You will not need t/bars for a lowering adjustment of that amount , i think if you go past 30mm then they will be an issue , 20mm or 25mm is no problem . TT shop done mine for £250.00 does make a big difference for pre 2002 models, mine a 2001 and sits a lot better and closes the arch a little espesh with bigger wheels , also told to keep an eye on the tyres for a couple of weeks and let the springs settle B4 you decide about 4 wheel alignment. mine have been fine. Done over a year ago , just taken my wheels off as got new ones,they haver even wear on all 4 tyres so alignment was not an issue in my case ... You are going to get peeps say this and say that , its what you are happy with mate , if you think you need to get it done then go for it , but like i said , let the new springs settle in first then see.