34T front rear drive pulley

[Roy]

Okay. The change to my bike is indicated by the subject of this topic .. you have the rear belt drive, 2 pulleys - 1 on either end, 1 on the rear wheel and 1 on the gearbox shaft behind the clutch. Its the latter that has been changed from the standard 32T to a 34T.

So with a bigger belt pulley:

1) the belt adjust would have been bought back towards the gearbox.

2) top end speed would have been sacrificed as the gearing up would have diminished the power at the rear wheel.

No I have not had it dynoed since changing the pulley and yes this is why I have started the tuning an EFI topic up.

Hope this is now clear

Roy

[simonDyna]

The 34t front belt pulley will give a greater theoretical top speed (providing you can pull it) less acceleration and lower rpm for any given speed.

It will allow you to spend longer in first gear because it can now pull a few mph more than it did originally. This may feel like greater acceleration because you spend longer going through the gears or possibly achieve a higher speed before shifting.

You have gone from a secondary drive of 32/70 to 34/70. Each time the front pulley completes a full circle the rear does 0.48571 revolutions. Previously it completed 0.45714 revolutions.

The amount of teeth on the belt and its relationship to the gearbox are null and void in this instant. Even if the rear pulley was six inches away from the front pulley or six feet away from it, it will still rotate at the same rate of 0.48571 revolutions per one full revolution of the front pulley.

As for power, you still have the same amount of power that you had before. Whether is is now utilised as effectively is a different matter.

If you had put a bigger pulley on the rear, you would get the effect you describe but again, no change to the power.

The key to gearing is looking at the driver pulley and the driven pulley. If in doubt, look at a kids mountain bike. They give a very simple example of 1st all the way through to 15th. First has a small driver sprocket and large driven sprocket. 15th is the opposite with a large driver and small driven.

[Roy]

Thanks, however my last post was to answer 2 previous questions, not to give any new information.

The key for me is what you said about theoretical high top end if you can pull it, this is why I am now looking at the next set of changes to my bike being for performance (hence the EFI tuning post).

I do have to say though, if your happy just below 100mph, then changing to a 34T front rear drive pulley is a big improvement. In the last 3 weeks since having it done I have covered just over 2000 miles, its been the nutz.

However, I now see the drop off in pulling power about 95mph, so .. Matts and EFI tuning post here I come.

Gonna sign of from this post now as feel the conversation has been to death.

Cheers, Roy

[grbrown]

Enlarging on Simon's point, let us take a look at what the gearing on a Dyna actually represents. Fifth gear is direct or 1:1 within the gearbox and Roy's original gearing gives a theoretical 135mph top speed in fifth. Raising the gearing with a 34T sprocket increases this to 143mph. In sixth gear, the new gearing corresponds to no less than 168mph.

By contrast I have reduced the gearing of my Dyna, a 5-speed, from 140mph theoretical top speed, to 118. The result is significantly improved acceleration in top gear and reduced gear changing. It now rides like a Harley should, in my opinion!

All Harleys, for many years now, are seriously over-geared as standard. This is entirely down to reducing engine speed, hence noise output, at the road speeds used for noise testing, to comply with emissions regulations.

While Roy may be pleased with the change to his bike, I am inclined to recommend that any change in gearing should be to reduce it and significantly. I now have a 21T crank sprocket, in place of the original 25T. It is the cheapest way of 'tuning' a standard Harley!

In contrast, to enable the engine to overcome the standard gearing, to the same degree my Dyna does, requires a dramatic increase in torque, something few of us undertake with the modest levels of tuning we normally use (Simon being one of very few exceptions!).