GMs in IT

[JeffYoung]

Of those choices, the Camaro is the cheaper build, by far, and may make the most power.

Obviously the ITAC agrees. I just don't see anyone in their right mind building one - when you have the choice of a 2,800 lb E46, a 3,000 lb S2000, a 3,050 lb 968, and a 2,950 lb Camaro, I think the Camaro comes dead last every time. I would also love to see one built, but my guess is if you do it will be another one of those 'sentimental' cars guys build, and not full-tilt pro build that will show what it really is capable of. Maybe when the Camaros age out of SSB next year we'll see a few of them migrate to IT.

Also, I agree with Ron on the live rear deal. I don't think there should be a weight break for it. Setup right, it is not, in my opinion, a real detriment. I do not perceive a handling deficit on my car to the best RX7s, 240s, etc.

[dickita15]

Also, I agree with Ron on the live rear deal. I don't think there should be a weight break for it. Setup right, it is not, in my opinion, a real detriment. I do not perceive a handling deficit on my car to the best RX7s, 240s, etc.

Interesting, so you do not think the advantage of adjusting rear camber and toe rises above the noise level in car differences.

[Knestis]

Point of interest - back in the early "stock car" era of TransAm (early '80s), some Corvette teams petitioned to use solid rear axles because they couldn't get their IRS to work the way they wanted...

K

[dickita15]

Point of interest - back in the early "stock car" era of TransAm (early '80s), some Corvette teams petitioned to use solid rear axles because they couldn't get their IRS to work the way they wanted...

K

Ah yes and Group 44 ran a live axel in the TR4A in nationals in the 70’s

[Ron Earp]

Interesting, so you do not think the advantage of adjusting rear camber and toe rises above the noise level in car differences.

I'm sure it probably does.

But, having driven Jeff's car and my Z back to back (he's done more of that than I have as I don't drive his in races) I feel the differences are negligible, at least at my level of driving.

I understand that the Z should have an advantage with tire contact patch while cornering, and should be superior in keeping the tire on the racing surface. But in practice, the TR8 doesn't seem to give up anything to the Zs or RX7s in tight corners, or long sweepers.

I feel (no data) that the independent suspensions would have a greater chance to shine if the surfaces were a bit more undulating or less smooth. But at Roebling Road and VIR, both very smooth tracks, the live axle works well.

Indeed, the latest Mustang live axle iteration comes from the factory with tri-link and panhard rod. It gets rave reviews even when compared against IRS designs from BMW, Nissan, GM, and others. What's old is new again.

Interestingly enough, solid axles aren't as heavy as you might think. The 7.5" rear axle, with stock arms and shocks, is lighter than the Z pumpkin, half shafts, batwing lower arms, and uprights. The former assembly I can struggle to move, the latter I have no chance in hell of moving. Maybe Nissan needs to get with the program and put a stick axle in the new Z.

[JeffYoung]

Correct.

Interesting, so you do not think the advantage of adjusting rear camber and toe rises above the noise level in car differences.

Dick/Earl, having driven Miatas, the 240z, the TR8 and Ron's Lola at speed at VIR, CMP, Roebling and others, I've yet to really see where the TR8 is at a serious disadvantage to the others.

Once we eliminated bind and settled the axle down with a good tri link and panhard setup, the back end does not mover around. I obviously don't get any camber back there, and that hurts some, but as someone pointed out I also don't get toe and camber change as the axle moves.

By subjective feel, the only place the TR8 seemed at a disadvantage to the Z and the Miatas before the tri-link was Hog's Pen. But now even there I pull most good RX7s and Z cars out of the hole -- watch the vid Ron posted (and that was BEFORE tri link).

Earl, yes, I can run the curbs at VIR fine. The car doesn't like the channelled FIA curbs at CMP, which I understand are coming to VIR for next year, yay, but not sure any of our cars really do.

I think with our 150-180 whp cars, the live rear just isn't that much of an issue.

Bill, no off the shelf fix for me either, but it was not hard to have one, a good one, fabricated given how open the rules are for a live rear axle with the 'traction arm" allowance.

[billf]

Want to know what happens to a live axle when jumping curbs??? Just watch ONE V8 SuperCar race from Australia, and you will see EVERY car jumping curbs. They are mandated a live axle, even though the chassis are originally built with IRS, and mandated to run a spool at all events.

When the cars jump the curbs, the wheels have liters of air under them. The effect is minimalized by the spool which delivers 100% power to the opposite (still in contact with the pavement) wheel.

Quite the lesson in drivetrain dynamics...

Jeff,

Sometimes the live axles "bend" in service and acquire some camber... I'm not sure the mechanisms are fully understood....

But the lack of camber and toe changes surely make the live axle a good choice if one can tolerate the expected unsprung weight.

Finally, I believe the lack of toe and camber change, in addition to the ability to harness the axle torque reaction, gives the live axle an advantage in traction out of the corners with especially high horsepower cars. The new generation Mustang is certainly competitive with the competition, all of which have IRS...and its corner exit is impressive. Only Porsche is better, and that probably is because of its greater rear weight percentage.

Bill

[erlrich]

Of those choices, the Camaro is the cheaper build, by far, and may make the most power.

Agree on the cost part for sure.

Also, I agree with Ron on the live rear deal. I don't think there should be a weight break for it. Setup right, it is not, in my opinion, a real detriment. I do not perceive a handling deficit on my car to the best RX7s, 240s, etc.

Jeff - out of curiosity, at VIR are you using the curbs going up through the esses (except for the last one at the top of the hill), and going through hog pen? I don't have tons of track time on the Camaro, but from what I've done I just can't imagine those curbs wouldn't play hell with the rear end of the car.

[Ron Earp]

Agree on the cost part for sure.



Jeff - out of curiosity, at VIR are you using the curbs going up through the esses (except for the last one at the top of the hill), and going through hog pen? I don't have tons of track time on the Camaro, but from what I've done I just can't imagine those curbs wouldn't play hell with the rear end of the car.

Yeah, he runs them like most everyone else. Stable and good. Or, it seems as stable as my car did in the same situation.

http://youtu.be/JWXt8qLsRAY?t=51s

[billf]

Of those choices, the Camaro is the cheaper build, by far, and may make the most power.

Also, I agree with Ron on the live rear deal. I don't think there should be a weight break for it. Setup right, it is not, in my opinion, a real detriment. I do not perceive a handling deficit on my car to the best RX7s, 240s, etc.

While I agree that the live axle is not in itself a detriment, the linkages to it can be. Incidentally, the Live Axle is only one of two designs that accomplish all goals in suspension geometry: constant camber regardless of chassis attitude, whether it is acceleration, braking, or cornering. The other is the De Dion. All others offer compromises under some condition, or the other. Incidentally, as we all know, the give-away with the live axle is of course the unsprung weight. While a De Dion has less unsprung weight, it still has more compared to an Independent Suspension.

Back to my statement about linkages... All live axle cars do not have the same linkage setup. The Camaro has the best, with the factory torque arm, as demonstrated in AS. The Mustang has to have the worst, with the four arm setup, which inherently binds when cornering, or under hard acceleration (when it doesn't matter). (For those who don't know, these four arms are controlling all longitudinal, and, lateral movement of the chassis...at least that's what we would like to happen.) All solutions except two, modify the bind, but do not eliminate it...just make it happen at a different time. Any bushing material replacement has the potential of increasing the bind...it cannot be eliminated because of the dissimilar arcs of motion created by three different planes of control.

The two solutions are the aftermarket three link (not four), and the aftermarket torque arm. Unfortunately, the offerings of torque arms for Mustang are enginereed for the 8.8 inch rear, not the 7.5 which the car is produced with. Thus, no aftermarket torque arm for the ITS or ITR V6 Mustang. Also, a Panhard Rod, or Watts Link must be added to provide the lateral location lost when the upper arms are removed...more weight.

Unfortunately, all solutions to the bind for the Mustang will add weight to an already overweight platform. If it ain't broke...you might find that the car can be driven without the need for additional linkages. I did for years with an ITB.

Just my two cents worth after dealing with the identical suspension in my '87 Mustang...7.5 rear also.

Bill

[dickita15]

When I look at the four link in a Mustang I see the ITA/ IT7. The three link conversion on that works pretty good and has already been accepted as IT legal

[Ron Earp]

When I look at the four link in a Mustang I see the ITA/ IT7. The three link conversion on that works pretty good and has already been accepted as IT legal

Yep, and it does a damn good job on those cars and Jeff's TR8. We're designing our own with the 7.5" in the stang and we have access to some CNC milling in ally. Putting it together in CAD we can design a tri-link setup that is very light and strong, thus minimizing the weight addition. Of course the physical pad/attachment to the car is done with steel. We could do a torque arm for the 7.5" but the weight there is pretty high, even with extensive use of ally. I'm also not convinced the torque arm is ideal.

Ford's tri-link on the new stangs is light and it works well I'm told. If we could reliably weld bosses on the 7.5" cast housing it'd be ideal, but that piece wouldn't be easy to attach to after the fact.