Have I got this right re; tyre replacement ?

Ralph · Post by **Ralph** » Sat Oct 06, 2007 10:55 pm

If the fronts are in fact smaller rolling radius than the
back and putting one of my fronts next to a back leads
me to think they are but not by a lot, the front prop
will be turning faster than the back, so in normal driving
the fronts will have a slight braking effect this will try
to drive the rear via the viscus coupling "Wow free
power" but it is only giving back some of the power
it as already stolen from the rear wheels as they push
the front ones faster than they want to go.
If on the other hand a rear wheel spins the rear prop
will speed up and will drive the front's via the viscus
coupling and the fronts will then drive and with any
luck get you out of trouble.
I have driven other 4wd vehicles and worked on quite
a few and if the Bongo Diffs are the same ratio and
the transfer box is 1 to 1 then I cant see how anything
else can happen, unless I am missing something that is.
As for winding up, the viscus coupling will stop that as
long as things are not a mile out, but I have seen it
on older land rovers that did not have a viscus coupling
when driven in 4wd on normal roads and it happens
quit quickly and is noticeable.
I may be wrong in this but cant see how it can work any
other way.

neilfraser · Post by **neilfraser** » Sat Oct 06, 2007 10:59 pm

so although the smaller/different profile front tyres have similar rolling distance to the larger rears they are not *exactly* the same and that this is intentional rather just "being within tolerance"?

Colin Lambert · Post by **Colin Lambert** » Sat Oct 06, 2007 11:01 pm

Is this quicker? Both those you mention did not apply to me. (2WD '99 V reg)

francophile1947 · Post by **francophile1947** » Sat Oct 06, 2007 11:15 pm

Lucky you Colin - but they were manufacturer's faults on a Bongo

trevd01 · Post by **trevd01** » Sun Oct 07, 2007 10:46 am

neilfraser wrote:
dandywarhol wrote: The reason for the different sized tyres (from what I can fathom out) is to introduce different speeds on the front and rear propshafts so the viscous coupling can allow a "Full Time 4WD" function.
Sorry to be replying to this so long after it's finished, but if the rolling distance of the front and rear tyres is the same how can there be different propshaft speed? Have I missed something obvious?

Thanks

Neil

As I said in my post above a couple of weeks ago:

trevd01 wrote:with the correct c1% different tyre sizes.

neilfraser · Post by **neilfraser** » Mon Oct 08, 2007 9:48 am

There have been many discussions about tyre sizes etc and I'm happy not to repeat all that here, but does anyone have an opinion on tyre noise from Continental Vanco 2's - this seems to be a popular recommendation technically but on a long journey tyre noise can get a bit tyresom :D

phunni · Post by **phunni** » Tue Oct 09, 2007 10:00 am

Got a 2WD with 195's all around - is that particularly bad?

thingswelike · Post by **thingswelike** » Wed Oct 24, 2007 2:18 pm

I've just had all the air leak out of my tyre due to corroding allows. Unfortunately I drove for a bit to find a safe place to stop and the tyre fitter is saying that it's irrepariable. However he is also saying that I have to replace all four tyres as it's 4WD - is this normal? It's £320!!

The tyres on there currently are commercially rated tyres and have quite a lot of tread left on them (about 16,000miles years old).

Cheers
Alex

dandywarhol · Post by **dandywarhol** » Wed Oct 24, 2007 9:04 pm

Depends how much different to new "quite a lot" is. 4WD with a viscous coupling tyres should all be changed at the same time to prolong the VC life.

thingswelike · Post by **thingswelike** » Wed Oct 24, 2007 9:45 pm

Thanks - as long as I know it's not just sales patter.
In the end another tyre specialist said it was fine to repair and it only cost £11. So crisis averted. I'll keep an eye on it though.