Springrates (Choices, Choices)

1345 Views 23 Replies 7 Participants Last post by Mr Slow, Mar 31, 2010

Mr Slow

Discussion Starter · Mar 26, 2010

I know next to jack about suspension, I currently have NB KONI's (so only one perch choice) with Koni sport springs and OEM ARB's. The front is stupid low and the rear heights are inconsistant side to side. I have a set of eBay threaded collars, (any naysayers here can bugger off

), and want to pair those with a set of 2.5" x 7" or 8" springs.

My last trackday was the first truely dry day and it showcased how much my car leans, compared to my old mans setup, (FM Springs KYB AGX FM ARB's), his car corners much flatter.

My car

Dad's Car

I'm not really inclined to increase the strength of my ARB's, from what i've read it'll keep the body under control at the expense of outright grip/more severe loads on the outside tyres.

My car is also my daily driver, and some of the roads i drive on are nasty with bad potholes etc, so DD comfort is also an issue, would the 'Ground Control' rates of 275/250 be sufficient for my needs? or should I go higher/lower? (FM's springs are 320/200?!?)

Whist I'm asking.... 'Front Roll Couple' as reference by this thread:

http://www.miataturbo.net/forum/t45188/

Why's that important? Is there anywhere online I can read about this kind of stuff?

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1 - 20 of 24 Posts

S S

· #2 · Mar 26, 2010

Why is the amount of roll annoying you? (out of curiosity..not asking in a horrible way!).
Roll helps with the "feel" of the car whilst its cornering and helps you to gauge how far you are from the limit.

You could always try and get "race car vehicle dynamics" by milliken.. the holy grail of suspension books!

StressedDave

· #3 · Mar 29, 2010

Mr Slow said:
I know next to jack about suspension, I currently have NB KONI's (so only one perch choice) with Koni sport springs and OEM ARB's. The front is stupid low and the rear heights are inconsistant side to side. I have a set of eBay threaded collars, (any naysayers here can bugger off

), and want to pair those with a set of 2.5" x 7" or 8" springs.

I'm not really inclined to increase the strength of my ARB's, from what i've read it'll keep the body under control at the expense of outright grip/more severe loads on the outside tyres.

My car is also my daily driver, and some of the roads i drive on are nasty with bad potholes etc, so DD comfort is also an issue, would the 'Ground Control' rates of 275/250 be sufficient for my needs? or should I go higher/lower? (FM's springs are 320/200?!?)

Whist I'm asking.... 'Front Roll Couple' as reference by this thread:

http://www.miataturbo.net/forum/t45188/

Why's that important? Is there anywhere online I can read about this kind of stuff?

There's nowhere online that I'd trust...

Theres a few issues to deal with:

1) Ride frequencies - just going ever stiffer and stiffer with main springs isn't a good thing. Very stiff suspension means very poor traction and handling because the load on the contact patch of the tyre is continually varying. A real recipe for squeaky bum time on track.
2) Ride frequency balance. Having the right ratio of ride frequency at front and rear makes for comfort - you can go a lot stiffer with careful balancing
3) Springs and dampers are a combined thing, If they're not set-up together, then you'll get crapper behaviour. The ability of a set of adjustable dampers (at least the single adjustables most people buy) to control a range of springs is relatively limited.
4) Roll couple (I prefer roll moment distribution) is a measure of how much of the weight transfer when cornering is carried by a particular axle. It's a function of spring rate, ARB rate and suspension geometry (FWIW, the roll couple on the FCM spreadsheet doesn't take account of the last bit, so gives erroneous results).
5) You need to strike a balance between springs and ARB. Going too stiff with one relative to the other means you don't get decent damping or either ride or roll. Either will make your car a bit of a pig on road and track.

Look at it this way: if you're going to change springs, you'll definitely have to change dampers and you may have to change ARB as well. Getting the information to do that with any degree of success is not going to be found on the internet. You will find plenty of people saying 'I did this and it's brilliant...' but very few who can quantify why and how it is.

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Mr Slow

Discussion Starter · #4 · Mar 29, 2010

StressedDave said:
I know next to jack about suspension, I currently have NB KONI's (so only one perch choice) with Koni sport springs and OEM ARB's. The front is stupid low and the rear heights are inconsistant side to side. I have a set of eBay threaded collars, (any naysayers here can bugger off

), and want to pair those with a set of 2.5" x 7" or 8" springs.

I'm not really inclined to increase the strength of my ARB's, from what i've read it'll keep the body under control at the expense of outright grip/more severe loads on the outside tyres.

My car is also my daily driver, and some of the roads i drive on are nasty with bad potholes etc, so DD comfort is also an issue, would the 'Ground Control' rates of 275/250 be sufficient for my needs? or should I go higher/lower? (FM's springs are 320/200?!?)

Whist I'm asking.... 'Front Roll Couple' as reference by this thread:

http://www.miataturbo.net/forum/t45188/

Why's that important? Is there anywhere online I can read about this kind of stuff?

There's nowhere online that I'd trust...

Theres a few issues to deal with:

1) Ride frequencies - just going ever stiffer and stiffer with main springs isn't a good thing. Very stiff suspension means very poor traction and handling because the load on the contact patch of the tyre is continually varying. A real recipe for squeaky bum time on track.
2) Ride frequency balance. Having the right ratio of ride frequency at front and rear makes for comfort - you can go a lot stiffer with careful balancing
3) Springs and dampers are a combined thing, If they're not set-up together, then you'll get crapper behaviour. The ability of a set of adjustable dampers (at least the single adjustables most people buy) to control a range of springs is relatively limited.
4) Roll couple (I prefer roll moment distribution) is a measure of how much of the weight transfer when cornering is carried by a particular axle. It's a function of spring rate, ARB rate and suspension geometry (FWIW, the roll couple on the FCM spreadsheet doesn't take account of the last bit, so gives erroneous results).
5) You need to strike a balance between springs and ARB. Going too stiff with one relative to the other means you don't get decent damping or either ride or roll. Either will make your car a bit of a pig on road and track.

Look at it this way: if you're going to change springs, you'll definitely have to change dampers and you may have to change ARB as well. Getting the information to do that with any degree of success is not going to be found on the internet. You will find plenty of people saying 'I did this and it's brilliant...' but very few who can quantify why and how it is.
[/quote]

Cheers for the response Dave

So hypothetically speaking, lets say I bought a set of springs with the same rate as supplied by GroundControl (375FR/250RR) - which on the internet is a very highly thought of setup with KONI's, Tokico Illumina's, and KYB AGX's.

What shocks should I replace the KONI's with, (this is hypothetical as it's not gonna happen I can't afford it, plus I like my KONI's

). Or more specifically what should the shocks be doing that's correct with those rates?

The Sportdrive setup isn't a valid answer either

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StressedDave

· #5 · Mar 29, 2010

Mr Slow said:
Cheers for the response Dave

So hypothetically speaking, lets say I bought a set of springs with the same rate as supplied by GroundControl (375FR/250RR) - which on the internet is a very highly thought of setup with KONI's, Tokico Illumina's, and KYB AGX's.

What shocks should I replace the KONI's with, (this is hypothetical as it's not gonna happen I can't afford it, plus I like my KONI's

). Or more specifically what should the shocks be doing that's correct with those rates?

The Sportdrive setup isn't a valid answer either

Hypothetically speaking you need to spend some money with an expert for advice like that

The Ground Control rates are close (but no cigar) to what we're using for SportDrive. I've not tested either the Koni or the Tokico, but the KYB would be wholly unsuitable. Without rig testing the dampers I wouldn't like to say if they're even in the ball park. If they've been designed for OE rates, then it's highly unlikely that they would be.

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Mr Slow

Discussion Starter · #6 · Mar 29, 2010

Heh touche

I'm not in the slightest bit inclined to replace my shocks, they're well thought of and I like them.

Accrding to the internec (sic), they're capeable up to rates of 550, but that sounds like a flipping strong spring to me and not my idea of a good time.

They also are apparently very nice with the FM springs (which have a similar - abeit slightly lower - rate to the ground controls). I'm also a massive fan of the ride on my dads car which has KYB AGX's and FM springs.

All interesting stuff, still not sure what to take a punt with though

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StressedDave

· #7 · Mar 29, 2010

Mr Slow said:
Accrding to the internec (sic), they're capeable up to rates of 550, but that sounds like a flipping strong spring to me and not my idea of a good time.

Might be possible for high speed damping, i.e. over bumps but would almost certainly not be the case for low speed damping which is the bit that controls traction, road holding and transient handling. The Koni dampers adjust high speed rebound only.

Mr Slow

Discussion Starter · #8 · Mar 29, 2010

StressedDave said:
The Koni dampers adjust high speed rebound only.

Segway....

When i crank up my adjusters I notice on initial turn in the car leans less, also it seems (to my untrained arse) to be riding firmer over bumps/cracks in the road.

How come if the damping is only being increased after the initial bump?

StressedDave

· #9 · Mar 29, 2010

Mr Slow said:
The Koni dampers adjust high speed rebound only.

Segway....

When i crank up my adjusters I notice on initial turn in the car leans less, also it seems (to my untrained arse) to be riding firmer over bumps/cracks in the road.

How come if the damping is only being increased after the initial bump?
[/quote]

1. Because the most important part of damping control is not controlling the lightweight wheel disappearing into the wheel arch, but the big heavy car trying to jerk itself upwards instead - rebound control is several orders of magnitude more important than bump control
2. If it's a double wheel bump then that's true, but if it's not the then ARB transferring weight around under the control of the dampers gives different results.

Mr Slow

Discussion Starter · #10 · Mar 29, 2010

Cheers for that Dave, makes sense

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The Gazman

· #11 · Mar 30, 2010

Ive played with loads of spring rates this last year and have arrived at 400lb front and 300lb rear which I reckon is a good compromise for road and track and the MOT boys agreed at the last track day at Blyton.
The only problem is that you do need bump and rebound adjustment on the dampers to be able to have the car well mannered on B roads and track with those rates.

Matt

· #12 · Mar 30, 2010

I have just had the Gaz Gold Pro's fitted by WIM and after indecision on the spring rates i went for the 350/250 on their advice. just did an airfield day and the body lean was tremendous, on some corners there were further compressions which caused a metallic graunch from the shock which i assume is something bottoming out.

If using for track work i should have gone for the 400/300 - just FYI

Matt

Mr Slow

Discussion Starter · #13 · Mar 30, 2010

Matt said:
I have just had the Gaz Gold Pro's fitted by WIM and after indecision on the spring rates i went for the 350/250 on their advice. just did an airfield day and the body lean was tremendous, on some corners there were further compressions which caused a metallic graunch from the shock which i assume is something bottoming out.

If using for track work i should have gone for the 400/300 - just FYI

Matt

Cheers Matt, are you on stock ARB's?

Could the 'graunch' be coilbind?

StressedDave

· #14 · Mar 30, 2010

Mr Slow said:
I have just had the Gaz Gold Pro's fitted by WIM and after indecision on the spring rates i went for the 350/250 on their advice. just did an airfield day and the body lean was tremendous, on some corners there were further compressions which caused a metallic graunch from the shock which i assume is something bottoming out.

If using for track work i should have gone for the 400/300 - just FYI

Matt

Cheers Matt, are you on stock ARB's?

Could the 'graunch' be coilbind?
[/quote]

If you're lucky... if you're not it's the piston hitting the base valve which generally means a U/S damper in short measure.

Matt

· #15 · Mar 30, 2010

stock ARB's, bit disappointed as my original Jap shocks didnt do this and i wasnt driving any harder on these Gaz Gold Pro's.

StressedDave

· #16 · Mar 30, 2010

It's worth ripping the dampers off the car and getting them tested on a dyno. If you're getting bottoming out and excess roll it might indicate a problem.

Matt

· #17 · Mar 30, 2010

they were only fitted a month ago

StressedDave

· #18 · Mar 30, 2010

And your point is?... it's not unknown for dampers to not work properly out of the box and if you've managed to bottom the piston then its possible they aren't working now. T'would be a terrible thing to slag off a damper solution if it's not actually working properly in the first place.

Gixer

· #19 · Mar 30, 2010 (Edited by Moderator)

Thing is Richy your separating your cars suspension into section, Springs, Shocks, ARB's.

You can't do that, the suspension works together as one package.
You could go out tomorrow and buy a set of Tein Flex's, but if you fit the stock springs with em the cars gonna feel like shite.

The shock damping rates need to be related to the spring rates, if you fit stiffer springs then on any old shock willy nilly then your gonna bollox up the rebound for a start.

As has already been said lean in itself is not always a bad thing, if on t'other hand your riding every corner on your bumpstops that's gonna give extremely unpredictable handling.

For me the ideal is to touch the bumpstops a few places round a lap.
That way you know your using all the suspension travel, but your not using it all, all the time.

On your limited budget i'd say bollox to the negatives and just bolt on aa set of FM ARB's

Cheers
Mark

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The Gazman

· #20 · Mar 30, 2010

Matt said:
stock ARB's, bit disappointed as my original Jap shocks didnt do this and i wasnt driving any harder on these Gaz Gold Pro's.

If thats a picture of your car as is is now then its more than likely that you are bottoming out and whacking bumpstops, indeed as Dave says you could have punched out the foot valves.
I had no idea that people were running that low on track use cars.
I should point out that we run 250 to 300lb springs on the rear of most of the Mazda race cars at a lowest height of 115mm to the lowest point of the sill and you look way below that point.

I can only suggest that you either make contact with me or your installer as a matter of urgency but I warn you that if you ring me and you're running at 100mm to the underside of the sill as I suspect, you can expect to be told a few home truths about running show car heights on a track use car and how crap its going to handle.

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