Gear ratios for tyre options

[JR.]

Hello all. I am trying to work out my options for tyre pairings on my T7210 AC. With the JD tractors the book gives you a calculation to work out what wheel pairings you can have and what the tolerance with rolling circumference variation is, because obviously not all tyres have the same RC but there is only so far you can push it.
I can't find this for my NH, Does don't seem to be able to provide me with anything and neither have NH yet, despite a direct approach.

Anyone else got any ideas?

 

[Flat 10]

JD do seem fussy. How about you look up the rolling circumferences and work out ratios of your current set (if you know they were on from new) and make sure new ones are the same? I am staggered how much the ratios between front and rears can vary (same nominal sizes obviously) between brands.

 

[Matt L]

Most manufactures can supply a booklet with they tyres in to work out the ratios.
Just ask your dealer what the lead ratio should be.
DONT just change brand but same size as previous as they may actually have a different rc and end up outside the recommended lead ratio.

 

[C.J]

What size and brand did it come with ?

What rim sizes do you have ?

What do you want to change to ? - wider/narrower,taller/lower.

 

[JR.]

The JD system - once in a spreadsheet works ok. I can’t find the same for NH. I have worked out the RC for current tyres but was surprised at variation between brands so there must be some tolerance. That with having newer wheels on the front or back could also throw things out. So it’s the tolerance I need to work out what I can pair.

I have 650/65r42 rear and 540/65r30 front Michelin’ Omnibib or mulitbib. I want to go wider and higher spec on the front only to avoid having to dual up front. Rear axle dualled with 650’s but damage already done with fronts.

Thank god for the Terry Elsey team who pointed out that I had been advised to buy the wrong set of wheels by Fieldens.

 

[C.J]

You could put Michelin xeobib 600/60R30 on the front but would need 20" rims.They can be run at 6psi or 0.4bar

 

[Against_the_grain]

I swear our machines start to experience ratio issues once the tyres get worn. Its like an unlocking/bang when you take your foot of the brakes.

 

[JR.]

That’s the size I was looking at - the 600. Fieldens told me I could run 710/55r30 and I had them on order when they went pop. Thankful Phil at TE put me straight.

There must be some tolerance because the RC of a tyre will vary so much in its life. Very often fronts wear faster than tears so is there a point at which the issue to replace tyres is not about lack of tread/grip but distortion of the ratio.

 

[Matt L]

I swear our machines start to experience ratio issues once the tyres get worn. Its like an unlocking/bang when you take your foot of the brakes.

Yes it is possible as there is a large circumference difference between new tread and bald tread. The lead amount should be between 1 and 5 % to enable the proper function of the 4wd system, I have seen tractors with new tyres fitted on only one axle causing massive transmission wind up on braking. Turns out it was running around 9%. He had been driving it for weeks before thinking it was the tyres

 

[Boohoo]

540/65r30 have a Speed Radius Index or SRI of 700, as do 600/60r30 and 600/65r28. 710/55r30 are taller with an SRI of 725.

Michelin have this guide to equivalent tyres in their data book.

 

[JR.]

Many thanks for the replies

 

[Gapples]

Determining the “lead” of your front tyres on a F.W.A. tractor.

Let’s deal with the first question- why do you need to know what the lead is anyway? Before you start, read the article on ‘Tractor tyres for Front Wheel Assist Tractors’. This sh…

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