Lowering standard coilovers.

[v8bloke]

I have bespoke double wishbone suspension with standard style coil overs ( an eye at each end ).
Extended length 305mm closed length approx. 230mm. Springs are 7inches long. This equates to 4inches total suspension travel.
With 300 lb springs I had 20mm of bump and 85 droop. I would like to go a lot stiffer say 400 to 450 lb springs but this will just give more (too much) bump travel and not enough droop.


How can I go stiffer while still having control of bump and droop travel?


Cheers
Mark

[v8bloke]

Yes 20mm. I bought these springs as a starting point, I wouldn't consider using like this.
I think with a 400lb spring I will have too much bump travel and not enough droop.
Must be a way round it?
The only adjustment I have is to add preload which just takes the spring closer to binding on full compression.

Edited by v8bloke on Sunday 6th January 11:48

[v8bloke]

Thanks for the replys.
yes I understand that the shock stops and spring rate will set the bump, droop and travel. But I don't see how spring length can alter ride height.
Say i'm using a 9inch 300lb spring and that corner of the car weighs 600lb. The suspension will settle by 2 inches.
If I use a 7inch 300lb spring and the corner weight is the same then the suspension will also settle by 2 inches.

How do I get a higher spring rate while controlling bump travel? my brain hurts.

[v8bloke]

stevieturbo said:

Adding pre-load will not change the spring compressed height, unless the vehicle weight changes. It will lift the vehicle a little higher though offering you more compression with less drop.

And if you think a 400lb spring will have too much bump vs a 300...then use a 325, 350, 375...whatever.

The platforms are adjustable for various reasons

And you've already made a statement of having only 20mm compression...there is no way any spring will coil bind at only 20mm of compression.

Ive got 20mm of bump compression 105mm total so the spring is compressed by 85mm when at ride height.

[v8bloke]

Thanks again, I will try a 375lb spring and see how that works out. When I can get it weighed I can work out the wheel rate and calculate settings better.

[v8bloke]

stevieturbo said:

No. What you seem to be asking is can you run a stiffer spring without it affecting the current ride height. And again 20mm compression seems massively inadequate, you need to raise that vehicle up anyway

If you need extremely stiff without affecting ride height, then a shorter strong spring with a short soft helper spring could achieve that, bit it will also affect how drop occurs too.

You're asking mixed questions here.

The title is about lowering the car, yet you've already said you have only 20mm of compression...so if you lower it you'll almost be sitting on the bump stops. That is in no way whatsoever good. If anything you currently need to raise the car.

Thanks and sorry if my questions are misleading.
The spring that I have at the moment is just the starting point. I aim for about 35 to 40mm of bump travel with stiff spring. ( 250 to 300 lb wheel rate ).

I think I will just have to do it by trial end error.

Thanks

[v8bloke]

75mm travel at the shock equals 105mm at the wheel.
Finding this really difficult. I think trial. Will see how 375 x 7 springs work.

[v8bloke]

My previous setup which was separate spring and shock had a mechanical ratio of 0.34 and a 650lb in spring which equals a wheel rate of 221.
I want to be at least as firm as this.
New coil over mechanical ratio is 0.53 so to get close to my original wheel rate I need a spring 425lb in.
The new coil overs have a stroke of 75mm and with a 7in spring with minimum preload has about 30mm of threads below seat.

I am at a disadvantage as I don't know yet the weight of each corner so cant calculate the spring deflection at ride height. I suspect that I will have more bump travel than rebound. Next step is to get a 425lb spring and measure where it sits at ride height.

[v8bloke]

gordmac said:

Your wheel rate depends on the motion ratio squared. A motion ratio of say 0.5 will give a wheel rate of a quarter of spring are.

Yes I have seen several formulas. can you explain why the result is squared?
I Would have thought that on a wishbone suspension the distance from fulcrum to shock mount divided by distance from fulcrum to centre of tyre would give an accurate Motion Ratio? Is this right/


Cheers

[v8bloke]

Thanks to all for your help!

I am starting with a 450lb spring , will update the results.

Cheers

[v8bloke]

Thanks to all for your help!

I am starting with a 450lb spring , will update the results.

Cheers