Conversion options: from standard to wide tyres
Using a practical example, we would like to show you everything you need to consider when converting an agricultural tractor to wider tyres. The dimensions/data of the tyres mentioned can all be found in the technical section of the Heuver Agricultural Tyre Book. Of course, we do not forget to look at the corresponding rims.
Conversion to wider tyres
If the customer indicates that he wants to equip his machine with wider tyres, we follow the same step-by-step plan as for the conversion to narrower tyres.
The questions that must be asked beforehand are:
- Which tractor is it (specify exact make and type)?
- What tyres are mounted (standard from the factory)?
- What width should the desired wider tyres have?
- What track width should the tractor have?
The corresponding answers in this case are:
- Fendt 724 Vario S4 / with fixed rear axle
- Standard tyres: 540/65R30 and 650/65R42 Trelleborg TM800
- Requested rear tyre width is 900mm, with matching tyres for front axle
- Desired track width is 2100mm
Based on this information, we proceed as follows:
- First, we record the technical data of the tractor (axle width, pitch circle, gear ratio, etc.).
- We also look at the conversion table as a first orientation, if we do not yet know the most suitable tyre combination.
We then proceed as follows:
What is the diameter of the rear tyres?
- The 650/65R42 Trelleborg TM800 ear tyre has a diameter of 1927 mm.
We take this diameter (plus a few extra millimeters) as a starting point to find the right tyre with a width of 900 mm. In this case, we now take a 900/50R42 Michelin MachXbib for the rear axle. Since it has a diameter of 1970 mm.
To find the right front tyre for the furrow, we need the gear ratio of the tractor. For the Fendt 724 Vario S4, this is 1.3222. The 900/50R42 Michelin MachXbib has a rolling circumference of 5826 mm.
If we now divide the rolling circumference of the rear tyres by the gear ratio, we get the result of the minimum rolling circumference that the desired front tyres must have.
So: 5826mm / 1,3222 = 4406mm
In this case, the distortion is exactly 0%, and we assume in this example that the desired distortion should be between 0% and 3%.
So: 4406mm + 3% = 4539mm
This should give the front tyre a rolling circumference that is between 4406mm and 4539mm. Next we come to the 710/55R30 Michelin MachXbib with a rolling circumference of 4491mm.
Now that we have found the right tyres, we just need to find the right rims with the right ET value to achieve the desired track width of 2100 mm.
Front axle:
710/55R30 Michelin MachXbib - the recommended rim for this is DW23x30. The tractor has an axle width of 1900mm, but we want to achieve a track width of 2100mm. This means that we have to go out 100mm further on both sides, which means that we need rims with an ET value of -100. The pitch circle in this case becomes: 10 / 281 / 335 / 22mm cylindrical.
Rear axle:
the recommended rim for this is DW27x42. The farm tractor has an axle width of 1840mm, but we want to get back to a track width of 2100mm. This means that we have to go 130mm further out on both sides, which means we need rims with an ET value of -130. The pitch circle in this case becomes: 10 / 281 / 335 / 24mm cylindrical.
All in all, this will be the new tyre-wheel combination for this agricultural tractor:
- 710/55R30 Michelin MachXbib on rim DW23x30 ET -100 and
- 900/50R42 Michelin MachXbib on rim DW27x42 ET -130
Like to know more?
Do you need advice? Please contact us, our experts will be pleased to assist you. Contact our experts at +31 (0)523 - 850 850 or by e-mail to info@heuver.com. Visit also our blogs about Cultural tyres and Conversion options: from standard to narrow tyres or the overview at the agricultural knowledge-page.