I'd worry more about the LCA. All of the acceleration is tied to that using a 6" lever. So if you have 300 ft lbs of torque, multiplied by a 10:1 reduction ratio that's 1500-3000 ft lbs at the hub, which I think translates to about half that on the LCA. You suspension guys could clarify that some. Anyway, 750 to 1500 ft lbs of torque is an awful lot to apply to an unbraced welded tubular LCA.

Jim

A radius rod doesn't do a thing about the torque applied to the LCA. It transfers straight line force only, but that force is being applied six inches above the tie-in point. If you have 1500 ft lbs of torque being applied through a 1 ft long lever to the contact patch then you have 1500 pounds of force being applied at the axle. The problem is that that 1500 lbs is also rotating around the radius rod six inches below the axle, putting 750 ft lbs of torque on the LCA itself. The Jag LCA is a very stout large diameter tube and will handle it just fine, but a tubular ladder has almost zero torsional rigidity. It will flex like a noodle.

Nobody seems to pay much attention to the counter torque that is generated in a stock Jaguar IRS system. But it is essential to its proper operation so this is a big big oversight.

Jim

No comment

Last edited by tyrellracing (10/27/2012 6:27 pm)

Rebel are you referring to my post maybe? If so I think I was only telling Daze about his site getting exposure. The exact opposite is true I think. I always try to add where I get any info I post and a link. This does to two things. First I can verify where I saw such (any) info. Then second if a person finds it useful, they can follow the link and maybe read more.  If you look at any pics I posted, you should for the most part see a link where it came from. I feel it makes this site more useful as a IRS data collection site.

Let me ask you this, have you seen the page where I put all the videos?  I collected 100 plus and tried to categorize them.

http://irsforum.boardhost.com/viewtopic.php?id=256

Ralphy

Last edited by Ralphy (3/15/2012 5:29 am)

Heidts is a great example of the problem, and I imagine their customers are having terrible problems with wheel hop, can't figure out where it is coming from, and blaming the original Jag IRS design for not having an upper link. That ladder appears well made, so it will store up an incredible amount of torque energy before permanent distortion sets in, just like a big old spring. Once the tire slips a little it will release and re-set. I imagine if you had a high speed video of the wheel you'd see it moving around all over the place, forward, back, up and down.

Jim

Were you here Jim when we were posting about an upper Watts link for the Jag?

http://img121.imageshack.us/img121/434/picture001.mp4

http://s350.photobucket.com/albums/q401/acmjg/?action=view&current=MOV04917.mp4

One thing I like about Roadster Shop's setup. Is the design controls the toe from behind the halfshaft. To me it seems a very strong position to eliminate the upright from twisting. Plus depending on how long you make that link, you can change the roll/steer. From zero to plus or minus.

Keeping the upright from twisting is one thing, the LCA is quite another entirely. I recall some discussions about the upper watts link, but from my perspective there are three very critical issues with it:
1) Space limitations mean it will not fit in the MGB without compromising tire width, suspension travel, ride height, or sheet metal, and perhaps several of those in combination. I have 315/35-17" tires under the car with a 3" flare.
2) The immediate result of the top link is to transfer all of the counter torque loading of the differential away from the LCAs and into the differential mounts. The only way to do this safely is to provide a sturdy and somewhat rigid lower mount from the differential to the body. Most do not do this. The stock design only applies longitudinal torque to the differential mounts, counter to the driveshaft and at roughly 1/4 to 1/3 the lateral torque. The half shaft counter torque is transferred to the LCAs where it is balanced out by the torque produced by acceleration forces acting on the upright, using the upright as a lever arm to produce the torque.
3) The add-on completely changes the way counter torque and acceleration loads are handled by the suspension, removing those loads from the admittedly beefy (stock)  LCA and applying them to the Watts link, which is usually diminutive. It now becomes a highly stressed member of the suspension package, yet I have not seen one so far that was sized to handle those loads.

Wheel hop is anything but a typical characteristic of the Jaguar suspension, and is very dependent on the specifics. It requires energy to be absorbed and stored in some component(s) of the suspension and then released as tire slippage occurs. So far we have had no instances of wheel hop in the MG-Roadmaster, despite the 455 Buick engine. The devil is in the details. If there is wheel hop, there is energy being stored somewhere. It may be in the linkages, the bushings, or in some cases perhaps even the tires but it is most definitely there somewhere. Eliminate that and the wheel hop will go away.

OTOH, if you are regularly winding the engine up and dropping the hammer, (Which means you are building a dragstrip car and would benefit from things like jacking the tires into the pavement on launch.) the Jag IRS isn't particularly well suited to this use, and a solid axle may be in your future. There is a good reason why top fuel dragsters do not run IRS.

Jim

Sounds pretty rigid, where do you think the energy was being stored, the inner ends of the LCAs maybe? Another thing that plays into it is that some recommend that the Timken bearings be set up with free play. Since you have Timkens both in the lower outer pivot and in the axle spindle, any excess play will aggravate the problem. Timken (the Manufacturer of the bearings) recommends preload, and in the case of the pivot bearings where rotational loading is exceedingly slow they easily tolerate a very heavy preload. This takes a great deal of slop out of the system.

There isn't a whole lot to be done about the inner needle bearings other than to replace them with a different type,  but this does present an opportunity to redesign the LCA to a lighter unit with more torque rigidity. I have such a design in the works.

Another problem area is the attachment of the LCA pivot brackets to the differential case. The bolts are too close together and are in single shear, quite clearly a design compromise, and the cage was relied upon to reinforce the attachment. I haven't addressed that shortcoming but at the very least the brackets should be pinned into the case.
Far better would be a strut from the top of the housing forward and down, but the only way that can be made to work is with a new monolithic LCA/strut assembly that transfers rotational loads into the strut to the top of the housing. This can be done rather easily once the new LCA is built but I won't be starting on that for some time yet unless someone orders a suspension package from me. Still, maybe after my car is back on the road I can take that design back up and do something with it.

Jim

Last edited by Jim Blackwood (3/16/2012 10:45 am)

No comment

Last edited by tyrellracing (10/27/2012 6:31 pm)

TR,
Trying to stay within the Jag concept. I'm throwing ideas out for Jag conversions. I lose track myself, however this is the Jag thread. The AU UCA may be limited but if Jim can copy the basic shape and make it fit? It's all good.

Anyhow I still have not decided which way I will go yet.
Ralphy

Last edited by Ralphy (3/17/2012 5:29 pm)

Guys, in all fairness the flow of forces is more complex than any of us have described up to this point. For instance, and again starting with the Jag, when TR adds his top link he is not simply redirecting all torsion and linear acceleration forces into the chassis. We are still left with the anti-torque from the differential. This is not all simply transferred into the frame of the car, it is also applied to the LCAs, and in unknown proportion. Plus although the  level is only 1/3 to 1/4 as much, the transverse anti-torque is also there.

Now, TR I must agree with Ralphy here, both of us have provided clear photos of our work and/or the concepts we've been discussing, and while your descriptions have been pretty clear some things are not. Example, your 45* strut braces. 45 degrees in which plane? Can't see that without a photo. In one plane they would resist one force, in a different plane another. I can think of at least one orientation where they would be completely ineffective but I've given you the benefit of the doubt. Not that happy about it, but trying to be fair.

The AU IRS aside, my application generally precludes a top link as in ANY iteration it will raise static ride height and/or decrease suspension compression. I feel that space would be better used to replace the solid half shaft with a light weight tubular one, but again the cost is the same. So my focus is to strengthen and lighten the Jag IRS with minimal fundamental design changes, like adding a top link. Not that I'm against it particularly as a concept, just that it's poorly understood and there is extremely little room for it. Consequently a firm understanding of the forces involved is essential, as the size of the links would have to be minimized in the extreme.

With that thought in mind it is first necessary to fully appreciate every aspect of the basic flow of forces, take every conceivable action to rigidify the transitions, and only then to look at what happens to those forces when the top link is added. Rather than mummify the body, apply a small band-aid in effect. If the force flow through the top link can be reduced to 5% of the total for instance, then a small and light link can be highly effective in controlling unwanted vibrations such as wheel hop.

I'll give you an example using a lathe. When turning a long slender piece it is common for harmonic vibrations to build up in the tool and part to the point that a visible and even rough chatter pattern can be seen on the surface of the part, including a vibration that can be felt in the machine and heard by the operator. This can happen even with the most rigid of machines, tooling, and even sometimes with short and rigid parts. However, despite the strength of heavy cast iron, alloy steel, carbide tooling and the metal being worked, frequently a finger placed on the rotating part will stop the vibration. What is the strength of the finger in relation to all the above? Miniscule. But it is just enough in just the right spot to shift the balance, alter the frequency, and dampen the vibration, resulting in a smooth cut.

For the Jag IRS this is what I see as the function of a top link. The fundamental structure is already there and well proven in the normal envelope of operation. Just because someone wants to exceed this envelope, or because they constrict it by installation compromises does not mean the basic design is flawed or that a fundamental design change is needed to fix it. In preventing chatter the approach is to stiffen the structure by shortening the most flexible members, change the speeds and feeds, look for compliance and eliminate it, and then only as a last resort apply band-aids or go to another machine design. I think that approach is equally valid here and I doubt we've exhausted our remedies.

Jim

A fairly good aid too, and providing the center section could be kept clear might not have to reduce travel. But unless very carefully designed, would necessitate CV halfshafts, a big complication with inboard brakes. Plus it is not the right design to stiffen the longitudinal axis, which I suspect is where most of the wheel hop comes from.

Jim

1965 Jaguar E-Type Lightweight-Style Vintage Racecar


I found this picture of a Jaguar lightweight racecar rear suspension set-up for racing on Hemmings.   This car is running the half-shafts horizontal with 3 degrees of camber.  Coil-overs are 825 pounds per inch.  I calculated 500 pounds/inch at the wheel on a 2350 pound car!  The description of this car is good reading: http://www.hemmings.com/classifieds/carsforsale/jaguar/e_type/1369722.html
I like the radius rods and carrier support.  The bearing air ducts are definitely cool.

Last edited by irstang (3/19/2012 5:59 pm)

So Ralphy,  Have you done anything to your kit car project or are you only here to critique the efforts of others?   Nearly every member here has at least worked on their projects. You just post the accomplishments of others.  What is with that.  You have more postings here than any one else and yet you have built nothing.  You have suggested that your life is too busy to build your IRS using things you volinteered to do as your excuses.  Maybe if you spent a few hundred less hours on the internet per week and a few in your garage building your perposed IRS I would not have any gripe.  After three years of you posting with out any display of your OWN accomplishments.  I just finished my second IRS instal.  This time in my Tiger.   Its been three years,  Lets see your work!

Last edited by tyrellracing (1/13/2013 9:12 pm)