Author Topic: Changing Final Drive Ratio  (Read 2464 times)

Offline basadia

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Changing Final Drive Ratio
« on: June 26, 2016, 08:11:44 PM »
I was visiting a mate of mine who used to have a VTX 1800 and I mentioned that the ST does tend to rev high when on the freeway and he said he changed the ratio in his final drive by buying a replacement pinion ring gear. I'm interested in looking into this as I'm currently pulling around 4000 RPM on the freeway, I reckon if I could drop this to 3000 RPM on the freeway would be much more economical and I still think that the ST1300 is still well within it's power band at 3000 RPM. Any suggestions on where I could locate parts to change the final drive ration appreciated.
cheers
Keith
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Offline West Aussie Glen

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Re: Changing Final Drive Ratio
« Reply #1 on: June 26, 2016, 10:52:15 PM »
You would have to buy a gear set, pinion and ring gear. I would be very surprised if any body makes them.
It of cause has an effect on all your gears so it will put more load on your clutch when starting off.
Glen
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Offline tding

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Re: Changing Final Drive Ratio
« Reply #2 on: June 27, 2016, 09:11:47 PM »
From memory when Honda upgraded the old CX500 to the CX650 they just changed the primary reduction gear on the crank shaft by one tooth.
 

Offline basadia

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Re: Changing Final Drive Ratio
« Reply #3 on: June 28, 2016, 07:33:54 AM »
First gear is so low that the extra strain of changing the gearing would be negligible, you can idle along in first gear doing 10 ks. I think that the 1100 even has better gearing than the 1300 as it used to cruise along the freeway at 110 KPH doing about 3500 RPM.
Keith
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Online Brock

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Re: Changing Final Drive Ratio
« Reply #4 on: June 28, 2016, 03:55:02 PM »
I think both bikes travel at about 30Ks per for every 1000 revs.

You cant just change one of the gear set by one tooth, they wont mesh properly.
Brock
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Offline basadia

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Re: Changing Final Drive Ratio
« Reply #5 on: June 28, 2016, 04:05:43 PM »
Yep understood. It would be both pinion and ring gear and from memory there is a fare amount of work in re-shimming the diff so it has the correct back lash, otherwise it will be either noisy or wear out quickly.
Keith
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Offline winston66

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Re: Changing Final Drive Ratio
« Reply #6 on: June 28, 2016, 05:14:15 PM »
Be careful about this one,
4000 Rpm with normal  final gear ratio should give you approx 120 Kph. that is fast enough for me.
Changing the final gear ratio to give a lower Rpm whilst maintaining that 120 Kph. will only act as an overdrive,  and put extra loading onto the engine, this will only necessitate a more aggressive and  a more open throttle position in order to maintain your road speed. IE. imagine a steep hill and opening the throttle in order to maintain the required 120 Kph.up that gradient.
An engine operated under a heavier loading, in order to maintain the required torque output to maintain the required 120Kph in my opinion will require a considerably more  open throttle position and consequently more fuel than as in normal use.
Hope this makes sense.
Cheers,
Winston66.
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Online cravenhaven

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Re: Changing Final Drive Ratio
« Reply #7 on: June 28, 2016, 10:23:50 PM »
Technically , as I understand it, an over drive is when the engine revs are higher than the drive shaft revs, ie the gear box steps the ratio down (depends how you look at it :)).
I have noticed that since I installed my Rostra cruise control with a limit on the max throttle opening there has been no shortcomings with hill climbs etc. In fact even though the max throttle opening on cruise is less than half full throttle, I have never encountered an instance of a power shortfall on highway cruising.
 
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Offline HOFFY

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Re: Changing Final Drive Ratio
« Reply #8 on: June 29, 2016, 08:32:27 AM »
Easier to fit a taller rear tyre and a lot cheaper,
 

Online Brock

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Re: Changing Final Drive Ratio
« Reply #9 on: July 04, 2016, 08:02:10 AM »
Also, keep in mind, the speedo will become very inaccurate (taller tyre does that as well).
Brock
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Offline basadia

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Re: Changing Final Drive Ratio
« Reply #10 on: July 04, 2016, 08:11:01 AM »
Also, keep in mind, the speedo will become very inaccurate (taller tyre does that as well).

That's an easy fix, I can re-calibrate using my speedo healer. Not sure how much difference you can get using a taller tyre, definitely not as much as changing the gearing but after doing a bit of searching I have not been able to locate any other gearing options that will fit the ST.
Keith
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Offline West Aussie Glen

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Re: Changing Final Drive Ratio
« Reply #11 on: July 04, 2016, 08:22:37 AM »
Also, keep in mind, the speedo will become very inaccurate (taller tyre does that as well).

For the 1300 a taller tyre may get the speedo closer to being true speed.
Glen
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1970 Suzuki T250 Hustler, Honda CL100 (125cc)
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Offline tding

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Re: Changing Final Drive Ratio
« Reply #12 on: June 09, 2017, 09:06:48 AM »
I think I may have found a way reduce the RPM ON st1300 down about the same as the ST1100.
I have found that the final gears between the gearbox and the shaft drive are different on the CTX1300.
ST1300     40t/37t
CTX1300   41t/36t
Yes it is only a small gain but I believe achievable with off the shelf Honda parts.
 :blu13
 

Offline Jdbiker

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Re: Changing Final Drive Ratio
« Reply #13 on: June 09, 2017, 10:47:30 AM »
Technically , as I understand it, an over drive is when the engine revs are higher than the drive shaft revs, ie the gear box steps the ratio down (depends how you look at it :)).
I have noticed that since I installed my Rostra cruise control with a limit on the max throttle opening there has been no shortcomings with hill climbs etc. In fact even though the max throttle opening on cruise is less than half full throttle, I have never encountered an instance of a power shortfall on highway cruising.

Exactly the opposite, overdrive is when drive shaft revs are higher than engine revs🤓
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Offline basadia

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Re: Changing Final Drive Ratio
« Reply #14 on: June 09, 2017, 11:10:02 AM »
Pictures of both differential look exactly the same, I wonder how much swapping out the diffs would change the RPM.

I think I may have found a way reduce the RPM ON st1300 down about the same as the ST1100.
I have found that the final gears between the gearbox and the shaft drive are different on the CTX1300.
ST1300     40t/37t
CTX1300   41t/36t
Yes it is only a small gain but I believe achievable with off the shelf Honda parts.
 :blu13
Keith
02 Ex Police ST1100
05 ST1300
 

Online cravenhaven

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Re: Changing Final Drive Ratio
« Reply #15 on: June 09, 2017, 03:49:57 PM »
 :H
Technically , as I understand it, an over drive is when the engine revs are higher than the drive shaft revs, ie the gear box steps the ratio down (depends how you look at it :)).
I have noticed that since I installed my Rostra cruise control with a limit on the max throttle opening there has been no shortcomings with hill climbs etc. In fact even though the max throttle opening on cruise is less than half full throttle, I have never encountered an instance of a power shortfall on highway cruising.


Exactly the opposite, overdrive is when drive shaft revs are higher than engine revs

Ah!! exactly what I meant to say...... :H
 
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Offline tding

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Re: Changing Final Drive Ratio
« Reply #16 on: June 09, 2017, 04:30:49 PM »
Pictures of both differential look exactly the same, I wonder how much swapping out the diffs would change the RPM.

I think I may have found a way reduce the RPM ON st1300 down about the same as the ST1100.
I have found that the final gears between the gearbox and the shaft drive are different on the CTX1300.
ST1300     40t/37t
CTX1300   41t/36t
Yes it is only a small gain but I believe achievable with off the shelf Honda parts.
 :blu13
changing the diff will have no effect on RPM. the only set of gears that are different between the to bikes are the last two in the back of the engine between the gear box and the output shaft at the back of the motor.