Tire pressure suggestions

[Zero7]

I'm 140 pounds and bike is 15.5.
Conti gp5000 tires on 21 internal, 28 external LB wheels with Conti Race 28 butyl tubes.
Riding on standard crappy roads in SoCal.
I've been using 25mm front and rear at 85 psi front and 90 rear.
Just put a 28 on the rear and wondering what would be a good pressure?

[Mocs123]

Step 1 - go measure the actual width of your tires mounted on the rim.
Step 2 - kit up with, water bottles, garmin, everything you'd normally ride with and go step on a scale to get your actual total system weight.
Step 3 - go to Silca's website and input your data into the tire pressure calculator

My guess - around 70psi

[Zero7]

Step 1 - go measure the actual width of your tires mounted on the rim.
Step 2 - kit up with, water bottles, garmin, everything you'd normally ride with and go step on a scale to get your actual total system weight.
Step 3 - go to Silca's website and input your data into the tire pressure calculator

My guess - around 70psi

Thanks. Silca says 72.5 for rear

[DaveS]

I prefer the Zipp pressure calculator. It's also important to verify the accuracy of your pump gauge. My old Silca read 8 psi higher than actual, as verified by several new gauges, so I installed a new 0-100 psi that was much larger.

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

[C36]

I prefer the Zipp pressure calculator. It's also important to verify the accuracy of your pump gauge. My old Silca read 8 psi higher than actual, as verified by several new gauges, so I installed a new 0-100 psi that was much larger.

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

Zipp calc has a bais since it promotes less than 5bar so their Hookless rims don’t hit the limit (need to weight 95kg as body weight to hit the 5b!)
It will give a significantly more comfortable pressure but leaves performance in the table.
The Silca integrates real width (extrapolated on the Zipp) and road conditions so you have the best rolling before vibrations transmission degrade performance.

[DaveS]

I prefer the Zipp pressure calculator. It's also important to verify the accuracy of your pump gauge. My old Silca read 8 psi higher than actual, as verified by several new gauges, so I installed a new 0-100 psi that was much larger.

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

Zipp calc has a bais since it promotes less than 5bar so their Hookless rims don’t hit the limit (need to weight 95kg as body weight to hit the 5b!)
It will give a significantly more comfortable pressure but leaves performance in the table.
The Silca integrates real width (extrapolated on the Zipp) and road conditions so you have the best rolling before vibrations transmission degrade performance.

That's not true. You can select any type of rim you want. If you put in hooked rims, it will give you the appropriate pressure. If hookless is selected, it will display a pressure over 5 bar and a warning that it's too high. You must be very heavy or using narrow tires to exceed 5 bar. As an example a 100kg rider on 23mm IW hooked rims and 28mm tires needs 5.09 bar in the rear tire.

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

[C36]

I prefer the Zipp pressure calculator. It's also important to verify the accuracy of your pump gauge. My old Silca read 8 psi higher than actual, as verified by several new gauges, so I installed a new 0-100 psi that was much larger.

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

Zipp calc has a bais since it promotes less than 5bar so their Hookless rims don’t hit the limit (need to weight 95kg as body weight to hit the 5b!)
It will give a significantly more comfortable pressure but leaves performance in the table.
The Silca integrates real width (extrapolated on the Zipp) and road conditions so you have the best rolling before vibrations transmission degrade performance.

That's not true. You can select any type of rim you want. If you put in hooked rims, it will give you the appropriate pressure. If hookless is selected, it will display a pressure over 5 bar and a warning that it's too high. You must be very heavy or using narrow tires to exceed 5 bar. As an example a 100kg rider on 23mm IW hooked rims and 28mm tires needs 5.09 bar in the rear tire.

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

No that is exactly what I mean… to preserve many people within the 5bar limit they recommend way lower pressures than the optimal performance one.

If would recommend over 5bar for most, they would shoot themselves in the foot and show their designs limits.

The best reference for performance values is the Silca one, discussing with performance engineers in teams their values match their owns findings.

[Zero7]

Silca has me at 80 front and 73 rear.
Zipp has me at 70 front and 64 rear.
It's interesting that zipp doesn't have you add the weight of your gear. They only include rider and bike weight. Also zipp doesn't have you measure actual width of tire.
I'll start with Silcas results and go from there.

[DaveS]

Add all weight on the bike. It doesn't matter whether it's you or your gear. Don't forget water bottles. Zipp uses rim IW to get tire width. A 25mm IW rim will require maybe 2 psi less pressure than a 23. Whether the tire has a thin or standard sidewall makes a larger difference. Remember that it's only a suggestion. I much prefer the lower values from Zipp, but I'm not racing. No one's stopping you from adding 5 psi for "performance".