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Changing spring rates on the fly
bi22le - 27/12/15 at 05:26 PM

Hi all,

I will be trying to dial out my under steer this year by following my books and changing my spring rates.

Any tips on how get replicate set up when changing springs?

For example, if I put stronger springs on the front what can I do to make sure corner weights are the same? Matching ride height would not be accurate enough.

Extending spring length by the percentage of spring rate chand sounds more sensible to my engineering brain. So increasing strength by 10% means adding 10% to length of old spring when it was in place.

Thoughts and suggestions please.

britishtrident - 27/12/15 at 05:41 PM

You seem to have picked up the wrong end of the stick on a couple of things,

First stiffening the front spring rate will (normally) increase understeer.

Secondly increasing the length of the springs or screwing the spring platforms upwards doesn't alter the rate spring rate.

The usual way to reduce understeer is to either soften the front or stiffen the rear. The controlling factor is the relationship between the front and rear suspension in roll.

CNHSS1 - 27/12/15 at 05:41 PM

I think even if you work it all out in theory, it wont be 100% in practice. If you have a lever type corner weight gauge you can get it pretty damn close again pretty quickly trackside

SPYDER - 27/12/15 at 06:19 PM

quote:
Originally posted by bi22le

For example, if I put stronger springs on the front what can I do to make sure corner weights are the same? Matching ride height would not be accurate enough.


Assuming that you change the springs and reset to the same ride height.
Why would the corner weights have changed?

Is the understeer on turn in only or all the way through the corner? You could change the turn in characteristic a fair amount with your shocks.
Once into the corner you could try a measured and possibly earlier application of power to neutralise the understeer. A small and correctable amount of understeer is surely better than a car that basically oversteers when the power is applied.

Does the car have anti roll bars? Are you still braking during turn in?

Break the corner down into stages and describe what is happening during each phase.

bi22le - 27/12/15 at 06:24 PM

quote:
Originally posted by britishtrident
You seem to have picked up the wrong end of the stick on a couple of things,

First stiffening the front spring rate will (normally) increase understeer.

Secondly increasing the length of the springs or screwing the spring platforms upwards doesn't alter the rate spring rate.

The usual way to reduce understeer is to either soften the front or stiffen the rear. The controlling factor is the relationship between the front and rear suspension in roll.


Oh sure, sure. Thats why i said for example, i thought it would be easier to explain when i went onto to my spring preloading theory!!
Which leads me onto the other point you picked me up on, i understand winding in the cap does not alter the spring rate, physically different springs do that, just the preload and therefore ride height.

TBC following my track day i feel my car is understeering mid to exit of the corner. According to Allan Staniforth i need to increase front rebound, Soften front spring rate and reduce front ride height amongst other things.

If it rolls too much at the front i need to tighten and increase everything

chillis - 28/12/15 at 01:25 AM

Understeer and roll, hmm!

What anti roll bars do you have? What tyres are you running and are they the same front and rear? What pressures? You say its understeering mid to late corner, does this get worse as the session progresses or is it the same all the way through a session? Suspension geo? What do you have on the front and rear currently?
Understeer and roll suggests to me the rears may be too soft. Is there any improvement when raising the rear platform/preload?

bi22le - 28/12/15 at 09:29 AM

Ooo I like this group diagnosis thing. I did not expect this!

I have a striker with no ARBs at all. They are in the plans. Full geo set up by procomp and checked by Elite Motorsport so all good.

A048 all round running 18psi cold. Procomp dedicated striker fronts with 300lb springs, gaz golds rear with 225 springs.

It seems consistent once tyres are warm but they do seem to get too hot after aboutb 30 mins.

The new procomp and springs made a world of difference but with only 150bhp and no LSD I can't exactly power my way to oversteer.

rodgling - 28/12/15 at 09:37 AM

In my experience you can swap springs and try and get the ride height roughly the same - you will end up miles out in terms of corner weights and geo, but it's good enough to be able to figure out what spring rates you want. Then you can go get the car set up properly again with the correct spring rates. Repeat once or twice if necessary. I have been round this loop a few times and have a load of 2.25" springs if you want to borrow them.

Andy D - 28/12/15 at 10:18 AM

Tyres 18psi cold could be on the high side? 18psi hot may be better.

bi22le - 28/12/15 at 01:30 PM

quote:
Originally posted by Andy D
Tyres 18psi cold could be on the high side? 18psi hot may be better.


Really? 18 seems to the cocensous, I tried lower and it felt less planted, what are you running cold?

Andy D - 28/12/15 at 02:37 PM

I tend to start about 18 cold, then keep dropping them after each session to 18 hot. They'll go up around 5psi on the first session. After the first couple of sessions they'll stabilise, then I just keep an eye on them. After a trackday when they properly cool down I'd say they'll be about 15?