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First off I read through every single topic on the board, including the older ones. I saved a ton of pics and got some more links you guys posted to check out, but I thought I would start to get some opinions from you guys on my project. Sorry for the convoluted posting, I figured this thread was worthless without pics and a link.
Last edited by husker (2/16/2012 8:14 pm)
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I want to run 24 x 15 wheels in the rear with 405/25 24 tires on them. My thinking is a fairly neutral backspacing of 7". My thought is that there is less stress with half the wheel on each side of the mounting. I don't know if there is any validity to that or not so feel free to call me an idiot. But that makes the width of my irs needing to be roughly 56", which from what I have been reading is very doable. But what I would like is at least 10" of wheel travel, and 12" would be better. I would like very flat camber curve, those tires aint cheap and I can't be tearing them up. I also would like the ride height to be about 4" off the ground so roughly 2/3 of the travel will be higher than ride height so that may pose a problem. Plus I don't know if I will know where ride height will be till I drive it for a while. My suburban I had that was bagged I usually only drove it about 4" up from the ground so I am hoping for the same with this truck.
Now I have located a complete front and rear assemblies from a 1986 xjs. Or a rear from a 1995 mark viii. Or the possibility of a completely homemade unit based on a winters quick change center section appeals to me . Can I get 10-12 inches of travel from either unit?
I need to swap the front suspension also and the guy will sell me all the jag stuff for $500 and I really like the look of the inboard brakes, and hopefully they will work good enough for what I want to do.
The mark viii is also $500 for the entire car, and then I get the dohc aluminum block 4.6, but I don't know if I want to use that or a 460 yet. I am hoping to build about 600 hp. with whatever engine I do go with(probably more with the 460). But with the mark viii I would have to still come up with front suspension, which isn't a big deal.
Which of the 2 options would be better for my goals?
I have also thought of using the coilover shocks but mounting the upper end that is usually mounted to the body/frame to a cantilever that is actuated by a air rod, then I get height adjustment but keep the coilovers and shocks for tuning.
Let me know what I am missing, what you think of all this, or feel free to run me out of town.
Last edited by husker (2/16/2012 8:34 pm)
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My project is a 1977 ford f100. My goal is mostly a street truck, but I drive by a road course everyday so it beckons me. I also have always been a fan of drag racing and there is a track less than a hour away from me. But like I said it will be mostly a street truck. Now my plan is a bagged rocker laying truck. Something similar to this(only with body panels that are gaped better).
If I use the jag rear I figure I am going to do the upper watts link, and build lower arms similar to this one, hopefully that would eliminate most wheel hop.
And here is a link to the winters rear I was thinking of using, haven't found a price yet so it may not be an option at all. But I might be able to build something similar out of used parts.
Last edited by husker (2/17/2012 3:36 am)
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I'm to much of a novice at this to be handing out advice yet. But I will say Welcome ! And look forward to what you come up with on this build. I'm not a low-rider kinda guy but from what I have done so far it definately made me think if I was going to Slam something to the ground this route is the way to go. Some advice I can give tho is make sure that Jag RA is not a POS and maybe even shoot for something that may have a Gear ratio that is going to be in line with what you want to do. I have knocked mine down to 58-1/2" so another 1" on each side would be no big deal in itself.
Good Luck
Joe
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That 10-12" of travel is going to be an issue with the Jag. I narrowed a xj6 IRS 5-1/4" and max travel is right at 8" so you can do a little math and see how long the arms have to be to get that much travel. Things start to bind up on you. I don't remember at the moment what the limitation was but it seems like it was the universals. To get that much travel you might have to actually widen the unit. That would mean more offset to the outside of your wheels but that is very common these days and the closer the bearings in the uprights are to the wheel centerline the less stress is on them. You'd have plenty of internal clearance, so it is just an appearance issue with the wheels. You didn't say what you are doing for the front but presumably something narrower.
There are a couple schools of thought on that watts link. The stock Jag IRS uses the torque generated by the lack of a top link to offset counter torque at the differential and a top link negates that effect. You need to thoroughly understand these dynamics before you change the basic layout. It's not that difficult. Wheel hop is not automatically going to be a problem for every installation, but if you plan on drag racing it you'll need a plan for dealing with it that has been proven to work. Unfortunately I can't make a recommendation there.
Jim
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The wheels I am looking at are basically custom built to order, you tell them the backspacing so it would be easy to change that if I have to.
Has anyone tried to put in bigger half shaft yokes? That would allow a larger u-joint, which would add strength and give you more travel before it binds. I don't have either unit yet so I am going by pictures and I don't know what would be possible.
I need to go look at the jag stuff to see the condition it is in, I was just pulled in the last couple months, I think the car was being driven up till then.
The front I am going to swap in the front suspension from the same donor jag as the rear. I want to run either a 22 x 8.5 or 22 x 10 front rim, depending on the clearance I have. Need to get some more measurements before I get that sorted out.
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Husker,
With all the criteria you wish to meet. I wonder why you haven't thought about a solid axle quick change? You can find used units on CL fairly reasonable. You may need to change out the wide 5 hubs however. Just a thought.
Ralphy
Last edited by Ralphy (2/17/2012 4:40 pm)
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I was playing with my jag set up today and getting 12" of UP is going to be impossible with a shortend LCA/Axle. I knocked out 2" on each side and I can safely? get 8" up from level and then interference happens between the LCA and Axle joint. Might have to get wild and crazy on something custom? 
Edit: If you were willing to make a new LCA that dropped more and got the tube out of the center, It would work. I think....
Last edited by Digz (2/17/2012 4:25 pm)
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Ralphy I have thought about a solid, and I am not set on anything yet. Just something sexy about a irs with inboard brakes, to me anyway.
Digz when you say 8" do the u-joints bind? So if you got 8" from flat on the lca then could you get 8" the other way also?
Thanks for the help so far guys. Trying to figure out if it will be what I want when I'm done, and if it worth the trouble.
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I don't mean to be a naysayer but for the type of duty you are talking about I don't believe IRS is the way to go. Several reasons first drag racing and IRS do not play well together. Even with the upper watts and other reinforcements, wheel hop is still going to be a major issue ESPECIALLY with 15" tires. All that power is going to be applied directly to the pavement and the suspension is going to want to jump all over the place. Not saying it can be done, just saying it is a tough road to travel to get a good drag car out of IRS. The static camber curve is not something you will be able to achieve al least not and maintain a "jaguar IRS". Camber curve is a function of the half shaft arc in relation to the LCA arc. The only whys to change the curve are to change the ratio between the two parts and/or change the inner pivot locations which will effect how the two arcs effect each other. If you maintain the over all Jaguar design than you are stuck with the UCA to LCA ratio created by the final length of the half shaft and LCA. Changing the inner pivots would be like designing an IRS from scratch and only using the differential and hubs for the original Jaguar design.
If the truck is going to be a track truck why would you need 12" of suspension travel??? If you choose to pursue this I have no doubt that we can help you, but what you are doing seems like trying to turn a VW van in to a race car. Can it be done, yes, is it the best way to go probably not.
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That was it, the knuckle hits the LCA at full compression. I don't recall the limiting factor on droop but believe it is the u-joint interfering with itself. Regardless, there is only so much angle they will tolerate. As best I recall, that 8" or so of travel I measured was the total so I wouldn't go getting overly optimistic until you can do your own measurements. And take note, the u-joints only bind at a couple of spots at the limit and it's easy enough to miss it if you don't do a full rotation when checking. I had narrowed one side 2-1/4" and the other 3" (to center the pinion) and I believe the 8" was on the 3" side so if Digz measured 8" with 2" narrowed it doesn't sound real promising for 12". If it was on the 2-1/4" side that could be within the measurement error, and a measurement with a full width axle should tell you how wide you'd have to be to get 10". But I wouldn't be too optimistic about getting 12.
Jim
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Husker, Hopefully by the end of next week I will have my halfshafts in and everything hooked up enough I can get some pics of the motion range and what it does to the hubface angles. What I was seeing on the UP bind was the yoke on the stub axle physically hits the Lower Control Arm. I can't tell you on the DOWN because I have it set up on the bench and do not have enough room for that kind of motion.... yet. Actual Ujoint bind may be a problem at the extreme ends of what you have in mind. You have my curiosity going. Edit: Sorry to repeat ya Jim . type/post overlap..lol
Last edited by Digz (2/17/2012 7:20 pm)
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No biggie Digz, that's what friends are for, right? Looking forward to what you find out on the total travel.
Jim
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In all reality it will not be a "track" truck, probably be lucky to do anything more than once or twice a year.
I am not married to the irs, but a few of the advantages I see for my build are
1. Cool factor
2. With extremely dropped vehicles the drives shaft can be an issue, it has to move up into the cab area so much sometimes. A two piece drive shaft takes care of some of the problems but there can still be clearance and pinion angle issues.
3. Better ride.
4. Having the rear tires negative camber and suck in a little when it is layed out(when all the air is let out of the bags to set the truck on the ground) helps clear the bed as it curves in at the top.
And I am not against modifying either rear to work the way I want it. Like I said I also have a mark viii rear readily available to me.
Now for the most part the truck would be driven at ride height, say 4" off the ground. Now when I was at a cruise night or show I would maybe drop it an inch or two and drive it real low. But that would be at a pretty slow speed. Raising the truck up would only be to clear speed bumps or on bad roads or something that required a little more clearance, and would still only be a couple three inches from ride height. So the actual used travel would only be say 6", but a couple more down to make it sit on the ground. The extra up travel is for extreme driveway inclines and getting the tires to clear the sheet metal to remove them. But on that issue I have been thinking of using dzus it fastener and making quick release bedsides, then I could pull them off if I needed to remove a wheel/tire.
Is there anyway to change the half shaft yoke to bigger units to run a larger u-joint? Does anyone have a pic of the inner and out yokes out of the rear?
Thought I would throw in a pic of a chassis with the same size rear wheel/tire combo I am looking at running.
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Husker, The U-joints are the big chevy type in the axles part NAPA#330 if you want to check them out. I'm putting a 468 BBC in front of mine, mostly doing it for all the same reasons as you are but not doing the Slam. But putting in some kind of air suspension is on my mind down the road or maybe in another build if I dont get old to fast,,lol
What is the overall height of the tires you want to run? I'm setting up for about 30"tall and 11" wide with room for maybe 12"width. Right now I'm shooting for a traditional 15x10 with a 3.75-4" backspace.
Last edited by Digz (2/18/2012 7:04 am)
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husker wrote:
1. Cool factor
2. With extremely dropped vehicles the drives shaft can be an issue, it has to move up into the cab area so much sometimes. A two piece drive shaft takes care of some of the problems but there can still be clearance and pinion angle issues.
3. Better ride.
4. Having the rear tires negative camber and suck in a little when it is layed out(when all the air is let out of the bags to set the truck on the ground) helps clear the bed as it curves in at the top.
And I am not against modifying either rear to work the way I want it. Like I said I also have a mark viii rear readily available to me.
Well that is something different all together. Sounds to me like you have really thought this out and know what you are getting in to. A lot of times people want to do IRS only because of the "cool factor" and they are not aware of some of the down sides of IRS.
Now for the most part the truck would be driven at ride height, say 4" off the ground. Now when I was at a cruise night or show I would maybe drop it an inch or two and drive it real low. But that would be at a pretty slow speed. Raising the truck up would only be to clear speed bumps or on bad roads or something that required a little more clearance, and would still only be a couple three inches from ride height. So the actual used travel would only be say 6", but a couple more down to make it sit on the ground. The extra up travel is for extreme driveway inclines and getting the tires to clear the sheet metal to remove them. But on that issue I have been thinking of using dzus it fastener and making quick release bedsides, then I could pull them off if I needed to remove a wheel/tire.
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is there any way to use two ways to rase the body?? in other words get the max travel you can out of the suspension and then raise the body off of the suspension even further by a separate mechanism above the suspension?? that would give you good suspension travel as well as the ability to raise the truck in extreme situations.
Also being concerned about the u-joints binding up due to suspension travel maybe you should look at what Slammy has done on his set up. check out this post
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Using two ways to raise the suspension crossed my mind yesterday while I was at work. I thought if used the original cradle, or built something similar, I could add small bags to that to raise/drop the entire assembly. But part of me thinks that is just more stuff to break, add weight, and adding more moving parts to a somewhat complicated system might make problems I can't even think up yet. But it is an idea I am hashing out. Ya I saw slammy's thread, looking at all options. But I think if I go that extreme maybe the mark viii would be a better starting point, but maybe not. It all ready has cv shafts instead of u-joints.
Last edited by husker (2/18/2012 9:50 am)
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You have one thing going for you. That is your building a full sized pickup, with a wider than most have wheel track width, plus bigger tires. If you run a larger wheel diameter with lots of offset, you may be able to tuck a bit of the suspension inside the wheel. Think, long control arms which will give you a longer half shafts. This will reduce the amount of total angle your suspension will change per inch of travel. Deep dish wheels are off the board! Also you may want to compare center section widths, looking for the narrowest. You have so much room to work under that bed, use it to your advantage.
Ralphy
Last edited by Ralphy (2/18/2012 1:49 pm)
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This info really interests me, but with having parallel upper and lower control arms you end up not having any roll steer, if I remember my suspension geometry correctly. So I am not sure how that would affect handling. Need to do a little refresher in my suspension 101.
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If interested in doing some "modeling" and you have Excel -or Open Office (works there too), you could give 'BonesApart' a try:
That one and a few other modeling software are discussed over at :
Won't be a suspension 101 - but a place to start. Jacking is a bit of concern with parallels as I recall. Worth a look though.
Cheers - Jim
Last edited by phantomjock (2/21/2012 3:41 am)
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PJ,
There yah go! I have been familiarizing myself at work and at home with Excel. Trying to figure out how to use the trig abilities.
husker, roll steer is not controlled by positioning of the UCA and LCA. I was a big advocate of roll steer once. However I have reversed my opinion on the need.
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Like I said I need to go back and re-familiarize myself with suspension geometry and handing.
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husker, thinking about your bagged suspension. With the ability to change your ride height, you definitely don't want to get involved with roll steer. Your toe would be all over depending at what height you were driving at.
Ralphy
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I think roll center is the term I am looking for.
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huckster -
First - Start with the Track/Organizations Regulations - What can you get away with.
Then - Tires and Wheels - looks like you have that sorted out (?)
Key objective is to produce a balanced set-up. One where the front and rear roll resistance.
This will get both ends of the car trying to reach the same roll angle at a given cornering condition.
So, if its Roll Center (RC) - I have a few 101's I've been using:
1. Front RC lower than rear -1.0 to +3.00 Above Ground Level (AGL) is about norm for high performance.
This is set as to reduce front end lift at high speed. (RAKE)
2. Rear higher than Front RC, up to about 3 inches AGL. Front to Rear RC relationship will determine initial under/oversteer setup.
2a. If the axis runs too much nose-down, the car tends to oversteer.
2b. If the axis runs nose-up, the car tends to understeer.
3. Analyze RC Movement (Evaluate at about 3 degrees of roll, 2 - 4 inches of bump)
3a. OBJECTIVE: minimize RC movement - under bump or roll
3b Watch for really wild movements of RC
3c. Looking to minimize Camber change - on outside wheel inside wheel unloads in the turn - so less critical for contact patch
4. If you need to raise RC; one method is incline Upper Control Arm (UCA) or Lower Control Arm (LCA) towards centerline of vehicle
5. Longer LCAs minimize RC Movement (haven't proven yet - seems true)
6. RATIO of UCA:LCA 0.6:1 to 0.8:1 the UCA:LCA length ratio affects the anti-squat rate of change but does not affect roll steer.
7. More to follow...
Cheers - Jim
Last edited by phantomjock (2/19/2012 5:02 am)
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Here are a few more quick One-O-Ones:
7. With a low RC - it reduces the lateral deflection of the wheels (and tires.) Downside: increases the roll angle.
7a. An extremely low RC needs anti-sway bars to stiffen the body roll to maintain Camber.
7b. With WIDE tires - you'll need sway bars anyway to increase roll stiffness.
Cheers - Jim
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PJ,
Just started looking at the Bones Apart modeling. First let me tell you the link you provided on this page does not work.
Second, I just started with it, but it seems to be locked into a geometry similar to the T Bird IRS. I can change control arm length. However I do not see where I can model static angles similar to my C3. Still playing around with it!
On another note. While driving my daily driver, I have been paying attention to how my car transfers into a turn. What I see is that the outer front wheel side tends to have the highest motion. The rear seems to stay put. I guess this is due to a lower RC plus it's where all the chassis weight transfers to. Imagining if the rear outer had more motion. I would have a car that wagged through a turn, Which would in my mind, not be good.
husker, don't take any of my posts as trying to school you or scold you, or trying to make you look bad. These IRS units are pretty complicated for the mind to follow. Then comprehend all that changes when you alter any point. Just trying to reel through all the points that my mind sees with any particular design. Trying to help in other words.
Ralphy
Last edited by Ralphy (2/20/2012 7:07 am)
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PJ,
Never mind, I see how BA works now.
Here is the link for Bones Apart, I have Excel 2007 and it is working fine. He mentions you need a newer version. I do not know if 2003 works. You need to download/enable macros, that's it. Unless you want to send some beer money! Note, he has the camber set at zero.
Ralphy
Last edited by Ralphy (2/20/2012 7:42 am)
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It works with open office org too - can't say 2003 Excel.
No angles - you input the data distances etc - but all in metric (mm) so a lot of calculator time unless you are Bi-Lingual.
The major limits I find are: Tire width - can't get above 275, Track max is 1700mm, and some of the display windows are messed up under Open office Org - but the data and results are good.
He's locked the features - password - so reverse engineering a fix is out of the question. How goes your spreadsheet model?
Haven't sent the beer money just yet - but will most likely I'll paypal once I get his email addy.
Cheers Jim
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No worries Ralphy, I used to know some of this stuff but I haven't been using it much lately so I need to go back and relearn stuff. Plus I never put it together with an IRS only a live rear axle, so it's another dimension I have to worry about.
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