That's better - got it now. Thank you.
How can you determine which bushes need increased "shore hardness" on specific cars given that some cars get fixed with a road force balance and others don't with some cars getting bought back by VW who, presumably, have the same [and possibly even better!?] knowledge of the tyre and suspension forces than you do?
Could you determine on a particular car model, such as the Touareg, the parameter limits for RFV and, subsequently, TFV, and then check individual tyres against these to?
Following through on this also raises the issue of what may happen when a new owner, with a T3 that had no problem when new, then requires a new set of tyres.
Are we going to see new threads saying "My car has done XX,000 miles on its first set of tyres with no problems, but, after fitting a new set of ABCs, I've got this steering wheel vibration and the tyre company and the dealer can't fix it?"
It takes a lot of time effort and equipment
First you need the tyre supplier on board and they have to proved measured samples for testing
Radial runout (RRO) needs to be measured during production
RFV - again end of production
TFV - requires indoor lab facility and the tyres cant be used afterwards
K and C measurements of the vehcile are required and an anlaysis of force moments to understand forcing functions, this tends to lead you towards the places to look first
the bush supplier is needed to provide shore hardness data or you need to make a rig and test to grade samples of suspension parts
measurements of the wheel and tyre assemblies are required and then accelerometers are placed on the suspension and the vehicle tested to gain a baseline
changing factors like the RFV of the assembly and then the bushes shore hardness is then asessed to understand contributions
typically on multilink suspensions G and H point bushes (inner lower levers) and E and F point bushes (upper lever inner) have the most influence.
If this doesnt provide the required results you then need to start looking at thinkgs like the yoke spring in the steering rack to dampen the oscilation (hydro p.a.s not e p.a.s)
it is not a small undertaking and requires time and equipment
these types of issues tend to occur in early production while the suppliers are under pressure to support large volumes of parts and are also maturing their production processes
to answer your question on parameters yes 80N for the assembly is the spec, the tyre alone can be 80N and by match fitting the 80N tyre can provide an assembly with less than 80N - match tyre high spot to wheel low spot etc as a rule aftermarket tyres are worse for uniformity than OE new tyres so i always advise checking the sidewall of your tyre for specific markings eg MO for Merecedes and N for Porsche and buying these tyres from your dealer, as a point to note most Porsche N rated cayenne tyres are also spec'd for Touaregs
it is worth checking the RFV value at the running pressure and not the 2.0 bar the hunter machine sets as standard as RFV does not always increase proportianaly to pressure th RFV point can actually move round the tyre significanlty so once fitted a 20N assembly can be a much higher N assembly at running pressure and in a different place so the force matching was done at the wrong point
hope this helps but in summary
1) check for flat spots
2) good quality tyres for the vehcile marked V0 or N0 or relevant OEM tyre
3) match fitted to correct low point on wheel using trained hunter operator and at road pressure no more than 80N max
4) check relevant suspension bushes
5) investigate rack (if T3 is oil based PAS)
