Tube frame car

[Greg F]

Suppose a 2nd gen RX-7 were totally cut up to make a Solo 2 car (using only the engine, drivetrain and suspension) what kind of tubing would have to be used for the frame?

Would the tubing have to meet the specs for rollcages outlined in the rules?

[Tony Kloosterma]

modified rules are pretty lenient

i would suggest on the side of safety that the tub be made out of roll bar material that is to spec.

Tony

[andrew1984]

greg there is no spec other then it being fire proof.



a good choice would be to use rollbar sizing..

[Brent]

Greg, check out some kit car sites. Most smaller 4 cyl. kits use 1" by 16 gauge tubing. The roll bars/cages are made of larger/stronger tubing.

[spanked apex]

Ohhhhh Greg,
the rust is that bad, huh? :(

[Marsh]

Greg the only spec is for the cage it self. So what you do is design a cage tha IS the frame. The front and rear sub frames can be anything you want. Roll bar tubing is over kill. You only need it to take suspension loads no impacts. In an impact you want the subframes to bend and absorb energy.

I thought you were a mechanical engineer? If so pick-up "Race Car Vehicle Dynamics" by Milliken and Milliken. With it you can calaculate the suspension loads involved and build in a reasonable factor of safety.

I've seen reliable SAE cars with suspesion tubes that looked like McDonalds drinking straws.

[Greg F]

I'm thinking the best idea is to just buy a roll cage, install it, then attach tubing to hold the rest of the car together...and start hacking away everything else.

Curtis, 170 hp in a 1200 lb vehicle does sound nice doesn't it? But 150 hp in a 2700 lb vehicle doesn't.

I'm still a little iffy on the whole idea though, but it is very tempting indeed.

[Wedge]

Originally posted by Marsh

I've seen reliable SAE cars with suspesion tubes that looked like McDonalds drinking straws.

They may be reliable, but how much chassis flex do they get in corners?

[max attack]

You'll never get a 2nd gen rx7 down to 1200lbs!:D

Sounds like c-mod might be fun this year.:cool:

[Greg F]

Originally posted by max attack
You'll never get a 2nd gen rx7 down to 1200lbs!:D

Sounds like c-mod might be fun this year.:cool:

Really, eh? I was actually thinking more like 1000 lbs. :p The cost for this project seems to be very good so far, but I'm not sure this car will be ready in time to run any events this year.

[Marsh]

Originally posted by Wedge
They may be reliable, but how much chassis flex do they get in corners?

VERY little. The tubes were loaded completely axially. In such an arrangement you get little to know "flex" as all bending is Euler bending. Generally it feels completely stiff until it bunkles and fails comletely (which I've seen).

Chassis flex rarely occurs at the suspension. It usually occurs at the engine, or drivers compartment, or any other spot where a big hole has to be made.

[Ron]

Originally posted by Greg F
Really, eh? I was actually thinking more like 1000 lbs. :p The cost for this project seems to be very good so far, but I'm not sure this car will be ready in time to run any events this year.

Greg,

I took an '86 GXL and made it into a tubed framed car (super seven clone) It took 3 years and it weighs 1400 lbs. Of course if I was to do it again it would take 6 months and weigh 1100 lbs :) I think if you were to add up the weight of the parts you need like mechanical and electrical bits of a 2nd gen minus the chassis, glass and soft interior stuff you would end up with more than 1200 lbs. Everything is big on those cars, like the passive rear steer sub frame. However, because of that, things tend not to wear out. Things like pads and tires. So it is not such a bad donor car, but don't kid yourself on how light it is going to be.

Ron

[dgg]

this would certainly solve any issues with insuring a vehicle that competes in solo2...

[Greg F]

Originally posted by Ron
Greg,

I took an '86 GXL and made it into a tubed framed car (super seven clone) It took 3 years and it weighs 1400 lbs. Of course if I was to do it again it would take 6 months and weigh 1100 lbs :) I think if you were to add up the weight of the parts you need like mechanical and electrical bits of a 2nd gen minus the chassis, glass and soft interior stuff you would end up with more than 1200 lbs. Everything is big on those cars, like the passive rear steer sub frame. However, because of that, things tend not to wear out. Things like pads and tires. So it is not such a bad donor car, but don't kid yourself on how light it is going to be.

Ron

So it is possible then, lol. Even at 1500 lbs it'll be an awesome performer. As for the suspension... I have some tricky ideas, but I'll have to spend a weekend in bed with the rule book first. :D

[spoonie]

ewww

[njansenv]

Sounds like a fun project Greg! Have you considered going the Super 7esque route. (ie: Locost) Weld up just the frame per Championmotorsports design, save on bodywork, and use the RX-7 as donor?

Nathan

[njansenv]

Some interesting reading, locost based but reasonably generic:

http://locost7.info/files/chassis/kitcaranalysis_V2.doc

[Greg F]

It looks heavy. :o

[njansenv]

lol. How light do you want to go? 171lb chassis with a 'stiffness' of 2500+ ft/lbs per degree twist. Should be relatively easy to build a 1500lb STREET car starting with that, less if you want to make it a track toy.

Nathan