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Author Topic:   Chassis flex.... good or bad?
JDF Motorsports
Member
posted November 01, 2003 11:25 PM
well some peopel biuld there cars to flex on pourpous in serton spots like the biknell dirt modifides to gain more bite i dont know much on it just remebering hearing it on speed watching the 358 mods

[This message has been edited by ssr1st (edited November 02, 2003).]

racer17j
Member
posted November 02, 2003 09:46 AM
it just depends on the rules alot of times personally i think in limited engine classes with no adjustable suspention parts it's good to have some flex in them we always got crap because we would never connect the stubs on our nova's but they were always fast and handled great but seamed like the guys that did connect them had a push more often then not. in my class we are not alowed to have any bars go thru either fire wall so on mine this year i tried putting my left kicker bar in as tight as i could get it and on the right side made it so it just fit didn't force it in like the left the car seamed to be alot better thru the middle of the corner then it was last year


snowman
Member
posted November 02, 2003 10:39 AM
The general consensus seems to be that a chassis that will flex is "more forgiving" than a ridgid chassis......"Missing the set-up won't hurt you as bad as it would if the chassis were stiffer".........

Ask the experts and that's what they will say. How do they know?? Well,that's what everyone says, all the mag articles, all the books.....

Must be Right.....Right????????

You will have to decide for yourself.

Personaly, I believe that suspension points should be very stiff.....

The whole "flex is better" idea has some holes in it.......First, they are pre-suposing that the "give" will be in the desired direction......Rarely would that be the case.......For example,the flex or "give" in lower a-frame bushings.....is this a good thing?? No, You are losing camber control and there probably wasn't enough built in, in the first place......

Next, they are making the chassis serve as a sort of "variable rate spring".....Few racers want to use those......

In short, I believe that suspension control should be left up to the shocks and springs.........and eliminate as many inconsistancies as possible.......

A person would have a very dificult time qualifing or proving that any flex is better......Not so difficult to field a discussion against it.........

In the case of a stock stub, it has quite a bit of flex.....Even if I believed that "flex is better".....(which I don't), I wouldn't try to build any more into it.

Good luck,
Snowman


snowman
Member
posted November 02, 2003 10:43 AM
Sorry 17.....not pulling your chain, posting at the same time


66jj
Member
posted November 02, 2003 01:22 PM
SNOWMAN,

Finally someone else on here who say, facts, not well I drive with two left shoes and win so you should...

Another thing to add is if your car flexes much it will eventually break. Thats why mods arent ran for long by top teams.



zeroracing
Member
posted November 02, 2003 02:20 PM
I am no rocket scientist,but adding flex to street stock may be a combo I would stay away from.

Don't we base our race set ups on weight transfer? Adding chasssis flex into the combo adds a unknown figure into a set up.

Sure we would like our chassis to respond to all the set ups we would put into it,but our cars are bigger,heavier,and are limited to suspension changes. We set back and watch the mods and late models race,see all that roll center,chassis flex,left tire off the ground and all the fancy geometry at work,but our street stocks are still based on rules that surround the "rules of stock appearing" or "using oem parts". When people talk about flex,that tells me that there is a weak link somewhere.....something,somewhere is going to break after all the abuse we give our cars.

When I look at building a car,I look at a rigid chassis to have my suspension to work off of. I do build "crash zones" into my cars.....meaning an area in the rear of the car and front of the car where an impact will more damage to the body and bumper area before it gets anywhere near the main chassis.



racer17j
Member
posted November 02, 2003 09:17 PM
don't get me wrong guys on our hobby stock we build them completely different with the x in the frame the the position of the front and rear bars but for my rules i can't x the frame or have front or rear hoop bars so it's gonna flex reguardless i'm just using the flex were it will be better for the car. we are on out 4th different design for this class and it seams to work the best for us so far like this. i will be adding 2 more rear bars this year to see how that effects it


SLEEPY GOMEZ
Member
posted November 02, 2003 09:18 PM
Hey Snowman, I think you have it right. If I may, let me add: When a chassis flexes under load it is a spring. In this case it is a spring that is not dampened by a shock absorber. You only have to drop a spring on the floor to see what an uncontrolled spring does. When a chassis flexes it is wearing out. It may be good now but will go away slowly, maybe so slowly you don't notice. I have never had the opportunity to X ray a chassis before and after a season but I sure would like to. Since this seems to creep into these conversations about flex, what about karts? They do have asuspension. A kart chassis is , in simple terms, two longitudinal torsion bars with one shock asorber - the driver. Now if we could solid mount the axles to the chassis of a Monte Carlo and put the engine in sideways at the rear it should be light an fast. Oh yeah, It sure would take a big driver the be the shock absorber. SLEEPY


robhbk24
Member
posted November 03, 2003 04:07 PM
Flex is for throwaway cars. Build it stiff. It makes the chassis more predictable, and it will last longer.


racerguy500
Member
posted November 03, 2003 05:59 PM
If your chassis flexes you will definitely feel it in the corners bogging down and notice it when they start going around you, especially on a dry track. Like Sleepy said, (I can't believe I actually agree with him on this one) but it becomes a spring, an uncontrolled, unrated spring that keeps getting worst and you can't tell it or notice it. Build it rigid side to side to prevent flex, let the flex happen when it takes a hit straight on or from behind. Good luck


ssr1st
Member
posted November 03, 2003 07:04 PM
hey 17 talk to your track owner and have them make you run a front hoop and rear kickers its stupid not to run them someone can get hurt real bad without them look at demo cars ive seen guys with there engines pritty much on there laps its not for a racing advantage but a safty factor. if theres a wreck and someone gets hurt i bet they will be wishing they had em. a guy at our track stoped dead in the middel of the track and a guy rearended him he was glad to have the front hoop ill tell you that much.

[This message has been edited by ssr1st (edited November 03, 2003).]

racer17j
Member
posted November 04, 2003 07:09 PM
all we can run is bars in front of the radiator the braces have to stay in front of the a frames and we run bars in the back to protect the fuel cell. if i said anything to un they would tell me to just move up.


dan ferry
Member
posted November 14, 2003 08:04 PM
that sounds like what they would say and probably say we are trying to keep it an affordable class. my question is wyhat is so affordable about injuries or having to build another car because of a crash that u could have kept on racing after if u had frt or rear hoops..


racerguy500
Member
posted November 14, 2003 09:22 PM
No offense, but I have never heard of or seen a car that was crashed that a front or rear loop saved or would have saved the car itself. I have seen the rear loop save the fuel cell and the driver, but never the car and most tracks allow them. The front loops become battering horns and rough driving gets much worst. They offer nearly no support to the chassis other than frontal impact but with the light tubing we run it won't save the car by any means in a hard crash. And Racer17j didn't make the rules, just has to run by them as we all do. Thanks and good luck to all of you.


zeroracing
Member
posted November 14, 2003 10:28 PM
we have all seen how well a super strong front ends works in a crash just ask earnhardt oh ya the stiff front end on his car is one of the reasons he's no longer with us along with a bunch of east coast mod drivers if the front end doesn't give in a head on crash you do.one thing they do account for in our class tho is we have to run the stock colum less likely to spear you in the chest in a crash that way


zeroracing
Member
posted November 15, 2003 12:16 AM
i realize that nascar is not the same as us saterday nite dirt trackers but my point was guys will take and build an entire car out of 1 3/4 tubing to make it so stiff that you wouldn't believe and think that makes it safer which is not the case. believe me if it was my choice i would run full front and rear hoop bars but in order to do that i would have to move up a class and there is no way i could ever afford to run up front in that class like i do in this one i would be a mid pack car at best, where all the other broke guys run and thats where most of the stuff gets torn up


cautrell05
Member
posted November 16, 2003 12:09 AM
This pic was taken the morning after I rearended a parked car going 60. The other guys bumper went over mine and used the bars as a cushion. It hit hard enough to push the water pump shaft into the timing cover, but the bars saved the motor. A properly designed front hoop is a very good idea.


neil rucker
Member
posted November 16, 2003 01:28 AM
im really more of a novice than alot of ya, but i think a stiff chassis would react to adjustments better or maybe the driver can feal whats going on, and feel the changes better. seems like your forcing the tires to work more this way. got to be better. tell me if im not right. i wont get bent out of shape. thanks, neil


racer17j
Member
posted November 16, 2003 01:49 AM
something like that our cars could take no problem with the limited bars we use


racerguy500
Member
posted November 16, 2003 08:47 PM
I don't disagree with bracing the front end. If you run two angled supports from the front cage uprights near the dash bar down to the frame behind the front control arms and a bar in front of the radiator with angle supports you have what you need. A full and complete front loop runs a single bar all the way from the uprights to the radiator area with some support bars down to the frame. Something has to give and a crash in any case is going to take the frame with it if hit hard enough. The car in the picture was saved because as he said, the other car went over his bumber so the frame damage was minimized. I think we all are arguing the same point here though. Keep it from twisting and flexing, but let it absorb frontal impact. Thats the way I build them for me and all my customers. We have cars with front loops in some divisions and some that don't allow them, in either case, the damage is about the same given the same circumstances and we have frames to repair. And .095" tubing isn't that strong on its own. It requires cross bracing and gussets to build strength. Overbrace and you loose the ability to absorb shock. Good luck to all of you.


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