Torque calcs for 1st and 5th or 6th gear

[mustangs]

I need to know the basic method for calculating torque at the flywheel and the wheels of a car. Any car will do, I have the gear ratios inside the transmission but need to know the ratios in the diff.

I then need to determine (assuming no losses or any kind of torque conversion device) the torque at the wheels for a given engine rpm. Lets say 1200 rpm and 3500 rpm (or somewhere close to max torque) I have the torque rating of the engine and the horse power. For simplicity we'll call it 300 hp @ 6000 rpm and 300 lbft @ 3500 rpm

Also is there any good web sites where I can find gear ratios for cars, trucks, etc. (transmission and differentials)

Thanks

Marc

 

[Metalguy]

Theoretical gearing is easy-you just multiply the ratios together to get the final (overall) ratio.

There is also an easy equation--Torque X RPM divided by 5250 gives you the HP at that RPM. Or, Torque=HP X 5250 divided by RPM gives you the torque at that RPM.

 

[Joest]

For torque at the tires, multiply the tranmission gear ratio X rear end gear X engine torque. For example:

Engine Torque = 300 ft-lb
1st gear ratio = 3.27
rear end gear = 3.50

Wheel torque = 300 x 3.27 x 3.5 = 3434 ft-lb

Make sense? Use this formula to go backward to calculate the engine torque knowing the wheel torque.

 

[mustangs]

That's what I was doing I just wasn't sure if it was the right way to do the calcs.

Thanks for the help....if anyone knows of any web sites that have various gear ratios that would be great....I'll keep trying on my own though.

Thanks again

Marc

 

[V12]

Isn't the torque halved at the differential (assuming both wheels have grip)???
3434/2=1717 ft-lbs

 

[Metalguy]

No. But it would be if one wheel were stationary, because the other would then spin at twice the "normal" rpm. The diff. is a "splitter" of torque and RPM, with 2 outputs which can vary from zero to twice.

 

[GregLocock]

V12 meant torque at one wheel, Joest menat total torque at that axle, I suspect.

An idealised conventional diff is a torque splitter, by the way, ie half goes to each halfshaft. It is the speed of each wheel that varies.





Cheers

Greg Locock

 

[Metalguy]

Oops-screwed up. You're right, open diffs. don't change torque at all-just RPM. The torque is always the same for each wheel, and it is not half of the math. ratio.

 

[sitbc]

one thing that joest forgot to include in his calculations is a method of providing a common denominator concerning tyre diameters. When comparing 2 cars if both have similar torque outputs and overall gearing,the one with the shorter tyre will have greater torque reaching the ground and will of course be slower for a given rpm.What i do is take the overall wheel torque and devide it by the tyre diameter and multiply by 24 which will give you a lb/foot
result.

sitbc

 

[carnage1]

http://www.bc4x4.com/faqs/yj.cfm?cat=6&faqid=82

http://www.prestage.com/community/Tech+Info/Transmission/default.aspx

I haven't seen any lists for rear ends except car specific one's

 

[notnats]

Ah, sitbc, the shorter tyre will give you a greater force, not torque, and the unit will be lb force.

Jeff

 

[sitbc]

notnats

you are right on both counts
but i think my point was understood.