The Ultimate Guide to Flywheel Marketing: Mastering the Strategy for B2B Success

1. Introduction to Flywheel Marketing: The Evolution of Customer Strategy

For decades, the dominant metaphor in marketing was the Funnel. It provided an essential, if simplistic, blueprint for strategic resource allocation, guiding leads from a vast Top-of-Funnel (TOFU) through a process of elimination down to a single point of Conversion at the Bottom-of-Funnel (BOFU). The Funnel served its purpose in an era where information was scarce, sales was gatekept, and the customer’s journey ended with a transaction.

However, the digital revolution fundamentally changed the customer-brand relationship. Today’s customers are empowered, informed, and connected. They ignore sales calls, research extensively online, and trust peer recommendations exponentially more than brand advertising. Critically, the purchase is no longer the endpoint; it is merely the beginning of the relationship. In this new landscape, the Funnel’s rigid, linear structure proved inadequate. It viewed customer success as a cost center and advocacy as an optional, secondary benefit—ignoring the immense energy generated by happy customers.

This strategic shift led to the necessary evolution of the blueprint, replacing the leak-prone, transaction-focused Funnel with the Flywheel. The Flywheel is not a path of elimination, but a system of perpetual momentum. It acknowledges that the energy you put into customer experience directly translates into force that drives future growth, positioning it as the essential modern framework for sustainable, long-term success.

2. What is Flywheel Marketing and What is B2B Marketing?

The Flywheel is the governing metaphor for modern, customer-centric business strategy, and it finds its most powerful application in the sophisticated environment of Business-to-Business (B2B) Marketing.

A. Defining Flywheel Marketing

The Flywheel Model, popularized by HubSpot, is a geometric representation of a business as a system that stores and releases energy. It is a circular, perpetual motion model where the momentum of happy customers is the primary driver of growth. Unlike the Funnel, which loses energy with every stage (leaks), the Flywheel gains speed from positive customer experiences.

The Flywheel has three interconnected, continuous stages:

• Attract: Drawing visitors and qualified prospects in with valuable content and information, often without explicit selling. This replaces the Funnel’s Awareness stage.

• Engage: Building relationships and trust with prospects by providing solutions and insights tailored to their goals. This is where sales and marketing align to solve the customer’s problems.

• Delight: Providing outstanding service, support, and success coaching to ensure customers achieve their goals and become enthusiastic advocates for the brand. This is the stage that generates the momentum that fuels the entire cycle.

B. Defining B2B Marketing

Business-to-Business (B2B) Marketing involves selling products or services to other companies, rather than to individual consumers. It is defined by unique complexities that make the Flywheel model particularly essential:

• Rational Decision-Making: Purchases are driven by logic, return on investment (ROI), and business need, not impulse.

• Long Sales Cycles: Decisions involve multiple stakeholders (committees, VPs, end-users, procurement), stretching the sales cycle from months to over a year.

• High Value: B2B contracts often represent high-value, recurring relationships, making customer retention (LTV) far more critical than single transactions.

C. Synthesis: The Flywheel’s Relationship with B2B

The Flywheel is the ideal framework for B2B for two critical reasons:

• Friction and Momentum: The Flywheel introduces the concept of Friction (anything that slows down the cycle) and Momentum (anything that speeds it up). In B2B, long sales cycles and multiple stakeholders are inherent friction. The Flywheel’s emphasis on seamless handoffs and consistent messaging is a direct strategy for reducing that friction, thereby accelerating sales velocity.

• LTV Maximization: B2B success is entirely dependent on Customer Lifetime Value (LTV). The Flywheel places the Delight stage—customer success, adoption, and retention—at the strategic center, recognizing that retaining and expanding a high-value B2B account is far more efficient and profitable than acquiring a new one.

3. The Crucial Difference: Why the Flywheel Replaced the Funnel

The shift from the Funnel to the Flywheel represents a fundamental paradigm change in how businesses perceive customer relationships and measure success.

A. Energy and Momentum vs. Leaks and Loss

• The Funnel Philosophy (Leaky Pipeline): The Funnel views the marketing process as a volume game where mass awareness is poured in at the top, and energy is constantly lost as leads drop off at each sequential stage. The transaction is the end goal, and the energy (money/effort) invested in a customer essentially stops there.

• The Flywheel Philosophy (Perpetual Motion): The Flywheel views the process as a continuous system where energy is retained and reinvested. Every successful customer interaction, particularly in the Delight stage, generates new energy (advocacy, testimonials, case studies) that directly powers the Attract stage, making the system self-sustaining and efficient.

B. Customer-Centricity vs. Transaction-Centricity

• Transaction-Centricity (Funnel): The Funnel is designed around the company’s process. The primary goal is to close the deal, often prioritizing short-term conversion tactics over long-term relationship building. Customers are objects to be processed and filtered.

• Customer-Centricity (Flywheel): The Flywheel is designed around the customer’s success. The primary goal is to ensure the customer achieves their goals, prioritizing relationship building, education, and support. The customer’s success is directly linked to the brand’s success, making them the gravitational center of the business model.

C. Measurement Philosophy: Volume vs. Velocity

• Funnel Measurement: Focuses primarily on conversion rates between sequential stages (e.g., Lead to MQL, MQL to SQL) and the volume of leads generated (TOFU).

• Flywheel Measurement: Focuses on momentum, which is calculated by the number of customers, the speed of the cycle, and the friction impeding that speed. Key metrics include Customer Lifetime Value (LTV), Customer Acquisition Cost (CAC), and Net Promoter Score (NPS), which directly measure the efficiency and advocacy generated by the Delight stage. The Flywheel is an optimization exercise, not a filtering one.

4. The Core Flywheel Frameworks: Components of Momentum

The Flywheel’s strength lies in understanding the interplay between its three forces and the counter-force of friction. Achieving momentum requires strategic balance and cross-functional alignment.

A. The Three Forces of the Flywheel

1. Attract (The Magnet):

   • Focus: Attracting the right people with content and experiences that are relevant to their needs, not just demanding attention.

   • Tactics: Search Engine Optimization (SEO), thought leadership content, non-interruptive social media marketing, and educational webinars. The goal is to provide value that naturally pulls prospects toward the brand.

2. Engage (The Connection):

   • Focus: Building trust and demonstrating expertise by solving the prospect’s problems and providing them with actionable insights. This is the crucial handoff between marketing and sales.

   • Tactics: Personalized email nurturing, consultative sales, AI-powered chatbots that offer tailored solutions, and interactive tools (e.g., ROI calculators) that help the prospect qualify themselves.

3. Delight (The Propulsion):

   • Focus: Ensuring the customer achieves exceptional value and becomes successful through the product or service. This is the stage that generates the momentum.

   • Tactics: Proactive customer success management, self-service knowledge bases, seamless support, and customer community building. Happy customers become the advocates that power the Attract stage, making the system circular.

B. The Counter-Force: Friction

Friction is anything that slows down the momentum of the Flywheel. It is the antithesis of the Flywheel philosophy and must be systematically identified and eliminated.

• Organizational Friction: Siloed teams (e.g., Marketing hands off an MQL to Sales, and Sales ignores the context provided by Marketing).

• Process Friction: Slow response times, complex contract signing procedures, confusing website navigation, or clunky product onboarding.

• Information Friction: Lack of centralized data or requiring the customer to repeat information across different touchpoints (e.g., sales, support, billing).

C. The Key Concept: Alignment

The Flywheel demands cross-functional alignment among Marketing, Sales, and Service. In a Funnel, these departments operate in silos. In the Flywheel, they function as a unified Revenue Operations (RevOps) unit.

• Shared Metrics: All teams must share metrics centered on the customer. For example, Marketing’s success is tied not just to MQL volume, but to Customer Lifetime Value (LTV), an outcome driven by the Service team.

• Seamless Handoffs: The transition from Marketing to Sales, and then from Sales to Service, must be engineered to be frictionless, typically by using a unified Customer Relationship Management (CRM) system that provides complete historical context to the next team instantly.

5. The Flywheel in B2B and SaaS: Strategies for LTV and Retention

The Flywheel is particularly effective for high-value, recurring revenue models like B2B and SaaS (Software-as-a-Service), where Customer Lifetime Value (LTV) is the single most important financial metric.

A. The SaaS Imperative: Retention is Revenue

SaaS businesses operate on a subscription model, meaning revenue is guaranteed only if the customer renews. This makes retention and expansion exponentially more valuable than initial acquisition.

• Delight as the Profit Center: In a SaaS Flywheel, the Delight stage is the primary profit center. Investment in Customer Success Management (CSM), onboarding, and support directly reduces churn and increases expansion revenue through upsells and cross-sells. The Flywheel forces the organization to invest in the back-end (Delight) just as heavily as the front-end (Attract).

• Product-Led Growth (PLG) and the Flywheel: The rising trend of Product-Led Growth (PLG) is a natural extension of the Flywheel. In PLG, the product itself is the core mechanism for Attract (freemium sign-up), Engage (in-app feature usage), and Delight (achieving success). The goal is to build the Flywheel directly into the user experience, ensuring that feature adoption and time-to-value (TTV) are constantly maximized.

B. Strategies for Long B2B Sales Cycles

Complex B2B sales cycles require sustained, high-value engagement across all Flywheel stages.

1. Account-Based Marketing (ABM) in the Attract and Engage Stages:

   • ABM is the opposite of the Funnel’s mass approach; it targets specific, high-value accounts. In the Flywheel, ABM content is used to attract the entire buying committee (multiple stakeholders) simultaneously.

   • Action: Content is hyper-personalized, focusing on the specific challenges and ROI metrics relevant to that account. For example, the IT manager receives technical white papers (Engage), while the CFO receives ROI case studies (Engage), ensuring all decision-makers are moved along the cycle together.

2. MQL/SQL Handoff as Friction Reduction:

   • The transition from a Marketing Qualified Lead (MQL) to a Sales Qualified Lead (SQL) is a massive friction point in B2B.

   • Action: The Flywheel solves this by ensuring the MQL definition is jointly agreed upon by Marketing and Sales (alignment) and requires a high-intent behavioral threshold. The handoff must be instantaneous, with the CRM providing Sales with every piece of historical context (web pages visited, content downloaded, demo requested) to continue the conversation seamlessly, rather than starting from scratch.

3. Customer Success as a Sales Engine:

   • In B2B, new sales often rely on social proof. The Delight stage must proactively identify customers who have achieved massive ROI.

   • Action: The Service team (Delight) flags these success stories. The Marketing team (Attract) turns them into testimonials and case studies, using them to reduce skepticism in the Engage stage for new prospects, thus efficiently generating new momentum.

6. Flywheel Marketing Examples: Illustrating B2B/SaaS Success

These hypothetical case studies illustrate how the continuous, interconnected nature of the Flywheel creates sustainable growth where the Funnel would stall.

A. Building Awareness via Delight (The Advocacy Loop)

A B2B SaaS company that sells a project management platform (Loomly).

• The Scenario: A current customer’s project finishes six months ahead of schedule thanks to the platform’s automation features (a massive Delight success).

• Flywheel Action:

  1. The Customer Success Manager (CSM, Delight) flags the customer for a success story interview based on a high Net Promoter Score (NPS) survey result.

  2. Marketing (Attract) turns the interview into a high-impact video case study focusing on the “Time Saved” metric.

  3. Sales (Engage) uses that specific video on a personalized landing page for a new high-value prospect currently struggling with long project timelines.

• Result: A delighted customer directly generated a low-cost, high-converting lead, demonstrating the perpetual motion of the cycle.

B. Driving Sales Velocity via Friction Reduction

A B2B software vendor selling cloud security tools with a 12-month average sales cycle.

• The Scenario: A prospect completes a product demo (Engage) but is stalling on the security compliance stage due to a complex internal review process (Friction).

• Flywheel Action:

  1. The CRM flags the account as “Compliance Stalled.”

  2. The Sales Engineer (Engage) is instantly notified and sends a personalized email with a link to a high-value white paper, previously created by Marketing (Attract), detailing “How Our Platform Simplifies 10 Key Global Compliance Standards.”

  3. Simultaneously, the Service team (Delight) initiates a proactive support thread with the prospect’s security team, offering free access to the compliance documentation portal.

• Result: The Flywheel uses cross-functional coordination and pre-built content to address a specific point of friction, accelerating the stalled deal and minimizing the risk of the customer leaking out of the system.

C. Building Thought Leadership through Delight and Engage

A consulting firm specializing in AI transformation (Thought Leadership).

• The Scenario: The firm hosts a free educational webinar (Attract) on “AI Strategy for Q4,” attracting over 500 attendees.

• Flywheel Action:

  1. Post-webinar, the Marketing team (Engage) segments attendees based on poll answers (e.g., “AI Budget” size).

  2. High-budget attendees are instantly segmented into a Sales follow-up sequence, while low-budget attendees receive an automated, personalized invitation to a new customer community forum (Delight) to ask follow-up questions.

  3. Questions raised in the community forum are collected and used by the consulting team (Delight) to write the next quarter’s thought leadership content (Attract), ensuring the cycle is constantly fueled by genuine customer pain points and questions.

The Flywheel categorizes channels based on their strategic function in creating and maintaining momentum, ensuring that the right channels are leveraged for the right purpose.

A. Attract Stage Channels (The Pull)

Focuses on drawing the right people in by providing utility and authority. These replace the Funnel’s TOFU.

• Content: SEO-optimized blog posts, educational video series, industry reports, high-authority white papers, and thought leadership articles.

• Channels: Search Engine Optimization (SEO), Organic and Paid Social Media (LinkedIn, YouTube), Industry-specific Podcasts, and PR/Media Outreach.

• Action: Investing in channels that offer passive, long-term returns, generating momentum through credibility rather than aggressive interruption.

B. Engage Stage Channels (The Connect)

Focuses on building trust and demonstrating how the product solves the customer’s specific problem. These combine the Funnel’s MOFU and BOFU.

• Content: Personalized email workflows, interactive ROI calculators, tailored demos, competitive comparison guides, and case studies.

• Channels: Marketing Automation Platforms (MAPs), CRM-integrated AI Chatbots, Sales Development Rep (SDR) personalized outreach, and Retargeting Ads (using dynamic content).

• Action: Ensuring all channels are integrated with the CRM to provide the prospect with a continuous, personalized experience that anticipates their questions and reduces friction toward the sale.

C. Delight Stage Channels (The Push)

Focuses on ensuring customer success and transforming them into advocates, directly generating new momentum. These were often ignored by the Funnel.

• Content: Self-service Knowledge Bases, dedicated onboarding tutorials, feature update videos, customer success playbooks.

• Channels: Customer Success Management (CSM) teams, Customer Success Platforms (CSPs), dedicated Net Promoter Score (NPS) Surveys, Customer Community Forums (e.g., Slack or Discord groups), and Customer Advisory Boards (CABs).

• Action: Channels must be utilized to proactively identify both advocacy opportunities and churn risks, ensuring the energy of the cycle is always maximized.

8. Steps in Flywheel Marketing: A Comprehensive Action Plan

Implementing the Flywheel requires a phased organizational and technical transformation, moving from siloed departments to a unified, customer-centric system.

Action Plan: 12 Steps to Building the Flywheel

1. Gain Executive Buy-in and Mandate Alignment: The C-suite must formally abandon the Funnel and mandate the Flywheel as the new organizational blueprint. This means enforcing the breakdown of departmental silos (Marketing, Sales, Service).

2. Define and Visualize the Customer Journey: Map the journey not as a line, but as a continuous circle. Identify all key customer interactions and the teams responsible for them, establishing clear handoff points.

3. Identify All Points of Friction: Conduct a company-wide audit to identify the top 5-10 points where the customer experience slows down. This includes internal process friction (e.g., lead scoring definition) and external friction (e.g., sign-up forms).

4. Agree on Shared Metrics (RevOps Focus): Marketing, Sales, and Service must agree to be measured by the same customer-centric metrics. Success is no longer measured by MQL volume, but by LTV, CAC, and Sales Velocity.

5. Build the Unified CRM Foundation: Implement a robust, single Customer Relationship Management (CRM) system that serves as the central data hub for all three teams. All customer context must be accessible to everyone instantly.

6. Redefine MQL/SQL for Quality and Alignment: Sales and Marketing must jointly define an MQL and SQL based on behavioral intent and fit, ensuring the handoff is high-quality and frictionless.

7. Engineer the Delight Stage Proactively: Invest heavily in the Service team and Customer Success Platforms (CSPs). Establish proactive programs for customer success (e.g., weekly check-ins, quarterly business reviews) rather than waiting for support tickets.

8. Implement NPS/CSAT Surveys as Triggers: Integrate Net Promoter Score (NPS) and Customer Satisfaction (CSAT) surveys directly into the product experience. A high score should automatically trigger a request for a review (Advocacy Loop). A low score should automatically trigger an urgent service follow-up (Friction Reduction).

9. Audit Content for Flywheel Stage Alignment: Ensure content is balanced across all three stages. Create “Attract” content (SEO guides), “Engage” content (personalized demos), and crucial “Delight” content (troubleshooting libraries and use-case videos).

10. Implement a Friction-Reduction Strategy: Assign a budget and a cross-functional team specifically to systematically eliminate the friction points identified in step 3 (e.g., automating the contract signature process, speeding up website load times).

11. Formalize the Advocacy Loop: Create a structured program to turn happy customers into content. This includes requesting video testimonials, writing case studies, and offering referral incentives. This fuels the Attract stage.

12. Continuous Monitoring and Optimization: Treat the Flywheel as a continuous system. Monitor LTV and TTC (Time-to-Conversion) constantly, using the data to identify the next point of friction or the next area where momentum can be accelerated.

9. Trends in Flywheel Marketing: Accelerating Momentum

The Flywheel is constantly being optimized by emerging technologies and strategic shifts that enhance alignment and increase momentum.

A. Revenue Operations (RevOps)

RevOps is the operationalization of the Flywheel philosophy. It is the business function that unifies Marketing, Sales, and Service under a single operational structure and a single set of shared metrics, typically managed by a central team.

• Impact on the Flywheel: RevOps enforces the removal of organizational friction by standardizing processes, tools, and data flows across the entire cycle, directly improving Sales Velocity and LTV. It ensures that the left side of the cycle (Attract/Engage) is perfectly aligned with the right side (Delight).

B. Community Building

Online customer communities (on platforms like Slack, Discord, or dedicated portals) have become powerful, self-sustaining Delight Nodes.

• Impact on the Flywheel: Communities allow customers to support each other, drastically reducing the burden on the support team (a massive Friction Reduction). They also serve as powerful Advocacy Nodes, where prospects can observe genuine customer success and interaction, acting as high-quality, authentic fuel for the Attract stage.

C. AI, ML, and Intent Data

Artificial Intelligence and Machine Learning are used to increase the precision and speed of the Flywheel.

• Predictive Lead Scoring: AI is used to move beyond simple demographic scoring, incorporating behavioral data and firmographic information to predict the likelihood of an MQL becoming a profitable customer (LTV). This increases the quality of the leads moving from Attract to Engage.

• Intent Data Activation: Third-party intent data (tracking what prospects are researching across the web) is used to activate the Engage stage precisely when the customer is actively searching. This reduces the Time-to-Conversion (TTC) by ensuring the brand delivers a contextual message at the exact moment of high intent.

10. Challenges and Pitfalls in Flywheel Marketing

While the Flywheel is a superior strategic model, its successful implementation is often hampered by key organizational and technical challenges.

A. Organizational Silos (The Momentum Killer)

The biggest challenge is cultural resistance to dissolving departmental silos. If Marketing continues to be measured only on MQL volume and Service is measured only on cost reduction, they will never invest in the cross-functional efforts (like case study generation or friction audits) that power the Flywheel.

• Solution: Executive leadership must enforce shared KPIs (e.g., LTV:CAC ratio) and tie a portion of all three department heads’ compensation to these metrics.

B. The Delusion of the “Perfect Circle”

Many companies adopt the term “Flywheel” but fail to eliminate process friction, resulting in a Wobbling Flywheel. They invest heavily in Attract and Engage (like the old Funnel), but under-resource the Delight stage.

• Solution: The organization must audit its budget and spending. If 70% of the budget is still focused on acquisition, the Flywheel is not truly spinning. A successful Flywheel typically redirects significant investment (e.g., 40%+) into Customer Success platforms, CSM hiring, and retention engineering.

C. Measuring Friction (The Invisible Enemy)

It is difficult to quantify process friction, which often leads to it being ignored. Friction points like a two-week contract approval process or a clunky product setup are often overlooked in favor of easily measurable metrics like email open rates.

• Solution: Implement metrics like Time-to-Value (TTV) and Average Sales Cycle Length. Assign ownership for reducing these specific metrics to cross-functional teams, forcing them to find and eliminate the underlying organizational or process friction.

11. Measuring and Analyzing Flywheel Marketing Performance

Effective Flywheel management requires measuring not just outputs (leads), but inputs (energy) and the resulting system momentum.

A. Measuring Energy and Efficiency

These metrics gauge the financial health and efficiency of the Flywheel:

• Customer Lifetime Value (LTV): The single most important metric, directly measuring the success of the Delight stage. A rising LTV is the clearest sign of a successful Flywheel.

• Customer Acquisition Cost (CAC): Measures the cost of acquiring one customer. The goal is to continuously lower the CAC by generating more low-cost, high-quality leads from the Advocacy Loop (Delight).

• LTV:CAC Ratio: The financial bedrock of the Flywheel. A ratio of 3:1 or higher is the industry gold standard, demonstrating that the Flywheel is generating significant, sustainable profit.

B. Measuring Momentum and Velocity

These metrics measure the speed and effectiveness of the continuous cycle:

• Sales Velocity: Measures how fast revenue moves through the sales pipeline. Increasing sales velocity is the primary operational goal of friction reduction.

• Net Promoter Score (NPS): Measures the likelihood of a customer recommending the brand. A high NPS is the direct measurement of the Delight stage’s ability to generate momentum for the Attract stage.

• Time-to-Value (TTV): The time it takes for a new customer to realize significant value from the product. Reducing the TTV is a crucial friction reduction tactic that ensures customer success and accelerates the start of the Delight cycle.

12. Expert Tips and Actionable Items

To accelerate your Flywheel and achieve sustained momentum, focus on high-leverage, cross-functional activities that eliminate friction and boost customer advocacy.

• Establish a “One-Day Response” Standard: Mandate a maximum response time of one day (or one hour for high-intent actions like demo requests) for every customer inquiry or handoff, regardless of the department. This is a simple, powerful way to reduce process friction.

• Systematize the Customer Story: Create a role or team responsible for managing the entire advocacy pipeline. Their job is to find a high-NPS customer, interview them for a case study, produce the content, and hand that content to the Sales and Marketing teams. This formalizes the Advocacy Loop and ensures the Attract stage is always well-fed.

• Bake Success into the Product (SaaS Focus): For SaaS companies, the biggest friction is product adoption. Use in-app messaging and automated, contextual guides to shepherd users to their first “win” within the first 48 hours. This accelerates the Time-to-Value (TTV) and kickstarts the Delight stage.

• Adopt a “Never Lose Context” Principle: Utilize your CRM and automation platform to ensure that no customer ever has to repeat their story or history, whether they are speaking to a Sales Rep, a Support Agent, or a Billing Specialist. This eliminates information friction and proves customer-centricity.

13. Essential Flywheel Tools and Technology Stack

The complexity of the Flywheel necessitates an integrated technology stack that supports shared data and automated handoffs across all three stages.

• The Foundational Hub: A unified Customer Relationship Management (CRM) platform (e.g., HubSpot, Salesforce) that serves as the single source of truth for all customer data. This is mandatory for alignment.

• Automation and Engagement: Marketing Automation Platforms (MAPs) for sophisticated lead nurturing, lead scoring, and automated handoffs to Sales.

• Service and Delight: Customer Success Platforms (CSPs) (e.g., Gainsight, ChurnZero) for proactive customer health scoring, churn prediction, and automated intervention when usage drops or risk increases.

• Advocacy and Feedback: Dedicated NPS/CSAT Survey Tools and Customer Community Platforms (e.g., dedicated forums, Slack workspaces) to capture feedback and formalize the advocacy loop.

• Velocity and Friction Reduction: Tools for Revenue Operations (RevOps) management to standardize processes and monitor cross-functional metrics.

14. Conclusion

The transition from the linear Funnel to the circular Flywheel is the defining strategic change of the modern, customer-empowered economy. It marks a philosophical shift from prioritizing a single transaction to fostering a continuous, value-generating relationship.

The Flywheel provides the essential blueprint for B2B and SaaS success by acknowledging that the most powerful force for growth is not advertising spend, but customer momentum. By aligning Marketing, Sales, and Service under a single mission, systematically eliminating friction, and investing strategically in the Delight stage, businesses can build a sustainable growth engine. The Flywheel ensures that every happy customer generates new energy, creating a perpetual motion machine that drives maximum Customer Lifetime Value (LTV) and efficiency. The future belongs to those who successfully trade the leaky pipe for the self-sustaining wheel.