I toured in Laos last January (the dry season) but I've not yet been to Cambodia. I was riding a Bike Friday with Schwalbe Marathon 20" x 1.5" tires with kevlar, and they worked out great. I was touring in the northern half of the country and the roads were mostly excellent. The same is true for the roads I was on in Thailand.
For money, I brought travelers checks, US$ cash, and an ATM card. I didn't use the ATM card because of the high fees involved. Also, Laos has very few ATMs and extremely low value paper money. No coins were in circulation while I was there. I'm not sure I saw any ATMs outside of Vientiane & Luang Prabang. There may have been one in Luang Namtha. The maximum amount of money you could withdraw in Laos was under the equivalent of US$100 because of the immense amount of paper you'd get back and the inexpensive prices for everything.
In Thailand, ATMs are everywhere. Still, it was a better deal for me to exchange cash or travelers checks.
I read that in Cambodia, the US$ is used everywhere and ATMs dispense them.
One small suggestion for future threads: it would help if you make the thread title more descriptive of what you're asking about. A lot of folks won't bother to click on a vague title like "Questions". Something such as "SE Asia tire & money questions" would be better.