#1
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Moving from 25’s to 28’s...different PSI?
Hi all,
Incoming bike that will accept 28’s. Bought a set of Conti GP5000 700 x 28. Do I keep the same tire pressure I run now on my GP4000’s 700 x 25 or adjust? I’m very happy with the tire pressure I run now. As always, thank you all in advance! Steve
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Livin’ the dream ( just like Mike ) |
#2
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Drop er 5-10 and give it a go. You have some more tire on the ground now so enjoy the ride.
Tubeless? |
#3
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Inflate to recommended factory-specified pressure.
Then deflate/test until you find *your* particular handling/comfort "sweet spot" that works. |
#4
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I haven't run 25's in a long time, but for 23's I run 90/100 (f/r). For 28's that would drop to 75/82 (f/r). YMMV
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#5
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A rough rule of thumb is that tire pressure is inversely proportional to tire width. Since 28mm tires are 12.5% wider than 25mm, a good starting point is to lower the pressure by 12.5%. Then adjust from there based on ride feel and preferences.
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#6
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3-4%
Josh at Silca recommends dropping 3-4% for each mm wider in tire width.
So 9-12% less than what you currently run. |
#7
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The wheel set I bought is tubeless compatible, but I decided to go old school this time around. Maybe the next set will be tubeless.
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Livin’ the dream ( just like Mike ) |
#8
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FIFY....C’mon ya Nancy!!
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Chisholm's Custom Wheels Qui Si Parla Campagnolo |
#9
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Quote:
Part 1 of our episode on Asymmetry starts to get into this topic and brings some context from racing: https://marginalgainspodcast.cc/asymmetry-part-1/ |
#10
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Quote:
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#11
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I'll just add that while lower pressure feels great on rough roads, on smoother roads it can feel funky if you don't spin smoothly or are sprinting out of the saddle - undamped suspension can get bouncy...
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#12
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This just doesn't feel right. I think the pressure should be more proportional to the square of the diameter (or cross-section area). I certainly don't need to go to a 50mm tire to use half the psi, but more like 35mm.
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#13
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I'll add that when I switched to 28s from 25s I found that there was a low pressure limit after which they became dramatically splashy. In this condition the tires also felt uncomfortably squirmy in corners. I now run it just a few pounds higher and it feels right. The performance seems to fall off a cliff after the low limit. On the other end I've run them as high as 100# and other than getting unforgiving in ride quality, the grip doesn't seem to change dramatically.
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Old'n'Slow |
#14
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How you scale depends on what you're trying to scale for. If you double the width of a tire, but you're still riding it on smooth pavement, it makes no sense to quarter the pressure. If you're riding a supple 1" tire on smooth pavement, and a beefy 2" tire on gnarly trails, then it might make sense to be running the 1" tire at 80PSI and the 2" tire at 20.
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#15
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Quote:
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