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Author Topic: Caster  (Read 224 times)

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Offline Robin_16v

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Caster
« on: September 16, 2013, 08:40:18 pm »
Hello folks,

I want to discuss caster. How much positive degree off caster would be a good starting point for a autocross car runing on dirt? If you watch Rally car go there about 20 degree? But this would be to much i gues..?

Who could tell me more about this?
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Offline Smudge

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Re: Caster
« Reply #1 on: September 16, 2013, 10:13:25 pm »
What car?

In a mk2 Golf it is hard to get over 4 degrees without cutting and moving back the top mounts or drastically re designing the uprights. I'm re designing the uprights ATM and will also push the front wheels forward in the arch a max 15mm.

My aim is to get ajustabilty up to around 7 degrees caster for Tarmac circuits.

As you say rally cars have considerably more than this and altering the uprights alone will not get you much over 7 degrees so you would need to look at moving the top mounts.

Are you allowed to alter the top mount position? If so make it adjustable so you can then test different amounts of caster out.

Rally
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Offline Robin_16v

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Re: Caster
« Reply #2 on: September 17, 2013, 08:55:04 pm »
the car in case is a scirocco mk2. I will be making some custom camber plates. The rules will allow me to move the complete mouting points. But nobody has done this before. First i want to know in what sort of range i need to be to make it work. I'd reed some where if you go beyond 6 degree it would be to much. But a rally car for sure run more then 6 degree.
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Offline Smudge

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Re: Caster
« Reply #3 on: September 17, 2013, 09:14:41 pm »
As you say rally cars and drifters run lots of caster i guess to control dynamic camber when they are on more lock (drifting/sliding) sideways and need more lock than circuit racers.  ???

Can you measure a rally car to give you an idea of what to start at?

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Offline Smudge

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Re: Caster
« Reply #4 on: September 17, 2013, 10:16:05 pm »
Quote
Increased positive Caster will also make the vehicle more reluctant to turn and also increase the self centring effect. However it should give more mid-corner grip and also better traction. Some people say you can never have enough, being realistic more than 10° is not going to win any prizes as after that it is a law of diminishing returns due to some of it's less desirable effects. Older FWD hatches may have a little 2-3° Caster so there is lots of room for modification!

HTH
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Offline Robin_16v

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Re: Caster
« Reply #5 on: September 18, 2013, 04:19:44 pm »
I had meassured the polo r angle from a picture when its in a jump on gravel. I would be around 15 degrees. So if we need to believe that we should need to start around 10 degrees.   
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Offline Tim Moll

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Re: Caster
« Reply #6 on: September 20, 2013, 06:25:41 pm »
I'm going to be increasing my caster angle on the race car I'm building using the balljoint spacer plate as shown in my build thread.  I'm not sure what the actual increase in caster angle will be but I'm moving the balljoint forward by 26mm  ???  I was kind of driven to this by the design of my bracket and wanting to pick up on one of the existing balljoint mounting holes on the wishbone!
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Offline Smudge

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Re: Caster
« Reply #7 on: October 14, 2013, 06:05:24 pm »
I think from memory pushing it forward 26mm will increase it more than two degrees, which is good! The mk3 16v hubs push it forward 12mm.

I'm planning on pushing my wheels forward in the arch and moving the lower ball joint mounting point to the hub forward to further increase caster, add top mounts and I may get close to 7 degrees. Looking at an Audi A3 stock they have around 9 degrees.

More static caster will result in more dynamic Camber, and the amount of caster we are talking will not be detrimental in my opinion.  :o
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