NC1: search for comfort on bad roads

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matthew-m
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Location: Santa Maria, CA

Re: NC1: search for comfort on bad roads

Post by matthew-m »

I just got new tires and while the wheels were off I had the rear bar disconnected. I have noticed a slight improvement in the 'bouncing'; the easiest way to describe the change is the bump reaction is less severe. I think I also notice more individual wheel motions transmitted through the chassis, ie individual bumps seem to affect one wheel rather than the whole rear end. I would say the improvement is roughly 10%.

Does any one know if I could replace the 8" springs and helper spring assembly with 11" springs? I can find the desired rates from Swift Springs (http://www.swiftsprings.net/products/un ... gs-65.html) in 11" for both front and rear, though only 280 lb/in in smaller lengths. Of course there are other brands, like Eibach. Does any one have an opinion about the brand of spring?

Matthew Metoyer
Matthew Metoyer
2010 Grey MX-5 GT, Manual, Sport Package, Street Single w/Baffle, FCM Coilovers - "GT" setup with KBO & Ripple Reducer, 16x8 wheels, Budget Big Brakes, Goodwin Underbody Braces, Cravenspeed Shift Knob
skeeler
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Re: NC1: search for comfort on bad roads

Post by skeeler »

If you have the "standard" FCM setup, then you have Eibach 65-mm main springs in front, Tein 90-70-mm tapered springs in rear, and Hyperco helper springs. The Tein springs are either out of production or very difficult to get. For this reason, FCM is moving to straight springs in the rear. A number of us with FCM or other coilovers have converted to straight springs in the rear to open up our spring options. Doing so is a bit of a project, since the RX-8/NC platform is designed to use a tapered spring. So you can't just buy a straight sprint in the rear. At a minimum, you'll need to use Brian Goodwin's adapters, but there are some wrinkles I can tell you about if you care. I'd suggest that changing out the front springs is the easier way to go. It's less work than the rear, and you don't have to worry about all the tapered-spring nonsense. You'll want 65-mm or 2.5-inch springs for the front. I think you probably have an 8-inch-long spring in the front, and you should have plenty of room for an 8-inch spring of a higher rate, though you will have to adjust the lower spring perch lower to get the same ride height. If you don't have a spring coupler (AKA spring stacker) in the front, I'd suggest getting one.

Hyperco, Swift, and Eibach all make good springs. I'm running a mix of Swifts and Hypercos on the NC and all Hypercos on the NA. Hypercos can be found for 50-60 bucks each. Swifts tend to be 85-95.

Another option would be to go with a stiffer sway bar in the front. I think I suggested a Red-Dot before. You could also try the Yellow-Dot. There are also plenty of non-Mazda options. The sway bar would only work in roll, not heave, so it wouldn't impact your ride quality as much. The front sway bar is a lot more work than the rear, however.

EDIT: Looking back at what I suggested before, I definitely suggest you go with a stiffer sway bar, even if you don't do the front springs.

BTW, since you have helper springs, you don't need a spring compressor to change out your springs.
2009, STR & DD. 1995, HPDE. 2004 MSM, sold. 2010 Mazda3, hers.
skeeler
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Re: NC1: search for comfort on bad roads

Post by skeeler »

Hyperco makes the spring I suggested for the front. Page 10 here: http://www.hypercoils.com/catalog.html#.Uwl4YEJdVR8

You might also consider the 275-lb/in spring in the front.

If you want to do the rear, you may be able to find the Tein tapered spring. It used to listed under standard springs here, but I can't get the page to load: http://www.tein.com/
2009, STR & DD. 1995, HPDE. 2004 MSM, sold. 2010 Mazda3, hers.
skeeler
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Re: NC1: search for comfort on bad roads

Post by skeeler »

Here are the Tein springs: http://www.tein.com/products/standard_s ... _list.html

It looks like the 224-lb/in (4 kgf/mm) spring is only available available in 6.8-inch and 9.8-inch lengths, so I'm not sure what you have on the car. The 280 is available in 6.8, 7.9, and 9.8. But, like I said, all of these seem to be almost impossible to get now.
2009, STR & DD. 1995, HPDE. 2004 MSM, sold. 2010 Mazda3, hers.
matthew-m
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Location: Santa Maria, CA

Re: NC1: search for comfort on bad roads

Post by matthew-m »

Thanks skeeler, I will crawl under the car to confirm what I have, and look to the Eibach or Hyperco springs.
Matthew Metoyer
2010 Grey MX-5 GT, Manual, Sport Package, Street Single w/Baffle, FCM Coilovers - "GT" setup with KBO & Ripple Reducer, 16x8 wheels, Budget Big Brakes, Goodwin Underbody Braces, Cravenspeed Shift Knob
matthew-m
Posts: 82
Joined: Tue Jun 09, 2009 7:23 pm
Location: Santa Maria, CA

Re: NC1: search for comfort on bad roads

Post by matthew-m »

skeeler wrote:
skeeler wrote: Given that your bounce frequencies are a little out of whack, I'd suggest some combination of much stiffer front sway bar and either softer front spring or stiffer rear springs.
OK, having played with the numbers a bit, here are my suggestions:

If you want to go slightly softer than your current setup, then go to 250/224 springs and red dot/green dot sway bars.
If you want to go slightly stiffer, then go 300/280 and red dot front sway with no rear sway.

Does your car have an LSD? In other words, is the rear sway bar green dot or blue dot?

But like I said, try just pulling off the rear sway bar first, to see if that helps.
Skeeler,

I am going to replace the front spring with a 250 lb/in, probably Eibach. As to the sways, when I disconnected the rear bar I now have slight understeer. I guess it is better to have traction off the line versus slight understeer at the limit...

What is the equivalent of the red dot/green dot sways you mentioned earlier from the available aftermarket options? For instance, an Eibach front bar with the stock (blue dot) rear bar? I can't see buying OEM parts for the same cost as the aftermarket parts. I don't want to go too aggressive, ie a full Pprogress Springs setup. Thanks!

Matthew
skeeler
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Re: NC1: search for comfort on bad roads

Post by skeeler »

The green-dot rear bar came on cars without LSD; it has an 11 mm OD and 2.6 mm wall thickness. It's the softest bar available for the NC; none of the aftermarket bars are close. The blue-dot rear bar came on cars with LSD; it has a 12 mm OD and 2.6 mm wall thickness, so it's about 42% stiffer, but these two bars are closer than to each other than any of the aftermarket bars. If you want to run the blue-dot rear bar and 250/224 springs, it looks like the Racing Beat front bar would be a good choice. The RB bar has three holes, so it should give you a range of FRC from 69.9% to 74.4%, according to my calculations. I'd suggest starting on the middle setting, wich gives 72.1%. (Note that three holes give you five different stiffnesses, since you can mix and match holes from one side to the other.)

Keep in mind that all this advice is worth exactly what you paid for it.
2009, STR & DD. 1995, HPDE. 2004 MSM, sold. 2010 Mazda3, hers.
matthew-m
Posts: 82
Joined: Tue Jun 09, 2009 7:23 pm
Location: Santa Maria, CA

Re: NC1: search for comfort on bad roads

Post by matthew-m »

skeeler wrote:Keep in mind that all this advice is worth exactly what you paid for it.
Well it has been good advice so far, and I appreciate it very much!

Andrew, how did your setup changes turn out?
Matthew Metoyer
2010 Grey MX-5 GT, Manual, Sport Package, Street Single w/Baffle, FCM Coilovers - "GT" setup with KBO & Ripple Reducer, 16x8 wheels, Budget Big Brakes, Goodwin Underbody Braces, Cravenspeed Shift Knob
matthew-m
Posts: 82
Joined: Tue Jun 09, 2009 7:23 pm
Location: Santa Maria, CA

Re: NC1: search for comfort on bad roads

Post by matthew-m »

Well I finally got everything installed (Progress front sway bar, Hyperco 250 lb front springs) and the results are as expected. Thanks everyone for their assistance!
Matthew Metoyer
2010 Grey MX-5 GT, Manual, Sport Package, Street Single w/Baffle, FCM Coilovers - "GT" setup with KBO & Ripple Reducer, 16x8 wheels, Budget Big Brakes, Goodwin Underbody Braces, Cravenspeed Shift Knob
matthew-m
Posts: 82
Joined: Tue Jun 09, 2009 7:23 pm
Location: Santa Maria, CA

Re: NC1: search for comfort on bad roads

Post by matthew-m »

Hello everyone,

I am once again considering my options for a more comfort-oriented suspension on my '07 PRHT. I feel it is time to rebuild the shocks on the FCM coil overs, after 80k miles. FCM has released Ripple Reducer & KBO v1.8 upgrades to their products since I bought mine. As a reminder, I have 250 lb front and 224 lb rear springs installed with a Progress Springs front sway bar and the stock (blue dot) rear bar. Shaikh took me on a test drive in his BMW and it was a lot smoother than my car, despite higher spring rates and aggressive lowering.

My options are to purchase the FCM upgrades and rebuild the shocks or go to a standard shock (Bilstein?) and Progress Springs. For roughly the same cost as the coil over rebuild, I can get the Progress springs, shocks and a underbody brace kit (lots of rattles after 126k miles). I am also considering Kosei 16 x 6.5" wheels and Firestone Firehawk Indy 500 195/55/16 tires for additional comfort (and lower weight & longer tread life).

There are many knowledgeable people on the list so what do you think of these options? My concerns are: the (possible) reduced capabilities of the Progress/Bilstein/Brace; the cost of the FCM rebuild and the unknown factor of the end result; and the reduction in tire size and grip going from 215/45/17 Max Performance tires on 17x8 wheels to the 16" Ultra High Performance tires mentioned earlier.

As you can see, I 'want my cake and to eat it too'. I know I am not using the car to its full (current) capabilities so I am probably over-thinking this. As mentioned earlier in this thread, I want to reduce/eliminate the tendency of the rear to pogo over dips and bumps. Hopefully fixing that will reduce the wheel hop on aggressive starts.

This is a lot of information so please give it some thought and reply regarding whatever topic you wish. Thank you!
Matthew Metoyer
2010 Grey MX-5 GT, Manual, Sport Package, Street Single w/Baffle, FCM Coilovers - "GT" setup with KBO & Ripple Reducer, 16x8 wheels, Budget Big Brakes, Goodwin Underbody Braces, Cravenspeed Shift Knob
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