<PAGE>   1

                                                                   EXHIBIT 10(W)



                               EIGHTH AMENDMENT TO
                                CREDIT AGREEMENT

         This Eighth Amendment to Credit Agreement, dated as of December 22,
1999 ("Eighth Amendment"), is made by and between POLARIS INDUSTRIES INC., a
Minnesota corporation (the "Borrower"); U.S. BANK NATIONAL ASSOCIATION, formerly
known as FIRST BANK NATIONAL ASSOCIATION, BANK OF AMERICA, N.A., formerly known
as BANK OF AMERICA NATIONAL TRUST AND SAVINGS ASSOCIATION and FIRST UNION
NATIONAL BANK, formerly known as FIRST UNION NATIONAL BANK OF NORTH CAROLINA
(collectively, the "Banks"); and U.S. BANK NATIONAL ASSOCIATION, as
administrative agent for the Banks (the "Administrative Agent").

         WHEREAS, the Borrower, the Banks and the Administrative Agent have
entered into that certain Credit Agreement dated as of May 8, 1995, as amended
by First Amendment to Credit Agreement dated as of November 15, 1995, Second
Amendment to Credit Agreement dated as of February 13, 1996, Third Amendment to
Credit Agreement dated as of September 30, 1996, Fourth Amendment to Credit
Agreement dated as of March 31, 1997, Fifth Amendment to Credit Agreement dated
as of August 24, 1998, a Sixth Amendment to Credit Agreement dated as of
December 7, 1998 and a Seventh Amendment to Credit Agreement dated as of May 10,
1999 (as so amended, the "Credit Agreement").

         WHEREAS, the Borrower has requested the Banks and the Administrative
Agent to modify certain provisions of the Credit Agreement to allow the
formation of a new Subsidiary in Australia and to change certain other
provisions thereof, and the Banks and the Administrative Agent are willing to do
so on the terms and conditions set forth herein.

         NOW THEREFORE, in consideration of the premises and for good and
valuable consideration, the receipt and sufficiency of which are hereby
acknowledged, the parties hereto covenant and agree to be bound as follows:

         Section 1.  Capitalized Terms. All capitalized terms used herein and
not otherwise defined herein shall have the meanings assigned to them in the
Credit Agreement.

         Section 2.  Amendments.

                 (a) The definition of "Additional Guarantors" in Section 1.1 of
the Credit Agreement is amended to read as follows:

                 "Additional Guarantors": Collectively, each Subsidiary other
than (i) the Canadian Subsidiary, (ii) the Australian Subsidiary, and (iii) the
Initial Guarantors.


<PAGE>   2


                 (b)    The following new definition of "Australian Subsidiary"
is added to Section 1.1 of the Credit Agreement in appropriate alphabetical
order:

                 "Australian Subsidiary": Polaris Sales Australia Pty Ltd.

                 (c)    Section 6.9 of the Credit Agreement is amended by adding
the following subsection 6.9(n) at the end thereof:

                 6.9(n) Investments in the Australian Subsidiary (including but
not limited to Investments in the form of any intercompany receivable or
contributions of or investments in plant, property or equipment); provided that
the aggregate cost of all such Investments outstanding at any time shall not
exceed $12,000,000 in the aggregate for the Australian Subsidiary.

                 (d)    Section 6.10 of the Credit Agreement is amended by
adding the following subsection 6.10(g) at the end thereof:

                 6.10(g)Indebtedness incurred by the Australian Subsidiary,
provided that the maximum aggregate amount of Indebtedness outstanding at any
time under this clause 6.10(g) shall not exceed $10,000,000 for the Australian
Subsidiary.

                 (e)    Exhibit 4.19-6 is deleted from the Credit Agreement and
new Exhibit 4.19-8, in the form of Exhibit 4.19-8 attached hereto, is added to
the Credit Agreement.

          Section 3.    Conditions to Effectiveness of Eighth Amendment. The
Amendments contained in this Eighth Amendment shall not become effective until,
and shall become effective when, the Administrative Agent shall have received
each of the following, in sufficient number to distribute to each Bank:

                  (a)   The Agent shall have received, with a counterpart for
          each Bank, this Amendment, duly executed by the Borrower, the Banks
          and the Agent, and consented to by the Guarantors;

                  (b)   The Agent shall have received, with a counterpart for
          each Bank, a copy of resolutions adopted by the Borrower (or a
          Subsidiary, as appropriate), authorizing the execution, delivery and
          performance of this Amendment by the Borrower, and authorizing the
          formation of the Australian Subsidiary and the transfer of certain
          assets of the Borrower (or a Subsidiary) thereto, certified by the
          Borrower's or such Subsidiary's secretary or assistant secretary
          together with a copy of resolutions of any Subsidiary subscribing for
          shares of the Australian Subsidiary and transferring assets thereto,
          authorizing such actions, certified by the secretary or an assistant
          secretary of such Subsidiary;



                                       2



<PAGE>   3


                  (c)   The Agent shall have received, with a counterpart for
          each Bank, a copy of resolutions adopted by each Guarantor,
          authorizing the execution, delivery and performance of that
          Guarantor's consent to this Amendment, certified by that Guarantor's
          secretary or assistant secretary;

                  (d)   The Agent shall have received, with a counterpart for
          each Bank, a certificate signed by the secretary or assistant
          secretary of the Borrower certifying (i) as to the incumbency of the
          person or persons authorized to execute and deliver on behalf of the
          Borrower this Amendment, and (ii) that the articles or certificate of
          incorporation and bylaws of the Borrower have not been repealed,
          rescinded, amended or otherwise modified since copies of the same were
          delivered to the Banks on or about May 8, 1995, pursuant to Section
          3.1 of the Credit Agreement;

                  (e)   The Agent shall have received, with a counterpart for
          each Bank, a certificate signed by the secretary or assistant
          secretary of each Guarantor certifying (i) as to the incumbency of the
          person or persons authorized to execute and deliver on behalf of that
          Guarantor its consent to this Amendment, and (ii) that the articles or
          certificate of incorporation and bylaws of that Guarantor have not
          been repealed, rescinded, amended or otherwise modified since copies
          of the same were delivered to the Banks on or about (x) May 8, 1995,
          pursuant to Section 3.1 of the Credit Agreement, or (y) the date such
          Guarantor became a Guarantor, pursuant to Section 6.5 of the Credit
          Agreement;

                  (f)   The Agent shall have received, for the account of each
          Bank, a written opinion from Kaplan, Strangis & Kaplan, P.A. covering
          the matters set forth on Exhibit A attached hereto;

                  (g)   The Agent shall have received a copy of the Articles or
          Certificate of Incorporation of the Australian Subsidiary, with all
          amendments thereto, certified by the appropriate governmental official
          of the jurisdiction of incorporation of such Subsidiary as of a date
          not more than 60 days prior to the date of this Eighth Amendment.

                  (h)   The Agent shall have received a certificate of good
          standing for the Australian Subsidiary in the jurisdiction of
          incorporation of such Subsidiary as of a date not more than 60 days
          prior to the date of this Eighth Amendment.

                  (i)   The Agent shall have received a copy of the bylaws of
          the Australian Subsidiary certified as of the date of this Eighth
          Amendment by the respective Secretary or an Assistant Secretary of
          such Subsidiary.

                  (j)   The Agent shall have received, with a counterpart for
          each Bank, such other documents, instruments, approvals and, if
          requested by the Agent, certified duplicates of executed copies
          thereof, that the Agent may reasonably request.





                                       3


<PAGE>   4

         Section 4.  Consent. On the effective date of this Eighth Amendment the
Banks consent to the formation of the Australian Subsidiary and the transfer of
property thereto subject to the terms and conditions of the Credit Agreement as
amended by this Eighth Amendment. The formation of the Australian Subsidiary and
the transfer of property thereto within the limits set forth in the Credit
Agreement as amended by this Eighth Amendment shall not be deemed a Default or
an Event of Default under the Credit Agreement.

         Section 5.  Acknowledgment. The Borrower acknowledges and agrees that
its obligations to the Banks and the Administrative Agent under the Credit
Agreement, as amended hereby, and the Revolving Notes exist and are owing
without offset, defense or counterclaim assertable by the Borrower against the
Banks and the Administrative Agent.

         Section 6.  Effect of Eighth Amendment; Representations and Warranties;
No Waiver. The Banks, the Administrative Agent and the Borrower agree that after
this Eighth Amendment becomes effective, the Credit Agreement, as hereby
amended, shall remain in full force and effect. The Borrower represents and
warrants that on and as of the date hereof and after giving effect to this
Eighth Amendment: (i) all of the representations and warranties contained in the
Credit Agreement are correct and complete in all material respects as of the
date hereof, as though made on and as of such date, except to the extent such
representations and warranties specifically relate to an earlier date, in which
case they were true and correct as of such earlier date; (ii) there will exist
no unwaived Default or Event of Default on such date; (iii) there has been no
change in any of the certificates or articles of incorporation, bylaws or
partnership agreements of the Borrower or any Guarantor since the Closing Date
or (if later) the date such Guarantor became a Guarantor; (iv) the Borrower has
the power and legal right and authority to enter into this Eighth Amendment; (v)
neither this Eighth Amendment, nor the agreements contained herein or therein
contravene or constitute a default under any agreement, instrument or indenture
to which the Borrower is a party or signatory or a provision of the Borrower's
articles of incorporation or, to the best of the Borrower's knowledge, any other
agreement or requirement of law; and (vi) no consent, approval or authorization
of or registration or declaration with any Person, including but not limited to
any governmental authority, is required in connection with the execution and
delivery by the Borrower of this Eighth Amendment, or the performance of
obligations of the Borrower herein or therein described.

         Section 7.  Incorporation of Credit Agreement and Other Loan Documents
by Reference; Ratification of Loan Documents. Except as expressly modified under
this Eighth Amendment, all of the terms, conditions, provisions, agreements,
requirements, promises, obligations, duties, covenants and representations of
the Borrower under the Credit Agreement, the Revolving Notes and any and all
other documents and agreements entered into with respect to the obligations
under the Credit Agreement are incorporated herein by reference and are hereby
ratified and affirmed in all respects by the Borrower. All references in the
Credit Agreement to "this Agreement," "herein," "hereof," and similar
references, and all references in the other Loan Documents to the "Credit
Agreement," shall be deemed to refer to the Credit Agreement, as amended by this
Eighth Amendment.




                                       4



<PAGE>   5

         Section 8.  Merger and Integration, Superseding Effect. This Eighth
Amendment, from and after the date hereof, embodies the entire agreement and
understanding between the parties hereto with respect to the subject matter
hereof and supersedes and has merged into it all prior oral and written
agreements on the same subjects by and between the parties hereto with the
effect that this Eighth Amendment shall control.

         Section 9.  Expenses. As provided in Section 9.2 of the Credit
Agreement, the Borrower agrees to pay all of the expenses, including reasonable
attorneys' fees and expenses, incurred by the Administrative Agent in connection
with this Eighth Amendment.

         Section 10. Counterparts. This Eighth Amendment may be executed in any
number of counterparts, and by the parties hereto in separate counterparts, each
of which when so executed and delivered shall be deemed an original but all such
counterparts together shall constitute but one and the same instrument.

         Section 11. Governing Law. THE VALIDITY, CONSTRUCTION AND
ENFORCEABILITY OF THIS SEVENTH AMENDMENT SHALL BE GOVERNED BY THE INTERNAL LAWS
OF THE STATE OF MINNESOTA, WITHOUT GIVING EFFECT TO CONFLICT OF LAWS PRINCIPLES
THEREOF.



                                       5



<PAGE>   6


         IN WITNESS WHEREOF, the parties hereto have caused this Eighth
Amendment to Credit Agreement to be executed as of the date and year first above
written.


                                      POLARIS INDUSTRIES INC., a Minnesota
                                      corporation


                                      By        /s/ Michael Malone
                                         -------------------------------------
                                             Michael Malone
                                             Vice President


                                      U.S. BANK NATIONAL ASSOCIATION,
                                      as Administrative Agent and a Bank


                                      By        /s/ David Shapiro
                                         -------------------------------------
                                      Name          David Shapiro
                                           -----------------------------------
                                      Title         Assistant Vice President
                                           -----------------------------------

                                      BANK OF AMERICA, N.A., as a
                                      Documentation Agent and a Bank


                                      By        /s/ Gretchen Spoo
                                         -------------------------------------
                                      Name          Gretchen Spoo
                                           -----------------------------------
                                      Title         Vice President
                                           -----------------------------------

                                      FIRST UNION NATIONAL BANK, as a
                                      Documentation Agent and a Bank


                                      By        /s/ C. Jeffrey Seaton
                                         -------------------------------------
                                      Name          C. Jeffrey Seaton
                                           -----------------------------------
                                      Title         Senior Vice President
                                           -----------------------------------



                                       6