O Shaikh επιτέλους μετράει το NC με ορισμένα πολύ ενδιαφέροντα πρώτα αποτελέσματα:
On Saturday a friend and I had a marathon of suspension swaps! We did the following tests:
1. Bounced his ’07 with stock springs and stock (filled/charged) OE dampers at both front and rear of the car.
2. Installed Mazdaspeed springs with OE Bilstein front shocks, bounced front.
3. Installed Mazdaspeed springs with OE Bilstein rear shocks, bounced front and rear.
4. Removed spring and measured bump stop contact position for rear shock.
5. Removed bump stop, added wheel and measured height where tire rubs bodywork.
6. Characterized mechanical motion ratio of rear suspension (shock travel vs. wheel travel)
7. Made some determinations of packaging requirements for adjustable Bilsteins on the NC.Still to perform will be:
8. Measure bump stop contact position for front shock, determine min front ride height and characterize mechanical motion ratio of front suspension, which will happen early next week.Will post results of these experiments later today!
Teasers:
- Mazda did make the rear frequency higher than the front for the stock springs, but the Mazdaspeed springs are LOWER front than rear… I have my ideas why this is.
- Bump stop contact occurs at 13.5″ rear ride height. Stock is about 14.5″ so you are definitely using the bump stops all the time with the stock suspension and are SITTING on them with MS springs
Αντιγράφω από το miata.net:
Shaikh@FatCatMotorsports
Suspension travel and bump stops
Approximately 7.5″ of total wheel travel up front, 8.5″ total travel for the rear. The LF static height was 15.0″, 14.5″ LR so the car, at least by visual estimation, has a reverse rake. Without knowing roll centers, we can’t tell if it’s an illusion or the actual case that the rear roll center is lower than the front.
Bump stop touch (factory NC front = 68mm, NC rear = 74mm) occurred at 13.75″ front / 13.5″ rear heights. Most lowering springs have the car on the bump stops at rest unless trimmed or substituted for another stop.
The front lifted off the jack stand at 11.1″ with about 1.3″ of of additional wheel travel available before any tire-to-fender contact would occur. This gives more room to safely lower the car and also select bump stops that are not in contact at static ride height.
The rear ride height at lift off was difficult to estimate accurate (~11.2″) and tire rub occurred at ~9.2″ however the axles were so skewed it would not be prudent to run this low. We do not recommend shortening the rear stops excessively unless stiffer springs are also added. Our bump stop recommendations take into account safety factors to ensure adequate protection exists for all suspension components.
One curious characteristic of the OE NC stops is that the front, while initially softer than the rear, begins to ramp in spring rate very quickly, quickly overpowering the rear. This results in a car with more steady-state understeer than using truly linear bump stops. Our FCM stops provide this solution as we discuss later.
As in the case of the NA or NB, bump stop spacers (or packers) are useful to prevent any minor fender rubbing or as a useful tuning aid to adjustment over/under-steer balance.
We noted that the OE Bilstein and any equivalent shock has 1.5″ more droop travel than the Tein Flex adjusted for 13 5/8″ // 13 7/8″ height.
Spring motion ratios via leverage measurement
We generated these as with our measurements on the NA and NB, comparing wheel travel (hub center to fender lip) to shock travel. Because the A-arms go through more severe angles later in the bump travel, we averaged the result excluding points lower than 11.7″ ride height.
Resulting average motion ratios (leverage ratios, really) were – surprise! 0.72 front and 0.88 rear. This is what we found via bouncing the NA and NB. We’re very confident in the front value but plan to repeat the measurement for the rear as we noted the added travel (and inward bending of the rear multi-links) made accurate measurement difficult for the later parts of bump travel. We find the bounce frequency tests more useful for characterizing how the suspension will behave with a given installed spring.
Bounce frequencies and effective spring motion ratio at the wheel
We performed bounce frequency tests (measurements repeated twice then averaged) on 4 sets of springs (2006 OE, MS/Eibach, Tein Flex standard 8/6 kg/mm rates) includes one ‘hybrid’ setup using MS front/OE rear. Three shocks were used (OE Tokico, OE Bilstein, Tein Flex) on two test cars, both 2006 models similarly equipped (the second (with Tein Flex) had a Hard Dog rollbar).
All shocks used in the test were fully charged and filled with oil. We realized that degassing and draining a brand-new Tein Flex would result in a very unhappy owner (hi Jim!) so for the interest of consistency we sought, as always, to generate useful qualitative data for the same of comparison. The resulting frequencies are going to be lower than actual by about 5%.
Physical bounce tests is the most effective way to predict what the suspension will do on the road (front and rear do couple together depending upon which vehicle mode is excited, pitch, heave, or some combination of both). The motion ratios in the NC spreadsheet will reflect these derived numbers.
Stock springs: 1.38 Hz f/ 1.45 Hz r
Mazdaspeed front springs/stock rear: 1.52 Hz f / not tested r
Mazdaspeed/Eibach lowering springs: 1.62 Hz f / 1.57 Hz r
Tein Flex standard 8/6 kg/mm springs: 2.05 Hz r / 1.92 Hz r
We realized that the factory springs are actually biased toward the rear, which is beneficial to ride and handling. The Mazdaspeed springs, while 17%/8% stiffer f/r, have a forward bias and would tend to promote a more understeery setup all things being equal. Our guess is that the factory didn’t want to create too wild a setup assuming someone only changed springs but not sway bars to compensate, or used a very large rear bar which would promote too much understeer.
The Tein setup did not have faster rear than front which was surprising since the standard NA/NB setups did.
Generating actual spring rates was and is difficult due to the progressive nature of both the OE and the aftermarket lowering springs. Once install, several coils go dead and the effective spring rate increases. We plan to repeat bounce tests for an FCM coil-over setup in development but our averaged bounce motion ratios work out 0.79 f / 0.84 r.
Sway bar motion ratios
We have not yet characterize installation/leverage ratios for the sway bar.
Camber curves
Jyri Virkki and I generated these last year with the generous donatoin of a test vehicle by Dennis (Notorious djw). Link is here.
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These are the standard kits that will be put on the website based on the spring rate/amount of lowering:
Front
Spring used/amount lowered Bump stop (and any packers)
Stock springs 58mm white
Racing Beat (1/2″ lower) 58mm red plus 1 packer
Eibach/MS (1″ lower) 58mm red plus 1 packer
Custom (3/4-1″ lower) 58mm red
C-Stock 58mm red plus up to 3 packersRear
Spring used/amount lowered Bump stop (and any packers)
Stock springs 76mm white
Racing Beat (1/2″ lower) 58mm blue plus 1 packer
Eibach/MS (1″ lower) 58mm blue plus 1 packer
Custom (3/4-1″ lower) 58mm white
C-Stock 58mm blue plus up to 5 packersThe intent behind the FCM NB bump stop kit for stock springs is to neutralize the built-in understeer from the factory setup. We believe this single change will make the car much more fun to drive at a minimal expense, esp. when simply adding shocks.
For both Racing Beat and Eibach/MS springs, a shorter and firmer bump stop is recommended, leaving more room for the suspension to work. Once the bump stops are utilized, the rate is linear over nearly half the travel. Additional packers can be used as a fine-tuning aid for steady-state balance.
By custom, we mean a stiffer-sprung setup utilizing stock shock lengths (such as we are designing!). This is our best guess given the data we’ve just gathered and existing information.
C-Stock cars (but the MS-R less so) typically have to fight understeer from use of a large front bar, but this can be remedied, as on the winning NA/NB Miatas at the SCCA Solo National Championships in 2007, by substituting bump stops. Generally, a stiffer rear vs. front stop promotes more neutral handling when a stiff bar is used. Again, since the recommended stops are shorter than stock, packers may be used to legally fine-tune handling.
Particularly for lowered cars, this is a real benefit.
When using the 58mm red (+1 packer) up front, you will gain 1/2″ more travel before the bump stop comes into play, and then another 1/2″ of bump stop travel. There would still be nearly an inch of clearance between tire and fender liner. A good option for those who wish to get the most travel possible.
For the rear, the 58mm bump stops gain 3/4″ of wheel travel before bump stop contact, and then 1/4″ of bump travel at full compression. We are not specifying a softer stop.
The ability to tune balance with bump stops may prove especially useful to those who with to compete in C-Stock class autocross but don’t want to or can’t purchase the MS-R package. Since the factory rear bump stop is 74mm, our 76mm white or blue (trimmed slightly to maintain legality) may provide a nice advantage again those still using stock stops).
Thanks for your patience as we design and performed the tests, compiled the data and reduced it to make careful recommendations! This is just the beginning for the NC where FCM is concerned!
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Επιτέλους πέφτει φως στο θέμα της ανάρτησης του NC.
Και το περίφημο excel του Shaikh: