compressing your tire right before a hop does give you a difference in height.
soooo…
if i have my tube at about 45 psi at a tube rated at 50 will I hop any higher?
how low is safe (not hitting the rim)
and comments or w/e?
I can hop about a foot SIF with no pre-hop. i can hope regular only about 6 inches
For my trials I have about 13-15 lbs. But that will go up as I increase my drop height.
You can go as low as you want, as long as you’re not bottoming out the tire (hitting the rim). The ideal pressure is a personal thing; from a physical standpoint, you’ll get the best bounce with the most air in the tire, but most people find they hop better with less air, as it makes the timing work better.
It’s a matter of semantics, but a tube does not hold pressure, the tire does. My good but slightly off-kilter friend during my junior high school years had a Sears Free Spirit ten-speed bicycle with 40 psi rated tires, while the rest of us had at least 90 psi gumwall tires on our bikes. Craig didn’t have enough money for a tire so he decided to ask the LBS guy for a “high pressure” inner tube instead, far less expensive than a whole tire. Of course the LBS salesman complied with his request. 
The boom of the exploding rim and tire when he hit 90 psi was pretty impressive.
Your ‘How low is safe’ question is purely speculative on our part and wholly depends on your body weight. It’ll be a trial and error method for you.
Re: Does the psi at which i have my tube affect my inability to hop?
On Tue, 7 Mar 2006 13:13:41 -0600, yoopers wrote:
>It’s a matter of semantics, but a tube does not hold pressure, the tire
>does.
Oh. Try cutting a little hole in the tube (without damaging the tyre),
and see if the tyre does still holds pressure. Ergo: you need both the
tube and the tyre to hold pressure.
I run my DX at 30psi, i can get a good bounce with it, and i dont bottem out when hitting edges or from large drops =p
I suggest filling it to its max, then take out little by little untill you get the pressure you want
yes it matters
OK I think if we’re going to get really picky the tube hold the pressure, but the tyre restricts the outward movement of the tube. A tube with no tyre will still hold pressure, but will expand as the pressure increases until the tyre bursts. A tyre will not hold presure as it is not air tight, but will restrict the movement of anything you put inside it, as it it a solid and moderately rigid body. The fact that the tube does not impart equal force at every point on the inside of the tyre suggest that using the word pressure in reference to the tyre is incorrect.
Now to answer the actual question…
Depends what tyre you have, if you’re on a mod trials tyre then drop it to 25 pounds or so and start trying it out. If you have a normal 20" tyre then put it at 10 psi below whatever’s written on the sidewall and decrease it from there. I’ve found there is an optimum pressure for hopping, but at this pressure the rim bottoms easily and also the tyre is very unstable on landings, so i usually run a little higher for trials.
I think that the tube merely acts more as a seal between the tyre and rim. The tube is not in itself capable of carrying 50psi. The tyre does the hard work.
Most car tyres are, after all, tubeless, they just have better sealing to the rims, there being a lack of spokes in a car wheel.
Nao
I run a creepy crawler pretty high, up to 37psi.
I think it’s because the temp varies so much from week to week during winter in michigan. One day it can be sunny and 45 degrees F, and the next 28 degrees F with a windchill factor of 0 degrees F.
So, no matter how cold it is out, if I run my tired near or on that pressure it’ll let me do what I want.
i run my luna at around 30-35 because im a heavy guy…