How much of a weight difference does less air in a tyre make?

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5/7/2018 1:15 PM

I was riding home on a flat on the front yesterday and it was around 3/4 flat by then and lifted my front end to hop up a curb and almost looped out and did the gnarliest bump jump I’ve done. This made me think, was my front end lighter from less air in the tyre? It sounds absurd to me cos how much of a difference does AIR make? Is it something to do with rotational weight? And if less weight has that much of a difference on the height of my hops, I’m gonna have a look into a lighter wheel set.

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An Indian on a small bike

5/7/2018 1:16 PM

sure why not

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It’s all bmx

5/7/2018 1:18 PM

Seriously?
Tyre pressure makes zero affect on the weight of your bike. More than likely it being a little flatter just gave you more bounce on the way up. What pressure do you usually use?

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5/7/2018 1:25 PM

grumpySteve wrote:

Seriously?
Tyre pressure makes zero affect on the weight of your bike. More than likely it being a little flatter just gave ...more

70PSI

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An Indian on a small bike

5/7/2018 1:28 PM
Edited Date/Time: 5/7/2018 1:32 PM

Ok, I tried to steal a formula from a car forum but the formatting got borked.

But basically the method stays the same. At the end of the day, the air in your tire is an extremely negligible amount of weight. Definitely not enough to notice, nor would dropping your PSI 10, 20, even 30 PSI make a difference.

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BMX over 30: Eat clean, Stretch, and Pray.

5/7/2018 1:35 PM

You preloaded into the front tyre and the "rebound" gave you a little extra pop...

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5/7/2018 1:36 PM

it may have been a tenth of a gram lighter but riding after a haircut would be a far greater difference.

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Hmmm

5/7/2018 1:54 PM

TheDarkEnergist wrote:

Ok, I tried to steal a formula from a car forum but the formatting got borked.

But basically the method stays the same. At ...more

I can quite blatantly feel 10psi difference.

Op, use a lower psi in both tyres, say 50-60. If it feels better leave it at that. If you go too low you'll get tyre roll when cornering, and more resistance.
I run anywhere between 50-60 and never get pinch flats, and I do a lot of bump jumps up curbs and stuff

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5/7/2018 2:08 PM

TheDarkEnergist wrote:

Ok, I tried to steal a formula from a car forum but the formatting got borked.

But basically the method stays the same. At ...more

grumpySteve wrote:

I can quite blatantly feel 10psi difference.

Op, use a lower psi in both tyres, say 50-60. If it feels better leave it at ...more

I think he meant the weight of the air but yes, 10 PSI is quite noticeable.

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My Sunday Soundwave V3 Build
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"You can't educate pork"
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"Life should not be a journey to the grave with the intention of arriving safely in a pretty and well preserved body, but rather to skid in broadside in a cloud of smoke, thoroughly used up, totally worn out, and loudly proclaiming "Wow! What a Ride!""
- Hunter S. Thompson

5/7/2018 2:35 PM

grumpySteve wrote:

I can quite blatantly feel 10psi difference.

Op, use a lower psi in both tyres, say 50-60. If it feels better leave it at ...more

Steve, don't go assuming because I'm on this side of the pond that I'm as colossally fucking retarded as some of my countrymen laughing

I meant strictly in terms of "weight of bike" feeling. Dropping 10, 20, 30 psi makes a huge difference in dynamics, of course.

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BMX over 30: Eat clean, Stretch, and Pray.

5/7/2018 2:55 PM

Less air sucks , it’s hard on your rims and it’s slow , no benefit to it at all

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5/7/2018 3:01 PM

eskimojay wrote:

Less air sucks , it’s hard on your rims and it’s slow , no benefit to it at all

To a degree, yeah absolutely. When I'm lower than ideal I feel like I'm riding in sand.

But I used to run 100psi front and back and the bike was such a tweaker during manuals. One day I forgot to top the air off and ran at about 70psi...I instantly added a good 3 feet (not much I know) to my manual. The tire giving me that extra contact on the ground was a huge help.

So basically thats why there is no ideal tire pressure for each rider. Everyone is different. I've switched from 100psi (which, I'll admit gets you moving SO fast) down to 70-80 since I'm riding shorter distances but mostly staying at one street spot. It's really all preference, but I don't understand how people run below 50 laughing

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BMX over 30: Eat clean, Stretch, and Pray.

5/7/2018 3:05 PM

eskimojay wrote:

Less air sucks , it’s hard on your rims and it’s slow , no benefit to it at all

TheDarkEnergist wrote:

To a degree, yeah absolutely. When I'm lower than ideal I feel like I'm riding in sand.

But I used to run 100psi front and ...more

sand stops you almost instantly and if you ride into it fast enough it will throw you over the bars.

Source of this information: i once lost a bet and had to do a small gap to sand and ended up with a mouthfull of it.

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Hmmm

5/7/2018 3:06 PM

I just pump a lot of air in both tires. I don't care about the psi and no wheel has ever exploded on me before. I do only weigh 138 lbs though.

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"STREET" all day, ere'day.

5/7/2018 5:29 PM

It's important to remember that it is rider weight dependent.

PSI is Pounds per Square Inch. So a 200 pound rider, with 100 psi in their tires, has one square inch of each tire in contact with the ground (two tires, two square inches, at 100 psi that's 200 pounds).

In the same way a 140 pound rider, with only 70 psi in their tires, will have just the same amount of tire squish.

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5/7/2018 5:54 PM

SirCaseAlot wrote:

It's important to remember that it is rider weight dependent.

PSI is Pounds per Square Inch. So a 200 pound rider, with 100 ...more

thats not how it works, the psi is inside the tyre and is a measurement of pressure not volume.
100 psi takes the same volume as 40 psi, if a tyre has 100psi then each square inch of the tyre will be under 100 pounds of pressure whereas a tyre with 40psi each square inch would be under 40 pounds. That is why tyres with more air are harder, the air inside is being pushed outwards aghainst the rubber more by the other air in the tyre.

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Hmmm

5/7/2018 8:07 PM
Edited Date/Time: 5/7/2018 8:18 PM

There is times at the end of a session when I am worn out I leak some air out of my tires, normally just my front tire cause I do a lot of manuals and hops so it does make it a tad lighter for me. I run my tires pretty hard with lots of air so letting some air out works but I make sure it doesn't go too flat for my liking, personal preference. Also, the whole thing about the weight of your tires actually is a huge factor when the bike is in motion or the wheel is actually spinning. Lifting up a tire by itself is much different than when the tire is on the bike wheel as you are riding. Alfredo over at OnSomeSh!t bmx shop tells it in this video in the link below at the 9:35 mark.. also he has another video all about just tires.



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5/7/2018 8:27 PM

SirCaseAlot wrote:

It's important to remember that it is rider weight dependent.

PSI is Pounds per Square Inch. So a 200 pound rider, with 100 ...more

Edman123 wrote:

thats not how it works, the psi is inside the tyre and is a measurement of pressure not volume.
100 psi takes the same volume ...more

Actually, I think the only wrong thing there is assuming a perfect weight distribution between the tyres.

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My Sunday Soundwave V3 Build
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"You can't educate pork"
- grumpySteve

"Life should not be a journey to the grave with the intention of arriving safely in a pretty and well preserved body, but rather to skid in broadside in a cloud of smoke, thoroughly used up, totally worn out, and loudly proclaiming "Wow! What a Ride!""
- Hunter S. Thompson

5/7/2018 10:59 PM

The only reason you hopped that way is physics, lol. The weight of air inside your tubes should be the last thing you look to for weight reduction. smile

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@scootereyn

5/8/2018 3:08 AM

A few rushed calculations says...

Bike tire of 20" x 2.35" @ 100 psi at 15'C and 50% rel. hum. = 330 grams (11.6oz)

@ 60 psi rest the same = 200 grams (7oz)

Completely flat all the rest the same = 49 grams (bit short of 2oz)

Basically, somewhere around an ounce per 10 psi

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5/8/2018 8:52 AM

PSI is Pounds per Square Inch. So 70 PSI means 70 pounds of air for every square inch in your tire. That's at least like 700 pounds of weight from each tire, you'll definitely notice that.

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5/8/2018 9:03 AM

Xxohioanxx wrote:

PSI is Pounds per Square Inch. So 70 PSI means 70 pounds of air for every square inch in your tire. That's at least like 700 ...more

That's some Ohio math if I've ever seen it.

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BMX over 30: Eat clean, Stretch, and Pray.

5/9/2018 8:32 AM

Science

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An Indian on a small bike

5/9/2018 9:19 PM

Xxohioanxx wrote:

PSI is Pounds per Square Inch. So 70 PSI means 70 pounds of air for every square inch in your tire. That's at least like 700 ...more

I wish there was an upvote button so I didn't have to add this comment

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