Onspot in Depth - How it Really Works

Written by Lars Holmgren,

At the flip of the switch, the chainwheel swings out. Then, strands of chain are slung under the tire, increasing traction. It’s as simple as that – for the driver. But, if we take a closer look at the ingeniously simple principle behind it, we realize that Onspot requires a good dose of engineering to become such a reliable tool for safety and convenience. Here is why!

Sometimes Moving, Sometimes Fixed

First, let’s give the rotating chainwheel some consideration. When engaged, it’s like a swing ride where the chains are moving freely in the air, pointing radially from the chainwheel center because of the centrifugal forces. Then, suddenly, the chain is trapped between the grip of rubber and road surface – the front of the tire’s footprint. Now, the chain is doing its job by increasing the static friction between the rubber and the road’s icy surface. And, at the back part of the footprint, as the drive wheel is rolling, the chain will release and swing around to the front, again and again.

tire chains

"What is traction, friction, and road grip?"

Chainwheel Positioning – Effective vs. Smooth

If the chainwheel is moved forward, a longer part of the chain strand will end up under the tire, thus increasing effectiveness. However, there’s a downside to this: A part of the chain will still be trapped under the tire when the chainwheel is rotating trying to pull it free. The chain will be pulled out by force, putting excessive strain on the chain mounting. Furthermore, the chain end – that is released under tension from the tire – may bend and hit the tire side instead of ending up under the footprint, if it’s not completely stretched out. This will cause an unreliable and rough operation, not to mention unnecessary wear on the tire and road surface. Actually, this is the result of a chainwheel positioned too far to the front.

By moving the chainwheel position back, the chains will release easily, resulting in a smooth and less rough operation. However, this comes at the price of reduced effectiveness since less chain would end up in the footprint. This is the result when the chainwheel is positioned too far to the rear.

Obviously, we should find a compromise.

Which is the Ideal Chainwheel Position?

Although measurements may vary, there is an ideal chainwheel position. For instance, to spin freely on a typical 11 R 22.5 tire, the chainwheel should be positioned at the ideal height of 3 ½” to 4” above the road surface.


But, which is the ideal length-wise position for the chainwheel? Countless calculations and computer simulations have been made to find out, and a range of field tests have been carried out to prove right or wrong. From extensive research and development over the years, we can conclude that the wheel axle center line is the “golden middle” for positioning the Onspot chainwheel.

When positioning the chainwheel exactly in the drive wheel axle center line, you get the optimal combination of effectiveness, reliability and comfortable operation. Plus, you have the same function whether driving in forward or reverse.

Onspots are not a one-size-fits-all product due to the variety of vehicles used across a multitude of industries.Measurement of every truck is highly recommended because no two vehicles are identical.“At Onspot, we design and manufacture a mounting system for your unique vehicle.” 

Click the link below for measuring instructions and a how to video!

Measuring Instructions

Engineering Automatic Tire Chains Explained

Lars Holmgren

About Lars Holmgren

Lars has been in the organization since 1988. He was involved in the transfer of the Onspot production from Linköping to Vänersborg (Sweden) in 1991/1992. He then worked with the Onspot brand till 2008 together with the R&D team. Since 2009 Lars is the Quality-/ Environmental Manager at the VBG Group Truck Equipment in Sweden, which includes the brand Onspot. When not working, he enjoys spending time with his family and in his summer house close to Vänersborg, Sweden.


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