28 vs 25mm

Apparently there isn't quite enough clearance to run 28mm continental GP 28mms on my Giant TCR so the Giant shop suggested I go for 25mms. Was thinking I'd go for GP5000 Tubeless.
Will I feel a big difference in terms of comfort?
Will I feel a big difference in terms of comfort?
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2020 Voodoo Marasa
2017 Cube Attain GTC Pro Disc 2016
2016 Voodoo Wazoo
And depth?
https://www.bicyclerollingresistance.co ... comparison
https://www.bicyclerollingresistance.co ... i-23-25-28
https://www.bicyclerollingresistance.co ... comparison
According to this you lose 3mm in height on 5000 28s vs 4000s alongside similar reductions in width.
One things for certain... GP4000s are huge vs their quoted size. If you went with GP4000 25s, they are pretty much 28s on other types of tyre.
Regarding comfort, it is more to do with tyre pressure than the width itself.
Either get low profile 28s or 25s that you are happy to run at the same pressure.
I am not sure. You have no chance.