Apologies in advance..... I've searched on here and on the interweb without any luck.....

Does anyone know if theres an online calculator out there that will tell you the torque at the wheels for any car?

Alternatively does anyone know (for certain) how to calculate this? As far as I can tell torque at the wheels = flywheel torque (adjusted for drive train efficiency/loss) x gear ratio x differential ratio

Any ideas?

 

The only way to get the torque for a car, is to measure it on a dyno.

From this you can work out the power at the wheels with a simple calculation.

Then with smoke, mirrors and finger in the air guesstimates you can work out the flywheel horsepower and torque.

 

Sadly there is no such thing as "Torque at the wheels". A Dyno Dynamics rolling road or chassis dyno as it is commonly known, can measure the amount of force applied at the tyres and expresses this as Tractive Effort in lbs. So for example Stephensons Rocket delivered 1500 lbs TE and on a Mitsubishi Evo 4wd on our DD dyno a good normal FQ320 would make 1500 lbs and this equates roughly to 300 ft lbs crank torque.

The machine will give you a ATW value for torque but it all calculated mathematically using the 5252 rpm etc.

Not a conclusive answer i am afraid but still no such thing as Torque at the wheels

Cheers

Allan

 

Torque at the wheels depends on the gear used.

In first gear even the S2000 will probably make over 500lb/ft

 

Bibbs is basically right. The only way to be truely certain is to get it onto a rolling road and get an empirical reading.

Providing you know all of the various ratios through the drivetrain and you knew the transmission loss then you could work it out but you'd have to have it on a rolling road/engine dyno to work that out

However (depending on design and platform sharing) there's normally one gear that should be a 1:1 torque. This is typically refered to as top gear (on a 5 speed box not necissarily 5th, this will typically be an overdrive gear to reduce NVH and increase economy).

Typically a transmission will probably be in the region of 96% efficient. Our work dyno's are typically about 5 (ish) kW's down on an approx 100kW engine on the validation bench in Japan. Since we have to put multiple engine types through our benches we use a vehicle transmission to interface to the dyno.

 

Can I rephrase the question slightly...... theoretically speaking is there no way to even broadly estimate the torque at the wheels? The limited info out on the interweb suggests (theoretically) that after transmission loss the torque exerted at the wheels is the flywheel torque multiplied up by the gear ratio and then the differential ratio (or final drive unless thats the same thing?)....... theoretically is that correct?

Obviously a dyno is the only way to test the reality but there must be a way to estimate the same????!!!!

150 odd ftlb of torque in the S2000 somehow translates to a lot more by the time it reaches the road..... but how?

 

Depends what gear you're in.

To be honest I don't understand how you can lose torque. Power can be lost through heat friction noise etc, however you can't just lose torque in a system.

 

If you've got friction in a system, surely you will loose torque too.

Ie if you press the brake pedal while driving, you reduce the torque at the wheels. Any friction in the drivetrain will have the same effect as pressing the brake pedal, ie reduce the amount of available torque at the wheels.

 

What exactly are you trying to achieve?

Power at the wheels is a more useful measure than tractive effort, since they are meant to be rotating.

 

Just wanting to see if theres a way to estimate the accelerative force being applied to the road in any gear..... on the basis that torque is the force causing the acceleration.

Eg. will a Ford Focus ST with 271bhp and 330ftlb of peak torque (1437kg) accelerate as quickly as an S2000 with 237bhp and 154ftlb?

Both cars have broadly the same power to weight ratio but the ST has double the peak flywheel torque of the S2000 yet I wouldn't expect the ST to out perform the s2k.......

Obviously all sorts of other factors infulence the above example such as RWD Vs FWD, traction drag etc. just trying to get my head round the science