Lightning axles

[Darren]

After some info I have a lightning extreme around 2008 I think. Having alot of trouble getting side bite and found it has a 50mm rear axle with 65mm hugs should it be a 40mm axle and if so which type. Any help would be appreciated.
thanks

[tom]

I think the rear axle is the most important component that you bolt onto your chassis, it certainly has a great impact on the way the rear of the kart handles.

You need to take into account the way your chassis works when choosing your axle. If the rear of your kart is stiff, it will tend to load both rear tyres more evenly. This is ideal for a track that has grip, but as you have noticed will be skatey on a slippery track.

The axle has to do a few things. Obviously keep the back of the kart off the ground by supporting the hubs. Also supports the rear chassis rails to stop them compressing under lateral load. As well as this because the axle deflection occurs as it is rotating, the axle acts as a one way shock absorber. (bump only, not rebound).

The things you can control with a given axle are:
- how the axle is tied in to the bearings. ie: axle collars/bolts/grub screws
- how far apart you have the rear hubs (track)
- what sort of hubs (and wheels) you use.

The original question is how to get more "side bite".

The 50mm axle is stiffer than the 40mm, and will not allow the kart to transfer as much weight to the outside tyre. This is good if you are 100kg+ driver, otherwise, when the track is slippery you are going to struggle to get enough weight onto the outside rear on corner apex to exit.

If you don't want to change axles, use the smallest hubs you can get as the small hub allows a greater distance of unsupported axle between bearing hanger and hub which will give more flex. (it is unfortunate that to get more side-bite it is better to move the hub in, but at the same time this stiffens the axle so especially with a 50mm axle, moving the wheels in doesn't always give you more grip, actually moving out may work better)

If you do change to a 40mm axle, you will be able to go too soft across the rear of the kart. You can tell if the rear is too soft as the kart will bounce through the apex of the corner as you start to put power on. This is due to the rear outside tyre overloading and releasing.

Just remember that with a dirt kart although the rear wheels are obviously locked together, you don't really need to release the inside rear wheel unless the track is really black, as the two rear contact patches of dirt aren't actually connected. Where this matters is in the higher powered classes where rather than trying to roll all the weight onto the outside rear to get side-bite you are better off moving the weight of the driver further back and planting both rear tyres to the track as much as possible.

[Mr X]

Tom, your on the money as always.

Anyways best bet will be to buy a 40m axle. That's what everyone runs. Well most in the Kt Classes.

[tom]

I'd actually like to spend more time with the 50mm axle, as i think with some work it could have advantages over the 40, especially at events where the track goes black. The main challenge with the dirt kart is to get it to handle correctly when the track is wet, and also as it goes black (and all the way in-between).

It's probably more expensive than changing axles, but give Ross Edwards a call and ask for a set of rear wheels made up so that they are "inside-out", or reverse offset. We used to use these on bitumen in the wet to give a greater working distance from the bearing hanger to the hub while still keeping the rear track narrow.