RE: Wheel Specs

[Mike Wattam <101714.1343@domain.elided>]

Using very low profile tyres with 15" rims would in theory 
sharpen up the handling.  However, if you look at the Stag
suspension movement, you will see there is a lot of 
camber and toe-in change particularly with the rear
suspension, and this will not give a consistent footprint 
with very low profile tyres, causing early break-away 
especially on wet roads, and especially at the rear.

Also, ultra-low profile tyres need very rigid suspension 
location - which the Stag doesn't have - and forces put
into the car will be very much higher.  Also the noise
generated by these tyres can be very high.  You will find 
the Stag has not been designed to absorb this noise 
and thus it may be rather unpleasant in this area also.

I don't know what tyres came off your car, but you should 
consider that modern high quality tyres such as Michelin
MVX are very suitable and are still made in HR rating in 
standard profile (82%).  I particularly like these because 
they are very quiet, don't go out of balance and have 
excellent roadholding, while absorbing road shocks well.

Therefore, if you are still sure you want to go up to a 6" rim, 
I would advise you (as Tony Hart has already done) at the 
most extreme to use 70 series tyres (note they were 
rejected by Triumph on production as the the tester felt 
the roadholding was not good enough: quote Ted 
Marchant).  Also bear in mind that the wider you make 
the tyre, the bigger the footprint and the lowere the 
loading per square inch, thus the lower will be its wet 
road road-holding.

If you fit non-standard wheels and tyres, you must inform 
your insurance company that you have modified the car 
away from standard specification and obtain their 
approval.  In the event of  an accident arising where loss 
of vehicle control occured, the examiners may look 
critically at the tyres and wheels.

Please do not under-rate the importance of the correct 
tyres.  For instance in Germany, it is not permitted on any 
car to fit non-standard wheels/tyres without the specific 
type approval of the TUV (State MoT authority), or the vehicle
 will be failed and barred from the road at the next test.

Mike Wattam
Triumph Stag Register