In the context of long rides*, how often is chamois cream meant to stay useful (whether measured in hours,km or whatever)? I typically don't carry it on the road, but wonder if a top-up might make the end of a ride more comfortable.
*To give a example of what I mean by "long": my longest single day ride so far was just under 20 hours/just over 400 km)
It massively depends on the brand/consistency of the cream, how much you use, and the weather conditions.
For me, a small amount of Assos cream will last 4-6hrs in normal conditions, but if its particularly hot (and hence sweating a lot) or if its rainy it lasts much less.
There are some products that are much more durable (morgans blue solid for example), but are also not easy to wash out of shorts again afterwards.
I never carry any with me on a normal ride, but it is always in my day bag if i'm doing a supported tour. If I was doing something properly long like PBP or LEL i'd definitely take some.
For very long days in the saddle, I use a wax-based chamois cream (I use QM4 and I believe Squirt does one too or you can just use regular Vaseline) that forms a layer on top of the skin, rather than being absorbed the way that Assos or Muc-Off are. Sweat seems to have little effect on it. When showering after a 10 hour ride, I'm still be able to feel it on my skin and need to use a soap to get it off as it isn't water-soluble.
Before I started using a wax-based cream for long rides, I would pack a tiny zip-lok bag with a single serve of chamois cream to re-apply after ~200 km.
As others have mentioned, chamois cream has a service duration depending on many things including perspiration and the degree to which you are depending on it.
To look at how it is sold, you have two inconvenient options: a giant tube (or for some brands, tub), or expensive little foil packets.
I just went and bought a 1 oz (28 ml) sample size tube of hand lotion, squeezed it out and washed out the tube. It's a little tricky to do, but at home I squeeze the large tube into the small one, and use whatever leaks in that process for my initial application when setting out. That little tube is perfect for a saddle bag.
