Go Back  Bike Forums > Bike Forums > General Cycling Discussion
Reload this Page >

The REAL tire pressure numbers

Notices
General Cycling Discussion Have a cycling related question or comment that doesn't fit in one of the other specialty forums? Drop on in and post in here! When possible, please select the forum above that most fits your post!

The REAL tire pressure numbers

Old 07-30-20, 09:21 AM
  #1  
rbrides
Senior Member
Thread Starter
 
Join Date: Nov 2018
Location: Triangle NC
Posts: 112

Bikes: Specialized Diverge Comp

Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 36 Post(s)
Liked 2 Times in 2 Posts
The REAL tire pressure numbers

IMHO, the guidance on tire pressures is often inaccurate because it does not account for the total weight on the bike. With the prevailing science recommending lower tire pressures the metric for setting them is the rider's body weight. I have recently opted to Gross Vehicle Weight GVW, by including the bike, helmet, water bottles, Wahoo, tools, etc that I actually ride with. All of that equipment, including the bike weighs 24 lbs. I'm adding that to my body weight and using this gross total when referencing the many charts and recommendations for tire pressures.


I've ridden 4 times with this updated calculation and it "feels" good. I don't know what the performance detriment is for under inflated tires. All the research these days is about avoiding over inflated tires and the watts, power loss therein. If my logic is correct, I am under inflating my tires if I don't account for the additional 24 lbs of "stuff".


What do you folks think?
rbrides is offline  
Old 07-30-20, 09:32 AM
  #2  
aclinjury
Senior Member
 
Join Date: May 2013
Posts: 463
Mentioned: 3 Post(s)
Tagged: 0 Thread(s)
Quoted: 356 Post(s)
Liked 99 Times in 75 Posts
when reading charts, it's up to the readers to understand that the recommened psi is fo a particular "weight", and adjust upward for equipment.
The people who come up with these charts can't possibly know how much your bike or the accessories you are carrying can add up, so it's up to you to add in this weight on top of the "weight on the chart".

But I reckon you're right in your questioning, some folks forget or don't understand about this part so they just use their naked weight, which is wrong because nobody rides naked on an air bike.
aclinjury is offline  
Likes For aclinjury:
Old 07-30-20, 09:36 AM
  #3  
wolfchild
Senior Member
 
wolfchild's Avatar
 
Join Date: Feb 2008
Location: Mississauga/Toronto, Ontario canada
Posts: 6,306

Bikes: I have 3 singlespeed/fixed gear bikes

Mentioned: 22 Post(s)
Tagged: 0 Thread(s)
Quoted: 1853 Post(s)
Liked 539 Times in 297 Posts
It's only a simple bicycle tire and I try to keep science, math, astrophysics, chemistry and all other complexity out of it. I inflate my tires according to the conditions that I ride in... When I ride on pavement I put enough air to prevent pinch flats/rim damage and keep the rolling resistance good. When I ride off road I lower the pressure just enough to give me better traction and handling. That's it, I don't worry about any numbers or calculations.
wolfchild is offline  
Likes For wolfchild:
Old 07-30-20, 09:57 AM
  #4  
cyccommute 
Mad bike riding scientist
 
cyccommute's Avatar
 
Join Date: Nov 2004
Location: Denver, CO
Posts: 22,923

Bikes: Some silver ones, a red one, an orange one and a few titanium ones

Mentioned: 113 Post(s)
Tagged: 1 Thread(s)
Quoted: 3473 Post(s)
Liked 944 Times in 587 Posts
Originally Posted by wolfchild View Post
It's only a simple bicycle tire and I try to keep science, math, astrophysics, chemistry and all other complexity out of it. I inflate my tires according to the conditions that I ride in... When I ride on pavement I put enough air to prevent pinch flats/rim damage and keep the rolling resistance good. When I ride off road I lower the pressure just enough to give me better traction and handling. That's it, I don't worry about any numbers or calculations.
I'd say that you have it somewhat backwards. On pavement, the chance of a pinch flats and rim damage are minimal while low rolling resistance is what most people want to optimize. Off-road, the chances of a pinch flat and rim damage is much more likely so plan the pressure accordingly. I'm often amazed at the pressure that people use while riding off-road, especially with regards to tubeless. While you can't necessarily pinch flat with a tubeless, pinch flats do say that your tire pressure is too low and you are risking rim damage. This wheel is an example of someone not paying attention to tire pressure to the detriment of the rim

Untitled by Stuart Black, on Flickr

That's a $300 to $500 wheel that is useless because someone opted for traction over protection.

I agree that there's not much need for calculations but there is a need for a bit of common sense. A pinch flat is a cry for more pressure.
__________________
Stuart Black
Gold Fever Three days of dirt in Colorado
Pokin' around the Poconos A cold ride around Lake Erie
Dinosaurs in Colorado A mountain bike guide to the Purgatory Canyon dinosaur trackway
Solo Without Pie. The search for pie in the Midwest.
Picking the Scablands. Washington and Oregon, 2005. Pie and spiders on the Columbia River!
Days of Wineless Roads. Bed and Breakfasting along the KATY
Twisting Down the Alley. Misadventures in tornado alley.
cyccommute is offline  
Likes For cyccommute:
Old 07-30-20, 10:24 AM
  #5  
shelbyfv
Banned.
 
Join Date: Jun 2007
Posts: 7,172
Mentioned: 28 Post(s)
Tagged: 0 Thread(s)
Quoted: 1810 Post(s)
Liked 1,180 Times in 670 Posts
Why would you not use the entire weight of bike, rider and accessories? Who would do that?
shelbyfv is offline  
Likes For shelbyfv:
Old 07-30-20, 10:36 AM
  #6  
Flip Flop Rider
Senior Member
 
Flip Flop Rider's Avatar
 
Join Date: Apr 2016
Location: South Carolina Upstate
Posts: 1,586

Bikes: 2010 Fuji Absolute 3.0 1994 Trek 850

Mentioned: 3 Post(s)
Tagged: 0 Thread(s)
Quoted: 596 Post(s)
Liked 242 Times in 148 Posts
the ideal tire pressure will vary from rider to rider, so there is no hard and fast number to hit. Many factors go into what your tire pressure should be
Flip Flop Rider is offline  
Likes For Flip Flop Rider:
Old 07-30-20, 10:41 AM
  #7  
wolfchild
Senior Member
 
wolfchild's Avatar
 
Join Date: Feb 2008
Location: Mississauga/Toronto, Ontario canada
Posts: 6,306

Bikes: I have 3 singlespeed/fixed gear bikes

Mentioned: 22 Post(s)
Tagged: 0 Thread(s)
Quoted: 1853 Post(s)
Liked 539 Times in 297 Posts
Originally Posted by cyccommute View Post
I'd say that you have it somewhat backwards. On pavement, the chance of a pinch flats and rim damage are minimal while low rolling resistance is what most people want to optimize. Off-road, the chances of a pinch flat and rim damage is much more likely so plan the pressure accordingly.
If you read my post you will notice that I said I lower my pressure for off road riding " just enough "...meaning not too much not too little. I have never had a pinch flat or rim damage yet when riding off road...or on pavement ..Pinch flats can happen on pavement too when hitting a pothole or cracks or something with not enough pressure in the tire, especially with a heavier rider or a bike that's loaded.
wolfchild is offline  
Old 07-30-20, 11:14 AM
  #8  
79pmooney
A Roadie Forever
 
79pmooney's Avatar
 
Join Date: Oct 2014
Location: Portland, OR
Posts: 8,628

Bikes: (2) ti TiCycles, 2007 w/ triple and 2011 fixed, 1979 Peter Mooney, ~1983 Trek 420 now fixed and ~1973 Raleigh Carlton Competition gravel grinder

Mentioned: 100 Post(s)
Tagged: 0 Thread(s)
Quoted: 2385 Post(s)
Likes: 0
Liked 828 Times in 558 Posts
Originally Posted by cyccommute View Post
I'd say that you have it somewhat backwards. On pavement, the chance of a pinch flats and rim damage are minimal while low rolling resistance is what most people want to optimize. Off-road, the chances of a pinch flat and rim damage is much more likely so plan the pressure accordingly. I'm often amazed at the pressure that people use while riding off-road, especially with regards to tubeless. While you can't necessarily pinch flat with a tubeless, pinch flats do say that your tire pressure is too low and you are risking rim damage. This wheel is an example of someone not paying attention to tire pressure to the detriment of the rim

Untitled by Stuart Black, on Flickr

That's a $300 to $500 wheel that is useless because someone opted for traction over protection.

I agree that there's not much need for calculations but there is a need for a bit of common sense. A pinch flat is a cry for more pressure.
Back in my car-less days, riding all winter on a fix gear and sewup cross-country tires, I ran whatever pressure was needed to keep my body off the road surface, Bottoming out on deep potholes happened. By March every year my wheels looked roughly like that bad section, but all around. (Nipples were frozen solid from road salt.. The worst dings would get pulled out., Bad lumps on the sidewall hammered and/or files.) Mafac brakes - the best caliper brake ever for really wonky rims! The ritual of spring - cutting out the spokes and rebuilding with new spokes and cheap 400 gm rims. The training sewups. New chain, cog and probably chainring. Freshly cleaned and greased bearings A new bike!

I loved that those tires simply didn't care how round the rim was. I've ridden home with sewup rims dented twice as deep as that one you show. (Bottomless potholes in deep puddles and loaded LowRiders do that! So does bunny hopping a routine crack on a 17,000 Pacific northwest miles old rim with no sidewall left from braking. That was mid-summer on my best rims and tires.

Sewups aren't pinch flat proof but pretty darn pinch flat resistant. (I did pinch flat on RR tracks in a race once but the year before I bottomed out and dented both rims on RR tracks a mile from the best finish I ever had in an important race. (Latex tubes. Start got delayed for two hours and I forgot to top off. Now miles 90 to 100 were going to be both very fast and on poor pavement so I didn't want my tires too hard there. Well, 6 1/2 hours after pumping up, not enough for those tracks! But those tires got me my most prized finish and were completely unhurt. Rims pulled out nicely later.)

Sewups. I"m going back to them. Just gotta wear out my current rims.

Ben
79pmooney is offline  
Old 07-30-20, 11:32 AM
  #9  
70sSanO
Senior Member
 
70sSanO's Avatar
 
Join Date: Feb 2015
Location: Mission Viejo
Posts: 2,210

Bikes: 1986 Cannondale SR400 (Flat bar commuter), 1988 Cannondale Criterium XTR, 1992 Serotta T-Max, 1995 Trek 970

Mentioned: 9 Post(s)
Tagged: 0 Thread(s)
Quoted: 480 Post(s)
Liked 217 Times in 161 Posts
Originally Posted by rbrides View Post
What do you folks think?
Iím thankful my Dad never talked about this when I was a kid.

John
70sSanO is offline  
Likes For 70sSanO:
Old 07-30-20, 11:47 AM
  #10  
genejockey
Klaatu..Verata..Necktie?
 
genejockey's Avatar
 
Join Date: May 2007
Location: SF Bay Area
Posts: 2,077

Bikes: Canyon Endurace, 105; Battaglin MAX, Chorus; Bianchi 928 Veloce; Ritchey Road Logic, Dura Ace

Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 509 Post(s)
Liked 600 Times in 337 Posts
Originally Posted by shelbyfv View Post
Why would you not use the entire weight of bike, rider and accessories? Who would do that?
Rider weight may vary from 100-300 lbs, whereas bike weight might vary between 15 and 30 lbs, and accessories between 1 and 10 lbs. So, even the heaviest (reasonable) bike and accessories (excluding bike touring) is a smallish fraction of the total weight on the tires.

Take me - I'm 220 lbs. So add the weight of the bikes, which varies between 18 and 22 lbs. Add 3 lbs for summer clothes and shoes, and +/- 3 lbs for water depending on how long I'll be riding. So the range for me is 241 lbs total up to 246. Say 250 in the winter with more clothing. All the variables add up to less than a 4% difference.

BTW, I think SRAM and Silca both ask bike weight, or total system weight.
genejockey is offline  
Likes For genejockey:
Old 07-30-20, 12:03 PM
  #11  
ofajen
Cheerfully low end
 
Join Date: Jun 2020
Posts: 304
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 83 Post(s)
Liked 127 Times in 80 Posts
I would agree, but every discussion and chart Iíve seen was already clear that total weight of bike and rider was the relevant quantity as the physics dictates.

What I think is appreciated less often is that front tire pressure should not be significantly lower than rear pressure in many cases.

While the weight distribution for seated cruising may tilt to the rear wheel, weight will shift forward to the front wheel when braking and so maintaining reasonably similar pressure in front will make for good, controlled handling in hard braking, especially on roads. I usually run front pressure no lower than 90% of rear pressure.

Otto
ofajen is offline  
Likes For ofajen:
Old 07-30-20, 12:16 PM
  #12  
cyccommute 
Mad bike riding scientist
 
cyccommute's Avatar
 
Join Date: Nov 2004
Location: Denver, CO
Posts: 22,923

Bikes: Some silver ones, a red one, an orange one and a few titanium ones

Mentioned: 113 Post(s)
Tagged: 1 Thread(s)
Quoted: 3473 Post(s)
Liked 944 Times in 587 Posts
Originally Posted by wolfchild View Post
If you read my post you will notice that I said I lower my pressure for off road riding " just enough "...meaning not too much not too little. I have never had a pinch flat or rim damage yet when riding off road...or on pavement ..Pinch flats can happen on pavement too when hitting a pothole or cracks or something with not enough pressure in the tire, especially with a heavier rider or a bike that's loaded.
My post was more of an FYI for anyone else. Many people take the low pressure thing to an extreme. I see lots of tubeless rims that have been ruined because the person seems to be chasing optimal traction over protection. Iíve seen such silly suggestions at ďtake your mountain bike out and lower the pressure until the tire burps off the rim on a jump...then add 2 poundsĒ. Just because the tire doesnít pinch flat doesnít mean the rim canít bang on something and dent it.
__________________
Stuart Black
Gold Fever Three days of dirt in Colorado
Pokin' around the Poconos A cold ride around Lake Erie
Dinosaurs in Colorado A mountain bike guide to the Purgatory Canyon dinosaur trackway
Solo Without Pie. The search for pie in the Midwest.
Picking the Scablands. Washington and Oregon, 2005. Pie and spiders on the Columbia River!
Days of Wineless Roads. Bed and Breakfasting along the KATY
Twisting Down the Alley. Misadventures in tornado alley.
cyccommute is offline  
Old 07-30-20, 12:50 PM
  #13  
Troul
:D
 
Troul's Avatar
 
Join Date: Oct 2013
Location: Mich
Posts: 2,221
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 6 Post(s)
Liked 194 Times in 142 Posts
i road ride, but I ride on surfaces that contain random potholes & debris scattered everywhere. I am not going to lower my speeds anymore than I already have to be watchful of hazards in my path, but I will inflate over the ideal psi that is suggested for my gross lbs. Riding anything less & I'd have an expensiver hobby replacing wheels all the time.
Troul is offline  
Likes For Troul:
Old 07-30-20, 01:49 PM
  #14  
pdlamb
Senior Member
 
Join Date: Dec 2010
Location: northern Deep South
Posts: 6,062

Bikes: Fuji Touring, Novara Randonee

Mentioned: 29 Post(s)
Tagged: 0 Thread(s)
Quoted: 1246 Post(s)
Liked 338 Times in 236 Posts
Originally Posted by Troul View Post
i road ride, but I ride on surfaces that contain random potholes & debris scattered everywhere. I am not going to lower my speeds anymore than I already have to be watchful of hazards in my path, but I will inflate over the ideal psi that is suggested for my gross lbs. Riding anything less & I'd have an expensiver hobby replacing wheels all the time.
This. And I'm not going to stop and pump my tires up in the middle of a ride, so I start with the tires inflated to the worst conditions I expect on the ride.

Assuming I don't have a flat, that is. Then I'll pump.
pdlamb is offline  
Likes For pdlamb:
Old 07-30-20, 05:10 PM
  #15  
aclinjury
Senior Member
 
Join Date: May 2013
Posts: 463
Mentioned: 3 Post(s)
Tagged: 0 Thread(s)
Quoted: 356 Post(s)
Liked 99 Times in 75 Posts
Originally Posted by shelbyfv View Post
Why would you not use the entire weight of bike, rider and accessories? Who would do that?
liberal arts majors?
aclinjury is offline  
Likes For aclinjury:
Old 07-30-20, 05:17 PM
  #16  
shelbyfv
Banned.
 
Join Date: Jun 2007
Posts: 7,172
Mentioned: 28 Post(s)
Tagged: 0 Thread(s)
Quoted: 1810 Post(s)
Liked 1,180 Times in 670 Posts
Originally Posted by aclinjury View Post
liberal arts majors?
Haha! I resemble that remark, History, 1971. Math phobic and senile but even I could figure that one....
shelbyfv is offline  
Old 07-30-20, 05:54 PM
  #17  
bobwysiwyg
Senior Member
 
bobwysiwyg's Avatar
 
Join Date: Jan 2016
Location: 961' 42.28į N, 83.78į W (A2)
Posts: 2,344

Bikes: Mongoose Selous, Trek DS

Mentioned: 8 Post(s)
Tagged: 0 Thread(s)
Quoted: 938 Post(s)
Liked 312 Times in 186 Posts
Originally Posted by shelbyfv View Post
Haha! I resemble that remark, History, 1971. Math phobic and senile but even I could figure that one....
bobwysiwyg is offline  
Old 07-30-20, 10:14 PM
  #18  
aclinjury
Senior Member
 
Join Date: May 2013
Posts: 463
Mentioned: 3 Post(s)
Tagged: 0 Thread(s)
Quoted: 356 Post(s)
Liked 99 Times in 75 Posts
Originally Posted by cyccommute View Post
My post was more of an FYI for anyone else. Many people take the low pressure thing to an extreme. I see lots of tubeless rims that have been ruined because the person seems to be chasing optimal traction over protection. I’ve seen such silly suggestions at “take your mountain bike out and lower the pressure until the tire burps off the rim on a jump...then add 2 pounds”. Just because the tire doesn’t pinch flat doesn’t mean the rim can’t bang on something and dent it.
that's exactly right. Furthermore, some folks run their mtb tubeless tires so low a psi that the tires get lobsided (ovalized) due to carcass being constantly overstretched.
aclinjury is offline  

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off


Thread Tools
Search this Thread

Contact Us - Archive - Advertising - Cookie Policy - Privacy Statement - Terms of Service - Do Not Sell My Personal Information -

Copyright © 2018 MH Sub I, LLC dba Internet Brands. All rights reserved. Use of this site indicates your consent to the Terms of Use.