What pressures are you running your 28mm's at?

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themidge
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Location: underneath sweet Scottish rain

by themidge

I'll throw in my data points for consideration, I weigh ~55kgs.

25mm (28mm actual) Michelin Pro4 Endurance at 80psi, but they get down to 60ish before I bother pumping them up again so call it 70psi.

For comparison's sake I run my 21mm tubs at 90psi.

hoojammyflip
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Joined: Fri Apr 16, 2010 4:02 pm

by hoojammyflip

spdntrxi wrote:
Sun Aug 04, 2019 10:14 pm
hoojammyflip wrote:
Sun Aug 04, 2019 10:02 pm
25mm Vittoria Open clinchers, 23mm rims, 115psi....64kg

If it hurts your butt, you are putting too much weight on your saddle/not pedalling hard enough. My tyres have a minimum written on the side, something like 110psi.
you didn't read the title did you ?
Riding with 25s on a 23mm rim produces a 28mm wide tyre. A simple way to measure this is with calipers.

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Rossin67
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by Rossin67

hoojammyflip wrote:
Thu Jul 15, 2021 7:34 am
Riding with 25s on a 23mm rim produces a 28mm wide tyre.
But that doesn't change the volume of the tire. The casing remains the same.

nismosr
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by nismosr

95kg
veloflex corsa evo TLR 28mm
80psi rear and 70psi front
2020 Colnago C64 Mapei-SR12 EPS-WTO 60
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2023 Colnago G3X-SRAM AXS Force-Levante

CustomMetal
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by CustomMetal

78kg, 28mm gp5000TL, 70 psi
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JoO
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by JoO

62 kgs
622-17 rims
Veloflex corsa
Width as measured = 28 mm
60 psi
Latex inner tubes
Coarse Belgian roads

JoO
Posts: 439
Joined: Thu May 04, 2017 7:30 am

by JoO

Rossin67 wrote:
Thu Jul 15, 2021 11:22 am
hoojammyflip wrote:
Thu Jul 15, 2021 7:34 am
Riding with 25s on a 23mm rim produces a 28mm wide tyre.
But that doesn't change the volume of the tire. The casing remains the same.
It does a bit.
More u shape instead of lightbulb.
Silca recommeds the width as measured as criterium for pressure.
So 28 mm on narrow rim or 25 on wide rime with same measured width is same recommended pressure.

Hexsense
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by Hexsense

Well, light bulb shape of the same width is usually taller than U shape tire. This is demonstrated in a height and width measurement chart in this article where 23c on 19.5mm internal is wider but not as tall as 25c on 15mm internal:
https://blog.silca.cc/tire-size-pressur ... got-to-now

So, if pinch flat/rim strike is a concern, add a tiny bit of pressure.

Rossin67
Posts: 31
Joined: Sat Feb 16, 2019 8:01 pm

by Rossin67

JoO wrote:
Thu Jul 15, 2021 7:01 pm
Rossin67 wrote:
Thu Jul 15, 2021 11:22 am
hoojammyflip wrote:
Thu Jul 15, 2021 7:34 am
Riding with 25s on a 23mm rim produces a 28mm wide tyre.
But that doesn't change the volume of the tire. The casing remains the same.
It does a bit.
More u shape instead of lightbulb.
Silca recommeds the width as measured as criterium for pressure.
So 28 mm on narrow rim or 25 on wide rime with same measured width is same recommended pressure.
The shape doesn't change the volume of the tire one bit. All it changes is the aspect ratio. There is literally no explanation as to why a 25mm tire on a 19mm rim needs higher pressure than a 25mm tire on a 23mm rim.

I haven't bought in to the wide rim fad. I prefer a narrower rim and a tire with a more round shape because it corners better, like a tubular. And I don't run pressure so ridiculously low that it's going to fold over, I don't like squishy tires. I've read that excuse in the wide rim debate. A wide rim is good for needlessly adding rotating weight.

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Veto
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by Veto

80kgs
Vittoria Open Pave 27c tyres on 21mm internal width rims.
88 rear/80 front

It's on the high side but latex tubes lose around 10 psi over night and with these pressures, i don't have to pump them up before every ride. :)
So, laziness dictates the pressures i choose. :)

Hexsense
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by Hexsense

Rossin67 wrote:
Fri Jul 16, 2021 11:24 am
The shape doesn't change the volume of the tire one bit. All it changes is the aspect ratio. There is literally no explanation as to why a 25mm tire on a 19mm rim needs higher pressure than a 25mm tire on a 23mm rim.
First of all, you are wrong. I can say in 3 ways why it is not correct.
1) The most far-fetched reason is to prove by contradiction. If aspect ratio doesn't matter, all the shape of the same surface area (or circimference) should have the same shape. If we exagerate an oval to have width=0, and height ->( tire casing width) /2, then the volume is zero. So aspect ratio does change the volume.
2) More realistic explanation: supposed we fix the whole circumference (surface area) to a fixed number. Then the shape that has most volume per surface area is a circle. The closer to the circular the shape is, the more volume there is inside the shape, for the same surface area. Light bulb shape of the same surface area have less air volume than another shape that look more circular.
3) Even more than reason number 2, wider internal width rim does add the surface area. Compare 15mm internal width to 25mm using the same tire. The 10mm extra wide base of the rim means the tire doesn't have to curve out that extra 1cm. So the tire casing can be used elsewhere to increase air volume. Thus the surface area does increase by that extra internal rim width. It doesn't even matter if the increased surface area make the tire shape less round and more square (that is also debatable, but let skip that today), the extra surface area add straight into the air volume when we let the tire shape itself from pressure inside.
Rossin67 wrote:
Fri Jul 16, 2021 11:24 am
I haven't bought in to the wide rim fad. I prefer a narrower rim and a tire with a more round shape because it corners better, like a tubular. And I don't run pressure so ridiculously low that it's going to fold over, I don't like squishy tires. I've read that excuse in the wide rim debate. A wide rim is good for needlessly adding rotating weight.
Since you are spreading big misconception, I'd have to stop others from misunderstanding the concept by counteract your misinformation. Here are some data from other source:
1) Rim width does increase air volume. More volume mean harder ride and lower rolling resistance by the same air pressure in psi. Bicyclerolling resistance test exactly that, and confirm that we have to reduce tire pressure because the air volume is increased by the rim width.
https://www.bicyclerollingresistance.co ... width-test
2) Wider internal width make the tire both wider and taller. See the chart, 23c tire on 15mm internal is narrower and less tall than 17.5mm internal. Yet again, same tire on 19.5mm internal is wider and taller than 17.5mm internal width. How could it keep volume the same when it is both taller and wider? It doesn't. Volume does increase.
Image
src: https://blog.silca.cc/tire-size-pressur ... got-to-now
3) Low pressure squish and fold easy exactly because your rim is too narrow. A wide base is more stable. So, if you like a tire that handle predictably and stable at low tire pressure, go wide rim.
Image
source: https://www.theproscloset.com/blogs/new ... -rim-width
4) Tubular tire shape more like quite wide (but not ultra wide) clincher rim than narrow rim. You never see light-bulb shape tubular. It is more round than everything else. To match that on clincher, you'd want to get that round shape by reduce the stiff restriction (clincher hook) at the base of the tire. Push that rim sidewall out make the tire shape rounder.
5) There is a point which rim is too wide for the tire. That point is especially noticeable when you use inconsistent tread pattern, such as smooth center with tall sidewall knobs gravel/mtb tires. By using wider internal width than tire designer intended, you roll straight line on the cornering knobs. Jeopardize the way it handle overall as well as cornering grip. However, that doesn't apply to road tires with smooth treads. What still matter for road tires are the center tread width. By going riddiculously wide rim, you expose more tire to the ground. A tire with narrow center tread will not like that. However, many tires that have plenty wide center tread will not mind it.
(sorry for no reference souce on these last two, I forgot where it was from...)

HaroldC
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Joined: Mon Oct 18, 2010 2:21 am

by HaroldC

86kgs
S-Works Turbo Cotton Hell of the North tires
Silca latex tubes
Roval CLX 50 (21mm internal)
67psi Front
71psi Rear

No flats for 2 years riding crappy NY/NJ roads.

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Aryeh
Posts: 489
Joined: Tue Oct 08, 2019 3:07 am

by Aryeh

66kg
ENVE SES 29mm Tubeless - measures 30mm on 25mm internal lightbicycle wheels.

65psi rear 60 front
On slow days I'll run 55 50

chuingbeans
Posts: 48
Joined: Wed Sep 05, 2018 7:57 am

by chuingbeans

76kg

Vittoria Corsas on 21mm internal
Grand Bois on 17mm internal

Both setups with latex tubes @ 69psi

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TobinHatesYou
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Joined: Mon Jul 24, 2017 12:02 pm

by TobinHatesYou

63kg, 28mm WAM tires

pristine pavement: 80psi
rough pavement: 65psi
rough pavement w/potholes: 75psi

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