PSM MAX 12KG Springs for PRO/ Competition CoiloversParts Shop MAX 12KG Springs for PRO Competition Coilovers 61mmID, 180mm long Listing is for: 1x Pair of Coilover springs Springs shorter than 6" must use helper springs sold separately. If you are putting 20KG plus on a McPherson strut car like S13 & BRZ, you will need helper springs. This will make sure you're not topping out your shocks, which will damage the shock. However, 20KG+ can be used on a big body Lexus and other double wishbone cars