dave c
400hp K20
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What happened to the original post?
Continued...
Original post by George K:
Putting vested interests to one side, I thought that some of the following comments might be helpful.
The o.e.m spring rates are a bit difficult to interpret as they are rising rate. The fronts start at 2.8 kg/mm and rise to 4.00 kg/mm (the Eibachs are marginally softer). The rears go from 3.00 to 8.00. I have measured the fronts on my facelift, and they are virtually linear at 4.00.
Most kits are at least 6.00 at the front and 9.00 plus at the rear. Some are 8/10 (Meister R) and others 8/12 – race set-ups are considerably stiffer.
As a comparison the Megane 250R Cup, a good handling car by most standards, is 6.5 front and rear 4.00 (rear is not valid comparison, as a totally different suspension system), and there is quite a lot of feedback to suggest that the ride is marginal on the road, and also it is a bit stiff for the wet. It weighs almost 1,400 kg, about 20% more than the DC5 – which would scale the fronts back to 5.2 for the weight of the DC5.
The are pros and cons to rising rate springs – great with large load variations or a big aero influence – personally I do not like the way in which the roll stiffness ratio front to rear can change, which is the main reason why I went to coil-overs. Also I only do a very small mileage, so longevity is not an issue. Just to say that I have received a lot of help from AST, who produced a custom set-up to met my specific requirements.
There is obviously more to ride and handling than just springs, and both arbs and dampers play a big role. However since dampers need to be matched to the springs to give realistic control, then just softening them off to compensate for stiff springs is a very poor solution from an engineering standpoint.
On the subject of dampers, they have two functions, 1; to absorb bumps and the like, and 2; to control the rate at which the car rolls or pitches – which is what influences handling. Most coil- over dampers deal with the latter (high speed damping), but do not have the additional valving to deal with low speed damping – on smooth tracks this is not a major issue, but on UK roads it is!. That is unless you spend a lot of money on three way adjustable damping systems (Ohlins or Nitron). Road o.e.m dampers do not always have the full valving system due to cost, but fudge the way the progression works.
The DC5 o.e.m rear dampers have a rating of 190/108 which is disproportionately high compared with the front.
It is also worth noting that some coil-over dampers do not have enough travel to work with softer springs, so they are in a catch 22 situation – even in standard form the DC5 is a bit short of bump travel.
One of the major reasons for having very high spring rates on a strut type suspension is that the roll centre moves all over the place, and so minimising the suspension movement reduces this problem. In the days of the Cosworth Sierra 500 touring cars, front springs were as stiff as 40 kg/mm – albeit with better damping it has now been possible to reduce this a lot.
What would I do for mainly road use? Probably Eibachs, shorter front bump stops and Konis at the rear (there are some for the Civic, so they could easily be adapted). Ideally I would convert the rears to take a linear spring.
Hope that this is of some help/interest.
Continued...
Original post by George K:
Putting vested interests to one side, I thought that some of the following comments might be helpful.
The o.e.m spring rates are a bit difficult to interpret as they are rising rate. The fronts start at 2.8 kg/mm and rise to 4.00 kg/mm (the Eibachs are marginally softer). The rears go from 3.00 to 8.00. I have measured the fronts on my facelift, and they are virtually linear at 4.00.
Most kits are at least 6.00 at the front and 9.00 plus at the rear. Some are 8/10 (Meister R) and others 8/12 – race set-ups are considerably stiffer.
As a comparison the Megane 250R Cup, a good handling car by most standards, is 6.5 front and rear 4.00 (rear is not valid comparison, as a totally different suspension system), and there is quite a lot of feedback to suggest that the ride is marginal on the road, and also it is a bit stiff for the wet. It weighs almost 1,400 kg, about 20% more than the DC5 – which would scale the fronts back to 5.2 for the weight of the DC5.
The are pros and cons to rising rate springs – great with large load variations or a big aero influence – personally I do not like the way in which the roll stiffness ratio front to rear can change, which is the main reason why I went to coil-overs. Also I only do a very small mileage, so longevity is not an issue. Just to say that I have received a lot of help from AST, who produced a custom set-up to met my specific requirements.
There is obviously more to ride and handling than just springs, and both arbs and dampers play a big role. However since dampers need to be matched to the springs to give realistic control, then just softening them off to compensate for stiff springs is a very poor solution from an engineering standpoint.
On the subject of dampers, they have two functions, 1; to absorb bumps and the like, and 2; to control the rate at which the car rolls or pitches – which is what influences handling. Most coil- over dampers deal with the latter (high speed damping), but do not have the additional valving to deal with low speed damping – on smooth tracks this is not a major issue, but on UK roads it is!. That is unless you spend a lot of money on three way adjustable damping systems (Ohlins or Nitron). Road o.e.m dampers do not always have the full valving system due to cost, but fudge the way the progression works.
The DC5 o.e.m rear dampers have a rating of 190/108 which is disproportionately high compared with the front.
It is also worth noting that some coil-over dampers do not have enough travel to work with softer springs, so they are in a catch 22 situation – even in standard form the DC5 is a bit short of bump travel.
One of the major reasons for having very high spring rates on a strut type suspension is that the roll centre moves all over the place, and so minimising the suspension movement reduces this problem. In the days of the Cosworth Sierra 500 touring cars, front springs were as stiff as 40 kg/mm – albeit with better damping it has now been possible to reduce this a lot.
What would I do for mainly road use? Probably Eibachs, shorter front bump stops and Konis at the rear (there are some for the Civic, so they could easily be adapted). Ideally I would convert the rears to take a linear spring.
Hope that this is of some help/interest.
