labeled wrong and I had been
too lazy to count the teeth in the pumpkin.
Re: Tire size: engineering
"http://messenger.yahoo.com/messenger/mboards.html"?"http://me
ssenger.yahoo.com/messenger/mboards.html""http://profiles.yahoo.com/so
undguy34421"
4/30/01 10:03 am
"would be so. Just off the top of my head they would seem to be
slipping the tire or winding up the shaft the same amount but just in
different directions. And why"
Leading to much, the tire spins,...lagging too much, the tire is
pushed... And they had no answer as to why one was better than the
other? Lets see... so all in all, one sige of the gear surface is
wearing more than the other? The ring and pinion should be equally
hard anyway? right? Kinda makes you wonder whay they didn't specify
why leading was better than lagging.
Re: Tire size: engineering
"http://messenger.yahoo.com/messenger/mboards.html"?"http://me
ssenger.yahoo.com/messenger/mboards.html""http://profiles.yahoo.com/ca
det32766"
(51/M/Orlando, Florida) 4/30/01 5:18 pm
To make it easy for you to understand the difference between leading
and lagging and the resulting wear caused by same, try this simple
experiment. Get a 20 foot length of 3/8 chain and pile it up in the
middle of your garage floor. Now reach down and pick up one end. Now
try and push the chain across the floor. If you haven't got it
figgured out yet, It's a lot easier to pull something than it is to
push it. Ergo front wheel drive. I just wish I had an engineering
degree so that I could explain it to you better. Egads. Enjoy, Dola.
Re: Tire size: engineering
"http://messenger.yahoo.com/messenger/mboards.html"?"http://me
ssenger.yahoo.com/messenger/mboards.html""http://profiles.yahoo.com/so
undguy34421"
5/1/01 7:24 am
Thanks, I'm up on the difference of leading and lagging. I was trying
to visualize what it was doing in the drive train, i.e. possibly
wearing heavier one side of the tooth surface of the ring and pinion
gear.... Seems like the windup would effect back through any
differential present and load the drive shaft. Anyway.. moot point
for me, as I only have a 2wd. Just a point to ponder.
Re: Tire size: engineering
"http://messenger.yahoo.com/messenger/mboards.html"?"http://me
ssenger.yahoo.com/messenger/mboards.html""http://profiles.yahoo.com/bw
c3647"
(54/M/Mpls MN suburbs) 4/26/01 11:55 pm
I have replaced rice tires on the rear wheels of 2 different 4WD
compact tractors. The first time I replaced the 8x22 rice tires with
9.5x22 Firestone tires. I meassured the rolling circumference before
and after. The two types of tires were within one inch of each other
at 114 and 115 inches. The tractor works fine. On the second tractor
I replaced 8x16 rices tires with 265R75/16 SUV tires. I measured the
rice tire rolling circumference at 90 inches. The SUV tires were 90
3/4 on the tire rack with no wheels. I put them on the tractor wheel,
25 lb of air pressure, and measured them again - 91" this time. Again
the 4WD worked just fine. I have a 4WD truck and a 4WD SUV, so I know
all about driveline wind up and how it feels. Neither of the tractors
feel like they have any.
Bruce
Re: Tire size: engineering
"http://messenger.yahoo.com/messenger/mboards.html"?"http://me
ssenger.yahoo.com/messenger/mboards.html""http://profiles.yahoo.com/ho
sejockey2002"
(34/M/Auburn, Washington) 4/28/01 11:18 am
I think I'll just go with the 265/75R16 tires and call 'er good. All
this talk about math and engineering and static loaded windup ratio
makes my head hurt.
Re: Tire size: engineering
"http://messenger.yahoo.com/messenger/mboards.html"?"http://me
ssenger.yahoo.com/messenger/mboards.html""http://profiles.yahoo.com/ro
ger_scotty"
(M/Colorado) 4/27/01 1:24 am
Just for clarification, I believe that the aspect of the tire being
measured for Rod's "tire size ratio" is what Firestone calls "rolling
circumference". The method seems sound, though it didn't work for me
when I last tried it about 5 years ago. When I tried it with any of
the tires on the ground I got irratic results. I confess that it has
been awhile and I haven't tried it again after doing it as follows,
so it might be a matter of practice. I did it slightly differently: I
jacked up all four wheels, did not start the engine, but put it in
4wd and rotated one rear tire slowly by hand. You know you are doing
this correctly when the opposite tire counter-rotates. You can feel
through the tire when any of the spiders start to rotate, and have to
start the count over. Doing it slowly by hand I didn't get confused
by relative rotation of the spider gears in either differential and
was easier able to count the slow movement of the tire.
Re: Tire size: engineering
"http://messenger.yahoo.com/messenger/mboards.html"?"http://me
ssenger.yahoo.com/messenger/mboards.html""http://profiles.yahoo.com/jb
85302"
(30/M/S/E Ohio) 4/27/01 6:05 am
I've been lurking during this whole tire thing.........I'm getting
dizzy and I think I'm gonna be sick......tooo much info at one time
causes brain damage !!
Re: Tire size: engineering
"http://messenger.yahoo.com/messenger/mboards.html"?"http://me
ssenger.yahoo.com/messenger/mboards.html""http://profiles.yahoo.com/ro
ger_scotty"
(M/Colorado) 4/27/01 10:19 am
JB, take a deep breath and for cripe's sake try not to puke all over
the keyboard. It really makes them sticky and hard to work.
Donsblack shows how to do it with a minimum of brain damage. Here is
what I get from his message. First of all he is aware that windup
exists and what it is. He knows its worth doing the extra work to
match his tire sizes as close as he can - His method is crude, but
better than nothing. And finally, he tests the limits of where he is
getting windup and decides when he can and can't use 4wd. It sure
makes sense to me, and all without cranial contusions or expense.
Of course there are those of us who enjoy trying to solve the gear
ratio problem in every picky detail. But then we have strong stomachs
and minds and get our kicks punting some numbers and physics back and
forth. Its a fairly diverse group.
Re: Tire size: engineering (Lurkers)
"http://messenger.yahoo.com/messenger/mboards.html"?"http://me
ssenger.yahoo.com/messenger/mboards.html""http://profiles.yahoo.com/do
nsblack"
(57/M/Maryland) 4/27/01 8:49 am
Also been lurking and also have changed from rice tires. Just went to
the Firestone web site got diameters for tires on tractor. Bought
same diameter and sized Diamond tread Bridgestones for rear, then
went to a local tire store bought nearly same diameter USED truck
tires. Got diameter on used tire from pamphlet at store. Bottom line,
only time I notice ANY driveline difference in 4WD is when on
pavement, so just don't use it there.
Re: Tire size: engineering (Lurkers)
"http://messenger.yahoo.com/messenger/mboards.html"?"http://me
ssenger.yahoo.com/messenger/mboards.html""http://profiles.yahoo.com/fa
rmerjohn_2"
(41/M/Cypress, TX) 4/27/01 10:22 am
I am thoroughly enjoying the engineering discussion going on here,
though it is making my 2WD 2200 look really sweet and simple.
Seems like you should be able to buy tires with the same rolling
circumference ratio, gear drive ratio and/or static load radius ratio
(just to get you close) and then adjust air pressure to deal with
excessive front wheel lead/lag which causes driveline windup. Isn't
that really the bottom line?
Re: Tire size: engineering (Lurkers)
"http://messenger.yahoo.com/messenger/mboards.html"?"http://me
ssenger.yahoo.com/messenger/mboards.html""http://profiles.yahoo.com/so
undguy34421"
4/30/01 10:13 am
"I am thoroughly enjoying the engineering discussion going on here,
though it is making my 2WD 2200 look really sweet and simple."
Comr to think of it... my 2wd 1700 doesn't have any of these problems
either.. <G>
Re: Tire size: engineering
"http://messenger.yahoo.com/messenger/mboards.html"?"http://me
ssenger.yahoo.com/messenger/mboards.html""http://profiles.yahoo.com/bw
c3647"
(54/M/Mpls MN suburbs) 4/27/01 8:40 am
I used the same marks on the floor/tire method to determine front to
rear axle ratio, I marked how far the tractor moved after the front
tires made one rev and marked where the rear tires made one rev,
measured both and divided one by the other. The only other math I had
to do was convert 1/4 inches to .25 inches.
Re: Tire size: engineering
"http://messenger.yahoo.com/messenger/mboards.html"?"http://me
ssenger.yahoo.com/messenger/mboards.html""http://profiles.yahoo.com/so
undguy34421"
4/30/01 9:38 am
"Well, that's the whole problem with selecting tires in a nutshell. I
wish we could too, but we don't get to use those nifty assumptions
and simple formulas. It turns out that the radius is not constant
because the tires do deform"
I know they do.
. They also do so unequally front to rear. We gotta get more
sophisticated with the math.
I know.. honestly, I wasn't trying to come up with a 2 page formula
for calculating gearing. I was just playing with a quick hash.
Besides.. if what one poster said was true, about a designed
slippage, a simple rolling circumference won't be accurate either. I
guess if we need complete accuracy, we need to see some design specs,
or to measure a few gears.
"http://messenger.yahoo.com/messenger/mboards.html"?"http://me
ssenger.yahoo.com/messenger/mboards.html""http://profiles.yahoo.com/ro
ger_scotty"
(M/Colorado) 4/25/01 9:14 pm
"The math works out the same. The compared ratio of the circumference
of the two tires in question will be equal to the ratio of the radii
of the same two tires."
Whoa...I'm not as sure about that. But I am sure that having an
engineer's perspective would be useful. Suppose that the tire is on
soft ground - As most ag tires are used. What radius do you use to
calculate the circumference...The radius from center to outer end of
the lug? Or the one to the ground surface? What if a tire is loaded
or low on air? what happens to the measurement then? And if anything
does happen which is more important: a full bucket in the front or a
heavy implement in the rear?
I've a feeling that these are pretty tricky questions, and it sure
would help to know the answers.
To get a Firestone engineer I just typed in a question where they
said to ask technical questions (at the Firestone web site) and
several of them answered me.... But I didn't ask the questions above.
After all, why let them have all the fun?
Re: Tire size: engineering
"http://messenger.yahoo.com/messenger/mboards.html"?"http://me
ssenger.yahoo.com/messenger/mboards.html""http://profiles.yahoo.com/so
undguy34421"
4/26/01 12:53 pm
"The math works out the same. The compared ratio of the circumference
of the two tires in question will be equal to the ratio of the radii
of the same two tires."
'Whoa...I'm not as sure about that. But I am sure that having an
engineer's perspective would be useful.'
Mathematically, it has to be, under set circumstances. For the
following, lets assume that the tires in question are circles, and do
not deform, or that they at least deform equally to a similar
degree.Ok, you have two circles, one larger than the other. Measur
ethe circumference of both circles. measur ethe diameter, and the
radi of both circles. Using C=piXd ( for all those non-geometrically
inclined, c= circumference, d= diameter, r=radious ( which is .5 d ),
and pie can be represented as 3.14 ) At comparison ( ratio )of the
circumferencs of both circles must equal a comparison ( ratoi ) of
the radi of both circles. Assuming the following: equal load between
front and rear,proper inflation of tires, zero, or similar rate of
deformation of both tires being measured including load and inflation
variables, and true measured depth of the tire from it's center, not
just where the tire penetrates the ground's surface. It is also
helpfull if the front and rear tires are of hte same design, both
knobby ag, or flattend turf. For the ag tires, circumference from
middle to the end of a knob can be used, if both front and rear are
ag tires. Even though real circumference will differ due to soil, and
other conditions.
Suppose that the tire is on soft ground - As most ag tires are used.
What radius do you use to calculate the circumference...The radius
from center to outer end of the lug? Or the one to the ground
surface? What if a tire is loaded or low on air? what happens to the
measurement then? And if anything does happen which is more
important: a full bucket in the front or a heavy implement in the
rear?
Equal load is assumed for the purpose of the above calculation, but
unequal load, uneven ground and other variables including tire
pressure and amount of tread wear will have some effect of the
compaired ratios. This is a static comparison, but should yeild a
ratio that is within an acceptable error range for choosing tire/rim
sizes.
Re: Tire size: engineering
"http://messenger.yahoo.com/messenger/mboards.html"?"http://me
ssenger.yahoo.com/messenger/mboards.html""http://profiles.yahoo.com/ro
ger_scotty"
(M/Colorado) 4/26/01 7:13 pm
Soundguy, I see where you are starting from when you say:
"Mathematically, it has to be, under set circumstances. For the
following, lets assume that the tires in question are circles, and do
not deform, or that they at least deform equally to a similar degree".
Well, that's the whole problem with selecting tires in a nutshell. I
wish we could too, but we don't get to use those nifty assumptions
and simple formulas. It turns out that the radius is not constant
because the tires do deform. They also do so unequally front to rear.
We gotta get more sophisticated with the math.
Re: Tire size: engineering
"http://messenger.yahoo.com/messenger/mboards.html"?"http://me
ssenger.yahoo.com/messenger/mboards.html""http://profiles.yahoo.com/bw
c3647"
(54/M/Mpls MN suburbs) 4/26/01 4:33 pm
It seems to me it is easier and a hell of a lot less controversial to
mark the tires, mark the floor, roll the tractor forward one
revolution of the tires, mark the floor again and measure. I am an
engineer too, but pragmatism has it's place.
Bruce
Re: Tire size: engineering
"http://messenger.yahoo.com/messenger/mboards.html"?"http://me
ssenger.yahoo.com/messenger/mboards.html""http://profiles.yahoo.com/so
undguy34421"
4/30/01 9:08 am
Actually, in all honesty, I was just trying to come up with a 'quick
estimate' way to calculate trie ratio's. Other variables aside, it is
alot faster to measure the radii on the tires, than start up the
machine, mark, roll and mark, then measure. ( albiet less acurate ).
And as a spin, and proof, on pargmatism, 'the more you over tic the
plumbing, the easier it is to stop up the drain'...
Re: Tire size: engineering
"http://messenger.yahoo.com/messenger/mboards.html"?"http://me
ssenger.yahoo.com/messenger/mboards.html""http://profiles.yahoo.com/ro
ger_scotty"
(M/Colorado) 4/26/01 7:40 pm
Marking the tire and then rolling the tractor is the method I've been
playing with for the past year (it is harder than it appears) - this
after I finally ran into an impasse with mathematical methods. There
are two big problems with the tire marking method. The first one is
that it only works AFTER you have bought and mounted the tires...So
it isn't much help in figuring out what tires to order. And secondly,
it doesn't tell you anything about what the ratio is between the
front and rear drive shafts - and after all, you are trying to buy
tires to match the existing drive shaft ratio. Not vice-versa.
Geeze! this is fun! Isn't it dandy problem! It makes me pity all
those new tractor owners who simply go to their dealer and buy
tires....I'll bet they don't even know what they're missing.
Re: Tire size: engineering
"http://messenger.yahoo.com/messenger/mboards.html"?"http://me
ssenger.yahoo.com/messenger/mboards.html""http://profiles.yahoo.com/so
undguy34421"
4/30/01 9:49 am
"Geeze! this is fun! Isn't it dandy problem! It makes me pity all
those new tractor owners who simply go to their dealer and buy
tires....I'll bet they don't even know what they're missing. "
A friend of mine once said that reverse engineering was akin to
forensic science.
Re: Tire size: engineering
"http://messenger.yahoo.com/messenger/mboards.html"?"http://me
ssenger.yahoo.com/messenger/mboards.html""http://profiles.yahoo.com/ro
d_ym240d"
4/27/01 1:02 am
Jack up one side of the tractor so both left or both right tires are
off the ground. Start up the tractor, put it in gear, 4WD and let it
idle with the raised wheels turning. Count revolutions of the front
and rear tires for a given time (say 2 minutes, doesnt matter as long
as you count both front and rear for equal times). The Front-to-Rear
driveline ratio is # of revolutions of front wheel divided by # of
revolutions of rear wheel. Then buy tires such that the Front-to-Rear
tire size ratio is the inverse of the Front-to-Rear driveline ratio.
For example: Assume the front tire turns 60 times and the rear tire
turns 20 times. The front-to-rear ratio is 60:20 or 3:1. Your tire
size ratio would then be the inverse, i.e. a front-to-rear ratio of
1:3.
Use standard safety precautions while performing this dangerous
experiment.
Rod
Re: Tire size: engineering
"http://messenger.yahoo.com/messenger/mboards.html"?"http://me
ssenger.yahoo.com/messenger/mboards.html""http://profiles.yahoo.com/tr
actorlaird"
4/26/01 10:39 pm
After a person has determined the ratio is between the front and rear
drive shafts........
True or false?
The circumference of the tire is nearly the same unloaded or loaded,
even throught the radius to the ground can be much different.
From Firestone: "The desired amount of lead is 2 percent, which means
the front wheels are 2 percent faster than the rear wheels. Anywhere
from 0 to 5 percent lead is considered acceptable. But no amount of
lag is acceptable"
Then after you have purchased your tires:
Here is the link to that Firestone article about tire Lead/Lag.
"http://www.firestoneag.com/tiredata/info/info%5Flead.asp"
Re: Tire size: engineering
"http://messenger.yahoo.com/messenger/mboards.html"?"http://me
ssenger.yahoo.com/messenger/mboards.html""http://profiles.yahoo.com/mt
wap"
(36/M/monroe, va) 4/26/01 7:52 pm
So in the end it comes down to a guess...because there are
differences in the deformation between the front and rear tires due
to side wall high's tire loading and just plane old differences in
tire construction so there is no constant so no mathematical equation
to figure the correct tire sizing so you make your marks and make
your guess....
Re: Tire size: engineering
"http://messenger.yahoo.com/messenger/mboards.html"?"http://me
ssenger.yahoo.com/messenger/mboards.html""http://profiles.yahoo.com/ro
ger_scotty"
(M/Colorado) 4/27/01 1:04 am
Excellent questions! And I'll be the first to confess that I don't
know the answers. As to the circumference question, I've heard good
arguments both ways. In my own experiments I varied tire pressure
instead of load and got results that I don't have much confidence in.
I don't have any answers on the lead/lag argument...although
Firestone's sounds confusing to me. They say that lag is more
destructive to tires (and hard on transfer cases)than lead. But they
don't explain why that would be so. Just off the top of my head they
would seem to be slipping the tire or winding up the shaft the same
amount but just in different directions. And why 2 to 5%? what is
magic about those numbers?
In cars I thought a front axle lead was so that the front wheels
would maintain steering control....and the 5% was so that it would
ALWAYS maintain steering control. I've personally built a 4wd vehicle
with the front lagging and have to say that it was a bear to steer.
Before you wonder, the axle ratio was labeled wrong and I had been
too lazy to count the teeth in the pumpkin.
Re: Tire size: engineering
"http://messenger.yahoo.com/messenger/mboards.html"?"http://me
ssenger.yahoo.com/messenger/mboards.html""http://profiles.yahoo.com/so
undguy34421"
4/30/01 10:03 am
"would be so. Just off the top of my head they would seem to be
slipping the tire or winding up the shaft the same amount but just in
different directions. And why"
Leading to much, the tire spins,...lagging too much, the tire is
pushed... And they had no answer as to why one was better than the
other? Lets see... so all in all, one sige of the gear surface is
wearing more than the other? The ring and pinion should be equally
hard anyway? right? Kinda makes you wonder whay they didn't specify
why leading was better than lagging.
Re: Tire size: engineering
"http://messenger.yahoo.com/messenger/mboards.html"?"http://me
ssenger.yahoo.com/messenger/mboards.html""http://profiles.yahoo.com/ca
det32766"
(51/M/Orlando, Florida) 4/30/01 5:18 pm
To make it easy for you to understand the difference between leading
and lagging and the resulting wear caused by same, try this simple
experiment. Get a 20 foot length of 3/8 chain and pile it up in the
middle of your garage floor. Now reach down and pick up one end. Now
try and push the chain across the floor. If you haven't got it
figgured out yet, It's a lot easier to pull something than it is to
push it. Ergo front wheel drive. I just wish I had an engineering
degree so that I could explain it to you better. Egads. Enjoy, Dola.
Re: Tire size: engineering
"http://messenger.yahoo.com/messenger/mboards.html"?"http://me
ssenger.yahoo.com/messenger/mboards.html""http://profiles.yahoo.com/so
undguy34421"
5/1/01 7:24 am
Thanks, I'm up on the difference of leading and lagging. I was trying
to visualize what it was doing in the drive train, i.e. possibly
wearing heavier one side of the tooth surface of the ring and pinion
gear.... Seems like the windup would effect back through any
differential present and load the drive shaft. Anyway.. moot point
for me, as I only have a 2wd. Just a point to ponder.
Re: Tire size: engineering
"http://messenger.yahoo.com/messenger/mboards.html"?"http://me
ssenger.yahoo.com/messenger/mboards.html""http://profiles.yahoo.com/bw
c3647"
(54/M/Mpls MN suburbs) 4/26/01 11:55 pm
I have replaced rice tires on the rear wheels of 2 different 4WD
compact tractors. The first time I replaced the 8x22 rice tires with
9.5x22 Firestone tires. I meassured the rolling circumference before
and after. The two types of tires were within one inch of each other
at 114 and 115 inches. The tractor works fine. On the second tractor
I replaced 8x16 rices tires with 265R75/16 SUV tires. I measured the
rice tire rolling circumference at 90 inches. The SUV tires were 90
3/4 on the tire rack with no wheels. I put them on the tractor wheel,
25 lb of air pressure, and measured them again - 91" this time. Again
the 4WD worked just fine. I have a 4WD truck and a 4WD SUV, so I know
all about driveline wind up and how it feels. Neither of the tractors
feel like they have any.
Bruce
Re: Tire size: engineering
"http://messenger.yahoo.com/messenger/mboards.html"?"http://me
ssenger.yahoo.com/messenger/mboards.html""http://profiles.yahoo.com/ho
sejockey2002"
(34/M/Auburn, Washington) 4/28/01 11:18 am
I think I'll just go with the 265/75R16 tires and call 'er good. All
this talk about math and engineering and static loaded windup ratio
makes my head hurt.
Re: Tire size: engineering
"http://messenger.yahoo.com/messenger/mboards.html"?"http://me
ssenger.yahoo.com/messenger/mboards.html""http://profiles.yahoo.com/ro
ger_scotty"
(M/Colorado) 4/27/01 1:24 am
Just for clarification, I believe that the aspect of the tire being
measured for Rod's "tire size ratio" is what Firestone calls "rolling
circumference". The method seems sound, though it didn't work for me
when I last tried it about 5 years ago. When I tried it with any of
the tires on the ground I got irratic results. I confess that it has
been awhile and I haven't tried it again after doing it as follows,
so it might be a matter of practice. I did it slightly differently: I
jacked up all four wheels, did not start the engine, but put it in
4wd and rotated one rear tire slowly by hand. You know you are doing
this correctly when the opposite tire counter-rotates. You can feel
through the tire when any of the spiders start to rotate, and have to
start the count over. Doing it slowly by hand I didn't get confused
by relative rotation of the spider gears in either differential and
was easier able to count the slow movement of the tire.
Re: Tire size: engineering
"http://messenger.yahoo.com/messenger/mboards.html"?"http://me
ssenger.yahoo.com/messenger/mboards.html""http://profiles.yahoo.com/jb
85302"
(30/M/S/E Ohio) 4/27/01 6:05 am
I've been lurking during this whole tire thing.........I'm getting
dizzy and I think I'm gonna be sick......tooo much info at one time
causes brain damage !!
Re: Tire size: engineering
"http://messenger.yahoo.com/messenger/mboards.html"?"http://me
ssenger.yahoo.com/messenger/mboards.html""http://profiles.yahoo.com/ro
ger_scotty"
(M/Colorado) 4/27/01 10:19 am
JB, take a deep breath and for cripe's sake try not to puke all over
the keyboard. It really makes them sticky and hard to work.
Donsblack shows how to do it with a minimum of brain damage. Here is
what I get from his message. First of all he is aware that windup
exists and what it is. He knows its worth doing the extra work to
match his tire sizes as close as he can - His method is crude, but
better than nothing. And finally, he tests the limits of where he is
getting windup and decides when he can and can't use 4wd. It sure
makes sense to me, and all without cranial contusions or expense.
Of course there are those of us who enjoy trying to solve the gear
ratio problem in every picky detail. But then we have strong stomachs
and minds and get our kicks punting some numbers and physics back and
forth. Its a fairly diverse group.
Re: Tire size: engineering (Lurkers)
"http://messenger.yahoo.com/messenger/mboards.html"?"http://me
ssenger.yahoo.com/messenger/mboards.html""http://profiles.yahoo.com/do
nsblack"
(57/M/Maryland) 4/27/01 8:49 am
Also been lurking and also have changed from rice tires. Just went to
the Firestone web site got diameters for tires on tractor. Bought
same diameter and sized Diamond tread Bridgestones for rear, then
went to a local tire store bought nearly same diameter USED truck
tires. Got diameter on used tire from pamphlet at store. Bottom line,
only time I notice ANY driveline difference in 4WD is when on
pavement, so just don't use it there.
Re: Tire size: engineering (Lurkers)
"http://messenger.yahoo.com/messenger/mboards.html"?"http://me
ssenger.yahoo.com/messenger/mboards.html""http://profiles.yahoo.com/fa
rmerjohn_2"
(41/M/Cypress, TX) 4/27/01 10:22 am
I am thoroughly enjoying the engineering discussion going on here,
though it is making my 2WD 2200 look really sweet and simple.
Seems like you should be able to buy tires with the same rolling
circumference ratio, gear drive ratio and/or static load radius ratio
(just to get you close) and then adjust air pressure to deal with
excessive front wheel lead/lag which causes driveline windup. Isn't
that really the bottom line?
Re: Tire size: engineering (Lurkers)
"http://messenger.yahoo.com/messenger/mboards.html"?"http://me
ssenger.yahoo.com/messenger/mboards.html""http://profiles.yahoo.com/so
undguy34421"
4/30/01 10:13 am
"I am thoroughly enjoying the engineering discussion going on here,
though it is making my 2WD 2200 look really sweet and simple."
Comr to think of it... my 2wd 1700 doesn't have any of these problems
either.. <G>
Re: Tire size: engineering
"http://messenger.yahoo.com/messenger/mboards.html"?"http://me
ssenger.yahoo.com/messenger/mboards.html""http://profiles.yahoo.com/bw
c3647"
(54/M/Mpls MN suburbs) 4/27/01 8:40 am
I used the same marks on the floor/tire method to determine front to
rear axle ratio, I marked how far the tractor moved after the front
tires made one rev and marked where the rear tires made one rev,
measured both and divided one by the other. The only other math I had
to do was convert 1/4 inches to .25 inches.
Re: Tire size: engineering
"http://messenger.yahoo.com/messenger/mboards.html"?"http://me
ssenger.yahoo.com/messenger/mboards.html""http://profiles.yahoo.com/so
undguy34421"
4/30/01 9:38 am
"Well, that's the whole problem with selecting tires in a nutshell. I
wish we could too, but we don't get to use those nifty assumptions
and simple formulas. It turns out that the radius is not constant
because the tires do deform"
I know they do.
. They also do so unequally front to rear. We gotta get more
sophisticated with the math.
I know.. honestly, I wasn't trying to come up with a 2 page formula
for calculating gearing. I was just playing with a quick hash.
Besides.. if what one poster said was true, about a designed
slippage, a simple rolling circumference won't be accurate either. I
guess if we need complete accuracy, we need to see some design specs,
or to measure a few gears.
