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.

[Agent4573]

The only thing we use the speedometer for in this years car is to correct the gear indicator. The speed doesn't get displayed at all on the dash. For most teams you don't need speed to correct your gear indicator, but we do our gear indicator a little different than most, and sometimes it needs some correcting.

[Denny Trimble]

If you're not using speed vs. lap distance to compare drivers, you're missing out.

[Andy Pate]

I`m normaly too busy driving to even look at the rev counter, I normally just "feel"?!?! when to change gear.

Andy

[syoung]

Denny: Log speed, sure, but don't confuse the driver and clutter up his display with a completely useless piece of information. How do you make an accurate, reliable plot of speed (or anything else) against distance?

As a driver, I'd say that you need 'idiot' warning lights (fuel, oil pressure) and a gear display (although we did without all except a neutral LED last year). It's also extremely useful to have a tacho indicator of some sort, which can be combined with programmable shift lights, and water temperature and oil pressure readouts (analogue is much easier to read than digital). Anything more than that - sorry, I'm never going to look and it'll just make my life more difficult.

[Denny Trimble]

Syoung,
We use the Motec ADL and Interpreter software. You can plot any data channel from the ECU or ADL against any other channel, and with time or distance as the horizontal axis.

Here's a speed and TPS comparison from a recent weekend in Everett:
http://students.washington.edu/dennyt/fsae/miket_vs_denny.jpg

We run shift and overtemp dummy lights that will burn the retinas out of your eyes (same as our brake light - LED clusters). We have analog gages for water temp and oil pressure as well. Oil pressure should be logged to indicate surge. The driver mainly uses these two analog gages to make sure the car is healthy before heading out.

There's less of a need for an analog tach if your engine has a wide powerband.

[Sam Zimmerman]

A tach and a water temp gage are absolutely necessary. Somebody should be telling the drivers the shift points based on the torque curve and the driver should be listening. If a driver is "feeling" his way around a torque curve, he is just way more likely to be shifting at a less than perfect point than not. Drivers tend to be a little too cocky (including me.)

The temperature gage is essential for the endurance and testing. If a driver can't take the time to glance at a temp gage (nicely placed of course) in the middle of a straight, he should do some breathing excersises. They must be a little uptight while they are driving.

[Denny Trimble]

Yeah, I'm just now learning to look at the temp gage after several years in the car.

On shifting, I read a quote from Jackie Stewart once, that went something like this:

He was leading a GP, and decided to take it a little easy and use a gear higher on some parts of the course. It turns out, he was turning faster lap times, because it was harder to upset the car, and he could focus more on what he was doing with the steering, brakes, and speed of the car.

Something to think about, especially for us drivers not as talented as Mr. Stewart. Sometimes it's less important to get that last few percent out of the engine, and more important to drive the course well.

[Sam Zimmerman]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Denny Trimble:
Sometimes it's less important to get that last few percent out of the engine, and more important to drive the course well. </div></BLOCKQUOTE>

I agree Denny. But the argument is usually that a good driver can feel when to shift, without ever having a tach in the car. Presumably, they are "feeling" for the max acceleration. My point is, why feel? With a tach placed correctly I can see the correct shift points in my peripheral vision.

Having said that, I do think the goal of the powertrain team should be to build a car that allows for minimal shifts (flat torque curve and high final drive ratio) because of the amateurs that will be driving the cars, until Juan Pablo Montoya enrolls in the U of I engineering program. http://fsae.com/groupee_common/emoticons/icon_wink.gif

I still want my tach, though.

[Garlic]

If you don't have a logger I guess you'd want a lot of gauges and pray that you get some feedback. If you log then you don't need much, the driver doesn't have to know what the RPM is he just needs to know when to shift. Make it as simple as you can for the driver and he'll drive faster. You can get shift points with a light or if you prefer, a series of lights. The number is insignificant and these cars accelerate so quickly watching a tach is tough. Warning lights for oil pressure, water, etc are all you need as well. Make then super bright, and the driver should know what they mean.

[Buckingham]

Garlic -

I would recommend gauges over the "idiot" lights. The driver is possibly the best feedback controller in your car. A light tells him that he is overheating. A gauge tells him by how much, how quickly he got there, how quickly he is getting back to a safe operating level, and exactly how much he needs to back off the throttle to stay there. Idiot lights are inherently going to either sacrifice lap time or your engine.

[SeanM]

Speedos aren't really necessary, call you have to focus on is staying ahead of the competition, a tach and temp reading are good to have, we use an Alfano digital tach shows RPMs and engine temp clearly as well as lap time.

[Garlic]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by dhaidinger:
The driver is possibly the best feedback controller in your car. A light tells him that he is overheating. A gauge tells him by how much, how quickly he got there, how quickly he is getting back to a safe operating level, and exactly how much he needs to back off the throttle to stay there. </div></BLOCKQUOTE>

Sorry but I couldn't disagree more. I don't agree with having extras in your car because your design isn't good. If your driver has to slow down just to ensure the car doesn't overheat, your cooling design sucks.

Your logic to me is the same as saying you need an oil pressure gauge so if the oil pan/sump is a bad design the driver can take left turns slower so he doesn't starve the engine of oil.

To me lights are there to say 'stop the car, something's wrong'. I understand that you can take the attitude of 'what if this happens in endurance' but you can take that a long way (too far). Just my opinion but if you have a logger (which you should) gauges don't have much use.

[gug]

you dont need a proper tach. we had two shift lights, next to the pneumatic shifter buttons. cant get any more brainless than that. if a light comes on, press the button next to it.

of course, we probably could have done without the downshift light. what do you drivers think, would a downshift light ever correct your driving?

[Patrick W. Crane]

If you can't doenshift without a light, you need a bit more seat time i think... you should pretty much know by looking at a track what gear you will be in and where. a tach is really useful for the learning/tuning stage, but once you have a good handle on the car, you probably won't belooking to dummy lights to tell you what to do.

I'd say that to many lights on the dash will take away from the obvious ness of Water/Oil warning lights.

[Sam Zimmerman]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by gug:
you dont need a proper tach. we had two shift lights, next to the pneumatic shifter buttons. cant get any more brainless than that. if a light comes on, press the button next to it.
</div></BLOCKQUOTE>

I would hate to build a car for a year and then expect a driver to be brainless. http://fsae.com/groupee_common/emoticons/icon_wink.gif

Serioulsy, I do understand that some people get into the car and forget to look at anything in the cockpit. I have seen people drive these cars while doing coolant system testing and never look at the temp gauge (they came back with the needle pegged.) That is a habit that can be broken, however.

If we agree that the driver doesn't need to know what the vehicle is doing during a race (which we don't, but that's ok http://fsae.com/groupee_common/emoticons/icon_wink.gif ,) I can't count the number of times during testing, driver training, or on a dyno that a tach and/or water temp gauge became important.

To each his own, and this is purely opinion but I would never want to build my own racecar or drive someone elses on a regular basis without the basic instruments.