tire pressure question

[abbabibble]

ok. I noticed today when i got gutsy at school and hopped off a 3' or so
drop to flat on my new torker, when i landed on the flat, i felt a
little jolt from my tire/rim. Is this a bad thing? should i run my tire
at a higher pressure when hopping off higher objects to prevent the rim
from hitting bottom? ( i run it higher than most, anyways, at about
40psi...)


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[Spudman]

You can feel it if you bottom out. There is a distinct thud when your
rim hits the ground. If you are bottoming out at 40 psi, then you need
to either loose quite a bit of weight or get a new pressure guage. I
have mine at 25 psi, and it doesn't come close to hitting down all the
way off of those size drops.

You may also be landing kind of awkward. Maybe you could post a short
clip for us to see.


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[abbabibble]

hmm... hang on... lemme go get the bathroom scale...
ok. i weigh 120 pounds on the dot. maybe i'm just not used to doing
this... that was the highest drop i've attempted yet, and i went into
it horizontally/sideways hop, not rolling. I'll get the tire gauge and
see if the pump's psi gauge was right...


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[Evan Byrne]

your tire guage is broken, i have run my tire at 40 and not bottomed out
on anything. thou right now i run it at 110...


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[forrestunifreak]

Like I've said, I've done a 5 foot drop to flat on the maxxis CC tire at
like..27 PSI and I don't relly remember bottoming out....

Maybe you just didn't roll out very well? Or maybe it didn't really
bottom out, but you just arent used to that high of a drop?


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[Loosemoose]

When you bottom out a rim its pretty noticeable, there's a very loud
thunk and a very sharp jolt. You can get similar feedback (but less so)
when you are coming close to bottoming out a rim, without actually
doing so.

Loose.


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[Mikefule]

I know naff all about doing drops, but a fair amount about physics, and
about dancing. I am used to taking off and landing with the minimum
impact to my leg joints.

Clearly, it is a bad thing for your rim to bottom out. You may damage
your rim.

More pressure in the tyre would be one way of preventing your rim from
bottoming out, but at the expense of the cushioning effect of a nice
soft tyre.

What you need to do is develop your entire shock-absorber system.

Tyre hits ground and deforms. That absorbs some shock.

Ankles flex - that abosrbs some shock.

Knees bend. That absorbs more.

A friend of mine used to do rock climbing. He fell about three feet
and landed with his legs straight. The impact shattered his ankles.
There was no gradual deceleration of the mass of his body. Just BANG!
Sotps dead.

I saw a street performer recently. As part of his act, he leaped as
high as he could then landed barefoot on a "bed of nails". As a
performer myself, i watched carefully. Every part of his feet, angles,
knees, hips, back and arms worked together to spread the deceleration
as evenly as possible. If he had worn Doc Martens, and just jumped and
landed without this gradual deceleration, I have no doubt that his Doc
Martens would have bottomed out, the soles would have been pierced, and
his feet injured.

If you apply these principles to your unicycle dropping, you will
realise that there is an optimal tyre pressure, but that the tyre is
only part of the problem. More pressure in the tyre will make that
part of the landing harder, putting more of the responsibility onto
your ankles, knees etc. Too little pressure will result in the rim
bottoming out, a sudden clunk, and, again, extra work for the rest of
your system.

Applying ideas I have picked up from other sports, I would suggest you
should go back to small drops, and work on the technique. When you are
working at 80% of what you can achieve, you have more time and space to
work on technique. If you are aiming for 105%, then your technique
will take second place behind your will to succeed at all costs. That
way lies a dented rim, broken cranks, and injuries.


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[Fuego]

It could have been your tire folding, though I doubt it. I'm pretty sure
you're not gonna bottom out on a 3 foot drop at 40 psi. I run a lot
less than that and never bottom out except on natural trials. (but this
is a 24x3, so that's a bit of a difference.)


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[abbabibble]

well, I'll go out and take the pressure with a car tire gauge. Then i'll
see. And i'll improve my landing technique. I did a side hop off and
didn't really roll out.

thanks for the help/advice, guys.


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[One on one]

Mikefule wrote:
> I know naff all about doing drops, ....... That way lies a dented rim,
> broken cranks, and injuries.



Excellent advice. Much more useful than checking to see if the tire
gauge is working correctly.


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[john_childs]

Mikefule wrote:
>
> What you need to do is develop your entire shock-absorber system.
>
> Tyre hits ground and deforms. That absorbs some shock.
>
> Ankles flex - that abosrbs some shock.
>
> Knees bend. That absorbs more.
>


And collapse the upper body as well by bending forward at the hip.

If you do it all right you can drastically reduce the shock on the
unicycle and your body.

If you land all rigid and stiff you end up doing what I call a Lawn
Dart landing. That is you end up landing like one of those old Lawn
Darts sticking dead in the ground and dissipating none of the impact
force. That gets hard on the body and the unicycle.


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