100a is infinitely hard

[chaindog]

100 a is the hardness of diamonds. 100a is as hard as it is physicaly possible to achive. http://www.ncdsa.com/3/Skateboard-Wheel-Reviews.htm

[large goat]

arent there 101a skateboard wheels?

[nsc1120]

they are lying

[chaindog]

actualy, due to the curvature of a skateboard wheel it is possible to messure in above 100a
but its not actualy that hard.

[easy]

arent there 101a skateboard wheels?

No. Oversimplifying, but 100a is "perfectly" hard; everything softer than a diamond is less than 100a. Using the 'a' scale, it's virtually impossible to measure anything over 97a or so - so they just make up a number. If last years hardest wheel was 98a, and this formula is harder, then it must be 99a or 100a... Where it's really more like 98.2a (assuming the 98a was a true reading). Anyone selling a urethane wheel harder than 100a is a liar, no other way to put it (steel isn't 100a).

[ChrisChaput]

In a discussion over some wheels that were labeled over 100A, I posted the following:

Aggregated Diamond Nanorods (ADNR synthesized) has been identified as the hardest and least compressible material in the world. Somehow, I doubt that a Powell Bones wheel is harder than this. And why would you even want to skate on them if they were? Urethane hardness is not the only factor in determining a wheel's speed or traction. The amount of resilience (rebound) has a profound effect on speed and traction, even in hard wheels. The quality of the material, the depth of urethane, the size and type of core (if any), the size of the contact patch (runnung surface), and the width of the wheel all effect the performance of the wheel. The weight of the rider, his style of riding and the surface he's riding on also change the wheel's performance.

Our industry is partly to blame for this notion that "harder is faster" and "softer always has more traction". But it doesn't make (logical) sense that we label wheels with an impossible scale reading. When the upper limit of the scale is 100, what in the hell does 104A mean to us? Perhaps that it's harder than their 102A wheel, which is harder than a diamond? The problem is that we really shouldn't be using the "A Shore" scale for all of our wheels - only the soft ones. At hardnesses above about 90A, the scale loses its accuracy and therefore its meaning. We should be using a different scale, like the D Shore, instead. Otherwise it's like using a rectal thermometer to measure the core temperature of the earth (5000 degrees Celsius?) or the coldest gas ever recorded (half a nanokelvin - one-billionth of a degree).

It makes (dollars and) sense to use the A Shore from a marketing perspective, but I wouldn't rely on its accuracy or its meaning. In fairness however, to those who label wheels over 100A, perhaps they are using a D Shore reading and then interpreting it onto an imaginary overlapping of the scales. You still end up with a nonsensical result, but at least they didn't confuse their customers by reporting a "61D" durometer which they may perceive to be soft. The images below show how some of the Shore scales compare to one another. Although I like the "simplicity" of only using one scale for wheels, a D Shore scale would be more meaning for pool/park/street wheels. Even then, don't be fooled into thinking that "the bigger the number, the faster you'll go". There's way more to it than that.





Why does the A scale end that way?

The A Scale doesn't really end in the middle of the D Scale. It just looks that way in the charts. There aren't accurate conversions between the two scales above 50D. There just aren't. And it's a mistake to pretend that there are readings on the A Scale above 100. There aren't. The scale only goes to 100. The idea that a wheel could test out at "103A" is not just nonsensical - it's impossible. In theory, 100A is "infinitely hard" and every wheel is less than 100A. For that matter, even the highest D Scale readings are less than 100A. The hardest wheels that are made are in the high 90's of the A Scale.

The hardest wheels that we ride are between 98A and 100A. Without going into decimal precision, there are only two ways to label a wheel using the A Scale, 98A and 99A. So instead of using the correct D Scale, and instead of using realistic 98A or 99A measurements, some vendors just make up these bogus readings as if to give a "relative" measurement of hardness among their own wheels. The problem is that different vendors use different "fake" readings and so BillyBob's 103A Street Creatures are actually softer than BettyBoobJob's 101A Silicone Sisters and no one with an A Scale durometer can dispute the claims.

I just want people to realize that many vendors just pull these numbers out of their ass and you can't trust any A Scale reading over 99A.




Isn't that confusing?

I understand that it may appear to be confusing at first, but the more that you understand (and the more you seek understanding), the more it makes sense. At least it's not as confusing as trying to interpret non-existent measurements. One way to look at this, is to consider the durometer tester itself. They are a little bit like a ball point pen, in that they have springs inside and a pointy tip at the end. This pointy tip comes out of the bottom end of the gage where there is a smallish flat area which acts like a table. This "table" is pressed down onto the surface of a piece of urethane (or rubber or plastic...) and the tip is pushed part way into the barrel of the gage. The further the tip is pushed in, higher the gage will read. The tip is pushed in like a finger tip into a thigh, and NOT like a needle into a pincushion. It doesn't penetrate the surface - the surface pushes it back.

1. The softer the spring, the more the tip will be pushed in.
2. The harder the material, the more the tip will be pushed in.

The spring in the A Shore gage is softer than the spring in the D Shore gage, so the A Shore gage is best when testing softer materials, such as 72A, 75A, 78A, etc. When we start measuring hard materials with a soft spring, they push the pin almost completely in (flush with the table) and the reading is always around 99. As you can see in the pictures, the scale only goes to 100. To say that something is over 100 is to imply that something is so hard that it pushes the pin BEYOND being flush with the table. This appears to be impossible, HOWEVER, there's another little twist. The pin has to poke out of a small hole in the bottom of the table. If the material being tested is a small hard sphere, the pin can actually be pushed back in PAST the surface of the table. In other words, convex surfaces can give higher than actual readings, and concave surfaces can give lower than actual readings.

The trick here, is to use the right spring (scale) for the right job. Most people can agree that the A Shore scale is appropriate for softer urethane and that the D Shore scales is best for hard plastics and urethane. Whether or not to introduce the B Shore scale is a matter of opinion. At that point, many of us may just tune out and go down by the C Shore and drink a Corona.

[MalakaiKingston]

well put, thanks for that...

[easy]

Which is why you have to give props to NHS for lableing Rictas with a 'd' scale number and Powell for using "SPF" instead of a bogus over 100 'a' number (along with the rest who just call a "98" a 98...).

[Sal Pic]

The numbers are just a suggestion IMO. 78a will feel softer than a 90-something. But wheel to wheel there are differences. My Powerballs and Flashbacks are both 78a, but the Powerballs ride harder. Like Chris said, its more than the hardness.

Fantastic report there by the way. A- cause I didnt see any citations.

[AJ]

In conclusion, after decades of research, the shopping cart wheel has been discovered to be the best wheel for sliding

[CrisVA]

Which is why you have to give props to NHS for lableing Rictas with a 'd' scale number and Powell for using "SPF" instead of a bogus over 100 'a' number (along with the rest who just call a "98" a 98...).

I don't think you realize how much Chris owned you.

No. Oversimplifying, but 100a is "perfectly" hard; everything softer than a diamond is less than 100a

So a shopping cart wheel is harder then a diamond! Shibby!

:P

[chaindog]

if oyud actualy read chris chaputs post youd understand that that is not correct due to the inacuracy of the scale

[CrisVA]

if oyud actualy read chris chaputs post youd understand that that is not correct due to the inacuracy of the scale

I'm not sure if you are talking to me but I will field it.

It may not be correct because the shore D goes farther, but there IS harder then 100a. To say 100a is perfectly hard is wrong, because if you look at the scale, shopping cart wheels are rated 'above' (or off the scale) a 100a wheel. As are hard hats.

There is harder then 100a young padawan.

[VolvoGuy]

if oyud actualy read chris chaputs post youd understand that that is not correct due to the inacuracy of the scale

I'm not sure if you are talking to me but I will field it.

It may not be correct because the shore D goes farther, but there IS harder then 100a. To say 100a is perfectly hard is wrong, because if you look at the scale, shopping cart wheels are rated 'above' (or off the scale) a 100a wheel. As are hard hats.

There is harder then 100a young padawan.

Um, you're wrong. Did you read what chris wrote at all?

[El Beefo]

if oyud actualy read chris chaputs post youd understand that that is not correct due to the inacuracy of the scale

I'm not sure if you are talking to me but I will field it.

It may not be correct because the shore D goes farther, but there IS harder then 100a. To say 100a is perfectly hard is wrong, because if you look at the scale, shopping cart wheels are rated 'above' (or off the scale) a 100a wheel. As are hard hats.

There is harder then 100a young padawan.

Haha no, 100a is the hardests.
100a = 75d, a shopping cart wheel is rated 55d, so that would equal out to something like 99.2735a. The d scale is just a more acurate way of measuring hard stuff, just like a millimeter is more acurate at measuring small stuff.

And now you know, young padawan.

[silversurfer]

So a shopping cart wheel is harder then a diamond! Shibby!:P

I noticed that too.

It appears that way on the chart above.

But that does not make any sense.

Can anybody explain how this could make any sense?

[chaindog]

ok READ CHRIS'S POST

"
I understand that it may appear to be confusing at first, but the more that you understand (and the more you seek understanding), the more it makes sense. At least it's not as confusing as trying to interpret non-existent measurements. One way to look at this, is to consider the durometer tester itself. They are a little bit like a ball point pen, in that they have springs inside and a pointy tip at the end. This pointy tip comes out of the bottom end of the gage where there is a smallish flat area which acts like a table. This "table" is pressed down onto the surface of a piece of urethane (or rubber or plastic...) and the tip is pushed part way into the barrel of the gage. The further the tip is pushed in, higher the gage will read. The tip is pushed in like a finger tip into a thigh, and NOT like a needle into a pincushion. It doesn't penetrate the surface - the surface pushes it back.

1. The softer the spring, the more the tip will be pushed in.
2. The harder the material, the more the tip will be pushed in.

The spring in the A Shore gage is softer than the spring in the D Shore gage, so the A Shore gage is best when testing softer materials, such as 72A, 75A, 78A, etc. When we start measuring hard materials with a soft spring, they push the pin almost completely in (flush with the table) and the reading is always around 99. As you can see in the pictures, the scale only goes to 100. To say that something is over 100 is to imply that something is so hard that it pushes the pin BEYOND being flush with the table. This appears to be impossible, HOWEVER, there's another little twist. The pin has to poke out of a small hole in the bottom of the table. If the material being tested is a small hard sphere, the pin can actually be pushed back in PAST the surface of the table. In other words, convex surfaces can give higher than actual readings, and concave surfaces can give lower than actual readings.

The trick here, is to use the right spring (scale) for the right job. Most people can agree that the A Shore scale is appropriate for softer urethane and that the D Shore scales is best for hard plastics and urethane. Whether or not to introduce the B Shore scale is a matter of opinion. At that point, many of us may just tune out and go down by the C Shore and drink a Corona."

[CrisVA]

So a shopping cart wheel is harder then a diamond! Shibby!:P

I noticed that too.

It appears that way on the chart above.

But that does not make any sense.

Can anybody explain how this could make any sense?

Because the D shore and A shore are just different readings. The A short ends at 100, so there can't be any reading above that like 106a, but there ARE harder things then a 100a wheel. 101a wheels are just a bad conversion from D shore to A shore.

It's like... imagine if celcius degrees stopped at 100, and you had a fahrenheit reading of 230 degrees (for newbs 100 degrees celcius is 212 Fahrenheit). It wouldn't make any sense if you tried to say that 100 degrees celcius was as hot as the world could get, it's just the end of that way of reading temperature.

And also, because you have to disregard chaindog and easy's posts for it to make sense since they are mixed up. I was simply making fun of them because 100a is NOT a diamond.

[El Beefo]

So a shopping cart wheel is harder then a diamond! Shibby!:P

I noticed that too.

It appears that way on the chart above.

But that does not make any sense.

Can anybody explain how this could make any sense?

Because the D shore and A shore are just different readings. The A short ends at 100, so there can't be any reading above that like 106a, but there ARE harder things then a 100a wheel. 101a wheels are just a bad conversion from D shore to A shore.

It's like... imagine if celcius degrees stopped at 100, and you had a fahrenheit reading of 230 degrees (for newbs 100 degrees celcius is 212 Fahrenheit). It wouldn't make any sense if you tried to say that 100 degrees celcius was as hot as the world could get, it's just the end of that way of reading temperature.

And also, because you have to disregard chaindog and easy's posts for it to make sense since they are mixed up. I was simply making fun of them because 100a is NOT a diamond.

No no no no nooooo!

The D scale does not go over the A scale, it is just a more accurate way of measuring hard stuff. Here is a little scale thing I made that will hopefully explain it to you. The scales aren't accurate, so don't use it to measure anything, but you should get the idea.

[ChrisChaput]

The pictures are deceiving, and even the charts can be a little misleading!

For some hardnesses they can give you a good idea of how one scale compares with another BUT,

THERE ARE NO SCALE READINGS ABOVE 100A.

THE D SHORE SCALE IS FULLY CONTAINED WITHIN THE A SHORE SCALE AND DOES NOT EXTEND ABOVE 100A.

I know that the pictures make it LOOK as if there are D Shore readings that are above 100A but it's only because you can't position a shopping cart wheel, a hard hat, a phone and a diamond between the 98 and the 100 in the drawing!

No matter how many times you push an A Shore durometer into a hard wheel, the needle is NEVER going to quite reach 100, unless the calibration is off.

So think about it. You have a super hard wheel, and you test it on the A scale and it comes out between 98 and 100. Then you test it on the D scale and you get a reading of 65. Why would you then go and put 103A on the wheel?

It's really the pictures that lie, and the occasional wheel vendor.