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Thread: tire data without TTC

  1. #1
    i would like to know if there is any way to get longitudinal tire stiffness without TTC (we are low budget first timer team)

  2. #2
    TTC is absolutely worth the money and you will need the data in the future too...
    HAWKS Racing e.V. - UAS Hamburg
    Head of Suspension 2010&2012
    STAT - Special Tools and Tactics 2011&2013

  3. #3
    TTC data is a $500 USD buy in and is good for a life time, there is a private forum to discuss the data and several professionals such as Bill Cobb who really knows what he is talking about.

    If you are able to afford a bunch of strain gauges, create an op amp for each of them, apply them to your control arms, obtain some sort of yaw sensor, acceleration (3-axis) and rotary/linear potentiometer to measure your steering input; this will give you something even better. Your actual steering forces.

    However, the cost of the sensors, implementation, and time it would take to wade through all of the data may be more than what it's worth to a team without very many numbers....rr you could just guess.

    Why are you specifically looking for the stiffness?
    If this is still related to calculating the forces, estimate the forces. Let's try this method. I'm going to try and point to in a direction assuming your budget is small and won't allow many pleasures of indulgence.

    Estimate your maximum lateral/longitudinal accelerations. How quickly do you think the car will corner and brake?
    1.3 Gs? 1.6Gs? 2.0Gs? Let's assume 1.6Gs for now.

    To be able to generate this acceleration, we take F = ma. What force at the tire do we need to generate to get these accelerations assuming the 'm' is our normal car force (Fz)? Assuming your car weighs 200kg (440lbs) Let's see: F = (1.6 G)(440 lbs) = 704lbs of force at the wheels. That's the total force produced by all tires combined. Apply a roll calculation to find what your weight on each tire will be to find individual outputs using the same methodology.

    This gets you on the ground running. However, take the accelerations with a grain of salt and try to find your own.

    Confused at all? Free body diagram, apply a force at the CG and find where it goes. (Track width is key)
    Braking. Do the same thing here. Wheelbase is the important factor to use this time. (Still a very simple calc).

    From here you have a baseline estimate to do all of your force inputs into your braking system, uprights, steering forces (except steering wheel torque...), driveline loads, etc.

    Worried about slip angles and ratios? Don't. Tires vary greatly and maximizing your tires isn't your biggest issue as a first your team. Just aim for parallel steer and call it a day. It may not be the fastest nor the most advanced, but it's surprising how fsat a car can go based on one simple estimate of the ultimate F = ma.
    Kettering University Vehicle Dynamics
    Formula SAE 2010 - 2015
    Clean Snowmobile Powertrain 2012 - 2015

    Boogityland 2015 - Present

  4. #4

    Be careful: the word "stiffness: could have different meaning. The tire cornering stiffness (in N/deg of slip angle) is not the tire lateral stiffness (N/mm). Similarly the tire longitudinal slip stiffness (N/% of slip ratio) is not the tire longitudinal stiffness(n/mm). They are somewhat linked (tire manufacturers as well as in-lab and on-track tire testers will confirm this) but they are not the same.

    The questions of MCoach are very relevant: what is (are) your goal(s)?

    For me the knowledge of the Fx versus slip ratio for different camber and vertical load will help me (in part) in the car suspension kinematic design, the differential setting, the traction and launch control setting, the engine tuning, the braking distribution, ABS if you have / want one.... just to give a few examples.

    For me TTC data, especially at 500 US$ is not even a question. As Ben Michell mentioned, you do not necessarily need the TTC data to win the competition. A super good driver (rare in FSAE / FS) would already help a lot. But you won't know WHY (and isn't it the purpose of an engineering competition, even more in design?) and it will probably take you much more testing time to achieve a good level of performance.

    And.... by the way....Who are you? Which team? Introducing yourself? Not worth the effort? You think people who read your post do not care / wonder? How about using the automated signature at the bottom of your post?
    Claude Rouelle
    OptimumG president
    Vehicle Dynamics & Race Car Engineering
    Training / Consulting / Simulation Software
    FS & FSAE design judge USA / Canada / UK / Germany / Spain / Italy / China / Brazil / Australia

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