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Increase LLT at the rear without lifting a wheel

Suspension Tuning & Optimization

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Good day!

Subaru impreza owner here. Weekend trackday car.

about 300hp, dccd gearbox. to follow my post on another topic: https://www.hpacademy.com/forum/motorsport-wheel-alignment-fundamentals/show/setup-tips-how-to-improve-tire-contact-and-minimeze-uneven-tire-wear

I was on track this weekend, quite twisty and with slow corners, and also a pretty fast one with about 150kph speed.

In slow corners I am lifting the inside rear wheel. Still getting some understeer mid corner at high speed (not too bad though) and quite more mid corner on the slower ones.

How would you go about increasing lateral load transfer on the rear axle (car is about 60-40 F-R static weight ratio, square tyre setup), without sacrificing wheel independence? I understand that increasing spring rates is a way to do it, but natural frequency is starting to be high (upper 2.7s Hz If i increase the springs). the goal is to keep traction while trying to help void some on the understeer.

Any input is appreciated

thanks

dx4

Where is the understeer most noticeable? If it's on the exit it may be partially down to not apexing late enough and running wide, if on the entry it may help to have a little more rear brake bias or downshift earlier/later (avoiding over-reving) to change the balance.

If you're lifting the inner rear in the slower corners you are at the maximum roll resistance there, and further stiffening won't help.

You may benefit a little from adjusting tyre pressures - the front looks like it has a lot of squirm and a little more may reduce the slip angle?

I can't recall, at the moment, how that vehicle balances the torque between the wheels when one is lifted - a tighter plate, or similar, LSD in the rear may give a little more drive on the outer and take some from the front and that "should" help with the traction circle. A torque biasing front may help on the front - they may be OEM, though?

I would say the most understeer I get is during steady state cornering / mid corner on medium to high speed corners

I am trying to tackle two issues here. To reduce steady state understeer (medium and fast corners, all wheels on the ground, not enough wheel torque to spin an unloaded rear), I would need to increase the rear rollbar (as rear spring frequency is already quite high)

but then again, I already lift the inside rear wheel in tighter corners which is detrimental (understeer and no power oversteer :D), so I know something stiffer may not help at lower speeds.

I would consider tyre pressure already enough, as I'm experiencing most wear on the middle of the tyre, and similalry but a little less on the outer shoulder, barely any on the inside

when DCCD is open (which is the case during cornering), it is about 60% rear torque and 60% front. Then on the front I do have a helical diff, and the rear is a subaru plated unit (45° ramp, max contact surface, max preload I could set which is 128Nm, diff internals are brand new), so it is about as agressive as this unit can be.

So that checks all the boxed you suggested :)

Hence my quest of increasing rear cornering lateral load transfer to improve cornering grip at medium to high speed, without impeding the rear slow grip/traction

thank you for your time Gord

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