rear sprocket for lower rpm on highway

[aussie7]

ok I've had a look on http://www.gearingcommander.com and not sure what to do

First up I have a Katana GSXF750 2006 model. I live in Australia so speedo is in kmh

I want to lower my rpm from around 5000rpm to around 4000rpm at 110kmh and I would like to know if changing the sprocket size will affect the speedo

I was thinking of going a front 16t and a rear 42t what do you think

Anyone got any ideas what I should do

TIA

[92xjunker]

16 tooth front, will require some grinding on the sprocket cover. In order to get where you want you would need a 17/40 setup, not recommended at all. 42 rear is the smallest you could buy, unless you custom order one.

[aussie7]

16 tooth front, will require some grinding on the sprocket cover.

ahh

is it worth going from a 45t to a 42t rear then

edit will changing sprockets size affect speedo ?

[92xjunker]

Yes it will so, you would need a speedo healer. 42 would yield a 260 rpm drop.

[aussie7]

Yes it will so, you would need a speedo healer. 42 would yield a 260 rpm drop.

Thanks 92xjunker

not sure if to go with a 40t or a 38t

edit just looked up speedo healer and its more than I want to spend on the bike, so no mod

[shpielers]

I put on a 42t rear, was commuting 100 miles a day for several years. On my 600, not worth it. I'd do 43 or 44 next time personally. The extra power from the 750 would help a little there.

[Stinger02]

If you did the gear swap, id just say forget the speedohealer and use your cell phone to show your accurate speed

[aussie7]

I put on a 42t rear, was commuting 100 miles a day for several years. On my 600, not worth it. I'd do 43 or 44 next time personally. The extra power from the 750 would help a little there.

If you did the gear swap, id just say forget the speedohealer and use your cell phone to show your accurate speed

Thanks for the input, at the moment I will leave the gearing stock with 15t front and 45t rear. Can't really afford to make the mod atm

atm at 110khm it is revving at 5000rpm which I can live with for the moment

[KAT TOY]

my 750 has 16/47. that's 5000 @65mph per GPS. so 16 on the front would help. probably won't have to change chain length. only takes minor grinding on cover with Dremel tool. my rear tire is 160/60R17. my speedo is still faster than actual.

[aussie7]

my 750 has 16/47. that's 5000 @65mph per GPS. so 16 on the front would help. probably won't have to change chain length. only takes minor grinding on cover with Dremel tool. my rear tire is 160/60R17. my speedo is still faster than actual.

thanks for the input, my rear tyre is also a 160/60/17 so my speedo displays a slower speed than actural speed

for example 5200rpm in 6th gear is
- 108 kmh 160/60/17 tyre
- 111 kmh 150/70/17 tyre

so its only 3k's out

[aussie7]

did a search and asked at the shop no 38t rear sprockets available

smallest is 42t so I have decided to go 16t front and 42t rear

anyone got pics of the front sprocket cover grinding to fit the 16t

EDIT:
bike is booked in for Friday this week, so if it is done then I will post pics here for future reference

TIA

[aussie7]

well changed my mind again and kept the 15t front sprocket and just got the 42t rear sprocket fitted

speedo is about 5k's out, but I will be getting a speedo healer in a few weeks

take off requires some minor clutch slippage, but the 750 has enough power and the bike seems to accelerate better than before.

[TRPUT]

Going to a 42T rear sprocket will have made your speedo more accurate by absorbing some of the inherent error in the original set up. If you were running a stock rear 150/70 tyre, your speedo would be close to perfect and no speedo healer necessary.

[aussie7]

Going to a 42T rear sprocket will have made your speedo more accurate by absorbing some of the inherent error in the original set up. If you were running a stock rear 150/70 tyre, your speedo would be close to perfect and no speedo healer necessary.

not sure if it is closer to the right speed or not now that I have fitted a 42t sprocket.

I will have to get a gps and see test it

[aussie7]

Going to a 42T rear sprocket will have made your speedo more accurate by absorbing some of the inherent error in the original set up. If you were running a stock rear 150/70 tyre, your speedo would be close to perfect and no speedo healer necessary.

Thanks TRPUT just taped the mobile phone to the handle bars with electricians tape and checked the speedo with a gps app
It is accurate with the new rear sprocket