AO Platinum Member
Join Date: Aug 2003
Location: London, England
Re: Tyres for 17" Rims
Not sure what a 155 Q4 was fitted with.
But yes it relates to the maximum load the tyre can safely take.
It is marked on the tyre, in this example it is "91": 205/55ZR16 91W
215/45R17 tend to have a load index of 87, but there are some XL or RF versions (Extra Load or Reinforced) with load index of about 94.
Edit: just checked on the Dunlop site, the original fitment looks to have been 205/50ZR15 with a load index of 86, so you are ok.