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-   -   FWD/hatchback rake (http://www.uphillracers.com/showthread.php?t=13071)

sambeeb 15-07-16 09:05

FWD/hatchback rake

I just have a question about the effects of setting up a car with rake. My car is actually the opposite. It sits virtually dead level looking along the sills perhaps a squeak lower at the back if anything. I'm running an open diff and was starting to wonder if setting the car up a little higher at the rear would help with getting the power down out of corners. Obviously a road registered class FWD'er with an open diff is always going to be traction limited but is this something worth looking into or is the effect other than aerodynamic, more to do with raising rear roll centres and rear grip than any direct benefit for the front?


Adam 15-07-16 09:58

Most importantly, what is the car?

sambeeb 15-07-16 10:05

vw polo gti 1.8T 20V. 230hp/320nm 1000kg bilstein B8's. It is sprung square so wheel rates perhaps front biased with 22mm adjustable front bar and 20mm adjustable rear bar. Front camber is only -1.00 neg, 5/1/2 degree castor. yoko advan A050 run at 26-29psi all round. It runs with about a 68/32 weight bias.

Adam 15-07-16 10:16

Does it have torsion beam rear suspension? If so raising rear rideheight shouldn't effect the roll centres at all. If not (are modern ones multilink?) then it might help or it might not. Best way to find out.... Give it a go! Raise the rear 15-20mm and try it.

The most effective way to improve laterally loaded traction is to drop the COG height. Even small amounts can make big differences!

sambeeb 15-07-16 10:31

yeah its torsion beam rear end like even the newest model. I thought as much re the effect on rear roll centre. I was told that raising the rear ride height 10mm would move the rear roll centre 2.5mm, which is why like you said I've been running it low to take advantage of the low COG. My front though is at standard ride height because any more lowering will mangle my front roll centre location as the control arms start to tip up towards the ball joints. That's why the car is slightly bum down. Its actually very good with lateral traction, its as I straighten the car up I just still can't get the power down. It was from reading about fwd drag setup where they run a lot of rake that I was starting to think rake could maintain a better front percentage as weight transfers rearward under acceleration.

Adam 15-07-16 10:52

I always thought the FWD drag cars ran like that purely to try and push static weight distribution forward for initial traction. Higher cog will always increase rwd weight transfer.

On second thoughts, Depending on your suspension, design raising the rear rideheight could lift your pitch centre. This would increase your inertial traction. You'd probably need to lift the rear suspension a loooooong way to find noticeable changes.

sambeeb 16-07-16 01:41

hmm. I have some slightly taller but softer rears. I could run those with spring rubbers fitted to get their rate back up and see how the extra ride height goes I suppose. Or put a spring seat shim under what I have in their now - probably easier if I find it doesn't work, then I can just slip out the shim and away I go on the same spring rate.

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