Tyre pressure / circumference and the VC. New dog old trick?

[seeker]

Hi
I thought that I needed to look after my VC (turns out it is tight anyway), so I measured the travelling circumference of my wheels, by using magnets to mark the wheels at the bottom, rolling the vehicle for two full rotations by the drivers wheel (the one you can see!), and seeing if all the others had the same position. Worryingly they were'nt by about 1" per revolution. Off to the local tyre fitters. I found when the wheels were off, that their circumferences were the same! Put them back after inflating to recommended pressure 40 front 50 back, (They were all over the place before 32 to 38psi). Measured again, still different. So I let air out (about 5psi) of the larger tyres until when measured again they were the same. It worked. More rotations to exaggerate the error, still good. Is this a new trick?

[toomanytoys]

Mmmm yes and no... but you might have just kicked off another one of thise threads.....

Other things to consider are things like "slip angle" (how much wheel spins against the ground driving the vehicle forward) etc etc... thats different at walking pace to 60mph...

What you dont tell us is what tyres they are, (ie all the same brand/wear level or not) size and what the std pressures say in the door slam (some variations)
My doka runs 43F and 48R on std 185r14...

[seeker]

Yes they are standard 185 14

[silverbullet]

See the other recent VC thread for the origins of this:
The disadvantage of a viscous coupling is that it engages too slowly and allows for excessive wheelspin before transferring torque to another wheels. This is especially critical in automatic all wheel drive systems - when cornering under acceleration, the rear end is engaged with a slight delay, causing sudden change in the car's behaviour fron understeer to oversteer. Also, when taking-off in sand, front wheels can become bogged down before all wheel drive is engaged.

In an attempt to reduce the coupling's activation time, VW Golf MkII Syncro always transfers 5% of torque to rear wheels (this is achieved by rear driveshaft rotating slower than front driveshaft in normal conditions, causing viscous fluid warm-up and slight solidification).
Was this feature designed into the T3 syncro inadvertantly?

[v-lux]

You could always see what peoples opinion is of getting a decoupler?

[silverbullet]

[jebiga41]

You could always see what peoples opinion is of getting a decoupler?

should ask syncrosimon and syncropaddy

[silverbullet]

We're so naughty

[syncropaddy]

Im gonna get a de coupler cuz they are great an.. an.. an.. when I need 4x4 I can pull a third knob ..... its all down to knob pulling I reckon .... an when I pull the knob nothing will happen .... an ... an ....

[seeker]

The "slip angle is a good point, so I'll devise a test for that sometime.
I've read the VC/decoupler thread; some passionate arguments.
For me, the vehicle is needed for patchy Welsh road conditions, steep wet roads,leaves, snow, ice and mild wild camping. Extreme offroad is something I like the look of, but am sure I can't afford the wear and tear.
A working VC would be best for what I want I think.
The big issue is looking after it, because if it gets tight there can be v expensive gearbox etc consequenses from transmission wind up. A friend of mine had this and lost £4.5K 10 years ago over it.
So then a decoupler is the answer for dry tarmac and long runs. Is it worth the money? How reliable is the vacuum system? Can it be set up with default 4wd on and vacuum activation to decouple? Its no fun pulling knobs and nothing happening.

[silverbullet]

I think the wiki should have a bit about difflocks, freeing off seized ones etc. but maybe not?
As you see, the whole "3rd knob" discussion does get folks going - it's your choice. If you can see the benefit, then fit one. You don't have to decouple...
Would be handy for those long hot Welsh summers I know they happen, the reports of endless rain are greatly exaggerated.
You can always reverse the vacuum connections at the control or the actuator, but the warning light will always be on when it's engaged. Might be a tad irritating.

[toomanytoys]

standard tyres standard pressures I would say.. VW have done a lot of calculations and testing to arrive at the factory numbers....... (or have they!!!!!!)

[jebiga41]

A working VC would be best for what I want I think.

As you said get a refurb rotate your tyres and that's it just waiting for syncrosimon

[Mudlark]

Simon ... dont bite .... pleeeeeeeeeeaaaaaaaassssssseeeeeeeee!

[hotpod]

just a quick thought about decouplers....

notice they are called de-couplers and not couplers.
if i had loads of money looking for something usefull to do, i would definately have a decoupler but purely to de couple when it would be handy instead of the other way round.

i know this isnt the right thread for this but the thought i should mention it whilst it is on my mind.