Peak torque


New member
I saw a thread that talked about using a bathroom scale to find peak torque if you don't have a dyno. How do you do that?

You can place the scale against your front bumper with the scale supported so when you go full throttle you are pushing against the scale without it moving, you must read the scale value and the RPM. Normally clutch engagement RPM is at or little below peak torque but that is debatable. I think a better way is to use a scale like a hanging meat or fish scale attach to your rear bumper and the other end to a solid object ( maybe a tree ) and repeat the process, it is hard on clutches but it will work if used carefully. Remember peak torque is usually around clutch engagement speed and is not at peak HP RPM.
What Magmo said. All I do is set the clutch to get the highest number on the scale.

I assume it's peak torque or what ever, but don't really care because the highest number is the most get up and go. ... :)

I think I remember Al Nunley saying on here the idea came from someone else. But we have Al to thank for passing it along to everyone else.

IMHO, it makes setting your clutch the only cut and dry thing in kart racing.
Remember peak torque is usually around clutch engagement speed and is not at peak HP RPM.
a very good post. But this last line is a little confusing. Peak torque is simply where it's at, and it can vary depending on the engine. And that's where you want the clutch to engage. I call it "stall" but...
Your idea of hooking your kart to a tree with a pull scale is interesting, but how many people have one of those, where as almost everybody has a bathroom scale and a strong wall. Plus, if you're doing it by yourself, you can see the tack and the scale at the same time.
If you have a tach with laptiming get two beacons and set them about 50 feet apart. Make a starting line just behind the first beacon. Be sure to set your obscuring time to 3 seconds or so.Test different engagements to see which is fastest, giving plenty of time for clutch cooling.
I was thinking a little about this and it might be better to pull some thing heavy rather then use a stationary object and tine the event over some distance that makes sense so you don't burn up the clutch but there is enough time involved so one can observe the differences in time.
The reason you use an old clutch to find out what stall you need is so you dont burn up a good clutch or put unneccesary wear on them. Using the scale trick to set stall is really hard on clutches. I have an old 2disc greased lightning that i use specifically for finding peak torque and setting the stall when i get a new engine, or if i make changes to my engine mods and think the peak torque may have changed, but usually i only do it once, when i get a new engine and finish the engine mods, so i know where that specific engine needs the clutch stall set. Then i write down what the stall Rpm is, i usually write it down on the bottom side of my top plate on that engine, or on the bottom side of the chain guard. If you have an engine builder who dyno's your engines before giving them to you, ask him for a graph of your engine's dyno pull and find out where the peak torque is, or simply ask him where your engine made peak torque, and avoid burning up any clutches trying to set it. That is actually the best way to do it.