I drive a lot with the FWD-Cars. XFG and XFR.

Am I a bad driver if I drive nearly the same laptime with 80% fuel and with 10% fuel??

I know an empty car is way faster on the straight, but I'm not able to drive any faster with an empty car.
How come? *g*

The difference is about 0.2 secs. And thats way too less (I think...).

For example you can look at my LFS-Stats. I made 60 Laps with the GTI on Blackwood on 6th November.

Tell me whats wrong with me please!!

With that little power, it doesn't make that much of a difference TBH - try drive something powerful and light (some extra fuel would make a much bigger % difference) and you could find ~1s difference but really it shouldn't be any more...

Its the same with the XFR.

Quote from --==Gogo==-- :

Its the same with the XFR.

But the extra mass doesn't really make that much of a difference - 1-2kph at the end of the straight... work out how much this would affect your average speed and see that it isn't anything significant. Singnificant difference can only come when the fuel load affects the balance of the whole car (eg. MRT5 - undrivable on a full tank IMO).

The car gets lighter, but the tyres wear also. Another factor is the extra grip you may get with the weight of more fuel. The car is potentially faster at lighter weights, but more difficult to keep on the track. Over a short distance you should notice a slight improvement in lap times as fuel diminishes, but over a longer distance these other factors may negate any noticeable advantage.

in an fo8 on westhill the differnece us much more higher. In a xfr i dont see much differnce as well.

Last night I had an 8 lap practice race around Aston GP in the UFR with Sparky Dave. We were both driving extremely consistenly and hard, and I got consistently faster each lap, it was about 0.8 difference between 40% fuel and empty, with about 0.1-0.2 secs a lap improvement. Although that was over a 187 second lap.

Basically the greater the fuelMass/CarMass ratio, the bigger the effect. Also, the better able you are to drive at the limit consistently, the more you will notice the effect.

Quote from Gunn :

The car is potentially faster at lighter weights, but more difficult to keep on the track.

Uhh, I'm going to have to go ahead and take an opposing veiw here. Less weight will always make a car handle better. Polar moment of inertia is a huge factor in designing race cars. Many people have a misinterpratation about how much weight on a tire effects the handeling. While I'll agree that it does indeed effect handeling, it doesn't effect it as much as CG shifts and polar moments affect handeling. There are always tradeoffs and I'll take less weight over less grip anyday. Keep in mind that the weight of fuel doesn't effect overall tire grip nearly as much as it will effect "tossability". This is born out by the fact that a car is always faster with less fuel and/or less people then it is with such things, and it's not all due to acceleration.

I think it's small enough to not worry about unless you're going for the WR.

And if the fuel changes the behaviour of the car too much, that can be countered with your setup.

did 11 laps of blgp in an fox with 100% fuel and r1 tires (62.9% left after race), compared to just having enough for the 11 laps i found the car to be a bit more stable out of cornors, not to much slower (about 1:10.30 fastest starting with 39% fuel, 1:10.80 fastest starting with 100%) the biggest difference is that the tires where starting to burst into flames at lap 4 instead of about lap 9. so i'd say its really not a massive deal to have a couple of laps more fuel then anyone else.

Quote from --==Gogo==-- :

I know an empty car is way faster on the straight, but I'm not able to drive any faster with an empty car.
How come? *g*

I think if you actually did the math, you would find that on most reasonably turny tracks the deleterious effects of the greater weight on cornering speed are at least as large as the effects on acceleration on the straights.

Particularly in relatively draggy/low power cars, where the influence of frontal area and drag is predominant above fairly low speeds. I believe you'll find that 5% extra mass will not effect time down the Blackwood straight in the XF GTI as much as 5% less drag would. I haven't done the calculations to prove that, but I'm fairly sure its true.

The accelerations are so small for good portions of the straights in the GTI that the weight is close to irrelevant.

However, since the traction available at the tire increases with an exponent of less than one applied to the normal force, you will always see lower cornering speeds with more mass on board. This effects your speed through most of the track, excepting the latter portions of straightaways. Higher cornering speed lets you brake later, begin straightaways at a higher speed, and obviously carry more speed through the turns.

In the more powerful/lighter vehicles, I think you'll find it makes a bigger difference. Maybe its just me, but I'm at least a second or two slower on BLGP in FV8 with a full load.

Quote from operator0 :

Uhh, I'm going to have to go ahead and take an opposing veiw here. Less weight will always make a car handle better.

How is that an opposing view? I never mentioned better handling. I mentioned grip. More weight helps to push the tyres down onto the road, it's as simple as that. As the car loses weight it is more prone to skidding or spinning over bumpy areas.

Just try not to worry about fuel too much, yes a lighter load means faster corners, but racing at 100% is'nt a major disadvantage 'cos of the extra stability you can gain. (what does the fuel do to CG height tho', Big factor in how fast round corners it'll go) it would be nice to find out exactly where the fuel tanks are. (and the CG heights would be nice too for that matter, not an easy thing to measure in LFS)

Quote from Gunn :

How is that an opposing view? I never mentioned better handling. I mentioned grip. More weight helps to push the tyres down onto the road, it's as simple as that. As the car loses weight it is more prone to skidding or spinning over bumpy areas.

I'm gonna have to disagree, a bit. You're both right, but less weight wins in the end, it's the nature of the tyres, the coeficcient curve etc. more weight is more stable (usually) but will pull less G's

Quote from Gunn :

How is that an opposing view? I never mentioned better handling. I mentioned grip. More weight helps to push the tyres down onto the road, it's as simple as that. As the car loses weight it is more prone to skidding or spinning over bumpy areas.

Assuming one doesn't then set the car up properly re: springs/damping I guess that's true...and I guess its true across vastly different masses of vehicle.

Lighter vehicles will always be faster, they will always corner faster and they will always accelerate faster.

Less weight, by itself, is beneficial to handling. However, if a car's suspension has been tuned to provide optimum handling with a 100% fuels load (or close to it), then as the fuel decreases, the balance of the car changes, which can have a detrimental effect on handling. Depending on what your setup is like, the two effects may roughly cancel out, leaving you with similar laptimes.