Hokkaido Summer self-drive or JR pass?

Hi I will be going to Hokkaido from 7 Aug to 12 Aug. So I have about 5 days to explore Hokkaido, short I know

That's why I am trying to arrange my time to get the best experience

My itinerary so far
Day1 7/8/15: Sapporo
Day2 8/8/15: Otaru
Day3 9/8/15: Asahikawa
Day4 10/8/15: Furano / Biei
Day5 11/8/15: Lake Toya / Noboribetsu

I am calculating whether to buy Sapporo Pass + 3 days JR pass or Sapporo Pass + 4 days rent car

3 days JR pass costs 15,430 x 2 = ard 31,000 yen
4 days car rent costs ard 22,000 yen (the cheapest I can find now)

I am not sure about the petrol cost, anyone can advise?

Is my route good?or I should go Sapporo last and go to Asahikawa first?

I afraid I will miss out the lavender season


Thank you for the advise

August there won't be much left
I'm not even sure whether the furano lavender rail pass or the lavender east station are available.

Either way, a vehicle is the best mode of transport in Hokkaido.
Unlike honchu and Kyushu, there are NO Shinkansen to bring you about cities. Most trains eg airport, asahikawa, furano, are small rickety local trains that move slowly, have few seats, and are all too hot in summer. In August it might be slightly cooler but anyone carrying luggage about would not want such an experience.

Get a car, dump your luggage in the boot, enjoy the aircon and music.

yeah of course driving is the best, I just need to have a picture how much will it cost

if it's too expensive, I will just buy JR pass

I am not sure about the petrol cost, anyone can advise?

About 135 yen/liter. There may also be some toll fees.

Still, I'd probably drive even if train is cheaper since a lot of the Hokkaido sights are not convenient by public transportation.

As always the informative input and objective view of yllwsmrf is highly appreciated.

Another additional cost for a car besides rental fee, toll and petrol is parking fee though not always yet sometimes applicable in hotels and tourist sites. But outside winter months a self-drive road trip is the best way to explore the vast area of Hokkaido, especially the scattered sites in Furano and Biei area.

If possible try to go to Asahikawa first. Early August is the perfect time for a side trip to the spectacular sunflower fields of Himawari no Sato in Hokuryu.

I will reach Chitose at 1230PM, how about this

Day 1 7/8/15: Asahikawa
Day 2 8/8/15: Furano / Biei
Day 3 9/8/15: Lake Toya / Noboribetsu
Day 4 10/8/15: Noboribetsu / Otaru
Day 5 11/8/15: Sapporo

Day 1 - 4 I will rent car

Otaru to Sapporo just take train

I never drive in Japan, I just afraid there are a lot of unexpected cost, like toll, parking, etc

Petrol I can estimate based on the distance

Is your day 1 (Aug 7) the date of your arrival!? Even if your flight arrives on time you need to go through immigration, baggage claimed, custom, paper work plus shuttle to car rental outlet. With just barely half a day it would be quite rushed going for Himawari no Sato together with Asahikawa. One option is to drive directly from New Chitose Airport to the sunflower fields (more than 2 hrs) before bedding down in Asahikawa. The long daylight time during summer can work in your favour.

1 day for Biei and Furano is already tight, but just to let you know the best time for seeing sunflower is during morning hours. So another possibility is to take in a bit of Furano and Biei first on the arrival day and save the sunflower fields for the morning on day 2.