allgoo19

I have been inflating my tires 700x20c 120psi for a long time. Lately I wanted to experiment a little lower pressure for comfort. I reduced it to 100psi. It was working for a while. Then today, after work I went to ride my favorite hill climbing. On the way, I had to go through a street full of gravel falling down from the hill running along side of it. I hit a small gravel, then I heard familiar sound of air coming out of the tube. It was a short course, so I didn't bring my pump, only CO2 cartridge. To make long a story short, I walked back to my house about 3.5 miles.

The tire is rated 100psi recommended. I guess that applies only to smooth road. I had never had flat even I hit a gravel with 120psi in the tire, at least not from snake bite. I'm relatively light weight of 140 lbs. I have been hearing other people with heavier weight inflating their tires 90 tp 100psi in this forum. Are you sure, you really don't get snake bite with those tires? From now on, there will be no experiment for me. 120 psi or higher, I can take a little harsh ride, it doesn't bother me.

Surferbruce

i think 90-100 psi works pretty well for 23mm tires, but i wonder if the smaller 20mm needs a bit more. i've never ran 20's but it makes sense.

allgoo19

After the rain, the streets around here are full of junks, mud, gravel, sand and the worst, the pot holes. It's not often that the front wheel hit the gravel squarely like it did today, if not for the rain, but still, I wold be more cautious. Higher pressure doesn't necessarily gurantee no flats, but it ensures that there will be much fewer flats.

miamijim

Actually in those condition lower pressures are btter. At a high pressure the tire cannot comform to road irregularities, therefore your more likely to cut down a tire from road debris.

Example: Inflate a party ballon. If the ballon is very tight its easy to pop it. Let some air out. Its much more difficult.

I have statistical data that proves 90-100 p.s.i. is too low.

ofofhy

I was thinking the same thing. Higher pressures do cut down on pinch flats, though. So I guess there is a balance. I know when I am down around 90 on my 23's they are really flat looking.

phantomcow2

I tried going around 100psi with my tires. Though keep in mind im on a MTB with slicks for city riding here, i didnt like it at all. Maybe im just spoiled by the plush ride on my 2.1's but it seemed too harsh. Now i use Ritchey Tom slicks and usually keep them at 75-80psi. Never gotten a pinch flat with them either.

my58vw

On my 2100 I have victorias and I run them at 120 PSI. I actually got a pinch flat on them over a small curb yesterday. I can not even think of running 100 PSI or I will constently flat out...

Noah Scape

If you want true comfort... go with some bigger tires... 28s, or perhaps 32s, or go for broke with 38s. Your life will start to make sense, food will taste better and you'll be better lookin too.

2manybikes

The small 20mm tires are closer to the rim, they need more air pressure to take a hit and keep it from hitting the rim. A larger tire is farther away from the rim and can be run with lower pressure and not have a bump hit the rim.

It's the size of the tire that is keeping you from being able to run low pressure. The riders with lower pressure have bigger tires. The comfort difference just going up to 23mm tires is pretty big. That's what you should try for comfort. That's why you don't see many 20mm tires around. I run 22 and 25 psi in my huge knobbies over large 3" high frozen footsteps in ice. And on rocky roads. No problems. Big tires

AndrewP

I you want to run 20s you should get tires that will take 160 psi. I run 28s at 105, but I weigh 230 lb.

smitty8

I've read many discussions about best air pressure over the years. Opinions vary widely. Then I found a chart that gave recommendations based on tire size and total weight. If I can find the link again I'll post it. For me (bike + rider and gear about 225 pounds) it recommended 115# rear on 23Cs. It recommends 10% less on front because less weight is on the front. (My regular riding partner weighs 120 and runs about 90 pounds.)
Pressure is a compromise between efficiency (high pressure) and snakebite resistance and comfort but I don't think that, other than snakebites, it makes any difference with respect to flats. I used to get frequent flats. I switched to Continental Gator Skins and flats immediately became very rare. I don't see how with equally thin tires it can make any difference, but is sure seems like it did for me! I don't find high tire pressure any less comfortable than low pressure, regardless of ride length.

allgoo19

Actually I rarely had flats when I inflated them to 120 psi. I had my same Park glueless patch kit for something like 10 years. that was the fourth patch I used out of 6. And I wasn't looking for more comfort but more like I was curious to see how much of a difference the pressure makes that people often talking about. Honestly, I didn't feel a big difference between two different pressures.


Additional story to this is that on the way to walk home, many people stopped to help me. One guy on LightSpeed bicycle stopped and offered me a help. (His name was Carl, just in case he was reading this. I told him about bikeforum.com and recommend to become a member.) He was pretty good equipped and lend me his pump. We found two holes, typical snake bite, and patched it and put it on the rim. Just when we thought we were going to inflate the tire, we found a small nut that holds small spindle in the presta valve was missing. We looked around for a while but finally came to conclusion that it was a goner. While we are working on it, a lady was standing in a litle distance away. I didn't know why she was standing. When I decided to walk towards home, she said she was leaving. Then I was realized that she stopped to give me a ride. So I asked her if she was there to give me a ride. She said yes. I was kind of embarrassed not to ask her the question sooner. I thought about it for a moment but decided to walk home. I told her it was only two miles to home(it's a guy thing, being independent). I thanked her and felt it was pretty heart warming. It's a good reason to stop when I see somebody in the same situation.
Just wanted to share the story.

tippy

www.bikeforums.net

dooley

Pinch flats are a real problem for BMXers, what I do is put loads of powdered chalk in the tyre and run tyres that are a pretty close match to my rims. It seems to work.

This link explains it pretty well, it's written for the average BMXer so it covers a lot of basic stuff, but it's still worth reading. https://www.gsportbmx.co.uk/support/r...punctures.html

allgoo19

He must be spending all day looking for the site that doesn't exist.

For the snake bite flats, I rode 65 miles today with tires inflated to 120 psi and no flat. I have to wonder why I even expeimented with lower pressure when there is nothing wrong with 120 psi.

doctorSpoc

How much do you weigh?

think i found the chart that smitty8 was refering to (see below)

From the chart you can see that for a rider+bike combined weight of 200lbs on 20s ride at 120lbs and with 23s ride just over 100lbs.

like the 2manybikes said, smaller tires require more pressure to prevent pinch flats, but the higher pressures needed for 20s lead to more cuts. If you want more comfort, larger contact patch on the road that allows you to get through corners faster (especially in the rain) and lower rolling resistance go for 23s. 20s are good for smooth, timetrials where there may be some gains in aerodynmics with the 20s but for road racing, group riding, recreational riding 20s are not that great.

If the recomended tire pressure is not enough to support your weight (i.e. you get pinch flats) the answer is not to put more pressure in your tires over the recomended pressure, the answer is to get larger tires... the recomened pressures are what the company has determined will give you the best performance.

operator

That chart doesn't look right. My total is 145 pounds. That means I should inflate my tires to only 55 psi with 700x28?? wtf?

I've also used 27x1 1/4 and the recommended psi on that graph is so low you can't even read it.

allgoo19

The chart is hard to believe. From the chart, recommended pressure, based on the total weight 165 Lbs, tire size 700x20c, it would be 100 psi. It may depend on the thickness of the tube too? Like operator said, the chart run little too low. It may work on paved road with no objects on the surface.

Having said that, it's a good start point. If you add 20 psi to the result you get from the chart, you'll be all right.

catatonic

that chart cant be right, my commutinng setup, bike, bag and myself is about 270lbs.

And I run 700x20c @100psi with no snakebite issues at all...and my commute has some seriously crappy road segments.

operator

I think we can safely say that that chart is as good as trial and error in tire pressures.

alanbikehouston

There are three steps for using the chart.

1. Use total weight. The bike, plus the rider, plus the rider's gear and equipment.

2. Use the REAL size of the tire. In the USA, the REAL size (the measureed size) is usually one size down from the "advertisided" size stamped on the tire. For example, if a tire sold in the USA is stamped "23", its measured width at 100 PSI is usually only about 20mm. So, if your tires are marked "23", use the "20 line on the chart.

3. Lastly, as the author suggests, add about 10% more pressure for the rear wheel.

Therefore, according to the chart, if the total weight is 165 pounds (rider, plus bike, plus gear) and the tires are stamped as size "23", the tires should be at 100 PSI front, and 110 PSI rear.

doctorSpoc

I think we can safely say that catatonic either has a broken tire guage or scale or is not reading the tire size right... 270lbs total weight on 20s and only using 100psi with no pinch flats on rough rodes??? 'cmon, THAT is a little hard to believe! sorry catatonic but that's just not possible unless you're riding on roads made of glass.

It's not my chart so I'm not going to defend it 'til I'm blue in the face...I happen to think it runs a little low (10-15lbs), but consistantly so. I think at the pressures they talk about you may get better rolling resistance but maybe sacrifice 'road feel' a little.

2manybikes

It depends on how good you are at missing stuff. I can ride on my 23's at 40-50 psi all day easily.
If I am too lazy to fill the tire after a flat. I'm not the only one. It just depends on what you are used to. I did a couple of decades of motorcycle racing off road, before really getting hooked on cycling. I was programmed for the higher speed and rougher surface than any road. It makes not hitting stuff at 20 mph like in slow motion. It's almost too easy. If you did the same things I did you would probably have the same habits. Most people would.
I rode on 19's for years. I have never had a pinch flat. I don't hit stuff. Most people can learn this.
I don't have tire problems when I ride my 17 lb. road bike carefully over the rocks on the railroad bed or
through a little mud. Slowly and carefully. The tires are thin, but have Kevlar belts. There is not a mark on them. Or any part of the wheels, for that matter.
There is always more than one way to find a solution to something. This in no way takes away all the real and practical benefits of larger tires. Both larger tires and learning to scan the road constantly are benefits to cycling. One does not invalidate or minimize the other. One can have both or just one. Having both is a terrific way to go for a newbie.

OK doctorspoc..........you can give me a letter grade,or just pass or fail if you like,on this part.....

Any knowledgeable cyclist would have to agree, wouldn't they? And surely you are a knowledgeable cyclist aren't you? Don't you become more aware of this as you ride more?

catatonic

Going by that chart I alone am more than what a 700x20c should be taking...but they are still going strong.

plus I don't think my tire would take 170psi...it's an old michelin hi-lite comp.

Seriously, I do think that chart is way off, or an important variable is missing.


edit: looks like for a 100psi 700x20c setup, basing a 20lb bike (pretty average), the rider has to be 140lbs.....140lbs is a bit light, don't you think.....maybe this chart was made based on tire/rim technology of that time...

allgoo19

While I agree that what catatonic is saying is hard to believe, it depends on how fast you are going also. If you are wise enough(like catatonic) to slow down when you see gravels on the road, you don't get as many flats. If you are stupid enought(like me) to go 20 mph and hit the gravel, you have a lot more chance of getting flats. So, I agree with some of the posts, you have to learn it by trial and error.