Promissory Note

Exhibit 10.21 PROMISSORY NOTE $12,000,000.00 New York, New York
as of January 1, 2005 American Railcar Industries, Inc. (" Maker" ), a Missouri corporation, hereby promises to pay to ACF Industries Holding Corp. (" Payee" ), a Delaware corporation, the principal sum of Twelve Million U.S. Dollars ($12,000,000.00) (the " Principal Amount" ), together with interest on such principal sum at the rate per annum equal to the prime rate, as established by Citibank, N.A. from time to time plus 1 / 2 %, which interest shall not be compounded. Interest shall be calculated on the basis of a year of 365 days and the actual number of days elapsed from the date hereof. Maker shall pay the Principal Amount and the interest accrued thereon on demand; provided that if the Payee has not made dema ...