15-42

[Rene EFE]

Due to slightly unforseen circumstances, it looks like I'm ending up with the above gearing; is this workable in the real world or should I try and find either a bigger rear or go 14 on the front?

I usually run 15-45 or 48 and I'm a bit of a numpty when it comes to these calculations. I know it will do 250Mph (in theory  ) but that's not really an issue. 

Engine is a 125Bhp 1127 with a lot more to come, so plenty of power. 

[Captain Chaos]

(45-42)/45 = 3/45 = 1/15th = 6,7%

15:42 is 6,7% taller than 15:45. It's not that difficult. And if it is, just download an app that calculates it for you.

[ads54]

This may be some help?

http://www.gearingcommander.com

[Burnout]

2 hours ago, captain chaos said:

(45-42)/45 = 3/45 = 1/15th = 6,7%

15:42 is 6,7% taller than 15:45. It's not that difficult. And if it is, just download an app that calculates it for you.

whats an app?

 

[markfoggy]

I've got a good one for you,

Imagine the energy in a bullet, it's about the same weight as a chain link.

Now you've got it zipping along at a fair old rate of knots. Next thing is you're going to ask it to turn around in the opposite direction and then get up to the same speed again. I'm guessing that you'll lose a lot of energy, if you were asking lots of bullets to do this for a prolonged period of time. Bullets don't like doing this.

This is a basic description of chain losses, which it's possible to calculate. They are seriously hungry little power eaters, when you get down to 14 and 15 tooth, they're seriously ugly.

God' sake, go bigger on the front and find a way of coming down at the rear. 

 

 

[markfoggy]

Sorry just getting my head around this, too used to road racing gearing, so to keep 3.0 to 1 (15,45) you'll be needing moon disc sized sprockets to replicate 15/48 using a 17 front. Having said that, you'll free up about 20% more energy than using a 14 front. This is, relatively, non cost horses, so worth considering.

[Rene EFE]

I'll need a custom sprocket on the rear and my pockets aren't deep enough atm. I'll just wing it, it's only a backup bike anyway. 

[Captain Chaos]

7 hours ago, Burnout said:

whats an app?

 

I have no f*cking idea, I hear it everywhere around me and it seems to be the bollocks.

*edit* just googled it:

Shortened form for appetizers

"Let's get some apps and drinks!"

 

http://www.urbandictionary.com/define.php?term=app

 

or not.

 

 

Edited January 16, 2016 by captain chaos

[tabby59]

markfoggy is on top of it. A 15/42{2.8:1}  combo will drop your rpm in high gear about 300 rpm{tach reading}. At least that is what it did on my 86 750. With that, you may get better fuel mileage, at the expense of a little loss in acceleration,,, on a stock motor. With my modded 907 I use a 16/40{2.5:1} combo because it has the power to pull that ratio. When I ran a 16/42 on my bike, I couldn't use full throttle in 2nd gear at the drags.

 

[clivegto]

6 hours ago, tabby59 said:

 When I ran a 16/42 on my bike, I couldn't use full throttle in 2nd gear at the drags.

 

Why ?

is running 16/42 not the same as 15/45 as near as dammit ? and if it is Rene only needs to change the front sprocket which is a lot cheaper than a custom back one.

[Captain Chaos]

1 hour ago, clivegto said:

 

is running 16/42 not the same as 15/45 as near as dammit

No. You are confusing 15:42 and 16:45.

[clivegto]

Just now, captain chaos said:

No. You are confusing 15:42 and 16:45.

OK

[tabby59]

it could be written this way 42/16 = 2.625, 45/15 = 3.0. These are final drive ratios, 2.625 being a "taller" ratio than the 3.0. Think  like you would if you had a rear drive hot rod car. You would divide the number of teeth on the ring gear by the number of teeth on the pinion gear in the differential to get your final drive ratio. Fortunately for us, sprockets are far easier and cheaper to juggle ratios with.  The bigger the diameter sprocket a chain gets to go around, the easier it is on the pins and rollers of the chain. Since the front sprocket is the smallest, that is the sharpest "corner" the chain has to go around. So I went up on the front  and down on the rear to get the ratio I wanted. If you didn't know this, 1 tooth on the front is approximately equal to 3 teeth on the rear.

 

[dupersunc]

I've been running 15/43 gearing on my 7/11m, stock 750 gearing, as I didn't realise 1127 motored gsxrs run 15/48 stock. Doh.   Combine with a tall 180/60 rear tyre, I was geared for 180+ mph. I actually liked this gearing on the road, I went every where in 2nd and 3rd, which was good for 134ish mph, and was plenty good enough to keep up with/embarrass all the local hotshots on their 2014 pcp payments.

I only started to wonder about it when I took the bike to Jerez, before Christmas, and was barely getting 4th gear on the back straight :D.  Running 14/48 for track now, but probably go back to 15/43 for road use.

[Dr Jon]

Yes, need to remember that the total diameter of the back wheel and tyre needs to be considered when comparing drive ratios from engine donor bikes to their new homes. I'm running 15:45 on my 1127 motor in a 600 teapot with a 150-70 17 tyre. 70mph is about 4750 rpm in top, 100mph just under 7000 rpm and it will easily do 135mph in 3rd at about 11000 rpm. Not sure where it would top out but a long way the other side of 150 anyway. General riding is very civilised with this gearing, no need to go anywhere near the real power if you don't want and still be getting up to 100mph or so. Ballistic acceleration when you do want to play. Feels like the perfect gearing, i went up one from 14 to 15 on the front and it does feel better. Standard gearing on the 1100f is 15:52.

[Ted M]

Sad chap that I am I got bored one day at work and calculated the road speed of a B12 and B6 for any given RPM on an Excel spreadsheet. It could prove useful for those racer and track dayers amongst you, I will upload it if you like.