Ducati Sporting Club UK > Model Specific - Discussion, Technical Problems and Help > 998 / 996 / 916 / 748 > 748s - 14/41 sprocket question ?

[Delooney]

OK - I've already got the 'Shazam' gear chart but he only lists the 14/38 stock ratio for the 748s.

Can anyone offer a MPH / 1000rpm chart for each sprocket option for a 748s gear box with 14/38, 39, 40, 41.

What I'm trying to calculate is the top speed at 11,000rpm with the 14/41 sprocket option ?

Delooney.

[Shazaam!]

The theoretical top speeds, or at least the speed differences between gear ratios can be calculated here:

http://www.cryohold.com/bike/gears.html

However, the actual top speed that can be achieved depends on the horsepower available and the combined drag coefficient of the bike and tucked-in rider. The drag force is proportional to the velocity-squared so it quadruples when speed doubles. At high speed, almost all the horsepower is needed to overcome aerodynamic drag. Because horsepower increases with increasing rpm, most bikes can reach a higher speed in 5th than in 6th gear because they can make more horsepower at the higher rpm reached in 5th, if that makes any sense. So you need to actually try each gearing combination to see which set-up will give you the highest top speed, or use a wind tunnel.

http://speedzilla.zeroforum.com/zerothread?id=43210

[moto748]

11000 rpm!


<Makes mental note never to buy a bike off Delooney...>

[misterpink]

So....with peak power on a 748S at say 10,000 or 10,500 and the increased drag quadrupling (although the pies/donuts-eaten coefficeint of +1.6 should be applied in some cases)this implies that at 11,000 rpm you could actually be going backwards. Yet if we down gear the bike so that at any given road speed the revs are higher we should reach terminal velocity sooner..............OK one more glass of chardonnay and i'm outtahere.

[m1keyp]

I have lots of pies on board

And have also gone 14/39 which I have found great fun, allied with a ligther clutch the engine spins up really fast and the gearing is excellent

748S here

[Edited on 15-5-2005 by m1keyp]

[Edited on 15-5-2005 by m1keyp]

[Delooney]

Shazaam,

Do you know the indivudual gear ratios so I can fill the chart out for my 748s ?

Delooney

[Delooney]

Just found them in my manual, all same as a 749 just different primary ratio.
So what does it tell me ?

The book says a 748 does 152 mph top speed with standard gearing. The chart calculates revs of 11,200 rpm to acheive this.

Using revs of 11,000 it now says it will do just 149mph.

With same revs of 11,000 but with changed sprockets to 14/41 top speed is reduced to 138 mph.

Interesting & thanks for the link !



Delooney

[nelly]

I ran 14/41 on my BP and didn't like it one bit......
After the novelty of revving through the gears like a banshee wore off, it became a pain changing gears all the time and just battering the rev limiter.
My motor is running an alloy flywheel and lightweight clutch which helps it spin up quicker anyhow. The limiter is set a little higher, at 11750, and it is set up pretty well

I've now geared it down to 14/36 which is stock 748R gearing and just enjoy riding the midrange, which for me is what a Ducati is all about.
In the real world it doesn't seem to suffer as I can hold a particular gear just that little bit longer where otherwise I might be changing up momentarily....................
It's topping out at about 150 ish............... with 14/41 it was pulling about 145 on the limiter.
If you want to try higher gearing, i have a rare 13T front lying around somewhere, that whilst not recommended for permanent use, will give some idea of what it'll feel like. You're welcome to try it out before spending on the 41T option. Remember, you'll need a new chain as well as the rear sprocket.

[skidlids]

Originally posted by nelly

If you want to try higher gearing, i have a rare 13T front lying around somewhere,

[Delooney]

Hi Neil,

Using a 13T front (not sure of that number) on a standard 38T rear gives same final drive as the 14/41 option - 138mph @ 11,000rpm.

14/41 is currently fitted to my bike but thanks for the offer. PS. still riding it like a banshee, novelty not yet worn off !



Whilst doing all this gear ratio checks and counting teeth I've since noticed that the rear sprocket has a few mm's side to side movement so I may be popping down soon for you to take a quick look over to see if all is OK.


Delooney

PS. bike going a dream since the service !

748s in YELLOW
50mm Full Termi system
JHP Eprom
14/41 sprockets
Ducati lightweight clutch

[Edited on 18-5-2005 by Delooney]