Gas tank.... do you run a full tank or half tank and why?

RodneyWright · **Posted:** Mon Nov 08, 2004 10:07 am

Usually I run nearly a full tank of gas at an event, but this time decided to back down to about a 1/2 tank for weight. I don't know if it was the lack of weight or the new front sway bar, but the car oversteered bad. What do you do? Full tank or not and why?

Wes Eargle · **Joined:** Mon Oct 27, 2003 9:47 am **Posts:** 3683

I run < 1/4 tank. 1/2 tank means that you can get into a NASCAR type "tankslapper" as the fuel sloshes around. Either a full or near empty tank eliminates that. Fuel starvation issues dictate which of those two philosophies you should follow.

Adam Ligon · **Posted:** Mon Nov 08, 2004 10:16 am

Well a new front bar, bigger I am guesing, shouldn't make the car oversteer more, just the opposite actually. And with less gas, ie less weight in the back the rear is unloaded more. So I would guess it was the 1/2 full tank, gas weighs almost 8lbs per gallon.

Scott Johnson · **Posted:** Mon Nov 08, 2004 10:18 am

As empty as I dare. Weight is ALWAYS the enemy.

Scott

Kevin Allen · **Joined:** Thu Aug 28, 2003 6:42 pm **Posts:** 3479

Full tank because I get fuel starvation at ~ 1/2 tank. If I could run on fumes like the WRX guys, I'd run on fumes. :roll:

jimpastorius · **Posted:** Mon Nov 08, 2004 10:40 am

I run with about 1-2 gallons in the car. It is a little nerve racking with the low-fuel light flickering though. Especially since I watched my friend Mark Davis' MR2 run out of gas on his last run at the Atlanta SE Divisional. Yes, weight is the enemy, running out of gas is worse

Vincent Keene · **Posted:** Mon Nov 08, 2004 10:54 am

scottjohnson wrote:

As empty as I dare. Weight is ALWAYS the enemy.

Scott

In the Talon we had to run nearly a full tank to prevent starvation and sputtering in hard LH turns.

In the Miata I try to keep it as near empty as possible. Scary trying to make it to the gas station though. I really thought I wasn't gonna make it yesterday!

Keith Quistorff · **Posted:** Mon Nov 08, 2004 11:01 am

Adam Ligon wrote:

Well a new front bar, bigger I am guesing, shouldn't make the car oversteer more, just the opposite actually.

This is true in theory, but almost never in practice when autocrossing cars designed for street use, for the following 2 reasons:

1. Suspensions designed for street use are too soft to avoid running out of travel (bottoming out) the outside front suspension under high cornering load. When a suspension bottoms out, the relative spring rate spikes "through the roof". This results in loss of traction (understeer).

2. Most conventional front suspensions gain (positive) camber on the outside front front wheel under high cornering load. This results in loss of traction due to reduction in tire contact patch area (understeer).

The simplest way to address both these issues is to install a stiffer front sway bar, which REDUCES understeer when either or both of the issues above are present.

MikeWhitney · **Joined:** Wed Aug 20, 2003 9:15 pm **Posts:** 4724

Keith Quistorff wrote:

Adam Ligon wrote:

Well a new front bar, bigger I am guesing, shouldn't make the car oversteer more, just the opposite actually.

This is true in theory, but almost never in practice when autocrossing cars designed for street use, for the following 2 reasons:

1. Suspensions designed for street use are too soft to avoid running out of travel (bottoming out) the outside front suspension under high cornering load. When a suspension bottoms out, the relative spring rate spikes "through the roof". This results in loss of traction (understeer).

2. Most conventional front suspensions gain (positive) camber on the outside front front wheel under high cornering load. This results in loss of traction due to reduction in tire contact patch area (understeer).

The simplest way to address both these issues is to install a stiffer front sway bar, which REDUCES understeer when either or both of the issues above are present.

Keith, that was an excellent explanation.

Diane Hall · **Posted:** Mon Nov 08, 2004 12:33 pm

Vincent Keene wrote:

In the Miata I try to keep it as near empty as possible. Scary trying to make it to the gas station though. I really thought I wasn't gonna make it yesterday!

I eventually started carrying a 1 gal gas can just so I wouldn't be so scared. Never had to use it, but it was nice peace of mind. Strapped nicely to the fender of the trailer too.

Vincent Keene · **Posted:** Mon Nov 08, 2004 12:42 pm

Diane Hall wrote:

Vincent Keene wrote:

In the Miata I try to keep it as near empty as possible. Scary trying to make it to the gas station though. I really thought I wasn't gonna make it yesterday!

I eventually started carrying a 1 gal gas can just so I wouldn't be so scared. Never had to use it, but it was nice piece of mind. Strapped nicely to the fender of the trailer too.

That's probably a good idea for me as well. I have run out of gas once in the Z-24 at Sanford just after crossing the finish line. Thank goodness Dick R. had some extra gas for his Formula Ford that day.

Thanks again Dick!

Mike Winn · **Joined:** Fri Aug 29, 2003 12:30 am **Posts:** 110

Wonderful!

Now if only those bench racer types that go out and read a "suspension tuning" book based on race cars would read something like this... *sigh*

I have to fight the "larger front swaybars mean more understeer" misconception constantly with the Subaru crowd.

Keith Quistorff wrote:

Adam Ligon wrote:

Well a new front bar, bigger I am guesing, shouldn't make the car oversteer more, just the opposite actually.

This is true in theory, but almost never in practice when autocrossing cars designed for street use, for the following 2 reasons:

1. Suspensions designed for street use are too soft to avoid running out of travel (bottoming out) the outside front suspension under high cornering load. When a suspension bottoms out, the relative spring rate spikes "through the roof". This results in loss of traction (understeer).

2. Most conventional front suspensions gain (positive) camber on the outside front front wheel under high cornering load. This results in loss of traction due to reduction in tire contact patch area (understeer).

The simplest way to address both these issues is to install a stiffer front sway bar, which REDUCES understeer when either or both of the issues above are present.

Adam Ligon · **Posted:** Mon Nov 08, 2004 2:20 pm

Well there are a few exceptions to this description. First it is assuming stock components, springs, shocks etc. Also the postive camber gain happens on strut type cars, not most multi link set or wishbone setups.

David Teague · **Posted:** Mon Nov 08, 2004 2:28 pm

I love my double wishbone front suspension. And on most honda's with a double wishbone and oem coil over shocks, adding a bigger front bar is the quickest way to get more understeer. However I am considering getting a bigger bar just to combar body roll and to help in transitions.

Michael Westerfield · **Posted:** Mon Nov 08, 2004 2:38 pm

The integra has a light that comes on that tells you when your at the appropriate level for autocrossing...

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