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Open Roads Forum  >  Tow Vehicles

 > FYI: what all those letters mean

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agesilaus

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Posted: 02/20/18 01:45pm Link  |  Quote  |  Print  |  Notify Moderator

Four Wheeler Mag

why are metric sizes 2/3rds metric but the tire radius is in inches? Do they do it that way in Europe?

I never heard of the yellow dot described in this article.


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BenK

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Posted: 02/20/18 01:50pm Link  |  Quote  |  Print  |  Notify Moderator

Those dots have been around since college days when working to pay for that schooling...Tire Monkey, Mechanic, Welder, part time designer/draftsman, etc, etc

No American tire OEM...just Eropean OEMs had them because American OEMs didn't have metric, nor VR rated, IIRC

There are several colors these days....back then...just yellow


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Posted: 02/20/18 04:27pm Link  |  Quote  |  Print  |  Notify Moderator

rim diameter is in inches worldwide. One exception was a michelin tire design that was metric, ford used if for a while. AFAIK no one makes that tire anymore.

while most of the world is metric, there are a few things that worldwide are in inches. Tire rim diameter for cars and motorcycles is one such case maybe with a few exceptions, spark plugs, virtually all use inch threads and inch sockets.


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theoldwizard1

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Posted: 02/20/18 08:50pm Link  |  Quote  |  Print  |  Notify Moderator

I always thought that the actual load rating had to be on the side wall in pounds and kilograms.

CapriRacer

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Posted: 02/21/18 06:52am Link  |  Quote  |  Print  |  Notify Moderator

Wow, there was a lot wrong with that article.

First let's talk about the rim diameter in inches. Yes, almost since the time tires were invented, the rim diameter has been expressed in inches - but so were the rest of the dimensions. It's only been since the introduction of radial tires that metric dimensions have been used - and since it isn't easy to express rim diameter in anything other than inches, the practice was retained.

As was pointed out above, there have been several attempts to introduce metric rim sizing - the most notable, Michelin's TRX series - but inevitably, that was rejected by the marketplace.

The dots on the sidewall? Those are supposed to be for uniformity (think runout and you'll be close!), not for balance. The high point of the tire is supposed to be matched up with the low point of the wheel, so the assembly is rounder. Every car manufacturer does that, but the valve hole is only sometimes used to mark the low point of the wheel. - AND - In the replacement market, tires aren't always marked - and red is the more common color.

There's no harm done matching up the dots on the tire with the valve hole on the wheel, but most of the time, it doesn't do anything of value.

And let me state this again. This is about out-of-round, not balance!

And, Yes, the US regulations require the load carrying capacity be delineated on the sidewall. I can't remember if the regulations say both English and metric units are required, but it is customary to do so.

And lastly: Starting in 2015, the DOT code - aka as the TIN (Tire Identifcation Number) - can be up to 13 digits long (formerly 12). That's because a 3 digit plant code is now permissible (as opposed to the old 2 digit plant code.) In 2025, it becomes mandatory.


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mkirsch

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Posted: 02/21/18 01:08pm Link  |  Quote  |  Print  |  Notify Moderator

IMHO way too much is made out of the whole metric/inch thing. You'll find that most places in the world can use them interchangeably. It's only here in the USA where we have this "one or the other, as long as it's not metric" attitude.

You don't need to need to know what the rim measures in millimeters. All you need to know is that the number matches. A 16 tire will not fit on a 17 rim. Notice how I removed the units of measure? It doesn't matter! 16 only fits 16, 17 only fits 17, 19.5 only fits 19.5. You can't mix and match, so who cares what the units are?

Same goes with the width to a degree. You can go up and down a size, like you always could. If you can count and know when a number is bigger or smaller than another number, you're good to go.

If you stop trying to think of the numbers as "measurements" and instead think of them as "sizes" like shoe sizes, they're a lot easier to comprehend.


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sneakygroundbuzzard

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Posted: 02/21/18 06:01pm Link  |  Quote  |  Print  |  Notify Moderator

[quote=CapriRacer]Wow, there was a lot wrong with that article.



The dots on the sidewall? Those are supposed to be for uniformity (think runout and you'll be close!), not for balance. The high point of the tire is supposed to be matched up with the low point of the wheel, so the assembly is rounder. Every car manufacturer does that, but the valve hole is only sometimes used to mark the low point of the wheel. - AND - In the replacement market, tires aren't always marked - and red is the more common color.

There's no harm done matching up the dots on the tire with the valve hole on the wheel, but most of the time, it doesn't do anything of value.

And let me state this again. This is about out-of-round, not balance!

[/quote/]

im going to agree and disagree with you on that

i worked as an auto tech for 25 years and have installed literally tens of thousands of tires.

the dot is there to help with out of round,but out of round will cause an imbalance issue

when mounting tires on modern vehicle wheels a good tire tech will always line up the yellow(most common color ive seen) with the valve stem hole on the wheel.then check the balance of the assembly,if is excessive a good tire tech will then break down the bead and rotate the tire on the wheel assy one quarter of turn and recheck the balance,and keep doing this until he finds the best position of the tire on the wheel assy that gives the best balance while needing the least amount of weights to be added.

most dealerships and tire specialty shops these days will also use a road force balancer and not just a spin balancer. a road force balancer applies force to the tire/wheel assy while spinning it.this force replicates the tire rolling down the road on a vehicle. this is the best way to get a true balance of the tire wheel assy. and usually when done properly can make for the least amount of weight to be added to the wheel,these machines are so high tech,they will actually tell you if your better off breaking down the tire from the wheel and tell you how far to rotate it in which direction for best possible balance(only way i have tires balanced on my vehicles). they will also tell you if you have an excesive hard spot in a tire and that the tire should be replaced,they will also let you know if your wheel assy is bad and needs to be replaced.

CapriRacer

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Posted: 02/22/18 06:08am Link  |  Quote  |  Print  |  Notify Moderator

sneakygroundbuzzard wrote:

CapriRacer wrote:

Wow, there was a lot wrong with that article.

''''''''

The dots on the sidewall? Those are supposed to be for uniformity (think runout and you'll be close!), not for balance. The high point of the tire is supposed to be matched up with the low point of the wheel, so the assembly is rounder. Every car manufacturer does that, but the valve hole is only sometimes used to mark the low point of the wheel. - AND - In the replacement market, tires aren't always marked - and red is the more common color.

There's no harm done matching up the dots on the tire with the valve hole on the wheel, but most of the time, it doesn't do anything of value.

And let me state this again. This is about out-of-round, not balance!



I'm going to agree and disagree with you on that

I worked as an auto tech for 25 years and have installed literally tens of thousands of tires.

The dot is there to help with out of round, but out of round will cause an imbalance issue

When mounting tires on modern vehicle wheels a good tire tech will always line up the yellow(most common color ive seen) with the valve stem hole on the wheel.then check the balance of the assembly,if is excessive a good tire tech will then break down the bead and rotate the tire on the wheel assy one quarter of turn and recheck the balance,and keep doing this until he finds the best position of the tire on the wheel assy that gives the best balance while needing the least amount of weights to be added.

Most dealerships and tire specialty shops these days will also use a road force balancer and not just a spin balancer. a road force balancer applies force to the tire/wheel assy while spinning it.this force replicates the tire rolling down the road on a vehicle. this is the best way to get a true balance of the tire wheel assy. and usually when done properly can make for the least amount of weight to be added to the wheel,these machines are so high tech,they will actually tell you if your better off breaking down the tire from the wheel and tell you how far to rotate it in which direction for best possible balance(only way i have tires balanced on my vehicles). they will also tell you if you have an excesive hard spot in a tire and that the tire should be replaced,they will also let you know if your wheel assy is bad and needs to be replaced.


Sorry, but I worked for a major tire manufacturer and we marked the tires at the high point, not the heavy spot. Where to mark was determined by a machine - Tire Uniformity Grader (TUG) - and it was a separate machine from the one that measured imbalance.

Proof? That Road Force machine you mentioned? That's a Hunter Engineering machine and if you watch carefully, the first part of the procedure uses a load wheel that measures the loaded runout (in pounds or Newtons). When that part is done - and before it spins the tire to determine the imbalance - it displays the amount of Road Force - THEN, the spin determines the amount of balance weights (in ounces or grams) and where they are needed. Those are 2 separate operations.

* This post was edited 02/23/18 06:07am by CapriRacer *

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