Am I the only one who feels the car doesn't feel as solid when the rear seats are down on those twistie runs? I haven't run a search so if I've missed a 62 page thread about this exact topic, you have permission to yell at me, but I know you won't. So anyway.. The exhaust roars incredible with the seats down but is it sacrificing any stability? It may be placebo effect but I believe I notice it most on those more extreme and precision-demanding downhill runs. Thanks guys.

 

Just getting back from the Dragon last week, I ran very hard with both seats up and down and truly didn’t feel any difference and those are the twistiest roads you’ll find anywhere.

 

I have done a few AutoXs with the seats up and then down. I didn't note a difference. I'd hate to think that it would matter if the seats were up or down. How flimsy would the chassis have to be if it were made more rigid with the seats up?

It definately makes the exhaust note more pronounced...MMMMMMMagnaflow

 

i don't have a mcs yet, but here's some relevant experience data:

rear fold down seats have a metal plate in them that does add structural rigidity to the chasis.

at track, my group has noticed that there is less rigidity in cars with rear seats removed. a remedy for this would be a roll bar/cage or making a plate (aluminum, cf, etc) to fill the void and add stiffness back into the rear of the car. sometimes a rear strut bar helps too.

can't tell a difference with much lower speed applications, ie: autox, canyon runs, street....

 

There is no difference what-so-ever. Think about it. The seats are split seats. There is nothing even connecting the seats together! They are hinged at the bottom in rubber/plastic grommets. If you are really concerned about performance, you should just take them out and save the 15 or so pounds.

 

[QUOTE=hayaku]



at track, my group has noticed that there is less rigidity in cars with rear seats removed.QUOTE]

What was the car, a Yugo? Any modern car manufactured, does not use the seat pads as a structural member of the frame. If the seats are removed, from a car with fixed back seats, the support frame remains. Usually only the padding and upholstery are removed. If you are sawing off the support frame of the seat back, then yes, to a certain small degree, you are lessening the strength of the frame. Seats with a split back are just that...split. They are not connected. Therefore, cannot possibly offer any increase to frame rigidity.

 

Is there no difference because of the theory of split seats or because you have felt no change from experience? I know they are split, but hey I thought I felt a difference. The reason this post came up was because everytime I think about removing some dead weight, I get the feeling those seats are helping the stiffness and it stops me there. Hayaku hints there may be some truth to the matter. To me, it seems it should make a difference even theoretically only because if you think of all the forces of a car, it's a lot of mass the chassis needs to deal with, even if it's said it's many times stiffer than a 3-series and splitseats or not, it's something that helps the frame hold it's form, yes? The Pilo rear brace or whatever doesn't seem very fortified from pictures either, but maybe that works a little too?

I didn't really think about the speeds.. I suppose at an autocross the difference would be insignificant compared to high speed canyons, if there is an actual difference that is. Thanks for all the feedback so far, more is welcome.

 

[QUOTE=Bisch]E36 M3, E46 M3, E46 325... CCA/SCCA H Prepped race cars, world challenge speed candidates.

yes, they all have split fold seats in the rear. have you taken your seats apart? there is a metal plate in them. and yes, there is a loss of structural rigidity without. thats why we put in welded and reinforced cages.

can i ask what level of track/racing you have pushed your car to to determine that there is no difference?

 

Have you considered a Rear Stress Bar?

http://www.mossmini.com/Shop/ViewPro...eIndexID=41780

 

Nope, not really. Maybe I should use my play jar towards one of these mods too sometime in the future. OctaneGuy, if you have one of these, how well do you feel it works? Thanks guys.

 

I don't have one, but I believe MaxMINI, Randy of M7 has one. You might PM him for advice.

Richard

 

my car rattles more with the seats down

 

[QUOTE=hayaku]

. have you taken your seats apart? there is a metal plate in them. and yes, there is a loss of structural rigidity without. thats why we put in welded and reinforced cages.
QUOTE]

hayaku, I'm not trying to get on your case. I know you don't have your MCS yet. When you do, take the rear seats out. You will see that all they do is "float" in the brackets. They are essentially just dead weight in the car. There is no possible way that they contribute anything to the stiffness of the frame. And yes, I have taken my seats apart (I've stripped the entire interior for that matter). Like what was mentioned above, If you want support, you have to put it there...ie, Pilo's bar.

 

 

Because I'm all about experience for this subject. Thanks.

 

I might think what is going on is that he is having some difference in the weight being shifted from a higher position to its lowered position or even completely out? I'm talking about the seats here. If those seatbacks weigh about 15 pounds apiece, thats 30 pounds that actually work against the suspension system putting weight higher on the center of gravity of the car (think SUV rollover). When those seats are down, thats more weight on the bottom of the car, i.e. more work for the suspension to do and more slippage in the back end. I know its only 30 pounds, but you guys and your weight saving code of ethics, thats a lot of weight to be adding to the rear suspension when its supposed to be doing its own job. Most high performance guys do take them out for that reason, dead weight and no use for the back seat. Just my take on it.......

 

[QUOTE=Bisch]agreed, if you want more structural rigidity, you need to add it.

Bisch, with your entire interior stripped out, what weight is your car at? I figure sub 2250-2350 dry is achieveable, no? no options on the car that is...

 

I cannot give you any weights, as I did not measure. I started out with just the seat back removal, and then the bottom...and then got carried away. I was just trying to shed a little for a few runs at the dragstrip. With the rear seat, pass. seat, carpet, panels etc., there was probably 150-175lbs of stuff in the pile. I had to put it all back in the next morning to haul my family of four . Wifey was not impressed by my actions .

Peter can give you a better idea of weight savings...

 

Being that the latches in the rear seats are allowed considerable side-to-side (opposed to up-down and fore-aft) movement with the seats up, there is nothing in the way of triangulation strength that is achieved there. Any difference in performance is most likely in the very slight lowering of the vehicle cg and polar moment with the seats down, as well as the 30 or so pounds of seatbacks in an essentially suspended/floating configuration instead of rigidly anchored. By the latter I mean that with the seats down, as the car bounces the seats now tend to be isolated in their own 'suspension' as they bounce on their padding while hinged at the back. With the seats up and latched, all car vertical motion transfers solidly into the seatback assemblies through the hinges and the latches. Statically, the car weight has not changed, but dynamically, 30 or so pounds of weight is more or less free to move vertically, occasionally subtracting or adding it's weight to the total.

 

thats exactly why corner balancing should be with a driver and not sand bags and other dead weight...

 

Awesome, so the rear seats are coming out afterall.

 

"thats exactly why corner balancing should be with a driver and not sand bags and other dead weight..."


???
corner weighting is a static measurement.

 

i disagree... body weight is distributed throughout the body from head to toe... weight from as high above the headrest to as low as the pedals and in the footwell. driver with headsock, helmet, hans device, etc can have as much as 10-20 lbs in the head area that moves.

all depends on how competitive you are i guess.

and if you were extremely competitive (ie: paid to drive, make money if you finish and place, lose money if you dnf or worst), you would corner balance the morning of, with driver fully suited and helmet on....

 

corner weighting is still a static measurement, at least for most of us with conventional ride height adjustment. I agree about driver weight placement, at least in the plan layout. I find i hard to believe there would be much corner weight difference if the driver wore his helmet or held it in his lap, however.

 

I dunno about you John, but I have the Williams/BMW Formula One team fly over every morning and corner weight my MINI before I drive to work; wallet, cell phone, and sunglasses in-place, of course.