Best weight distribution front/rear

[Greg Locock]

Engine location is a bit of a binary choice, in front of the cabin or behind (or beneath in the case of my Commer and at least one Toyota minivan).

As in all things with car design it is a compromise. The market or fashion decided stupid-cars were going to be mid engined 2 seaters, and so that's what you get.

Incidentally when designing a stupid-car, handling is not really a high priority. It tends to be good because of tire sizes and low cg, and customer acceptance of poor ride.

[Tommy Cookers]

... Naturally, at higher speeds the aero effects become greater and especially at high speeds in yaw ....

well ....
aero DF at higher speeds has increased the tyre forces so much that these (tyre forces) are actually what becomes great

we could also say that the aero lateral force tends to reduce (or worse) post-apex and with understeer any time
(ok current floor ground effect might be somewhat different eg with roll ? - but better or not ??)

I don't think an F1-weight F1-power wheel-less winged vehicle could lap Silverstone as fast as F1 does

[PhillipM]

Which engine placement location in the car would be the best/optimal place for best handling or has the least negative drawbacks? A front engine car, mid/rear engine car or rear engine car?

Why did designers choose the 42/58 front to rear weight distribution for...

1990 Acura/Honda NSX
1993-1998 McLaren F1 road car
1995 Ferrari F50
2019 McLaren GT

?

Honda used the CRAY supercomputer to aid in the design of the NSX's frame to find where to stiffen it.

There's no one answer because it depends entirely on your drive system and the conditions you want to run in. There's a reason rear engined, rear heavy Porches, Beetles, etc, used to do so well on rallies and safaris and that's because the traction advantage overruled every other concern.

60/40 or 40/60 might not make much difference for an F1 car with it's aero on a tarmac surface on slicks, whereas that might be the difference between even being able to get going on a RWD rally or safari car.

[Honda Porsche fan]

Engine location is a bit of a binary choice, in front of the cabin or behind (or beneath in the case of my Commer and at least one Toyota minivan).

As in all things with car design it is a compromise. The market or fashion decided stupid-cars were going to be mid engined 2 seaters, and so that's what you get.

Incidentally when designing a stupid-car, handling is not really a high priority. It tends to be good because of tire sizes and low cg, and customer acceptance of poor ride.

Which cars on the market are considered stupid-cars and what cars are not ?

[Greg Locock]

It was a bad pun on supercar. I've worked on a couple and unless you are designing an innovative system on them, then they are rather dreary to engineer compared with a B class car. I'd make an exception for Koeniggsegg.

[Testdrive]

Which engine placement location in the car would be the best/optimal place for best handling or has the least negative drawbacks? A front engine car, mid/rear engine car or rear engine car?

Why did designers choose the 42/58 front to rear weight distribution for...

1990 Acura/Honda NSX
1993-1998 McLaren F1 road car
1995 Ferrari F50
2019 McLaren GT

?

Honda used the CRAY supercomputer to aid in the design of the NSX's frame to find where to stiffen it.

There's no one answer because it depends entirely on your drive system and the conditions you want to run in. There's a reason rear engined, rear heavy Porches, Beetles, etc, used to do so well on rallies and safaris and that's because the traction advantage overruled every other concern.

60/40 or 40/60 might not make much difference for an F1 car with it's aero on a tarmac surface on slicks, whereas that might be the difference between even being able to get going on a RWD rally or safari car.

60 / 40 on a F1 car, you will lose the rear fairly easily and spin out because there is not much weight on the rear. You start to get over steer after 40 frontal. 37% frontal you can go early on the gas, come out of corners quicker, but 40% frontal you can go into corners quicker. I suspect It all depends on the track for which is best.

[PhillipM]

You're still talking about a percent or two of performance, not multiples, orders of magnitude or even the difference between even being able to get to the finish line or not.

[garacer]

... the c.g. is essentially defined by the FIA by front/rear weight distribution.
.. The closer the front/rear mass c.g. is to the car's c.g. .... the more responsive the car will be to turning forces.

turning forces ?

to turn from a road going north to a road going east the car does 2 jobs ....
1. change where it's going from north to east - this is a big job
2. change where it's pointing from north to east - this a small job
PMI is only involved in job 2

if the car 'loses grip' it eg can do job 2 without doing job 1
it will rotate about the point of minimum rotational inertia - this won't be the cg
rear-engined cars have less inertia about this point than do comparable mid-engined cars


low-PMI (in yaw) is also low-PMI in pitch - such road cars have inferior ride
as cars did pre-WW2 - until independent front suspension came along so enabling increased PMI

Hi, could you explain more about the point of minimum inertia being different than the center of mass. I thought these were the same. Thanks

[Tommy Cookers]

... the c.g. is essentially defined by the FIA by front/rear weight distribution.
.. The closer the front/rear mass c.g. is to the car's c.g. .... the more responsive the car will be to turning forces.

turning forces ?
to turn from a road going north to a road going east the car does 2 jobs ....
1. change where it's going from north to east - this is a big job
2. change where it's pointing from north to east - this a small job
PMI is only involved in job 2
(low-PMI (in yaw) is also low-PMI in pitch - such road cars have inferior ride
as cars did pre-WW2 - until independent front suspension came along so enabling increased PMI)

if the car 'loses grip' it eg can do job 2 without doing job 1
it will rotate about the point of minimum rotational inertia - this won't be the cg
rear-engined cars have less inertia about this point than do comparable mid-engined cars

Hi, could you explain more about the point of minimum inertia being different than the center of mass. I thought these were the same. Thanks

well spotted !
yes I was wrong

what I had in mind was that ....
the mid-engined super car has got the lowest PMI about its mid-wheelbase (but not the lowest PMI about its CG) ....
the rear-engined sports car has got the lowest PMI about its CG (but not the lowest PMI about its mid-wheelbase)
so the rear-engined car yaws (or departs in yaw really) quicker than the mid-engined car
in the early 80s 'Motor' magazine did some turntable tests explaining and demonstrating this

and that ...
unfortunately online descriptions of PMI usually present mass symmetry (as minimising PFI) .....
and ignore the fact that yaw etc comes from 4 tyre forces (whose effects are strongly dependent on wheelbase etc)

[JordanMugen]

Weight distribution by itself is a fairly meaningless parameter IN ISOLATION if you don't know much about the tires and especially if they are different front to rear. I ran a lap simulation for a car with identical tires all round and varied the weight distribution from 40:60 right through to 60:40 and the differences weren't huge.

So front wheel drive, front weight biased cars aren't actually that bad despite the claims of RWD purists (not that you can buy any RWD hot hatchbacks anymore, with move of the BMW 1 Series move from the 3 Series platform to MINI Cooper platform)? That's good to know!

...customer acceptance of poor ride.

Wasn't Ford Falcon handling, including FPV GT, notoriously boaty until FPV were allowed to ignore NVH and ride comfort guidelines for the R-Spec suspension used on the FPV GT R-Spec, Falcon XR6 Sprint and Falcon XR8 Sprint?

The Tesla Model 3 has received a softer suspension on its facelift, I'm sure it's still OK on steady state, but there are numerous complaints of excessive body roll and delay in body motions when making aggressive inputs at highway speeds or higher.

[Greg Locock]

FWD still has problems with traction out of corners unless you fit an LSD and then you get power-on understeer. That's why you often see the inside rear wheel in the air, they've softened the front off a lot to get traction. I also seem to have spent most of the 80s curing power-on axle tramp, especially, but not only, on turbocharged FWDs.

Sorry didn't have a whole lot to do with FPV product, ride on AU through to BF base seemed OK (subjectively) to me, and of course the NVH was excellent (grins) but I was 75% Territory at the time. In that timeframe most ride work was on physical prototypes, I was CAE mostly concerned with steering, handling and rollover. In the last 10 years our ride modelling has improved to the extent that most tuning is done on the computer. It helps having mm resolution scans of the ride roads, and of course tire models have improved beyond recognition.

[Tzk]

So front wheel drive, front weight biased cars aren't actually that bad despite the claims of RWD purists (not that you can buy any RWD hot hatchbacks anymore, with move of the BMW 1 Series move from the 3 Series platform to MINI Cooper platform)? That's good to know!

Well, in (very) simple terms: You're always traction limited on a wheel. So when you're using the traction for turning and acceleration (FWD), then you can't accelerate as fast as on a car which splits turning and acceleration to different wheels (RWD). So on an older 1 series car, the front wheels will turn the car while the rear wheels will push it. On a newer 1 series in contrast, the front wheels will have to turn and push the car, resulting in a slight disadvantage.

Note that this oversimplified in laymans terms.

[Stu]

FWD still has problems with traction out of corners unless you fit an LSD and then you get power-on understeer. That's why you often see the inside rear wheel in the air, they've softened the front off a lot to get traction. I also seem to have spent most of the 80s curing power-on axle tramp, especially, but not only, on turbocharged FWDs.

Sorry didn't have a whole lot to do with FPV product, ride on AU through to BF base seemed OK (subjectively) to me, and of course the NVH was excellent (grins) but I was 75% Territory at the time. In that timeframe most ride work was on physical prototypes, I was CAE mostly concerned with steering, handling and rollover. In the last 10 years our ride modelling has improved to the extent that most tuning is done on the computer. It helps having mm resolution scans of the ride roads, and of course tire models have improved beyond recognition.

Potentially off-topic point, but I recall Ray Mallock (RML) stating that they achieved power oversteer on the BTCC Nissan Primera Touring Car (probably the best Super Touring car built). I don’t know what the weight distribution for the car was, but do know that every effort was made to centralise mass (engine & gearbox behind front axle, etc).
How much of a role would diff settings have on achieving this phenomenon & how would mass distribution help?

[Greg Locock]

Shrugs, power on oversteer in a RWD? Sounds like normal behavior, just dial out your fixes to get more understeer. Weight distribution does have an effect - ask any pre-nanny F150 driver who is (as usual) carrying nothing in the back. I doubt moment of inertia contributes much. They've also made the rear track greater than the front which helps, more lateral load transfer at the back. So soften up the FARB, stiffen RARB, less roll steer at the front. LSD would tend to increase oversteer.

[Stu]

Shrugs, power on oversteer in a RWD? Sounds like normal behavior, just dial out your fixes to get more understeer. Weight distribution does have an effect - ask any pre-nanny F150 driver who is (as usual) carrying nothing in the back. I doubt moment of inertia contributes much. They've also made the rear track greater than the front which helps, more lateral load transfer at the back. So soften up the FARB, stiffen RARB, less roll steer at the front. LSD would tend to increase oversteer.

No. The Primera was FWD Super Touring…