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Front End Weight Reduction = Increased Understeer?

Sig

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There has been a lot of talk recently about weight reduction for better performance. Spare tire removal seems to be the most popular. My question is this: If you remove something like the spare tire from the front end without removing equal lbs from the rear, will this upset the weight distribution enough to increase the inherent understeer already present in an NSX?
 
No. You're talking about removing 30 pounds. That's not enough to affect the weight distribution significantly.
 
Great question! When I removed my spare, I also removed the jack, tools and engine cover from the rear. If there was a balance problem with taking out the spare, this would address the issue. My next removals will be muffler in the back, battery in the front.
 
I would venture to guess that Alignment settings will affect understeer/oversteer quite a bit more than removing weight.
A Crude way to go about changing the steering Characteristics would be to soften/stiffen sway bars on the appropriate side. Softer in front=More oversteer,where softer in rear =more understeer. You could also help the sway bars out by getting adjutable shocks and further exaggerating the difference front to back to whichever type of response you want.
I am guessing that reducing the Toe-in on the rear tires could also result in more oversteer, as would reducing the tire width.
I certainly dont believe that removing 50-60lbs from a particular location would greatly affect the handling of the car, Which in either case can be negated by Corner balancing the car.

I am by no means an expert so if anyone knows otherwise please let me know. Suspension gemoetry is VERY complex stuff. I think.
smile.gif
 
Originally posted by nsxman:
I'd like to see a formula to support the claim that steering would not be affected.

While GROSS changes in weight distribution can and will affect oversteer/understeer (think of a 428 Mustang or big block Corvette with all of that weight on the front wheels), it has much less influence than the suspension setup. I used to have a big block 66 Vette that pushed like a motherf*cker but made it handle like a dream without changing the weight distribution at all. Just had to completely revise the suspension. Sure, if you put an enormous amount of weight on either axel, you will work it too hard for the suspension to compensate, but it takes a LOT to do that.

Changes to the polar moment of inertia influence the oversteer/understeer because once the car starts turning, it heavily influences how it comes around and where the mass of the car rotates.

[This message has been edited by David (edited 24 April 2001).]
 
Suspension component selection (and "tuning") is a function of vehicle mass and distributions. Indeed, it is not the converse.

The polar moment is a complex calculation, most likley beyond the scope of this forum. Using the classic textbook case of a rotating beam as a guide to an understanding of this concept is faulty, as it ignores the complex dynamics of a vehicle subject to a twisting (torque) at the "four" endpoints of this "single" beam.

As simplistic examples of the complexity of the calculation, consider the cases of a rotating sphere and a tumbling cube. For the sphere, the polar moment is obvious. For the cube, the polar moment changes depending on the instant in time.

*** At this time, nsxman calls on all calculus wizards to standup and be counted. ***

In Honda's engineering wisdom, they placed the spare tire close to the center of the vehicle. We can guess that its removal makes only a slight difference in the moment calculation, as the mass on an empirical basis, appears to be on a centerline with, and near to, the fore-aft locus of weight distribution.
 
The logic (or lack of!) behind my question is: the more something is weighted = more downward pressure. Less weight = less downward pressure = easier the slide around. So if the the weight were to be removed from the front end, understeer would increase as the weight decreased. This could be a fundamentally poor assumption though. Granted 30 pounds is not a huge difference, but I would think that on a CONCEPTUAL basis the front wheels would have fractionally less traction for every pound removed that is part of their load. How flawed is this thinking?
 
Well, for one thing, the battery is between the front wheels and the rear wheels, so part of its weight is on each set of wheels, not just all in front.
 
Originally posted by Sig:
...but I would think that on a CONCEPTUAL basis the front wheels would have fractionally less traction for every pound removed ...B]


Are you old enough to remember the famous Pinto commercial bragging about "road hugging weight"?

Yes, the logic seems a bit flawed. Someone check me on these assumptions: Weight distribution not withstanding and ignoring issues like sprung vs unsprung weight and spring rates vs damping (all part of the finer points in real life), more weight actually equals less traction in corners (lateral Gs) for a given tire. This is simply because one G is the equivalent of the weight of the car trying to break the tire loose sideways, so more weight is more force working against you at the same speed. The added traction you get from the extra downward force is not sufficient to offset the lateral force. The goal therefore (again boiled down to simplest terms) is to match weight and tire size to achieve the same lateral G potential on all four corners, but always at the lowest wiegts possible. That of course is quite different from straight line acceleration traction where you want the suspension to shift existing weight over the driven wheels under acceleration (short of lifting the front end).
 
Ah... this is what makes this issue so much fun as both SIG and SJS are right. As you remove variables from the complex subject of handling, it does reduce itself to Newton's famous insight on momentum.

In stock form, given what we know about the NSX, the removal of weight from the front should increase understeer. However, because of the spare tire's location, it is a subjective matter whether a driver could tell the difference.

*** nsxman does not assume, given the experience of forum members with the NSX, that someone might notice a difference with the tire gone. ***
 
Are you old enough to remember the famous Pinto commercial bragging about "road hugging weight"?

At least we can salute that car for its innovative approach to weight reduction by introducing the technique of exploding on contact.
biggrin.gif
 
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