JD optimal gearing

[asavolai]

Hi,
I have following gearing in my 28 JD:
18/43 primary, secondary 48/27. Total ratio is 4,25.
The top speed is about 100 km/h, but good travelling speed is 90 km/h.
Motor revs are apps. 3400rpm when driving 100 km/h (top speed in my case)

I'm thinking of changing the gearing to drop the ratio to get more comfortable revs/maybe to get 100 km/h to travel speed.
What do you think which is the optimal gearing for JD? What if I change 48->40. Total ratio would be 3,53. Theoretical revs in 100km/h would be 2800 rpm.
Is that too big change, any comments?

Antti

[Robert Luland]

So where ya planing on getting all these here fancy gears from mate?

[asavolai]

Hi!
That is a good question. And also mainly the reason I'm asking the ratio as the testing is do difficult... I'm planning to cut old worn tooth off from rear sprocket and welding new one on old sprocket center.
Obviously I'm talking about the sprockets here, not gears..
Antti

[MMasa]

Well engine sprockets with different tooth counts are readily available on eBay and someone in Europe is making 40 and 44 tooth rear sprockets, so...... I would say that you have some options.