Suspension question regarding spring rates

[DuncanM]

Hello everyone,

I have been looking into suspension a lot recently and have a question regarding spring rates.

The question is this:

Why is everyone running stiffer springs at the front?

I ask because having done quite a bit of reading lately, racing and fast road set ups usually advise for stiffer rear springs to maintain a balanced wheel rate.

I'm sure I read on here that the cerbera comes with stiffer rear springs.

So again, and in particular to Joolz and the other suspensions tuners, why stiffer front to rear rather than rear to front?

Interested in all answers and opinions

[DuncanM]

Bump.

Surely someon has an opinion/view on this?

[Brummmie]

I have 325lb rears, the fronts are whatever Gaz comes with. They would be stiffer at the front cos thats where the engine is.

[TT Tim]

More weight over the nose.

500 lbs front - 400 lbs rear

Tim

[DuncanM]

I have 400 front 325 rear.

But that's not the question.

The questions is why stiffer at the front?

The balance of the Cerb is pretty close to 50-50.

The main body of reading on suspension tuning for racing setup points towards running stiffer (only slightly) springs at the rear to maintain a balanced wheel rate.

So what I would like to know, and in particular from Trackcar amd the other suspension tuners, is why stiffer front to rear on the Cerbera?

Duncan

[JensenA]

The back end is pretty light. It needs to be compliant so it can 'squat' down under acceleration, also if you have a hard set up at the rear, it will tend to bounce around corners, and you dont want that to happen with a rear wheel drive car, you want the tyres to be in contact with the road.

[trackcar]

The front doesn't have to be stiffer than the rear, it depends what you want from the car.

[julian64]

trackcar said:

The front doesn't have to be stiffer than the rear, it depends what you want from the car.

Anyone that has an answer that isn't "To go round bends really really fast" please put your hand in the air.

[C2HYM]

Mine are protech dampers with 425lb springs at the front & 375lb at the rear. I've no complaints, although I've been told it feels very 'stiffly' sprung compared to other Cerbs.

[GreenV8S]

Traction at the rear wheels will usually be the limiting factor on a rwd car since the rear wheels are being asked to corner and provide traction at the same time. To compensate for this the rear springs and dampers can be made softer than the fronts so more of the weight transfer occurs on the front, reducing front grip and increasing rear grip. The more power and grip you have available the more pronounced these effects are and the more you would need to bias the suspension stiffness towards the front to get maximum performance. Unfortunately this usually means that when you are *not* accelerating hard you are more likely to get understeer.

[DuncanM]

trackcar said:

The front doesn't have to be stiffer than the rear, it depends what you want from the car.

Hi Joolz,

Just interested as to why it has been recommended to go stiffer front?

I know it doesn't have to be but I'd love to hear a good technical explanation of the pros and cons of stiffer front vs stiffer rear.

Like I have mentioned, I have been reading up about suspension tuning and the main thing that comes up regarding spring rates is stiffer rear springs to balance the wheel rate.

This is all new to me. I came to you a few years back for new springs and am very happy with the set-up.

I stumbled across this as I have an old 318iS to run about in at the moment and was surprised to see that the suspension kits offered were all supplying stiffer rear springs.

I find all this very interesting and just wondered what people had to say about it.

Is it true that the original TVR set-up for the Cerb is stiffer at the rear?

Has anyone tried, or is anyone willing to try changing the spring rates round?

Yours

Duncan

Edited by DuncanM on Monday 15th September 16:49

[itsallyellow]

I used to run the race car stiffer at the rear.

I ran 850 on the back with 750 up front.

Were now 900 up front with 850 at the back and its much better.

Mike

[BCA]

Running mikes rates on a road car would be flex-tastic.

Mike, have you done anything to the front of the chassis in terms of bracing? I can imagine that even with the cage and such, you'll still be getting a fair bit of flex at the front?

[trackcar]

DuncanM said:

trackcar said:

The front doesn't have to be stiffer than the rear, it depends what you want from the car.

Hi Joolz,

Just interested as to why it has been recommended to go stiffer front?

I know it doesn't have to be but I'd love to hear a good technical explanation of the pros and cons of stiffer front vs stiffer rear.

Like I have mentioned, I have been reading up about suspension tuning and the main thing that comes up regarding spring rates is stiffer rear springs to balance the wheel rate.

This is all new to me. I came to you a few years back for new springs and am very happy with the set-up.

I stumbled across this as I have an old 318iS to run about in at the moment and was surprised to see that the suspension kits offered were all supplying stiffer rear springs.

I find all this very interesting and just wondered what people had to say about it.

Is it true that the original TVR set-up for the Cerb is stiffer at the rear?

Has anyone tried, or is anyone willing to try changing the spring rates round?

Yours

Duncan

Edited by DuncanM on Monday 15th September 16:49

Ah but you're not comparing like for like. On the front of the beemer you have a strut type suspension with the spring almost vertical and well outboard so it's mechanical advantage over the wheel is greater than that of an inclined spring. At the rear of the beemer you have semi trailing arms with the springs well along the arm, so to get a favourable wheel ratio front to rear you would fully expect the rear springs to be stiffer, but may still have a lower rear wheel rate. The other thing that car designers have to bear in mind is that you will one day run with passengers in the back, full tank of fuel and boot full of luggage and the car still has to support this load without bottoming out .. so whilst you may often see the rear spring rates of rwd cars higher than front, and indeed may also find rear wheel rates higher than front that doesn't mean that it's the correct thing to do if carrying load isn't your primary concern.
Peter's post above gives a fair brief summary of why it is preferential to run a powerful rwd car with higher front wheel rate.

[itsallyellow]

BCA said:

Running mikes rates on a road car would be flex-tastic.

Mike, have you done anything to the front of the chassis in terms of bracing? I can imagine that even with the cage and such, you'll still be getting a fair bit of flex at the front?

John has on his. However we dont seem to have any flex at all??

Mike

[DuncanM]

Thanks for the replies everyone .

Joolz, Thanks for explaining the difference between the BM and Cerb .

Pete, Sorry I missed you post before replying (good post).

Mike, Yikes! From what I've read about your track adventures (fantasic btw!) it looks like your set-up is working bloody well.

I must admit I wanted to ask you what you were running but didn't know whether you'd be happy sharing the info .

Thanks again everyone.


DuncanM