WOOD, Circuit Judge.
Although this appeal arises out of the extensive alleged conspiracy to fix prices in various copper markets that this court addressed in Loeb Indus., Inc. v. Sumitomo Corp., 306 F.3d 469, 477 (7th Cir.2002) (Loeb I), the issues that concern us here would find a more comfortable home in a civil procedure class than an antitrust class. We must decide whether, on the basis of any of the theories the plaintiffs have presented to us, some or all of their claims are entitled to go forward. The district court found that the plaintiffs filed their suit too late, based on an accrual date that it thought could not be disputed. It also rejected plaintiff Southwire’s argument that the earlier litigation that reached this court in Loeb I tolled its claims against two of the defendants long enough to make them timely in this case. Finally, it concluded that the federal statute of limitations applicable to the plaintiffs’ claims was not tolled during the pen-dency of certain state class actions in the California courts, which were necessarily based on state rather than federal antitrust law.
We conclude that the district court erred in its conclusion that the undisputed facts demonstrate that the plaintiffs’ right to sue J.P. Morgan has to be measured from July 23, 1996. Whether viewed as a question of the time when the plaintiffs reason[785]*785ably could have discovered that Morgan had anything to do with their injuries or viewed as a question of equitable estoppel and fraudulent concealment, the facts taken in the light most favorable to the plaintiffs could support a finding that their suit was timely. We find, however, that the plaintiffs’ claims against Sumitomo and Global were correctly dismissed, as that set of claims does not benefit from any form of tolling. We therefore affirm in part and reverse and remand in part for further proceedings consistent with this opinion.
I
Loeb I describes the allegations about the extensive manipulations of the copper market that gave rise to these suits. We therefore limit our discussion of the facts (taken for present purposes in the light most favorable to plaintiffs) to those that are of particular relevance. See generally 306 F.3d at 474-78. Briefly, in the underlying actions that were consolidated under the multidistriet litigation (MDL) statute, 28 U.S.C. § 1407, a group of purchasers of copper rod and cathode sued J.P. Morgan Chase & Company, and Morgan Guaranty Trust Company of New York (collectively referred to as Morgan) for their participation in the copper price-fixing scandal of the 1990s, claiming that the defendants had violated the Sherman Act, 15 U.S.C. § 1, et seq., and the Clayton Act, 15 U.S.C. § 15, et seq. In a separate action, plaintiffs Southwire Company and Gaston Copper Recycling Corporation, a wholly owned subsidiary of Southwire (collectively referred to as Southwire), sued Sumitomo Corporation and Global Minerals & Metals Corporation (Global), claiming that the latter two companies had combined to manipulate the price of copper by artificially restricting the physical supply of copper and creating a false demand for it. These manipulations allegedly “caused the price of primary copper to rise more than 50% over a two-year period.” Loeb I, 306 F.3d at 477. In June 1996, when Sumitomo announced that it had lost over $1.8 billion as a result of the supply restriction scheme perpetrated in large part by its employee Yasuo Hamanaka, “the trading price for copper dropped by a third almost overnight. The prices of physical copper cathode, rod, and scrap crashed comparably.” Id.
In Loeb I, we upheld the district court’s dismissal of a putative class that included purchasers of only copper scrap, because their injuries were indirect. 306 F.3d at 475. In the same decision, we held that the purchasers of copper rod and cathode could go forward with their antitrust claims against Morgan because they had suffered “direct and independent” injuries. Id. This case raises the question whether the next chapter of the litigation can proceed.
A. The Parties
The majority of plaintiffs now before us are purchasers of copper cathode and copper rod. This group includes the following companies: Asarco Inc., American Insulated Wire Corp., Essex Electric Inc., Kenne-cott Utah Copper Corp., Levitón Manufacturing Company, Inc., Mueller Copper Tube Company, Inc., Mueller Copper Tube Products, Inc., and Superior TeleCom, Inc. (now known as Superior Essex, Inc.). We collectively refer to this entire group of plaintiffs as the Asarco Group. Plaintiff Southwire Company manufactures and distributes electrical quality copper rod, wire and cable.
Defendant Sumitomo is a Japanese trading corporation that allegedly engaged in various trades and transactions to fix the price of copper from September 1993 to June 1996. Global is a copper merchant that allegedly engaged in transactions with Sumitomo to restrict the physical supply of [786]*786copper. Morgan provided loans to Sumito-mo during the relevant time period.
B. The District Court Proceedings
Our decision in Loeb I allowing the claims of purchasers of cathode and rod to go forward gave rise to a new round of litigation. The dates when these suits were commenced are important to the central statute of limitations issue. Southwire filed its complaint against defendants Morgan, Sumitomo, and Global on December 30, 2002. On June 13, 2003, the Asarco Group filed their actions against Morgan, except for plaintiff Superior TeleCom, Inc., which filed its action on July 11, 2003. On September 4, 2003, the district court consolidated the actions with the rest of the copper antitrust litigation for pretrial purposes.
On March 3, 2004, the district court granted Morgan’s motion for summary judgment against the Asarco Group and converted Morgan’s motion to dismiss against Southwire into a motion for summary judgment. The court granted these motions, finding that all of the plaintiffs’ claims against Morgan were filed after the expiration of the applicable four-year limitations period. See 15 U.S.C. § 15b. It came to the same conclusion for South-wire’s claims against Sumitomo and Global.
The first issue that the court addressed was when the plaintiffs’ claims accrued. In one order, it confirmed that Southwire’s claims against Sumitomo and Global accrued on June 14, 1996, as Southwire had admitted in its complaint. In another order, it selected the date July 23, 1996, as the point when all claims against Morgan had accrued, placing conclusive weight on the fact that by this time, the general press had reported that Sumitomo had financed its transactions through Morgan. For example, an article published in The Neto York Times on June 17, 1996, reported that the Commodity Futures Trading Commission was investigating ties between Sumitomo and Global. This article also reported that Morgan and Bankers Trust had taken “an active part” in the hedging transactions of the copper market. The court also referenced an Associated Press release dated July 23, 1996, stating that “[I]oan agreements between Sumitomo and Chase Manhattan Corp. and J.P. Morgan & Co. are under scrutiny because they may have played a role in [Yasuo] Hama-naka’s attempt to buy large supplies of copper and artificially boost copper prices.” Finally, the court relied on a Wall Street Journal article published the same day discussing loans that were made in the form of derivative contracts from Chase to Sumitomo in the amount of $500 million and from Morgan to Sumitomo in the amount of $400 million. The article described the loans as being “unusually structured.” Based on these reports and articles that appeared later in 1996 and 1997, the district court reasoned that:
[pjlaintiffs do not argue that as of July 23, 1996, they did not know that they had been injured or that Sumitomo was potentially responsible for the injuries. They argue only that despite the newspaper reports, they did not know and could not have known as of this date that the J.P. Morgan defendants had played a part in producing their injuries. They are correct, but the point is not whether they would have known that defendants played a part; it is whether they knew enough to suspect a violation that they could have detected with due diligence or whether they had knowledge of facts that would have led to actual knowledge in the exercise of reasonable diligence. It is clear- that they did. The articles did not say simply that Sumitomo Corporation did its banking with defendants and that defendants might suffer losses as a result of their [787]*787banking role; they said that the Commodities Futures Trading Commission was investigating who might have helped Yasuo Hamanaka arrange fictitious trades and that defendants were among the institutions that took an active part in those transactions. One does not have to be a sophisticated corporation to infer a possible connection between “who helped” and “the institutions that took an active part in those transactions.”
Next, the court considered the plaintiffs’ argument that, at least with respect to Morgan, the statute of limitations was tolled on grounds of equitable estoppel or fraudulent concealment. To support this point, plaintiffs alleged that Morgan had concealed its involvement in the conspiracy in several ways: by entering into confidentiality agreements in the lawsuits and investigations with which it was involved; by giving untruthful statements to the New York State Banking Department and the New York Federal Reserve Bank during their investigation; by allowing its head of media relations in London to destroy a notebook containing his notes of conversations with media contacts; and by declining to give information to the London Metals Exchange about a customer of Morgan Guaranty Trust Company. The court was unpersuaded. It found instead that each one of these actions could be characterized only as a denial of liability.
Even if that were not the case, the court found, the plaintiffs acted too slowly in bringing their suit. It explained that by August 13,1999, the date on which Sumito-mo’s complaint against Morgan was unsealed, the plaintiffs “had the requisite factual support to sue defendants for violation of the antitrust laws,” a claim the court noted that plaintiffs conceded. Relying on its previous holding that the claim accrued on July 23, 1996, this meant that plaintiffs still had eleven months after Sumitomo revealed its complaint to file suit before the four-year statute of limitations expired on July 23, 2000. Plaintiffs filed this case on December 30, 2002, more than six and a half years after the accrual — too late, in the district court’s view.
Finally, the court concluded that the statute of limitations was not tolled during the pendency of certain state antitrust class actions that had been filed against Sumitomo and Morgan. In order to benefit from the tolling rule for plaintiffs covered by a class action announced in the Supreme Court’s decision in American Pipe & Constr. Co. v. Utah, 414 U.S. 538, 94 S.Ct. 756, 38 L.Ed.2d 713 (1974), the court ruled, identical legal theories must be involved in both cases. Both the Asar-co Group and Southwire were unnamed class members in a class action that had been filed in California state court on July 8, 1996, Heliotrope General, Inc. v. Sumitomo Corp., No. 701679 (Cal.Super.Ct.1996) (Heliotrope I). The class in Heliotrope I was defined as businesses that “purchased copper-based products and paid prices for such copper-based products that were inflated due to the defendants’ manipulative and unlawful actions.” On February 14, 2000, Morgan was added as a defendant to the Heliotrope I litigation action. In June 2000, the Heliotrope I litigation was abandoned, but on June 5, 2000, a group of plaintiffs filed a new action, Heliotrope General, Inc. v. Credit Lyonnais Rouse, Ltd., No. 749280 (Cal.Super.Ct.2000) (Heliotrope II), that included Morgan as a defendant. The California Superior Court granted class certification in Heliotrope II on January 22, 2003. All of the plaintiffs except for Southwire opted out of the Heliotrope litigation on March 21, 2003. (Although the court initially rejected plaintiff Asarco’s request for exclusion, the court granted it on June 20, 2003.) Plaintiff Southwire [788]*788filed its opt-out request for Heliotrope II on March 22, 2003.
If the time between the commencement of Heliotrope II and the date when the various plaintiffs opted out of the state class did not count against the four-year limitations period, then the suit against Morgan filed at the end of 2002 was easily brought in time. The district court concluded that this time is excludable only if the American Pipe rule makes it so. It then found that American Pipe did not save the plaintiffs’ actions “[b]ecause the Heliotrope actions did not involve the same causes of action as those in plaintiffs’ present case against defendants, plaintiffs may not claim any tolling benefit from the Heliotrope class actions.” Although the court also found that the plaintiffs could benefit from tolling under American Pipe and Crown, Cork & Seal Co. v. Parker, 462 U.S. 345, 103 S.Ct. 2392, 76 L.Ed.2d 628 (1983), for the federal antitrust class action filed against Morgan in Loeb Indus., Inc. v. J.P. Morgan & Co., No. 00-C-274-C (W.D.Wis.2000) (Loeb II), this time period was not great enough to make a difference. The court calculated that Loeb II’s tolling benefit ran from the day the complaint was filed on May 8, 2000, until January 2, 2001, the day the district court dismissed the action, for a total of seven months and 25 days. The court rejected the plaintiffs’ contention that the period lasted during the pendency of the earlier appeal to this court that culminated in Loeb I.
Finally, the court declined to answer the question whether the tolling agreements entered into by the defendants in the In re Sumitomo Copper Litigation, No. 96 Civ. 4584(MP) (S.D.N.Y.), tolled the statute of limitations in this case. Even if the agreements had that effect, they would not have sufficed to save the plaintiffs’ claims from dismissal, assuming the accuracy of the court’s choice of the date of accrual and the unavailability of any other ground for tolling.
II
We review a district court’s grant of summary judgment de novo, taking all facts in the light most favorable to the non-moving party. See, e.g., Moser v. Ind. Dep’t of Corr., 406 F.3d 895, 900 (7th Cir.2005). An award of summary judgment is proper when “there is no genuine issue as to any material fact and that the moving party is entitled to a judgment as a matter of law.” Fed. R. Civ. P. 56(c); Celotex Corp. v. Catrett, 477 U.S. 317, 322-23, 106 S.Ct. 2548, 91 L.Ed.2d 265 (1986). Here, plaintiffs present three arguments for reversing the district court: (1) material issues of fact exist on the question whether their claims against Morgan accrued on July 23, 1996; (2) material issues of fact exist on the question whether the statute was tolled by the doctrine of fraudulent concealment; (3) even if their claims accrued on June 14, 1996 (for Southwire’s claims against Sumitomo and Global), and July 23, 1996 (for all claims against Morgan), as the district court held, the cases are timely because the statute of limitations was tolled as a matter of law during the pendency of the state court class actions. This opinion addresses only the first two of these points in detail. Judges Cudahy and Rovner have rejected the third argument, for the reasons explained in Judge Cudahy’s separate opinion.
A. The Accrual Date of Plaintiffs’ Antitrust Injuries
The plaintiffs argue that the district court improperly selected July 23, 1996, as the date on which their claims accrued and contend instead that August 13, 1999, the date on which Sumitomo’s complaint against Morgan was unsealed, is the proper date. Plaintiffs further argue that even [789]*789if their actions accrued as early as 1996, they should benefit from tolling under the doctrine of fraudulent concealment because of Morgan’s efforts to hide its involvement with Sumitomo’s price-fixing. We first address the question of accrual. Whether the district court selected the proper accrual date depends on the application of the discovery rule to these facts.
As an initial matter, plaintiffs’ antitrust claims are subject to a four-year statute of limitations. 15 U.S.C. § 15b; see also Zenith Radio Corp. v. Hazeltine Research, Inc., 401 U.S. 321, 338, 91 S.Ct. 795, 28 L.Ed.2d 77 (1971) (“The basic rule is that damages are recoverable under the federal antitrust acts only if suit therefor is ‘commenced within four years after the cause of action accrued’.... ” (quoting 15 U.S.C. § 15b)). Generally, an antitrust “cause of action accrues and the statute begins to run when a defendant commits an act that injures a plaintiffs business.” Zenith, 401 U.S. at 338, 91 S.Ct. 795. As in other areas of the law, however, in the absence of a contrary directive from Congress this rule is qualified by the discovery rule, which “postpones the beginning of the limitations period from the date when the plaintiff is wronged to the date when he discovers he has been injured.” See Cada v. Baxter Healthcare Corp., 920 F.2d 446, 450 (7th Cir.1990). “This principle is based on the general rule that accrual occurs when the plaintiff discovers that ‘he has been injured and who caused the injury.’ ” Barry Aviation, Inc. v. Land O’Lakes Mun. Airport Comm’n, 377 F.3d 682, 688 (7th Cir.2004) (quoting United States v. Duke, 229 F.3d 627, 630 (7th Cir.2000) (emphasis in original)).
Plaintiffs discovered that they had suffered some kind of injury on June 13, 1996, when Sumitomo announced that it had incurred almost $1.8 billion in losses from its illegal activities. At this point, the plaintiffs knew that their businesses had been injured by Sumitomo's actions, but they did not know that Morgan might also be liable. As the district court noted, however, several articles indicated that Morgan had financed Sumitomo’s copper transactions. The district court thought that the plaintiffs should have suspected Morgan’s possible culpability by July 23, the date when the Associated Press reported that Morgan and other banks were under investigation by the Commodities Futures Trading Commission (CFTC), because by this date, “plaintiffs had enough information to trigger their obligation to make further inquiry.” The court concluded that whether it applied the discovery rule to when the claim accrued or the fraudulent concealment doctrine to toll the statute of limitations, by July 23 the plaintiffs “knew enough to suspect a violation that they could have detected with due diligence.” Absent any alleged wrongdoing on Morgan’s part, the court thought that the plaintiffs should have known of Morgan’s liability too.
The problem is that in making its determination, the court never explained what facts the plaintiffs’ diligent inquiries would have revealed. (Sumitomo, it should go without saying, was in a different position; as a party to the deals with Morgan, it had access to information that was not accessible to outsiders.) The court cites several articles that mentioned Morgan and its loans to Sumitomo in June and July 1996, none of which indicated that Morgan’s actions were unlawful or even that Morgan knew about Sumitomo’s fraudulent transactions. Even the articles published in the spring of 1997 reporting the federal investigation of Morgan did not state that Morgan had been charged with violating the law. For example, on April 3, 1997, The Wall Street Journal reported that state and federal authorities reprimanded Morgan after their investigation of Morgan’s financing the trades of Yasuo Hamanaka, [790]*790Sumitomo’s key copper trader. The article suggested that Morgan may have had knowledge of Hamanaka’s purposes behind the loans and it referred to a six-month federal investigation, but it stopped short of saying that Morgan had been charged with violating any laws.
Perhaps most significantly, as the district court noted in its opinion, Morgan was not named in any copper litigation until February 2000, six months after Sumitomo unsealed its complaint against Morgan. See R.W. Strang Mechanical v. Sumitomo Corp., No. 701680 (Cal.Super.Ct.1996) (complaint amended to add defendant Morgan on February 14, 2000); Heliotrope I, No. 701679 (Cal.Super.Ct.1996) (complaint amended to add defendant Morgan on February 14, 2000); Nat’l Metals, Inc. v. Sumitomo Corp., No. 734001 (Cal.Super.Ct.1999) (complaint amended to add defendant Morgan on February 14, 2000); Heliotrope II, No. 749280 (Cal.Super.Ct.2000) (complaint filed against defendant Morgan on June 5, 2000); Loeb Indus., Inc. v. J.P. Morgan & Co., No. 00-C-0274-C, 2000 WL 34228172 (W.D.Wis.2000) (complaint filed on May 8, 2000); Ocean View Capital, Inc. v. J.P. Morgan & Co., No. 00-CV-3756 (S.D.N.Y.2000) (filed May 17, 2000). The district court cited these cases in support of its belief that plaintiffs could have filed their cases before July 23, 2000, four years after the accrual date the court selected. But if the soonest that the plaintiffs were put even on inquiry notice about Morgan’s role was late 1999, that was when the four-year period began to run; plaintiffs were not left facing only an equitable extension of time dating from some earlier point.
Under these circumstances, we conclude that a dispute of material fact exists regarding when a diligent inquiry on the part of the plaintiffs would have revealed Morgan’s involvement. The only information available in the public domain was insufficient to suggest activities on Morgan’s part that went beyond the normal role of a financial institution. The press had reported that Morgan was financing some of Sumitomo’s trades; that it was engaged in hedging deals in the copper market; that it may have participated in loan agreements supporting the Hamanaka trades; that it was trading in derivative contracts; and that the CFTC was investigating someone. We do not see how this amounts to indisputable evidence of inquiry notice that Morgan had stepped over any legal lines.
B. Equitable Estoppel and Fraudulent Concealment
The facts taken in the light most favorable to the plaintiffs also support a finding that equitable estoppel should be invoked to toll the statute of limitations. In their appeal, plaintiffs allege that Morgan affirmatively acted to conceal its involvement using a variety of mechanisms: confidentiality agreements; its separation agreement with Keith Murphy, Morgan’s former head of its base metals desk, prohibiting him from disclosing confidential business information in exchange for $225,000; its media strategy; the destruction of evidence; and the withholding of information or giving of false information to regulatory investigations.
“Equitable estoppel [in the statute of limitations context] suspends the running of the statute of limitations during any period in which the defendant took active steps to prevent the plaintiff from suing.” Barry Aviation, 377 F.3d at 689 (internal citation omitted). The typical example of equitable estoppel is when a defendant “promis[es] the plaintiff not to plead the statute of limitations pending settlement talks.” Singletary v. Continental Ill. Nat’l Bank and Trust Co. of Chicago, 9 F.3d 1236, 1241 (7th Cir.1993). [791]*791Fraudulent concealment is a type of tolling within the doctrine of equitable estoppel. Fraudulent concealment “presupposes that the plaintiff has discovered, or, as required by the discovery rule, should have discovered, that the defendant injured him, and denotes efforts by the defendant — above and beyond the wrongdoing upon which the plaintiffs claim is founded — to prevent the plaintiff from suing in time.” Cada, 920 F.2d at 451. In order for a plaintiff to benefit from tolling for fraudulent concealment, he must show “that he neither knew nor, in the exercise of due diligence, could reasonably have known of the offense.” Klehr v. A.O. Smith Corp., 521 U.S. 179, 194-95, 117 S.Ct. 1984, 138 L.Ed.2d 373 (1997) (holding that “reasonable diligence” was required to invoke the doctrine of fraudulent concealment in the context of civil RICO by analogy to antitrust cases).
The district court found that the plaintiffs could not benefit from tolling on the ground of fraudulent concealment because “[t]o sustain such a claim at trial, plaintiffs would have to prove that defendants took active steps to prevent plaintiffs from suing before the statutory deadline.”
After reviewing considerable quantities of discovery materials, plaintiffs have unearthed three incidents that they contend add up to obstructionism sufficient to entitle plaintiffs to claim equitable estoppel. Defendants’ managing director of global commodities made an allegedly untruthful statement to examiners of the Federal Reserve Bank and New York State Banking Department that defendants had had no suspicion about Hamanaka’s dealings and no concern that a March 1996 trade with Sumitomo was unauthorized; defendants’ London head of media relations destroyed a notebook containing his notes of conversations with media representatives; and J.P. Morgan Securities Ltd., an entity related to defendant J.P. Morgan Chase, declined to give information to the London Metals Exchange about a customer of defendant Morgan Guaranty Trust Company. These three incidents add up to nothing of significance.
In our view, this does not do justice to the facts the plaintiffs have presented for purposes of the summary judgment motion. Plaintiffs began by pointing out that Morgan was not contesting the fact that it had engaged in fraudulent concealment prior to June 17, 1996. Other representative facts plaintiffs proffered included the following: (1) Morgan provided false information to authorities, by telling them that Hamanaka’s trades were fully authorized by Sumitomo’s top management when it knew that they were not; (2) Morgan publicly offered innocent alternative explanations to explain away events related to the price-fixing conspiracy, knowing that they were misleading; (3) Morgan affirmatively instructed other conspirators not to divulge the existence of the conspiracy; and (4) in violation of Morgan’s record retention policy, its Head of Media Relations in London destroyed the notebooks in which he recorded information about his contacts with the press. Most suspiciously, almost two years after it fired Murphy, who had headed Morgan’s base metals business for a time and who was at the heart of the arrangements with Sumitomo, Morgan entered into an agreement with him requiring that he not disclose any information relating to the business and that he give Morgan notice of and an opportunity to resist any subpoenas. Notably, the silence was not simply vis á vis the press; it was directed toward official inquiries. In exchange for these promises, Morgan made a generous special payment of $225,000 to Murphy and “reinstated” options for approximately 7,000 shares of Morgan stock, which Murphy had forfeited at the time of his forced resignation.
[792]*792We certainly do not rule out the possibility that Morgan may have explanations for its actions. That is not the point. At the summary judgment stage, this evidence is enough to show that material facts are in dispute as to whether plaintiffs can benefit from tolling under fraudulent concealment. See, e.g., Morton’s Market, Inc. v. Gustafson’s Dairy, Inc., 198 F.3d 823, 832-33 (11th Cir.1999) (reversing a district court’s grant of summary judgment for defendants because material facts existed on plaintiffs’ claim regarding fraudulent concealment). In Morton’s, the Eleventh Circuit noted the “stringent” standard of review at summary judgment for determining whether the defendants’ conduct “prevented the plaintiff from discovering his claim prior to the expiration of the limitations period.” Id. at 832. The court stated that, “[i]t is not enough for summary judgment to point to facts which might have caused a plaintiff to inquire, or could have led to evidence supporting his claim. A defendant who does this has succeeded in demonstrating only that there is a jury question regarding the tolling of the statute of limitations by fraudulent concealment. To award summary judgment on such a showing is error.” Id. at 832-33 (emphasis in original).
Similarly here, defendants answer the plaintiffs’ evidence only with references to articles that reveal information about Morgan’s loans to Sumitomo that, it contends, should have prompted further inquiry. But this evidence does not, by itself, erase the contrary evidence that the plaintiffs have proffered. The doctrine of fraudulent concealment protects “both the diligent and the non-diligent plaintiff ... from the expiration of claims the factual basis for which was shrouded by the veil of fraudulent concealment.” Id. at 836. While denying liability or failure to cooperate is not enough to invoke the doctrine of fraudulent concealment, see Singletary, 9 F.3d at 1241, plaintiffs went far beyond simple denials. We conclude that there are facts in dispute regarding Morgan’s fraudulent concealment and on that basis we reverse the district court’s summary judgment decision in favor of Morgan.
C. Timeliness After Discovery
As we noted earlier, the district court found in the alternative that the plaintiffs acted too slowly in bringing their suit, regardless of questions of discovery or fraudulent concealment. It was on August 13, 1999, that Sumitomo’s complaint against Morgan was unsealed, and it cannot be disputed that the revelation of the information in that complaint gave the plaintiffs the requisite factual support for an antitrust suit against Morgan. In fact, plaintiffs did not file their action until December 30, 2002, more than three years later.
Because the district court’s view of the equities may have been affected by its conclusion that the correct accrual date was really July 23, 1996, we would reverse and remand for further consideration of this point even if our only ground of disagreement related to the equitable estop-pel or fraudulent concealment ground. Here, in addition, our holding (based of course on the summary judgment record) that the plaintiffs could not reasonably have discovered Morgan’s role as early as the district court thought means that the court was not free to shorten the four-year limitations period in this way. Under the discovery rule, the statute does not begin running until the plaintiff discovers that he has been injured and who caused the injury. Here, the statute did not begin running until August 13, 1999, and thus the plaintiffs had until August 13, 2003, to file their action. That was a deadline they easily met.
[793]*793D. Tolling Based on Loeb I: Sumito-mo, Global
Southwire hopes to save its claims against Sumitomo and Global through the argument that the statute of limitations was tolled during the pendency of the federal class action filed in Loeb Indus., Inc. v. Sumitomo Corp., No. 99-C-377-C, 1999 WL 33981535 (W.D.Wis.1999). The defendants respond that Loeb I tolled the statute of limitations only from the date when the action was filed on June 8, 1999, until the district court dismissed the action with prejudice on August 24, 2000. If they are correct, then Southwire is out of luck. If, on the other hand, the statute was tolled until September 20, 2002, when this court handed down its Loeb decision, then Southwire’s ease can go forward.
The general rule is that the judgment of a district court becomes effective and enforceable as soon as it is entered; there is no suspended effect pending appeal unless a stay is entered. There is no reason why the class certification question should somehow be exempt from this rule. Culver v. City of Milwaukee, 277 F.3d 908 (7th Cir.2002), holds that the statute of limitations begins running again as soon as class certification is denied or, as we added, as soon as a party opts out of a class. Id. at 914. At that point, the parties are on notice that they must take steps to protect their rights or suffer the consequences. This is particularly true now that Fed. R. Civ. P. 23(f) makes it possible for parties to seek an interlocutory appeal of a class certification decision, but it was true as well before the advent of Rule 23(f). Furthermore, this rule is clear and easy to enforce. Southwire is therefore not entitled to take advantage of tolling from Loeb I beyond the date when the district court dismissed the case in its suit against Sumitomo and Global.
Ill
In summary, we conclude that Morgan was not entitled to summary judgment with respect to the claims filed by plaintiffs Southwire and Asarco Group, because issues of fact pertinent to the date by which the plaintiffs should have discovered their claims and to the related questions of equitable estoppel and fraudulent concealment remain. We also conclude that the district court correctly granted summary judgment in favor of defendants Sumitomo and Global, because plaintiffs filed those claims too late. Judges Cudahy and Rov-ner also reject plaintiffs’ contention that the statute of limitations was tolled as a matter of law during the pendency of the Heliotrope class actions, for reasons explained in Judge Cudahy’s separate opinion. Judge Wood dissents on this point alone. The judgment of the district court is therefore Affirmed in part and Reversed in part, and the case is Remanded for further proceedings consistent with this opinion. Costs are to be taxed equally between Morgan, on the one hand, and the appellants, on the other.