CSG and RCE tag-team suspension Q&A thread! Ask us anything!

[wparsons]

Originally Posted by leicaboss

Do you mean to say -2 front and -1 rear? It seems most opt for more camber up front on their FR-S, I wonder if I need to adapt this since the BRZ does have a tighter front?

Definitely didn't mean -2 front and -1 rear. Stock is 0 front and -1.5 rear, the last thing I would do is reduce either end, especially without testing data to support it.

You could do -2/-2, but what will work best will ultimately come down to your setup and driving conditions. Too much static camber will make the car less stable in a straight line and give less grip under braking, so you want to balance it with how much you actually need.

-1 front / -2 rear is pretty mild, but will definitely give you a bit more grip in hard cornering.

[fatoni]

Originally Posted by wparsons

Higher spring rates at one end of the car tend to increase weight transfer at the other end of the car, so stiffer rear will give more front grip.



Not an official response, but RCE seems to be more focused on auto x, which favours quick transitions and the higher front rate will definitely help that.

thats the exact opposite of whats being said. it doesnt help with my confusion haha

[solidONE]

Originally Posted by wparsons

Higher spring rates at one end of the car tend to increase weight transfer at the other end of the car, so stiffer rear will give more front grip.



Not an official response, but RCE seems to be more focused on auto x, which favours quick transitions and the higher front rate will definitely help that.

Makes sense. Tho, I'd probably run a bigger anti-sway bar and softer rates for that purpose as to let the front end 'dive' a bit under braking but still have decent stiffness under roll at the front end. I guess it would largely depend on driver preference.

[wparsons]

Originally Posted by fatoni

thats the exact opposite of whats being said. it doesnt help with my confusion haha

Where did anyone say that increasing stiffness will also increase weight transfer to that end of the car?

Originally Posted by solidONE

Makes sense. Tho, I'd probably run a bigger anti-sway bar and softer rates for that purpose as to let the front end 'dive' a bit under braking but still have decent stiffness under roll at the front end. I guess it would largely depend on driver preference.

It's all a balance. Too much dive will make the car squirm under braking, and too stiff of sway bars takes away independent wheel travel which can make it handle a bit funny over bumps. You're definitely right that the ideal setup for anyone is going to involve their preference to a large amount though.

[200hp/tonne]

Originally Posted by Racecomp Engineering

Not a bad choice. For track work (and in general) I prefer linear spring rates and I wish the Bilsteins were slightly firmer up front but they have good valving. I'd add a front bar at least.

Sorry for being such a suspension newb, but what size bars should i get? I have a budget earmarked for both front and rear sway bars. Will the RCE bar set be a good fit for my application?

[Wepeel]

Originally Posted by fatoni

i think were veering away from the point. there are ways to exert more force on the springs than the car weighs but it doesnt matter for this discussion. all i want to try and understand is how a higher spring increases weight transfer on that portion of the car.

The softer end will want to roll more, and will "pick up" the inside of the stiffer end (through chassis stiffness and twist). So this lightens the inside wheel of the stiff end and weighs down the inside wheel of the soft end more.

It's not rare to see the inside rear of a GTI or the inside front of a Porsche lifting wheels - it's because the other end is relatively softer, the chassis has some torsional rigidity, and the softer end in roll is picking up the inside of the stiffer end.

So the end of the car that has the inside wheel picking up has more uneven distribution across it's inside/outside tires and is transferring more weight (it actually has zero weight on the inside lifted wheel). Think of a car with corner weights

Front
100 100
100 100
Rear

Put it through a left turn that generates lateral acceleration that causes a total weight transfer of 100 lbs, and assuming identical stiffness front and rear, you have

50 150
50 150

(assuming no fore/aft weight transfer in this example, no braking, accel, etc)

Note the total weight on the right side is now 300 lbs, total weight on inside is 100 lbs. If you stiffen the rear by some amount, you might get something like

75 125
25 175

Still same totals as before, but now the front is more evenly loaded, and more evenly loaded tires generate more aggregate grip (since tire friction reduces as load increases).

In the case where the rear is lifted, you'd get

100 100
0 200

This is awesome for front grip and terrible for rear. Two tires evenly loaded will generate more grip than one tire supporting all of the load.

Note that since we didn't have any fore/aft weight transfer, the front axle weight and rear axle weights totaled 200 lbs in all scenarios. And all examples under cornering load always maintained 100 lbs of weight shift, so left side always totaled 100 and right side always totaled 300.

So I didn't mean for that last example to show no load xfer in front and all in rear, as if the front isn't doing anything, realistically this doesn't make a lot of sense but it's just how my example numbers happened to end up. It would have played a little better if I assumed more weight xfer than 50 lbs.

In a completely unreasonable scenario where the chassis has zero torsional rigidity, front/rear roll stiffness wouldn't affect each other.

[ZDan]

Originally Posted by wparsons

Higher spring rates at one end of the car tend to increase weight transfer at the other end of the car, so stiffer rear will give more front grip.

Higher spring rates at one end of the car increases weight transfer at that same end of the car, reduces it at the other end, which gives more grip at the other end.

Stiffer rear will increase outside rear loading, putting it more in the nonlinear part of the grip vs. load curve where increasing load doesn't give as much increased grip, thus reducing grip at the back of the car.

[Racecomp Engineering]

Last two posts above are good on weight transfer!

Originally Posted by solidONE

Question for Andy @Racecomp Engineering :

I noticed that RCE like to run squared spring rates, so effectively they are much stiffer out front. Does this not produce a very under steering prone set up? Was this the goal? What was the reasoning behind these rates?

The goal with our even spring rates is quick reactions from the front end of the car, plus minimizing front geometry changes. We also want to keep the front of the car off the bumpstops and use the spring instead. On lowering springs rather than coilovers this is especially important...a lot of the springs out there may have lower front rates but understeer like crazy. That's because with their soft rates and large drop they're cornering on the bumpstops every turn. We try not to do that and also include shorter bumpstops to help.

Also it helps put power down on corner exit. A little stability is nice.

With firmer spring rates (in the 10k range) we have used rear biased springs.

We do have a lot of auto-x customers but we do a lot of our testing at the track.

Originally Posted by FirestormFRS

You said anything...
How do the RCE Yellows pair with Koni Sport inserts from a ride/handling trade off stand point?

Very well. Konis are good shocks and the adjustment is real. Need more time to fully compare to Bilstein, but you'd be good either way.

- Andy

[wparsons]

You guys are forgetting that more roll stiffness at one end of the car will also increase weight transfer to the other end longitudinally. You'll never lift an inside front or rear tire if the weight isn't shifting to the other end of the car. A FWD car with the inside rear tire in the air has a TON of weight on the outside front, a RWD car with the inside front tire in the air will have a TON of weight on the outside rear.

Without doing REALLY complicated math, I would still bet that if you looked at how much weight is actually on each tire you would find that stiffening an end results in less weight on the outer tire at that end because more weight went to the other end.

[ZDan]

Originally Posted by wparsons

You guys are forgetting that more roll stiffness at one end of the car will also increase weight transfer to the other end longitudinally.

Front/rear weight transfer = braking g's x c.g. height / wheelbase

Whatever you do with front/rear roll distribution, it doesn't affect the front/rear load distribution OR the left/right load distribution.

I.e., RR + LR and LF + LR are the same for a given combination of lateral and longitudinal accelerations, not affected by roll stiffness distribution.

Roll stiffness distribution affects dynamic corner loading, RR+LF and LR+RF, under lateral or lateral/longitudinal combined accelerations.

Without doing REALLY complicated math, I would still bet that if you looked at how much weight is actually on each tire you would find that stiffening an end results in less weight on the outer tire at that end because more weight went to the other end.

The math isn't complicated.
Stiffening one end of the car will result in MORE load on the outer tire at that end of the car. That's what "stiffening" means! More load per deflection. Relative to the suspension, the body of the car is fairly rigid. The amount of ROLL is the *same* at both ends of the car. Therefore, you'll get more lateral load transfer at the *stiffer* end of the car.

[wparsons]

I'm not talking about under braking... I'm talking about how stiffening the rear will increase weight transfer to the front (or vice versa).

I'm not arguing that increasing rear roll stiffness won't increase weight transfer to the outside rear, all I'm saying is that you're also getting more weight transferred to the front end overall as well.

[ZDan]

Originally Posted by wparsons

I'm not talking about under braking... I'm talking about how stiffening the rear will increase weight transfer to the front (or vice versa).

That does not happen. No fore/aft acceleration, zero fore/aft weight transfer.

I'm not arguing that increasing rear roll stiffness won't increase weight transfer to the outside rear, all I'm saying is that you're also getting more weight transferred to the front end overall as well.

No, you're not.

Fore/aft weight transfer is longitudinal acceleration in g's multiplied weight multiplied by the c.g. height and divided by the wheelbase.

No braking or acceleration, no fore/aft load transfer.

[solidONE]

Bumpstops... I wonder how much of the 'at-the-limit' handling characteristics I attributed to springs, but were in fact bumpstops. I always assumed that once the bumpstops were engaged in the the compression stroke the effect would be very very abrupt. I don't think this is the case with our 86's stock bumpstops.











bumpstops.

[7thgear]

Originally Posted by solidONE

Bumpstops... I wonder how much of the 'at-the-limit' handling characteristics I attributed to springs, but were in fact bumpstops. I always assumed that once the bumpstops were engaged in the the compression stroke the effect would be very very abrupt. I don't think this is the case with our 86's stock bumpstops.

on a smooth road you wouldn't feel the transition

but next time you take an off/on ramp at speed, aim for a pothole with your loaded front tire.... if you get kicked up harshly with almost no delay then you know you've had no more travel left for that bump.