Setting castor on PPP subframe?

[pettsy]

Just about to send my rebuilt G for its first MOT after fitting a PPP subframe. What and how should i be setting the castor of the subframe? What settings are people running on here?

Pettsy

[Etches]

Presume its similar to my pps one , using the adjustable arms

[hayesey]

this page seems to have a reasonable explanation of castor angle part way down:

http://www.tirerack.com/tires/tiretech/techpage.jsp?techid=4

Not sure of the factory angle for a mk3 polo but +5deg or +6deg is common I think.  For a road car you probably want it set about there.  Increasing the angle can help with stability round corners but gives heavier steering and the cornering advantage is minimal to un-noticeable on road.  But the big issue is that with the fixed anti-roll bar, lowering a polo cocks up the standard castor angle, reducing it significantly and the subframe allows you to get it back to normal or increase it if you want to.

[Andy]

If you've previously had the G-laderseite blocks fitted, then measure your wheelbase before fitting the subframe - then set the subframe up to give a similar wheelbase measurement. The frame allows you to get it even both sides.

[pettsy]

i understand the theory of castor, was just kind of after a ballpark figure to set it upto? I seem to remember someone talking about a measurement from the centre of the rear wheel to the centre of the front hub?

Never had g-laderseite blocks fitted,they're still sat in the garage 

[hayesey]

have you not got any polos with standard suspension in your collection to measure the wheelbase of?

[Andy]

What suspension and wheel/tyre combo are you using? I can go and measure mine to give you an idea, but it'll only be relevant if you're lowered by the same amount (40mm) and are running the same wheels/tyres (175/50 R13)

[giorgio]

Polo wheelbase is different left to right (when I measured) so I wouldn't use that as a reference point.

I will try to dig up my sheet but in the end I just put it on a ramp with a set of laser trackers and messed about for a day until I found the right balance between nice turn in and barely acceptable parking.

[Yoof]

Wheelbase should be the same- that's the point of the subframe.

You need a straight back axle though.

[G-spot]

What suspension and wheel/tyre combo are you using? I can go and measure mine to give you an idea, but it'll only be relevant if you're lowered by the same amount (40mm) and are running the same wheels/tyres (175/50 R13)

Wheel base is not effected by size as long as you measure off the same location front and back, ie; leading edge of front rim and leading edge of rear rim(prividing you have the same wheels front and rear ), or likewise with the centerline of the wheel

[Yoof]

True Jason, I always take it from the centre of each wheel, made a small adapter to help the measurements.

Getting the rear axle straight is the biggest pain in the arse!

[jez1272gt]

your best bet is to use a digital castor/caber tool on the front struts to set up your frame. with this set equally on both front struts then you can measure the distance to the rear wheels on both sides to set/square up the rear beam if possible...

[giorgio]

True Jason, I always take it from the centre of each wheel, made a small adapter to help the measurements.

Getting the rear axle straight is the biggest pain in the arse!

If you ever take it off (brackets off the chassis) then scribe around them so you can put them back in the same place. Might not be right but its a good place to start.