Suspension options and questions for 07 NC STR build

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Suspension options and questions for 07 NC STR build

Postby keithchung » Mon Jun 14, 2010 12:52 pm

Hi Brian,

I am one of those who have read probably too many posting on Miata.net
on suspension options for a capable NC Autocrosser, and ended up being even more confused.

I am in my Year one to this exciting sport (did a driving school + 3 autocross events so far this year). My car has been stock (was a lease) except for the Roastersport Q exhaust from you (loving it !). Now I own the car I am planning to compete in the new STR class as it's one of the more exciting classes (with several S2000s, NC, MR2 Spyder, etc.) at our local club and the mods allowed + street tires align with what I want to do with the car better. My NC will be my weekend and autocross toy and occasional DD.

I have a set of 17x9 235/40/17 RE-11 on the way from TR. I have been doing my readings on
the suspension upgrade options.

1. I prefer the coilover options, as they allow the car to be lowered than what Eibach lowering springs can do, plus height adjustability and corner weight balancing, although the $$$ for a decent set is pushing the limit of my budget.

I see you have 2 different JIC packages, one with OEM springs (335/279) and one with CSP springs (670/391). I suppose the shocks are the same ? My question is which spring rates would be better suited for STR class with street tires. I think the high spring rate would work nicely with the super grippy 285/35/18 R-comp CSP tires, and may be too much for street tires ?
Would a combo that's in between (say 500/350) be a better option for STR ?

2. More of spring rates:

I noticed the stock spring rates of other coilovers are all over the places. 330/230 for Bilstein PSS-10, and 230F for KW. I suppose those spring rates are well suited for stock NC with street application. I seem to make assumption that higher spring rates are better suited for autocross
and higher grip tires. Am I on the right track? Am I over-simplying things?

3. As an alternate to coilovers, are there aftermarket shocks and springs combo that
will provide strong handling performance given the higher ride height ?

Thanks,
Keith C.
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Re: Suspension options and questions for 07 NC STR build

Postby Brian » Mon Jun 14, 2010 2:57 pm

Welcome.

No regular spring and shock combo will compare with a full coilover setup. In general, higher spring rate setups will be more competitive for autocross days....but give you a firmer ride on the daily drive. Thus, it is a trade off and only you can say how much daily ride you want to give up for speed in that STR class. I run Ohlins with almost 800 pound front springs but I live in San Diego and the roads are pretty good here...and the Ohlins do an amazing job of handling the higher rates without much additional harshness. Yes, the JIC are the same shocks with either spring rate (note JIC is currently switching production to the USA and they told us August before their updated product is ready). Ohlins just updated their product this year to the latest "Road and Track" spec. Ohlins are the best...but if the Ohlins are not in the budget I would look long and seriously at our KW variant 3.....that's a VERY NICE setup for the money that won't compromise daily ride quality: :mrgreen:

http://www.good-win-racing.com/Mazda-Pe ... -0175.html
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Re: Suspension options and questions for 07 NC STR build

Postby keithchung » Mon Jun 14, 2010 5:56 pm

Thank you for the quick response and helpful feedback, Brian.

I have looked at the KW variant 3 as it fits my budget and it's the choice of Tirerack's STR NC project. My only reservation is that in stock spec they come with relatively low spring rate (230 front, progressive rear). As my NC will be mainly a weekend and autocross toy ( I live too close to work not to be green in daily commute :( ) and roads around here are fairly nice so I am willing to trade most of the ride quality for autocross performance.

Questions:
1. Do you think the KW V3, as a package, offer competitive performance over other coilovers in similar price range such as JIC ?
2. Are there optional harder springs available for the KW V3 and if so can I potentially purchase
a set of "KW V3 STR package" from you similar to the JIC CSP package you are offering? :lol:

Thanks again.
Keith C.
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Re: Suspension options and questions for 07 NC STR build

Postby Brian » Mon Jun 14, 2010 8:18 pm

To some extent there is no replacement for higher rates. But, a daily driver is a compromised race car by design...and that's okay. I like the KW because the rates are so mild yet they have the double adjustment....that's a rare combination of control with mild ride. They don't offer us a higher rate spring package and I am not aware of those being valved to accept much higher rates. If you go that way, and you find you need a little more roll resistance, then you still have sway bars and could get real stiff with those (and sways don't have much impact on ride quality).
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Re: Suspension options and questions for 07 NC STR build

Postby keithchung » Tue Jun 15, 2010 11:23 am

Thanks again, Brian.
So my take is that for daily driver and street performance, the KW V3 would be awesome.
For hardcore autocrossing, it may need to be complemented with beefer sway bars to control the roll. I have read more on Tirerack's experience with their STR NC development and their feedbacks are consistent with yours. One positive comment about that setup is that it's more flexible as there are more variables to play with on the race day depending on the course conditions (hot, dry, wet, cold, etc.)
That's great to know ! Thanks.

Keith C.
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Re: Suspension options and questions for 07 NC STR build

Postby keithchung » Thu Jun 17, 2010 5:03 pm

Hi Brian,

Do you have any suggestion on the alignment for my NC (stock suspension, 235/40/17 RE-11 on 17x9 )
for autocross ? I am willing to trade some tire wear for max autocross performance.

Also, as a general rule, what alignment adjustment should I make once I lower the car with coilovers and sways
from the above setting ?

Thanks again.

Keith C.
keithchung
 
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Re: Suspension options and questions for 07 NC STR build

Postby Brian » Thu Jun 17, 2010 5:11 pm

If not concerned about the tire wear...then take what you can get on the camber. As you likely know, as you go lower the max camber you can get will be higher and higher. But, so far the FASTEST STR guys are going with 255/40/17 tires which are a little tall and will limit how much you can lower the car and still do a 'legal' fender lip roll for clearance. Let's say that means you only lower the NC by 1.5 inches. At that point perhaps you get 2.2 deg max camber. I would take what you can get and then zero front and rear toe and max the front caster with the above specs.
Brian Goodwin
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Re: Suspension options and questions for 07 NC STR build

Postby keithchung » Fri Jun 18, 2010 3:29 pm

Thanks again, Brian !

So let's say I could get 2.2 max camber at front with my max 1.5 inches lowering,
and same for the rear. I came across your comment on the better rear camber curve
on NC (as compared to NA/NB) therefore the rear can use less camber.

So would Front 2.2 Rrear 1.9 be a good starting camber setting with 1.5 inches lowering?
Should I start with more/less bias ?

I understand I need to test various setting to find the ones that work with my driving/car/course/etc., but thought I would seek your advice for a good starting point.
I am in the process of negotiating an alignment package ( 3 alignments for the cost of 2 )
with local shops. So far no bites yet as I am in a small town :(

As for caster, I understand that more caster preserves straight line stability and would make the steering wheel harder to turn. I guess I am less certain why Max caster is suggested
for aggressive autocross setting as I was thinking it would make the car react slower to the steering input ?

Thanks

Keith C.
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Re: Suspension options and questions for 07 NC STR build

Postby jboemler » Fri Jun 18, 2010 9:53 pm

Camber changes with the turning of the wheels. How much it changes is dependent on caster -- more caster means more "camber gain".

jim
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Re: Suspension options and questions for 07 NC STR build

Postby keithchung » Sat Jun 19, 2010 4:43 pm

Jim,
Thanks for the explanation. Although I probably need to see
some sort or 3D visualization to fully understand it but it makes good sense.
It's nice to have one less variable to play with at the beginning, as I can simply tell the shop to get the max caster they can. :)

Keith C.
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