under slung,..over run????

[dirty white boy]

witch is better an why?? under slung chassis or over run chassis???

[ALF401]

Underslung!!

I hope the better is an underslung.........that's what I have!

[twisterf5]

upper slung has more flex. it is really what the driver likes most all my wins were in upper slung. ran lower slung last two years and our new car is back to upper slung this year.

[grt74]

underslung,takes the some of the flex out,overrail flexes more,jimmy owens(bloomer car)is an underrail and he sure has won a ton of races,i would rather use my shocks and springs than depend on chassis flex,of coarse if it is a ridgid chassis if you make the wrong adjustment it will magnify it but thats another question altogether

[4bangerhotrod]

i like a under slug chassis, although most car's today are over rail most of this is because of the travel and movement of the 4 bar car's and weight saving's, but underslung car's are making a comeback. i prefer a underslung car because they are stiffer car's and tend to react better to change's, but it makes it easier to tune yourself out of the ballpark. the over rail cars work fine they just have alittle more flex which make's for a bigger sweet spot that will help the car be better in all condition's and a wrong adjustment wont ruin your night you'll still be able to drive the car. overall it's driver preference and setup skill, i dont think your going to win race's just because you have one or the other.

[dirty white boy]

thanks for the replys,..wouldnt a chassis that flexed be more prone to cracking???

[4bangerhotrod]

the more the metal flex's the more fatigue it will have, it will crack weld's and wear the tubing out to where it loses strength. that's why a car with 2" main rails will last longer and be competitive longer than a car with 1 3/4" main rails, the smaller rails will lose there strength and the car will start flexing more and more eventually getting to where you have to make major adjustments to feel any change in the car. thats the reason most of your bigger driver's get new car's every yr, or they will get one new car for there primary car and move there primary from the previous yr to there backup car. once the tubing get's wore out the car just dont react to adjustments like they should. alot of guy's run bloomquist car's multiple yrs because they are built like a tank and dont have alot of flex built into the cars, an the flex they do have is built into specific area's which helps them last and take adjustments longer. not saying a old car cant be competitive because they can it just take's more work and not as consistant as a new car would be. underslung and overrail come's in there to, a underslung car will be stiffer than the over rail will be so the stiffer underslung wont flex as much an fatigue the tubing as quick.

[zeroracing]

I am going to agree/disagree with the post so far. I will agree that the underslung will flex less, if twisted from the front and back bumpers. This issue is we do not twist the cars from those points. We twist from 4 link mounts, spring mounts to front mounts. The only items that connect behind the main cage (what I would call the start of the rear stub) is the shock and spring mounts. With the arrangement of tubing in a traditional underslung practically no real spring load force will travel through these tubes. For structural design GE box structure around the rearend as viewed from the side is horribly inefficient. Your load will go into your upper rails in bending and your brace to top of halo, beyond that point I would bet much more compliance happens on the channel piece used for the shock mount than in the actual cage itself. Flex, twisting, all of this is about loads and load paths. The high load areas are going to be from four bar links forward. Of course swing arm or something like that throws this out the window.

Think of it like this, I have a bridge, adding reinforcing and bracing beyond the actual bridge, on the ground afterward will do nothing to strengthen, of course barring some type of cable structure. Another way to think of it is, does a stiffer front bumper make the car handle different?

The underslung does make the car more rigid for rearend crashes, this is probably why you see them on bloomquist cars, it will make the car stronger for impact. Now an over slung can tend to be weaker, but putting a new rear stub on a car is not complicated, nor even needed often (in last 5 seasons with overslung never being bent).

The positives to overslung are, weight is higher, less overall weight, and my favorite much easier to work on. Now always remember on a tacky track tubes catch mud, mud weighs weight... So static clean weight my not be the only negative. Finally, depending on roll over, older mods often would dig the underslung on the Rr into the track, not always an issue but you must always keep it in mind.

That said is is all preference both can win, both do win, both are fine just two ways of doing it.

[HEAVY DUTY]

Zero covered it all. One more thing to think about is that with an overrail car, the damage on the rear clip is less likely with an overrail because there isnt anything hanging down to hit and the car will likely go under which will deflect damage. An underslung car doesnt deflect and can take a solid hit which can bend it. They do protect the fuel cell better. There isnt much if any difference in weight because the overrail cars have larger diameter heavier tubing, whereas the underrail cars use an over and under smaller tubes. The weight difference is about the same as that dinner the driver ate.

[4bangerhotrod]

so you dont think the tubes, connecting from under the 4 bar brackets to the rear clip make the car stiffer, i dont understand how it couldnt, maybe you need to do some testing to see it does transfer more weight from corner to corner. its not a whole lot but it does transfer more.

[zeroracing]

so you dont think the tubes, connecting from under the 4 bar brackets to the rear clip make the car stiffer, i dont understand how it couldnt, maybe you need to do some testing to see it does transfer more weight from corner to corner. its not a whole lot but it does transfer more.

I did say there may be some, do not see much though, all suspension points either start before the underslung or are just shock and spring mounts, which most all of their load will be into the upper frame, with compliance in the mounts. The proper way to test it would be to jig two frames of identical build only one under and one over. Then twist using only 4 bar mounts, with max spring mount loads under 1k. Then see or determine a difference. There may be some, but not a major difference on cars.

[3wheelinphotos]

This question always make me laugh....how many of your race cars don't have top rear frame rails becauase it has under rails? It's not a question of overraill vs under rail. It's to under rail or not to under rail, ive never seen a DLM not have top rear fram rails.

Here at Warrior in the mid 2000's we did build ea style a lil differnt if it was a"overrail" car it had larger diameter rear rails than if it was built to have underrails then "overrails" were smaller. But sense 2007 all of our cars have the same diameter rear main frame rails and under rails were a option to our customer untill 2010 when they became standard.

So look at it that way to under rail or not to....

[Matt49]

Has anybody ever messed with some sort of "bolt on" under rail setup?

[JHobbs26]

Has anybody ever messed with some sort of "bolt on" under rail setup?

This is available from GRT

Bolt-On UnderRail Frame Kit
* No Welding Required
* Will Stop Flex in All Conditions
$300.00 Including Powdercoating

[fastford]

i personally agree with zero on this one, but would like to say that i prefer an under rail chassis. i dont understand the more travel theory on the overslung chassis, if you have to use a chain to limit travel, whats the advantage? most underslung chassis have moved the rail in board and put a slight bend in it to give more than enough travel . if you over extend shock either way your backing up.