Tyre size

[Bob12]

Tyre sizes on a new tractor. We currently work 650s on a 38inch rim however on a new tractor we were thinking of going 650s on a 42inch rim as we thought it might be better for traction however we have been told that a 38 gives more clearance. Tractor is mainly drilling and cultivation/ploughing. Would be interested to hear opinions. TIA.

 

[Matt L]

All depends on the next number. The percentage of width. Ie you can have a 650 the same overall diameter on a 38 or 42 inch rim.

 

[glasshouse]

Tyre sizes on a new tractor. We currently work 650s on a 38inch rim however on a new tractor we were thinking of going 650s on a 42inch rim as we thought it might be better for traction however we have been told that a 38 gives more clearance. Tractor is mainly drilling and cultivation/ploughing. Would be interested to hear opinions. TIA.

38 gives less clearance

 

[snipe]

38 gives less clearance

No it doesn’t. A 650/85 38 is taller than a 650/65 42. A 650\75 38 is similar height to a 650/65 42. whats The tallest tyre(diameter in cm) they will allow you to fit?

 

[ED.D]

It’s aspect ratio that makes the difference, expressed as a percentage of the nominal width (in mm).

 

[glasshouse]

No it doesn’t. A 650/85 38 is taller than a 650/65 42. A 650\75 38 is similar height to a 650/65 42. whats The tallest tyre(diameter in cm) they will allow you to fit?

You dont say

 

[snipe]

If you know that, why did you say a 38 gives less clearance ?.

 

[tr250]

We’ve got a tractor on demo at the moment it’s got 650/85r38 and they are a very tall tyre I’d prefer 38 rims anyway then you get more air capacity in the tyre and a better squabbing effect for a long foot print

 

[glasshouse]

If you know that, why did you say a 38 gives less clearance ?.

Because a 38 RIM gives less clearance

 

[Matt L]

Because a 38 RIM gives less clearance

No it doesn’t. You can have a larger diameter tyre on a 38 inch rim than a 42 inch rim. It is all dependant on the tyre.
A 650/85R38 is a taller tyre than a 650/65R42 therefore between the two I just mentioned the 42 has less clearance.

 

[glasshouse]

No it doesn’t. You can have a larger diameter tyre on a 38 inch rim than a 42 inch rim. It is all dependant on the tyre.
A 650/85R38 is a taller tyre than a 650/65R42 therefore between the two I just mentioned the 42 has less clearance.

Really ?

 

[snipe]

Please could you explain your point, because I think I’m missing something. You keep stating that 38 inch rim would give less clearance, but when people state the facts showing this to be incorrect you respond with a sarcastic answer as if you know that already?..

 

[C.J]

The opening post is a bit short on detail so I think he wants to compare either a 650/75R38 with a 650/65R42 or he wants to compare a 650/85R38 with a 650/75R42.

In both cases the 38" rim has a theoretical 28mm greater diameter so a potential 14mm greater ground clearance.

The biggest variable in terms of grip will be if a VF tyre is available in the permited tyre choice.

 

[No5]

Also depends on the hp of the tractor. 650/65x42 aren't rated for high torque use above 200hp whereas the650/75x38 are.

 

[yellow belly]

650 85 38 for non land work
800 70 38 for land work

 

[glasshouse]

650 85 38 for non land work
800 70 38 for land work

Why not 650?

 

[dowcow]

My preference would be for smaller rims with a larger sidewall depth. Having recently replaced some 540/65 R38s with 520/70 R38s and fronts similarly, it is a noticeable increase in comfort on the road. Haven't had chance for any cultivation/top work yet. Our most comfortable tractor is on /85s and it doesn't even have an air seat. What is the point of all the /65s anyway? I'm going to guess that with high traction forces smaller rims with large sidewalls the tyres might slip too much on the rim?