1.75" vs 2" Round Rail

[LM14]

Reead a comment about this on another thread and got me to wondering.....

What is the difference between the two? Is one size better suited to specific purposes? How about rail size vs horse power? Rail size vs track configuration or roughness?

Always had square rail cars before and we now have a car with 1.75" and another with 2". Everything else is the same except the main rail diameter (Warriors). Which would be better for limited motors and open motors?

Is there an actual difference?

Thanks,
SPark

[billetbirdcage]

My expeirence with 2" square vs 1 3/4" round has shown that the smaller round tube car will cut better in the middle of the corner but have less forward bite and the square car go forward better but don't cut or diamond like the round tube cars. The square tube cars seem to be consistent as far as chassis to chassis, meaning you are more likley to get a round tube car that just doesn't work then a square tube one. By consistent, I mean the frame itself not performance on the track. Every once in a while you can get a frame that for whatever reason just flat don't work, this seems to be much rarer with a square tube car.

These are just my experiences but different maufacturers use different tubing and thicknesses along with tube placement and trianglation that can make all of this react different.

[bizkit]

I agree with b'cage. I really like this 2" round tube TNT I got though

[billetbirdcage]

I will say that if you get thur the middle (a good round tube) better the car will be faster even without the added forward bite (square tube car).

At least in general.

I never had a 2" round car so no opinion here on them.

I seems to me that more people like the 2" rocket then the 1 3/4". The 1 3/4" Rockets, you either like them or hate them not alot of in between on them from what i have heard.

[billetbirdcage]

Spark,

I would have to think when underpowered that the more flex a car has the better off you'd be. I have nothing to base that off of but experience and guessing.

The more underpowered a car is the easier it will bow up or be tight across the middle. No matter how good a driver is or can feel wheel spin, these cars all drive with a lot more wheel spin then you would believe. That small amount of wheel spin the the best driver in the world can not fell, is enought to help the car turn.

Ever put a smaller or less powerful engine in a car and have it bow up more then the more powerful car or be alot tighter. A lot of this is due to the wheel spin that is there with the bigger engine and not with the smaller one.

So this would leave me to believe that because the more flexible cars seem to cut better that this would only help an underpowered or limited car.

Maybe right could be way off.

[Rocket Bonehead]

My expeirence with 2" square vs 1 3/4" round has shown that the smaller round tube car will cut better in the middle of the corner but have less forward bite and the square car go forward better but don't cut or diamond like the round tube cars. The square tube cars seem to be consistent as far as chassis to chassis, meaning you are more likley to get a round tube car that just doesn't work then a square tube one. By consistent, I mean the frame itself not performance on the track. Every once in a while you can get a frame that for whatever reason just flat don't work, this seems to be much rarer with a square tube car.

These are just my experiences but different maufacturers use different tubing and thicknesses along with tube placement and trianglation that can make all of this react different.



I would agree as well, and that seems to be very significant with Mastersbilts (the difference between the two). I will add that based on feed back I have gotten from drivers who have driven both styles of Rocket's (1.75" & 2" round tube), the 1.75" cars were looser cars than the 2" cars, and they struggled to get off the corner. I have found that once you get a 2" car in it's "sweet spot", you can run that same setup pretty much every where you go with maybe one or two changes (regardless of condition).


I will also add that the type of steel used in the car will have just as big of an effect in the handling as the size of the rails. Moly cars will be much stiffer than DOM or mild steel cars, and thus will be much tighter as well. The new Rockets ('05 to present) are MUCH TIGHTER cars than anything older. I have had many people contact me and complain about being too tight, BUT most of it is self inflicted. It is very easy to make these cars too tight.



RB

[LM14]

We are sitting here with a 1.75" round main rail moly car and a 2" round main rail mild car. I guess we were thinking the 1.75 rail car for the open motor (750-800HP) and the 2" rail car for the spec motor (635HP). Figured the moly car would be stiffer even if it was a smaller diameter tube. Will probably try to run each way to make comparrisons next summer.

Thanks, and keep the info coming,
SPark

[billetbirdcage]

I'll add something to RB's statement about moly being stiffer.

Keep in mind that some (if not most) of the cars built out of moly are thinner wall tubing (same strength less wieght) so they may not be necessarily stiffer. Alot is going to depend on wall thicknesses of either tubing.

[Rocket Bonehead]

I'll add something to RB's statement about moly being stiffer.

Keep in mind that some (if not most) of the cars built out of moly are thinner wall tubing (same strength less wieght) so they may not be necessarily stiffer. Alot is going to depend on wall thicknesses of either tubing.


Absolutely... I would agree with that. The only thing I would wonder is if a guy used 'x' meaurement of Mild/DOM, how light would you have to go on the Moly to get a car that has more flex (assuming that two frames were built off the same jig, but with the different types of steel)? I am not an engineer and I don't know of a way to measure the torsional rigidity of a full-size bare frame, but maybe someone out there is and does know how that can be tested.


RB

[bizkit]

Very few of these chassis builders are putting the trangulation in the exact same place, to give a torsional numbers, .25" here and there on all the bars really changes the loads at each traingle. I've did it in the past on some of my cars, but its really just one of those deals. Where you have to find the "sweet spot" as you called it. Once you find that with any car then changes become minimal for most tracks..IMO

I agree, I think a 1.75" car is going to hold side bite longer, which could make a car to tight across the center, thus making it looser off. I had always prefered a 1.75" car but This 2" car I'm in now has been fantastic. It is really a better open motor car than a limited engine car. It was always to tight across the center with the 600HP engine. With this 780HP engine its been great.

Spark, I drove a 1.75" 2002 Warrior over rail car some last year. It was a much better limited engine car than it was open motor. It had to much flex for the speed you would carry in with the open motor and we never could get RF to stick right or we would get the car to soft and it would bounce your eyeballs out.

[Jimmy Judd]

Spark, I drove a 1.75" 2002 Warrior over rail car some last year. It was a much better limited engine car than it was open motor. It had to much flex for the speed you would carry in with the open motor and we never could get RF to stick right or we would get the car to soft and it would bounce your eyeballs out.


I to will fall in line on this 1. my 02 1.75 DOM was a missle as a limited, christ it nearly had a 50% win ratio over 2 1/2 years. Through in the 800hp open motor, compleetley different ride.

[LM14]

.....if I am understanding all so far.....

I would be better off to test the structural rigidity of each chassis in bending (flex) both about a longitudinal and transverse axis and use the more flexible chassis for the limited spec motor and the stiffer chassis for the open motor?

Now all I have to do is figure out is how to tie it down and test them!

Thanks all for coming to a site that is better suited for conversation about ideas, glad to see you all here!
SPark

[billetbirdcage]

I think you need to keep in mind that we are all baseing these statements on opinions. Meaning none of us (I would assume) have tested the rigidity of the frames we are talking about and are asumming that the smaller tube car is more flexible (we could be wrong).

They may also flex different, as one may give easily for the first 1/4" then get stiffer or vise/versa. They just may not have the same curve of flex thru the range of stress on the chassis. We are guessing that the more flex is doing this when it could be just flex curve that is making the biggest difference.

There are alot a varaible that he just don't know.

[Timmay]

Billet's got a good point. You're making an assumption that bigger tubing means stiffer chassis. If everything is equal except for the tube size, then this probably is the right assumption. But, I've seen some builders brace the chassis slightly differently between a big tube and small tube chassis. This can throw everything off.

I think as a general rule of thumb, you can say a "flexible" chassis will be more consistent and less sensitive to setup changes. the down side of a "flexible" chassis is that it will fatigue out quicker. A "rigid" chassis will be more sensitive to track condition changes and setup changes.

I think you can get either a 2" car or a 1-3/4" car to work just as well. I think the optimum setup between the two would be different.

As a side note on Rayburns. Most traveling guys are favoring the round tube over-rail car instead of the under-rail car. I think some guys feel that the more flexible over-rail car is more consistent night after night. These guys aren't concerned about longevity since they have at least 2 or 3 other cars, and they get new ones every year. I know of at least one guy who cuts out some of the bracing in his under-rail car to free that chassis up to flex.

Have fun!

[billetbirdcage]

What up timmay? Glad to see you come over.


I do think there is little question that the more flex a car has the wider sweet spot a car has. Extremely stiff chassis just are right or way off and one small change can totally junk or hero the car. I say leave those to the asphalt guys that have a much more consistant track conditions.

How much flex is to much? Hard to say, with anything you can go to far.

Until there is some hard research done we are all educatedly guessing and at this point that is about all you can ask for.

[Rocket Bonehead]

I would agree with Timmay and Billet. Thru my experiences, there are definitely some different things done with 1.75" cars vs. 2" cars, and the same could be said for round tube vs. square tube.


I would still like to figure out a way to measure the torsional rigidity of a frame, but I don't think it would be possible on a full size model, and I certainly don't think it would be cheap.



RB

[Raider1]

SParky, Both years we won the Burlington 100 lap race with Burgtorf and Erb they were both 1 1/2" round .083" rail DOM swing arm chassis.

More flex, spec engine.



PS: this forum looks good!

[ScottyRocket]

The only way to find out is to do one of 2 things.... Physically test it in bending and torsion or run a computer simulation in Finite Element Analysis (FEA) software.

If you physically test it, you have to constrain the chassis in a way that lets the thing flex how it's suppose to. If you just clamp it down to a bed plate on the bottom rail...that won't work. You kind of need to clamp it down on the roll cage...upside down and then load it front and back for bending and then twist it in someway to get torsion.

Setting up the FEA is also a lot of work....pipe diameters, material properties, wall thickness, loads to use and accurate CAD geometry. Then the setup is pretty time consuming as well. Once all that is complete, it goes pretty fast and has good results.

My thought would be that you won't see too much difference in bending deflection, but torsion should be the biggie.....and of course it's the hardest to measure. It could be that the larger tube chassis are built to be more durable but flex the same. Yes, the larger tube is technically stiffer given the same length and wall thickness. But if you combine that with less cross bracing or vertical bracing you could achieve the same bending with greater durability....IE More races before it "takes a set" or the metal work hardens.