# Road Cycling - Psimet's tip of the Day

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Psimet2001
04-23-08, 01:31 PM
I thought I would create a place to share some of the nuggets I have gotten or given while on BF. I will come back and update this thread when I think about it. Probably no more than once a day though.

Tip 1 - Inflate your tires before every single ride. Know what the proper inflation pressure should be for your tires. Inflation requirements will vary by rider, bike, tires, conditions, etc.

Below you will find equations that you can use to help determine an appropriate starting point using your weight and the tire's size. Adjust from these baselines to suit needs and conditions.

Proper inflation is the easiet way to avoid flats.

Tire Width=20: Pressure(psi) = (0.33 * Rider Weight in lbs) + 63.33
Tire Width=23: Pressure(psi) = (0.33 * Rider Weight in lbs) + 53.33
Tire Width=25: Pressure(psi) = (0.33 * Rider Weight in lbs) + 43.33
Tire Width=28: Pressure(psi) = (0.33 * Rider Weight in lbs) + 33.33

Tire Width=32: Pressure(psi) = (0.17 * Rider Weight in lbs) + 41.67
Tire Width=37: Pressure(psi) = (0.17 * Rider Weight in lbs) + 26.67

Example: You are 150lbs running 28's

Pressure (psi) = (0.33*150) +33.33 = 82.83psi (rear)
Front Pressure = .9*Rear Pressure = .9*82.83psi = 74.55psi front

EDIT: I added () in order to make the equations make more sense. I think some people are doing the math incorrectly.

Kimbercop
04-23-08, 01:37 PM
My tire doesnt hold enough air, now what??

BTW, do you accomplish ANYTHING at work, thats WORK related?? ALSO... I saw that little comment in the other post about someone descending. Might cost you a few beers this weekend for me to "forget" it.

ridethecliche
04-23-08, 01:42 PM
You have a typo, the front pressure should be multiplied by rear pressure not by front pressure ;)

This should be a fun thread.

aham23
04-23-08, 01:43 PM
first i need the freaking tip on how to tell what tire size i have?!@? geesh.

later.

steaktaco
04-23-08, 01:43 PM
Front Pressure = .9*Front Pressure = .9*82.83psi = 74.55psi front

Can't... get it... to work.

Head hurts. Is it like the sound of one hand clapping?

Talewinds
04-23-08, 01:44 PM
My tire doesnt hold enough air, now what??

BTW, do you accomplish ANYTHING at work, thats WORK related?? ALSO... I saw that little comment in the other post about someone descending. Might cost you a few beers this weekend for me to "forget" it.

Are you sure he works? I just thought everybody posting here during the day didn't work, like me...

jsharr
04-23-08, 01:48 PM
Psimet works at UselessBikeTriviata Inc., a subsidiary of PCadhatesyou Worldwide Holdings Ltd.

cmh
04-23-08, 01:58 PM
I come in at 109 rear, 98 front. That is about what I use on wet, relatively smooth roads in a race. Seems a little low to me for dry conditions. On bad pavement I'd be risking a pinch flat.

04jtb
04-23-08, 02:01 PM
I come out at 99.8psi for my 23s

i think that is a bit low really - according to my gauge on my pump (probably wrong) I put 120psi in often

alanfleisig
04-23-08, 02:02 PM
Now I have to carry a scale as well as a pump in my bike kit?

No need to reduce tire pressure while riding to compensate for fluid loss; your tires will do it for you.

With a little practice, of course, one should be able to do these calculations in one's head.

chipcom
04-23-08, 02:11 PM
Holy crap, I did the math, but the answer I got was
"Pump your tire up as much as you can you fat b@stard. If the tire blows, stop the lesson."

RichinPeoria
04-23-08, 02:14 PM
Thanks, I havent seen this before.

Ive been trying to dial in my pressures during my last few rides few rides.

Ill try the front pressure=0.9Xrear pressure tonight.

huytheskigod
04-23-08, 02:15 PM
Front Pressure = .9*Front Pressure = .9*82.83psi = 74.55psi front [/COLOR][/I]

Infinite Loop!!....ERROR...Core Dump

prendrefeu
04-23-08, 02:21 PM
Psimet, it doesn't matter how many excuses you want to come up with (tire pressure being one of them), you'll still get dropped and we'll still yell at you.

That is all.

Psimet2001
04-23-08, 02:22 PM
I fixed the infinite loop :D

Yes...I do work...although we did block access to Bikeforums on our firewall here....wonder why.

Not to worry. BF nerds helped me supply my addiction.

I do not currently - nor do I have plans to - work for pcad or any of his subsidiaries. I should though because then maybe I could afford some Zipps...even if they were used and from ebay.

I will forever remain ....off the back...

Kimbercop - You know I was joking *as I reach for my wallet and hail the waitress*

ColorChange
04-23-08, 02:31 PM
This is funny PSI.

My WalMart tires on my schwinn commuter only go to 100psi. I'm in trouble.

botto
04-23-08, 02:32 PM
I never did calculus in HS, but thanks.

crydee
04-23-08, 02:33 PM
Lets make more jokes about how stupid we are.

CyLowe97
04-23-08, 02:36 PM
The tires on my Radio Flyer three wheeler don't seem to have a place to put air in them.

What now, genius?

artifice
04-23-08, 02:49 PM
so, 89.6 rear, 80.64 front? that seems seriously... low.

steaktaco
04-23-08, 02:52 PM
Maybe these values are for charity rides...

joecool2727
04-23-08, 02:56 PM
Ya those numbers seem low. Here's a useful tip: The easiest way to prevent flats is to buy a pair of Specialized Armadillo tires. Unless you run over a razor blade or an industrial sized nail, you will not get a flat, and they last for ever.

chipcom
04-23-08, 03:09 PM
yeah, everyone knows armadillos will prevent pinch flats.

SushiJoe
04-23-08, 03:14 PM
Psimet works at UselessBikeTriviata Inc., a subsidiary of PCadhatesyou Worldwide Holdings Ltd.

Psimet2001
04-23-08, 03:15 PM
:D - *shakes head* - most riders ride with their tires pumped way too high. Seems they all decided to post today.

caloso
04-23-08, 03:15 PM
Oh, great. Now I need to bring a calculator and the bathroom scale into the garage each morning.

Psimet2001
04-23-08, 03:15 PM
The tires on my Radio Flyer three wheeler don't seem to have a place to put air in them.

What now, genius?

chipcom
04-23-08, 03:17 PM
:D - *shakes head* - most riders ride with their tires pumped way too high. Seems they all decided to post today.

According to your formula, mine are too low at 120psi.
I'm just glad you didn't post this before RAIN last year, or I would have surely had a pinch flat!

Psimet2001
04-23-08, 03:24 PM
The formulas don't take into account those at the far ends of the spectrum ;)

They provide a good baseline for those that don't know where they should be. Too many rider pump their tires to what is on the sidewall as the max without any other reason other than ....that's what's on the sidewall as a max....

artifice
04-23-08, 03:35 PM
The formulas don't take into account those at the far ends of the spectrum ;)

They provide a good baseline for those that don't know where they should be. Too many rider pump their tires to what is on the sidewall as the max without any other reason other than ....that's what's on the sidewall as a max....

so, where is the fancy formula to determine if u are at the far end of the spectrum?

Brian Ratliff
04-23-08, 03:42 PM
Seems to work. I get something around 115psi for my 23mm tires which is feasible, though on the high side. I actually run them closer to 103 front/108 rear. I weigh in at 185lbs.

I get relatively few flats, though I might be working on the good will banked up with the flat gods after my 4 puncture flats in two days run last fall with the one-in-a-million-run-over-a-razorblade-and-cut-the-tire-in-half day the week before.

gurana
04-23-08, 03:58 PM
I've definitely been running at about MAX - 5 p.s.i. for both tires the last couple of years. I had figured I didn't want to put it all the way to max, but had no info on how much under it should be.

So for me, 175lbs, 23c tires...

Tire Width=23: Pressure(psi) = 0.33 * Rider Weight in lbs + 53.33
111.08 rear, 99.972 front. I guess I'll need a more accurate guage ;)
Actually, I guess I haven't been that bad on the rear tire. Only about +4 psi there, but I'm closer to +15psi on the front. I will give it a try, but if I get a flat I'm coming for your head.

otismedina
04-23-08, 05:23 PM
Is this total bicycle load, or just rider weight? That could be 15-20 lbs (pounds) difference. Is this love, baby, or is this confusion. (http://www.lyricsfreak.com/j/jimi+hendrix/love+or+confusion_20071535.html)

aham23
04-23-08, 07:11 PM
my head hurts. cant someone just pump my tires up for me. this is just crazy. later.

Psimet2001
04-23-08, 07:24 PM
Is this total bicycle load, or just rider weight? That could be 15-20 lbs (pounds) difference. Is this love, baby, or is this confusion. (http://www.lyricsfreak.com/j/jimi+hendrix/love+or+confusion_20071535.html)

Just rider weight. Their is a chart with curves that Bicycling put out many moons ago that uses total weight, but honestly how many of you would suit up, with bottles and tools, etc on the bike and get on a scale??

Like I said - it gives you a great starting point.

For me formula yields 103FX114R. I run at 7.2bar front and 8 rear on 23mm tires. (104FX116R). Rides great and no flats.

EDIT: Can't wait until my next tip.

JMT114
04-23-08, 07:35 PM
Wow, according to your formulas I have been inflating my tires to the proper inflation +/- a couple pounds.

Scummer
04-23-08, 07:37 PM
I just pump until my arms are to weak to fill more air into my tires. Is that OK or am I underinflating my tires and ego too much?

Reynolds
04-23-08, 07:43 PM
102/92 for me. Close to the 100/95 I normally use.

KirkeIsWaiting
04-23-08, 07:43 PM
This is really making me rethink my body weight.
How much does 14 inches of thick hair weigh?!!
should I keep my nails short too? I could weigh GRAMS less!

chipcom
04-23-08, 07:47 PM
so, where is the fancy formula to determine if u are at the far end of the spectrum?

If you use the formula and the recommended inflation exceeds the max rating of your tire, welcome to the far end of the spectrum. We serve pizza at noon. :D

slim_77
04-23-08, 07:49 PM
so, where is the fancy formula to determine if u are at the far end of the spectrum?

1. look down--do you see your toes? Yes: within 68%, NO: you are on the tail end of spectrum.
2. look down--is it hard to find your body? Yes: see a doctor...wait, stop at Hardies/taco bell/DDs, McDs, eat, then see a doctor, NO: you are within the 68%

Kimbercop
04-23-08, 07:58 PM
I'm past the far end of the spectrum. I fill my tires to max psi and I still hear them groan when they see me approch in my shorts.

caloso
04-23-08, 10:01 PM
Can't wait for tomorrow's Tip o' the Day. It'll probably involve a slide rule and an astrolabe.

rollin
04-24-08, 01:13 AM
If you use the formula and the recommended inflation exceeds the max rating of your tire, welcome to the far end of the spectrum. We serve pizza at noon. :D

Now that's funny!

See you at noon:o

RichinPeoria
04-24-08, 05:13 AM
109 rear
98 front

was 120 and 120

I could tell the difference right away. The front end felt softer and had more grip in the corners. I felt more comfortable leaning farther over and I had more confidence with higher entrance speeds. I did not sence an increase in rolling resistance. I was able to "spin-out" in top gear in several places.

Psimet2001
04-24-08, 06:38 AM
I have pretty extensive morning meetings this morning. Post the tip near lunchtime. :(

GeeBee650
04-24-08, 07:07 AM
So my tubes are always getting pinched by the tire bead at the valve stem. What am I doing wrong?

nick burns
04-24-08, 07:21 AM
So my tubes are always getting pinched by the tire bead at the valve stem. What am I doing wrong?

After you seat the tire on the rim, push the valve stem inwards into the tire. Otherwise the section of tube surrounding the valve stem may get trapped under the tire bead.

DougG
04-24-08, 07:21 AM
Mine came out to 100.08 rear, so now I have to find a tire guage that reads to hundredths of a psi.

CyLowe97
04-24-08, 07:23 AM
I used Psimet's formula to not only pump up my tires, but to calculate my IQ.

Wait...the phone's ringing.... Hello? Oh, hi MENSA!