Race Car Tech Discuss anything related to road racing and auto X.

FD suspension motion ratios

Old 10-29-06, 10:35 PM
  #1  
Senior Member
10 Year Member
Thread Starter
iTrader: (1)
 
Sandro's Avatar
 
Join Date: Mar 2002
Location: Plainfield, NJ - USA
Posts: 480
Likes: 0
Received 0 Likes on 0 Posts
FD suspension motion ratios

Maybe I should rather post this in the Suspension section...anyhow.

Today, I jacked the suspensions and measured directly spring and wheel motion from unloaded (wheel hub hanging down) to fully loaded. I calculated a motion ratio 0.60 Front and 0.68 Rear.

Has anyone else done this I could compare notes with or, are such figures available anywhere?

I am doing this because I am moving from stock class and upgrading my suspension. I wanted to calculate spring rates at different frequencies, and get some reference points before starting playing with real springs.

Thanks,

Sandro
Sandro is offline  
Old 10-31-06, 11:30 AM
  #2  
~17 MPG
iTrader: (1)
 
scotty305's Avatar
 
Join Date: Jan 2004
Location: Bend, OR
Posts: 2,741
Received 18 Likes on 14 Posts
I haven't done much suspension work, but thanks for posting your info.

If you're interested in corner weights, I had access to some racing scales a couple of months ago, and posted the info in this thread:
https://www.rx7club.com/race-car-tech-103/had-my-fd-corner-weighed-advise-comments-suggestions-430565/

-s-
scotty305 is offline  
Old 11-06-06, 01:50 PM
  #3  
Senior Member
 
Join Date: Jul 2003
Location: San Jose
Posts: 291
Likes: 0
Received 0 Likes on 0 Posts
Hi Sandro,

Those look like they are in the ballpark, though I'd need to check my suspension model. If you lower the car significantly, you'll need wheel rates in at least the 300's to keep roll reasonable for an ASP car (very low cars with stock suspension probably have the front roll center under ground).

Best thing to do is use your calc's as a starting point, then real world experience to fine tune.

-Andy M.
AMRX7 is offline  
Old 11-06-06, 04:21 PM
  #4  
Senior Member
10 Year Member
Thread Starter
iTrader: (1)
 
Sandro's Avatar
 
Join Date: Mar 2002
Location: Plainfield, NJ - USA
Posts: 480
Likes: 0
Received 0 Likes on 0 Posts
Originally Posted by AMRX7
Hi Sandro,

Those look like they are in the ballpark, though I'd need to check my suspension model. If you lower the car significantly, you'll need wheel rates in at least the 300's to keep roll reasonable for an ASP car (very low cars with stock suspension probably have the front roll center under ground).

Best thing to do is use your calc's as a starting point, then real world experience to fine tune.

-Andy M.
Thanks Andy.

Yes, that's what I coming to. Like 12 kg/mm in the F and 10 in the R. That would give an equal frequency of about 140 cpm. I will start with that, then try going up. Next year project at this point...

- Sandro
Sandro is offline  
Old 11-06-06, 05:06 PM
  #5  
Senior Member
 
Join Date: Jul 2003
Location: San Jose
Posts: 291
Likes: 0
Received 0 Likes on 0 Posts
Originally Posted by Sandro
Thanks Andy.

Yes, that's what I coming to. Like 12 kg/mm in the F and 10 in the R. That would give an equal frequency of about 140 cpm. I will start with that, then try going up. Next year project at this point...

- Sandro
Hi Sandro,

IMHO, for a serious ASP car those rates are too soft unless you plan on using the bumpstops as added spring rate. I think you need to be 30% or more stiffer than that.

-Andy M.
AMRX7 is offline  
Old 11-06-06, 08:59 PM
  #6  
Senior Member
10 Year Member
Thread Starter
iTrader: (1)
 
Sandro's Avatar
 
Join Date: Mar 2002
Location: Plainfield, NJ - USA
Posts: 480
Likes: 0
Received 0 Likes on 0 Posts
Originally Posted by AMRX7
Hi Sandro,

IMHO, for a serious ASP car those rates are too soft unless you plan on using the bumpstops as added spring rate. I think you need to be 30% or more stiffer than that.

-Andy M.
I value your opinion Andy and will therefore follow your suggestion. 30% more over 12/10 kg/mm would make something like 900/750 lb/in F/R I will start with those rates then.

Thanks again,

Sandro
Sandro is offline  
Old 11-06-06, 10:42 PM
  #7  
Junior Member
5 Year Member
 
fd20b's Avatar
 
Join Date: Apr 2003
Location: SD, California
Posts: 33
Likes: 0
Received 0 Likes on 0 Posts
spring rates

Those sound like good rates... Good job Andy...

Jeff
fd20b is offline  
Old 11-07-06, 11:31 AM
  #8  
Full Member
10 Year Member
iTrader: (1)
 
Join Date: Jul 2002
Location: Austin, TX
Posts: 106
Likes: 0
Received 0 Likes on 0 Posts
Originally Posted by Sandro
I value your opinion Andy and will therefore follow your suggestion. 30% more over 12/10 kg/mm would make something like 900/750 lb/in F/R I will start with those rates then.

Thanks again,

Sandro
Sandro,
Those rates sound very good, as we are running 950/750 on Topeka ashalt on our 3-rotor which does have some extra weight on the nose. Make sure you get a good shock to control these springs.
streldoc is offline  
Old 11-07-06, 11:31 AM
  #9  
Senior Member
 
Join Date: Jul 2003
Location: San Jose
Posts: 291
Likes: 0
Received 0 Likes on 0 Posts
That sounds more like it, though you will need to balance with your swaybar choices. You're going to want something sizable up front like the Tripoint bar, but shouldn't need alot of bar in the rear. If you can get the car to work with no rear bar that would be best for putting power down. I run a near stock sized rear bar and one of these days I'll try and get rid of it altogether.

-Andy
AMRX7 is offline  
Old 11-07-06, 11:45 AM
  #10  
Full Member
10 Year Member
iTrader: (1)
 
Join Date: Jul 2002
Location: Austin, TX
Posts: 106
Likes: 0
Received 0 Likes on 0 Posts
Originally Posted by AMRX7
That sounds more like it, though you will need to balance with your swaybar choices. You're going to want something sizable up front like the Tripoint bar, but shouldn't need alot of bar in the rear. If you can get the car to work with no rear bar that would be best for putting power down. I run a near stock sized rear bar and one of these days I'll try and get rid of it altogether.

-Andy
We have the 0.188" wall thickness Tripoint bar, and it is available in 4 wall thickness from 0.093" to 0.250". Also as Andy and I have discovered, you must get a KAAZ 1.5 limited slip (set to 67% locking) for autocross, as you will be spinning the inside wheel with the stock differential. This will help the most on getting power to the ground.
streldoc is offline  
Old 11-07-06, 08:34 PM
  #11  
Senior Member
10 Year Member
Thread Starter
iTrader: (1)
 
Sandro's Avatar
 
Join Date: Mar 2002
Location: Plainfield, NJ - USA
Posts: 480
Likes: 0
Received 0 Likes on 0 Posts
Andy, Eric,

Thanks a lot for your valuable advices.

As for the shocks, I have been using the Koni 8211 (matched to the stock springs so far) for a number of years now and found them very reliable and consistent. I asked Paul at Koni NA (who has been tuning them to perfection) about using them with higher spring rates (1,000 lb/in or so). He indicated that after proper revalving the 8211 should be still adequate for handling those rates. Having said that, I know you Eric have been very happy with the 2812, which you recommended to me in the past. I will give a try to my 8211 first, but if they won't work I will definetly go with the 2812.

It's good to know about the Kaaz. With the car stock and a super beefy front sway bar I had never experienced wheel spinning. With one exception, when one of the aluminum arms of a tubular Racing Beat front sway broke off in the middle of a run. The rear wheels were spinning so badly that I though the clutch was gone, as the rpm needle kept spiking up while the car would not accelerate...

Best,

Sandro
Sandro is offline  
Old 11-08-06, 12:13 PM
  #12  
Senior Member
 
Join Date: Jul 2003
Location: San Jose
Posts: 291
Likes: 0
Received 0 Likes on 0 Posts
Originally Posted by Sandro
Andy, Eric,

It's good to know about the Kaaz. With the car stock and a super beefy front sway bar I had never experienced wheel spinning. With one exception, when one of the aluminum arms of a tubular Racing Beat front sway broke off in the middle of a run. The rear wheels were spinning so badly that I though the clutch was gone, as the rpm needle kept spiking up while the car would not accelerate...

Best,

Sandro
When you put enough rubber on the car in ASP/SM2 trim, you can unload the inside rear enough for the stock Torsen to spin. This tendency is worse if you run a larger rear swaybar. On lower traction surfaces, the effect won't be as pronounced.

-Andy
AMRX7 is offline  
Old 11-08-06, 03:33 PM
  #13  
Senior Member
10 Year Member
Thread Starter
iTrader: (1)
 
Sandro's Avatar
 
Join Date: Mar 2002
Location: Plainfield, NJ - USA
Posts: 480
Likes: 0
Received 0 Likes on 0 Posts
Is there any advantage in keeping the rear sway bar? It certainly helps with the stock springs, but why would you need it when you can use stiffer springs?

-Sandro
Sandro is offline  
Old 11-08-06, 05:34 PM
  #14  
Senior Member
 
Join Date: Jul 2003
Location: San Jose
Posts: 291
Likes: 0
Received 0 Likes on 0 Posts
If you can get the car to transition well without one, then I would definitely do it. I played around without one for awhile, but never got the spring rates right and ended up keeping a small rear bar.

-Andy
AMRX7 is offline  
Old 12-03-06, 09:24 PM
  #15  
FD / LSX
iTrader: (2)
 
Join Date: Jun 2004
Location: wawayanda, NY
Posts: 1,359
Likes: 0
Received 0 Likes on 0 Posts
Originally Posted by streldoc
We have the 0.188" wall thickness Tripoint bar, and it is available in 4 wall thickness from 0.093" to 0.250". Also as Andy and I have discovered, you must get a KAAZ 1.5 limited slip (set to 67% locking) for autocross, as you will be spinning the inside wheel with the stock differential. This will help the most on getting power to the ground.
hi erik, my kaaz is set to 33% but i have never really used it with good sticky tires...just used up kumhos victoracers. next season i'll have fresh v710's. what will i experience with the 33% that the 67% would fix?

i can't believe the springs rates you guys run with. i have old mazdaspeed coilovers (kyb) with like 5kg/mm front and 4 rear. i thought those high rates would guess skipping in a bumpy lot.

i race a little with sandro so i think we'll both be learning a lot this coming season (i don't even know what sandro is talking about with motion ratio but i'll save that for his email haha).
2MCHPWR is offline  
Old 12-03-06, 09:34 PM
  #16  
Full Member
10 Year Member
iTrader: (1)
 
Join Date: Jul 2002
Location: Austin, TX
Posts: 106
Likes: 0
Received 0 Likes on 0 Posts
Originally Posted by 2MCHPWR
hi erik, my kaaz is set to 33% but i have never really used it with good sticky tires...just used up kumhos victoracers. next season i'll have fresh v710's. what will i experience with the 33% that the 67% would fix?

i can't believe the springs rates you guys run with. i have old mazdaspeed coilovers (kyb) with like 5kg/mm front and 4 rear. i thought those high rates would guess skipping in a bumpy lot.

i race a little with sandro so i think we'll both be learning a lot this coming season (i don't even know what sandro is talking about with motion ratio but i'll save that for his email haha).
Since you will be able to put more power down, you may create some extra push. I really didn't see much difference from the factory Torsen other than I didn't spin the tires all the time. It did help to be able to drive the car more with the rear-end, as the locking stays consistent.

I have tried rates all the way up to where we are at now, and with good shock valving, the ride is suprisingly "soft".
streldoc is offline  
Old 12-03-06, 09:43 PM
  #17  
FD / LSX
iTrader: (2)
 
Join Date: Jun 2004
Location: wawayanda, NY
Posts: 1,359
Likes: 0
Received 0 Likes on 0 Posts
awesome thanks.
do you run with a rollbar or cage? if so, curious where they mount to.

i actually just learned of your success and andy's from sandro, and posted this lookin for your setup:

https://www.rx7club.com/race-car-tech-103/rotaries-make-great-showing-solo-nationals-582888/
2MCHPWR is offline  
Old 12-03-06, 10:05 PM
  #18  
Full Member
10 Year Member
iTrader: (1)
 
Join Date: Jul 2002
Location: Austin, TX
Posts: 106
Likes: 0
Received 0 Likes on 0 Posts
Originally Posted by 2MCHPWR
awesome thanks.
do you run with a rollbar or cage? if so, curious where they mount to.

i actually just learned of your success and andy's from sandro, and posted this lookin for your setup:

https://www.rx7club.com/showthread.php?t=582888
No rollbar or cage. Extra weight not needed in autocrossing.
As for Andy and my setups, Jeff Kiesel will be opening back up his website at www.7parts.com in a week or so, and both of our cars will be in there, complete with pictures and stats. I hope to get up to Dallas within a few weeks to have Steve Kan tune on the car again, as when we dyno'ed it earlier, it had a log manifold, trailing spark out on rotor 1 , and leading spark out on rotor 3, and it was 107 degrees. I will say that the accidental boost spike to 26psi on the first pull had about 500 ft/lbs of torque at around 4500 rpms. Exhaust guy flipped the hoses to the wastegate. Thank god for Steve's quick reflexes/ignition settings/and 112 Octane.
streldoc is offline  
Old 10-18-12, 10:13 AM
  #19  
Full Member
iTrader: (2)
 
Join Date: Jan 2004
Location: Wimberly, TX & Mazon, Il
Posts: 137
Received 0 Likes on 0 Posts
The consenous in this 5 year old thread is that 900#/inch front and 750#/inch rear are desirable spring rates for a FD prepared to SCCA A Street Prepared rules.

Are there any new opinions gleened over the past 5 years? The application would be on 275/15 A6's with the Street Prepared aero, i.e., small splitter and spoiler, not the SSM extended splitter and big wing.

Thanks, Philip
RX7M5GUY is offline  
Old 10-18-12, 08:22 PM
  #20  
Searching for 10th's
iTrader: (11)
 
jkstill's Avatar
 
Join Date: May 2002
Location: Portland OR
Posts: 2,192
Received 4 Likes on 3 Posts
Originally Posted by RX7M5GUY View Post
The consenous in this 5 year old thread is that 900#/inch front and 750#/inch rear are desirable spring rates for a FD prepared to SCCA A Street Prepared rules.

Are there any new opinions gleened over the past 5 years? The application would be on 275/15 A6's with the Street Prepared aero, i.e., small splitter and spoiler, not the SSM extended splitter and big wing.

Thanks, Philip
I believe those rates still stand.

My FD is currently 700/550 with 285/30/18 A6's, and the springs are way to soft.

Once I get my shocks rebuilt this winter, I will be going with about 900/750
jkstill is offline  
Old 10-18-12, 11:30 PM
  #21  
Senior Member
 
Join Date: Jan 2006
Location: nanaimo
Posts: 428
Likes: 0
Received 5 Likes on 5 Posts
i roadrace with slicks and run 1400 front / 1150 rear! car does not feel stiff.
racingdriver is offline  
Old 10-19-12, 08:29 AM
  #22  
Full Member
iTrader: (2)
 
Join Date: Jan 2004
Location: Wimberly, TX & Mazon, Il
Posts: 137
Received 0 Likes on 0 Posts
Thanks guys for those two data points and your comments about them.
RX7M5GUY is offline  
Old 10-21-12, 11:11 AM
  #23  
Searching for 10th's
iTrader: (11)
 
jkstill's Avatar
 
Join Date: May 2002
Location: Portland OR
Posts: 2,192
Received 4 Likes on 3 Posts
I just recalled that I did the motion ratio exercises a few years ago and put them in an excel spreadsheet.

Just set the spring rates in Sheet1 in the green boxes to see the wheel rates.

My measurements for the motion ratios are pretty close to those that Sandro calculated.
Attached Files
File Type: zip
RX7_93_Wheel_Rates.zip (4.8 KB, 236 views)
jkstill is offline  
Related Topics
Thread
Thread Starter
Forum
Replies
Last Post
Postman09
3rd Generation Specific (1993-2002)
0
09-29-15 11:23 AM


Thread Tools
Search this Thread
Quick Reply: FD suspension motion ratios


Contact Us - Archive - Advertising - Cookie Policy - Privacy Statement - Terms of Service

© 2019 MH Sub I, LLC dba Internet Brands

We are a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for us to earn fees by linking to Amazon.com and affiliated sites.
 
  • Ask a Question
    Get answers from community experts
Question Title:
Description:
Your question will be posted in: