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80 psi too low for my 700x28 tires?

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80 psi too low for my 700x28 tires?

Old 01-31-21, 03:17 PM
  #51  
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Originally Posted by DaveSSS View Post
I've rejuvenated my 30+ year old Silca pump with a new Hirame chuck and a new and much larger liquid filled 0-100 psi gauge that's accurate to plus or minus 1.5%. Now I can read the gauge easily and be confident in the pressure. The old gauge was reading about 8 psi higher than the actual pressure.

https://cimg8.ibsrv.net/gimg/bikefor...00b021c44a.jpg
The Hirame chuck is so good! I smile every time I use it. I know itís not cheap but even this cheapskate thinks itís worth it!
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Old 01-31-21, 03:27 PM
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After running through my stash of Victoria Corsas, I put on some 4 Seasons. Holy smokes, they seem as stiff as Gatorskins. I was under the impression they were closer to GP4000ís than Gatorskins. I havenít rode them yet, so I will hold judgment.
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Old 01-31-21, 06:09 PM
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Originally Posted by Symox View Post
where can I find that calculator?
The calculator is based on the 15% drop graphs described here.

I used to use the Dorky Pants Tire Pressure Calculator which is based on that, but now it appears to just be an excel spread sheet. I think the owner of it must be asleep at the wheel.

But keep in mind, any of the pressure calculators are just starting point. Though for me, those 15% drop graphs are in the ballpark for me. For larger tires, I end up lower than the chart. For smaller tires I go a tad higher or I get pinch flats (actually, I don't do tires under 35mm anymore)

Some tires deal better with lower pressures that others. You just have to experiment. each tire is different, even ones of the same size.
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Old 01-31-21, 08:04 PM
  #54  
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Went riding on my favorite hilly area. This time used 70 psi front and back. Was awesome. Bit more cushy and stuck to the road beautifully.

For those who don't like Gatorskins, you might want to drop the pressure and try again if you have not. I'm quite impressed with the performance.
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Old 02-01-21, 12:07 AM
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Originally Posted by Symox View Post
do you use the all weather GP4000s?
I have the GP 4000 sII on 2 bikes. I have another pair in my garage, bought just as the 5000s was announced, to install when one of the other pairs wear out. When the garage pair wear out, I will probably buy the GP5000.
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Old 02-01-21, 07:57 AM
  #56  
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I run Gatorskins on the "long trip" bike, because those western jersey roads have decent shoulders covered with an amazing amount of sharp crap - I was flatting once or twice a month. I run GP4000 on the "quick bike" because I'll trade up into some extra performance versus flat risk. Now, having run Gators for quite a few thousand miles, maybe I have Stockholm Syndrome, but I don't think Gators deserve the ill-will I sometimes see around here. - Not as nice as the GP's, but certainly a good ride and a great tire that lives up to its promise. I guess some riders are much more sensitive to that kinda thing. (insert rule#5 pls). I have to add a couple PSI of air to both tires every 3rd day or so, and at 155lbs, I run them "about 80" PSI without much thought. I have gotten a pinch flat on GP4000's at about 70PSI when I hit a small pothole at about 15mph. BANG. ooooh, getting squishy... yep, pull over. A pothole in New Jersey? Shocking. I'll keep 'em all around 80 going forward. Works for me.
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Old 02-01-21, 08:37 PM
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Originally Posted by blacknbluebikes View Post
I run Gatorskins on the "long trip" bike, because those western jersey roads have decent shoulders covered with an amazing amount of sharp crap - I was flatting once or twice a month. I run GP4000 on the "quick bike" because I'll trade up into some extra performance versus flat risk. Now, having run Gators for quite a few thousand miles, maybe I have Stockholm Syndrome, but I don't think Gators deserve the ill-will I sometimes see around here. - Not as nice as the GP's, but certainly a good ride and a great tire that lives up to its promise. I guess some riders are much more sensitive to that kinda thing. (insert rule#5 pls). I have to add a couple PSI of air to both tires every 3rd day or so, and at 155lbs, I run them "about 80" PSI without much thought. I have gotten a pinch flat on GP4000's at about 70PSI when I hit a small pothole at about 15mph. BANG. ooooh, getting squishy... yep, pull over. A pothole in New Jersey? Shocking. I'll keep 'em all around 80 going forward. Works for me.
Agreed. I don't claim to be a road tire connoisseur, but for the weekend 30+ hilly rides I do, the Gatorskin 28s at 70psi feel fantastic to me. Cushy and confidence inspiring on turns.

Just for kicks, I pumped them up to 110psi to test out. BIG difference in twitchiness and road feel (as in, I feel everything).

I highly recommend anyone who hasn't tried it to run Gatorskins at lower pressures and reevaluate.
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Old 02-02-21, 12:26 AM
  #58  
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Every tire is going to feel way better if inflated to a pressure which is on the "comfort" side of optimal pressure rather than inflated to maximum possible, that holds for good tires as well as Gatorskins.

With good tires, you simply get more speed and comfort at the same effort and tire pressure; the differences between a Gatorskin and a GP5000 are big enough to actually be able to measure them pretty easily with a decent hill, GPS and a powermeter, you don't need fun with maths to tease out the data. They kind of made sense for people who really needed the flat protection but now road tubeless works well, that'd be my first port of call if I had big issues with flats.

Last edited by Branko D; 02-02-21 at 12:39 AM.
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Old 02-03-21, 05:17 PM
  #59  
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Originally Posted by Symox View Post
I have foldable Continental Gatorskins (I happen to love 'em but I'm sure there may be better options) in 700x28. Someone on this forum suggested running tires at a lower pressure to help with downhill riding. This suggestion literally changed my confidence in descents. I was running 23s at max pressure and the bike always felt glitchy and on the verge of losing control. With the 28s running at 80 psi it feels like a totally different bike - for the better!
It's more than you need in your front tire.

https://www.quora.com/How-much-air-s.../Drew-Eckhardt

The Continental website says 95-116 is the range for this particular tire. I weigh 155 lbs and haven't experienced pinch flat (knock on wood) with 80psi. I only ride on tarmac roads (no gravel) but there are occasional potholes that I do my best to avoid. Should I be concerned about running at this low a pressure? These are NOT the hardshell versions btw.
At 155 pounds with an all-up weight around 180 and 45/55% weight balance you might have 80 pounds on the front wheel which suggests 60 psi according to the 15% drop rule of thumb and 100 on the rear calling for 75 psi.

I'd leave the rear alone and see how the front feels with 10 psi less.

At your weight I start my week on 25mm GP4000SII tires at 85/95 psi and finish at 75/85 without pinch flat problems.

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Old 02-03-21, 07:18 PM
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Originally Posted by Drew Eckhardt View Post
It's more than you need in your front tire.

https://www.quora.com/How-much-air-s.../Drew-Eckhardt



At 155 pounds with an all-up weight around 180 and 45/55% weight balance you might have 80 pounds on the front wheel which suggests 60 psi according to the 15% drop rule of thumb and 100 on the rear calling for 75 psi.

I'd leave the rear alone and see how the front feels with 10 psi less.

At your weight I start my week on 25mm GP4000SII tires at 85/95 psi and finish at 75/85 without pinch flat problems.

I think this is very reasonable.

That said, is there really any science behind the 15% drop rule?? I suspect not. Why not 12%? Or 18%?? A different percent drop will of course give you a different pressure.
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Old 02-03-21, 07:26 PM
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Originally Posted by datlas View Post

That said, is there really any science behind the 15% drop rule?? I suspect not. Why not 12%? Or 18%?? A different percent drop will of course give you a different pressure.
Frank Berto determined it empirically as the point at which you got a good ride but rolling resistance did not increase appreciably.
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Old 02-03-21, 08:07 PM
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I am guessing that the precise amount of optimum drop is going to change depending on the tire. I take 15% as a good ballpark. I reference that chart a lot, but I never treat it like the final word. With hard garden hose tires I run them higher, with high quality supple tires (like RH Superlights) I run lower.
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Old 02-04-21, 07:44 AM
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Originally Posted by datlas View Post
I think this is very reasonable.

That said, is there really any science behind the 15% drop rule?? I suspect not. Why not 12%? Or 18%?? A different percent drop will of course give you a different pressure.
No. It's not an a well answered question how accurate are the pressures to achieve 15% tire drop across various tires, even.

Bicyclerollingresistance.com guys tested GP5000s and to achieve 15% tire drop with a 42.5kg (94lb) load the pressures were 108 psi (23mm), 100 psi (25mm), 90 psi (28mm) and 75 psi for the 32mm version. That's a big disagreement with the chart especially for the 32mm tires, about 15 psi which is a difference of 25%.

It stands to reason that tire drop would depend not only on pressure and wheel load but also on how stiff the tire sidewalls are (which would allow using more supple tires at higher pressures to achieve the same comfort), the overall shape and height of tire as inflated, rim width and so on.
​​​​​

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Old 02-04-21, 02:35 PM
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Originally Posted by Branko D View Post
No. It's not an a well answered question how accurate are the pressures to achieve 15% tire drop across various tires, even.

Bicyclerollingresistance.com guys tested GP5000s and to achieve 15% tire drop with a 42.5kg (94lb) load the pressures were 108 psi (23mm), 100 psi (25mm), 90 psi (28mm) and 75 psi for the 32mm version. That's a big disagreement with the chart especially for the 32mm tires, about 15 psi which is a difference of 25%.

It stands to reason that tire drop would depend not only on pressure and wheel load but also on how stiff the tire sidewalls are (which would allow using more supple tires at higher pressures to achieve the same comfort), the overall shape and height of tire as inflated, rim width and so on.
​​​​​
I was wondering how the tire construction and only width was factoring into this. That makes sense.
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Old 02-04-21, 03:32 PM
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I'm running 50 psi with WTB Exposure 30-622 (measures 32) and 200 lb train weight. This is a bit less than the Berto chart but seems to work very well. I also have 26-622 Cayuse Pass (widest that fits my Pug) at 70 psi.
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Old 02-04-21, 04:28 PM
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Those quoting really low pressures might want to check their gage accuracy. I recently found mine to be off by 8 psi. Zipp's calculator recommends some really low pressures for tubeless tires, but they wouldn't go anywhere near 50 psi for a 200 lb rider.

https://axs.sram.com/guides/tire/pressure

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Old 02-05-21, 02:23 PM
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I normally pump it just under 80 psi and it's in the mid 60s when refilling two to three weeks later. At 170-180 lbs, I would say 70psi is my sweet spot and never had a problem with pinch flats.
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Old 02-05-21, 03:59 PM
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Originally Posted by cxwrench View Post
So in the cold when you have less traction you raise the pressure a bunch?!?
The tire pressure will decrease once the temperature lowers. So it will still be similar once outside
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Old 02-05-21, 04:14 PM
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Youíve inspired me

Did a bunch of experiments and am finding

75psi rear and 65psi front seems to be the sweet spot with 28cm Gatorskins, 700cm Mavic Open Pros, my bike weight of 18lbs, my weight of 155lbs, my style of riding and my road conditions.


thanks for everyoneís help, I have learned a lot and improved the quality of my ride due to the replies so far.

love this forum!
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Old 02-06-21, 06:22 AM
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Originally Posted by DaveSSS View Post
Those quoting really low pressures might want to check their gage accuracy. I recently found mine to be off by 8 psi. Zipp's calculator recommends some really low pressures for tubeless tires, but they wouldn't go anywhere near 50 psi for a 200 lb rider.
Excellent point about gauge accuracy, especially at low pressures. SRAMs guide gives me 53 psi with tubed 32 mm tyres on 21 mm rims and 200 lb gross weight. Berto's chart gives about 58 psi with 100 lb per wheel for nominal 15% drop. WTB give 35 - 65 psi for the 30-622 Exposure (measures 32 mm). 50 psi seems quite low but seems to be working well so far.
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Old 02-11-21, 04:05 PM
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At 160lbs, I run 80-90psi in 25mm tubeless tires.

If I were moving to 28mm tires, I'd be trying 60-70psi and see how they ride.
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Old 02-15-21, 05:07 PM
  #72  
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I have been riding 75psi rear and 65psi with Gatorskin 28s front for a while now and it is fantastic. Great grip in rain or shine as well as damping.

Don't know how Gatorskins compare to higher end tires but I am absolutely a fan of these tires!!!
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Old 02-16-21, 08:00 AM
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Originally Posted by burnthesheep View Post
IMO 155lbs and 80psi on a 28mm tire is still WAY too much. Depending on your rim width. Either way, I would think for that size tire and your weight a 28mm you'd be down around 60-65 psi.

I run the wide road width HED wheels and run the front 23mm at like 82 and the rear 25mm at 72 or so.

For your weight, even for a narrow width rim, you wouldn't need to run those 23's at max pressure. Maybe 85psi.

If the 28's fit fine, keep running them. But, I think you would have been fine airing down on anything if you weigh only 155 and were at "max".

Ninja edit: I weigh 160, to qualify the similarity to your size and give those pressures.
What this guy said. I run my 25s at 80F/90R and I am 185. You could be running 28s even lighter than 80 if you are only 155.

And to add, I've never had any issues with running 80/90. In fact, I've run slightly less without any issue either.
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Old 02-16-21, 10:18 AM
  #74  
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Originally Posted by am0n View Post
What this guy said. I run my 25s at 80F/90R and I am 185. You could be running 28s even lighter than 80 if you are only 155.

And to add, I've never had any issues with running 80/90. In fact, I've run slightly less without any issue either.
+1. 80F/85R here at 215 on 28's here w/o any problem.
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Old 02-16-21, 11:45 AM
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I run 70/70 weighing 175 with an 18mm internal rim. Works great for me.
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