J3 pilot experiences engine failure due to fuel starvation and lands on dirt road with minor damage to wing tip.

Narrative

I have been flying all over the country with this company to tow banners at many different locations. I would be flying a plane in a flight of 2 but I was running late; having just moved out of the guest suite I'd been staying in. En route to the airport; I had contacted the Pilot I would be following up and was informed the weather was still IMC en route. This gave me a sense of calm in that we were waiting on weather still anyway. On arrival was notified by him that the weather had improved to VMC and that he was going to get a head start since he had a slower aircraft. I was wheels-up 25 minutes after him and caught-up with him 1 hour and 15 minutes into my flight; running at 2475 rpm. After joining-up; was now running about 2275 rpm and estimated I should have an extra 30-45 minutes of fuel than if I was still at 2475 rpm. About 10 miles and 10 minutes short of destination and 45 minutes past our last option for fuel; the engine sputtered as fuel ran out; which confirmed what the fuel gauges now showed. Flying at 500'; I immediately spotted a dirt road to land on; made a successful landing; but hit a small tree with the left wing tip as I rolled-out and the road narrowed. No substantial damage occurred. I miscalculated in estimating more fuel than I actually had with the power reduction and was pushing fuel a bit.