Clutch Engament Speed - RED Slide

What is a good engagement speed for a Hillard Fire clutch and red slide? Would 4 white springs be too low? Peak torque is pretty low I believe.


I’m not sure, but I’m here to see the responses :slight_smile:

4 black springs with the shoes non-leading and weighted up should be your lightest engagement speed, but depending on your application that might be too low.

@spribyl any ideas from your own experience or maybe conversations with others?

I have this from briggs just for your question.

Most of the slides are best engagement 2900-3000, but the red slide is lower, almost 2500, you can probably 2700 and be about right. Its also likely you won’t reach 6100 on most tracks and will need to gear for maximum speed with a bit of guessing, we actually geared the green slide for 5800 on Concept Haulers which has a long back stretch. The key to the slide is don’t slow down and keep the revs up.

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Thanks. I put in 4 whites to see how that works. I agree with you Steve, the key is to carry the speed through the corners. My boy is 6 and still figuring things out. He has tons of seat time with the senior slide. It was a lot more forgiving. Now that he has started racing and is limited on power we need to work on running a good line on every turn. I doubt the clutch will make a noticeable change until we have everything else in place.

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This is good timing because I have to move my kid from black slide to red as well.

The engagement speed generally doesn’t matter for much other than standing starts.

Unless some folks are slipping them on track? I have seen some (Masters) do this, not sure if it helped them however.

James, you would be surprised. Many will say once it’s locked up it doesn’t matter but there are times when it’s not and how much slip and time slipping plays a big role in lap times. We’ve tested a few different things and I can say that the old rule of just put the springs on and race isn’t ideal at the top levels when you’re looking for any tenths you can find.

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ok…can you please explain how else you would tune the clutch if not for just peak torque?

When is clutch slip a good thing? To me anytime a clutch is slipping it isn’t sending torque to the rear.

Consider this; engines don’t produce horsepower (HP) they produce torque, at various RPMs in various amounts, then HP is calculated. “torque x RPM / 5252.1 = HP”. Look up James Watt for an explanation of that formula. When the axle RPM, multiplied by the gear ratio, is less than the engine, the clutch is slipping. At what ever RPM the clutch is slipping, the torque being produced by the engine, at that RPM, is transferred through the chain to the axle. There are some losses to heat and friction, but we’re not going to worry about that now. You can use that formula to calculate the horsepower at both the engine, and the axle. If the torque, at the engine, and at the axle, are the same (and they should be) but the RPMs are different, you have less horsepower calculated at the axle then you do at the engine. If the clutch is holding the engine at peak torque, that means you have peak torque at the axle. With peak torque at the axle, you have maximum HP at the axle. Sounds good to me. The only conclusion I can come to is; set the clutch to hold the engine at peak torque, always!
To find peak torque, at the axle, use the old bathroom scale against a strong wall trick. Put a bathroom scale between the front your kart and a strong wall. Sitting in the kart, warm the engine up, floor it, observe the RPM and the number of pounds on the scale, quickly, you don’t have a lot of time, write them down. Now, adjust the clutch to slip more or less and repeat. Do this until you find the RPM where you get the highest reading on the scale. It works every time.

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