250lbs Front Springs On Coilovers

[dino20vt 3]

Following on from this thread:

http://forum.205gtidrivers.com/index.php?s...115584&st=0

 

 

And my post:

"I received 8" 250lbs springs, I'm guessing this will be quite harsh for a road going/occasional track day alloy 16v 1.9? 

 

Trouble is if I return them for softer springs will they be mis matched to the dampers as they would have been 'valved' for the 250lbs springs?

 

But if I stick with the springs I'm going to need some f@cking thick/expensive TB's and ARB to match.

 

What to do?"

 

 

 

 

My questions are:

 

Will the 250 lbs springs be to harsh for the road?

 

If not what spec rear ARB and TB's should I go for and where can I can some from?

 

Cheers

[Baz 421]

About 22/23/24mm's IMO. Depending on personal preferences, whether you prefer the front or back to be harder.

 

You could just stick some lower poundage front springs on it if you don't want to ruin the comfort levels too much, i don't think it's a major issue with running lesser springs on these coilovers, let's face it they're budget coilovers in the great scheme of things anyway, i don't think they're *that* specifically valved.

[Cameron 16]

Somebody posted a brilliant table a while back, showing the spring rate of various thickness torsion bars. I chose to go with 24mm bars to match my 350lb/in springs, it works out at about 300lb/in and I have to say it's a pretty perfect combination. It is a bloody firm ride but it's actually surprisingly smooth.

 

I'd say with 250lb something like 22-23mm bars would be good. Basically what Baz said.

Edited February 23, 2010 by Cameron

[Cameron 16]

Here you go!

 

Short Swedish dicitonary; stavdiameter = bar diameter, hjulkonstant = wheel rate (spring rate at contact patch).

[Cameron 16]

Just to add a little more, the table above shows the wheel rate rather than the actual spring rate. This means you have to know the installation ratio (the ratio between wheel movement and shock movement) to work out what your front wheel rate is.

 

The IR for the 205 front suspension is something like 4:5, so (4 x 250lb) / 5 = 200lb wheel rate with your 250lb springs. So you probably want to go for the 22mm bars, which will give you a 183lb rear wheel rate.

 

Hope that makes sense!

Edited February 23, 2010 by Cameron

[Baz 421]

That was the table i was trying to remember!

[dino20vt 3]

Just to add a little more, the table above shows the wheel rate rather than the actual spring rate. This means you have to know the installation ratio (the ratio between wheel movement and shock movement) to work out what your front wheel rate is.

 

The IR for the 205 front suspension is something like 4:5, so (4 x 250lb) / 5 = 200lb wheel rate with your 250lb springs. So you probably want to go for the 22mm bars, which will give you a 183lb rear wheel rate.

 

Hope that makes sense!

 

It makes perfect sense if what im about to say is correct!

 

22 mm tb's which is 183lbs which is the nearest match to the front which is 200lb wheel rate?!

Edited February 23, 2010 by dino20vt

[dino20vt 3]

Ps what about anti roll bars, keep standard 205 diameter or go thicker, what options are available for the front?

I have a thicker 309 gti front ARB if it's any use?

 

Thanks for the quality replies by the way.

[Cameron 16]

Yeah that's right, you won't want a higher spring rate at the back as there's less weight there.

 

Anti-roll bars are a personal preference so don't be too keen to accept the massive rear ARB trend. An ARB is basically used to tune the handling, and the only way you're going to know if it needs it is to drive your car and then decide weather you think it understeers a bit too much or is alright. I have a standard rear ARB and at the moment it seems to be pretty nicely balanced, but then I like a neutral chassis rather than an oversteering one.

 

The thing to remember is that an ARB is used to balance a chassis, and it does that by reducing grip at one end - the end you fit the ARB to.

[Alastairh 47]

Rather than looking at spread sheets. I use to own a 205 Mi16 running 275lb front springs on Gaz coilovers and standard 205 front ARB with a 309 rear beam and 23mm torsion bars and 25mm anti roll bar.

 

It handled very well, even better once i tried a few different makes of tyres to suite the character of the car and suspension and kept on top of all the other bushes and ball joints connected around it because it put more strain on these. This was strictly a hard core road going car but its now being used on track by the new owner.

 

Al

[Cameron 16]

Funny that, because 257lb springs work out at a 220lb wheel rate, which almost exactly matches 23mm torsion bars (219lb).

 

Don't knock the spreadsheet, it's a really handy quick reference guide if you need a ball-park figure!

[shalmaneser 26]

That spreadsheet is bloody useful.

 

This topic well and truly bookmarked.

[Alastairh 47]

Funny that, because 257lb springs work out at a 220lb wheel rate, which almost exactly matches 23mm torsion bars (219lb).

 

Don't knock the spreadsheet, it's a really handy quick reference guide if you need a ball-park figure!

 

Thats ok then. Its good to refer the spread sheet to real life experience and see positive results!

 

Al

[Baz 421]

Yes but is the spreadsheet for 205 or 309 bars, or does it matter even??

[Rippthrough 98]

The IR for the 205 front suspension is something like 4:5, so (4 x 250lb) / 5 = 200lb wheel rate with your 250lb springs. So you probably want to go for the 22mm bars, which will give you a 183lb rear wheel rate.

 

???

 

Motion ratio of 5:4 wheel/damper?

 

Which means that a 250lb spring is 160lb wheel rate, no?

 

Which kinda cocks this up:

 

Funny that, because 257lb springs work out at a 220lb wheel rate, which almost exactly matches 23mm torsion bars (219lb)

Edited February 24, 2010 by Rippthrough

[Cameron 16]

How the hell did you work that out?

 

Wheel rate = Spring rate x Installation ratio = 250 x (4 / 5) = 250 x 0.8 = 200.

 

Can't for the life of me figure out how you got 160lb!

[Rippthrough 98]

How the hell did you work that out?

 

Wheel rate = Spring rate x Installation ratio = 250 x (4 / 5) = 250 x 0.8 = 200.

 

Can't for the life of me figure out how you got 160lb!

 

 

Your equation is wrong, wheel rate = spring rate * (motion ratio)^2

Edited February 24, 2010 by Rippthrough

[taylorspug 7]

Rather than looking at spread sheets. I use to own a 205 Mi16 running 275lb front springs on Gaz coilovers and standard 205 front ARB with a 309 rear beam and 23mm torsion bars and 25mm anti roll bar.

 

It handled very well, even better once i tried a few different makes of tyres to suite the character of the car and suspension and kept on top of all the other bushes and ball joints connected around it because it put more strain on these. This was strictly a hard core road going car but its now being used on track by the new owner.

 

Al

 

How dare you use real life as a reference- back of the line now! What we need here is more theory!

[Baz 421]

PMSL!!

[Cameron 16]

Your equation is wrong, wheel rate = spring rate * (motion ratio)^2

 

Well s*it, so it is!

 

How dare you use real life as a reference- back of the line now! What we need here is more theory!

 

Take the piss all you want, wheel rates are a very important thing to know.

[Rippthrough 98]

Well s*it, so it is!

 

 

Wheel rates are only much good if you have the corner weights to go with 'em really

[shalmaneser 26]

Your equation is wrong, wheel rate = spring rate * (motion ratio)^2

 

Where did you get ^2 from?

 

this is simple mechanics....I'm sure Cam's right?!

[Cameron 16]

I've been meaning to take the corner weights on mine for ages.. I want the CG height for Lotus Shark.

[Cameron 16]

Where did you get ^2 from?

 

this is simple mechanics....I'm sure Cam's right?!

 

No he's right. The force at the wheel is simply Spring rate x Installation ratio, but the actual wheel rate is Spring rate x IR^2.

 

It's because the wheel rate is force @ wheel divided by wheel movement, so you need IR twice.

 

I know that's going to make no sense to 99% of people, but it does.

Edited February 24, 2010 by Cameron

[Henry 1.9GTi 36]

Why should a 205 with rear wheel rate of 219 and front wheel rate of 160 feel alot stiffer at the front?

 

Can only get tyre deflection on the front without bending my wings!

 

edit: units in elephants

Edited February 25, 2010 by Henry 1.9GTi