I think the AWD cars in LFS lose too much speed in the straight compared to other cars in their class. I know there should be a difference, but I don't think it should be that much. All things being equal, the AWD cars lose about 10 kph in top speed.

AWD have center diff and an additionnal diff that will take away more power than 2WD cars, that's a given. From what i've found, 2WD cars lose about 15-17 % power in the drivetrain, and AWD lose around 20-25 %.

Let's compare let's say the FZR and FXR. FZR losing 15 % would be about 73 HP, FXR losing 22 % would be 108 HP, that's a difference of 35 HP. When you compare the FXR and FX2 for example, there is a 123 HP difference and around 20 kph top speed difference. If you take into account that aerodynamics work exponentialy, just how much power are the AWD cars actually losing.

My point is AWD cars lose more power than the 2WD cars and thus don't have the same top speed, but the speed difference in the game now is just too exagerated.

Maybe the Turbo cars are much less aerodynamic as well?

I don't see what the turbo has to do with aerodynamics ... XRR has the same top speed as FZR, FXO, RB4 and XRT are all turbo and the RB4 is much slower in the straights. I chose to do an example with GTRs because they have the same weight and power as each other, unlike the TBO cars.

I suspect the cars to be set at 15 % powertrain loss for the 2WD and 30 % for AWD cars. It would mean 15 % for the transmission and differencial, and another 15 % for a second diff and the center diff. Let's assume the second diff takes as much power to run as the first one, it would mean the center diff takes as much power as the actual transmission and clutch, that doesn't make sense to me.

Sorry, I didn't mean turbo, I meant 4WD

Maybe the cars that have 4WD are also less aerodynamic than the ones that don't, which would also increase the difference in top speed.

I don't think that is the case. When fine tuning my RB4 gear ratios I noticed that i had a fairly limited rpm range within which the revs would drop for the shift to feel correct, however in the XRT, the torque just pulls from much lower in the rpms. I would love an accurate in-game torque/kilowatt curve to see weather or not I'm imagining things, but I tested using LFS tweak offline, by adding a 6th gear to the RB4 and redoing the gear ratios to suit. End result was not very satisfying, even though the RB4 with 6 gears is capable of keeping up with the FXO and the XRT in terms of top speed and maintaining cornering capability, it just isn't right that the power band for a 4WD turbo feels so small.

P.S. @ Tristan, I'm curious about what you mean when you say "Maybe the cars that have 4WD are also less aerodynamic..."

@ OP: Hm, if you look around I'm pretty sure that Bob had figured out the drivetrain losses and posted them somewhere. Might have to dig a bit.

@ Above: Tristan was just saying it could be coincidental; not making a direct correlation between 4wd and aero.

Oh okay, thanks BBT

Could it also be that when using 4WD cars in LFS we sacrifice our first gear in order to reduce clutch wear while trying to optimise acceleration, Leaving the RB4 for example with 4 usable gears?

/rambling thoughts

Quote from DeathItself :

I don't see what the turbo has to do with aerodynamics ... XRR has the same top speed as FZR, FXO, RB4 and XRT are all turbo and the RB4 is much slower in the straights. I chose to do an example with GTRs because they have the same weight and power as each other, unlike the TBO cars.

I suspect the cars to be set at 15 % powertrain loss for the 2WD and 30 % for AWD cars. It would mean 15 % for the transmission and differencial, and another 15 % for a second diff and the center diff. Let's assume the second diff takes as much power to run as the first one, it would mean the center diff takes as much power as the actual transmission and clutch, that doesn't make sense to me.

Surely torque & horsepower are not the only things that define acceleration?

The torque curve could be different, so they accelerate differently, there could be more drag due to different size tyres, the turbo-ed cars higher compression ratios could also add more drag (not sure if this would effect it while at WOT but it would while coasting...)

Theres a million and one reasons why car x could be slower or faster than car y, and drivetrain is just one...

Quote from tristancliffe :

Maybe the Turbo cars are much less aerodynamic as well?

From memory all the cars in LFS have the same cd value (or at least it's coded that way).

You could change the CD with LFSTweak so it's not hard coded...

Also the compression ratios in turbo cars would generally be lower but LFS doesn't have much sophistication in the engine simulation yet, and thus it's a moot point in this context .

Quote from Jakg :

Surely torque & horsepower are not the only things that define acceleration?

The torque curve could be different, so they accelerate differently, there could be more drag due to different size tyres, the turbo-ed cars higher compression ratios could also add more drag (not sure if this would effect it while at WOT but it would while coasting...)

Theres a million and one reasons why car x could be slower or faster than car y, and drivetrain is just one...

From memory all the cars in LFS have the same cd value (or at least it's coded that way).

Turbo cars will have less compression than normally aspirated engines and the due to the 6 gears of the GTRs the usable powerband is less than 1500 rpm, I doubt the torque varies that much on cars running these rpm.

As far as aero of the car FXO and XRT are pretty close together so I doubt there would be significant differences between their GTR counterparts.

Currently in LFS, all 2WD cars are 85% efficient, all 4WD cars are 80% efficient.

Quote from Bob Smith :

Currently in LFS, all 2WD cars are 85% efficient, all 4WD cars are 80% efficient.

thats why the FXR is so underadvantaged..

when u racing in tbo,and u drive rb4,all other cars just fly by you,its very annoying. but it does have advantage in slow turns.

And at the start.

But yeah, without restrictions (especially for the FXOs), it's impossible to be competitive with an RB4 on any track with more than 1 straight if you aren't an alien like Worm or Jouman.

Quote from Bob Smith :

Currently in LFS, all 2WD cars are 85% efficient, all 4WD cars are 80% efficient.

Sorry to doubt you but unless I see the numbers I just won't believe that. The RB4 gets killed by an FXO down the straight with less power,if those number were true ,the RB4 would be 194 HP at the wheels and the FXO 199, you wouldnt really notice a 5 HP difference. The FXR sets usually run less downforce than FZR and XRR because it's more stable and it ends up quite a bit slower.

Quote from DeathItself :

Sorry to doubt you but unless I see the numbers I just won't believe that.

lol M'kay. Considering your 4 posts and recent join date, we can forgive you for not knowing Bob enough to
trust that in this whole community, if someone went through all the numbers and tested/simulated every possible
situation and variable, it's Bob Smith.

I for one, believe you without needing any proof Bob.
You're my LFS physics wiki

Don't forget the RB4 is 70kg heavier than the FXO. And it has more wheel surface than the other TBOs (thus more roll resistance (?). The latter should apply to the FXR too in comparison to the XRR.

maybe fxo should get 4% and xrt 1 or 2 % ? did anyone try it yet?

If you want proof, the data is available in the .bin outputs LFS creates. My VHPA has a reader for the .bin files (the format was basically a request I made to Scawen so I could analyse the cars as thoroughly as possible).

Quote from Bob Smith :

If you want proof, the data is available in the .bin outputs LFS creates. My VHPA has a reader for the .bin files (the format was basically a request I made to Scawen so I could analyse the cars as thoroughly as possible).

English please bob. So there's a program that can set car's equal to eachother restriction wise your saying? Like evening the GT2 class out perfectly etc?

All he's saying is that there is an advanced data output mode in LFS.

Evening out the "GT2" class is more than just working out the drivetrain loss - remember fuel tank sizes, tyre wear rates, the effect of 4WD on cornering and lap time stability, and the added complexity of driving a turbo car... Plus the GTR class is not *meant* to be exactly equal (XRR and FZR are harder to drive than the FXR...)

If you click the VHPA link in his sig, you'll get a great piece of software that'll answer your questions.