hi-lo vs old straight chassis?

[gwood1]

Hello - I am getting into inline hockey (been playing ice for ~4 years). I am looking to buy my first pair of dedicated hockey skates (I am currently using my circa 1988 Ultrawheel "lace-up ski boot" with a straight chassis(!)). I'll try to formulate an intelligent rocker chassis question for tomorrow, but here are my questions for today:
Why is hi-lo so popular?
Does it put you more on the balls of your feet, or is the boot more or less flat, and only the front wheels lowered?
Assuming a hi-lo DOES put you more on the balls of your feet, doesn't that make going backwards more difficult? Or is backwards skating considered less important in in-line?
Thanks!

[DannyG]

Hey, Gwood dude:

1. Don't even worry about the blade-rocker-touch on the floor with wheels, it doesn't matter. You will be very used to the "straight-edge" touch of wheels on the floor in no time.

2. The hi-lo concept works because of physics, your speed-to-energy-input ratio is determined by the largest wheel on your skates. The hi-lo's have larger back wheels, more speed for the same effort.

3. The lie of the boot is no different than with any other chassis. You are not positioned so as to be about-to-fall-on-your-face. Each skate boot does have a different "feel," and , again, this is a "get used-to very quickly" thing.

4. all lateral, backward, and stopping movements (agility-the ability to maintain balance during changes in speed and direction) are critical skills on wheels...indeed, as an ice-transitionee, you will be spending most of your time, and frustration, on acquiring and honing these skills...

5. Have fun, and we'll see you out on the blue floor...

<font color=purple>DannyG</font color=purple>

[chrisg21]

2. The hi-lo concept works because of physics, your speed-to-energy-input ratio is determined by the largest wheel on your skates. The hi-lo's have larger back wheels, more speed for the same effort.


Danny,

Could you please explain this statement for me? I am not flaming, or trying to cause trouble, but I would like to know how you figure this, because any speed advantage gained by the larger rear wheels would have to be negated by the smaller front wheels which are also in contact with the floors surface. If you make a mark on an 80 mm wheel, and then roll it out one revolution, it would obviously measure longer in distance traveled, than if you did the same thing with a 72 mm wheel. So then if you assumed both wheels traveled at 500 rotations per minute (made up number for this example) then obviously an 80 mm wheel would cover more ground than the 72 mm wheel, thus it would get from point A to point B more quickly based on the energy involved. The only problem is the speed can't be determined by rotations per minute because the two smaller front wheels are working in conjuction with the larger rear wheel. So to travel the same distance as the example above, while the larger rear wheels may travel at the 500 rotations per minute, the smaller front wheels are actually traveling at a greater rotation per minute to cover the same ground. So any energy gain that might be percieved in the larger rear wheels would automatically be negated by the speed robbing small front wheels. The only way I can see any tangible benefit being acheived, would be a system where when speed was needed only the rear two wheels touched the ground, but since that is impossible, there is really no speed benefit gained from the larger wheels. If anyone can refute this, please do, since I believe the whole speed advantage claimed by Hi-Lo manufacturers is nothing more than advertising hype.

The only real benefit I can see with Hi-Los, is exactly the point the first poster made, in that it allows the ball of your foot to get lower to the skating surface, thereby promoting better turning ability, based on a lower center of gravity.

This is really not a flame, I would really like someone to explain this.

Thanks

Chris

[MDE3]

To jump in in Danny's defense(not that he needs it lol).

Chris your logic is ok but based on an assumption which may be incorrect. When they(the hi-lo's) first came out most of the traditional chassis were on 72 mm wheels all the way across - there was in fact a gain (drag loss) with 2 wheels being 80 mm and only two being 72 mm. Remember it is the sum of the bearing drag which counts. It was like going from 72 mmm to 76 mm on average - maybe inspired by speed skaters who traditionally used the 76 mm wheel at the time. I wont bother you with the math(I can if you'ld like), but the effective theoretical gain is around 10%. Remember if you are going to do your own calculations that drag is related to the square of the rpm not a linear relationship.

The other gain is that the 72 mm front wheels make turning the skate under load a little easier than if you had large diameter(76 or 80 mm) wheels all the way across the chassis. So the principal of the hi-low was to get the rolling resistance gain of the larger average wheel size without compromizing the agility of the skate fitted with smaller wheels.

An additional benefit was that you could get the pitch of the skate (the forward angle at which the skate boot is set on the chassis) with no change in the overall height above the floor(again versus chassis fitted with all 72 mm wheels). In order to &quot;rake&quot; the boot with the traditional 72 mm wheels, the heel of the boot sat well above the rear wheels. This space was &quot;filled in&quot; by the larger 80 mm wheels - netting the lower rolling resistance but not compromizing the height of the skate above the floor.

[RichardGraham]

MD,

You are utterly and completely incorrect. . . .

There is no "z" in compromising. /wtimages/icons/wink.gif

Sincerely,

Richard Graham
Editor
Inline Hockey Central

[MDE3]

Blew it again - damn I hate when I get caught blowing smoke like that.

[DannyG]

All the energy transfer, muscle/chemical to mechanical to rotational (the axle/bearing components) to wheels/frictional to playing surface is roughly the same to each wheel.

To be sure, the larger wheels lose a little energy because of mass and friction, when compared to the larger wheels...

-however-

even with four different size wheels on one skate, the larger wheel will determine the overall distance traveled per bearing rotation. This assumes that all the bearing/axle assemblies are the same size, which they are on skates.

Distance traveled per energy expenditure is the same as distance traveled per the time it takes the energy to rotate the axle. Distance per time is the definition of speed.

I am sure you remember seeing pictures of some old-time bicycles with extra large front wheels. The pedals were directly attached to the large wheel.

What Mike has reported above about the rotation/turning ability of the smaller wheels is indeed true, but I frankly feel that effect is negligible. It does give Mission, and others, the ability to tout the "smaller wheels for turning ability" song-and-dance, and not be false advertising.

The fact is, the largest wheel does the work, and its smaller buddies are just along for the ride...or to handle the other jobs that their position on the chassis dictates (stopping, turning, etc.).

Hope everybody's buying this, 'cause, unlike Mike, i only took the one Physics course in college, and we've about exhausted my knowledge here...


<font color=purple>DannyG</font color=purple>

[MDE3]

Actually as relates to bearing drag:

Assuming equal load/weight per wheel, which is rarely the case in a hockey skate under dynamic load, and assuming equally efficient bearing/axle assemblies in each wheel, the relative drag for each wheel is represented by a constant divided into the square of the rpm.

At 100 RPM a 72 mm wheel will travel 22619.5mm in one minute.
To travel the same distance in the same time, an 80 mm wheel will only have to rotate at 90 rpm

Therefore the difference in drag between the 2 wheels is calculates as [(100 X 100) / k] / [(90 X 90)/k] or 1.2346 x the rolling resistance for an 80 mm wheel(k) or expressed as a gain, the drag for a bearing in an 80 mm wheel versus a the drag for the same bearing in a 72 mm wheel requires only 81% of the energy to rotate over the same distance.

But because we have a 50/50 mix of these two wheels on a hi/lo chassis the gain is only half of the difference (as compared to all 80 mm wheels versus all 72 mm wheels) or approximately 10%.

As to the "physics" of why a change in direction is easier on a smaller diameter wheel - it is quite simple. Larger wheels have a slightly large contact patch than smaller wheels and so have more grip(assuming the same compounds). It is easier to make a smaller diameter wheel "push" sideways then than a larger diamenter wheel resulting in an easier change of direction. The down side is that some "push off" grip is also lost for the "toe push" versus a larger diameter wheel.

Are we really bored yet?

[missionhockey21]

"Are we really bored yet?"

God yes, I think I feel asleep;-) j/k

[JMUDukes26]

umm... dorks... all of you...

Gary

[DannyG]

certainly not bored, but I was hoping there was some sort of "physics cross" I could hold out in front of me to stave off the physics vampires out there...

<font color=purple>DannyG</font color=purple>

[chrisg21]

Not bored at all, that was an excellent answer, and one I have asked to be explained many times. Seriously, thanks for explaining that.

So to summarize, by your math you estimate a 10% increase in speed over (4) 72mm wheels, or 10% over a flat chassis with 76mm wheels?

The way I read it, you meant a 10% gain over the (4) 72 mm wheels, but how then does the Hi-Lo compare speed wise to the (4) flat chassis wheels at 76 mm's. I am guessing the speed is equal to the Hi-Los would that be correct?

Thanks for the answers.

Chris

<P ID="edit"><FONT SIZE=-1><EM>Edited by chrisg21 on 05/15/03 00:08 AM.</EM></FONT></P>

[MDE3]

Correct - when the hi-lo's first came out the majority of the chassis were using 72 mm wheels and 76 mm wheels were usually reserved for speed skates - although I think there were a few 76 mm chassis for hockey but I dont remember which ones. Agaist those - the "agility" advantage would be the main reason to convert.

[MDE3]

glad we made you feel better about yourself lol