My spedo is off more than 5%, but I don't care. I'm aware of how of it is, and I'm also aware that it saves me almost 10kms for every 100kms in distance I drive (thats good 4 me anyway). I'd say the size you were looking at is appropriate, they shouldnt rub, i'd maybe go with 245-40-19 and I know those forsure wont rub. Whatever you decide, just remember to get them big enough that it doesn't look stupid and doesnt leave you with a gaping wide open wheel well. I have the most typical of aftermarkets on here (i think), 245-35-20, and have never had rubbing.