bike gear ratios, help please

[lag waggon]

Ok i am going to change my sprokets but im not to sure how far i can go. I've got 15 45t standard and ive done some looking and i can get a 16t front but just not sure what i should do on the back, i think a 43. It's only a 600cc 4 banger sport bike lump, and i dont want to load it up to much.

Any help would be great thanks, nathan.

[Rob]

You could always take all four for a few combinations, rounded to two decimal places the ratios would be:

15/45 3:1
15/43 2.87:1
16/45 2.81:1
16/43 2.69:1

Cheers,
Rob

[lag waggon]

Thanks rob, ill have to buy 4 new sprokets cause the 16 i want is 520 and my old is 525. Looking at the ratios, those 4 give a good range for change, but is going from 3:1 - 269:1 ok ? not to bigger drop?

[Rob]

but is going from 3:1 - 269:1 ok ? not to bigger drop?

I'm the wrong person to ask on that one sorry, hopefully one of the experienced bike guys will chime in for you.

Cheers,
Rob

[DirtyDave]

lag waggon.. 1 tooth on the rear is about 400 RPM it won't pull in top and 1 tooth on the front is about 4 off the rear,, I've googled gear ratio's in the past and you can find heaps of info...and spread sheets..

[lag waggon]

lag waggon.. 1 tooth on the rear is about 400 RPM it won't pull in top and 1 tooth on the front is about 4 off the rear,, I've googled gear ratio's in the past and you can find heaps of info...and spread sheets..

Thanks Dirtydave, i have a gearing program and it says 1 on the front is worth 3 off the rear. I just cant find out if the bike will still move off the start without a push off the line with a 1 up 3 down , how far can you go before that happens? anyone?

[Last Minute Racing]

If you can take off in 2nd or 3rd gear that will be OK to gear to in 1st but thats not saying you will be able to pull top gear with that sprocket combination, so probably work on top gear as i think taking off will be the least of your problems.
Im taking a selection of sprockets and will change them as circumstances change eg. wind and temp.
The problem is going to be the rpm drop between 5th and 6th i think, trying to keep in the rather narrow power band.
If you gear too high you might find your top speed in 5th is higher than 6th(or 4th and 5th in a 5 speed)
Its all a learning curve but the gearing calculators are a great help.
I will be dropping 1050 rpm between 5th and 6th so no need to over rev, change at 11500 and it should pull top gear, in theory
Then you have wheel spin to take into consideration. Im told its about 10%. so the rpm might drop an extra 10% so might have to rev out an 10%?
Now ive confused myself.
Will find out in 40 days if it all works out.

Thanx
Dave

[Greg Watters]

You may be able to find a 44 , look at other models of your bike i know the gsxr,s vary from 40-45 and a zx 14 rear will fit a busa

if your bike is fairly stock it may not pull much higher gearing than std to or near redline , and bring a lower than std option just incase

[grumm441]

These guys used to have a hard copy catalogue which had pics, but the website works ok. The sprockets are available locally and quite reasonably priced
G

http://www.jtsprockets.com/48.0.html

[lag waggon]

Thanks to everyone for your help. I've been loooking on the web and have found some interesting things. I'm going to keep the stock ratio and buy a 1 down for the rear to try on the dyno, and see if it can pull in top with that.

[gennyshovel]

Lad Waggon, will the bike pull redline in top woth the stock gearing ?
What internal ratio is top gear (including primary reduction) beware of overdrive top , gear for the gear closest to 1 /1 to be the gear you use, and aim for getting revs as close to maximum horsepower range, in an ideal situation, changing gears at peak horsepower and being close to peak torque when the taller gear is selected soumds a good plan , but in the real world, you have to take what get , unless the engine power curve was tailored to LSR when the engine was designed.
Tiny

[lag waggon]

Lad Waggon, will the bike pull redline in top woth the stock gearing ?
What internal ratio is top gear (including primary reduction) beware of overdrive top , gear for the gear closest to 1 /1 to be the gear you use, and aim for getting revs as close to maximum horsepower range, in an ideal situation, changing gears at peak horsepower and being close to peak torque when the taller gear is selected soumds a good plan , but in the real world, you have to take what get , unless the engine power curve was tailored to LSR when the engine was designed.
Tiny

Ok not sure if it pulls red line in top, but before i backed off it was still pulling hard. max power @12750 max torque @11000.
Primary drive 1.864 and 6th gear 1.083. My brain is now melting down the more i read the more confused i get

[gennyshovel]

Something like this will help
http://www.catherineandken.co.uk/sti/tyres.html
or this (my fave)
TopSpeed 1.0
But all the planning in the world won't be worth diddley squat until you get on,,,,,, The Big White Dyno
Tiny

[colinjay]

I have made up an Exel spreadsheet that calculate theoretical top speeds for different final drive ratios/rpm/tyre diameters etc and all other variations/combinations for my SR500. If you email all the internal gearbox and primary drive ratios to me I will redo the spreadsheet to suit your bike and send the speadsheet back to you.

CJ

[gennyshovel]

I have made up an Exel spreadsheet that calculate theoretical top speeds for different final drive ratios/rpm/tyre diameters etc and all other variations/combinations for my SR500. If you email all the internal gearbox and primary drive ratios to me I will redo the spreadsheet to suit your bike and send the speadsheet back to you.

CJ

Are you going salt side this year slob?