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Underbody braces, turbos and more!

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PostPosted: Wed Sep 02, 2015 6:22 pm 
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Joined: Wed Apr 22, 2015 6:59 am
Posts: 19
Location: Krakow, Poland
My GTI has been transformed into a rally car by a previous owner. It has some suspension modifications, including polyurethan bushes. Lastly I have had suspension geometry adjusted. The result is not satisfactory:
Left; Right
Front Camber: -0deg 55' ; -0deg 27'
Front Caster: +1deg 04' ; +1deg 05'
Rear Camber: +1deg 03' ; +0deg25'

The biggest problem is the rear positive camber (however, the shop doing the adjustment was doing it wrong, it was ajdusted just after lifting the car, so in real it can have lower values, but still positive). What can cause positive camber on the rear? I have at the moment stock gti springs, the main modification are polybushes. The bigger ones (D-shaped) are asymmetrical:
Image and what is more they are put in the same direction, so they look like:
As you can see it's not symetrical neither vertically nor horizontally.
What is interesting, on the other side of the vehicle, the bushing is put in other way, the bushings are not symmetrical to each other. Horizontally it looks like:
|-o---| |-o---|
so it looks like someone did something wrong.
Additionally there are signs of friction on inside sides of rear tyres:
Image
I cannot find anything that could do that to them..

Someone in other thread pointed out that maybe these are the bushes that should be placed in the front control arms (where people use assymetrical pattern for more positive caster), but I checked it out and they are a bit different in shape. The rear ones have something like a collar, they are thinner under the iron mounting. The front ones are a bit bigger and simpler in shape, here is photo of one:
Image
and the rear contol arm bushing for a comaprison:
Image
Additionally, as you can see, front control arms are sometimes coliding with the anti-roll bar (you can see the spot) - why is it so? If I put assymetrical bushings, the control arms would be coliding with the anti roll bar permanently.. Can I put some washers before the front bushing of the front control arms to move the whole control arm a bit to the front? This could improve caster and prevent control arm from hitting the anti roll bar, or at least this is my theory :)


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PostPosted: Thu Oct 01, 2015 4:11 am 
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Joined: Wed Apr 22, 2015 6:59 am
Posts: 19
Location: Krakow, Poland
Anyone?

To summarize, my problems are:

1. Positive camber at the rear.
My polybushes at the rear look very similar to these ones:
http://www.superpro.com.au/show-product ... PF0673-70K
As you can see, the whole isn't perfectly in the middle, the bush is a bit assymetrical. Which way should they be fitted to the car?

2. Too little caster in the front.

3. Front sway bar meeting front control arms.


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PostPosted: Sat Oct 31, 2015 4:01 pm 
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Joined: Fri Sep 29, 2006 4:20 am
Posts: 76
The rear D bushes are correct but should be installed with the hole closest to the outside of the car on both sides. |-o---||---o-| You can get an offset strut top to add more negative camber. Harris Motorsport had them on eBay a while ago.

The front caster bush kit can have spacers (up to 3 per side) at the spot you suggested to move the whole arm forward and the rear bush offset hole should be to the outside of the car (same as back)

Measure along the cednterline of the rims (axles) front to back. One side will be a 'little' longer than the other (mine is about 5mm different with all the modified poly bushes in place and the 3 spacers each side) That compensates for the crown on the road and helps keeps the car pointed straight down the road for a standard road car. I have seen one car with 15mm difference side to side - it had a hit on one side and pushed the mount point back - bent the floor. A lot of the caster difference was taken out by careful assembly of the offset bushes and spacers to equalise the side to side measurements. As bent as it was - still drove OK on the road, toe was on zero, camber was at -.5 and didn't chop tyres.

Some kits were sold with only one offset front bush and others didn't have the spacers. The spacers are washers big enough to fit over the spindle but not so thick that you take up all the thread for the lock nut. You need a couple of threads out the end of the nut when finished. If you have a front lower body, brace that will decrease the thread you have to work with and how far you can pack the arm forward. With the bushes and spacers you should be able to push the axles about 10mm forward. Don't know how many degrees of caster that will give you.

As to why the sway bar hits - does it have the correct drop links and bushes fitted and does the swaybar have more than one hole to mount the drop link?

All the above observations are based on my RHD car that has had a very hard life and will be different to your setup and adjustments. Link to Whiteline on how to make a GTi handle REMEMBER - this is a RHD road car article so additional caster will be on passengers side (left in this article) and your setting may well be different for rally use.


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PostPosted: Fri Feb 05, 2016 12:10 am 
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Joined: Fri Sep 21, 2012 9:23 am
Posts: 178
Location: Mount Vernon, WA
Just to add some additional measurement to Whiteline +- 1.5 castor correction front control arm rear bushings. With two washers/spacers that come with the kit and a Turbine Tech Brace on:

front left:
camber: -0.1 degrees
caster: 2.7 degrees
toe: 0.70 degrees (not sure why they left the toe so far in)

right front:
camber: -0.4 degrees
caster: 2.8 degrees
toe: 0.61 degrees (not sure why they left the toe so far in)


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PostPosted: Fri Feb 05, 2016 4:18 pm 
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Joined: Mon Dec 01, 2003 12:47 pm
Posts: 11669
Location: columbus, ohio
when i did the suspension on my red vert i also used some special wound coil springs for a track car that lowered the suspension enough that it required me to build custom adjustable upper front strut mounts to correct camber. there wasn't enough adjustment allowable to correct the camber from the bottom side.

the negative camber was enough that i would have worn the inside tire treads. after i corrected camber using a digital angle measurement tool normally used to set the angle on a table saw i had things back to where i wanted.

the upper strut camber plates allow me to dial in a fairly wide range of camber on the front wheels. there's no really good way to deal with camber on the rear wheels as the tunnels for the rear struts and the upper mounting surface areas are really small, not allowing for much movement of the tops of the struts. anyway, the negative camber on the rear wheels helps to keep the ass end in line on really tight corners.

there are pics of my adjustable front camber plates in my red resto-rod project thread and in my gallery. :wink:

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