Spring rates? Why not 3:2 ratio on HSD, yellowspeed etc?

[botisto]

I've spent all day reading far too mathematical books trying to work out my ideal spring rates and have gotten into a rut. So old mate keith says you want a 3:2 ratio with the front and rear springs and this should give you a balanced car, so if i can work out my ideal spring rate at that ratio then i can easily adjust under/oversteer characteristics with a set of three way adjustable whiteline bars.

So why oh why do all the coilover kits I'm looking at buying have really stiff rears once they get into more track focused rates? Are they just assuming your gonna run no rear sway bar and a heavy front and not worry about the natural frequency?

Trying to keep my build cheap I'm looking at the HSD and yellowspeed, the track yellowspeed are 12-11kg ????
And the HSD's are 10-8kg, which is still a fair way off keiths recommended 10-6.4kg. So if anyone could shed some light on whether its me being retarded or it's all these coilover companies...


Also, this is all for a stripped and hopefully caged NA8 that will get equal road and track driving, but I'm wondering if the 10-8kg HSDs (ignoring the ratio) would be ideal for this or still too stiff for the road usage? I figured the 8-6kg yellowspeed wouldn't be enough and the 12-11 yellowspeed too stiff... And i don't have my corner / unsprung weights yet to work out the natural frequency, so if anyone with more experience than me could shed some light on this as well i would be very grateful. (I'm looking at getting AXIS 15x8 wheels which should be 6.6kg with 205 Federal 595RS-R in a package from mx5mania if they ever reopen / reply..

Thanks for reading my end of day rant!

[tbro]

A bit of info I gave out before,

Sit down read and DON'T overthink everything.
You can not run big spring rates AND big sways its doesn't work. Read http://www.fatcatmotorsports.com. Just remember the yanks set their cars up for smooth tracks which is ok for Lakeside and now QR, but if you go to Morgan be prepared to chase spring rates.
http://www.camsmanual.com.au/ use it, think about it and then reread it, this is a legal document, it is open to interpretation and not everything is black and white. BUT make sure you have a convincing argument if your gunna try something too far of the block.

http://www.bmsc.com.au/forums/rallying- ... orums.html, interesting stuff.


Some of the best reading I've come across for helping to set up your car and the whys and wherefore it works and doesn't. Great for novices and pros.http://farnorthracing.com/autocross_secrets.html

Books that have helped,

Speed Secrets & Speed Secrets 2 by Ross Bentley, there are a few in the series ,I prefer these two.

How to make your car handle by Fred Pugh?? an old book but very informative if at times a bit heavy. Remember, suspension is nothing but compromise on a production based road car!!!! even a GT2 or 3. And a sway bar cannot work properly if the linkpins are not straight up and down as per the factory!!!!!!(think about it and how to get around it, look at the pics)

Track Data by Craig Pearce, avail in ebay.com. Cheap as, as the list are something that we all think we should do , but never do. ALWAYS in the transporter and my suit bag. BOAGS and Crewman should really have this book.

A few things to think about BEFORE you start to play on your car.

Do you have the ability to do the job and the ability to ask for HELP when the sh*t hits the fan???

Just because everyone else does it DOESN'T make it right or work the way they say it will!!!!!!!!

Dynos do lie, use them to guage on % of improvement, but your best dyno is track times and PBs.

If it doesn't say you can do it , you can't. Seeming a quote from CAMS. I've never seen it written in the book, and if we go by that theory no-one will ever try anything new, so to me a load of Crap!!!!! But again stay within the gray areas!!!!

Try that lot

Terry

[Lokiel]

Consider BC Racing BR coilovers.

You can specify your required spring rates when ordering them; in your case you'll want 9Kg front and 6Kg rear. By default, in Australia, they come with 8kg front and 6 kg rear springs (ie. the ratio is 8:6=1.333 which is closer to Keith Tanner's 3:2=1.5 "ideal" ratio than some others out there - 10:8=1.25, 7:6=1.1666).

I have BCs and am happy with them, 8:6 is a great ratio for a car which spends most of its time on the road rather than the track but you still want great handling.

[rascal]

I've spent all day reading far too mathematical books trying to work out my ideal spring rates and have gotten into a rut. So old mate keith says you want a 3:2 ratio with the front and rear springs and this should give you a balanced car, so if i can work out my ideal spring rate at that ratio then i can easily adjust under/oversteer characteristics with a set of three way adjustable whiteline bars.

So why oh why do all the coilover kits I'm looking at buying have really stiff rears once they get into more track focused rates? Are they just assuming your gonna run no rear sway bar and a heavy front and not worry about the natural frequency?

Trying to keep my build cheap I'm looking at the HSD and yellowspeed, the track yellowspeed are 12-11kg ????
And the HSD's are 10-8kg, which is still a fair way off keiths recommended 10-6.4kg. So if anyone could shed some light on whether its me being retarded or it's all these coilover companies...


Also, this is all for a stripped and hopefully caged NA8 that will get equal road and track driving, but I'm wondering if the 10-8kg HSDs (ignoring the ratio) would be ideal for this or still too stiff for the road usage? I figured the 8-6kg yellowspeed wouldn't be enough and the 12-11 yellowspeed too stiff... And i don't have my corner / unsprung weights yet to work out the natural frequency, so if anyone with more experience than me could shed some light on this as well i would be very grateful. (I'm looking at getting AXIS 15x8 wheels which should be 6.6kg with 205 Federal 595RS-R in a package from mx5mania if they ever reopen / reply..

Thanks for reading my end of day rant!

No you are not retarded, its the coilover companies.. I also wondered why the coilovers seem to come with unbalanced spring rates.

I specified softer rear springs when I bought my Teins, to keep as close to the correct 3:2 balance as possible, and added adjustable bars at each end to finetune.

Makes no sense to me to run the heavier rear springs and then no rear sway to try and balance it up as this removes one of your means of adjustment.

As to whether your selected spring rates will be too much for street usage, is very much a personal thing. I run 7f5r with big bars on my half caged NB and while they seem to work great on track, I find them too stiff for road use.
Others have 12kg fronts and say they are super comfy.... Each to their own....

[NMX516]

What ratio front to rear are the Mazda spring rates? Surely they put more time and development effort into getting things right than anyone else. Why change the ratio front to rear from what Mazda set??

[botisto]

Thanks so much for the replys guys, they are a serious help.. i was just starting to confused myself.

The stock springs are 2.8 - 1.7 Kg/mm which is actually very close to 3:2.

I had forgotten about the BC Coilovers... 9-6kg sounds pretty good with some big sway bars. I'll have to get to some more serious reading and see if that seems right thanks terry. Oh and for the BC racing coilovers are the V1 better then the BR?

[NitroDann]

9-6 AND big sways will not work on street tyres.

Dann

[NitroDann]

Yeah but rs3s arent street tyres.

You knew what I meant.

Dann

[manga_blue]

9/6 AND big sways won't work with any tyres. Once you start getting above 5-6Kg/mm then the stiffer the spring the smaller the sway bar you can use. Otherwise the car just gets hopelessly skittish.

Good advice from rascal and tbro here. 3:2 is about the right ratio for our cars, plus fine tuning from sways as the secondary consideration. The spring rate combinations put out as standard by many of the coilover suppliers are absurdly biased towards oversteer.

I know that if you buy Teins from someone like Emilio at 949 racing then you can specify whatever rates you like: 9/6, 10/7, 8/5, 7/5, 6/4, 5/3 are all workable. You can also buy different springs later from Emilio or Tein USA for about $50-60 each - so much cheaper than sways. It takes me about 2 hours to swap a full set of springs on my old Teins. You'd think that changing sway bars would be faster but it's not because something always goes wrong with aligning end links.

Just a bit more advice about Shaikh and his FatCat settings: remember he specialises in autocross. Those guys like to stand on the brakes as they turn in to a cone, rotating the back wheels around almost stationery fronts at times. They want much more stiffness at the front than most of us would want for street/track work. Sticking to Mazda's original FRC values of around 57% is wise until you can afford to fiddle about a bit.

[project.r.racing]

Both BCs and YSRs coilovers, you can select specific spring rates you require +/-1kg from what is advertised.

On my Astina, the YSRs advertised rates were 7/4, so I got 8/5 instead. Car weighs 1150kg, and I've run 7.5/5.2 D2s before on older coilovers with issues. So I ordered new YSRs with stiffer springs. The only issue I see is the fronts maybe being too stiff. MY old JIC Magics were 7/5, perfect from memory at the time for motorkhana/sliding.

There are also alot more factors that go into the equation if you are tracking the car. Rear wing, weight reduction, braking power etc.

Agreed also that most spring rate combos are oversteer heavy.

If I was running a MX5 without a LSD, then I would consider asking for a softer spring for the rears, so maybe 8/5 from either BC or YSR.

p.s. Who is Keith?

[botisto]

Ok well i still have a lot of reading / learning to do but what do people suggest, something like 8 - 5.5kg with sway bars? I do like the idea of having front and rear sways to adjust rather than running no rear i think. Keep in mind this is on a caged NA with 595RS-Rs and definitely a LSD. And keith is Keith Tanner the crazy flying miata guy, was going through some of his books

[botisto]

16mm in the rears does seem far too stiff, the FCM calculator is just telling me that's going to give lots of oversteer no matter what you do.

I'm thinking 8 - 5kg springs with 25 - 14mm signature bars should suit me. Gives a perfectly balanced bounce frequency front and rear of 2Hz and an FRC of 57% with the adjust ability of the sways allowing fine tuning. This is all very theoretical but seems a good start, just have to pick some coilovers

[project.r.racing]

I'm about to pull out my BCs and swap in my new YSRs when they arrive. If you can be bother to come for a drive to Beerwah sometime, you can have a looksee at the differences between both. Different car to MX5 but will give you an idea of what both ar like. Sorry no Help with the HSDs.

[bootz]

I've found a 16mm rear sway bar is way too much i've been trying to get an oem SE rear 14mm with no luck.

Personally i think the best sway bar combination is the RB 1.125" front and the oem MazdaSpeed 14mm rear with 949 endlinks all round. But as with anything sway bars come down to personal taste, get a front adjustable for sure (and rear if you can) as it really helps fine tuning of the car.

Funny, thats exactly what I am going to do.

Surely the damper settings on adjustables will modify the characteristics of the spring rates so that you can fine tune to your heart's content. I don't see the 3:2 ratio as being any more than a target to shoot for.

[botisto]

Yea that looks a good sway setup, the 1.125" tubular is roughly equivalent to a 25mm, just a bit lighter obviously.

My understanding is that it's best to get your springs around the 3:2 ratio to match the front and rear bounce frequency and get them at a stiffness for the bounce frequency your after, so 2-2.5Hz for track and then adjust the shocks to match the spring rate.
Then you can play around with FRC and get the dynamics your after through different combinations of swaybars, aliments, tire pressures, wheel spacers etc

And thanks for the offer project but i think thats a bit too far for me