My water pressure regulator is set to 60 psi and it holds that fairly well. When my water heater is heating the pressure spikes to 140 psi. Our city requires a backflow valve and and my water heater has an small expansion tank on it.

I realized something was wrong after I started seeing the TPR valve release after showers. I then bought a gage and found they had the water set at 75 psi. I turned down the press to 60 and that helped stop the TPR from tripping but the 140 psi spike seems high to me.

Turn it down to 45 psi. If you continue to have such high spikes in your pressure you may need a larger expansion tank. What is the temp setting on the heater, 120 should be enough.

Turn it down to 45. If you continue to have problems, then the expansion tank is certainly a possibility.

my water heater has an small expansion tank on it.
BINGO! By George I think he's fount it! You hit your T & P Valve with a double whammy. You didn't say but I'd bet the farm you have a gas hot water heater. It's bad enough that you have a expansion tank that's either misadjusted or too small to handle the hot water expansion but then you booted that poor defenseless valve in the butt with excesive house pressure. The solution, as I see it, would be to cut your house pressure back to 45PSI, your burner back to 120 F or medium on the control and get a larger expansion tank. Good luck, Tom

Thanks all!

Is there any danger from these spikes? I kind of like the higher pressure as long as my water heater doesn't explode.

Sure there can be a danger in this situation. Your pressure relief is just another mechanical part and could fail, not likely but it could. Also, when it blows pressue someone could get burned if they were near the heater. I'd cut that heater down to low until you can get the psi down to 45. In the maentime you can open the cold faucet once the haeter has heated and expanded your water, that will lower the psi without calling for more hot water.