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<h3>Rear Truck Angle Calculator</h3>
<p style="text-align:left">Adjusting your rear truck angle changes your board's turn/lean ratio and turning feel. If you've found an ideal setup on your current deck, this calculator helps maintain similar turning behavior when switching to a deck with different wheelbase.</p>
<p style="text-align:left">Simply input your current rear angle setting, your current deck's wheelbase, and your new deck's wheelbase to determine the appropriate rear truck angle for your new setup.  This helps you transfer your preferred riding feel to different equipment with minimal trial and error, saving you time and enhancing your surfskating experience.</p>
<p class="small" style="text-align:left">* <em>This calculator is mainly for comparing two sets of Synergy trucks. In the calculation, the front truck angle is ruled out, focusing solely on how the rear truck angle affects the board's turning feel.</em></p>
<p class="small" style="text-align:left">** <em>Credit: ChangingAngles.com: <a href="https://changingangles.com/2020/11/17/pivot-axis-angles-and-wheelbase-open/" target="_blank">https://changingangles.com/2020/11/17/pivot-axis-angles-and-wheelbase-open/</a></em></p>

Embed

<div style="width: 500px; margin: 0 auto; padding: 20px;">
    
    <div style="margin-bottom: 40px;">
        <label style="color: white; display: block; margin-bottom: 10px; font-size: 18px;">Current Rear Angle Setting</label>
        <input type="number" style="width: 100%; padding: 10px; box-sizing: border-box; border: 1px solid #ccc; border-radius: 8px; font-size: 16px; outline: none;" id="r1" step="any" required placeholder="degrees">
    </div>
    
    <div style="margin-bottom: 40px;">
        <label style="color: white; display: block; margin-bottom: 10px; font-size: 18px;">Current Deck Wheelbase</label>
        <input type="number" style="width: 100%; padding: 10px; box-sizing: border-box; border: 1px solid #ccc; border-radius: 8px; font-size: 16px; outline: none;" id="wb1" step="any" required placeholder="inner truck holes, inches">
        <span style="color: red; font-size: 12px; display: none;" id="wb1Error">Input Value Must Be Greater Than Zero</span>
    </div>

    <div style="margin-bottom: 40px;">
        <label style="color: white; display: block; margin-bottom: 10px; font-size: 18px;">New Deck Wheelbase</label>
        <input type="number" style="width: 100%; padding: 10px; box-sizing: border-box; border: 1px solid #ccc; border-radius: 8px; font-size: 16px; outline: none;" id="wb2" step="any" required placeholder="inner truck holes, inches">
        <span style="color: red; font-size: 12px; display: none;" id="wb2Error">Input Value Must Be Greater Than Zero</span>
    </div>
    
    <button style="background-color: white; color: black; padding: 15px; margin-top: 30px; border: none; border-radius: 8px; cursor: pointer; width: 100%; font-weight: bold; font-size: 24px;" onclick="calculateRearAngle()">CALCULATE</button>
    
    <div style="margin-top: 20px; padding: 15px; min-height: 120px; text-align: center;" id="result"></div>
</div>

<script>
    function calculateRearAngle() {
        // 获取用户输入
        const wb1 = parseFloat(document.getElementById('wb1').value);
        const r1 = parseFloat(document.getElementById('r1').value);
        const wb2 = parseFloat(document.getElementById('wb2').value);
        
        // 验证wb1和wb2是否大于0
        let isValid = true;
        
        if (wb1 <= 0) {
            document.getElementById('wb1Error').style.display = 'block';
            isValid = false;
        } else {
            document.getElementById('wb1Error').style.display = 'none';
        }
        
        if (wb2 <= 0) {
            document.getElementById('wb2Error').style.display = 'block';
            isValid = false;
        } else {
            document.getElementById('wb2Error').style.display = 'none';
        }
        
        if (!isValid) {
            return;
        }
        
        // 已知f的值
        const f = 56;
        
        // 将角度转换为弧度
        const r1Radians = (r1 * Math.PI) / 180;
        const fRadians = (f * Math.PI) / 180;
        
        // 计算tan(r1)和tan(f)
        const tanR1 = Math.tan(r1Radians);
        const tanF = Math.tan(fRadians);
        
        // 计算公式中的分母部分
        const denominator = wb1 / (1 + tanR1 / tanF);
        
        // 避免除以零
        if (denominator === 0) {
            document.getElementById('result').innerHTML = '<span style="color: red;">Division by zero error. Please check your inputs.</span>';
            return;
        }
        
        // 计算tan(r2)
        const tanR2 = tanF * (wb2 / denominator - 1);
        
        // 计算r2的弧度值
        const r2Radians = Math.atan(tanR2);
        
        // 将弧度转换为角度并取整
        const r2 = Math.round((r2Radians * 180) / Math.PI);
        
        // 显示结果，字体颜色为白色
        document.getElementById('result').innerHTML = '<span style="color: white; display: block; font-size: 18px;">Rear Angle Setting for Your New Deck:</span><span style="color: white; font-size: 28px; display: block; margin-top: 20px;">' + r2 + ' degrees</span>';
    }
</script>