Rear Axle and Hub Tuning

So I’ve been running a new DR Kart this year, and things have been going pretty okay for the most part. Out of the box the kart hasn’t had any issues, just a little tuning stuff to mess around with. We went to Road America, and with the track being so smooth and dusty, there’s almost no grip on the kart. I’m thinking about for the next race putting a CRG 3 axle in from the 5 we have right now, but would longer or shorter hubs work better to help get more flex in the frame as well? I believe we have 85mm rears on right now

Typically, longer/stiffer hubs would stiffen a portion of the axle, which allows the outside rear tire to plant into the track more effectively. This creates a feeling of additional rear grip.

Changing the overall axle is likely going to be a bigger change than adjusting hubs, but both adjustments can work in parallel or in combination to get the desired feel.

General practice is to try hubs, then axle. If you’ve got long hubs and want to “soften” things, go with the shorter hubs first.

That said, unless someone from DR suggested you go to a different axle for the next track, I think I’d leave everything alone for now.

We spent a bunch of time tuning our other driver’s kart and want to try what worked on his kart on mine now to see if I like it the same or not, just experimentation in some new circumstances.

@Eric_Gunderson so you would say a softer axle and longer hubs to get the kart to plant the outside rear more? I understand what you’re saying but am just so lost on just about everything tuning the back half of a kart.

@Aaron_Hachmeister_13 We are trying to add more grip all around for stability/consistency

It’s really hard to judge this track right now. Never know if the track will be heavy or light on the dirt level when you go out. Hoping that a few more weeks we can get the grass growing at apex. Or us racers just need to help and stay on track :smile:

That just depends on the group ahead of you! I know us KA’s definitely didn’t have keeping the track clean as a top priority for us

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Keep in mind when you change to a different length hub, you’re changing the deflection point of the axle and how the tire’s surface interacts with the track surface. When you change an axle, you are making a consistent change to the stiffness of the entire length of the axle.

So while long hubs and a hard axle both will stiffen the rear of the kart, the end result will feel different between the two adjustments.

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@Aaron_Hachmeister_13 yes, but as TJ mentions both achieve somewhat different results, and will feel different. A hub change for many drivers is more subtle than an axle change.

Changing hub length will give you more of that ‘planted’ feel without generally sacrificing the overall feel or behavior of how the kart flexes (well, as much). However, an axle change really changes how the kart twists and transfers weight between the bearing cassettes, which is a much more significant change in driving feel for most drivers.

Many racers have more axles than they do hubs. Hub options aren’t as common to try, but are a great option that is often overlooked by smaller operations.

Another option to try (one of my favorite) is to adjust ride height in the front or rear depending on the grip situation you want. This adjustment can really make a difference, but also allow the kart to flex approximately the same way, avoiding some of the unfortunate side effects of adjusting something like front end geometry, etc.

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Ride height is my go-to for a big change these days. Like you said, it can completely change the balance of the kart without changing the flex or feel of the chassis.

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Do you raise or lower front to add grip?

@Wally might be time to create a new thread @KartingIsLife. But to answer your question, with ride height in the rear you would lower rear ride height to add (comparatively) more front grip.

Again, to be clear, this is a relative adjustment, meaning that you are taking grip out of the rear, which can also be viewed as adding grip to the front.

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