Three simple questions - pls point me

[WOODY@DDLLC]

You have two issues to consider.

For a give speed X you have some hp Y that you must deliver to the ground to over come both aero drag and rolling resistance. If you cannot get that much power to the ground you can't get to X speed.

But what some people miss is on piston engines you also have to deal with the shape of the torque curve and gearing. It is possible to have an engine that generated the required hp to deliver Y hp to the ground including parasitic losses in the transmission, differential and wheel bearings etc, but still not be able to reach your design speed because of your choice of gearing. If the gap between gears is wrong you can have a situation where you can pull up to red line in your next to last gear but when you shift to your top gear you drop to a part of the torque/hp curve that the engine no longer produces enough power to pull back into the peak power point on the power curve.

On page 2 of this thread I have a simple basic program I wrote that figures some of the hp and weight values.

http://www.landracing.com/forum/index.php/topic,7775.15.html

There are other programs out there such as gear split that also provide some of the info you are looking for.

If you can gear the car so it always has surplus power to the wheels for the speed it is going you can avoid the problem of falling out of the power curve on the last shift. Since power required for a speed increases at the cube of the speed, the last gear split needs to be very close in ratios to allow the engine to pull back into the power peak after the shift.

Larry

Go down the page a bit for a spreadsheet version that I posted ........

[lsrengineer]

Larry,
Lots of good stuff in your program.
Right now I'm assuming the mechanical losses (chain/etc and tire loss) are in the dyno data I used.
For inertia I'm using is just dead mass and not rotational inertia, those will be errors but might be overwhelmed by aero drag on the big end.
Would be interesting to see some data logger info. comparing driven and undriven wheel speeds.  We are not seeing much if any wear on the tire but I'm not a tire expert and don't know exactly how many runs the tires have.
Does my available tractive force chart seem correct or interesting?
Thanks,
-Henry

[interested bystander]

Henry, a lotta stuff you're asking makes you sound like you are one of those "design my car, tell me how to run it, get me a record" type individuals that have cropped up since the "World's Fastest Indian".

This is not intended as a criticism, but you will get TORN APART by a lot of us posters. AND get more than enough help/advice from the same.

The rookie question you asked about the "Goodyear 2011" tire makes me think your engineering school didn't emphasize RESEARCH enough.

 Goodyear's people are easily reachable and their job is not to embarrass Goodyear.

Take this to heart. Yrs truly for instance, has humble fabrication/design skills with a 1/2 assede list of accomplishments and will be more than willing to pass on items in my areas of expertise. Along with many other more experienced, more knowledgeable others.


Think out yer project a little bit more  be 4 you ask questions.

There' a a guy out there named TOM BURKLAND he should be and ONLY he, LSRENGINEER!

CHECK HIM OUT!

[wobblywalrus]

Henry, the book "The Racing Motorcycle:  A Technical Guide for Constructors" Volume 1, by John Bradley ISBN 0 9512929 1 9 presents all sorts of information about gearing.  It is the best source I have seen for this info.

     

[maguromic]

Take this to heart. Yrs truly for instance, has humble fabrication/design skills with a 1/2 assede list of accomplishments and will be more than willing to pass on items in my areas of expertise. Along with many other more experienced, more knowledgeable others.

He is being humble.  Listen to what he has to say, he wont steer you wrong.  Tony

[Stan Back]

Ya know, I'm so dumb I still stand by my simple formula.  Most of us don't have the ability ($$$) to manage different gear splits for our projects.  And most should know that a big split in the upper range where you're hooked up won't work for most powerplants.  And a lot of us run in a class where the guy with a xxx-inch motor in a yyy is running zzz, and we want to beat him and get the record.  Or maybe the record is not the goal -- maybe it's 150 or 200 'cause we can't complete with the leaders.  But we have the goal.  So gear for the goal.  If you don't make it, you need to add horsepower.  When you come up short, you can't get there by adding more gear.  You can't go faster with less horsepower.  So gear for the goal at what you believe is your peak horsepower (because you haven't been able to spend the money on the dyno and have selected the parts to give you a peak at an informed-guess level).  I'm done (temporarily).

Stan

[lsrengineer]

Henry, a lotta stuff you're asking makes you sound like you are one of those "design my car, tell me how to run it, get me a record" type individuals that have cropped up since the "World's Fastest Indian".

This is not intended as a criticism, but you will get TORN APART by a lot of us posters. AND get more than enough help/advice from the same.

The rookie question you asked about the "Goodyear 2011" tire makes me think your engineering school didn't emphasize RESEARCH enough.

 Goodyear's people are easily reachable and their job is not to embarrass Goodyear.

Take this to heart. Yrs truly for instance, has humble fabrication/design skills with a 1/2 assede list of accomplishments and will be more than willing to pass on items in my areas of expertise. Along with many other more experienced, more knowledgeable others.


Think out yer project a little bit more  be 4 you ask questions.

There' a a guy out there named TOM BURKLAND he should be and ONLY he, LSRENGINEER!

CHECK HIM OUT!

email sent to Tom Burkland
apparently I didn't enter the forum humble enough, it could well be (probably) that analysis I can come up with will have no value to the team, to reduce my embarrassment it seems I should do much more research, with my limited knowledge and intelligence, before posting, input well taken

[Peter Jack]

Well said Stan!!!

Pete

[Interested Observer]

lsrengineer,
If, instead of plotting tractive effort versus speed, you plotted horsepower in the upper gears along with the drag (expressed as HP) optimum shift points would virtually leap off the page, and the effect of changing gear ratios would be much more apparent and easily matched to each other and to the drag curve.

[lsrengineer]

lsrengineer,
If, instead of plotting tractive effort versus speed, you plotted horsepower in the upper gears along with the drag (expressed as HP) optimum shift points would virtually leap off the page, and the effect of changing gear ratios would be much more apparent and easily matched to each other and to the drag curve.

Give me a bit of time and I'll replot per your instructions,  my rpm was limited to 13.5k and it looks like (assuming my calcs are correct) the shift points to 4, 5, and 6th are about 14k (force line crosses the next gear force line).  I hope that is correct thinking.  Driver thinks he remembers shifting around there.  I could find no info. on what the rev. limiter is set at from the factory.

[Glen]

What type of vehicle are you talking about 2 wheel or 4 wheel, stream liner or other. I just went thru the entire thread and never saw it.

[jimmy six]

You can make yourself mad by using gear-calc. Drive you nuts....

40 or so years ago at El Mirage a 64 Impala went 115 with 3.08 gears...changed to 4.11 gears and went 115.....Go figure.........................JD

[wobblywalrus]

Henry, the only shift I worry about enough to think about is the one from 4th to 5th.  First, I want to be in 5th gear after the shift at a point at or beyond the peak torque rpm.  This is 5,250 rpm in the example.  Next I enter a figure for the rpm drop during the shift.  Someone gave me the 250 rpm figure years ago.  I shift my bike quick so it is probably an overestimate.  Now I look up the gear teeth numbers in the shop manual or count them.

All of this goes into the handy little formula on the attached.  It tells me to wind up to at least 6,310 in fourth before I shift.  This is no big deal.  The engine will rev 1000 rpm more than this without problems.  The trouble comes when the minimum shift rpm in 4th is is higher than the engine redline.  In this case I would need to either lower the peak torque rpm, increase the redline rpm, or select 4th and 5th gears with closer ratios.

This is a silly and simple method and it has worked for me.  An advantage is I can calculate it using a pencil and paper on the back of a Smith's receipt.  No need for a computer.  

[lsrengineer]

You can make yourself mad by using gear-calc. Drive you nuts....

40 or so years ago at El Mirage a 64 Impala went 115 with 3.08 gears...changed to 4.11 gears and went 115.....Go figure.........................JD

I googled around and found a number of people describe the same top speed in 5th and 6th, with a variety of modern cars.  This might be similar to what happened with the Impala.   Google "Final gear makes no difference to top speed" and you should be able to pull some accounts up.

[wobblywalrus]

Lots of time was spent on my first motor to get the exhaust length, induction length, and cam to work together.  It produced a nice strong torque spike at high rpm.  It worked well if the engine was at full throttle through the mile at the rpm when it produced maximum power.  Otherwise, it was weak.  It was sensitive to gearing.  The new motor has not been optimized yet.  It has a nice broad torque curve with no big humps or dips.  It runs about the same with any reasonable sprocket combination.  It is not sensitive to gearing.  What I learned is that engines differ and it is best to put in some dyno hours followed by seat time to figure them out.  Good note taking helps, too.