With the T 15 I recommend 20% nitro fuel with no more then 12% oil content. I would not go over 20% nitro. Unless you race I do not recommend over 20% nitro as it does not make that big of a difference for bashing. Sorry to say the T-15 is not the best engine but have fun with it and save up for a different one like the OS CV-R or RX!

Sorry guys I cannot take credit for the above post on shock springs, as it is a cut and past job. Easier to cut and past then type it all out. But either way very good reading.