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

[thetyrant]

Just for info on the Ohlins R&T kits, ive been speaking with my contact at Ohlins HQ in Germany and the reasoning behind the spring rate changes was brought about after UK customers with the earlier 60/60 springs complained about the ride being too firm for roads over here (they are terrible!)... so they went back to development to see what they could do and after testing a few options it was found the lower springs rates (with increased spring preload) were found to give much improved road manners/comfort with still more than acceptable track performance, obviously a compromise and mroe road than track now but it still works well they tell me.

Dampers havent changed as the valving was found to work well with the lower rate springs, so those wanting to make it more track focused can increase the rates to the 60/60 or a touch more i would think if required.

Looks like im going to try this new Ohlins kit in a few weeks and will first try the lower rates and move up if i find the need, as my car is mostly road im hoping they will be ok but no hassle to change them if needed and i think rear will most likely be first to upgrade, will report back once i have on car.

Ian

[strat61caster]

Originally Posted by Purist

Thanks mate. That's pretty much what I thought. I've been told that the OEM springs are too big in diameter to allow enough movement of the strut with a camber plate so looks like its going to be a set of coilovers or nothing.

That's not true for this car, I got over -3 degrees on OE coilovers with a camber plate and camber bolt.

I went with Raceseng so I could just swap spring perch and top nut to adapt the camber plate to whatever coilover I ended up with, expensive up front to save a bit on the backend figuring out what hardware was needed to change coilover setups.

[Tokay444]

Originally Posted by Gforce

You'd think so but it ain't so. Tire loading makes a difference to lateral grip (well contact patch grip technically but for roll effects are talking about lateral grip ).

http://www.morsemeasurements.com/wheel-lift/

[nikitopo]

Originally Posted by thetyrant

Just for info on the Ohlins R&T kits, ive been speaking with my contact at Ohlins HQ in Germany and the reasoning behind the spring rate changes was brought about after UK customers with the earlier 60/60 springs complained about the ride being too firm for roads over here (they are terrible!)... so they went back to development to see what they could do and after testing a few options it was found the lower springs rates (with increased spring preload) were found to give much improved road manners/comfort with still more than acceptable track performance, obviously a compromise and mroe road than track now but it still works well they tell me.

Can you provide evidence of this "official" information? Many people asked in the past and the people at Ohlins were not allowed to give any details of the changed spring rates. Additionally, there are no headquarters in Germany. They have just a distribution and test office at the Nürburgring. I live in Germany, so I know a bit better

[Gforce]

Originally Posted by Tokay444

http://www.morsemeasurements.com/wheel-lift/

Not sure about your point here.

To realize why lifting one contact patch off the road cannot reduce total grip by 25% think about the grip distribution just before the tire lifts off the road. Then do the same thought experiment back to the initiation of the corner. You will see that contact patch grip distribution is never at 25% per corner and, to boot, never the same from second to second.

[Gforce]

Originally Posted by Purist

Thanks mate. That's pretty much what I thought. I've been told that the OEM springs are too big in diameter to allow enough movement of the strut with a camber plate so looks like its going to be a set of coilovers or nothing.

Apparently one other thing Subaru did differently from the Impreza front axle is fit much smaller diameter springs. They could then put the strut more vertical and did so. I'm fairly sure the hub mounting will be at the same angle to the top strut mount, I.e. the camber gain (and loss after a certain spring compression is reached) is about the same as for the Impreza version. The point in doing this was apparently to get the hoodline lower. Note the nifty Maserati birdcage/ Porsche style fender bumps they were able to use because of this size of front spring. One if my favourite features of the styling, especially as you turn in hard. You get really good visuals to go with the steering weight up and seat of the pants g.

The extra flexibility for front negative camber adjustment seems to be a freeby arising from this design choice.

[Purist]

Originally Posted by Gforce

Are you sure it's not the Torsen diff developing push? Are you allowed by your Rules to add front negative camber? For your requirements the front axle would benefit from more static front camber. If the surface is loose (paved or unpaved course?) then especially at low speeds with some significant steering lock the Torsen will behave as if it is a pure locker and simply drive the front tires sideways.

Ah. Makes perfect sense, thanks! So more front end grip (by way of some camber) would help but are you saying to be more gentle on the throttle so the diff doesn't lock up? I'll also try going into the corner a bit hotter then trailbraking to release the diff as you say. It's a scary corner though, narrow and with a rock wall on the outside.

After researching the Torsen diff, I've also realised that on other corners I'm lifting the inside rear effectively turning the diff into an open one. I suppose a bit of left foot on the brake would help it lock up in these situations. Cheaper than a viscous LSD anyway.

[Purist]

Originally Posted by strat61caster

That's not true for this car, I got over -3 degrees on OE coilovers with a camber plate and camber bolt.

I went with Raceseng so I could just swap spring perch and top nut to adapt the camber plate to whatever coilover I ended up with, expensive up front to save a bit on the backend figuring out what hardware was needed to change coilover setups.

Great info. Thanks so much! Did your toe change much with the camber?

[strat61caster]

Originally Posted by Purist

Great info. Thanks so much! Did your toe change much with the camber?

It changes noticeably even with a few tenths of a degree of camber change, more camber = toe in, less camber = toe out from my experience. You'll have to spring for alignment on at least the front axle after getting the camber plates, in my experience be precise about what you want (maximize camber bolts first, have camber bolts give even numbers then move plates to get X degrees, the plates should be on equal marks left to right, or if you'd rather the plates not be even and max the bolts, that sort of thing, etc.)

[Gforce]

Originally Posted by Purist

Ah. Makes perfect sense, thanks! So more front end grip (by way of some camber) would help but are you saying to be more gentle on the throttle so the diff doesn't lock up? I'll also try going into the corner a bit hotter then trailbraking to release the diff as you say. It's a scary corner though, narrow and with a rock wall on the outside.

After researching the Torsen diff, I've also realised that on other corners I'm lifting the inside rear effectively turning the diff into an open one. I suppose a bit of left foot on the brake would help it lock up in these situations. Cheaper than a viscous LSD anyway.

The Torsen biases torque whenever the grip at the contact patch provides different torque reaction from left to right. Even slight differences in grip begin the torque biasing. Therefore, it is important to get the turn in commenced before you tip into the throttle aggressively, once the front axle digs in the Torsen becomes your friend by encouraging the rear axle to utilize all its available grip, and perhaps a tad more, aiding rotation into the bend. Step on the gas just a fraction too early, before the front tires have begun pushing the nose in towards the apex, and you will get serious understeer from the Torsen.

The Torsen also biases torque when you lift-off but not when you brake. The Torsen biases torque between the prop shaft and the axles. It is feasible to build a Torsen with different bias ratios under power than on lift off. When you brake the contact patches are slowing but not trying to drive the prop shaft so the diff is open under braking. Clever device but operates differently to clutch type LSD.

As the Torsen cannot limit slip but only bias torque across to the axle with more grip once grip is lost at one axle there is no torque to bias. Left foot braking has long been used by the Scandinavian rally drivers as a substitute for an LSD when front wheel drive was de rigeur. A clutch type diff locks the selected steering angle when the driver tries to alter it during the corner!!!! Torsen does not do that because it biases torque but does not prevent differentiation forced back by the wheels. So yes, any diff will "bias" torque if there is any. Torsen is just more effective at doing so. Left foot braking a Torsen equipped car will create more grip where none is available from the road.

My old SAAB 99 and 900 turbo had the handbrake operate on the front drive wheels. Handy poor man's LSD that was.

PS loving that video mate. So, fully paved, piece of cake then. Um, the tricky part was exactly where, again, ? Har har.

[Tokay444]

Originally Posted by Gforce

Not sure about your point here.

To realize why lifting one contact patch off the road cannot reduce total grip by 25% think about the grip distribution just before the tire lifts off the road. Then do the same thought experiment back to the initiation of the corner. You will see that contact patch grip distribution is never at 25% per corner and, to boot, never the same from second to second.

My point is, you can be faster with all 4 contact patches on the ground.
If you're lifting a tire, potential grip is reduced.

[Purist]

Originally Posted by Gforce

Left foot braking a Torsen equipped car will create more grip where none is available from the road.

That's what I thought, a bit of brake to provide a small torque reaction on the lifted wheel. Great feedback mate. Thanks for taking the time.

[Gforce]

Originally Posted by Tokay444

My point is, you can be faster with all 4 contact patches on the ground.
If you're lifting a tire, potential grip is reduced.

So you might think. In the real world, weirdly, it ain't so.

Research tire load v grip at the contact patch.

As load goes up so does grip. That's how aerodynamic downforce finds grip that wasn't there before the aero load. It's not linear though.

Even F1 cars can usefully increase roll resistance such that the inside tire lifts off the road and yet the other three tires deliver more grip than is lost.

Chassis engineering is INCREDIBLY complex.

[nikitopo]

Originally Posted by Gforce

So you might think. In the real world, weirdly, it ain't so.

Research tire load v grip at the contact patch.

As load goes up so does grip. That's how aerodynamic downforce finds grip that wasn't there before the aero load. It's not linear though.

Even F1 cars can usefully increase roll resistance such that the inside tire lifts off the road and yet the other three tires deliver more grip than is lost.

Chassis engineering is INCREDIBLY complex.

They are simple to explain, but a few seem to ignore the details while others intentionally don't mention them.


Anyone imagined what happens when we remove weight from a vehicle? Less tire load, less grip! We see racing cars that are lightweight, but we don't count the massive downforce from the aero. If you remove one parameter from the equation (aero), then you just screw up things.