Chassis design Question...

[F22 RAPTOR]

Which design is better, Over-Rail or Under-Rail and why?

I see pro's and con's in both, but what's your take? The Under-Rail I think would be structurally superior, but the Over-Rail would probably be easier to work on and get the mass up higher for easier weight transfer.

[supercomet32]

for me the underslugn cars are just too weak. there isnt enough triangulation for them not to flex. also after seeign the results of chub's car disentigrate in the front end i cant understand why anyone would run and underslung car. the back of the drivers compartment wouldnt have any structural integrity under a similar but rearend collision. ther isnt enough bars between my butt and the rearend with an underslung car.

1. structural rigidity
2. safety
3. the rearend is less likely to take a bite into the ground with the loss of a wheel
4 also more rigid structure to box in the fuel cell

[hall99]

After a recent conversation with a chassis builder I was told that the under rail car would be more rigid vs. the over rail possibly making spring selection a little more sensitive but not really gaining a performance edge either way. Like you said the over rail car being easier to work on as well.

So again only from my conversation with the chassis builder the over rail car would be a little more forgiving setup vs. the under rail car.

[F22 RAPTOR]

for me the underslugn cars are just too weak. there isnt enough triangulation for them not to flex. also after seeign the results of chub's car disentigrate in the front end i cant understand why anyone would run and underslung car. the back of the drivers compartment wouldnt have any structural integrity under a similar but rearend collision. ther isnt enough bars between my butt and the rearend with an underslung car.

1. structural rigidity
2. safety
3. the rearend is less likely to take a bite into the ground with the loss of a wheel
4 also more rigid structure to box in the fuel cell

I'm a little puzzled by your response. You say your Against Under-Rail, yet your descriptions of what you like sound very much Pro Under-Rail. The Under-Rail cars typically have more bars, so less torsional flex, the fuel cell area especially is more structural. And I can't figure for the life of me What Chub's car wrecking in the front has to do with under-rail cars in the rear, Chub drive's Over-rail Rockets... Could you please clarify, maybe we just have our wires crossed.

Under-Rail(Underslung) = Frame rails run above and below the rear end housing.
Over-Rail = Frame rails run above the rear end housing only.

[F22 RAPTOR]

After a recent conversation with a chassis builder I was told that the under rail car would be more rigid vs. the over rail possibly making spring selection a little more sensitive but not really gaining a performance edge either way. Like you said the over rail car being easier to work on as well.

So again only from my conversation with the chassis builder the over rail car would be a little more forgiving setup vs. the under rail car.

Makes sense, Under-Rail would be torsionally more rigid.

[Matt49]

I'm a little puzzled by your response. You say your Against Under-Rail, yet your descriptions of what you like sound very much Pro Under-Rail. The Under-Rail cars typically have more bars, so less torsional flex, the fuel cell area especially is more structural. And I can't figure for the life of me What Chub's car wrecking in the front has to do with under-rail cars in the rear, Chub drive's Over-rail Rockets... Could you please clarify, maybe we just have our wires crossed.

Under-Rail(Underslung) = Frame rails run above and below the rear end housing.
Over-Rail = Frame rails run above the rear end housing only.

Raptor, Comet said he was against underSLUNG not underRAIL. A lot of people call an "over rail" chassis "under slung" because the rear is slung under all the frame rails.

[F22 RAPTOR]

Raptor, Comet said he was against underSLUNG not underRAIL. A lot of people call an "over rail" chassis "under slung" because the rear is slung under all the frame rails.

I see, that's the first I've ever heard that. Around me it's always been that Under-Rail & Under-Slung were the same, going back to 1985 when I first got involved. We had Custom Chassis cars back then that were Under-Rail/Canti-lever cars. Thanks for clearing that up.

[supercomet32]

I prefer cars with a box of rails triangulated both on top of and below the rearend assembly...I refer to that as underslung.

the front end triangulation on a rocket (I drive rockets as well, modified with bolt in structure under the rearend to both stiffen the chassis and ad protection) is constructed creating a box around the engine compartment which is essentially the same thing as a underrail type construction. Chub's car came apart even with all that front end triangulation. there is no way i want a underslung car with nothing under the rearend or fuel cell

[phenom08]

If you back into the wall with an overail probably get by with just a clip an underail will transfer into the center of the car.

[F22 RAPTOR]

If you back into the wall with an overail probably get by with just a clip an underail will transfer into the center of the car.

I could see why someone might think that. The older GRT Under-Rail format I thought held up pretty well. I've known a few of those that got by with only having to reclip the fuel cell area, multiple times, not Sure About the GRT over-rail though. Maybe it helps having the rails under the rear end to be offset inward to keep the impact from moving into the driver area.

@ Supercomet32 Was the extra triangulation bolted in or welded? I would think welded would've held up better.

[supercomet32]

My underrails are a triangulated section built on a jig. it consists of two rails and that attach at each end to the frame and 2 cross pieces and an x going under the fuel cell. it takes 8 11/16 bolts to attach it to the car and then i fabricated two brakets using the 2" round tube clamp design but in steal versus aluminum and welded one to each end of a foot long piece that in the event the 8 bolts break the bolt in sub frame section is still held in place. not as strong as welded I know but its just as strong as the bolt in front shock brace and a hell of alot easier to remove the rear end and fuel cell when you need to get under it to work or rebuild it over the winter.

[F22 RAPTOR]

My underrails are a triangulated section built on a jig. it consists of two rails and that attach at each end to the frame and 2 cross pieces and an x going under the fuel cell. it takes 8 11/16 bolts to attach it to the car and then i fabricated two brakets using the 2" round tube clamp design but in steal versus aluminum and welded one to each end of a foot long piece that in the event the 8 bolts break the bolt in sub frame section is still held in place. not as strong as welded I know but its just as strong as the bolt in front shock brace and a hell of alot easier to remove the rear end and fuel cell when you need to get under it to work or rebuild it over the winter.

Is this the sort of thing that was mentioned to be on Chub's car?

[supercomet32]

No I just feel that given the amount of tubing in the front versus the rearend that seeing how chubs car came apart in the front as it did the rear would be far worse and also given that there isnt anything solid between the rearend and the drivers butt on an underslung car that either I would only run an overslung or underrail car or modify the chassis as i did to add protection to both myself and the fueal cell if the rearend came out form under the car

btw why do they call it overslung...shouldnt it be throughslung since the rearend has to usually be fitted through the bars to mount it up