Stiga Park 120 tyre change

The Stiga Park 120 comes with studded grass tyres, which are great for minimising lawn damage, but not so great for grip on wet grass and/or slopes. Time for a Stiga Park 120 tyre change to improve matters!

Stiga make specific winter wheel and tyre combinations for many of their larger machines, but not for the Park 120 (at least not at the time of writing).

After much searching, I managed to find some tyres with a more grippy tread pattern. Read on to find out how I did it!

Tyre and wheel sizes explained

The Stiga Park 120 has 8 inch steel wheels.

The tyres fitted from new were 155/50-8. This is the usual messed up combination of metric and imperial measurement:

• 155 = width of the tyre in mm.
• 50 = sidewall height, expressed as a percentage of the tyre width. So in this case the sidewall height is 50 % of 155, i.e. 77.5 mm.
• 8 = the wheel diameter in inches.

To add an extra challenge, all of the contenders for replacement tyres had their sizes specified in a different way:

[overall height] X [width of tyre] – [rim diameter]

All in inches, of course!

Stiga Park 120 tyre choice

At this point I reached for my calculator. I had found some tyres with a tractor style tread pattern and wanted to work out if they’d fit.

The total height of the existing tyres was: [sidewall height] x 2 plus rim diameter. I used Google to convert mm to inches and came out with a total height of 14.1 inches.

The existing tyre width was 6.1 inches.

The closest I could find to these measurements was a 16 X 6.50 – 8 tyre. Fairly similar in width but a substantially bigger height.

I measured the additional clearance available on the Stiga (it has rear wheel arches!) and it seemed that these tyres would just about fit. Good job really as there wasn’t anything else readily available and I didn’t want to buy different wheels if possible.

So I ordered a pair of BKT TR315 tyres in the 16×6.50-8 size.

Time to get on with the Stiga Park 120 tyre change!

Removing the old tyres

You may choose to have someone else remove the old tyres and fit the new ones. I guess this will depend on a lot of factors, including time available, proximity to a tyre shop, desire to have a go yourself etc. I quite like the challenge of fitting tyres, although I don’t have much in the way of specialist equipment. I don’t fit tubeless car or motorcycle tyres myself.

Remove the wheel

In this case the wheel and driveshaft are keyed, so removing the wheel is straightforward. Jack up the Stiga and support with blocks of wood. Remove the plastic cap, then the C clip and washer(s), then slide the wheel off.

Remove the valve cap and valve. Put them somewhere safe! You’ll need a valve key / tool or you could use some very small pliers.

Break the bead

These tyres are tubeless, so the next thing to do is break the bead. When inflated, the tyre makes a firm seal against the outer part of the wheel rim. You need to break this seal, so the sides of the tyre can be moved into the smaller centre part of the wheel, to allow the one side of the tyre at a time to be stretched over the edge of the wheel.

There are various ways of doing this. Obviously the best is to use a tyre machine or specialist bead breaking tool. But there are plenty of other ways:

• Put the wheel on the ground and use your heel.
• [If working on a motorcycle] use the side stand.
• Place a block of wood on the tyre as close to the wheel rim as possible, and hit it with a hammer. The wheel needs to be on a solid surface for this to have any chance of working.
• Squeeze both sides of the bead in a vice.
• Finally, if you don’t care too much about the tyres you’re removing, just let all the air out and drive the mower around. The weight of the mower, especially combined with some cornering, will soon break the bead.

I used the vice method in this case, but use whatever works best for you.

You need to break the beads on both sides before proceeding to the next step.

Remove tyre from wheel

With the edges of the tyre sitting in the central ‘gutter’ on the inside of the wheel, use tyre levers to stretch one side of the tyre over the wheel rim.

Use some plastic wheel rim protectors if you’re feeling precious about your wheels. I didn’t, and didn’t cause any new damage either, but your experience may be different!

Keep working around the tyre, levering up small sections at a time. It’s best to put the next tyre lever in place before putting too much tension on the tyre with the first lever.

With one side off, carry on and do the same with the other side. You may find this easier if you lubricate the tyre bead first – I use washing up liquid diluted with a little water.

Refitting new tyres

Preparation before fitting the new tyre

Check the valve stem is in good condition and not perished.

Clean any dirt and corrosion off the inside of the rim, especially where the tyre needs to seal against the wheel. The wheels I was working on were very clean, but even small bits of corrosion can cause a leak so it’s worth spending some time on this step

Apply copious amounts of your chosen lubricant to the wheel rim and tyre.

Fit the tyre

Insert the wheel rim into the tyre. I did this by putting the tyre flat on the floor and pressing the wheel into it (with my foot).

Use the tyre levers to get the remaining lip of the tyre over the wheel rim. Some people use a clamp or mole grips to stop the tyre coming off as soon as you lever the next bit on. I didn’t do this because I didn’t have anything that wouldn’t damage the rim. I used 2 or 3 tyre levers at a time instead.

Inflate

I’d recommend eye protection for this bit. Inflate the tyre using compressed air, without the valve removed from the valve stem. This allows more air to flow, which helps force the sides of the tyre out against the bead.

You may be able to do this without compressed air, but it will likely be more difficult and success will depend on how flexible the tyre is, and how well you can hold both sides of the tyre against the wheel rim whilst pumping the air in!

Don’t exceed the maximum inflation pressure marked on the side of the tyre! If the bead isn’t seating, deflate, apply more lubricant and try again.

With the bead seated, let the air out, refit the valve, then inflate again to your desired pressure.

Refit the wheel to the mower

This is a straightforward reversal of the removal process, and I’m very pleased to say the wheel fitted just fine with the new larger tyre.

Lawn test

The final step was to see how the new tyres performed. I’m pleased to say they worked really well. Of course there is still a limit to their traction, and if you give the mower full beans from a standing start on a steep hill, it will spin the wheels. The one disadvantage is that wheel spins with these tyres damage the grass more than the others.

Overall the Stiga Park 120 tyre change gave a pleasing result, enabling the mower to be used on the whole of the garden, even the hilly bits!

So now you know that 16 inch tyres can be fitted to your Stiga Park 120 🙂

Here is a video of me doing the tyre change!

I’ve also written about servicing the Stiga Park 120 here.