IRS LOADING DISPARITIES
IRS LOADING DISPARITIES
(OP)
Some 48 years ago, I was taught that, with an IRS, right-to-left load variations are unaffected during acceleration. But, I just realized that, if anti-squat is present, some of the reaction torque must be diverted to appear as vertical loading on the unsprung mass, resulting in a load disparity opposite to that which occurs in a beam axle. This would be a function of the relative compliance of the gear housing mounting and the suspension links, of course.
So, has anyone investigated this and, perhaps, established a relationship between load disparity and percent anti-squat? Is the disparity even significant? Obviously, if it was as bad as that which occurs with a beam axle, it would have been immediately noticed. So, how bad is it?
So, has anyone investigated this and, perhaps, established a relationship between load disparity and percent anti-squat? Is the disparity even significant? Obviously, if it was as bad as that which occurs with a beam axle, it would have been immediately noticed. So, how bad is it?





RE: IRS LOADING DISPARITIES
RE: IRS LOADING DISPARITIES
Cheers
Greg Locock
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RE: IRS LOADING DISPARITIES
I've seen the above related topic elsewhere and presented the logic that the effect is going to be dependent on the relative roll stiffnesses of the front and rear suspensions and the torsional stiffness of the chassis, and is independent of anti-squat (up to the point where one front wheel lifts clear of the ground, anyway). I did not attempt any derivation or present any numbers.
Anti-squat needs to work from the longitudinal traction forces, which are dependent on the wheel loads, so that effect is a step downstream from the effect of engine torque reaction and the X-axis stiffnesses. A-S may also be of unequal percentages, left vs right, so the A-S share of wheel load won't necessarily be the same L vs R even if the instantaneous vertical wheel loads happened to be identical.
Norm
RE: IRS LOADING DISPARITIES
Best example of this is in the ~1988 Camaro or MX5, where the diff is part of the engine structure. Then there is no external Tx, only a Ty.
Cheers
Greg Locock
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RE: IRS LOADING DISPARITIES
The MX5 may be different.
Norm
RE: IRS LOADING DISPARITIES
(Norm, it sounds like we've both been encouraging dragracers to increase the ratio of rear-to-front roll stiffness. A few of them are putting big bars on the rear, but it's like pulling teeth to get them to remove the one at the front! And, this next season, a few will be running higher rate springs at the right front.)
RE: IRS LOADING DISPARITIES
And if you get sideways half way down the track at a reasonably high speed, that could be even more interesting.
RE: IRS LOADING DISPARITIES
But, I would agree that there's a better way to achieve a more stable launch. Specifically, the driveshaft torque can be dynamically canceled by forces in an asymmetric link arrangement and the rear (or front)suspension springs don't even have to be involved. That's certainly a much "cleaner" way to do it!
RE: IRS LOADING DISPARITIES
What's of somewhat greater concern is that some (many?) of these cars are street-driven, and that not all of those who have taken this approach understand that this is not a particularly street-friendly set-up under all likely conditions. A few that do recognize this and take it seriously (or have perhaps had a less than pleasant experience) have mentioned disabling the big rear bar for the street.
Billy - from time to time I actually do see some discussion regarding the removal of the front bar or the disconnection of at least one front sta-bar endlink for strip duty. But I have no idea how representative that is of the way the typical drag racer's car shows up in staging. And I'm a bit skeptical about how many of those that do either of those mods understand that they're tinkering with the front:rear roll stiffness distribution in addition to losing weight off the front or allowing the front to rise a bit more easily.
Norm
RE: IRS LOADING DISPARITIES
It worries me that guys in the lower street classes might start fitting huge rear antiroll bars, and then try to drive to work every day in the same car.
RE: IRS LOADING DISPARITIES
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