Petrol tank full or half full at start ?

Petrol tank full or half full at start ?

Author
Discussion

majordad

Original Poster:

3,430 posts

164 months

Saturday 29th May
quotequote all
Im wondering what the current best practice is for this , does having the tank full at the start risk leakage or fuel overflowing onto track ?

Pica-Pica

8,450 posts

51 months

Saturday 29th May
quotequote all
If you’re using an OEM tank there is no risk of leaking whatever during extreme vehicle manoeuvres, as long as you do not fill beyond the manufacturer’s maximum fill procedure. That is all tested. If modified, that’s another matter.

brillomaster

621 posts

137 months

Saturday 29th May
quotequote all
TDOs ive been to mention not brimming caterham/lotus 7 type cars, but everything else is good to be brimmed before tracking.

Unless you're a weight weeny, in which case start with a quarter of a tank, anf put 5litres in after every session.

alfa-alex

39 posts

19 months

Saturday 29th May
quotequote all
Fuel is heavy!

Quarter tank and add as required smile

ecain63

10,422 posts

142 months

Saturday 29th May
quotequote all
Just fill it up to avoid regular trips to the pump. My car (Exige 410) uses a 1/4 tank for 15 mins on track. My mates M2 uses about 1/3 tank for the same time on track and his tank is bigger.

I always fill up and run to the red light. 3 fills a day at Silverstone or 2 at Goodwood for example.

majordad

Original Poster:

3,430 posts

164 months

Sunday 30th May
quotequote all
Thanks for the answers.

Tommie38

496 posts

161 months

Sunday 30th May
quotequote all
What is the car?

I’d fill just to save trips to the pump. Unless you are chasing times it really doesn’t matter, but you will probably be able to notice the change in handling.

majordad

Original Poster:

3,430 posts

164 months

Sunday 30th May
quotequote all
Its a general question related to our Porsche track day here in Ireland.

bigothunter

1,414 posts

27 months

Sunday 30th May
quotequote all
alfa-alex said:
Fuel is heavy!

Quarter tank and add as required smile
Can you consistently detect the difference in lap times between a quarter and a full tank? scratchchin

brillomaster

621 posts

137 months

Sunday 30th May
quotequote all
I can certainly feel the difference when i have a passenger to when i don't, thats about 70kgs.

And a big car could easily have an 80litre tank, so the difference between full and a quarter could be 60kgs.

Though, i wouldnt normally notice when i do a mid afternoon fill as the track is normally running faster then and ive got my eye in by then.

E-bmw

6,205 posts

119 months

Sunday 30th May
quotequote all
bigothunter said:
alfa-alex said:
Fuel is heavy!

Quarter tank and add as required smile
Can you consistently detect the difference in lap times between a quarter and a full tank? scratchchin
No use to man-nor-beast in an e36, it will fuel-starve on right-handers more than a few seconds long.

alfa-alex

39 posts

19 months

Sunday 30th May
quotequote all
The car I drive isn’t very powerful, it was built as a race car and so everything is setup for just enough fuel to complete a race.

The difference in handling on a dry track is quite noticeable.

Fuel starvation isn’t an issue!

If you’ve gone to the extent of stripping the interior weight why would you want to add 40kg back in?

My way is right for me, though I completely appreciate my way isn’t right for everyone!

Alex


bigothunter

1,414 posts

27 months

Monday 31st May
quotequote all
alfa-alex said:
The car I drive isn’t very powerful, it was built as a race car and so everything is setup for just enough fuel to complete a race.

The difference in handling on a dry track is quite noticeable.

Fuel starvation isn’t an issue!

If you’ve gone to the extent of stripping the interior weight why would you want to add 40kg back in?

My way is right for me, though I completely appreciate my way isn’t right for everyone!

Alex
Given that 40kg of petrol equates to 12 gallons, your race car must have a 16 gallon tank. Wow eek

Dr Jekyll

21,553 posts

228 months

Monday 31st May
quotequote all
brillomaster said:
I can certainly feel the difference when i have a passenger to when i don't, thats about 70kgs.

And a big car could easily have an 80litre tank, so the difference between full and a quarter could be 60kgs.

Though, i wouldnt normally notice when i do a mid afternoon fill as the track is normally running faster then and ive got my eye in by then.
More like 45kgs.

pablo

15,722 posts

240 months

Monday 31st May
quotequote all
Indeed, petrol weighs about 750g/litre. An average tank capacity is 40 litres so a full tank weighs 30kgs....

foxsasha

1,355 posts

102 months

Monday 31st May
quotequote all
Just brim it. Refilling after each sessions is a faff and I'll bet a packet of cheese and onion Seabrook that you see zero lap time difference. Not least because you no doubt won't be timing.

C70R

8,390 posts

71 months

Friday 4th June
quotequote all
Pica-Pica said:
If you’re using an OEM tank there is no risk of leaking whatever during extreme vehicle manoeuvres, as long as you do not fill beyond the manufacturer’s maximum fill procedure. That is all tested. If modified, that’s another matter.
This. So much this.

Unless you're running a kit car or something with a modified fuel tank, I wouldn't give this question a moment more thought.

The driving heroes saying how they can 'feel' a weight difference of a 3-4% through rubber suspension bushes, road-legal tyres and PAS make me laugh.

shalmaneser

4,833 posts

162 months

Friday 4th June
quotequote all
foxsasha said:
Just brim it. Refilling after each sessions is a faff and I'll bet a packet of cheese and onion Seabrook that you see zero lap time difference. Not least because you no doubt won't be timing.
This.

Fuel does make a big difference to feel though it does depend on the car - my 996 feels very different with a full tank vs an empty tank as when the tank is empty it highlights the f/r weight balance. Probably less noticeable in front engine rear wheel drive cars though with more normal weight distribution.

But it's a pain if you run out halfway through a session and have to waste track time leaving the circuit to fill up. Much better to do so over lunch.

ChrisCh86

264 posts

11 months

Friday 4th June
quotequote all
Just fill it up to one click (i.e. don't overfill).

You'll use the petrol up so quickly that it's best just to put in as much as you can and be done with it. More time on track is the most important thing given how much you've paid to be there - and you won't notice the weight difference in your lap times.

MOTK

257 posts

101 months

Friday 4th June
quotequote all
Worth considering also to not run too low depending on your car and which track. An example would be saddle bag tanks on say an e46 m3 going up the hill after the old hairpin at donington, gauge says just under 1/4 tank left but no fuel reaches the engine, ask me how I know.