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[Flagship]

A good solid roll bar would probably do the trick. In FSAE the spec is 1.00inx0.095in round steel tubing, which is pretty solid and can take a lot of sliding and grinding on pavement.

The trick would be designing attachment points that still allow the chassis to flex the way it needs to. I could sketch something up in SolidWorks for you if I had some rough dimensions.

Oh I'm sure it'd do the job, and I'm an AutoCAD nerd so the drafting won't be a problem. I'm just wondering if it'd be legal to compete with.

You could easily add a cage on, but anything added on the frame is going to ruin the handling of the kart. The frame is actually the suspension. You would not dream of welding something onto the coil spring of a car's suspension, right? For the same reasons, you don't want to add any additional structural members to the karts frame. It is a very delicate and complicated system, but in order for the kart to turn, the frame has to twist. Since there is no differential, caster in the front suspension lowers the inside tire and raises the outside tire as you turn. This action twists the frame as you turn the wheels, which then unloads the inside rear tire in order to allow the kart to turn. I have experimented with less caster angle and shorter front axle stubs and it doesn't take too much change to get the kart "out of wack" where you can turn the front wheels and the kart just keeps plowing straight ahead.

To fine tune the "suspension" of the kart, you can buy rear axles with different stiffness specs, longer or shorter wheel hubs, seat braces (which provide a more direct load path from the drivers mass to the rear axle bearings) and even seats with different stiffness ratings. These parts along with various settings such as front and rear ride height, front and rear wheel track, seat placement, caster and camber settings, and various choices for steering ackerman give you an infinite number of things to play with ( and theoretically optimize performance) but significantly altering the frame stiffness and / or bending modes would probably get you into an area that could not be compensated for by the limited adjustment ranges available.

Hmm. So theoretically, mounting the roll bar from two places on the chassis, between which see no twist or bend, shouldn't affect the dynamics at all. But that relies on there being a part of the chassis that sees essentially no load. Is there a length of the chassis that doesn't see any torsion or flex?

 

[Rix6]

Oh I'm sure it'd do the job, and I'm an AutoCAD nerd so the drafting won't be a problem. I'm just wondering if it'd be legal to compete with.



Hmm. So theoretically, mounting the roll bar from two places on the chassis, between which see no twist or bend, shouldn't affect the dynamics at all. But that relies on there being a part of the chassis that sees essentially no load. Is there a length of the chassis that doesn't see any torsion or flex?

As far as legality, I don't think the roll bar itself is specifically agaianst the rules - however, a roll bar does nothing if you are not belted into the vehicle and I believe there is a rule against any type of harness or restraint system.

As far as chassis flex, from what I can tell there is no part of the chassis that does not bend or twist. The front part of the chassis obviously flexes because there are provisions to mount a cross bar between the frame rails just behind the steering pivot points. there are different stiffness bar available to allow chassis tuning in this area. I have tried a variable rate stiffener bar in that location and it does alter the handling of the chassis but not in a good way.

From that point back, the frame rails twist during steering. This twist is significant enough that the rear axle would bind up if the kart manufacturers had not designed in a very clever feature to allow the twist to occur. The axle bearings are very unique in that they have a spherical outer race surface. These bearings then fit into what is called a "cassette" and that piece rigidly mounts to the frame rails. The cassettes have a notch that allows the bearings to slip in at a 90 degree angle (without the axle) and then rotate into the locked position. This design allows the bearings to be fixed so they cannot move vertically, longitudinaly or horizontally, yet they can still pivot as the chassis rails twist.

Maybe more detail than you wanted, but it gives you an idea of the challenge you face if you want to add a roll bar and not mess up the handling of the kart.

 

[JamesCH]

It's not a trivial problem.

How much do Kart's weigh? If it's light enough it's probably not a huge deal...

 

[Rix6]

It's not a trivial problem.

How much do Kart's weigh? If it's light enough it's probably not a huge deal...

Shifter Karts weigh about 240-250lbs.

 

[Flagship]

As far as legality, I don't think the roll bar itself is specifically agaianst the rules - however, a roll bar does nothing if you are not belted into the vehicle and I believe there is a rule against any type of harness or restraint system.

As far as chassis flex, from what I can tell there is no part of the chassis that does not bend or twist. The front part of the chassis obviously flexes because there are provisions to mount a cross bar between the frame rails just behind the steering pivot points. there are different stiffness bar available to allow chassis tuning in this area. I have tried a variable rate stiffener bar in that location and it does alter the handling of the chassis but not in a good way.

From that point back, the frame rails twist during steering. This twist is significant enough that the rear axle would bind up if the kart manufacturers had not designed in a very clever feature to allow the twist to occur. The axle bearings are very unique in that they have a spherical outer race surface. These bearings then fit into what is called a "cassette" and that piece rigidly mounts to the frame rails. The cassettes have a notch that allows the bearings to slip in at a 90 degree angle (without the axle) and then rotate into the locked position. This design allows the bearings to be fixed so they cannot move vertically, longitudinaly or horizontally, yet they can still pivot as the chassis rails twist.

Maybe more detail than you wanted, but it gives you an idea of the challenge you face if you want to add a roll bar and not mess up the handling of the kart.

NP. The more I learn, the better.

I can't believe you can't use a harness at all. And yea, F the rollbar idea if I can't have a belt of any kind.

 

[BigDaddyMS3]

MS3 Opinion

I guess it depends on what you want to do with the car. My daily driver is an Acura TL Type S, (comfortable, gadget heavy, luxury sports sedan). I also have a Roush 427R Mustang that I use for HPDE events in Nor Cal. Fun car, nose heavy feel at track, oversaturated aftermarket, poor gas mileage.

I enjoy AutoX and HPDE, (road course) driving and the MS3 is hands down the biggest bang for my buck! It cost me about half as much as my other cars and gives me so much more enjoyment. Insane amount of power for a FWD car. Adequate mod market. Handles well and for a few bucks more for coilovers and RSB performs great at the track. No major repairs at 22,000 miles but I change my synthetic oil after every HPDE event or every three months, or 3,000 miles, (its a turbo). Only mods have been CAI, Cobb RSB, Barone shift plate, Koni Yellows, Saikou Mitchi OCC. Hankook Ventus on order.

If I had to do it all over, I'd buy a 2010 V6 Mustang, (305 HP) and drive it to Shelby in Vegas for a post title Terlingua application with the supercharger.

 

[Flagship]

If I was going to buy one, it'd be the 2011 GT with the Coyote DOHC engine, no doubt. I just can't do the Mustang thing anymore. They seriously lack refinement and they're too popular among 18 and 50 year old women. Do you know how hard it was for me to find a Stang nearby that wasn't an auto?

 

[BigDaddyMS3]

Flagship

Agreed, the Coyote 5.0 is a completly new engine design for the Mustang platform. It will weigh about 300 lbs. less than the modular 4.6 SOHC and features the Ti-VCT DOHC. One camshaft each to operate the intake and exhaust valves. This allows 412 HP as opposed to 315 HP between them, (stock). The 4.6 is on Wards' Ten Best Engines list and probably the Coyote will be next year. The interior is hard plastic in the 05-09 model years with very little trim and creature comforts that the Japanese easily seem to put in there entire car line. However, the 2010 has made great strides in interior trim appeal and feel, (check one out). The original customer base of the Mustangs were secretaries and when ya sell hundreds of thousands of them per year the only way to have a special one is to buy a Shelby, Roush, Saleen, Griggs, Steeda or tens of other tuner turn key cars, which costs another $15,000 and more above MSRP.
This is why my 07 Roush sits covered in the garage in between track events with about 5,000 miles on the ODO and I drive the MS3 everyday and everywhere, (great bang for the buck car). I'm gonna miss her when my son graduates college and takes her away. But maybe the next gen MS3 will look better by then.

 

[Flagship]

Agreed, the Coyote 5.0 is a completly new engine design for the Mustang platform. It will weigh about 300 lbs. less than the modular 4.6 SOHC and features the Ti-VCT DOHC. One camshaft each to operate the intake and exhaust valves. This allows 412 HP as opposed to 315 HP between them, (stock). The 4.6 is on Wards' Ten Best Engines list and probably the Coyote will be next year. The interior is hard plastic in the 05-09 model years with very little trim and creature comforts that the Japanese easily seem to put in there entire car line. However, the 2010 has made great strides in interior trim appeal and feel, (check one out). The original customer base of the Mustangs were secretaries and when ya sell hundreds of thousands of them per year the only way to have a special one is to buy a Shelby, Roush, Saleen, Griggs, Steeda or tens of other tuner turn key cars, which costs another $15,000 and more above MSRP.
This is why my 07 Roush sits covered in the garage in between track events with about 5,000 miles on the ODO and I drive the MS3 everyday and everywhere, (great bang for the buck car). I'm gonna miss her when my son graduates college and takes her away. But maybe the next gen MS3 will look better by then.

I've driven the 2010 GT. Even with all of the improvements over the 05-09, the 2010's tweaked S197 chassis is still Mustangy, if that makes any sense. Don't get me wrong, I love my Stang, but I'm tired of the live axle, the modified MacPherson struts (not true MacP struts), the quad shocks, and all of the other cost cutting on the chassis. The things definitely have soul, but as I said before, they lack refinement. I love the gear whine, the clicky tranny, and the live axle's anti-squat properties under launch when I'm driving hard, but every other second of the day I feel like I'm fighting with the car.