tyre question

[Lakes Nash]

got 13.6 x 38 tyres on rear now, how would a set of these be different ,

380/85R38 (14.9R38)​

dont want the tractor to look down hill and has to match up to the 12.4 x 24 fronts,
they are a wider profile but will they jack it up,

 

[john432]

13.6x38 would be probably 340/85 R38 in metric size
To match the fronts drive ratio and go wider, you would probably need something like 380/70R 38, being a lower profile... You'll have to log on to say BKT's web site and compare the rolling circumference of different sizes, and what's the max width of tyre that can fit on your existing rims.

 

[Lakes Nash]

1. 3.6x38 would be probably 340/85 R38 in metric size
To match the fronts drive ratio and go wider, you would probably need something like 380/70R 38, being a lower profile... You'll have to log on to say BKT's web site and compare the rolling circumference of different sizes, and what's the max width of tyre that can fit on your existing rims.

rolling circumference ive just read is not much different, rim size is ok, it just a tad more floatation , we have lower profile on the 105, but 34's. just toying with this in which way to go ,

 

[Boohoo]

You might get away with it, it depends on the tractor, the interaxle ratio, how worn the fronts are and the brand of tyre because they're all different.
I'm not sure you'll see much difference in flotation, changing to 16.9r34 or equivalent would give a lot more flotation. As far as I know there isn't a low profile equivalent of 13.6r38

 

[Agri Spec Solicitor]

If it’s a 785 etc I am fairly sure it’s in the operator manual. There are various options so that the rolling radius of F and R match. As I understand it the radius is what matters. How much is tyre and how much is rim doesn’t matter. Just the total. I am sure the ex dealer can help if u get stuck , I could be wrong!

 

[Lakes Nash]

If it’s a 785 etc I am fairly sure it’s in the operator manual. There are various options so that the rolling radius of F and R match. As I understand it the radius is what matters. How much is tyre and how much is rim doesn’t matter. Just the total. I am sure the ex dealer can help if u get stuck , I could be wrong!

When the manual was printed I’m sure low profile tyres were not invented! I see what you mean, the rolling circumference is the same within a few mm, the price is 2 tyres at 13.9 = 1 tyre at 380/85……

 

[e3120]

You might get away with it, it depends on the tractor, the interaxle ratio, how worn the fronts are and the brand of tyre because they're all different.
I'm not sure you'll see much difference in flotation, changing to 16.9r34 or equivalent would give a lot more flotation. As far as I know there isn't a low profile equivalent of 13.6r38

@Nearly 's chart says 380/80 and 400/75 are options for a 38 rim, but these sound pretty oddball and unlikely to be economic if even available. As you say 16.9 34 would be much more common, or chance it.

It's possible to see if there's any leeway in the OP's favour with the current tyres with some chalk, concrete and a helper.

 

[Boohoo]

When the manual was printed I’m sure low profile tyres were not invented! I see what you mean, the rolling circumference is the same within a few mm, the price is 2 tyres at 13.9 = 1 tyre at 380/85……

Beware of cheap tyres, they're often narrower than they should be. I had a pair of cheap and nasty 16.9 that were only an inch wider than 13.6 Goodyear

 

[Oliveau]

I think that in old money you are comparing 12/38 with 14/38.
Think of the 12/38 as being one of the options on a Ford 5000 - if you wanted 14” tyres you went for the 14/34 and the two were roughly the same rolling circumference.
The 14/38 on the other hand is a bigger thing altogether - think TW 10.

 

[livestock 1]

I’ve had a couple of alliance fitted to a yard/feeding up tractor a couple of years ago 16.9 34 the tyre folks came with a metric equivalent which they said was the same. I fixed a puncture on one the other day had some chew breaking the beads when I blew it back up it was hellish tight on the rim. Fits but slightly different size

 

[Lakes Nash]

1

I think that in old money you are comparing 12/38 with 14/38.
Think of the 12/38 as being one of the options on a Ford 5000 - if you wanted 14” tyres you went for the 14/34 and the two were roughly the same rolling circumference.
The 14/38 on the other hand is a bigger thing altogether - think TW 10.

the 13’s on are original Goodyear, 10% left and crazing, the 380/85 are a lower profile tyre, bit more floatation than the 13’s, means we can use same rim / centre, other option is new rim/ centre and 16.9/ 34’s , bkt do all these sizes, have Trellborgs on the 105 and they seem to be wearing fast,

 

[Boohoo]

1

the 13’s on are original Goodyear, 10% left and crazing, the 380/85 are a lower profile tyre, bit more floatation than the 13’s, means we can use same rim / centre, other option is new rim/ centre and 16.9/ 34’s , bkt do all these sizes, have Trellborgs on the 105 and they seem to be wearing fast,

The 380/85 aren't a lower profile, they're just the modern equivalent of a 14.9.
Using figures from BKT the 340/85r38 has a rolling circumference of 4613mm and the 380/85r38 has a rolling circumference of 4841mm. So going to the bigger tyre gives a 4.94% increase in rolling circumference which will probably turn the 4wd lead into 4wd lag