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What is optimal tire pressure for GP5000 32 tires?

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What is optimal tire pressure for GP5000 32 tires?

Old 07-10-20, 04:47 AM
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kosmo886
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What is optimal tire pressure for GP5000 32 tires?

I've been messing around with difference pressure and don't notice massive differences. I believe the max on the sidewall says 87 PSI. I've generally been running around 75PSI or so. What is the optimal pressure (if any)?
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Old 07-10-20, 05:09 AM
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Depends on rider weight, road surface etc.
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Old 07-10-20, 05:11 AM
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160lb weight. Road riding...in MA so the road stink!
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Old 07-10-20, 05:41 AM
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There are charts out there, like the one below, that go by tire size and weight and give some guidelines. The weight across the bottom is total wheel load, not your weight. So, at my weight of 225 plus 25 lbs of bike and gear is 250 lbs. If I say 60% of the weight is on the rear wheel, that gives me about 150 lbs, which would say a bit under 90 psi for 32 mm tires.

If you look here, I think Continental says 85 - 102 PSI for the 32mm tires. The max on the sidewall on mine say 102.

I use 32mm GP 5000's and run them at 80 psi because I found over years (before the GP 5000s) that dropping to 80 did not make a difference in speed on the roads I ride on and did seem to increase the time between flats.

You are lighter, on the chart below looks like you could run lower than 75.

Last year I did the Seattle to Portland ride on a rental bike road bike with 32mm tires - did 123 miles the first day and felt great. I had forgotten to check the tires the first day, that night I saw they were only inflated to 70 PSI! Psychologically, that made me feel slow - after not feeling slow at all for 123 miles! I pumped them up to 80 for the final 83 miles, couldn't really tell the difference.


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Old 07-10-20, 05:53 AM
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60 front, 65 rear.
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Old 07-10-20, 06:15 AM
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Wheels/rims matter, too - the larger the volume, whether through larger tires and/or wider rims, the lower you can go. Tubeless allows you to run even a little lower, if desired. For reference, I'm 185lbs, riding (modern) 28s, tubeless, on an 23mm internal width rim at ~62r/~59f.
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Old 07-10-20, 06:17 AM
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Look no further, Continental provides a completely meaningless and useless guide to tire pressure on their web site

Continental Tires: What is the right air pressure?
https://www.continental-tires.com/bi...q/air-pressure

The part about their "FAQ" that I find the funniest is:

Therefore, check and set the pressure correctly on a regular basis.
What is "correctly"? They certainly haven't defined it in the FAQ!!?!?!
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Old 07-10-20, 06:56 AM
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Originally Posted by kosmo886 View Post
160lb weight. Road riding...in MA so the road stink!
I'm 185lbs and run 75r/65f, and the roads here are pretty crappy. You could prob go down to 60-65 as mentioned, maybe lower. The Silca calculator says I should be running 60psi, but I don't want to risk pinch flats, so I keep a lil extra pressure, still very comfortable. I've dropped it down to 70r/60f without issues when I knew I was just going to be taking it easy.
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Old 07-10-20, 07:09 AM
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Originally Posted by WhyFi View Post
Wheels/rims matter, too - the larger the volume, whether through larger tires and/or wider rims, the lower you can go. Tubeless allows you to run even a little lower, if desired. For reference, I'm 185lbs, riding (modern) 28s, tubeless, on an 23mm internal width rim at ~62r/~59f.
+1

I'm the same weight, using 23mm internal width rims and 30mm tires 60r/55f works well for me.
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Old 07-10-20, 07:19 AM
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I have a spreadsheet with a formula that seems to work pretty well most of the time. I don't remember where I got the formula originally.

F/R PSI=(((153.6*W)*p)/(t^1.5785))-7.1685

W: rider+bike+gear weight in lbs.
p: Wheel load %
t: Tire width in mm
On my bike with 32s I run around 55 front and 65 rear
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Old 07-10-20, 07:21 AM
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Originally Posted by Dean V View Post
60 front, 65 rear.
Agree. Feel free to tweak up or down 5PSI depending on conditions etc.
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Old 07-10-20, 07:31 AM
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Originally Posted by kingston View Post
I have a spreadsheet with a formula that seems to work pretty well most of the time. I don't remember where I got the formula originally.



On my bike with 32s I run around 55 front and 65 rear
Good numbers headed in right direction.

What... does the OP want.. ride comfort or "speed"? The latter is not increasing exponentially w high psi's... but the ride goes to hell.. see rough roads.

Depends on ride position.. more upright or how aggressive forward? Drop bar or ??

195 me... rear 60 front 48 Ultra ll's run TL. Mr Conti does NOT recommend that.. albeit works fine. Your weight w tubes... run same psi's range as mine. Yet.. you did not state tire brand.. another variable..........


Front sees load of around 34% of rear.. no need to run high psi to roll.. the 'pinch flat neurosis' only applies to actual flatting and failure to know when
your rubber is actually low prior to leaving.
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Old 07-10-20, 08:12 AM
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Formulas don't know what your road surface and other riding conditions are. If you have smooth roads with fine aggregate, you can pump those tires up to a much higher pressure than a chip seal road with coarse aggregate.

Experiment. Keep track of a dozen or so of the same route at one pressure and then another of the same rides at less or more pressure. Keep notes of both your perceived effort and your data from your gps/cyclometer/phone aap if you have it.
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Old 07-10-20, 08:12 AM
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Originally Posted by kingston View Post
I have a spreadsheet with a formula that seems to work pretty well most of the time. I don't remember where I got the formula originally.



On my bike with 32s I run around 55 front and 65 rear
Seems I may be running at too high of a pressure then. I don't mind the right at 75 or so PSI. I figured a firmer tire would be faster...is this not the case? Seems like with 32 tires on a wide rim..something like 21mm internal width I believe. I should go in the 60-65 range for more comfort. Would 80 PSI equate to more speed? curious the difference? I've seen some studies on rolling resistance on these tires specifically and does look like firmer is better for less rolling resistance and presumably more speed...
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Old 07-10-20, 08:20 AM
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Originally Posted by kosmo886 View Post
I've seen some studies on rolling resistance on these tires specifically and does look like firmer is better for less rolling resistance and presumably more speed...
Only on very smooth roads.
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Old 07-10-20, 08:32 AM
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Originally Posted by kosmo886 View Post
Seems I may be running at too high of a pressure then. I don't mind the right at 75 or so PSI. I figured a firmer tire would be faster...is this not the case? Seems like with 32 tires on a wide rim..something like 21mm internal width I believe. I should go in the 60-65 range for more comfort. Would 80 PSI equate to more speed? curious the difference? I've seen some studies on rolling resistance on these tires specifically and does look like firmer is better for less rolling resistance and presumably more speed...
Lower pressure isn't just a matter of comfort - smooth is fast. Higher pressures with less than pristine surfaces lead to suspension losses - some of your forward energy is being deflected upwards in the form of bumps and vibration. Unless you ride primarily in the glass smooth vehicle tire tracks of recently laid asphalt, you're probably much better off closer to 60psi than to 80psi.
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Old 07-10-20, 08:55 AM
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I think people take this low pressure is faster thing way too far. While I understand the concept of rough roads imparting a energy vector in the wrong direction for tires exceeding "optimal" psi. The "optimal" PSI is unique to the road, tire and the bike load going over it.

We've evidently got some smooth roads and paved trails here because for the most part, my legs feel much better on a 25 mm rear tire pumped to 125 psi than any other lower pressure. The data collection I did many years ago to see if what I perceived is what I actually did is long lost as I didn't make comments about tire pressure in the notes. So I've no data to show you.

Still, why trust a formula or what others say when it's fairly easy to determine for oneself.
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Old 07-10-20, 09:01 AM
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Originally Posted by Iride01 View Post
Still, why trust a formula or what others say when it's fairly easy to determine for oneself.
I use a formula because I have 13 bikes with 8 different tire sizes and need something to aim for when I pump up the tires before a ride. It's certainly better than guess-and-check with random PSI's.
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Old 07-10-20, 09:08 AM
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Originally Posted by kingston View Post
I use a formula because I have 13 bikes with 8 different tire sizes and need something to aim for when I pump up the tires before a ride. It's certainly better than guess-and-check with random PSI's.
Why would it be a guess. You have years of experience and should know what works well for you on what road surface on what size tire and bike.

There is nothing random about the guess. Certainly not anything more random than the formula not knowing what the road surface is. If the number given is supposed to optimize ride comfort and/or speed.

I do lower my tire pressures when I'm going on routes that have a rougher road surface. No one like being beat up by chip seal for 10 or more miles. Is chip seal all you people have ?
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Old 07-10-20, 09:14 AM
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Originally Posted by Iride01 View Post
Why would it be a guess. You have years of experience and should know what works well for you on what road surface on what size tire and bike.

There is nothing random about the guess. Certainly not anything more random than the formula not knowing what the road surface is. If the number given is supposed to optimize ride comfort and/or speed.

I do lower my tire pressures when I'm going on routes that have a rougher road surface. No one like being beat up by chip seal for 10 or more miles. Is chip seal all you people have ?
I ride 25's 90 percent of the time and honestly can't remember what pressures I run on the other bikes, so I have to look at my spreadsheet. The formula is just a starting point, so I agree with you that people should experiment and figure out what works for them. The two aren't mutually exclusive.
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Old 07-10-20, 09:15 AM
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Originally Posted by Iride01 View Post
I think people take this low pressure is faster thing way too far. While I understand the concept of rough roads imparting a energy vector in the wrong direction for tires exceeding "optimal" psi. The "optimal" PSI is unique to the road, tire and the bike load going over it.

We've evidently got some smooth roads and paved trails here because for the most part, my legs feel much better on a 25 mm rear tire pumped to 125 psi than any other lower pressure. The data collection I did many years ago to see if what I perceived is what I actually did is long lost as I didn't make comments about tire pressure in the notes. So I've no data to show you.

Still, why trust a formula or what others say when it's fairly easy to determine for oneself.
Yes, it's going to vary, but it's not as if people are pulling these numbers out of their keisters. If you haven't listened to the Cycling Tips podcast, it's worthwhile - https://cyclingtips.com/2016/08/cycl...and-pressures/

As far as trying to determine for oneself, no, it's not fairly easy. As is discussed in the podcast, one big factor is that perception is usually backwards - what feels fast often isn't.
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Old 07-10-20, 09:17 AM
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Originally Posted by WhyFi View Post
Yes, it's going to vary, but it's not as if people are pulling these numbers out of their keisters. If you haven't listened to the Cycling Tips podcast, it's worthwhile - https://cyclingtips.com/2016/08/cycl...and-pressures/

As far as trying to determine for oneself, no, it's not fairly easy. As is discussed in the podcast, one big factor is that perception is usually backwards - what feels fast often isn't.
Correct. And although some aspects of the formulas used are arbitrary (like 15% drop, who came up with that?), they are a reasonable starting point to which you can tweak a few PSI up/down based on roads and comfort.
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Old 07-10-20, 10:12 AM
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Originally Posted by Iride01 View Post
Formulas don't know what your road surface and other riding conditions are. If you have smooth roads with fine aggregate, you can pump those tires up to a much higher pressure than a chip seal road with coarse aggregate.
.
While I have no idea what the actual formulas are that drive this calculator, seemingly formulas can and do take into account road conditions -- at least with the better PSI calculators.

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Old 07-10-20, 11:46 AM
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Originally Posted by Iride01 View Post
I think people take this low pressure is faster thing way too far. While I understand the concept of rough roads imparting a energy vector in the wrong direction for tires exceeding "optimal" psi. The "optimal" PSI is unique to the road, tire and the bike load going over it.

We've evidently got some smooth roads and paved trails here because for the most part, my legs feel much better on a 25 mm rear tire pumped to 125 psi than any other lower pressure. The data collection I did many years ago to see if what I perceived is what I actually did is long lost as I didn't make comments about tire pressure in the notes. So I've no data to show you.

Still, why trust a formula or what others say when it's fairly easy to determine for oneself.
I agree that pressure is a personal preference within reason. Having a referenced starting point and tweaking from there seems like a reasoned approach. I couldn't imagine anyone running 125 PSI on 25m tire however if you perform better that way good on you.
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Old 07-10-20, 11:55 AM
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Originally Posted by Iride01 View Post
I think people take this low pressure is faster thing way too far. While I understand the concept of rough roads imparting a energy vector in the wrong direction for tires exceeding "optimal" psi. The "optimal" PSI is unique to the road, tire and the bike load going over it.

We've evidently got some smooth roads and paved trails here because for the most part, my legs feel much better on a 25 mm rear tire pumped to 125 psi than any other lower pressure. The data collection I did many years ago to see if what I perceived is what I actually did is long lost as I didn't make comments about tire pressure in the notes. So I've no data to show you.
So i just posted this on a different thread (that GP5k train wreck):
https://blog.silca.cc/part-4b-rollin...-and-impedance

Looking at the info presented here, it appears that the optimal tire pressure is somewhere in the 80-100psi for a 25mm tire, depending on the road type (although really ratty roads may require reduced psi). So you are right - there may be a tendency to take lower pressures a bit too far.

That said - the other interesting thing in the article is that it is better to be slightly lower, as far as tire pressure goes vs higher. Being 10psi lower than optimal only reduces efficiency by about 1W - being 10psi higher reduces it by 6-10W.

[On an unrelated noted, I have not found any aerodynamic data showing wider rim + tire combos to be faster than thinner rim+tire combos. If anyone has any links, pls do share]
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