Hello im hopeing you lot can help me, i am aware that this is not exactly what you deal with but a good friend (paul the 6th) raves about this place and the vast knowledge on tap, so here goes

i bought the wife a motorcycle based trike (650 dragstar) which as a ford diff ( ive been lead to belive a 4.1.1)
the issue is this (apart from it leaking) first gear is more or less redundant, it pulls off exceptionally well in 2nd inc hill starts
its also has a top end of 75mph at full chat in top gear

so im here to ask the obvious questions
will changing the diff to a 3.?.? make a huge difference
will it as i suspect up the top speed and make first gear usefull
which ford diff would you recommend for a change
any pit falls you forsee that i dont

now i know this is scant intel at the minute and i can get more details on the current diff when back at home after work
but at least we can start with if my premis is correct or if i just need to stay away from anything that resembles a engine or running gear

so now i shall give my great thanks for all your help in advance and look forward to putting this info into action

cheers
Dave

Firstly - welcome to the forum.

To answer your question: I would think that given the trikes ability to pull off unhindered in 2nd gear you could certainly look at a lower diff ratio (That is lower numerically). What I would do is calculate the overall ratio of second gear plus current diff and then calculate the diff ratio needed to give the same ratio for first gear and the new diff. I would then go one ratio up from that just to make sure I reduce the strain on the clutch a bit.

And yes a lower numeric ratio will reduce the revs per MPH and hence possibly increase your top speed, if the engine has enough power to overcome aerodynamic drag, and also reduce the revs when at cruising speeds and possibly reduce fuel consumption.

The calculation would look like this:

New diff ratio = (2nd gear ratio X Current Diff ratio)/1st Gear Ratio.

[Edited on 12/4/13 by Ivan]

Hi Dave and welcome.

It looks like the Dragstar rear bevel may be 3.07:1 LINKY

I have a 3.14:1 Sierra diff and approx 24" o.d. (265/50/14) tyres on my Yamaha XS1100 Trike.
The gearing is just about spot on.

Most Trikes use the Reliant Robin axle which has either a 3.25:1 or 3.5:1 ratio diff. I think you definitely need to get somewhere near these ratios or get huge rear tyres.

HTH

Neil

[Edited on 12/4/13 by trikerneil]

[Edited on 12/4/13 by trikerneil]

quote:

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Originally posted by DavePreston
Hello im hopeing you lot can help me, i am aware that this is not exactly what you deal with but a good friend (paul the 6th) raves about this place and the vast knowledge on tap, so here goes

i bought the wife a motorcycle based trike (650 dragstar) which as a ford diff ( ive been lead to belive a 4.1.1)
the issue is this (apart from it leaking) first gear is more or less redundant, it pulls off exceptionally well in 2nd inc hill starts
its also has a top end of 75mph at full chat in top gear

so im here to ask the obvious questions
will changing the diff to a 3.?.? make a huge difference
will it as i suspect up the top speed and make first gear usefull
which ford diff would you recommend for a change
any pit falls you forsee that i dont

now i know this is scant intel at the minute and i can get more details on the current diff when back at home after work
but at least we can start with if my premis is correct or if i just need to stay away from anything that resembles a engine or running gear

so now i shall give my great thanks for all your help in advance and look forward to putting this info into action

cheers
Dave

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unless you got a 3.0 litre capri axle at 3.08 or whatever it was

And pop on the largest front sprocket you can get

3.88 diffs are very easy to find fo rFord english axles, 3.77 less so 3.55 more rare.

Thankyou very much people
this info is seriously helpful
right off to find a nice lower (numerical) rated diff , from a ford sierra
that being as long as the bell housing wasnt changed from the lower rated one to the 4.1.1, god im soooooo hoping it will be a straight swap

thanks again
dave

if yours is a 4.1 i would be interested in buying the cwp or part exing plus cash for you for my spare 3.9 or 3.62 cwp? so long as its sierra of course

I'll fire up the serial number of the one i have this weekend for you