I PM'd this to Paul in response to a query. its not perfect but I tidied it up a bit to post here. I go into why I and others think many coilovers are too stiff for the road.
This is likely to make people's head's explodes but if you do a search on CPM and springs then I'm sure they'll be some good info out there on the net to fill in the gaps.
Jim
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I run Teins with 4kg/mm front and 3Kg/mm rear. These are a good road spring IMO, just keep the dampers soft.
For the track if it rains they're good too as stiff just slips in the wet.
The JIC/K-Sport/etc all seem to be around 7.5Kg/mm Fr and 5.1kg/mm rear. IMO, this is too high for the road, too high for the wet and too high for some tracks.
I won't go into too much detail but each spring performs depending on the weight it supports. For our cars you can calculate the natural frequency of any given spring. The JIC/Ksport etc have a (cycles per minute) CPM of 124 F and 149 R. In comparison to the Tein which are 91 F and 115R. Big deal? Well real suspension gurus, like Gordon Murray et al who design formula 1 and road cars consider a CPM of around 60-80 for a normal car, 100 for a sports car and 120 for a track car. Incidentally a CPM of 30-50 is menat to induce motion sickness :lol: . They also reckon the only reason you need to go above 150 is if you have aerodynamic downforce as the weight of the car increases the faster you go. So the cheaper brands are at the top limit for a dry track car without aero. Another problem with really stiff springs is you're becoming too dependent on your tyres spring rates as they do all the bump absorption. If you are still getting too much roll at the top limit, the solution is a stiffer ARB rather than more spring rate.
The cheaper brands will still handle fine on corners and better on others but if you throw in a bump, rumble strip etc then it is more likely to become unstable which might help keep the front in the right direction or might see you fighting with oversteer.
Great, I like oversteer you might say... well not exactly, the 7.5/5.1 once converted to CPM for our cars this gives a F/R ratio of 0.83 very close to the standard Sunny setup of 3/2 of 0.84
The Teins however make the back slightly stiffer and shift the CPM ratio down to 0.79. this might not sound a lot but it means you're making the front softer and premoting a touch more oversteer than standard without resorting to creating oversteer through a total loss of grip. I believe the cheaper spring rates are a function of lazy engineering and swaying towards the Amercian/drift market were if stiff is good then stiffer is better.
The balance of F/R is also dependent on damper settings, ride height, tyres etc but my feeling is a smidge more wouldn't hurt Something around 0.77. Suspension setup is about subtlety, If this is too much then an extra 5mm raise in the back would solve it or softening your rear ARB.
This wis roughly where I'm at, I'm busy with a few other things on the car but my plan was to buy some springs and try them out.
I've caluclated loads of spring combos to try but it really depends on what driving you do and what springs are available on the coilovers you buy. For example:
4F/3R kg/mm Safe bet, well proven with Tein
These calculated ones are all based on standard lb/ft springs converted to kg/mm
4F/3.2R kg/mm A tweak better?
4.5F/3.6R kg/mm more track biased whilst still road worthy
4.9F/4.0R bit more
5.8F/4.5R bit more
6.3F/4.9R Average UK track in dry
7.2F/5.4R Maximum the maths says you should use, though the back is a little high.
Now these might all look a bit "soft" if you'll excuse the pun but after trawling the SR20 forum, of the people who seemed to know what they were talking about (One guy used springs so stiff he openly admitted his shell was the actual spring:shock: ), I found 11 track setups, of those, 9 were softer than the K-sports etc whilst the two heavier both had weld in roll cages. The average dry track setup is somewhere between these 2:
4.9F/4.0R
5.8F/4.5R
A quick calulation of your friends evo you don't like shows it has Fr 7kg/mm and CPM 120 with Rr 5kg/mm and CPM 148. This is text book stuff for the max for a dry circuit car.
IMO, looking at the Tein guide, they have put some effort into recommeding an overall suspension setup which is commendable. Just because what I use is different doesn't means its better for the next person.
I've said it before but handling is subjective depending on your goals. Softer than Tein might be optimum for you if you have bad B-roads or a lot of rain and a drift setup is very different to everything I've just said. The way the rest of your car is setup is important but hopefull this waffle has given a few pointers.
This is likely to make people's head's explodes but if you do a search on CPM and springs then I'm sure they'll be some good info out there on the net to fill in the gaps.
Jim
======================================================
I run Teins with 4kg/mm front and 3Kg/mm rear. These are a good road spring IMO, just keep the dampers soft.
For the track if it rains they're good too as stiff just slips in the wet.
The JIC/K-Sport/etc all seem to be around 7.5Kg/mm Fr and 5.1kg/mm rear. IMO, this is too high for the road, too high for the wet and too high for some tracks.
I won't go into too much detail but each spring performs depending on the weight it supports. For our cars you can calculate the natural frequency of any given spring. The JIC/Ksport etc have a (cycles per minute) CPM of 124 F and 149 R. In comparison to the Tein which are 91 F and 115R. Big deal? Well real suspension gurus, like Gordon Murray et al who design formula 1 and road cars consider a CPM of around 60-80 for a normal car, 100 for a sports car and 120 for a track car. Incidentally a CPM of 30-50 is menat to induce motion sickness :lol: . They also reckon the only reason you need to go above 150 is if you have aerodynamic downforce as the weight of the car increases the faster you go. So the cheaper brands are at the top limit for a dry track car without aero. Another problem with really stiff springs is you're becoming too dependent on your tyres spring rates as they do all the bump absorption. If you are still getting too much roll at the top limit, the solution is a stiffer ARB rather than more spring rate.
The cheaper brands will still handle fine on corners and better on others but if you throw in a bump, rumble strip etc then it is more likely to become unstable which might help keep the front in the right direction or might see you fighting with oversteer.
Great, I like oversteer you might say... well not exactly, the 7.5/5.1 once converted to CPM for our cars this gives a F/R ratio of 0.83 very close to the standard Sunny setup of 3/2 of 0.84
The Teins however make the back slightly stiffer and shift the CPM ratio down to 0.79. this might not sound a lot but it means you're making the front softer and premoting a touch more oversteer than standard without resorting to creating oversteer through a total loss of grip. I believe the cheaper spring rates are a function of lazy engineering and swaying towards the Amercian/drift market were if stiff is good then stiffer is better.
The balance of F/R is also dependent on damper settings, ride height, tyres etc but my feeling is a smidge more wouldn't hurt Something around 0.77. Suspension setup is about subtlety, If this is too much then an extra 5mm raise in the back would solve it or softening your rear ARB.
This wis roughly where I'm at, I'm busy with a few other things on the car but my plan was to buy some springs and try them out.
I've caluclated loads of spring combos to try but it really depends on what driving you do and what springs are available on the coilovers you buy. For example:
4F/3R kg/mm Safe bet, well proven with Tein
These calculated ones are all based on standard lb/ft springs converted to kg/mm
4F/3.2R kg/mm A tweak better?
4.5F/3.6R kg/mm more track biased whilst still road worthy
4.9F/4.0R bit more
5.8F/4.5R bit more
6.3F/4.9R Average UK track in dry
7.2F/5.4R Maximum the maths says you should use, though the back is a little high.
Now these might all look a bit "soft" if you'll excuse the pun but after trawling the SR20 forum, of the people who seemed to know what they were talking about (One guy used springs so stiff he openly admitted his shell was the actual spring:shock: ), I found 11 track setups, of those, 9 were softer than the K-sports etc whilst the two heavier both had weld in roll cages. The average dry track setup is somewhere between these 2:
4.9F/4.0R
5.8F/4.5R
A quick calulation of your friends evo you don't like shows it has Fr 7kg/mm and CPM 120 with Rr 5kg/mm and CPM 148. This is text book stuff for the max for a dry circuit car.
IMO, looking at the Tein guide, they have put some effort into recommeding an overall suspension setup which is commendable. Just because what I use is different doesn't means its better for the next person.
I've said it before but handling is subjective depending on your goals. Softer than Tein might be optimum for you if you have bad B-roads or a lot of rain and a drift setup is very different to everything I've just said. The way the rest of your car is setup is important but hopefull this waffle has given a few pointers.
