Stiff springs - more or less grip?
02-20-2009, 02:13 AM
#61
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If Archer Girl jumps up and down on my hood, I don't think I'd care too much about spring rates, shock damping, sway stiffness, squatting . . .
Surprised someone brought up variable rate springs and nobody jumped all over them.
Surprised someone brought up variable rate springs and nobody jumped all over them.
02-20-2009, 09:21 AM
#63
Team Owner
02-20-2009, 10:05 AM
#64
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02-20-2009, 01:23 PM
#65
Three Wheelin'
Formula 500 is pretty close to that. No dampers, rubber pucks for springs, Watts link rear with a solid rear axle. Most of the compliance ends up coming from the tires.
02-20-2009, 03:54 PM
#66
Instead of talking in "spring rates" we should be talking in terms of suspension frequency.
Spring rates are, of course, misleading - because it's really your wheel rate that's important (wheel rate is motion ratio squared divided by spring rate). On two cars with 400 lb springs, one might have a wheel rate of 200 lbs and one might have a wheel rate of 350 lbs, depending on where and how the spring attaches to the suspension arms - so comparing spring rates isn't "apples to apples".
Now, even wheel rates have their problems. Having a 300 lb wheel rate on a 1600 lb 914 will feel much stiffer than a 300 lb wheel rate on a 3400 lb 928. This is because there is a different amount of weight at each corner. I'm actually using incorrect nomenclature - springs are really measured in lbs/inch. For a 400 lb spring, it takes 400 lbs to compress it 1 inch; another 400 lbs to compress it another inch. So, in my example, a 928, being heavier, will compress the same "weight" spring more than a light-weight 914.
So how do we compare the two? Enter suspension frequencies! A formula that takes into account wheel rate and unsprung weight (how much weight is acting on the spring). This suspension frequency is usually measured in cycles per minute.
So, going back to the original question at hand, it should be: High suspension frequency = more or less grip?
Or, put in a more useful way: What is the suspension frequency sweet spot for different cars / tracks?
Spring rates are, of course, misleading - because it's really your wheel rate that's important (wheel rate is motion ratio squared divided by spring rate). On two cars with 400 lb springs, one might have a wheel rate of 200 lbs and one might have a wheel rate of 350 lbs, depending on where and how the spring attaches to the suspension arms - so comparing spring rates isn't "apples to apples".
Now, even wheel rates have their problems. Having a 300 lb wheel rate on a 1600 lb 914 will feel much stiffer than a 300 lb wheel rate on a 3400 lb 928. This is because there is a different amount of weight at each corner. I'm actually using incorrect nomenclature - springs are really measured in lbs/inch. For a 400 lb spring, it takes 400 lbs to compress it 1 inch; another 400 lbs to compress it another inch. So, in my example, a 928, being heavier, will compress the same "weight" spring more than a light-weight 914.
So how do we compare the two? Enter suspension frequencies! A formula that takes into account wheel rate and unsprung weight (how much weight is acting on the spring). This suspension frequency is usually measured in cycles per minute.
So, going back to the original question at hand, it should be: High suspension frequency = more or less grip?
Or, put in a more useful way: What is the suspension frequency sweet spot for different cars / tracks?
02-20-2009, 06:23 PM
#67
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A little OT, but related, I was reading the latest "European Car" magazine and some tuner had warmed over the BMW 135i, and in addition to spring work, they beefed up the front sway bar and UNCOUPLED the stock rear bar. Basically, no rear bar. And this was supposedly a car that in original form understeered.
Maybe their chosen spring/shock package made the tail end too loose.
Maybe their chosen spring/shock package made the tail end too loose.
02-20-2009, 06:57 PM
#68
Team Owner
Some BMW guys swear by this set-up.
02-20-2009, 09:41 PM
#69
Rennlist Member
I just made a substantial change in my spec car by moving from a relatively soft spring to almost a double rate and backing off the sways. Grip was increased but the biggest issue is the ability for the car to take a set quickly and shortening transition time in short coupled corners.
02-20-2009, 09:54 PM
#70
Team Owner
I just made a substantial change in my spec car by moving from a relatively soft spring to almost a double rate and backing off the sways. Grip was increased but the biggest issue is the ability for the car to take a set quickly and shortening transition time in short coupled corners.
02-20-2009, 10:14 PM
#71
Rennlist Member
...well ya no brainer... except the soft setup on the car was one that set a long standing lap record on one of our local tracks...(with Chris at the helm)... over much higher sprung cars. I was a bit reluctant to make the change, and tried to adapt to the style of a softer setup, but in the end didn't suit me. In the hands of someone who was comfortable with it could be quite fast...
Last edited by J richard; 02-20-2009 at 10:46 PM.
02-21-2009, 12:38 AM
#72
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Ok, I'm not an expert in the field of chassis tunning, but this primer on shock absorbers and "Natural Frequency", taught me everything I need to know...
http://www.shockabsorber.co.uk/bounceometer/shock.html
http://www.shockabsorber.co.uk/bounceometer/shock.html
02-21-2009, 03:10 AM
#73
Rennlist Member
Plug in DD. I think VR needs that for his Avitar.
mk
mk
Ok, I'm not an expert in the field of chassis tunning, but this primer on shock absorbers and "Natural Frequency", taught me everything I need to know...
http://www.shockabsorber.co.uk/bounceometer/shock.html
http://www.shockabsorber.co.uk/bounceometer/shock.html
02-21-2009, 03:15 AM
#74
Rennlist Member
One of our SCCA ITE Camaro competitors had a bunch of power but never was a factor in our races. Tough, but about 1 -2 seconds back in lap times. Someone out at Thunderhill had him remove is rear swaybar one day, and he knocked of 3-4 seconds a lap and has been a pain ever since to run with! It looks pretty funny around those 70mph turns with the car all twisted, but it handles and runs in a straigth line REAL fast now.
mk
Potomac-Greg;6306317]A little OT, but related, I was reading the latest "European Car" magazine and some tuner had warmed over the BMW 135i, and in addition to spring work, they beefed up the front sway bar and UNCOUPLED the stock rear bar. Basically, no rear bar. And this was supposedly a car that in original form understeered.
Maybe their chosen spring/shock package made the tail end too loose.[/QUOTE]
mk
Potomac-Greg;6306317]A little OT, but related, I was reading the latest "European Car" magazine and some tuner had warmed over the BMW 135i, and in addition to spring work, they beefed up the front sway bar and UNCOUPLED the stock rear bar. Basically, no rear bar. And this was supposedly a car that in original form understeered.
Maybe their chosen spring/shock package made the tail end too loose.[/QUOTE]
02-21-2009, 11:44 AM
#75
Rennlist Member
A little OT, but related, I was reading the latest "European Car" magazine and some tuner had warmed over the BMW 135i, and in addition to spring work, they beefed up the front sway bar and UNCOUPLED the stock rear bar. Basically, no rear bar. And this was supposedly a car that in original form understeered.
Maybe their chosen spring/shock package made the tail end too loose.
Maybe their chosen spring/shock package made the tail end too loose.
Peter
