Diff Ratio's

Sure, I can help you with that. The easy part is finding out rolling circumference (a bit of paint / oil on a tyre will do this quite well) and deciding what speed you want it to reach. Then it's just a question of deciding how you want the gears to be spaced in terms of what rev range you want in each gear to fit in with the engine power curve.

There will be a limited number of gear ratios in the gearbox, and they'll be spaced reasonably well, so the only thing you actually need to do is set the rear diff ratio to bring the revs into line with your planned top speed / red line.

Can do this in Excel very simply, but broadly speaking you're suggesting sixth gear is 0.829 and diff of 2.75 so at 6,000 rpm the wheels will be rotating

160,00 times per hour. 445.70/15 is a rather odd size, I don't think you mean 70% of 445 millimeters is tyre height, so I'm a bit puzzled about that, but 32 inch diameter means about 250 mph at 6000 in top, which I would guess is not likely to be reached with 130 bhp. So there would be a lot of point in doubling the last ratio from 2.75 to, 5.50 and giving it a speed at 6,000 in top of 125 mph, or thereabouts, I imagine it would be realistic. You can also put different sized wheel / tyre combinations on it to get the ratios where you want them.

So there would be a lot of point in doubling the last ratio from

thanks for that, i think i have it sussed the only other question is do you know of ant diffs that have a 5.50 ratio???????????

different size wheels aint an option as i spent a small fortune on the the rims and 445 tyres

Thanks Yoda

The 1:2.75 would become this if you put a 1:2 reduction drive in. Otherwise, putting smaller wheels on, basically with half the diameter, would achieve the same effect. The best thing to do is find out what diffs you can use / obtain / fit and see what they will do for you. Mostly they come around 3 to 4 : 1 and you change the wheel sizes to suit, e.g. if you have an Escort on a 4 : 1 diff, and 25 inch tyres, putting 32 inch tyres on means reducing the diff to 5 : 1 instead, or accepting you lose a lot of acceleration. This is sort of what you are doing, although I'm not sure what your wheel diameter is as 445/70.15 is a forty inch wheel (445/50.15 would be 32 inch.)

Bear in mind that top speed will largely be irrelevant on UK roads and you may want to sacrifice acceleration in favour of fuel economy / relaxed cruising, particularly on a six speed box. Now I think of it, 5.5 is a bit high, perhaps, at 90 mph you would be doing 4200 rpm, which is perhaps better in 4th or 5th. A ratio of 4.0 or thereabouts might be better if you can live with the acceleration, and want to save gear changes. This is all down to how a trike works, I don't really know how they are and assume you tend not to travel at high speeds, but that's possibly wrong.

If you normally cruise at 90mph, it makes sense to set the gears so that maximum torque from the engine comes in around there in whatever gear you cruise at, e.g. sixth. This is how I'd set up a road car. A trike or on track is a bit different. What sort of thing are you trying to get?

Limits the options, but fair enough. It does mean you have to buy more expensive tyres in future too, of course, because otherwise the diff you fit will be wrong again ;)