I ask hankook today and they told me most likely if i only buy the rims from stamford, they wont let me trade in my rims and tyres
yup, that's correct. Unlike other tyre shops, Hankook sells only hankook tyres, and does not re-sell 2nd hand tyres, hence hankook cannot accept trade in, more so when the rims are bought from Stamford. Its a different business model.
Have you tried asking stamford if you brought down 4 pc of tyres and buy their rims, can they do a trade in for your existing stock set? If can, of cos that will be best for you!
