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I have parked on a lot of boards, almost always flattening them some now, depending on how steep they are.
Things to note:
Can you break or crack a board driving over it? Yes - seen a few although never had it happen to me personally.
Can you over flatten them? Yes absolutely - feels like a very flexed out almost broken board that was not good for anything much.
Can you ever fix a flattened board if it is too flat? Never - once flexed out, it is going to stay that way for good.
Does the board bounce back after you drive over it or park on it? Yes definitely - often I would park on it, then stand on it and think "What have I done?" but then leave it a day and it should come back about half way on average to what it was before.
Overall I prefer my boards about 20' tail and 21' or so nose, but definitely need the tail to be flattened some compared to a normal brand new crispy board. I also like the flex that just driving over it creates too, which breaks it in and gives it that week or so old feeling, which is not a worry to me, as boards last me a while, but I don't like boards that are really stiff and crispy but most definitely not boards that are too steep in the tail.
Depending on your vehicle or the weather, or even if you have warm or cold tyres, all this stuff will change how the board reacts. Colder weather means the board is more likely to crack or break than flex. Also warm tyres will flatten it out much more than cold tyres, as well as the weight of the vehicle, all being thing to consider.
I have a small Corolla, usually park on or drive over boards on the front wheels only as they have a little more weight than the back wheels, usually do it in the warmest part of the day, or if it is in winter, leave the board out in the sun for a while first, but I don't usually drive over it with warm tyres as it flattens the deck too much.
More often than not, just to drive up to the bolts, sit for a minute, then back off, turn the board around and do the same for the other kick, as that is plenty to mellow a board out. Really steep boards I have parked on for a while, but I have flattened some boards too much leaving them under the car.
If you only drive up to the bolts and not past it, the theory is the kick will be mellowed out a bit, but the board will not flex too much in the middle. Driving right over the whole thing is usually not a big deal with a really steep or stiff board, but I do notice that the board stays a little more in shape without flexing right out if I don't drive right over it.
Could share a whole lot more, but that should do for now. Any other questions or anything else, please ask.