Landracing Forum
Introductions => Formulas => Topic started by: Ratliff on May 30, 2008, 09:50:09 PM
-
The formula I have is N = W x V x T / 270 where N is the power required, W is the weight in kilograms, V is the speed in kilometers per hour, and T is the rolling resistance of the tire.
The factors are
T = 0.015 on concrete
T = 0.025 on crushed rock/asphalt
T = .05 unpaved dirt road
T = .10 dirt field
The estimate for T on wet salt at Bonneville is .04 to .05
This is an older formula but should still give useful results.
-
"This is an older formula but should still give useful results."
To a question not asked.
DW
-
"This is an older formula but should still give useful results."
To a question not asked.
DW
Responded to by a person who doesn't know there are multiple formulas for calculating rolling resistance.
-
Pressing ignore again.
DW
-
Pressing ignore again.
DW
Dan all you have to do is resist the "desire" to press the ingnore feature and after a day or so it will be very easy. :mrgreen: and this is all you will see "This user is currently ignored."
J
-
Pressing ignore again.
DW
Dan all you have to do is resist the "desire" to press the ingnore feature and after a day or so it will be very easy. :mrgreen: and this is all you will see "This user is currently ignored."
J
15 now...
-
Updated 16 now...wow
-
make that 17
-
:-o :-o
-
Updated 16 now...wow
John,
I stand corrected.
Don
-
Slowly it dawns on me.
Posts here are evaluated as follows:
1. peer rank of author: 99%
2. accuracy or factual content: 1%
-
18 now
-
ROTFLMAO.... :-D
Will it go up yet again? :?
-
Slowly it dawns on me.
Posts here are evaluated as follows:
1. peer rank of author: 99%
2. accuracy or factual content: 1%
I think those ignore buttons are being pressed by racers and builders. The person they're ignoring is neither. :roll:
Personally, I expect that my own peer rank in this group should be low until I have some of my work actually running down the salt or dirt.
I have seen less than one in ten posts of the nearly 200 he has deluged us with in one week be both applicable to topic and not obsolete. That's a lot of good posts, but it's just too many bad ones. Right now, he's creating a massive percentage of the traffic on this site and devoting that space to (for lack of a better term) spam.
I tried to put up with it, but now I'm #18.
-
I'd like to know more about the motivation behind the public display of righteous indignation "I pressed the ignore button".
This is, of course, the exact opposite of ignoring him, but instead commenting on him rather than his post.
-
I'd like to know more about the motivation behind the public display of righteous indignation "I pressed the ignore button".
This is, of course, the exact opposite of ignoring him, but instead commenting on him rather than his post.
It may be a way of publically admitting that you have had enough..just the ****teen people currently.
Any idea of recent pumping on the salt? ?
J
-
OK, I'll bite:
3000kg*200km/h*.025(t)/270 = 56
56 kw? hp? fig-newtons?
-
I do know that tire design has a far greater impact than surface texture does on most racetracks.
Example, 3360lb car goes down the dragstrip on steel radials, nets 118mph. Switch tires to bias ply DOT racing tires, and trap speed goes to 116mph. In this performance envelope, each MPH is about 10rwhp on a dyno, so 20 rwhp additional power was consumed.
The formula in the first post yields "10". Even if it were kw, it's still less than the extra loss going from steel to fabric, and soft to medium compounds. Tire pressure was the same, 20 PSI.
-
I do know that tire design has a far greater impact than surface texture does on most racetracks.
Example, 3360lb car goes down the dragstrip on steel radials, nets 118mph. Switch tires to bias ply DOT racing tires, and trap speed goes to 116mph. In this performance envelope, each MPH is about 10rwhp on a dyno, so 20 rwhp additional power was consumed.
The formula in the first post yields "10". Even if it were kw, it's still less than the extra loss going from steel to fabric, and soft to medium compounds. Tire pressure was the same, 20 PSI.
To extend your conclusions to other surfaces, you would first have to do that same experiment with the same car and same tires at Bonneville, El Mirage, etc THEN compare the results to pavement. It is possible on softer surfaces the results could be much less pronounced, or just the opposite.
-
I copied this from the Forum Rules: "Condescending, rude, and annoying remarks and insults will not be tolerated."
The only worthwhile posts in this thread are about calculating rolling resistance. The rest of them illustrate why I forgot about this place for years and almost never post here.
Dave Mann
(602) 233-8400
http://www.roadsters.com/
-
I'm a new member on this board, but not new to performance website forums or racing.
This is intended as purely helpful advice:
If you want participation on a forum, trashing folk for posting tech info is a terrible thing.
Basically it show casual readers that they are not welcome to post. No posting = no readers.
Me, I have a thick skin. Most folk don't.
It's free advice, so worth every penny you spent on it... ;)
-
Dave, I thank you for visiting landracing.com. I'm Jon, the new owner of the site, and I do appreciate not only that you've chosen to stop here for a while -- but also your reasoning for having abandoned the place in the past. I'm sorry that on your first visit in a long time you find stuff that's -- that's -- well, stuff that sure isn't what we want to have on the site. I'm trying to ride herd without getting to intrusive/cutting folks off. But when I see your comments I feel that maybe I've been lax in allowing some of the stuff to go on when I should have cut it out.
To the others of you that post here on a regular basis -- gee-zul-man, please think about what you're posting. Land speed racing stuff is what we want -- moronic activities and actions and words aren't what belongs here.
Thanks, Dave -- and I hope you find it worth a visit now and then to see if you can put up with us for another day.
-
Disabling the ignore button may not be a bad idea.
-
Disabling the ignore button may not be a bad idea.
What does that have to do with Rolling Resistance?
Tom G.
-
Franklin, I had thought that you were "getting better"about not posting too much stuff and not being too far from the topic du jour -- but you're honing a scab on your behind, to paraphrase something my mother used to use. Please do stick to land speed stuff and not go off on personal rants, and quoting all of the old data may be informative to some -- but not really germaine to the purpose of landracing.com. I expect you'll claim that others appear to be doing just what I'm asking you to not do -- and that's not anything I want, either. But concern yourself with you and not them.
Please straighten up and fly right, using another phrase, or I'll use the big ignore button on you. Understand me this time?
-
guick question ,, are these # for a slick tire ??
-
The estimate for T on wet salt at Bonneville is .04 to .05
This is an older formula but should still give useful results.
Can I ask what is the estimate for dry salt, or is that being too optimistic?
What are the other formulas, and how much do the outcomes vary from one formula to another?
-
Can I ask what is the estimate for dry salt, or is that being too optimistic?
What are the other formulas, and how much do the outcomes vary from one formula to another?
Probably too optimistic. :-) Salt is hygroscopic (it attracts water). In the 18 years I have been going there I have yet to see dry salt. During the middle of the day it may appear to be dry and hard but it is deceptive. If you sit or kneel on it your pants will develop a wet spot instantly. Larry Mayfield (Dr. Mayf) did some salt-friction studies a few years ago but I never heard the final results. Maybe he posted here in the past or he will chime in here.
-
Also worth remembering is that the salt usually gets more moist (repeat MORE moist) as the day progresses. The heat of the sun warms the surface and also the water just below the surface, which expands, which means the salt surface gets wetter in the heat. It's contrary to what you'd expect -- but it does happen.
Morning runs have good traction, as a rule of thumb, and afternoon runs have thinner air...both because of the heat of the day.
-
Dave, I thank you for visiting landracing.com. I'm Jon, the new owner of the site, and I do appreciate not only that you've chosen to stop here for a while -- but also your reasoning for having abandoned the place in the past. I'm sorry that on your first visit in a long time you find stuff that's -- that's -- well, stuff that sure isn't what we want to have on the site. I'm trying to ride herd without getting to intrusive/cutting folks off. But when I see your comments I feel that maybe I've been lax in allowing some of the stuff to go on when I should have cut it out.
To the others of you that post here on a regular basis -- gee-zul-man, please think about what you're posting. Land speed racing stuff is what we want -- moronic activities and actions and words aren't what belongs here.
Thanks, Dave -- and I hope you find it worth a visit now and then to see if you can put up with us for another day.
Jon,
I have belonged to several different sites that have completely different focuses from this one. When it comes to staying on topic, relevant comments to the topic and the information on the site that is helpful, this is the best one I have seen.
Even though I have not started my project, the information I have received so far has been invaluable. I have also made many contacts that will make the project much easier to get through.
I know that when I get to the Salt, that it will be an extension of the time I have spent here, first.
I wouldn't get to heavy with the edit button, those that are wasting others time on the site know who they are, and there really are not enough of them to sweat it.
Rocky
-
The formula I have is N = W x V x T / 270 where N is the power required, W is the weight in kilograms, V is the speed in kilometers per hour, and T is the rolling resistance of the tire.
(snip)
Units for "N"? Newtons or KWH, or something?
Thanks!
-Bill
-
You'll need Ratliff to answer about the formula he posted. To utillize his formula, you'll also need (besides units for N) units for T.
The units for N must represent power; Newton is the MKS unit of force, not power, and KWH is a unit of energy, not power.
-
One thing I've never got a solid answer out of, is if LSR tires slip. Slip is not spinning. It's the stretching of the rubber. With no loss of traction, a tire can move the vehicle less than it's circumference when torque is applied. This is normal on non-LSR tires.
Think of a centipede crawling. Tires do the same thing when torque is applied.
-
The units for N must represent power; Newton is the MKS unit of force, not power, and KWH is a unit of energy, not power.
No rolling resistance is a force, to compute the power needed to over come it you need to know how fast the car is going.
N = newtons the force resisting motion.
There are several other rolling resistance formulas out there in various engineering texts and some books on aerodynamics, mention it as well.
The best way to determine it is to use low speed coast down information where the dominant form of drag is rolling resistance rather than aerodynamic drag.
Larry
-
Talk about muddying the water...
-
A Newton is equal to .2248089lbs force. Or, 1lbf = 4.448222 Newtons. :roll:
And of course, one needs to consider a sign change for resistance in calculations. :-P
Once you get started in force calculations for a salt rider, lots of things are happening (in motion) at the same time. :-D
It is however much more simple than attempting to keep up with the National Debt Clock. :-o
Regards to All,
HB2 :-)
-
The best we can do with this complicated situation is to collect data from our runs and to develop slip coefficients for the combination of driver and vehicle. There are so many things happening and one of the most significant is the driver/rider. Some people know how to go fast by minimizing the application of excess power and the resultant slip. Others do the opposite.
-
About 2 years ago I started making plans to build a bike for the salt-flats. I knew it would be a Triumph Cub with about 20 hp and rather light, yet it had to carry my 200 lbs. of body weight. I did not consider the amount of energy or power I would need to overcome rolling resistence. Rather, I thought about selecting the lightest, roundest, narrowest, firmest, and most reliable tires and wheels available within my almost nothing budget. From a practical point of view, I know that once the wheel is put into motion, a larger diameter is easier to push or pull with my own strength, such as a wheelbarrow or wagon. Practical experience seemes to work. I can almost effortlessly push my bike across the salt with one hand and when I stop I actually have to reverse my effort on the bike if I want it to stop with me. That's my formula......Oh, BTW.....how many minutes does your wheel keep spinning when suspended after you give it a good start ?
-
One thing I've never got a solid answer out of, is if LSR tires slip. Slip is not spinning. It's the stretching of the rubber. With no loss of traction, a tire can move the vehicle less than it's circumference when torque is applied. This is normal on non-LSR tires.
Think of a centipede crawling. Tires do the same thing when torque is applied.
I can imagine that an LSR tire could slip (in relation to the wheel that holds it). But on salt or dirt, which provides less
traction than asphalt or concrete, this is probably not very common, especially since land speed racers typically use a lot
of air pressure in their tires. This would tend to hold the bead of a tire pretty firmly against the rim, discouraging slippage.
You probably know about dragster tires being secured to their wheels using screws. I'd lean more toward adhesive
material to do this trick, if I had a tire slippage issue in land speed racing.
-
This thread is 12 years old