Equal spring rates front to rear, why?

[tomislavp4]

Can someone explain to me the logic behind having the same spring rates front and rear?

The stock suspensions have higher spring rate at the rear and so do the lowering springs we can buy. This makes sense because FWD cars understeer and having a stiffer rear counteracts that understeer. So why do all the coilovers have matched spring rates? Doesn't make sense to me.

 

[Yiannis197]

A coilover "usually" has more sophisticated damping than a damper fit by a manufacturer and therefore the rear control is being looked after this way i.e. you don't have to go rock hard on a spring and match the damping of a twin tube setup to work. Also, good coilovers give you the possibility to adjust the rebound or rebound/compression bringing the car where you want. Remember, our cars have an intense oversteery behaviour on a lift off, not everybody likes it. The majority of people are looking for a more neutral setup and that's why most of the time spring rates of mass produced coilovers are the same.

Sometimes though even big companies don't know what they are doing, HR coilovers for our car have been reported to cause understeer. I suspect that they didn't get the setup right ie either go too stiff at the front or too soft at the rear.

Having said that, our car's behaviour is compromised by the cup chassis as it is only good for track. Give it a bumpy road and it won't be able to cope. A coilover will perform much better. Hope this helps.

 

[tomislavp4]

A coilover "usually" has more sophisticated damping than a damper fit by a manufacturer and therefore the rear control is being looked after this way i.e. you don't have to go rock hard on a spring and match the damping of a twin tube setup to work. Also, good coilovers give you the possibility to adjust the rebound or rebound/compression bringing the car where you want. Remember, our cars have an intense oversteery behaviour on a lift off, not everybody likes it. The majority of people are looking for a more neutral setup and that's why most of the time spring rates of mass produced coilovers are the same.

Sometimes though even big companies don't know what they are doing, HR coilovers for our car have been reported to cause understeer. I suspect that they didn't get the setup right ie either go too stiff at the front or too soft at the rear.

Having said that, our car's behaviour is compromised by the cup chassis as it is only good for track. Give it a bumpy road and it won't be able to cope. A coilover will perform much better. Hope this helps.

Ok, so what you're saying is that stock suspension deals with the understeer/oversteer balance mainly by spring stiffness while coilovers do it by damping stiffness. That is valid for the transitional parts of the corner but not for the steady state part because dampers only affect the rate of load transfer. The load transfer when the car is settled in a corner is still dependent on the spring rates, not the damping.

So by installing a good coilover with equal spring rates on our cars, we should be getting better entry and exit out of corners but mid-corner we should end up with more understeer compared to stock.

 

[Yiannis197]

Hi Tomi,

What I tried to say is that If you decide to fit a stiff spring on a normal twin tube damper then you'd have to have damping to suit, and traditionally the damping range of such an item is relatively small. That means that such a setup would be overdamped as a result, exactly as the 197/200 cup is. The rear tunes out understeer which is fine but it comes with a price, harsh ride, snappiness and bounciness. You say mid corner stock setup "should" be better with stiffer rear, I would kindly disagree with that as stiff front gives understeer at the entry but it's needed (especially high rebound) mid-corner and exit to help keeping the line tight (depending how early on the throttle you are of course). Stiff rear would counteract that so it kind of disputes the "better mid corner" statement.

Also, with such OEM rear stiffness if you hit a bump mid corner you'd have to be ready to catch as the grip will go through the window.

A good coilover has a wider range of operation, it can be matched with progressive springs with lower stiffness rate without the grip to be compromised and by the same token it has the ability to control a stiffer spring much better. As a result it doesn't need to be overdamped that's why a 50/50 N/mm coilover feels softer and more compliant than a <50N/mm OEM spring rate damper. Digressive pistons, dual flow valves etc they all do such things. And of course it's all down to the application. IIRC the cup racers have massively higher rates at the front.

My 2p of course

 

[tomislavp4]

Hi Tomi,

What I tried to say is that If you decide to fit a stiff spring on a normal twin tube damper then you'd have to have damping to suit, and traditionally the damping range of such an item is relatively small. That means that such a setup would be overdamped as a result, exactly as the 197/200 cup is. The rear tunes out understeer which is fine but it comes with a price, harsh ride, snappiness and bounciness. You say mid corner stock setup "should" be better with stiffer rear, I would kindly disagree with that as stiff front gives understeer at the entry but it's needed (especially high rebound) mid-corner and exit to help keeping the line tight (depending how early on the throttle you are of course). Stiff rear would counteract that so it kind of disputes the "better mid corner" statement.

Also, with such OEM rear stiffness if you hit a bump mid corner you'd have to be ready to catch as the grip will go through the window.

A good coilover has a wider range of operation, it can be matched with progressive springs with lower stiffness rate without the grip to be compromised and by the same token it has the ability to control a stiffer spring much better. As a result it doesn't need to be overdamped that's why a 50/50 N/mm coilover feels softer and more compliant than a <50N/mm OEM spring rate damper. Digressive pistons, dual flow valves etc they all do such things. And of course it's all down to the application. IIRC the cup racers have massively higher rates at the front.

My 2p of course

Ah, ok. That makes sense. I think. Thanks!