Speedometers, Speedo, how many have them, useful?

[Christopher Chow]

Hey peeps,
Im wondering about the usefulness of a speedometer in our first FSAE car. Whats your take?

Thanks!

[Christopher Chow]

Hey peeps,
Im wondering about the usefulness of a speedometer in our first FSAE car. Whats your take?

Thanks!

[Garlic]

I'm wondering about why you'd ever think you'd want one?

[adrial]

Useless...

Really the only thing you need is a shift light or tach at most. I never look at the dash while driving, which I was surprised by initially because in my street car I have a tendency to check everything periodically...things are happening way too fast in an FSAE car though. Only reason to have other gauges is to monitor the engine during testing.

If you're looking at a speedo to tell you how fast you're going...you probably just missed the apex...

[BStoney]

Dashes are virtually worthless while driving, because if you are looking at the dash while driving, you aren't driving fast enough. Just need a shifter and steering wheel, and maybe, just maybe, some dumby lights (oil, water, shift, Neutral) if you desire. Experienced drivers should be able to feel where they are in the RPM range and that takes care of the tach issue.

My .02

[Buckingham]

Sometimes racing is racing and things just go wrong. In 2001, our car was on the verge of overheating during the endurance event. Our attentive driver rode the temp gauge at the limit for the entire 2nd half of the event. After he crossed the finish line and stopped, the cap literally blew off and a rooster tail of steam shot 20 feet in the air. We we considered to have finished the event successfully since nothing went wrong before we crossed the finish line. (ended up 4th overall that year). So, if not finishing endurance sounds like fun to any of you, I encourage you to omit gauges.

However, I do agree that the speedometer is the single most useless gauge on the racecar. The driver should be thinking in gear and rpm (which define speed anyway).

[DJHache]

Yeah, I agree with dhaidinger. You don't need a speedo cuz there's really no way it'll give you any useful info during an event (may be good for testing though). Warning lights are essential though, especially on a new car and doubly so if it's your first car and cooling, lubrication and all your other engine related systems aren't fully tested. How else will you know if your engine is sufficiently cool if you don't have a light? (short of total engine meltdown).

As far as the tach goes you can do without one but once you have one you'll wonder why you hesitated. It'll give you proper launch RPMs for the accel, it'll help you run skidpad at constant speed for test purposes, it'll help you teach new drivers, it'll help you characterize your engine map and find any slow spots in the RPM band, there's all kinds of things you can do with a tach. Plus many come with shift lights. Also, a tach is a godsend for noise testing. If you don't have a tach then you must bring a laptop plugged into your ECU to test noise. Detroit is rainy and cold, and you'll want to avoid dragging around a laptop and a 20ft power cord and opening your electronics compartment if you can.

As for your specific question, speed and RPM are linked by known gear constants, so if you know one you know the other. Speeedos are overconstraining, as any swimmer will tell you.

[95M3Racer]

All you need speed for is data logging...

[Cement Legs]

....Unless your flux capicitor is set to go off at a certain speed then a speedometer would be a pretty valuable piece of equipment....

[1975BMW2002]

We toyed around with the idea of having a detachable instrument unit that we could use for testing and tweaking, but take out for real driving. The only things that would remain on the dash for racing woudl be an oil pressure light, a temp guage and a temp light. On the removable display we would have a tach, exhaust temp, and oil pressure.

We never got around to doing it this way, but I thin it's a good idea.

But a speedometer? Absolutely no reason. The only thing a sppedowoudlbe good for is bragging how fast you went in the car. With about two minutes of measuring and calculating, you could get that anyways with only a tach.