I finally saw a Jag IRS setup

[strictlypersonl]

Originally Posted by cobrashoch

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So my question to the original question is still valid. Why the Jag setup in the first place, over other designs? As with all engineering designs there trades to be made. So you do's your research, pays your moneys, and takes your chances. The Jag setup is relatively inexpensive and has history, but its not perfect.
cobrashock

If your primary use is hole shots, then by all means stick to a solid axle. It's been engineered over the years to work pretty well, and it's hard to beat zero camber for traction.

On the other hand, a standard wheelbase Cobra replica with the engine in the proper place has a driveshaft that's only about 12" long between joints. If you stick to the recommended maximum joint angle, that translates into about 4.5" wheel travel, total of jounce and rebound. That's OK for a smooth track when you're using stiff springs, but not so good on real-world roads. Maybe my (in)tolerance for bottoming out is less than yours, but I think that a car whose suspension can't soak up normal bumps is not acceptable. I can only grit my teeth so much.

It's much easier to control the roll center height on an IRS, so that there's less jacking and more predictable handling, and the lower unsprung weight allows softer damping without losing wheel control.

RWD high performance production cars universally have IRS because it combines good handling with good ride, something that's much harder with a solid axle.

[cobrashoch]

strictypersonl - we can debate the various engineering advantages and disavantages till the cows come home, and in the end it comes down to personal choices. I know what you are saying, and agree only partially with what you said above. For example, there are many ways to make that drive shaft longer, (mine is 24") and there are many ways to incraese and control travel in any kind of suspension setup. The guys that run Baja would love to read your thread too, and this only illistrates that the various types of orthodoxy in use out there is only limited by that orthodoxy. Yes, most Cobras are built using some sort of limiting orthodoxy, but it's fortunate for all of us there is other ways. I stand by what I said. Note; I didn't say the Jag setup was not any good, I only said it has advantages AND disadvantages and IRS setups are in most cases overkill. BYW- in some cases some rear camber in a drag car is a good thing, as they hook up and the rear end is driven down. My Cobra is a drag car.
cobrashock

[82ACAUTOCRAFT]

Originally Posted by cobrashoch

strictypersonl - we can debate the various engineering advantages and disavantages till the cows come home, and in the end it comes down to personal choices. I know what you are saying, and agree only partially with what you said above. For example, there are many ways to make that drive shaft longer, (mine is 24") and there are many ways to incraese and control travel in any kind of suspension setup. The guys that run Baja would love to read your thread too, and this only illistrates that the various types of orthodoxy in use out there is only limited by that orthodoxy. Yes, most Cobras are built using some sort of limiting orthodoxy, but it's fortunate for all of us there is other ways. I stand by what I said. Note; I didn't say the Jag setup was not any good, I only said it has advantages AND disadvantages and IRS setups are in most cases overkill. BYW- in some cases some rear camber in a drag car is a good thing, as they hook up and the rear end is driven down. My Cobra is a drag car.
cobrashock

I agree, the jag IRS, having owned several E-Type has 3 main flows
1) it's heavy
2) it's complicated, difficult and expensive to service. (in-bord brakes overheat easily) It cost me $2K 20 years ago to fix a frozen parking brake on an E-Type to pass Connecticut inspection. The whole rear end had to be brought down to get to the parking break mechanism. The convertible does not have an access panel in the trunk.
4) it's suffers from too much camber change on turns and has to be set up extremely stiff for good handling on the track.

That said when set up properly, it's a great an very reliable system. For a drag car, a solid axle is a much better system for the reason stated above. Less overall weight, you can use a much beefier differential, and both tires are alway perpendicular to the ground.
Actually, when you look at Jaguar racing history, they always used solid axles even for the D type which was their most successful racing car.

[RallySnake]

OldDog,

I can echo your concerns about the Jag rear end. It's taken a lot of time and money to get it right. The main thing is to reinforce the lower control arm tube where it is welded to the cast yoke that goes around the brake. I made 6 inch by 4 inch triangles out of 1/4 inch mild steel plate and welded them to the control arms. The rest of the story is below:

"When I built my car (1981), my budget was very tight and I used assorted parts from the local junkyards. The result was disasterous and almost killed me. The right lower suspension arm broke, shooting me off the road at 90 mph. Ten years ago, I went to CWI and learned a lot about the Jag setup and got the parts I needed to make a safe and good handling setup. Last November, I was fed up with the rear brakes not working and the gears making noise, so I took the whole thing apart and had Kurt Hamilton (818-943-2323) rebuild it all. I got a little carried away with vented rotors, new Dana gears, new u-joints, all new bearings and had him fabricate a stainless steel bottom plate that holds everything together. I have spent $3,400.00 to make it all that a Jaguar rear end can be. Now, I can throw the car into corners at ridiculous speeds and smile, knowing I'll live to tell about it."

My experience with live axle sports cars is not so good because they ride hard on rough roads. They tire you out pretty quick. The jag suspension gives a lot of travel and soaks up everything. I have driven the Arntz on 15 hour rallies and it's not too bad. If I were starting over and building a new chassis today, I would pick something more modern like the late Ford Thunderbird rear end. It's so much lighter and cheaper.

Paul