Wheel contact patch

[David Kemp]

In my ongoing quest for more modern tyres.....I would like opinions on correct offset /inset for Jowetts to give the best handling steering for every day use.
I ask as Jowetts appear to have ZERO offset.inset , new cars have large amounts of Offset ,cars of the seventies have large amounts of inset .Is this due to the change front rear drive cars to FWD which required change to keep kingpin alignment to the centre of the tyre, giving better tyre contact?
Also if modern rims are fitted to a Javelin ,is it better to have offset ? Inset ? or neutral?

[Keith Clements]

In my opinion the contact patch for road use should be in alignment with the king pin and in the centre of the tyre when normally loaded on a Jupiter.

If you expect to have abnormal loads on the wheels such as in circuit racing where the outside tyre takes a lot of load then to keep the contact patch in alignment then you might try altering the camber or even castor. Radial tyres move a lot more than cross plies because the walls are more pliable, thus they maintain a contact patch better but it might not be in the same place as a crossply.

When I made my wheels with the wider tyres and rims for the Saharan Marathon I gave them more offset but added shims to bring back into alignment. Similarly for racing shims were used with the SAAB wheels. Obviously the profile or height and diameter of the wheels greatly affects the location of the contact patch. A rough static alignment can be done with a plumb line and something to show where the king pin axis might touch the road.