What is the stock ITR weight distribution? Ive recently removed some weight from my car, and got to thinking about the balance of the car. I think its 60/40(f/r) but Im not sure. And, does anyone know what the ideal distribution would be and is there a way to measure your current distribution after removing weight? Im guessing the stock distribution is pretty close to perfect or else they would have made it differently off the production line. I was just kinda wondering if maybe you balanced it out more to 50/50 or so, would it handle better and be less suseptable to the infamous "life throttle oversteer" due to more weight in the back. Can you actually give the illusion of 50/50 balance with different spring rates? Or maybe run some heavier wheels in the back, relocate the battery to the trunk, other ideas? Im just curious to see what you guys(especially the track ******) had to say about it. cheers

 

62/38

 

Is that what you think is ideal or is that what its rated at stock?

 

62/38 is the stock weight distribution

The ideal weight distribution would be of course 50/50 but I don't think it's possible unless you added weight to the back

You could calculate your current weight distribution by bringing your car to a shop that does corner weighting.

 

I don't think there is a way to weigh the distrtbution of weight. The only thing you can do is try to calculate it for example

Stock F R
2600 1560 1040
60% 40%
Now say you remove the rear seats say 50 pounds so subtract 50 from 1040 = 990
so then just figure it the percentage from 2550
2550 1560 990
61.2% 38.8%

Obviously it wouldn't be perfect like that but it gives you an idea of what you are doing. Moving your battery to the trunk would also make a 1% difference.

 

I stand corrected

 

I knew that statement would bring up this discussion
IMO 50/50 isn't ideal to everyone but why wouldn't you want a perfectly balanced car.

 

I hope it does start a discussion, and I hope to get a lot on input from the track guys. Im curious if they try to keep the balance the same or close to stock, or if any of them have tried to balance it out to 50/50 or take it the other direction to something like 70/30.

Also, is the "lift throttle oversteer" more of an engine/power issue than it is a weight issue? Obviously we all know that staying on the throttle through a turn is what the ITR likes, but would it be any less suseptable to lift throttle oversteer if the weight was more balanced and maybe even like it more with a 50/50 distribution. I would think(totally guessing on this one) that you would be able to get into the corners with more speed, and be a little safer if you wanted to let out of the gas/brake while in the turn if you had a more even balance of the car because you wouldnt have to worry AS MUCH about the rear end coming around. Im a total n00b when it comes to track techniques, but Im faily sure that with a car like the ITR(and most other cars) exit speed is more important than entry speed. And if you can get a higher entry speed with a better balace of the car, and if the car liked a better balance while going through the turn, then you could carry that speed out of the corner. Again, Im totally guessing because I have yet to touch a track with my R.

 

Ok, to throw another twist into this mess, if you had a car that is evenly balanced 50/50, how much of an affect would spring rates play in the actual balance of the car while driving/cornering?

 

Turning too easily = unstable rear...
Formula 1 cars have 50/50 weight dist. nowadays.....

 

Are you comparing us to F1 cars hahahaha. Unstable rear

 

Huh? What do you mean? Balancing the weight only or balancing weight + suspension?

I think if you balance everything (weight and suspension) and then fine tune it for you taste, you'll get the maximum out of the car....

 

Ive dealt with the "unstable rear" situations before, and the fact that you guys think its FUN worries me

I guess it just depends how you drive the car. Any car that is 'stable' for one person, may not be stable for another due to driving techniques. It all comes down to how YOU feel the car is handling and how you would LIKE it to handle. If you are a person that likes to "throw it into the corner", lift and point the nose, and gun it, does that mean that maybe you are over driving the car(or the setup you have)? Maybe you could change the balance of the car, either physically by moving weight around, or buy using sprint rates, you wouldnt have to throw it into the corner, and would just be able to drive through the corner at speed. Then once you get comfortable doing that, you can start to throw it into the corner again and then make adjustments again so you dont have to throw it in until the point where you basically cant go any faster through a turn. But hey if you like livin on the edge then by all means, continue to do so because whats the point if you arent having fun Thanks for the input fellas. Hopefully some of the other guys will throw in their 2 cents as well.

 

But you forgot one thing, that's the inertial momentum or rotational inertia. That effects the ability to turn. So, more weight in the middle is better for turning. I don't think extra weight in the back is good for fast cornering....

 

Well, it depends how you want to turn the car. With the turning axis in the middle of the car, in the front or in the rear. I would rather have the turning axis in the middle of the car, then it's better to have all the weight in the middle of the car as possible. Just like a mid engine configuration.....

 

- Adding weight to a car, even if it brings the car closer to 50/50, will NEVER make it faster. Weight is ALLWAYS the enemy.

- 50/50 weight distribution is NOT the ideal weight distribution for FWD cars. With the front wheels doing ALL the work you need more weight over them. What is considered IDEAL in most circles is somewhere closer to 60/40.

- Corner balancing does nothing to the weight distribution but ensures that each corner is loaded with its correct weight percentage. This promotes more consistent cornering dynamics.

 

50/50 is ideal in theory. However, cars like the ITR and 911 prove that good engineering can more than compensate. Most purpose built cars are closer to 50/50 than most production-based racecars. Club racers don't spend a whole lot of time worrying about it because there isn't anything to be done about it within the rules (assuming body work, engine location, battery placement are restricted).

You cannot change the weight distribution of a car by corner-weighing. To get 50/50 left-right and front-rear, you have to move things around (well, technically, you could jack the car until it was about to roll over, but short of that you can't). Corner weighing can only adjust the cross weights. Moving small things like the battery can help (especially if it is located in front of the engine bay). I wouldn't do anything to add weight, a lighter car will always handle "better" at the limit (no guaruntee that driving at that limit will be easy).

Spring rates can be adjusted to help overcome deficiencies in balance. Thus the whacked out rear rates that most dedicated FWD track cars use (last I heard, Realtime was using ~1200lb rear springs and running a giant rear sway bar).

 

If this is regarding my statement, I just meant putting the car on the balance and not actually corner balancing the car

 

I wasnt really talking about adding weight to the car, but basically using the weight that the car came with and moving it around. Forexample, taking the rear seats out, or even just the spare tire, and then moving the battery to the trunk. Or, if you get lightweight wheels, just use them in front, and keep the stock wheels or similar in the rear.

 

50/50 weight distribution is considered Ideal when discussing RWD cars. The reasoning behind this thinking is that braking, acceleration, and cornering are all optimized.

But with FWD cars the front wheels do all the work and therefore this rule does not apply.

The primary problem is experienced under acceleration out of corners. With 50/50 distribution a FWD car would off load the front wheels too much causing excessive wheel spin. With more power, this problem only gets worse. Moving the CG closer to the front helps mediate this problem.

If there is too much weight over the front wheels cornering and braking will be compromised significantly, outweighing any acceleration benefits. This is where the correct compromise in cornering, braking, and acceleration comes in. 50/50 might be perfect for some drive train configurations, but not FWD. The TypeR actually comes pretty darn close to what many believe is the "best" compromise.

 

The S2K has a 50/50 weight distribution.

 

So?

 

Pertinent points from the wacky world of physics...

1. Corner weight adjustments can jack weight onto or off of adjacent corners or opposite pairs of corners ONLY. By adjusting the perch on one corner to "push that wheel down" (raise the ride height), you jack weight onto IT and the corner diagonally opposite it. You may strive for a 50/50 diagonal split - where the sum of the LF and RR equals the sum of the RF and LR corners. You may also try to equalize the fronts, left-to-right, letting the rears fall where they will.

2. In order to shift weight from the front to the rear, you would theoretically have to jack the front high enough that the center of gravity shifted rearward. The extreme case - hard to picture - would be balancing the car vertically, nose up, with its entire weight completely on the rear tires. The CG is directly above the rear contact patches while the fronts support 0% of the weight. If you raised the front ride height to 3 feet - driveshaft angles would suck - you MIGHT get a measurable change in front-to-rear vertical loading.

3. Removing the back seats takes static load off of the rears AND off of the fronts. The amount that each is impacted is proportional to the distance of the removed item from the CG (which I should add is the theoretical center of the car's mass, its balance point). If you take weight out right at the CG, it comes off equally from both ends. If you take weight out right on top of the rear axle, the front is unchanged.

4. The statement above about more weight never being a good thing is absolutely, 100%, inescapable fact.

5. I don't buy that 60/40 is necessarily an ideal weight distribution for a FWD car. There are WAY too many variables involved to be able to fall back on a generalization like that. Having said that, it just isn't much of a concern with most FWD circuit raicng and rally cars, since there isn't a whole lot that can be done to change F/R weight distribution.

6. Percentage weight distribution has NOTHING to do with polar moment of inertia - the resistance to rotational state change. The latter is all about the mass and where it is located relative to the center of rotation. A low-polar-moment car with more mass in the middle might have the same % weight distribution AND total mass as a car with a higher polar moment - the latter will be more resistant to changes in rotational state, both initiating rotation AND stopping it. More resistant to starting the scary spin and harder to catch once it goes. This is, in turn, a COMPLETELY different thing from mechanically influenced directional stability, which is primarily impacted by alignment - both static (initial, not in motion) and dynamic (resulting from movement of the suspension and/or chassis).

7. Dynamically, oversteer and understeer - as felt and controlled by the driver - are the result of a bazillion influnces. Lap time is a whole 'nother degree of complication even beyond that.

8. Once it hits the track, the car almost NEVER sees its static wheel-weighted weight ditribution. If it did, the springs would never compress and the dampers would never go up and down. The most important issue might be how things behave in the transitions between the various possible states of balance - that's the art of suspension set up.

Have fun!

Kirk

 

Knestis,

I agree 100% with all your points.

 

weight distribution is only one factor in a multitude of things that contribute to the cornering dynamics and capabilities of a car. 50/50 contributes to neutral charataristics, while overloading the rear (porsche) tends to make things a bit tail happy. this of course being in RWD cars, i'm not going to try and argue FWD stuff, as i just don't know. i whole-hartedly agree with the acceleration issues involved with removing weight from the front

i would think.......

while relocating weight to the rear of the car in a FWD may not be beneficial, relocating weight so that it is primarily inbetween the axles would be a good thing.

i'm going to stop now cause i'm getting into things i'm just not sure about

Travis
98 240sx FOR SALE
Midwestern Council of Sports Car Clubs

EDIT: welp, i think Knestis just put an end to this discussion.




[Modified by tnord, 5:57 PM 12/15/2002]