Gents,
I have an adjustable rear suspension kit, comprising shocks, thread tube (6" long), 10" 140lb springs, Avo inserts. Question is how far from the top of the strut tube to weld the threaded adjuster?
Anyone help? I guessed maybe 1 inch.
In the first photo it shows the threaded portion just to the top of the strut tube. I was being some what lazy, I didn’t want to cut the original spring perch completely off, I wanted the threaded portion to rest on something and I just epoxied the threaded portion into place. I wish that I had them somewhat lower, maybe a half inch to an inch as you say. I have the 10 inch 140lb springs with 20 inch tall tires and it seems pretty close to where I want it to ride with the perches adjusted an inch and a half to the bottom of the threaded pearch. At the present time the rear ride height is raised approximately an inch and a quarter and the rear A arms droop nearly the same.
The static ride height for most cars should be set with the lower A-arm parallel to the ground plane. This ensures that negative camber is introduced to the rear suspension upon turning, due to weight transfer. In racing situations, it may be desirable to lower the inboard pickups, relative to the outboard pickups, to speed up the rear suspension camber change and reduce weight transfer effects during braking.
How far down you can lower the spring platform is set by the brake disk. Set the brake disk up on the hub an you will see how low the threaded sleeve needs to be set to get maxium movement downwards. Its about 4 inches above the alloy casting
Where you end up setting the adjustable platform then depends on the sprngs being used and your application but the 6 inch length of the sleeve up from the lowest setting is normally plenty for any application
For 10 inch 140 lb springs I would expect a fitted length of around 7.5 inches and the spring platform around 1 1/2 inch from the bottom for a typical race car ride hieght setting. This is a pretty good point to be at as it leaves room for playing a little with ride height and corner weights. I assume you are building a competition car with this sort of rear spring rate and are using around 200 lb front springs and a 7/8 inch roll bar.
Thanks to all who replied. Rohan, the front springs are 9" at a rate of 175lb. Antiroll bar closer to 1". I want a fast track day car that can be used on the road also. Any comments on this set up?
Setup sounds reasonable. I personally prefer a little softer track car as its more flexible and usable in a wider range of conditions. Your setup will be a bit of a handful in the wet or on a rough track but nice and quick on a dry smooth track when dialed in right.
A 1 inch bar is stiff and risks breaking the shock bolts off with extreme suspension movements as the suspension also bends the arms of the roll bar in and out laterally as it moves. You may want to fit drop links to get some lateral flexibility in the system with a bar above 7/8 of inch
The ride will be hard for road use but not impossible on good roads.
I inherited fairly heavy springs on mine (250/180), which is fine for track work, but can get a bit hairy in a tarmac rally. Mind you, the car is heavy (700 Kg with all the gear on board). Do you mind if I ask what you run? (And how heavy your car is?). It would be a hell of an effort to have a wet set of springs to swap in if you know it’s going to be a wet event, but I wonder if the handling improvement (ease of driving, really) would make it worht it?
I run 150 lb fronts, 115 lb rear and 7/8 inch roll bar. My car is 700 kg like yours. The rear rubber bump stops are also spaced down 20mm to come into play earlier. I set around 110 mm front and 120 rear ride height at the bottom of the sills with driver on board on Yoko 175 /60 x 13 AO32R tyres
I find this a good compromise that works well on a dry smooth track and also well on a bumpy or wet track. Probably not optimum for either as a little softer again for wet tracks and a little harder for dry tracks would be a little quicker but changing springs for a dry or wet race is beyond my time availability.
My setting is the soft end of the range for a track car and is similar to the Dave Bean recommended race setup. Your setup is at the hard end and is like the TTR recommended race setup. Where you set in that range is driven by tracks, tyres, weather and personal preference.
Here is what we did on the last set installled. Slap the whole assembly in a lathe cut off the old perch leaving a band welded onto the tube. Take the threaded colar and put this in the lathe, increase the inside diameter so that the assembly slips over the band left from the old perch. I put epoxy on top of the band and slipped the new assmbly over this. last step was to run a second beed of epoxy at the top to stop water from penatrating. The bottom thread is right at 4.25 inches from the top of the casting.
Hi Rohan,
Yes, they are TTR springs. He considers that a tarmac rally set up and has even heavier ones for track work. Those European roads and tracks must be glassy smooth (and no kangaroos to dodge).
When I last stripped the car a couple of years ago, all the tower tops were bent to varying degrees. I wonder if the TTR frame suffers any of this, with all its reinforcing? Has anybody experienced this?
Cheers
Patrick
Just a note about bending the towers. The stuff I am fitting is for a 26R chassis for an S4 I am rebuilding but I also have a set of exactly the same items for my Sprint with a standard Galv chassis. Would there be any possibility of bending bthe towers with the spring rates I mentioned above?
Thanks for calling me on that one elandoc. I didn’t think it through properly. In reality, there’s very little camber change with the struts. What camber change there is, is dependant on body roll at the rear, so the camber change is positive on the outside wheel. Still, I think if you set the ride height according to the Worshop Manual, I believe you will end up with the lower A-arm parallel to the ground plane.
Yes, it probably doesn’t make much difference. I had been thinking about it in the past during one of my “develop the car” frenzies, as the tarmac rally rules here allow a 25 mm repositioning of suspension pick ups, and I was trying to figure out if there was any advantage…
Cheers
Patrick
The 26R chassis and the TTR chassis had varying styles of reinforcement of the rear strut top as these bending is common even in road cars with standard spring rates.
Bending of the front towers also maybe problem and TTR and 26 R chassis had reinforcing. Looking at the details of what was done I am not sure they do much and its not been a problem on my car which had a standard Lotus replacement chassis fitted in 1980 but that may be due to the softer spring rates I run compared to TTR though the orginal 26R’s used spring rates comparable to what I do.
With your spring rates and I presume matching stiff dampers and Australian roads some chassis deflection over time does not surprise me and some chassis reinforcing would not go astray!
I’ve gusseted the rear perches (shorter version of the TTR ones) and plated the front ones, so we’ll see how that goes. If I could get 100 Kg out of the car, I could probably run softer springs, but that will have to wait for the super-dooper lightweight project - which will have to wsit for the home reno’s. If I’d coughed up for a real 26R 11 years ago, I think it would have cost me less by now! (I thought an Elan was like a Spitfire 11 years ago, and had never heard of a 26R).
Has anybody actually measured the stiffness of a standard chassis against a reinforced one (a la TTR)? It would be nice to see some actual numbers justifying all the trouble.