http://www.optimumg.com/
Download the pdf's under tech tips
Q has 146 front and 123 lb/inch rear springs so 146/123= 1.187 exactly equal to Q's 54/46 weight ratio.
wheelbase 113.2"track/tread 61.8"
The math behind springs and shocks
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elwesso
- Posts: 30810
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2007 BMW M Coupe
2007 Infiniti G35 S 6MT - Location: Indiana
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Re: The math behind springs and shocks (Q45tech)
Tech those are fabulous articles. Amazing to see what goes into making a race car corner... Seems they use springs/dampers in place of regular links and things that most street cars use...
It appears to me the notion of using progressive springs isnt really considered.. Makes you reconsider using progressive springs on a Q.... BUt for most people they work.
It would be interesting to see what ride frequency Infiniti was going after when they were designing the Q (I havent tried to use the equation yet). It would then be interesting to compare what other cars with more desireable handling characteristics have in terms of ride frequency.
Just to clarify I would assume that in determing what ride frequency the mass would be the sprung mass, so for the front itd be (just to pick an even number) 4000 x .54 /2 ? That would be for one corner? Ride frequency should be the same front and rear since the spring stiffness ratio equals the weight distribution
Seems as if determining what you want as an ideal ride frequency is the starting point, and then you simply use the supplied equations to make shocks and springs and put them on the car...
The question remains, lets say we made the springs 50% stiffer, to 219 lb/in and 185 lb/in, would you then need to make the sway bars that much stiffer? Of course, with teh 28/20 setup you are a bit stiff in the front, but assuming they were suited for the spring/shock setup..
I know that this all has to do with computing the roll gradients of the spring, and then you simply plug the roll gradient numbers into the sway bar stiffness equation.....
It just seems hard to find a good middle point for a decent roll gradient and also have a decent ride frequency for daily use... I guess I just dont get by reading the first three articles how you can treat ride frequency and roll gradient seperately... Seems like that if use stiffer springs the vehicle will roll less under cornering. I guess you just assume that when going straight, the sway bars are passive, and under cornering the springs are passive... THUS, WHY THEY DONT USE PROGRESSIVE SPRINGS!
Sorry if I'm thinking out loud, but I love reading this kind of stuff, maybe try and bring some practicality to all those engineering classes!!
It appears to me the notion of using progressive springs isnt really considered.. Makes you reconsider using progressive springs on a Q.... BUt for most people they work.
It would be interesting to see what ride frequency Infiniti was going after when they were designing the Q (I havent tried to use the equation yet). It would then be interesting to compare what other cars with more desireable handling characteristics have in terms of ride frequency.
Just to clarify I would assume that in determing what ride frequency the mass would be the sprung mass, so for the front itd be (just to pick an even number) 4000 x .54 /2 ? That would be for one corner? Ride frequency should be the same front and rear since the spring stiffness ratio equals the weight distribution
Seems as if determining what you want as an ideal ride frequency is the starting point, and then you simply use the supplied equations to make shocks and springs and put them on the car...
The question remains, lets say we made the springs 50% stiffer, to 219 lb/in and 185 lb/in, would you then need to make the sway bars that much stiffer? Of course, with teh 28/20 setup you are a bit stiff in the front, but assuming they were suited for the spring/shock setup..
I know that this all has to do with computing the roll gradients of the spring, and then you simply plug the roll gradient numbers into the sway bar stiffness equation.....
It just seems hard to find a good middle point for a decent roll gradient and also have a decent ride frequency for daily use... I guess I just dont get by reading the first three articles how you can treat ride frequency and roll gradient seperately... Seems like that if use stiffer springs the vehicle will roll less under cornering. I guess you just assume that when going straight, the sway bars are passive, and under cornering the springs are passive... THUS, WHY THEY DONT USE PROGRESSIVE SPRINGS!
Sorry if I'm thinking out loud, but I love reading this kind of stuff, maybe try and bring some practicality to all those engineering classes!!
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Q45tech
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1995 G20t 5 speed 334,000 miles 16" 2002 wheels - 205/50/16 Sr20ve vvl
Re: The math behind springs and shocks (elwesso)
Remember the springs have rubber upper seats, as do shocks, and the rubber in sway bars also the springs and bars do not couple perfectly to the wheels.
Plus you must calculate the sidewall stiffness in series with the spring bar stiffness.................hint use 0.9 x spring to correct for tires.
I'll bet the seat subtrtacts another 10% in the first inch so the wheel rate is:
146 x 0.81 or ~~~ 118 then 131 thereafter123 x 0.81 or ~~~ 100 then 110 thereafter
Somewhat progressive even oem.
I'm happy they spent so much time explaning the need for springs and shocks on sway bars........................what happens when you exceed the rear 20mm [30-40 lb/inch at rear road surface] limits.
Why bigger rear bars bang your head in fast l/r transistions.
http://www.efunda.com/DesignSt...#calc
http://www.smithees-racetech.c....html
1.1-1.25 Hz
Plus you must calculate the sidewall stiffness in series with the spring bar stiffness.................hint use 0.9 x spring to correct for tires.
I'll bet the seat subtrtacts another 10% in the first inch so the wheel rate is:
146 x 0.81 or ~~~ 118 then 131 thereafter123 x 0.81 or ~~~ 100 then 110 thereafter
Somewhat progressive even oem.
I'm happy they spent so much time explaning the need for springs and shocks on sway bars........................what happens when you exceed the rear 20mm [30-40 lb/inch at rear road surface] limits.
Why bigger rear bars bang your head in fast l/r transistions.
http://www.efunda.com/DesignSt...#calc
http://www.smithees-racetech.c....html
1.1-1.25 Hz