**Car Physics**
- Thread starter alex_gt
- 90 comments
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First off, it seems to me a "rev limiter" and "fuel shutoff" are the same thing... the computer just stops giving the engine fuel, and it stops revving.
Now, the reasons for it existing are numerous, but most of them have nothing to do with the speed rating on the tires. Most of the time, a "rev limiter" or "fuel shutoff" are installed to prevent a driver from running the engine past it's natural powerband, which is not only inefficient, but harmful for the engine. If a company wants to build a high-performance car, it's easy enough to spec tires with a higher speed rating. Not to mention, any manufacturer who builds a car capable of exceeding the speed rating of it's tires through a simple chip-mod would likely be sued quite vigorously, and tend to have to pay millions of dollars to injured customers.
Speed limiters are installed on cars by certain manufacturers, like BMW and Mercedes, because of a "gentleman's agreement" they take part in to limit the top speeds of their cars to reduce the need to get that little bit of extra top speed that marketing would otherwise want to brag about. If you check, all high-performance BMWs and Mercedes (and other cars, for that matter) have suitably good tires, not H-rated Pep Boys bicycle rubber, despite their artificial "top" speeds.
- 217
This is a series of 26 articles in .pdf format that are excellent in explaining the physics of racing, greatly recommended:
THE PHYSICS OF RACING
Enjoy!
THE PHYSICS OF RACING
Enjoy!
- 13,827
- Down under
Can someone explain the concept of "lateral accelaration" to me?
- 217
Read the "physics of racing" series linked on my last post in this folder... it will explain that and way more...
- 13,827
- Down under
Roger that 
- 1
I was searching for a torque multiplication calculation on the web when I came across this thread, and I have to say, WOW, this is excellent! It is now book-marked so I can come back and read (and hopefully understand) all that it contains. But for the torque multiplication calculation, I have a bit of confusion
Now that we know this, how do you calculate the TQ being put to the ground? I suppose it has to do with the tire diameter ratio to something, but what?
I need to preface by stating that my GTP specific knowledge is virtually nonexistent, and that my current interest is in drag racing my hot rod on occasion (an 86 Buick Turbo Regal). I have a bit of a traction problem when I launch, and Im curious as to roughly what peak TQ is being produced in 1st gear, more for entertainment than anything else. I realize that the torque converter complicates the issue compared to a stick car, but for the moment, Ill ignore that part of the equation... unless someone would like to take a shot at explaining how to figure that out too.
I have the RWTQ value of my car to work with from a dyno session, but no absolutely known engine output. I can make a guestimate using 15% parasitic loss, which equates to ~630ft.lbs. (550ft.lbs. + 15%).
Using Hooligans simplistic calculation of (Engine TQ) x (Gear Ratio) x (Final Drive Ratio) = (Final Output), I get this:
1st gear: 630 x 2.75 x 3.42 = ~5925ft.lbs.
2nd gear: 630 x 1.57 x 3.42 = ~3383ft.lbs.
3rd gear: 630 x 1.00 x 3.42 = ~2155ft.lbs.
4th gear: 630 x 0.67 x 3.42 = ~1444ft.lbs.
Yikes! No wonder I have a bit of a traction problem!!
TIA!
Now that we know this, how do you calculate the TQ being put to the ground? I suppose it has to do with the tire diameter ratio to something, but what?
I need to preface by stating that my GTP specific knowledge is virtually nonexistent, and that my current interest is in drag racing my hot rod on occasion (an 86 Buick Turbo Regal). I have a bit of a traction problem when I launch, and Im curious as to roughly what peak TQ is being produced in 1st gear, more for entertainment than anything else. I realize that the torque converter complicates the issue compared to a stick car, but for the moment, Ill ignore that part of the equation... unless someone would like to take a shot at explaining how to figure that out too.
I have the RWTQ value of my car to work with from a dyno session, but no absolutely known engine output. I can make a guestimate using 15% parasitic loss, which equates to ~630ft.lbs. (550ft.lbs. + 15%).
Using Hooligans simplistic calculation of (Engine TQ) x (Gear Ratio) x (Final Drive Ratio) = (Final Output), I get this:
1st gear: 630 x 2.75 x 3.42 = ~5925ft.lbs.
2nd gear: 630 x 1.57 x 3.42 = ~3383ft.lbs.
3rd gear: 630 x 1.00 x 3.42 = ~2155ft.lbs.
4th gear: 630 x 0.67 x 3.42 = ~1444ft.lbs.
Yikes! No wonder I have a bit of a traction problem!!
TIA!
- 2,312
- Misnblu
- Misnblu
Lsd or limited slip differential will have both front wheels or rear wheels put power to the ground. On most front drive and rear drive autos, only one wheel is pulling or pusing the vehicle.
For those ppl that like to add power to their cars and race these cars, the lsd will help them put more power to the ground with less wheel spin.
Quaife and Phantom Grip are the two major playes in the front wheel drive segment.
Here is some information on the Quaife Product.
Here is the information on the Phantom Grip LSD.
Hope this helps.
Misnblu
- 21
hey go to this site and it will tell you how to make your car faster for free http://www.pistonheads.com/gassing/topic.asp?t=61988&f=23&h=0 . Quite possibly the funniest thing I've seen all week
- 1,008
Yep its true if you applied one pound on a 1 foot wrench youd get 1 ft-lb of torque, newton metres are the standard now however.Originally posted by CrackHoor
The units got you, ASL! One Newton at one foot wound give you a resulting unit of Newton-feet, whatever those are... More common would be lb-feet, or Newton-Meters for smart countries who use the metric system...
- 1,008
Curb weight is a strange term but i refers to the car without a driver but with fuel (Strange...) As it would be if you parked it outside the front of you house, to measure it drive onto a weighbridge like the trucks use get out of the car and read the number, strangely enough to work out weight distribution they simply put one axle on at a time.
CAMAROBOY69
Premium
- 18,567
- Michigan
- CAMAROBOY69
That is an excellent answer. Short, sweet, very close to accurate, and straight to the point. 👍
- 1,267
I didn't particularly understand the biker one, but here is an excellent one.
Imagine your car runs out of gas. It takes 50 lb-ft (a guess) to push it at 5mph. It takes the same force (50 lb-ft) to push the car at 10mph, but twice as much horsepower. It's obviously harder to push the car at 10mph than at 5, even though they require the same force. That's how torque relates to horsepower!
Imagine your car runs out of gas. It takes 50 lb-ft (a guess) to push it at 5mph. It takes the same force (50 lb-ft) to push the car at 10mph, but twice as much horsepower. It's obviously harder to push the car at 10mph than at 5, even though they require the same force. That's how torque relates to horsepower!
PublicSecrecy
(Banned)
- 1,488
HooliganI should preface this by saying that I did not come up with this myself. It's good stuff regardless.
Darn right you didnt get that stuff urself, you got that from www.howstuffworks.com, if anyone wants to look around.
PublicSecrecy
(Banned)
- 1,488
Piglet
Actually, curb weight is the weight of the car, filled gas tank, and 150lbs to simulate a driver with it. That way you have a much more accurate reading of performance and handling figures.
PublicSecrecy
(Banned)
- 1,488
ExigeExcel
An LSD, or limited slip differential, allows for less wheel spin not only at take offs, but also improves traction at cornering. An LSD allows 2 wheels on the axel to spin at different speeds, to allow for much more traction during corners. This is because as you are cornering, the inside wheel travels a distance with a certain time. the outside wheels however need to cover more ground, or go farther in the same time thus making the outside wheels spin faster. An LSD controls this and allows them to turn at whatever speed necessary.
- 1,267
The EDiff in the new Ferrari F430 is an absolutely amazing differential... Ferrari used it and then it got banned from F1 it was so effective.
It can electronically control the individual wheel speeds at the rear, making maximum traction under heavy cornering. It's much more complicated, but I'm tired at the moment. A lovely device, it is.
It can electronically control the individual wheel speeds at the rear, making maximum traction under heavy cornering. It's much more complicated, but I'm tired at the moment. A lovely device, it is.
- 68
This is fantastic. I laughed so hard I nearly fell off my chair, it was THAT good! Recommended reading.mr schell
PublicSecrecy
(Banned)
- 1,488
ooh yah ive seen that. did the guy even give permission for them to do that?!
- 94
PublicSecrecy
Do they actually place 150lbs of weight into the car?
I can think of an easier way without having to lift so much.Mike
- 794
This is an old thread... but it seems to be stickied, so I'll respond anyway 
A differential, any type of differential, not just an LSD, allows the inside and outside wheels to spin at different speeds.
Most cars have open differentials. These are pretty simple little devices, the downside to them is that they will send power to whichever wheel is easiest to spin. So if one wheel slips, then the engine's power is sent to the spinning wheel.
A limited slip differential will send power to the both wheels, even if one is slipping or has less traction than the other one. Better for performance, but more complicated and expensive.
PublicSecrecy
A differential, any type of differential, not just an LSD, allows the inside and outside wheels to spin at different speeds.
Most cars have open differentials. These are pretty simple little devices, the downside to them is that they will send power to whichever wheel is easiest to spin. So if one wheel slips, then the engine's power is sent to the spinning wheel.
A limited slip differential will send power to the both wheels, even if one is slipping or has less traction than the other one. Better for performance, but more complicated and expensive.
- 120
A little more on LSD's...
Following on from above, in the situation when one wheel has very little traction, (due to being in the air, or on loose dirt for example) whilst the other is firmly planted on the road, with a normal open diff the amount of torque required to turn the raised wheel will be identical to that supplied to the grounded wheel. So if it only takes 5Nm of torque to turn your raised wheel, that's all that the grounded one will get, which isn't going to drive the car anywhere. The engine's power in this case is non existent (well, not really, but bear with me) as with just a low throttle opening the lack of resistance in the driveline will have you bouncing off the limiter in no time.
A limited slip diff of whatever type, usually having some sort of clutch between the output pinions will increase the torque supplied to the grounded wheel by effectively fooling the system into thinking the raised wheel is actually on the ground. This isn't totally accurate, but it gives you a good impression.
The question of Yaw control, raised earlier, involves a lot of fancy bits. On a 4WD, each of the three diffs needs to be a flashy electronic active differential. In an active diff a control unit will take sensor readings from around the car, corresponding to wheel speeds, engine speeds and such, determine which wheel has traction, and push the power to that wheel. These are commonly used on WRC cars I believe, as they've not been banned yet. (maybe they have, I don't follow WRC very closely) Yaw refers to the rotation of the car in it's horizontal plane, as in "pitch" refers to a back and forth brakes-gas type rotation, and "roll" refers to a left-right rotation. You would see yaw if viewed from above the car, like the old Micro machines games or the early GTA series. The active yaw controller will use the active difs to assist the steering process by powering the outside wheels, causing the car to behave differently, usually by drifting gently. On GT4 this can be seen if you buy a lance, pop one on and go to a dirt track and play around with it. It can be a little disconcerting at first.
thanks for reading,
Kurtis.
Following on from above, in the situation when one wheel has very little traction, (due to being in the air, or on loose dirt for example) whilst the other is firmly planted on the road, with a normal open diff the amount of torque required to turn the raised wheel will be identical to that supplied to the grounded wheel. So if it only takes 5Nm of torque to turn your raised wheel, that's all that the grounded one will get, which isn't going to drive the car anywhere. The engine's power in this case is non existent (well, not really, but bear with me) as with just a low throttle opening the lack of resistance in the driveline will have you bouncing off the limiter in no time.
A limited slip diff of whatever type, usually having some sort of clutch between the output pinions will increase the torque supplied to the grounded wheel by effectively fooling the system into thinking the raised wheel is actually on the ground. This isn't totally accurate, but it gives you a good impression.
The question of Yaw control, raised earlier, involves a lot of fancy bits. On a 4WD, each of the three diffs needs to be a flashy electronic active differential. In an active diff a control unit will take sensor readings from around the car, corresponding to wheel speeds, engine speeds and such, determine which wheel has traction, and push the power to that wheel. These are commonly used on WRC cars I believe, as they've not been banned yet. (maybe they have, I don't follow WRC very closely) Yaw refers to the rotation of the car in it's horizontal plane, as in "pitch" refers to a back and forth brakes-gas type rotation, and "roll" refers to a left-right rotation. You would see yaw if viewed from above the car, like the old Micro machines games or the early GTA series. The active yaw controller will use the active difs to assist the steering process by powering the outside wheels, causing the car to behave differently, usually by drifting gently. On GT4 this can be seen if you buy a lance, pop one on and go to a dirt track and play around with it. It can be a little disconcerting at first.
thanks for reading,
Kurtis.
- 120
Ah,
just read further up, the howstuffworks URL to the diff description is very good and far more in depth, take a look.
cheers,
Kurtis.
just read further up, the howstuffworks URL to the diff description is very good and far more in depth, take a look.
cheers,
Kurtis.
