57 Chassis C4 Corvette Front and Rear, Stage 4 + SS Kit + 32 Gallon Fuel Tank by Hot

[rat_rod_russell]

Originally Posted by ccracin

Technically, that is not correct. With an independent set up like you have all torque loads essentially will be reacted by the center section. The knuckles in this case are just carriers and do not react any torque. If they do, you have a bad bearing. Therefore when under acceleration the wheels are pushing forward on the chassis. Consequently all 4 bars of the 4 bar are in compression with this design. This is unlike a solid rear axle with fixed bird cages and a 4 bar. As I said before, I can't say that you will definitely have a problem without much more info. If you have run this before and have success then you should be good. It never hurts to discuss these types of things. The chassis looks nice, I'm sure your customer will be pleased. Keep up the good work.

And I appreciate the conversation. So many people treat IRS suspension like a black box and never really discuss it. I was of the understanding that on the C3 / C4 corvette suspension and Jag type IRS suspensions that use a U Joint half shaft for the driving shaft AND one of the suspension links that a percentage of the torque reaction was pushed out to the knuckles?

And your right I got my link forces backward. I sat down to draw it out and realized my mistake. What can I say, I'm dyslexic and I still get my left and right backwards all the time. I'll leave my post unedited so I can receive my flogging.

I know right now I have a 71 corvette and a stock 88 corvette in my shop both getting work and I've driven both quite a bit in the last few days (buddies cars, they told me to ). The 71 with its single forward arm (and very short instant center) will squat if you look at it wrong. Stand on the brake and put it into gear and the back end will try to squat, any acceleration with traction will squat hard and the moment you break traction the back end tries to jump from the unloading spring. The 88 (and my past 57's) don't squat like that because of the dual forward arms. The instant centers moved up to the front of the car giving the load a longer lever against the car's suspension. Is that not torque reaction transmitting through the suspension to the tires?

Thanks again
-Russell

[ccracin]

Originally Posted by rat_rod_russell

And I appreciate the conversation. So many people treat IRS suspension like a black box and never really discuss it. I was of the understanding that on the C3 / C4 corvette suspension and Jag type IRS suspensions that use a U Joint half shaft for the driving shaft AND one of the suspension links that a percentage of the torque reaction was pushed out to the knuckles?

And your right I got my link forces backward. I sat down to draw it out and realized my mistake. What can I say, I'm dyslexic and I still get my left and right backwards all the time. I'll leave my post unedited so I can receive my flogging.

I know right now I have a 71 corvette and a stock 88 corvette in my shop both getting work and I've driven both quite a bit in the last few days (buddies cars, they told me to ). The 71 with its single forward arm (and very short instant center) will squat if you look at it wrong. Stand on the brake and put it into gear and the back end will try to squat, any acceleration with traction will squat hard and the moment you break traction the back end tries to jump from the unloading spring. The 88 (and my past 57's) don't squat like that because of the dual forward arms. The instant centers moved up to the front of the car giving the load a longer lever against the car's suspension. Is that not torque reaction transmitting through the suspension to the tires?

Thanks again
-Russell

First let me say I am not overly familiar with the differences between generations of Vette IRS designs. I am merely speaking from looking at general geometry.

What you are talking about with one design squatting and the other not has to do with the percent ani-squat built into each design. Anti-squat is independent of torque reaction. This is completely geometry dependent. The theoretical convergence point of the 2 links forms the Instant Center. The location of this instant center in relation to the CG is one of the factors that go into this calculation. With this in mind if you look under the newer car as you state both arms are point up to the front of the car. On the older design or single arm design this angle is not as steep. With the 2 arms pointed up to the front, when the tires start to roll forward and push the chassis the tires are forced down as they try to drive under the chassis. The reaction to this is actually trying to lift the chassis to some degree. This counter acts the reaction to the torque being applied to the center section. This reaction is trying to lift the front end of the car and because of the moment arm length, the rear goes down. The center section and it's mounting are the only components that are affected by torque. Without this angle, there is less to counter act the torque being reacted from the center section so the rear squats.

These are just my thoughts on what you are seeing. Suffice it to say, I still believe your links will be in compression during acceleration. So, as you are accelerating out of a corner with body roll involved you will be loading those links in compression and bending. Is it going to be a problem? Don't know. Could it be? Yes. Were it me I wouldn't take the chance and just tweek the bar design a bit. I attached a quick sketch of how maybe to change the swaybar mount to stiffen the bar and not worry. Anyway, please don't take any of this as more than some interesting conversation. I love talking about this stuff. Keep up the great work!

[rat_rod_russell]

Originally Posted by ccracin

First let me say I am not overly familiar with the differences between generations of Vette IRS designs. I am merely speaking from looking at general geometry.

What you are talking about with one design squatting and the other not has to do with the percent ani-squat built into each design. Anti-squat is independent of torque reaction. This is completely geometry dependent. The theoretical convergence point of the 2 links forms the Instant Center. The location of this instant center in relation to the CG is one of the factors that go into this calculation. With this in mind if you look under the newer car as you state both arms are point up to the front of the car. On the older design or single arm design this angle is not as steep. With the 2 arms pointed up to the front, when the tires start to roll forward and push the chassis the tires are forced down as they try to drive under the chassis. The reaction to this is actually trying to lift the chassis to some degree. This counter acts the reaction to the torque being applied to the center section. This reaction is trying to lift the front end of the car and because of the moment arm length, the rear goes down. The center section and it's mounting are the only components that are affected by torque. Without this angle, there is less to counter act the torque being reacted from the center section so the rear squats.

These are just my thoughts on what you are seeing. Suffice it to say, I still believe your links will be in compression during acceleration. So, as you are accelerating out of a corner with body roll involved you will be loading those links in compression and bending. Is it going to be a problem? Don't know. Could it be? Yes. Were it me I wouldn't take the chance and just tweek the bar design a bit. I attached a quick sketch of how maybe to change the swaybar mount to stiffen the bar and not worry. Anyway, please don't take any of this as more than some interesting conversation. I love talking about this stuff. Keep up the great work!

Holly crap I can't believe I forgot about this. Just got cough up in work and it went to the back of my head.

But the way I understood it was that the torque reaction trough the diff on a live axle was why the the instant center of the froward arms was pushed so far back in the car, closer to the center than the front of the wheels. So I thought the torque reaction would transfer through the cv or half shaft and would influence the anti squats location because of that transfer. Is that off track?

-Russell

[legend]

over time it'd rip the threads out of the top of the diff

[rat_rod_russell]

Originally Posted by legend

over time it'd rip the threads out of the top of the diff

there are no threads on the top of the differential, so ripping them out would be difficult. FYI the rear wing bushings are 90 series urethane so they won't deflect like normal rubber or even the 60 series urethane most bushing are made from.

-Russell