Front/Rear Weight Distribution

[xbgs351]

Here is a bit of a technical quiz.

What do you consider to be the ideal front/rear weight distribution for a car that has to turn left and right as well as accelerating and braking?

[Bossxr8]

Depends on where the engine is located doesn't it, cause mid engined or rear engined supercars have a totally different perfect front/rear bias to a front engined car.

For a front engined rear wheel drive car 51/49 front to rear, 51/49 because under acceleration/on the move the weight shifts back to be a perfect 50/50. Thats what i've heard anyway.

[Rev28K]

My FWD is 60/40 F/R, it still handles okay (but not brilliantly) but I think that the engineers fiddled with a few things to overcome the stock weight distribution.

Ideal for a racing car I’d be going 40/60 (like most racing cars and Porsche 911’s) – less load on the front tyres for cornering, more traction to the rear. As long as the back doesn’t want to over take the front under brakes it should be fine.

Polar moment of inertia – initially I thought low (which is good for turn in) but high is good for predictability.

What happens to a static 50/50 weight distribution under braking? 70/30 with soft suspension?

[ebxr8240]

50/50 but will never happen on rwd car... There's other things that come into handling etc.. but IMO as close to 50% but 10% either way isn't going to make too much difference.. A fwd will have bias towards front too..
At least with fwd you can control oversteer with throttle..
The Alfa GTV6 with its front engine and rear mounted transmission was nearly 50/50...

[4Vman]

IMO.. It will depend on the car's braking and acceleration ability (G's), as well as its aero assisted down force and tyre width (grip) front to rear....
Assuming the car can accelerate and brake at about the same rate, has the same tyre width (grip) front to rear and its front to rear aero influence is set roughly "neutral" than id say 50/50.
Weight distribution can and will be altered to compensate for variations in these factors....

[|||]

65/35 for fat skids

[xbgs351]

I should also have stated for a rear wheel drive, but I reckon most people had probably taken that assumption.

[ohzone]

Actually I was just thinking about this subject after reading some posts on understeer affecting BA/BF V8's
Does anybody know what the weight distribution of AU with windsor and six, and BA/BF V8 and Six?.
Also it would be interesting to know the weights of the engines are as well as these are the most obvious suspect to cause any understeer

[ZA-289]

I wouldn't have a clue to be honest!

Dont really care either, I drive each car different accordingly to how it responds.

[Gammaboy]

Originally Posted by ebxr8240

50/50 but will never happen on rwd car... There's other things that come into handling etc.. but IMO as close to 50% but 10% either way isn't going to make too much difference.. A fwd will have bias towards front too..
At least with fwd you can control oversteer with throttle..
The Alfa GTV6 with its front engine and rear mounted transmission was nearly 50/50...

4cyl GTV was 51/49 I think, the GTV6 was 53/47 and you could really feel the difference (I had a GTV at the same time as my old man having a GTV6). The GTV6's fuel tank was mounted up above the transaxle, the 4 was in the boot floor - combined with the hevier motor it lost its nimbleness. The GTV was 1080kg, the V6 was 1170kg i think?

The GTV6 had such a sweet sound at full noise though.

For big HP/light weight circuit cars I'd be aiming for more like 60% over the back wheels, but not the way Porsche manage it - huge Polar moment.

50/50 makes for a sweetly balanced road car though - so without more definition of the question I'm not going to state an "ideal" :P

[xbgs351]

Originally Posted by Gammaboy

so without more definition of the question I'm not going to state an "ideal" :P

Good point. Lets say ideal as far as being the quickest, as opposed to being the sweetest to drive.

[4Vman]

V8SC's are set-up at 50/50 F to R, L to R, and will place lead as low as possible to achieve it.

[xbgs351]

Originally Posted by 4Vman

V8SC's are set-up at 50/50 F to R, L to R

That would be a hard ask with the rules written as they are. The driver would have to sit behind the wheelbase middle line.

Originally Posted by http://www.v8supercar.com.au/content/attachments/extranet/2008_season/opps_manual/division_c-_technical_rules/files/9540/2008%20Div%20C%20FIA%20Approved.pdf

C 4.1 Minimum Weight
4.1.1 The minimum weight of a Car is 1355kg excluding the Driver and the Driver’s apparel.
4.1.2 The minimum weights stated in C 4.1.1 above must be achieved at all times throughout a Meeting with the exception that during any session or Race in which refuelling is permitted, the minimum weights must be achieved without fuel.
4.1.3 In addition to the requirements of C 4.1.1 and C 4.1.2 above, all Cars competing in the VCS must achieve a minimum weight of 1435 kg including the weight of the Driver wearing his complete Driver’s apparel, as recorded by the CTD at the Driver’s first Meeting for the year, both during and immediately after all practice, qualifying sessions and Races.
4.1.4 The minimum front axle weight of a Car, measured at the front axle centreline, is 740kg. This minimum weight must be achieved at all times, without fuel, Driver or Driver’s apparel on board.
4.1.5 TEGA/V8 Supercars reserves

[ac-460]

How this for spec's my cobra weighs 550 on the front 590 on the back 580 on the front with me in it 660 on the rear roughly 55 45 f-r it has 11 inch rims on the front and 315 tyres and 335 on the rear with 13 inch rims a 650hp stroked big block all comes down to the size of your golfballs

[ac-460]

sorry 55% rear 45% front

[new2ford]

Originally Posted by ebxr8240

50/50 but will never happen on rwd car... There's other things that come into handling etc.. but IMO as close to 50% but 10% either way isn't going to make too much difference.. A fwd will have bias towards front too..
At least with fwd you can control oversteer with throttle..
The Alfa GTV6 with its front engine and rear mounted transmission was nearly 50/50...

Leyland P76 was exactly 50/50 and boy did you notice the difference back then, as the Holdens and Falcons were very front heavy. The P76 handled like a small car and stuck to the road like shyte to a blanket. Presumably as a result Ford and Holden worked towards changing the weight balance but I reckon it took Falcon 20 years to catch up judging by its handling!

[Rev28K]

Didn’t the “P38” also have struts on the front? While the weight distribution helped there would’ve been other factors at play. Didn’t their cast iron straight 6 weigh as much as the alloy V8?

The 2 seat version of the 260Z had 52/48 weight balance, the longer 2+2 version had exactly 50/50 weight distribution but most people weren’t willing to settle for less agility, more weight, slower times for the sake of perfect weight distribution.

I can remember something about a system being tried on one of the DTM cars back in the 80’s/90’s (before it spiraled out of control with $$$) were one of the manufacturers was experimenting with having the weight (tungsten?) dynamically slide front or aft to suit the conditions. i.e. more weight at the rear under acceleration, 50/50 for cornering.

[Citric GT]

I chose 55f/45r so as to allow for a bit of weight in the back while staying close to perfect.

[CAT600]

Originally Posted by ohzone

Actually I was just thinking about this subject after reading some posts on understeer affecting BA/BF V8's
Does anybody know what the weight distribution of AU with windsor and six, and BA/BF V8 and Six?.
Also it would be interesting to know the weights of the engines are as well as these are the most obvious suspect to cause any understeer

My AUI XR8 had 54/46 Weight distribution and I would think that a VCT XR6 would be even closer to the 50/50 mark than that. This was with a 1/2 full fuel tank and me out of the car.

The AUII/III would be a little heavier over the front due to additional deadening and the laminated firewall they got.

AU's (with IRS) have better F/R distribution than B-Series, mainly due to lighter engines and heavier IRS.

Daniel

[pb02]

Originally Posted by ebxr8240

50/50 but will never happen on rwd car...

The Honda S2000 is 50/50 and rear wheel drive

[mustang70]

i would imagine the little mid engined offerings of the Fiat X19, the early MR2 and the Fiero and would be close to 50/50. all these handle really well form what i've driven, if not all underpowered in stock form.

[ohzone]

Originally Posted by CAT600

My AUI XR8 had 54/46 Weight distribution and I would think that a VCT XR6 would be even closer to the 50/50 mark than that. This was with a 1/2 full fuel tank and me out of the car.

The AUII/III would be a little heavier over the front due to additional deadening and the laminated firewall they got.

AU's (with IRS) have better F/R distribution than B-Series, mainly due to lighter engines and heavier IRS.

Daniel

I thought that may be the case with the lighter engine and heavier IRS and it explains a lot of the neutral handling the Au's have.

[xbgs351]

65% Front, 35% Rear 3 4.35%
60% Front, 40% Rear 8 11.59%
55% Front, 45% Rear 14 20.29%
50% Front, 50% Rear 23 33.33%
45% Front, 55% Rear 15 21.74%
40% Front, 60% Rear 6 8.70%
35% Front, 65% Rear 0 0%

The results are looking interesting so far. I'm surprised that more people haven't chosen the 50/50 option as it seems to be the figure that the common press usually bandies about as optimal.

[GORDZ]

well i drive a ute. 60 f 40r my vote.... lol, poor rear tyres.

[bathurst77]

HOw much does a full tank of fuel weigh? that migth alter your balance depending on how much fuel and whats in the boot today.
OR how much food n grog i shoved under me belt last night

[Rev28K]

1 litre of fuel weighs about .8kg so a 40 litre tank weighs 32kg, 60 litre weighs 48kg and 80 litres weighs 64kg. Keep it low (drop tank) and it shouldn’t hurt distribution too much on full/empty tanks.

Interesting to note that a lot of the front mid-mount European GT’s are aiming for a slightly rear balanced 45/55 ratio. There seem to be a lot of transaxles going in to cars these days as well and if you go with an automatic like the new Nissan GTR you don’t have the problems with long linkages that they had in the past.

[outback_ute]

Here's a quote for you - "static weight distribution is valid only in the parking lot".
I'd vote for 45/55, with much wider tyres on the rear. Under acceleration most of the weight will be on the rear wheels for good traction, and the rear wheels can also do a better share of braking. The tyre size differential takes care of cornering, which can also be adjusted by accelerating through the corner.

[xbgs351]

Quoted from: Brabham Ralt Honda The Ron Tauranac Story

"WEIGHT DISTRIBUTION: Rear-wheel-drive cars have traditionally had 60% of the weight on the rear as the tyres were developed around this distribution and a deviation of as little as 1% was enough to restrict performance. However, with the advent of an increasing number of regulations restricting the overall tyre width, the front tyres have become wider in relation to the rears and therefore we have needed to take similarly increased percentage of front weight. Current F1 and mid-engined GT cars (as of 1999) for example, carry about 58% at the rear. The governing factor is tyre operating temperatures, which should be the same at the front as the rear."

Ron was the designer of the Brabham cars which took Sir Jack Brabham and the late Denis Hulme to Formula One World Championships in the 1960s as well as a myriad of Brabhams for other formulae from Indycars to Formula 3 and everything in between. In all, Brabham built about 500 racing cars in total. Oh, they won in every class too! Ron then sold Brabham to Bernie Ecclestone. Later, Ron started Ralt, a race car production company that built cars for many formulae all over the world, and for many years were the chassis you needed to win in F2, F3, F3000, and FAtlantic etc. About 1000 Ralts of various types were built, and many are still racing. He later sold the Ralt Company to March.

[outback_ute]

I remembered an interesting case of weight distribution, back in the 60s & 70s there was a company in NSW that made the biggest 2wd tractors going around, they were the same size as your Steiger/Versatile etc with 350hp. Even with the engine in the front, most of the weight (80%!!!) was on the rear wheels thanks to some very thick steel being used, and this got closer to 90% when the tractor was pulling. It used huge earthmover tyres to keep the ground pressure low (& traction high).

[xbgs351]

Carroll Smith is another that favours a lot more weight on the rear. He mentions 35/65 to 40/65 in at least one of his many books.