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Self Centering
rallyingden - 6/7/09 at 01:17 PM

At what speed do they test the self center of the sterring during the SVA / IVA

Got my lad to tow me last night to check it and its POO though we were not going that fast.

I have taken the caster angle to as much as I can get it without removing and rewelding brackets, but I have no idea how much I am running.

Its a book built chassis with cortina hubs.

Any suggestions ?

Cheers
RD

nick205 - 6/7/09 at 01:53 PM

The SVA/IVA test is done at low speed 10-15mph. The tester will drive the car on full lock, let go of the wheel and check for self centering tendancies.

Different car (MK) but on my test the examiner said he felt the car "try" to self centre so was happy to pass it. TBH I think he was being generous.

Have you checked that the rack, column and track rod joints, upright ball joints are all nice a free/smooth?

Can you gain any more castor by moving the front lower wishbones forward (same effect as moving the top bones back)?

Mr Whippy - 6/7/09 at 01:55 PM

you can easily find what the angle is by simply stretching string from the bottom ball joint to the top one and measuring the angle to the ground. Have a look at the cortina manual to see if it’s close. Also make sure you have not got the steering rack too tight, with the wheels off the ground you should be able to turn the steering wheel with you little finger. I also think towing a car is a bad way to test the centering as the car is getting dragged by the tow car and will not behave properly. Wait till the car is able to drive itself before jumping into moving things. Another thing is to make sure the tyres are at the right pressure, if under inflated the car will struggle to center.

procomp - 6/7/09 at 02:02 PM

Hi

You are ideally looking for a minimum of 3.5 degrees. It would be nice to have 5-6 though in order to make the car pleasurable to drive and give the correct geometry.

Cheers Matt

wicket - 6/7/09 at 02:47 PM

My Locost 'book' chassis has 5.1/2degs and just self centre's but to drives very nicely.

StevieB - 6/7/09 at 04:50 PM

quote:
Originally posted by nick205
The SVA/IVA test is done at low speed 10-15mph. The tester will drive the car on full lock, let go of the wheel and check for self centering tendancies.

Different car (MK) but on my test the examiner said he felt the car "try" to self centre so was happy to pass it. TBH I think he was being generous.

Have you checked that the rack, column and track rod joints, upright ball joints are all nice a free/smooth?

Can you gain any more castor by moving the front lower wishbones forward (same effect as moving the top bones back)?


I had the same thing on my test - examiner put it down as a pass as the car made 'an attempt'. I think he was being a bit generous too, but not complaning about that

I had max castor (not much on an Indy, but planning on some Wosher wishbones at some point to get that sorted), running 30psi in the tyres and so mush toe out it was hard to push the car in a straight line.

mad-butcher - 6/7/09 at 05:54 PM

Examiner told me that using springs is a waste of time as he drives it round the compound normaly and does not use full lock,
my MK also made an attempt, Wozshers wishbones are the way to go made a hell of a difference.

tony

rusty nuts - 6/7/09 at 06:27 PM

If you are using the Sierra steering column and lower bush, the bush can bind and can interfere with the self centering. Changing mine to a self aligning bearing has made a huge difference

rallyingden - 7/7/09 at 06:40 AM

Thanks Guys

Will wait until under own power but in meantime I will check what I am running angle wise.

One more question ... What or Who are "Wozshers wishbones are the way to go made a hell of a difference. "

Do they put the ball joints at a different angle to the book type arms.

Cheers for all the comments



RD

procomp - 7/7/09 at 06:55 AM

Hi

Not sure whether Wozshers wishbones will fit the BOOK dimensions. His are designed for the MK Indy as replacements as that comes with almost zero castor as standard. It also uses Sierra uprights so will more than likely involve re jigging of the chassis brackets. In which case just move them to suit your top arm. They are possibly to long in length also to fit your aplication.

However if anyone knows where Wozshers is hiding could they let him know there is call for other desighn wishbones for the ST/Aries also in fully adjustable form. Which is also BOOK dimensions.
Not heard or seen him on here for a while.

Cheers Matt

wozsher - 7/7/09 at 08:58 AM

Due to two break-ins at the workshop we are in the process of moving to a new more secure (I hope) workshop.I am on with Book dimension wishbones for a forum member at the moment.Sorry for the delay on wishbones already ordered,will get them sent out as quickly as possible,have had to wait for insurance to replace my equipment/tools.
Many appologies Warren

t16turbotone - 7/7/09 at 12:56 PM

on my seven, it worked out that i have 22mm of off set between top and bottom joints (top joint 22mm further back than bottom) sva man said it centered nicely