Using "Tire Drop" for Optimal Tire Pressure

[Sreepathi Pai]

Does anybody use "tire drop" to determine the optimal pressure to
inflate your tires to? If so, how does it feel?

Here's the explanatory article I found:

http://www.bikequarterly.com/images/TireDrop.pdf


--
Sreepathi Pai

[Sunil Raghavan]

Hi Sreepathi,

I have been using the idea - most imprecisely of course - read the article when someone posted it online - I rarely ride the road bike with pressure above 100 - I usually use 80-90 - I find I move the same speed with much greater comfort. At 100 the pneumatic effect seems to be lost and the bike vibrates much more on the road - and I think it slows me down - not measured scientifically - just perception.

Sunil

[Sreepathi Pai]

I'm going to try this now, thanks Sunil. Let me see what I find.

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Sreepathi Pai

[Opendro]

I have never heard of this terminology. But I personally follow this. On my 23 road bike, I typically fill about 70 psi in front and 80 psi for rear on brevet days specially if the road passes through country roads. But on BBCh race days, I fill about 80 in the front and 100 in the rear. If I'm riding to the race venue, I typically reduce the air again after the race to ride home.

What the article didn't tell us was that the average speed reduces beyond a point in pressure as our roads are not perfect 100% smooth. I had tried this on car as well on NICE road. Top speed drops (at full throttle) as pressure goes up further. Again, I had not read any technical details. But my own intuition is that as the road surface is not 100% smooth, there are two factors that will contribute to the drop in speed. First, you need sufficient grip contact to transfer all the power you are delivering to the wheel. If the pressure is too high, chances are that the wheels are slightly off the air and losing grip (again on imperfect road) and thus all that power may not get transferred to forward motion. Second, there is those tiny rebounds from the uneven edges. It is easier to understand on off road, because it is quite measurable in our experience. The pressure should be such that you can roll over by flexing the tire with minimum rebound, but not too low that it forms too much of a contact on flat surface. If the pressure is high, it will rebound and that rebound is in the negative direction (backward). Though negligible, this effect will be definitely present on the roads as tarmac is also not 100% smooth flat. If it were 100% smooth flat, then we wouldn't even need tires. We could ride on rims like the railway tracks.

I'm so famous for low pressure that in my team, I'm known as 30 psi. Literally that is what I use for my dirt races on my 40C hybrid tires or now 2.25 inch MTB tires. I don't know why I'm telling all my secrets? :-D Nah. I wouldn't share such things on my own as these are mostly my intuitions and folks out here go pretty much by what is on the internet.

[Sreepathi Pai]

On Tue, Apr 16, 2013 at 10:18 AM, Opendro <ope...@gmail.com> wrote:

> What the article didn't tell us was that the average speed reduces beyond a
> point in pressure as our roads are not perfect 100% smooth.

It does:

"As pressures increase, tires roll faster, but the performance, levels
off at a certain pressure. Beyond this point, higher inflation brings
only negligible performance improvements (1)."

The note (1) further goes on to say: " At higher pressures, internal
losses due to flexing of the casing decrease, but
suspension losses due to vibrating and
bouncing of the bike increase"

The article also does not assume 100% smooth roads :)

On an aside, gut feel or intuition are bad explanations. If you need
to convince others in your team (who literally do not share your gut)
to ride at low pressures, all your "logic" won't help -- but a roll
down demonstration will definitely convince people *regardless* of the
actual theory. Thus, every time you sit down to write a long
explanation or theory, spend some time trying to come up with an
experiment to demonstrate (and measure) the effects of the theory :)
After all, "To measure is to know." (Lord Kelvin). That way, you might
find that tires being in the air leading to loss of grip happens so
rarely that it is entirely insignificant. Your team mates might also
not get confidence when you say "though negligible, it is there" -- if
it is negligible, then why care?

--
Sreepathi Pai

[Opendro]

It actually didn't say that performance will drop.

True, to measure is to know. My gut feel is from my experience and apply the intuition to explain. I don't have time to accurately measure. That is why I don't write here :-)

But I insist my team mates, because according to me, the only way I beat them is by following some basics on physics, because I don't train even a 10% of what most riders or runners do and I own the cheapest bike with no upgrades on core components. But I agree, it is tough to convince people without some links and I sometimes do google and post some random link in my team facebook group page :-D

[Gana...]

Ok so here goes my experience to back Opendro. 4 flats in total all were with liners. To start with, i rode the Bliss in Hills brevet from start point with about ~90PSI in the tyres with Mr.Tuffy liners and felt i should've pumped it up more. So there's a first flat after which i take the suggestion of opendro and remove the liner from rear wheel. The pressure continued it was pumped to was about 60/70 PSI and certainly not more. The tyres in use were 26c Kenda Kontender, which were stock with the Flite 300 (Max pressure is 125PSI supported). The second flat was due to a metal pin stuck in the tyre, and the third one had similar but longer metal pin. Had the liner not been inspected the liner we'd have probably put the replacement tube and ended up with a flat again. However i continued with the liner but with much lower pressure. The ride became a lot more supple and the vibrations were much lesser. The problem areas for lower pressures, cornering speeds increase due to wider surface area contact on the road, however, if you have liners, there is a chance that you get a sound similar to a worn tread on a truck/bus tyre when on the roll on a highway. I felt the same when cornering and riding the downhill to mettupalayam. Half way through the downhill, the front tube had to be replaced as it had a flat due to super low pressure and me running over a stone. I had to use the brakes so much that the rim overheated there by losing air from tube and the pressure going downright to probably 30-40PSI. The tube couldn't be replaced right away as as they were too hot to touch. The liner overlap area caused an uneven spin of the front wheel and very noticeable during cornering. So at the base, the liner is out and new tube is in, and pressure is at bout 60-70 and we are good to go. Trust me or not, i didn't have a single flat post that which means 600kms of further riding without a flat with no liners. I felt the tyre pressure being too low and feared the worst as the chandapura flyover had tiny gravel perfect to cause a puncture. However, i managed to glide over them due to the superior 'give' offered by the tyres and not allow the sharp objects to poke right through had it been for a tyre pumped to maybe over 80 or 90PSI. The bike is resting at home and is probably running 40 or 50 but i'm super happy about the effects of no liners and using just the right pressure. Having said all of this a few more factors that play a role, are your luck and the way you manage your weight on the bike especially on the bad sections of road. Gliding over potholes or broken patch of road is possible and hardly noticeable on tyre with about 50-60% of its recommended pressure. These have been tried and tested mostly in the dry 70%, 5% wet and 20% moist road conditions. The result might vary when there is constant/consistent rain on these tours. 

To summarize -- My roadbike is now liner free and my commuter will see the same treatment in a couple of days. My sincere thanks to Opendro. Heck,  I have gotten flats on MTB with liners while I see Opendro just flying by the same terrain on his Hybrid with the low pressures. I wonder how is it that this man is able to defy the flats on a course like turahalli. :) Now i know the secret. 

[anil s kadsur]

Very interesting read Gana.....thank you for the nice reply.

Got to agree....to this line....

"The way you manage your weight on the bike"

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[Ravindra BR]

Pradeep
Pradeep
Pradeep

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[Pradeep Naidu]

Ya Yaaa..Ravindra...i read the words liners and rest ignored it 😜

---

From: Ravindra BR
Sent: ‎05-‎10-‎2015 10:38 PM
To: Gana...
Cc: Bangalore Bikers Club
Subject: Re: [BBC] Re: Using "Tire Drop" for Optimal Tire Pressure

[Opendro]

I did agree that liners will theoretically reduce flat. But whether we get one flat with liner or two flats without liner in a ride of 1000 km is hardly immaterial to me. I can always fix the puncture, patch the tube if required. But ride with lower pressure is much more plush and superior, specially in brevet rides. Also, in some of the nasty steep climbs where I was standing up and pounding, I would be more scared of the shards if pressure is higher simply because contact/grip area is smaller.

BTW, I didn't get any flat last year. I got two flats in a span of 30 mins this year. It was my mistake of parking the bike on a touch me not plant during nature call. It was a tiny poking.

I also used the same tires and brake pads of last year... no change.

Anyway, this thread was primarily about performance of tire, not about punctures. You got to try the pressure as given in the chart.

[Pradeep Naidu]

Ya Yaaa..Ravindra...i read the words liners and rest ignored it 😜

---

From: Ravindra BR
Sent: ‎05-‎10-‎2015 10:38 PM
To: Gana...
Cc: Bangalore Bikers Club
Subject: Re: [BBC] Re: Using "Tire Drop" for Optimal Tire Pressure

[Gandharv Bakshi]

Hey,

Apparently someone did an experiment for this - You can read this at http://www.bikeforums.net/bicycle-mechanics/628465-do-tire-liners-reduce-odds-having-flat.html . To reproduce the experiment here, this is what the guy did:

"My test went roughly like this.

1. toss 100 goatheads onto the ground (about 2 handfuls). They land in roughly a 5-ft diameter circle
2. ride a bike at 20mph through the goatheads
3. continue riding for another 12miles (I chose this distance because it was the distance from the shop to my house).
4. repeat 10x (number of same rides in a week to work and back)
5. count number of goathead spines left in tyres
6. count number of flats.
7. change a variable and repeat.

The results were as follows:

1. the tyres pick up 3-5 goatheads when running through the thorn-field, regardless of liner
2. Without liners = 2 flats immediately, 5 flats within 5-miles, 3 flats in 6-12 miles, 100% flat rate
3. with liners = 1 flat immediately, 3 flats within 5-miles, 4 in 6-12 miles, 80% flat rate
4. with liners + scraping = 1 flat within 5-miles, 2 flats in 6-12 miles, 30% flat rate

This test is easily repeatable by anyone with similar results. Most goatheads never puncture right away. Most of the time, you'll never even notice when you ran one over and by the time you get a flat or slow-leak, only the spiny thorn is left in the tyre. Liners do reduce rates of flats given the same odds of running over debris. Liners along with scraping reduces flats even further" 

An isolated experiment proves nothing, but still it was interesting to read! 

Gandharv 

[Prashanth Chengi]

Also note that the goatheads mentioned here are notorious in many parts of the US and I've encountered them in some places in Europe, but I've never seen anything like that on the Indian roads I've biked upon.  Indian roads have more of mechanical debris, nails, pins and screws which cause most flats, and the ability of a tire liner to stop a nail or a drawing pin is rather questionable!

/Prashanth

[Opendro]

That is a no brainer and it does not need an experiment.

However, you are completely disregarding the pressure of the tire here. If the shards are not razor sharp, the chances of pierce reduces as you reduce the tire pressure. This also does not need an experiment. It is that simple.