GT350 vs. Z/28

[thePill]

Consider two types of roll centers... The RC you determine while setting your geometry and the RC under load.

DO NOT under estimate CG changes. Something as little as increasing tire pressure in a single corner can increase cross weight distribution dramatically.

Edit: Here's a better explanation of CG vs. RC. Both front and rear RC's constantly move. Some, if not most of that movement is caused by deflection (spring rate) among other influences. Lowering the CG has a dramatic effect on body roll. Body roll itself is a major factor in deflection. The lower the CG, the less body roll... Less body roll induces less stress on springs and spring rate. This changes the behavior of the RC and limits the RC's movement under load and weight transfer... Limiting your RC movement fr/rr will allow greater suspension and tire tune-ability due to a more compliant system as a whole. Suspension stability leads to better predictability and data acquisition.

Now... that's enough outta Kevin, let's go back to thePill...

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[Jim968]

...and don't just rip your passenger seat out either. You need all four corner weights, the percentages and cross weights before you determine that. That 40lbs, with some of that in the "reclined" position can help your cross weight distribution as well as lower your CG and RC.

How are you going to recline a seat with a roll cage in the way?

 

[Stuntman]

Consider two types of roll centers... The RC you determine while setting your geometry and the RC under load.

DO NOT under estimate CG changes. Something as little as increasing tire pressure in a single corner can increase cross weight distribution dramatically.

Edit: Here's a better explanation of CG vs. RC. Both front and rear RC's constantly move. Some, if not most of that movement is caused by deflection (spring rate) among other influences. Lowering the CG has a dramatic effect on body roll. Body roll itself is a major factor in deflection. The lower the CG, the less body roll... Less body roll induces less stress on springs and spring rate. This changes the behavior of the RC and limits the RC's movement under load and weight transfer... Limiting your RC movement fr/rr will allow greater suspension and tire tune-ability due to a more compliant system as a whole. Suspension stability leads to better predictability and data acquisition.

Now... that's enough outta Kevin, let's go back to thePill...

I agree on the benefits of a lower CG. However, lowering the CG does not change the instant center and thus does not lower the Roll Center.

If you need the passenger seat to meet a minimum weight requirement, it would be far better to have the same weight in lead sheets bolted on the floor where you want the weight for distribution purposes. This will lower the CG far more (but still probably not significant) than leaving the passenger seat intact and reclined.

If you do not need to meet a minimum weight requirement, I personally would take the corner and right side weight loss that goes with removing the (say 40lb) seat all together.

 

[thePill]

Your missing the main idea... Your RC location isn't altered, the natural arch the RC moves in is reduced. A Watts link does this as well only, it eliminates the arch and just limits the RC movement to just up and down.

Almost any change on the car will alter your RC. It doesn't lower it... I have no idea where you read that.

As far as total weight vs. weight dist....

This is where techs like me come in handy. Before you change anything, come get your baseline numbers. A lot of drivers don't know what they are doing, ESPECIALLY if they don't have the equipment to determine that.

Autocross... This is a place where WD tricks are used most. Pro is different but a z28 SHOULD be at the AM level. In a 4200lb car, 40lbs is nothing BUT, sliding percentages around will help it reach it's advertised (falsely) near 50/50.

A driver shifting his body back in a recliable seat can shift a % fr/rr on the scales. Don't remove your seats until you know exactly where you stand.

What's more important on a 4200lbs car? 40lbs from the left or near 50/50/50/50 WD? Everyone always thinks weight because the z28 is fat... It's also unbalanced too.

 

[Stuntman]

Your missing the main idea... Your RC location isn't altered, the natural arch the RC moves in is reduced. A Watts link does this as well only, it eliminates the arch and just limits the RC movement to just up and down.

Almost any change on the car will alter your RC. It doesn't lower it... I have no idea where you read that.

I know, I just pointed out your incorrect statement:

...and don't just rip your passenger seat out either. You need all four corner weights, the percentages and cross weights before you determine that. That 40lbs, with some of that in the "reclined" position can help your cross weight distribution as well as lower your CG and RC.

________________________

As far as total weight vs. weight dist....

This is where techs like me come in handy. Before you change anything, come get your baseline numbers. A lot of drivers don't know what they are doing, ESPECIALLY if they don't have the equipment to determine that.

Autocross... This is a place where WD tricks are used most. Pro is different but a z28 SHOULD be at the AM level. In a 4200lb car, 40lbs is nothing BUT, sliding percentages around will help it reach it's advertised (falsely) near 50/50.

A driver shifting his body back in a recliable seat can shift a % fr/rr on the scales. Don't remove your seats until you know exactly where you stand.

What's more important on a 4200lbs car? 40lbs from the left or near 50/50/50/50 WD? Everyone always thinks weight because the z28 is fat... It's also unbalanced too.

Techs or Engineers?

I'm not experienced with the nuances of autoX, but for road racing, I would almost always take a 40lb loss even if it adversely affected my right-side and rear weight distribution.

I'm not quite sure you could get a whole % shift (40lb swing from the front to rear axle on a 4000lb car) by just reclining the drivers seat while keeping the bottom portion stationary.

 

[DHG1078]

I know, I just pointed out your incorrect statement:


________________________

Techs or Engineers?

I'm not experienced with the nuances of autoX, but for road racing, I would almost always take a 40lb loss even if it adversely affected my right-side and rear weight distribution.

I'm not quite sure you could get a whole % shift (40lb swing from the front to rear axle on a 4000lb car) by just reclining the drivers seat while keeping the bottom portion stationary.

I haven't been keeping up with this thread so if my post is way off point please disregard it, but I believe we are taking the seat thing out of proportion here. If reclining the seat truly moved 40lbs, we are still only talking about less than 1% of the entire cars weight. Yes, reclining the seat may change the weight distribution, but the weight is still transferred to the car in the same contact point, just possibly slightly more biased to the rear contact points. We are talking weight distribution numbers prob. so insignificant, it's not worth mentioning with the seat. And that's not even considering the fact that a good seat position is FAR more important that manipulating it to get a better weight distribution.

Yes, weight distribution and weight transfer is huge for auto-cross and other types of racing. Lets just not get carried away here.

 

[thePill]

If you ever scaled a car you wouldn't be skeptical. Sorry if you thought it would lower you RC, a lower CG will help control your roll center.

This is why technical talk is impossible on forums. Nobody here is a tech.

 

[DHG1078]

If you ever scaled a car you wouldn't be skeptical. Sorry if you thought it would lower you RC, a lower CG will help control your roll center.

This is why technical talk is impossible on forums. Nobody here is a tech.

I have not scaled cars, but I am still calling BS on how big of an impact reclining a seat will have and that it is a useless argument since a proper seat position takes precedence over weight distribution.

 

[thePill]

Lol, yeah... Call BS all you want, I myself know better. Until you corner scale a car, you have NO idea what's happening. I can shift percentages drastically by adding or reducing tire pressure. Add in actual weight in a specific position and you get results.

Keep in mind, all this is centered around a 4200lbs, unbalance street car. Not ideal to begin with. As long as your broken argument sounds good... Keep it going though...

In this scenario, I am trying to offset the 200+lbs the driver and seat add to the left side (both AutoX and RR). The left side and it's effect on the RC vs. the right is HUGE. You are taking 40lbs out and potentially creating a much larger issue.

Being a tech is 90% engineering and 10% fabricating. Some people need to go to school and get off forums. Just my opinion...

 

[Stuntman]

Lol, yeah... Call BS all you want, I myself know better. Until you corner scale a car, you have NO idea what's happening. I can shift percentages drastically by adding or reducing tire pressure. Add in actual weight in a specific position and you get results.

Keep in mind, all this is centered around a 4200lbs, unbalance street car. Not ideal to begin with. As long as your broken argument sounds good... Keep it going though...

are you saying you can change Front to rear weight distribution by changing tire pressure?

I do it frequently. However you are continuing to backpedal on your incorrect statement that reclining the seat lowers the roll center, or the fact that lead bolted to the floor lowers the CG more than a reclined seat.

 

[DHG1078]

I do it frequently. However you are continuing to backpedal on your incorrect statement that reclining the seat lowers the roll center, or the fact that lead bolted to the floor lowers the CG more than a reclined seat.

I agree, you have made contradictory statements. Makes it hard to trust the credibility of them.

 

[DHG1078]

Lol, yeah... Call BS all you want, I myself know better. Until you corner scale a car, you have NO idea what's happening. I can shift percentages drastically by adding or reducing tire pressure. Add in actual weight in a specific position and you get results.

Keep in mind, all this is centered around a 4200lbs, unbalance street car. Not ideal to begin with. As long as your broken argument sounds good... Keep it going though...

adding in weight is not the same as reclining a seat, of course it will change things. Depending on placement and the amount of weight, it can have none, little, or a drastic affect. Remove tire pressure from 1 tire and you are going to change how the car sits i.e. shifting weight to one corner so of course it will have some sort of an impact. Not sure how much of one though. That's besides the fact that it's also a dumb idea. I am not going to set up my race car with different tire pressures to balance a car. Neither of those responses have anything to do with reclining a seat.


Edited, added text to above paragraph.

 

[thePill]

It's a widely used AutoX technique, these people have had the car scaled... They know the difference.

Most of these petty arguments are from the butt-hurts. It's pretty much the only defense for a car as useless as the z28. That's all, don't look into any further.

Just pointing out how much some don't know about their "race cars". It's all theory until we weigh a z28 and find out. I can tell you an SS benefits until a bar is added.

 

[Stuntman]

are you saying you can change Front to rear weight distribution by changing tire pressure?

 

[DHG1078]

are you saying you can change Front to rear weight distribution by changing tire pressure?

That's what I got out of it. I see it making a marginal difference at best. and that's if you really take the pressures to the extremes so there is large differences.

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