Spring Rates With Std Tbs

[skinner2k3 3]

I am fitting a set of AVO GTZ500 coil-overs to the 205 tomorrow. The springs are currently 250lb 8" 2.25ID. I am on std TBs and ARBs. Pretty much a dedicated track car but is driven to and from.

 

250lb springs will be to stiff for std bars, I am considering 180lb or 200lb. The dampers are AVO adjustable front and rear.

 

I want to avoid the springs being to light that they could become coil bound.

 

Having assembled them with the 250 8" springs as a test I can see the length is about right so I am sticking with 8" free length.

 

Any actual experience of similar set ups, advice or knowledge of what I should expect would be greatly appreciated.

 

Ben

[skinner2k3 3]

Should add, 8v XU engine (encase you didn't notice in the sig). Ta.

[Henry 1.9GTi 36]

anything higher than standard rates with a standard rear it will tend towards understeer. Try and go as soft as you can without bottoming out. rear arbs are cheap and easy to fit which would solve your problem.

[skinner2k3 3]

Thanks, that's what I was thinking. Thing is I am going to go and buy them this morning and I have no idea what actual rate to get?

 

I have read on here some where the Eibachs I have now are progressively wound from 70lb to 200lb, no idea if that is correct but I have assumed it is and am basing my choice to go with approx 200 on that as the car is nicely balanced, once it has rolled over as much as it will. That could be silly logic, but its all I have to go on so far.

 

Next on the to do list is the rear ARB. Then bars when funds allow.

 

Off to Merlin Motorsport now, got to beat the rice grinders in!

[Baz 421]

I'd go with the lesser option at 180, perhaps a bit less even tbh.

[welshpug 1,646]

as Baz said, the standard bars are a bit weedly even for 180 lb, having driven a tarmac 205 rally car with 200's up front and a standard rear, I'd confirm it was pretty crap compared to my standard 205!

 

been a passenger in another 205 with 225's up front and 21's on the rear, and it behaved so much better.

 

I'm running 180 lb on my heavier ZX which has 21's on the rear as standard.

[skinner2k3 3]

Cool, cool. I was over there as you guys replied. Luckily I did buy 180lb.

 

Got it all on this morning. Set the top mounts to as close to where they were before as I could, wishbones about horizontal where they were before......and it feels pretty good.

 

The only things that concerns me a bit is that the 8" spring is compressed to 5.5" under the weight of the car, not sure how much travel that leaves! The gaps between the coils is probably a mm or two more than the diameter of the coils themselves. Problem?

 

Which brings me to me to my next question, can springs be changed without removing the dampers from the hubs? (They were an absolute b*tch to fit, even with an allen key opening up the slot!)

 

Cheers chaps

[skinner2k3 3]

Cant find much info on the net about the travel of an 8" coil spring before it becomes coil bound. I am guessing there is a simple Free length - (Coil Dia * number of coils) method of calculating it.

 

I found a few suggestions there is approx 5" of travel on a 8" spring which if correct means half the travel is being used bareing the weight of the car.

 

Still not sure, any ideas?

[skinner2k3 3]

Spoken to Faulkner springs and they confirmed the solid length of their 8*180lb is 3" so just under 5" of movement, but about 4.5" usable. So I have used approx half the usable travel with the weight of the car.

 

Then called a suspension setup guy (recommended by Merlin Motorsport) who's suggested the above is ok, providing I don't bottom out the damper obviously. He did suggest going to to 9*185lb to gain the extra 0.5" of travel (travel confirmed by Faulkner).

 

So I called AVO to check damper travel, they confirmed they do not go solid metal to metal and bottom out (no idea how that works) and full travel is more than 5" anyway, I pointed out I currently don't have any bump stops and asked if I should fit some and was told they were not required.

 

So now I have two basic choices, swap to 9*185 or stick with 8*180.

 

The way I see it (and this is just my logic, please correct me if I am wrong)) I have moved an 180lb/in spring through 2.5", this should require 450lb (205kg). I know my front axle weight is approx 450kg so that ties up (ish). So to use a further 2" of travel I would need to add a further 327kg of load to the front of the car. That's pretty well the weight of my entire car on the front axle, assuming my dampers are man enough to prevent a bump causing that sort of movement which I would hope they are, I think I will be ok. Over simplified, no doubt, but its the best I could come up with.

 

Now I need one of the guys on here who are clued up to point out the blatantly obvious mistake and point me in the right direction.

[welshpug 1,646]

I would look to have more spring travel so you dont go coilbound, it sounds like the AVO's have internal bumpstops, I'd not want to use the coil on its own as a stop to the travel, gives quite a bang when you hit them all together!

[skinner2k3 3]

I have temporarily put the 8*250 springs back on will drive it a bit just to get an idea of how they feel, but this afternoon I took the 8*180 back and swapped them for 9*200.

 

May even wait until the next track day and run both back to back for a better comparison.