G8 GXP review - wheelhop?

[Robert91RS]

Monday I will take a look at the old GM catalog and see if I find anything about the G8 axles but I can't remember if the GXP is in the system yet.

[SoFlaZ]

Just try to ignore the riced 4th gen v6.
I can't find anything about the G8's shafts.

[camaro5]

CORVETTE ZR1:

GM uses unequal-diameter half-shafts in the rear - 40mm on the left, and only 33mm on the right. Although the manufacturer has not explicitly stated why it does this, it's very likely that the left shaft experiences larger torque loads during hard acceleration. Making both shafts the same diameter would result in increased weight, and the Corvette team fights for every pound.

http://www.autoblog.com/2008/01/14/d...assis-display/

GM won't explain, but autoblog thinks, and it sounds reasonable, that it is done for weight savings alone.

The physics of unequal LENGTH half-shafts on a Front wheel drive car, to prevent or diminish torque steer, should not be confused with issues and remedies for axle hop on a SRA or IRS vehicle.

EDIT: I believe they want the half shafts EQUAL LENGTH on FWD cars to lower torque steer.

[carfansince73]

20 mpg highway... OUCH. That final drive ratio the GXP gets is most likely the reason. It doesn't weigh much more if any than the G8 GT, and they just wanted the quickness right from the factory. They should have made those gears a no-charge option. I know the AFM isn't there, but it could have been a little better to keep it out of the tax, or at least a smaller dollar amount. :(

[fbodfather]

Important to understand that the G8 is not the same as the Camaro.

G8 is, for lack of a better term, "Zeta 1" -- and the Camaro is "Zeta 2" -- many more improvements.

I'll quote Al Oppenheiser when asked about Axle Hop: "....WHAT axle hop???..."

Now -- that said, I'm CERTAIN that there will be a few that TRY to get axle hop -

.........let's face it - no matter how 'robust' we design it, there will always be those who try to 'blow it up".........

[GTAHVIT]

^That ought to answer that question.

I believe the technical term is "asymmetric half shafts." But yes, basically one, is bigger and heavier than the other. Which eleiminates the wheel hop.

[garagelogic]

Originally Posted by gtahvit

^That ought to answer that question.

I believe the technical term is "asymmetric half shafts." But yes, basically one, is bigger and heavier than the other. Which eleiminates the wheel hop.

I think you are wrong. Based on physics, whether the shafts we asymmetrical or not, that alone is going to have little, if any influence on whether or not you have wheelhop. More likely, they use a stiffer bushings or something along those lines to reduce the amount of deflection caused by immediate torque to the wheels.

[GTAHVIT]

^ Well sir, I have no intention on debating this with you.

We've got more than a few GM people here who will attest to what I've stated. You are of course free to find your sources and dispute this technology if you wish. But, it's been around for a while and it works. Maybe I should have called it axle hop. To me they mean the same thing.

[garagelogic]

Originally Posted by gtahvit

^ Well sir, I have no intention on debating this with you.

We've got more than a few GM people here who will attest to what I've stated. You are of course free to find your sources and dispute this technology if you wish. But, it's been around for a while and it works. Maybe I should have called it axle hop. To me they mean the same thing.

Nah, I have no interest in geting into a technical debate on something I have very little knowledge of. I'll take the word from the folks who know the car better than I do and assume they solved the issues.

[rayhawk]

Originally Posted by garagelogic

I think you are wrong. Based on physics, whether the shafts we asymmetrical or not, that alone is going to have little, if any influence on whether or not you have wheelhop. More likely, they use a stiffer bushings or something along those lines to reduce the amount of deflection caused by immediate torque to the wheels.

Ok, I am doing a bit of speculation here, but as I understand it axle hop is due to resonance in the system. That is why it shows up more pronounced at a particular rpm. Obviously, it is a complex system that involves rotating tires, flexibility in the suspension and the car, etc. It is not quite as simple as a resonant frequency of a string, as there are many degrees of freedom to a car's suspension. However, with that said, it appears the reason for the different size shafts is intended to shift or minimize the natural resonant frequency of the suspension as a whole without adding excessive mass to the structure. Two different diameter shafts will have a different resonant frequency, so even if on their own they would be prone to some inherent vibration, the fact that they "ring" at a different freq. means they no longer combine to magnify the problem into noticeable or damaging wheel hop.

I would love some more technical data on this system but my guess is that most of their engineering data is not going to be released, as I believe they have patents on the design (although Chrysler uses it in the Challenger as well-I don't know how that works).

By the way, thanks for the info fbodfather, it sounds like you guys have done a lot of work on this.

[rayhawk]

Originally Posted by carfansince73

20 mpg highway... OUCH. That final drive ratio the GXP gets is most likely the reason. It doesn't weigh much more if any than the G8 GT, and they just wanted the quickness right from the factory. They should have made those gears a no-charge option. I know the AFM isn't there, but it could have been a little better to keep it out of the tax, or at least a smaller dollar amount. :(

With the G8 gt, you get most of the performance, AFM, and no gas guzzler tax. If I was'nt getting a camaro, I would probably get the G8 gt, just because it is a performance bargain, looks nice, and gets great mileage for the amount of power it has.

[SoFlaZ]

Originally Posted by rayhawk

Ok, I am doing a bit of speculation here, but as I understand it axle hop is due to resonance in the system. That is why it shows up more pronounced at a particular rpm. Obviously, it is a complex system that involves rotating tires, flexibility in the suspension and the car, etc. It is not quite as simple as a resonant frequency of a string, as there are many degrees of freedom to a car's suspension. However, with that said, it appears the reason for the different size shafts is intended to shift or minimize the natural resonant frequency of the suspension as a whole without adding excessive mass to the structure. Two different diameter shafts will have a different resonant frequency, so even if on their own they would be prone to some inherent vibration, the fact that they "ring" at a different freq. means they no longer combine to magnify the problem into noticeable or damaging wheel hop.

I would love some more technical data on this system but my guess is that most of their engineering data is not going to be released, as I believe they have patents on the design (although Chrysler uses it in the Challenger as well-I don't know how that works).

By the way, thanks for the info fbodfather, it sounds like you guys have done a lot of work on this.

+1

[Hesh]

Thanks Fbodfather didnt feel like looking for the post you made saying the same thing. They took care of the axle hop for the Camaro.

[camaro5]

Hop on over to this thread with DETAILS on IRS Design and how they stopped the hop, from Dragon.

http://www.camaro5.com/forums/showthread.php?t=9146