View Full Version : How to select/compute spring rates for any car

David Pozzi

12-14-2005, 06:50 PM

I'm starting this to get some tech discussion going on how to choose a good spring rate for a car.

It usually involves determining what frequency you want at the wheel, and calculating the spring rate that will provide it.

Here is a page on spring frequency and a spreadsheet to try out:

http://www.geocities.com/bry593/springrateselector/springrateselector.htm

I'd appreciate any info on what frequency in cycles per second is desireable for:

1. mild street 1.25 cps?

2. high perf street 1.4 to 1.5 cps?

3. road course uses 1.6 to 1.7 cps?

I'd like to see some discussion on how to calculate the proper spring frequency/rate needed, and your comments on the above spreadsheet. Is it useful or even correct?

Thanks, David

dhardison

12-14-2005, 06:52 PM

David, That URL does not work.

Dan

nancejd

12-14-2005, 06:57 PM

Does this work?

http://www.geocities.com/bry593/springrateselector/springrateselector.htm

David Pozzi

12-14-2005, 06:57 PM

Dan,

try it now, I think I fixed it.

dhardison

12-14-2005, 06:58 PM

Yep, sure does! Thanks.

Dan

nancejd

12-14-2005, 06:59 PM

Interesting that rear spring rate decreases as speed increases, but the front srping rate stays unchanged. I would think the opposite would be true, that you would need a stiffer spring to control an increase in road (jounce rebound) frequency, and that consequently you would need a stiffer shock.

David Pozzi

12-14-2005, 07:09 PM

James,

The concern is the front and rear suspension hitting a bump in quick succession and reacting to that bump causing a front to rear pitching vibration of the chassis. The faster you go, the higher the frequency input to the suspension. The trick is to keep the front and rear from vibrating in tune with each other. The rear is probably going to recieve a higher added load either from passengers or load in the trunk or even possibly a trailer, so a higher rate than the front was recomended in the web page.

I havent done much of this type spring selection, so I need to read up on it more. I've usually taken a proven spring rate compensated for the motion ratios.

One error I see on that web page is that he used the full spring rate, his car has McPherson strut suspension and although the coils sit right on the strut , they are on an angle and there should be a motion ratio reduction for that in his calculations.

todd8541

01-03-2006, 10:29 AM

Ah, I think this should be retitled and rewritten to try and determine the "Wheel Rate" not "Spring rate". Just because two cars have the same wt (both sprung and unsprung) doesn't mean they need the same "Spring". Someone can change the spring location on the same car and it would require a different spring to maintain the same handling characteristics.

Todd

David Pozzi

01-04-2006, 07:59 PM

Todd,

Yes I thought about that but really I'd like this discussion to include calculating the spring rate to achieve the desired wheel Hz.

I modified the spreadsheet from the above link to calculate the spring required for a given wheel HZ, and it uses some motion ratios if you have the needed A arm dimensions to input in to the spreadsheet. I was hoping someone with better math and spreadsheet skills would come by and do it, but that hasn't happened.

I need to finish it up and will upload it for you guys to try out if there is any interest.

Chevy350

01-05-2006, 11:51 AM

I'm interested, and I think it could help others as well.

David Pozzi

01-05-2006, 06:45 PM

My thought is, we could work out what frequency in Hz is ideal for:

(Quote from my first post)

"I'd appreciate any info on what frequency in cycles per second is desireable for:

1. mild street 1.25 cps?

2. high perf street 1.4 to 1.5 cps?

3. road course uses 1.6 to 1.7 cps?"

A member could select what his use is, enter the frequency in the spreadsheet along with motion ratio info, the spreadsheet would calculate the spring rate needed.

There may also be a way that would predict suspension travel for a given Hz, so if your car is lowered and had limited travel, you could select a higher Hz setup.

Damn True

01-06-2006, 09:59 AM

Ouch. This makes my head hurt.

When the time comes I'll hit you up for help.

Norm Peterson

01-19-2006, 07:11 AM

near-duplicate post

Norm Peterson

01-19-2006, 07:13 AM

I was hoping someone . . . would come by and do it, but that hasn't happened.

I need to finish it up and will upload it for you guys to try out if there is any interest.I'd worked through the most recent version of a FlatRide spreadsheet about a year ago, and didn't see this thread until just a few minutes ago. Give me a little time to go through yours, see how it compares/what it's intentions are. Mine almost certainly requires more inputs, and I'm sure has a couple of additional outputs.

I've occasionally considered offering it for sale (for beer money kind of $ to help defray the development time - suggestion of which I hope doesn't get me busted) if I could get past a couple of obstacles like guaranteeing the integrity of the equations. Based on some professional experience in developing engineering spreadsheets, I can tell you that people can get VERY creative when it comes to screwing them up. Perhaps I could let a "FlatRideLite" version go as a teaser "freebie".

Norm

David Pozzi

01-19-2006, 03:27 PM

Norm,

I'm all for it if we can work something out. I'd kick in some cash to get something useable going. Perhaps larry could sell the spread sheets on the site thru his PT store.

I'm a hack at spreadsheets and not good at the math.

I took the spreadsheet and added inputs to calulate motion ratios for the car, and started on calculations to do the rear rates, but with a stick rear axle there is one motion ratio for a two wheel bump, another for a one wheel bump. Using the spreadshet formulas I'm getting very high recomended rates for the rear spring using the one wheel bump motion ratio method.

I haven't had much time to work on it since I've got other things going on.

Norm Peterson

01-20-2006, 05:29 AM

James - understand that his analysis is only applying the user-specified frequency to the front suspension. The rear frequency is always higher, but as speed rises it will drop. That's where the 'intended usage' frequency numbers such as those in the original post come in. This doesn't mean that you can't use a 'comfort' frequency for ride quality at 125 mph, only that the resulting springs would be different than if you'd picked a more hard-core frequency.

Dave - I think my sheet is more along the approach that you've normally taken. But there isn't much effort involved to add the option of forcing solutions for spring rates based on user-specified frequencies. There are at least a couple of ways to handle this, but since it isn't possible to quantify things like individual ride preferences and tolerance for NVH I'd suggest letting the user specify his own target frequency from a table such as you've already provided, perhaps with a note suggesting the choice of a slightly lower frequency if ride concerns are particularly important.

I think there are more than a few auto-x and open-track cars running well above 1.7 Hz (I specifically know of one up around 1.9 f/2.4 r Hz).

I think this sort of analysis is best limited to the two-wheel bump mode; otherwise you're getting into roll effects and would need to include sta-bar contributions as well. It's not that you can't be slightly 'off' in your spring selections and still have an acceptable ride at the target speed.

Suspension type certainly enters into this, as you generally need to spring a McStrut stiffer than a control arm suspension for reasons of camber control.

After all that, it really gets interesting when you throw some front and rear damping terms into the mix and generate a plot. Note that damping helps "cover" for slight differences in available spring rates vs theoretical ones and nonlinearities in motion ratios.

Norm

Norm Peterson

01-20-2006, 08:43 AM

Dave - this is what it looks like (I wasn't at all sure that it would upload in sufficient clarity). There is quite a bit of stuff that could be moved off-screen, which would free up some real estate for inputting a desired frequency (could set it up for either front or rear) or controls to run other iterative solutions. It wouldn't save much file size to delete the optional inputs, though.

Norm

David Pozzi

01-23-2006, 10:56 PM

Norm,

That's quite sophisticated, I was thinking of something a lot more basic, something that would come up with just a front and rear spring rate for a given wheel frequency F/R.

The shock damping calcs etc are great, but beyond anything I've considered trying to work on, and probably above most of us here.

Norm Peterson

01-24-2006, 07:49 AM

I agree that there are more input variables in that sheet than you need for a quick and dirty estimate. More than I would use if I was doing this with a slide rule and pencil/paper, actually. It's just that a spreadsheet makes it much easier to write the formulas once and avoids having to explain away the more obvious stuff that you didn't consider. And it provides a better record of what conditions were being evaluated. FWIW, all of the inputs and most of the outputs are defined/described on the 'HELP' page.

Granted that all of that stuff in the

ADDITIONAL INPUTS FOR ITERATIVE ESTIMATE OF "PitchKpsquared/ab" (OPTIONAL)section really isn't necessary even though it results in some additional understanding of the overall motion. Truth be told, I haven't used that part all that much past crunching the formulas.

However, I do think you need to consider damping even for 'simplified' evaluations. Ignoring damping terms is a legitimate approach when the damping is a very small percent of critical damping (as it is for structural damping, where low-single-digit percentages of critical are typical). Or if you only want to investigate the condition where the shocks are almost completely shot.

But "proper" suspension damping involves much higher damping, 15% or so when ride quality has priority up to perhaps 45% for best performance. With that much damping, not only will the magnitude of pitch motion as the suspensions reach one full cycle be affected, but the theoretical "Flat Ride" speed or rear spring selection will also be skewed a bit by the slight frequency shifts involved.

Note that including damping terms allows you to investigate the change in ride (specifically pitch motion) as the shocks do deteriorate. A 15 mph difference between the damped and undamped flat ride speeds is entirely possible just by fitting new performance shocks to one end and leaving the dead players or even good ride comfort shocks on the other - with no change in the springs.

Basically, I'm suggesting that the undamped approach may be a little too basic for a sheet that could be used to look at an unknown variety of situations. There seems to be up to about a 10% difference in Flat Ride speeds, damped vs undamped, when the same percent damping is applied to both ends. That's enough to better suggest which spring to choose, given that there may be two or more that have rates that are close.

Norm

David Pozzi

01-24-2006, 02:05 PM

Norm,

You are right as usual.

I guess it was wishful thinking that it could be more simple.

Your help files probably need to list some typical damping values to enter, for those of us who have not done this before.

I'm hoping the forum can generate some Roll center height, CG and motion ratio data to help get a good baseline to start people out.

I sent Larry a PM asking him to help make your spreadsheets available, for whatever fee you need, possibly through his PT.com store.

David

Norm Peterson

01-26-2006, 10:45 AM

I'm still picking away at this, and it appears that the values on the "Help" page (ranging between 0.1 and 0.45) may be a bit low, but only a little so. Higher values than what appear in RCVD (0.15, 0.25, 0.45, and 0.5 being commonly presented) are probably being used for tuning transient handling response rather than for flat ride considerations anyway. There's some readily available Koni data that I think can be manipulated to give % damping values good enough for this. Perhaps it's just my approach, but even if I knew a shock was 0.45*critical damping, I'd probably run the numbers for at least one case where the damping was assumed to be half that or even less, just to get an idea of how bad the ride might "tank" over time.

I've also found a bit of frequency information that includes suggestions a bit beyond 1.7 Hz, even for dual-purpose vehicles. And it looks like a rather simple formula describes the displacement vs frequency plot that appears in Fred Puhn's book.

There's a current thread over at corner-carvers on this very topic that might be of interest if only for the attached plots (shameless plug).

Norm

David Pozzi

02-05-2006, 07:13 PM

Norm,

Sorry I was out of town for a fiew days.

Look here for some tech: http://www.optimumg.com/tech_springsdampers.htm

They mostly work on formula cars but are very advanced and do some consulting on sedans.

Check his newsletters too, one had a chart showing suspension travel for a given freqency, it might be a way of predicting suspension travel.

David

Norm Peterson

02-06-2006, 08:20 AM

Thanks for the link. I'll have to print that one out.

Norm

Norm Peterson

02-07-2006, 09:17 AM

It looks like for most "flat ride" purposes that a damping value slightly less than the 0.25 that's repeatedly referred to across the literature still represents an acceptable lower bound for getting a handle on ride (pitch) comfort over the long run. Anything much less than, say 0.15, would probably resulted in replacement/upgrade.

At the other end, increasing the damping beyond about 0.5 doesn't seem to affect the pitch much after about 3/4 of a front suspension cycle, as there isn't much amplitude left by that point unless the spring rates are way out of whack to begin with. In that case the plots at 0.2 are really ugly. So I think it's safe to conclude there's no need to analyze beyond 0.5 for flat ride purposes even for competition-oriented shocks. Even 0.4 might be a good enough place to stop. Decent street performance shocks perhaps a bit lower.

Tangentially related to this is what must be happening in SensaTraks (one of my favorite whipping boys). With a significant amount of damping removed from around the OE ride height position, there must be quite the progression in the damping as the piston moves and the grooves close up. No progression would tend to give a sea-sickish ride, and a step change would give a pretty good jolt. Then sharply digressive so the high frequency stuff doesn't sting.

Norm

David Pozzi

02-07-2006, 06:50 PM

Norm,

I was hoping we'd see more posts from people interested in this project. I don't want you to spend a lot of time on this if there is no interest... :)

Norm Peterson

02-08-2006, 04:52 AM

Sometimes curiosity gets the better of me, and once in a while something unexpected but perhaps useful is uncovered as a result. Like finding out that 40% critical damping correlates pretty closely to a 10% frequency shift.

Norm

DLinson

02-09-2006, 09:01 PM

I'm interested in this as well. I've been watching this thread trying to learn before I make the big purchase. I was thinking of going with a front/rear ride freq. of 1.75/1.85. I'm affraid of getting too soft of a ride and bottoming the car. I have about 4.5" of ground clearance so I don't want it too soft. I have to be honest about the use of the Nova, it will see almost all street use. I don't think it will ever make it to an open track day. The wife doesn't like the idea of taking this huge investment onto a track.

Anyway, I may have to rethink the the spring rates because I wasn't taking into account the damping. I have a spreadsheet that I got from a GM suspension engineer that I went to school with but it isn't the easiest thing to use.

I'd like to know what wheel rates other big block cars are running up front.

As far as ride frequencies vs. useage, if I had say a 3000 lb Nova and a 4000 lb Impala and both were intended for the same street/track useage, would I still shoot for the same frequencies for both cars or would you drop the frequency for a lighter car? I know the weights are considered when calculating the frequencies but I was curious if it the same frequency will result in the same ride in two cars of vastly different weight.

Please keep up the disscusion. Although as a mechanical engineer, some of this is still making my head hurt.

Thanks,

Dennis

Norm Peterson

02-10-2006, 07:24 AM

The same frequencies in the lighter car will involve wheel rates that would be lower in direct proportion to the reduction in mass, so the springing itself would be lighter. What would vary would be the relationship between front and rear wheel rates, as the wheelbases are not the same for those two examples and things like the weight distribution and unsprung weights will be different as well.

I'd look at relatively lower frequencies for any given intended usage mostly in cases where the car has a particularly low CG but retains a relatively "normal" roll axis height. Lower amounts of roll moment per g means you don't need as much roll rate to hold the roll angle itself in check.

Damping should help. Although the calculated frequencies drop slightly, the spring stiffnesses/wheel rates remain unchanged and the damping reduces the peak displacements even within the first cycle.

Norm

67LS1T56

02-12-2006, 04:47 PM

I would love to learn more in depth about suspension but this is too complicated for me even to read.

Delinson, as an engineer your head is hurting what we are going to do as a ordinary Joe? lol.

DLinson

02-23-2006, 10:18 AM

I got this info from a GM suspension engineer. It's the ride rates for the 2001 C5 and the 1999 Dodge Viper. He suggested staying closer to the Viper numbers as it does better at higher speeds.

2001 C5 FE4 (Z06):

Front:

Ride Rate (N/mm)=18.4

Roll Rate (Nm/deg)=1250

Tire Radial Rt (N/mm)=292

Ride Freq. (Hz.)=1.15

Rear:

Ride Rate (N/mm)=26.1

Roll Rate (Nm/deg)=1040

Tire Radial Rt (N/mm)=284

Ride Freq. (Hz.)=1.45

1999 Viper GTS:

Front:

Ride Rate (N/mm)=26.1

Roll Rate (Nm/deg)=1048

Tire Radial Rt (N/mm)=320

Ride Freq. (Hz.)=1.37

Rear:

Ride Rate (N/mm)=35.8

Roll Rate (Nm/deg)=1040

Tire Radial Rt (N/mm)=357

Ride Freq. (Hz.)=1.51

Dennis

David Pozzi

02-23-2006, 12:02 PM

How do you convert N/mm to lbs/in?

I know I can look it up but if someone has it handy, please post it.

The vette is a little lower than I expected.

David

Norm Peterson

02-23-2006, 12:18 PM

1.0 N/mm = 5.710146 lb/in

Norm

David Pozzi

02-23-2006, 08:12 PM

Wow! look at the viper ft tire spring rate! 320 N/mm = 1,827. lbs/in.

Norm Peterson

02-24-2006, 06:29 AM

You might also be interested in the roll rate conversion.

1.0 Nm/deg = 8.85075 in-lb/deg

There's a little units conversion and calculation software called 'convert.exe' (duh) that I find really helpful from time to time, not to mention handier than my Marks' handbook. As far as I know, it is freeware, and is a little over half a meg, if you'd like a copy. With any luck, the custom conversions I've added would go along with it.

Norm

DLinson

02-24-2006, 09:26 PM

If you want to know the spring rate for your tires, you may be able to use a Hunter GSP9700 tire balancer to measure it. Log onto www.gsp9700.com, there is a locator search engine in there. Type in your zip code and it will give you all of the shops in your area with one. If the tech knows how to use it, he should be able to give you the spring rate for your tire. I'll check with one of the engineers that design the GSP9700 and see what it takes to get that data. It may not be straight forward and known by the average tech.

DLinson

Norm Peterson

02-25-2006, 07:20 AM

Hmmm. Must be a road force balancer (the page linked doesn't say).

Norm

David Pozzi

02-25-2006, 10:11 PM

Norm,

Thanks for the tip, I downloaded it from the net.

I mostly use a Mac on the net and general use. I have some conversion calculators for it but they are not intended for engineering use, just more general weights and measures.

I do have a laptop I run PC programs on like Perf Trends for suspension stuff, but It's a pain to have to fire it up just to convert something I read on the web.

DLinson, thanks, There are three nearby, so let me know if you find out how to get the data.

DLinson

02-25-2006, 10:14 PM

Click on the " How it works" tab at the top of the page. It goes over the steps of measuring tire spring force and rim runnout and means to use the rim runout to offset varying tire spring rate. It measures the tire spring rate all the way around the tire. Measures the rim runout and then insturcts the tech to align the highest spring rate spot with the lowest runout spot. It gives a force variation number. Usually a car is sensitive up to about 16 lbs. force variation. I balanced and force matched a set of Michelins for a friends GTS Viper. It would develop a shake about 120 miles per hour. The force variation on one of the front tires was 54 lbs. After matching the tire with the rim, the force variation was down to about 20 lbs. and it really improved the ride. Most force variations or tire imbalances resonate at about 65 mph but considering the viper's ride freq. is much higher at about 1.4 versus 1 for the average passanger car, it would make sense that it would show up at a higher speed.

David Pozzi

02-26-2006, 12:35 PM

Does it read out tire deflection rate in lbs/in or only force variation.

That's a neat machine!!! :)

DLinson

02-26-2006, 07:32 PM

The machine does measure the spring rate lbs/in. The tech only needs to know the force variation in lbs. in order to diagnose the vibration problem and try to solve it with matching to the rim runout. There is a way to get the spring rate, I'll have to check it out at work tomorrow.

Some of the machines with the Lateral Force measuring system will help diangonse a pull in your alignment even though your alignment is in spec. If the tires have ply-steer or a conicity problem, the machine will measure it and suggest how to match offsetting pulling tires on each axle. This isn't catching on as like the radial force variation did but it is a helpfull tool. It worked on my k1500.

Dennis

rattus

05-23-2006, 03:03 PM

Here is a Matlab script I whipped up to calculate spring rates / suspension frequencies.

I adopted the forumlas from various websites (and my undergrad physics textbook) and I'm not 100% sure I have things right (I'm waiting for my copy of RCVD to show up). The vehicle constants are rough approximates for my 69 Firebird.

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% %%%%%%%%%%%%%%%%%%%%%%%%%%%

vehicle_weight = 3400; %total vehicle weight

f_weight_dist = 0.54; %front weight percentage

f_wheel_unsprng = 100; %front wheel unsprung weight (per wheel)

r_wheel_unsprng = 200; %rear wheel unsprung weight (per wheel)

f_mr = 8./16; %approx. front motion ratio from LCA

r_mr = 0.9; %approx. rear motion ratio (live axle)

f_sprate = 850; % given front spring rate (lb/in)

r_sprate = 250; % given rear spring rate (lb/in)

f_damp_ratio = 0.35;

r_damp_ratio = 0.35;

f_freq = 1.7; %Hz

r_freq = f_freq + 0.15.*f_freq; %Hz, rear freq is 15% greater than front freq

wheelbase = 100; %approx. (inches)

avgspeed = 80; % mph

% convert to SI units

fmass = ((vehicle_weight.*f_weight_dist)./2-f_wheel_unsprng).*0.45359237;

rmass = ((vehicle_weight.*(1 - f_weight_dist))./2-r_wheel_unsprng).*0.45359237;

f_sprate = f_sprate.*175.126835;

r_sprate = r_sprate.*175.126835;

% calculate wheel rates

f_wheel_rate = f_sprate.*(f_mr.^2);

r_wheel_rate = r_sprate.*(r_mr.^2);

% calculate undamped spring rates given frequencies

Ksf = 4.*(pi^2).*fmass.*(f_freq^2)./(f_mr^2)./175.126835

Ksr = 4.*(pi^2).*rmass.*(r_freq^2)./(r_mr^2)./175.126835

% calculate undamped frequencies given spring rates

f_freq_undamp = (1./(2.*pi)).*sqrt(f_wheel_rate./fmass)

r_freq_undamp = (1./(2.*pi)).*sqrt(r_wheel_rate./rmass)

%calculate damped frequencies given spring rates

f_freq_damp = f_freq_undamp.*sqrt(1-f_damp_ratio.^2)

r_freq_damp = r_freq_undamp.*sqrt(1-f_damp_ratio.^2)

% calculate damped time constants

f_tau = (2.*pi).*f_freq_undamp.*f_damp_ratio;

r_tau = (2.*pi).*r_freq_undamp.*r_damp_ratio;

% whip up time independent variables

tf = linspace(0,f_tau,1000);

f_to_r_timlag=wheelbase./(avgspeed*63360/3600);%time lag from bump front to rear

tr = tf-f_to_r_timlag;tr = tr.*(tr >= 0);%offset rear time, get rid of neg times

% plot damped trajectories

figure(1); clf;

plot(tf,exp(-f_tau.*tf).*sin(2.*pi.*f_freq_damp.*tf));hold on;

plot(tf,exp(-r_tau.*tr).*sin(2.*pi.*r_freq_damp.*tr),'r');hold off;

title('damped suspension trajectories');

xlabel('time (s)'); ylabel('amplitude (arbitrary units)');

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

Results:

Ksf = 967 lb/in, front spring rate given 1.7Hz (undamped)

Ksr = 281 lb/in, rear spring rate given 2.0Hz (undamped)

f_freq_undamp = 1.6 Hz, front freq. given 850 lb/in spring rate (undamped)

r_freq_undamp = 1.8 Hz, rear freq. given 250 lb/in spring rate (undamped)

f_freq_damp = 1.4931 Hz, front freq. given 850 lb/in spring rate (damped 35% of critical)

r_freq_damp = 1.7280 Hz, rear freq. given 250 lb/in spring rate (damped 35% of critical)

Attached is a plot of the front and rear trajectories:

Norm Peterson

05-24-2006, 08:33 AM

Looks pretty good, although 200 lbs per rear corner sounds a bit high unless you have a real beast of an axle. Are leaf springs really that heavy (remembering that perhaps a third to half of their weight is sprung)?

I ran a sanity check for one of my spreadsheets and got . . .

Ksf = 965 lb/in, front spring rate given 1.7Hz (undamped)

Ksr = 293 lb/in, rear spring rate given 2.0Hz (undamped)

Note that Ksr = 280 lb/in if I use 1.15*1.7 = 1.955 Hz instead of 2.0 Hz.

f_freq_undamp = 1.60 Hz, front freq. given 850 lb/in spring rate (undamped)

r_freq_undamp = 1.85 Hz, rear freq. given 250 lb/in spring rate (undamped)

f_freq_damp = 1.49 Hz, front freq. given 850 lb/in spring rate (damped 35% of critical)

r_freq_damp = 1.73 Hz, rear freq. given 250 lb/in spring rate (damped 35% of critical)

(Sorry for the crappy thumbnail resolution - it's easier to see as a full screen display and then expanded with the sizing button in the lower right hand corner.)

Norm

rattus

05-25-2006, 04:40 PM

Cool, thanks Norm. After I posted, I thought that the rear unsprung weight should have been about half of what I entered. D. Pozzi has 110 lbs (per rear wheel, 220 total) unsprung weight listed on his web site.

David Pozzi

05-25-2006, 10:19 PM

I forgot to include the weight of the wheels and tires in that calculation!

Here's some info:

REAR SUSPENSION

rear axle 12 bolt with drm brks, posi -complete 185

leaf spring - multi stock 32

Hotchkis type leaf closer to 40 - 45.

shock 3

Wheel and tire is around 50 lbs

sway bar is probably around 10 lbs

I think you'd take half the weight of the spring, bar, and shock.

somewhere around 287 lbs total depending on your exact wheel/tire weight.

paul67

09-11-2006, 02:53 PM

would you not have to take the weight of the driver , and tire pressures ?

Norm Peterson

09-11-2006, 03:57 PM

(1) Best results would consider the driver's weight and his own CG location. And the weight and CG of any other variable loading.

(2) Tire pressures will make a generally small difference, but this effect isn't very usable unless you have some idea of the correlation between inflation pressure and tire vertical/radial spring rate.

Norm

silver69camaro

09-14-2006, 11:38 AM

Just for a reference, Racecar Engineering quotes:

1 Hz for Caddy rides

1.3Hz for sports cars

1.8Hz high performance road cars

2+Hz for racecars w/o aero aids

It also mentions that ground effect racecars could have attained up to 10Hz! Wow!

Anyway, my personal experience hasn't followed the above guidelines. I've done vehicles with a frequency slightly above 2.0, and it had a very pleasant ride with excellent handling (.95G).

Bjkadron

04-14-2010, 11:59 AM

I know this is a REALLY old thread... But none of the links work. Does anyone have any new info or spreadsheet links?

Thanks!

Benjamin

Norm Peterson

04-15-2010, 08:09 AM

What links?

All I see are thumbnail pics.

I probably have one version or other of my sheet on most of the computers I ever use, but nowhere that can be linked to directly.

Norm

John Wright

04-15-2010, 08:45 AM

What links?

I guess he was speaking of David's link in the first few posts in the thread....

Sorry, the GeoCities web site you were trying to reach is no longer available.

Bjkadron

04-15-2010, 09:06 AM

I guess he was speaking of David's link in the first few posts in the thread....

Yes that was it. So nobody knows of another one that I can get too? Or how I could possibly get my Grubby little hands on one of those spreadsheets? I suck at excell.:)

Thanks

Norm Peterson

04-15-2010, 09:21 AM

If you PM me with an e-mail address, I can send out the latest version that's on this computer.

Forum e-mails don't generally permit attachments.

Norm

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