i want to lower the car about 1.5 inches and have a stiffer suspension, and i am going with bilstein shocks and 18x8/9 wheels. any sugestions on spring rate or size? thank you

 

I have been looking at this very same thing and have found it difficult to find info on what front spring rate TWR used - rear spring rate was apparently stock XJS on the TRW XJS.

All I can find with aftermarket springs is either listed as standard or HD lower. I am planning on giving King Springs a call today to see if they can add some info to what HD lower are, I'll post back with results.

You could try cutting say 1/2 a coil from the front spring - this will increase its stiffness and set ride height by using the 2 spacers - it may require some trial and error.

 

let me know! i want something that will be stff enough to handle like a sports car vs the wishy-washy body roll i have now

 

King springs are 30% stiffer and are available 30mm lower about 2inches you can use the original spaces to adjust ride height. I have decided to go this way.

 

30% will be enough to avoid bottoming out? How much performance difference will they make?

 

They will firm the ride up significantly

 

could you post up a link? please and thank you!

 

Check This Site Out!

www.thedrivenman.com

It's the only place in the US that I've found that sells performance suspension parts for the XJS.

 

You can buy them on ebay for $400 you would have to check out shipping. Might be cheaper than $700 and King make springs for V8 Supercars.

www.kingspring.com

 

Just a thought Aston Martin DB7 springs will fit an XJS these are slightly firmer, if these are more readily available in the USA - I don't know.

Just found these out of Aus for $570 shipped

http://www.ebay.com/itm/Jaguar-XJS-X...be6f28&vxp=mtr

 

will they lower the car? and where can i find thoes?!?

 

what year of the db7? and is the vantage included? because that had a v12 of aproxamatly the same size

 

Why not try the eBay link

 

i was just wondering if aston springs were avalible in the us, i think ill go with the king springs if they are not.

 

I think you will find the Kings will be cheaper even with the freight.

DB7 I6 and V12 around 1995/6

Any spring will be ok so long as the rate and dimensions fit.

The Jag front spring spec is
Overall lenght Length 12.125"
Outside Diameter 6.25"
Wire Diameter 0.68"
Active coils 6

Estimated spring rate 320 lb/in and both ends are tapered square

 

Warren,

Just spoke to Bilstein re stiffening my front shocks when they get rebuilt. The tech suggested a 25% increase for compression with no change in rebound. I'm looking for something conservative right now so that seems about right. I'll plan to do the same with the rears. Your thoughts? Larry

 

Are you using standard springs?

My thoughts are to keep standard springs replace shocks with Bilstein (mine are stock for bump and rebound at the moment) and upgrade my sway bar from the already 24mm (1") to 26-28mm and make it adjustable and add a rear adjustable bar.

The benefits I see in this setup are:
1.Softer springs will keep tyres in contact with the road hence the ride quality will be good for road use and I can adjust sway bar for track.
2. Sway bar will easily adjustable to control weight transfer. For road or track.

I like to watch the V8 supercar series here in Aus and one of the most successful teams in the series for years is "Vodafone" and watching their cars they seem to be softer sprung than the others as they ride the track bumps better.

I was reading reading a writeup from a NASCAR guy who was saying the spring rate should be just enough to keep the car from bottoming then control the weight transfer with swaybars and the oscillation with dampers.

To answer your question increasing bump stiffness on the front dampers could increase turn in understeer, it could also affect braking weight transfer to the front wheels (ie Dive). This is really unknown as it will depend on spring rates, swaybar rates and tyre size and compound.

I would be asking questions of the guys rebuilding the shocks.
1. Why do they suggest increasing bump and what effect will it have?
2. Will this effect change with different tyres? The answer to this question should be yes so what tyres are the dampers tuned for?

The job of a damper is to control how fast the wheel is allowed to travel up or down. Having them too stiff will slow down the weight transfer, so overly stiff dampers in say a slalom under worst conditions will have the car understeering badly.

Hope this gives you a starting point.

 

where can you get adjustable sway bars? i want a firmer ride, im building a road car that i want to really handle, and be somewhat comfortable. aiming for the feel of the BMW m6s

 

Adjustable sway bars for the XJS will need to be custom made, I have not found anywhere I can buy them off the shelf.

BTW as I am modifying things I will be relocating the engine oil cooler lines and installing solid front subframe mounts I am planning on running a straight sway bar with splined ends mounted on the subframe.

 

I am modifying things too, were gonna be great friends. i have a manual trans swap with a mrleod throwout bearing and a mustang cobra t5. i wanted to put a larger sway bar in the back, almost or identicle diameter to the front so i could keep understeer to an absolute minimum.