Jaguar IRS question
Jaguar IRS question
(OP)
I'm still new to all of this, and since the people on here obviously know what they are talking about I'd rather learn from here, so pardon my simple questions.
Anyway my question is in the early Jaguar IRS they used 2 springs/dampers on each side, so a total of 4 in the rear alone. I haven't found a good explanation as to why this is. I've heard the longer a spring is the more comfortable the ride is, however it can create roll. I'm wondering if this reduces roll, while the 2 combined lengths of spring help with comfort. I can assume all day long, but would really like to understand it properly.
Anyway my question is in the early Jaguar IRS they used 2 springs/dampers on each side, so a total of 4 in the rear alone. I haven't found a good explanation as to why this is. I've heard the longer a spring is the more comfortable the ride is, however it can create roll. I'm wondering if this reduces roll, while the 2 combined lengths of spring help with comfort. I can assume all day long, but would really like to understand it properly.





RE: Jaguar IRS question
Maybe that spring/damper configuration can be shorter (not protruding into the trunk as much) or they don't impart a twisting force into the lower link?
RE: Jaguar IRS question
I'm trying to figure out the Jaguar suspension so that I can determine if 2 coilovers will give me the benefit of a smoother ride with less body roll. My thought being I can go with a bit stiffer springs without sacrificing ride quality as much. But that is again if that's why Jaguar used 2. I have read they used 2 short ones rather than 1 long one for trunk space, so I was thinking of utilizing the principal for a different purpose.
RE: Jaguar IRS question
A single spring/damper would load the lateral arm in torsion, as would offsetting the lateral arm relative to the axle line. Ultimately, the axle end would wander a bit longitudinally (once you consider bushing compliances at the chassis end of the arm). The half shaft performs a lateral location function only for the top of the upright, so it is of no help.
Norm
RE: Jaguar IRS question
RE: Jaguar IRS question
So if I have room for a longer travel, couldn't I utilize the idea of twin coil overs to retain a smooth ride with a stiffer spring rate, or would twin coil overs not be beneficial in a performance environment? I'd like to retain a smooth ride for street use but also be able to handle properly in a performance environment. I know it's often a trade off, but I'm trying to come up with less trade off and thus more benefit.
RE: Jaguar IRS question
What's the problem with a careful makeover of the Nissan's suspension? Jag rearends have been "done to death" in Socal. I'm not a fan.
Rod
RE: Jaguar IRS question
The first as Lionel Hutz suggested being a flat floor for the luggage compartment which was a complaint from some about the previous car.
The second was to allow the rear subframe to be installed and removed as a unit since the coil over dampers were fitted to this and not to the body.
The E type (XKE in the US) used the same arrangement for basically the same reasons.
Peter.
RE: Jaguar IRS question
I suppose my question is less why they used short ones as much as why 2. Would 2 coil overs give me the benefit of a softer ride with less roll. I'm specifically working on my rear suspension right now as I feel the Semi Trailing Arm is not all that great for even the weekend track racer.
RE: Jaguar IRS question
The fundamental problem you face is that for racing your shocks want to be about 70% or more critical damping, whereas on the road 35 or so is more like it.
If you want a double wishbone IRS then the Mustang Cobra IRS modules are around $1500 or less from a breakers and are not a bad starting point, although personally I think they went a bit mad with the axis of the UCA. I'd use the lower arms and hubs and diff and fab a new upper half.
Cheers
Greg Locock
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RE: Jaguar IRS question
For the rear, wishbone may not be the ideal choice but I think it would be for both street and track use, or at very least a HUGE advantage over Semi Trailing. If there is a better option for mainly street use please let me know.
Greg, just out of curiosity what are the notional advantages to twin coil overs? I had looked into the Mustang Cobra IRS actually. When mentioning it to my cousin who is a Mustang fanatic he said a lot of Mustang guys get the Jag IRS because it's easier to come by, which is what led me that. I do prefer the Mustang IRS over the Jaguar one, though as I recall they chose mounting points over function. They designed it to mount to the existing mounting location on the mustang chassis, even if it was not ideal locations. I believe that is why it looks a bit mad.
Thanks again.
RE: Jaguar IRS question
However, as in your example of a Miata...Yes, I see them every race weekend. Yes, for a stock car, they are fast and handle reasonably well. Still, they are a compromise...
For street they are fun and a bit rough around the edges, depending a lot on your age and ability to accept the ride qualities...rather, the 'lack' of ride quality. I like them, but then I drove a '60 Sprite on a 3000 mile trip and rode a motorcycle to Mexico City and back...I'm not a kid, either.
A stock Miata laps most tracks at about the same times as my '63 Mini Cooper with an all up wt of ~1700 lbs. and an engine of only 1300 cc's (a vintage pushrod 5 port, at that). What I mean...The Miata, while a great compromise, it is still a compromise. What makes racing Miatas so impressive is the fact that there are so many of them racing against other stock Miatas. A fully prepped EP SCCA Miata is probably a good ten seconds plus per lap quicker...but...it would be a lousy/illegal street machine.
Trust me on one thing that I've learned in the last 50+ years (often the hard way), you can have a great race car or a great street car, just not both in the SAME car. The old cliche...
Fast, Reliable, Cheap...Pick any two!
Rod
RE: Jaguar IRS question
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RE: Jaguar IRS question
Regards
Pat
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RE: Jaguar IRS question
I too have heard the reason given as being packaging - the Jags were often criticised for a lumpy boot floor.
Norm also mentions that a possible reason was the more equal distribution of the spring forces about the rear upright's centreline. This is an additional point that I've wondered over myself.
My own car has the delibrate facility built into the chassis for a similar doubling up of the springs about the upright, though it was never originally used.
What in your opinions would be the benifits of doing so from a force perspective? My car is a SLA rear setup and I've puzzled over where the dominate forces are and how symmetry would make any difference.
Thanks, Colin.
RE: Jaguar IRS question
BG.
RE: Jaguar IRS question
However, that is not true of the dual hydraulic dampers.
On the Jag, these are fitted at a rather extreme angle for packaging reasons, and doubling up on these may be an attempt to reduce the detrimental effect of this fairly radical mounting angle.
Twice the piston area and twice the fluid displacement, is an interesting solution to the rather inefficient motion ratio of the dampers.
RE: Jaguar IRS question
Rod
RE: Jaguar IRS question
RE: Jaguar IRS question
It was that you needed two. Every week you went to the dealer to swap them over. Later we changed it to BMW
Regards
Pat
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