Tyre experts Tractor tyre size upgrade

[Ian j]

Hi all I am looking to upgrade the size of tyres on my old semi working 4 wd tractor I am happy width way but am looking for hight /rolling radius I am presently running 18.4 x34 rears and 13.6 /12x24 fronts I want to keep the front wheels the same size as now and increases the tyre size but have a set of 38x15 rims to go the rear any ideas please

 

[Gerbert]

Simple answer, you can not fit bigger tyres on the back without changong the fronts.

 

[Nearly]

 

[C.J]

15" x 38" rim is perfect for a 18.4R38 (460/85R38) tyre but you will need to change the front tyres.

14.9R24 on the front will reduce lead by 1.6% and need 11,12 or 13" rim.
16.9R24 on the front will increase lead by 3.7% and need 14 or 15 " rim.

Assuming you currently have the correct tyres for your gearing with a lead of 2-3% then the 14.9 front is the best choice and will probably fit your current front rims.

 

[manttys]

I bought JD 6620 with 600/65 r38 and 480/65 r28 (that's what papers say), would like to switch to 650/65 r38 and 540/65 r28, will I be fine?

 

[daveydiesel1]

I bought JD 6620 with 600/65 r38 and 480/65 r28 (that's what papers say), would like to switch to 650/65 r38 and 540/65 r28, will I be fine?

Yes youl be ok

 

[Boohoo]

Hi all I am looking to upgrade the size of tyres on my old semi working 4 wd tractor I am happy width way but am looking for hight /rolling radius I am presently running 18.4 x34 rears and 13.6 /12x24 fronts I want to keep the front wheels the same size as now and increases the tyre size but have a set of 38x15 rims to go the rear any ideas please

Does your operators manual say what size combinations are recommended?
What tractor is it? Quite small fronts make me think Case or DB? 18.4x34 wouldn't be that common on them so I'm wondering how much room there is for changing the lead.
12.4r28 are the closest match for 18.4r38 but you want to stay with 24s so 14.9r24 are the closest although they will reduce the lead.
Might be worth mixing tyre brands if you're not worried about looks, Goodyear for example were always a tall tyre.

 

[Ian j]

Simple answer, you can not fit bigger tyres on the back without changong the fronts.

Sorry if it's unclear but I only intend to change all 4 tyres but change the rear wheels only as I want to keep the fronts

 

[Gerbert]

What?

 

[Ian j]

Simple answer, you can not fit bigger tyres on the back without changong the fronts.

Sorry if it's unclear but I only intend to change all 4 tyres but change the rear wheels only as I want to keep the fronts

15" x 38" rim is perfect for a 18.4R38 (460/85R38) tyre but you will need to change the front tyres.

14.9R24 on the front will reduce lead by 1.6% and need 11,12 or 13" rim.
16.9R24 on the front will increase lead by 3.7% and need 14 or 15 " rim.

Assuming you currently have the correct tyres for your gearing with a lead of 2-3% then the 14.9 front is the best choice and will probably fit your current front rims.

Yes from enquires the lead for the model is stated at around 5% so working on that 16.9 could be used as they are within tollerance

 

[C.J]

Yes from enquires the lead for the model is stated at around 5% so working on that 16.9 could be used as they are within tollerance

In that case the 16.9 would increase the lead to 8.7 % which is too much.

The 14.9 would reduce the lead to 3.4 % which is more acceptable especially on hard surfaces.

 

[Ian j]

Does your operators manual say what size combinations are recommended?
What tractor is it? Quite small fronts make me think Case or DB? 18.4x34 wouldn't be that common on them so I'm wondering how much room there is for changing the lead.
12.4r28 are the closest match for 18.4r38 but you want to stay with 24s so 14.9r24 are the closest although they will reduce the lead.
Might be worth mixing tyre brands if you're not worried about looks, Goodyear for example were always a tall tyre.

You are correct with the assumption on make its a 1690 4wd the operators manual has got a list of comparable tyres size wise but things have moved on a long way in recent years as far as the tyre sizes available goes there is plenty of room to go bigger part of reasoning behind the move is to unclear rolling radius leading to a faster road speed as I do quite a lot of road work both to shows and events the tractor is fitted with the fast reduction and as you said has the smallest wheels available fitted attached is a picture of the recommendations in the manual

 

[Ian j]

Thanks for that

In that case the 16.9 would increase the lead to 8.7 % which is too much.

The 14.9 would reduce the lead to 3.4 % which is more acceptable especially on hard surfaces.

Thanks for that and I take it that would be working on a 85 profile both back and front so it would be 460/85 X 38 rear and 380/85x24 fronts

 

[Boohoo]

You are correct with the assumption on make its a 1690 4wd the operators manual has got a list of comparable tyres size wise but things have moved on a long way in recent years as far as the tyre sizes available goes there is plenty of room to go bigger part of reasoning behind the move is to unclear rolling radius leading to a faster road speed as I do quite a lot of road work both to shows and events the tractor is fitted with the fast reduction and as you said has the smallest wheels available fitted attached is a picture of the recommendations in the manual

Wasn't expecting a 1690! Our Case 844 is on similar size tyres to what you've got at the moment. If it was me, I'd put 16.9r38 on. 18.4r38 will only get you an extra 1mph. If you like the width of the 18.4 you could put 480/70r38, which are the same height as 16.9r38.
If your heart is set on 18.4s though, as said go with 14.9r24 on the front and maybe try to look for a big 14.9 and a small 18.4. At least you haven't got 4 wheel braking to worry about.

 

[Ian j]

Wasn't expecting a 1690! Our Case 844 is on similar size tyres to what you've got at the moment. If it was me, I'd put 16.9r38 on. 18.4r38 will only get you an extra 1mph. If you like the width of the 18.4 you could put 480/70r38, which are the same height as 16.9r38.
If your heart is set on 18.4s though, as said go with 14.9r24 on the front and maybe try to look for a big 14.9 and a small 18.4. At least you haven't got 4 wheel braking to worry about.

Yep a 1690 good old girl yes it basically to gain some road work speed as it has the fast reductions fitted

 

[daveydiesel1]

Wasn't expecting a 1690! Our Case 844 is on similar size tyres to what you've got at the moment. If it was me, I'd put 16.9r38 on. 18.4r38 will only get you an extra 1mph. If you like the width of the 18.4 you could put 480/70r38, which are the same height as 16.9r38.
If your heart is set on 18.4s though, as said go with 14.9r24 on the front and maybe try to look for a big 14.9 and a small 18.4. At least you haven't got 4 wheel braking to worry about.

An ozka will have a higher sidewall compared to other brands if this helps

 

[C.J]

O.K I've redone the calculations using the other combinations in your photo at post 12.

The 16.9R24 is the best match for 18.4R38 rears but will require a wider front rim than you currently have.

 

[Rogeo1983]

Good evening,

I’m just enquiring with the same issue.

1988 case 1594 rears 16.9R38, front 12.4-28.

we want to widen the front tyres, as they are a bit narrow. Maybe up to 380 from the current 320.

would any of you know the mechanical front drive ratio for these tractors?

I found a formula online to calculate the ratio %
(((Front radius x mechanical front drive ratio) - rear radius ) / rear radius ) X 100.

does this make sense to anyone?

also 1394 same year, rear 460/85R30, front 320/85R24, we want to increase this to 380 also.

same question, if anyone knows what tyres and rims we need.

the rims on both are bad, so going to replace them anyway.

many thanks.

 

[Boohoo]

Good evening,

I’m just enquiring with the same issue.

1988 case 1594 rears 16.9R38, front 12.4-28.

we want to widen the front tyres, as they are a bit narrow. Maybe up to 380 from the current 320.

would any of you know the mechanical front drive ratio for these tractors?

I found a formula online to calculate the ratio %
(((Front radius x mechanical front drive ratio) - rear radius ) / rear radius ) X 100.

does this make sense to anyone?

also 1394 same year, rear 460/85R30, front 320/85R24, we want to increase this to 380 also.

same question, if anyone knows what tyres and rims we need.

the rims on both are bad, so going to replace them anyway.

many thanks.

A 320/85 can be replaced by a 360/70 or 420/65.

Below are the inter axle ratios from a Case IH service bulletin. They depend on the axle fitted and the gearbox.
Permitted tyre combinations are also listed in the operators manual. If you haven't got them I should be able to get the relevant page. It's always good to check you've got the correct sizes on at the moment, although at first glance they look OK.

 

[Will 1594]

Yes youl be ok

How do you know eh,
what are axle to diff ratios ,
look on back axle near lift ram or side of radiator ,or silver sticker some times on side panel , then when you know that ,ask your wheel tyre supplier ,and give him the tyre brands , as they all differ even if same size , then you then only know the correct lead
too many variables