Transmission Ratio Change Question - Kawasaki Vulcan Forum : Vulcan Forums
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post #1 of 17 (permalink) Old 07-02-2011, 08:15 PM Thread Starter
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Transmission Ratio Change Question

Hello forum members, I had a 2006 900LT and was not happy with the high RPM strain when on the highway at 70 MPH or so speeds.

Has any of the newer models of the 900's series had an additional gear added or has the transmission been re-ratioed to be more highway friendly?

I am considering purchasing a new 900LT, but before I do, I want to make sure I will not be disappointed with the high RPM scream at 70 MPH.

Or is it better to go go up to a 1700 model? Opinions and comments welcome.

Thanks from Cousin Vinnie Boombatz.

Last edited by Cousin Vinnie; 07-02-2011 at 08:16 PM. Reason: Clarification
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post #2 of 17 (permalink) Old 07-02-2011, 08:33 PM
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No change to the bikes. However, Scootworks produces a front and rear pulley that addresses this very subject.

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post #3 of 17 (permalink) Old 07-02-2011, 09:26 PM
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I went with the 170/80 instead of the 180/70; the speedo is more accurate and it feels as though each gear was lengthened out just enough to minimize that high rpm feel. I shift into 5th at 60 to 65 mph and I do not feel as though I am reving the bike at all hard; I've caught myself on occasion running 55mph in 4th. Never could do that with the stock size. Cheaper than the Scootworks pulleys.

2006 VN900 Classic LT - Red and Black
Stage III Stock Pipes - K&N Filter in Stock Box - Amsoil - 170/80 Kenda Kruz - Saddlemen Explorer - Willie & Max Windshield Bag - Mutazu Passenger Floor Boards - Shorai Heavy Duty Battery - Kawasaki Lowers - Black Universal Trunk mounted on Mutazu Rack - Osram 70/65w Plus 50
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post #4 of 17 (permalink) Old 07-03-2011, 07:58 AM Thread Starter
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Appears nothing has changed on the the 900's. I have an issue buying a new bike and changing pulleys and tires to get it right.
Looks like I should go for the 1700 or a different brand; Suzuki, Yamaha or Honda.
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post #5 of 17 (permalink) Old 07-03-2011, 10:36 AM
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Quote:
Originally Posted by Cousin Vinnie View Post
Appears nothing has changed on the the 900's. I have an issue buying a new bike and changing pulleys and tires to get it right.
Looks like I should go for the 1700 or a different brand; Suzuki, Yamaha or Honda.
If you're running at 70+ mph all of the time and don't want to make the tire/pulley changes, then yes, it sounds like you'd probably be happier with a bike that is better geared for the higher speeds.

Like you, I wasn't happy with the bike's performance and noise at highway speeds. I have a Scootworks rear pulley and a larger rear tire on my 900 LT and I'm satisfied with the performance of the bike now. For me, making those changes were cheap and easy, when compared to the costs of the larger bikes. I looked at insurance cost comparisons and new/used prices of the larger bikes, before deciding that the 900 with those mods, was the most cost effective way to get what I wanted.

The good thing is that there are a lot of really nice bikes available today, so you shouldn't have too much difficulty getting something that suits your budget, wants and needs.

2010 Vulcan 900 Classic LT
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post #6 of 17 (permalink) Old 07-04-2011, 07:13 AM
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Quote:
Originally Posted by King43 View Post
I went with the 170/80 instead of the 180/70; the speedo is more accurate and it feels as though each gear was lengthened out just enough to minimize that high rpm feel. I shift into 5th at 60 to 65 mph and I do not feel as though I am reving the bike at all hard; I've caught myself on occasion running 55mph in 4th. Never could do that with the stock size. Cheaper than the Scootworks pulleys.
King43, could you explain what the wheel change does exactly?
Can you fit a bigger wheel in there?
Thanks
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post #7 of 17 (permalink) Old 07-04-2011, 12:07 PM
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170/80/15 versus 180/70/15. The first number is the section width in millimeters, meaning how wide the tire is across the tread. The second number is the aspect ratio, meaning how tall is the sidewall from rim to tread as a percentage of the section width. The last number is the rim diameter in inches.

On our bikes, the stock rear is 180/70/15, meaning the section width (tread width) is 7.09 inches or 180 millimeters. The aspect ratio is 70% of 180, meaning 126 millimeters or 4.96 inches. So the total tire height from tread on the ground to the tread on the top is (diameter, including rim) is 24.92 inches or 633 millimeters.

By changing to the tire I use, I am decreasing the section width (180 millimeter to 170 millimeter) and increasing the aspect ratio (from 70% to 80%), thus making the tire taller in overall diameter. The following chart is from Senior Member Whiting57:

Tire____________170/80-15___180/70-15___200/70-15
Sidewall Height_____5.35________4.96________5.51
Section Width______6.69________7.09________7.87
Overall Diameter___25.71_______24.92_______26.02
Circumference_____80.77_______78.29_______81.76
Revs per mile_____784.49______809.27______774.99

Now, how does this translate into rpm at speed. Take the revs per mile listed (it is actually the engine revolutions at the crank per every 10 mph) and multiply it by the speed you are looking for.

On the stock rear tire, at 70 mph, is 7 X 809.27 or 5,664.89 rpm; the engine can handle this sustained rpm without problem (as an aside, my son's 82 KZ550 LTD is turning over 6,000 at 70 and I have held 90+ mph or 7000+ rpm for miles on end trying to keep up with big bore bikes on my V9D with zero problem, but it took me a lot of getting used to). With the 170/80 tire, it is 5491.43 rpm at 70 mpg. 170 rpm doesn't sound like a lot, but at speed, to me, it makes a difference. The 200/70 is 5424.93 rpm at 70 mph. There are those who put a 230/70 and 240/70 tires on the rear.

There are the ScootWorks front and rear pulleys. The premise here is like on a multispeed bicycle; the larger the front sprocket (more teeth), the fewer cranks of the pedals required to maintain a given speed, and on the rear, the smaller the sprocket (fewer teeth) for fewer cranks to maintain a given speed. According to the Scootworks site (http://www.scootworks.com/shop.cgi/p...223118943.2313), the front pulley is up two teeth over the stock front pulley and the rear is down four teeth over the stock rear pulley for a 5.9% or 6.1% reduction in rpm at speed. You can combine pulleys and tire sizes to suit your needs and budget. Thus, with the stock tire size, at 70 mph, would be 809.27 X .941 (1 - .059) X 7 or 5330.66 rpm for a front pulley and 5319.33 rpm for a rear pulley. Front pulley and 170/80 tire would be 5167.43 rpm at 70 mph, rear would be 5156.45 rpm at 70 mph. Some do one or the other pulley mod, some do both.

As for modification, none was needed for the 170/80, but from what I have read, for the 200 and up, modifications are needed (inner fender, pulley change, new belt).

As for drive-ability, I've noticed no negative. Take off is just as good and I can run higher speed in each gear before I feel she needs to shift. Works much better in the twisty two-laners; I can run 40 to 45 mph in second and not feel I am hurting the engine yet still have plenty of pull to not be a snail to those behind, even two-up.

Price wise, the pulleys are kind of expensive (I would suggest only purchasing new pulleys; from what I have read, the older ones had an issue with a belt squeal) and the 200+ tires are spendy. The 170/80 are cheaper than the 180/70, handle just as well if not better, and were the cheapest way I could find to drop rpm for now.

Those with experience with different combos of pulleys and tire size, chime in with your opinions as to how these mods helped make the best midsize cruiser on the market even better.

Hope this helps.

2006 VN900 Classic LT - Red and Black
Stage III Stock Pipes - K&N Filter in Stock Box - Amsoil - 170/80 Kenda Kruz - Saddlemen Explorer - Willie & Max Windshield Bag - Mutazu Passenger Floor Boards - Shorai Heavy Duty Battery - Kawasaki Lowers - Black Universal Trunk mounted on Mutazu Rack - Osram 70/65w Plus 50

Last edited by King43; 07-04-2011 at 12:24 PM.
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post #8 of 17 (permalink) Old 07-04-2011, 02:37 PM
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Quote:
Originally Posted by King43 View Post
170/80/15 versus 180/70/15. The first number is the section width in millimeters, meaning how wide the tire is across the tread. The second number is the aspect ratio, meaning how tall is the sidewall from rim to tread as a percentage of the section width. The last number is the rim diameter in inches.

On our bikes, the stock rear is 180/70/15, meaning the section width (tread width) is 7.09 inches or 180 millimeters. The aspect ratio is 70% of 180, meaning 126 millimeters or 4.96 inches. So the total tire height from tread on the ground to the tread on the top is (diameter, including rim) is 24.92 inches or 633 millimeters.

By changing to the tire I use, I am decreasing the section width (180 millimeter to 170 millimeter) and increasing the aspect ratio (from 70% to 80%), thus making the tire taller in overall diameter. The following chart is from Senior Member Whiting57:

Tire____________170/80-15___180/70-15___200/70-15
Sidewall Height_____5.35________4.96________5.51
Section Width______6.69________7.09________7.87
Overall Diameter___25.71_______24.92_______26.02
Circumference_____80.77_______78.29_______81.76
Revs per mile_____784.49______809.27______774.99

Now, how does this translate into rpm at speed. Take the revs per mile listed (it is actually the engine revolutions at the crank per every 10 mph) and multiply it by the speed you are looking for.

On the stock rear tire, at 70 mph, is 7 X 809.27 or 5,664.89 rpm; the engine can handle this sustained rpm without problem (as an aside, my son's 82 KZ550 LTD is turning over 6,000 at 70 and I have held 90+ mph or 7000+ rpm for miles on end trying to keep up with big bore bikes on my V9D with zero problem, but it took me a lot of getting used to). With the 170/80 tire, it is 5491.43 rpm at 70 mpg. 170 rpm doesn't sound like a lot, but at speed, to me, it makes a difference. The 200/70 is 5424.93 rpm at 70 mph. There are those who put a 230/70 and 240/70 tires on the rear.

There are the ScootWorks front and rear pulleys. The premise here is like on a multispeed bicycle; the larger the front sprocket (more teeth), the fewer cranks of the pedals required to maintain a given speed, and on the rear, the smaller the sprocket (fewer teeth) for fewer cranks to maintain a given speed. According to the Scootworks site (http://www.scootworks.com/shop.cgi/p...223118943.2313), the front pulley is up two teeth over the stock front pulley and the rear is down four teeth over the stock rear pulley for a 5.9% or 6.1% reduction in rpm at speed. You can combine pulleys and tire sizes to suit your needs and budget. Thus, with the stock tire size, at 70 mph, would be 809.27 X .941 (1 - .059) X 7 or 5330.66 rpm for a front pulley and 5319.33 rpm for a rear pulley. Front pulley and 170/80 tire would be 5167.43 rpm at 70 mph, rear would be 5156.45 rpm at 70 mph. Some do one or the other pulley mod, some do both.

As for modification, none was needed for the 170/80, but from what I have read, for the 200 and up, modifications are needed (inner fender, pulley change, new belt).

As for drive-ability, I've noticed no negative. Take off is just as good and I can run higher speed in each gear before I feel she needs to shift. Works much better in the twisty two-laners; I can run 40 to 45 mph in second and not feel I am hurting the engine yet still have plenty of pull to not be a snail to those behind, even two-up.

Price wise, the pulleys are kind of expensive (I would suggest only purchasing new pulleys; from what I have read, the older ones had an issue with a belt squeal) and the 200+ tires are spendy. The 170/80 are cheaper than the 180/70, handle just as well if not better, and were the cheapest way I could find to drop rpm for now.

Those with experience with different combos of pulleys and tire size, chime in with your opinions as to how these mods helped make the best midsize cruiser on the market even better.

Hope this helps.
King, you're in the right area, but your numbers don't quite add up.
Assuming Whiting57's tire size info is correct, and with the vn900's final drive ratio of 4.338/1 in fifth gear- that means the engine turns 4.338 revolutions to turn the drive tire once.
At 60 MPH, with the standard tire, the engine will turn 3510 times to go a mile, or 3510 RPMs. Since 70 MPH is 1.1667 times greater than 60 MPH, or 16.67% greater, then the engine will be turning 4095 RPM at 70 MPH with the standard tire (or any tire!). This equates to what most of us with tachs see at 70 MPH indicated.
With the non-standard 170/80/15 tire, the RPM's to achieve 70 actual MPH will be 3970, and with the non-standard 200/70/15 tire, the RPMs at 70 actual will be 3922.

The difference between the standard tire and the 200/70/15 tire is a 4.2% reduction in engine RPM to achieve the same highway speeds. This compares favorably with the aftermarket pulleys which offer a 5.9% reduction in highway RPMs over the stock setup.

The reason that "actual" and "highway" are in bolds above is because only the actual "over-the-road" speeds will change. Nothing that you do with either tires or pulleys will show-up as any change in the relation between speedometer vs. tachometer speeds!
This is because the speedometer reads only the drive pulley shaft RPM and converts that to a speedometer indication. The relationship between fifth-gear output shaft rotational speeds and speedometer speeds will always remain constant no matter what size pulley; or no pulley at all, for that matter!
Changing to a larger drive pulley, or a larger rear tire will only make your bike travel faster down the road for any given speedometer reading you had before. Since we know that the factory speedometers are off by about 10% on the fast side, then a 4%,5%, or 6% change through either a tire upgrade, or a pulley upgrade (or both!) will get your speedometer a lot closer to what's actually going on, and will allow your engine to turn at a lower RPM speed at the road speed desired.
Hope this helps.

Ron in Cincinnati

Wish I didn't know now what I didn't know then.
.........Bob Seger

Last edited by pacomutt; 07-04-2011 at 02:51 PM.
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post #9 of 17 (permalink) Old 07-04-2011, 04:06 PM
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In my opinion adding a taller tire doesn't really make much difference. I first started by replacing the rear 180 to a 200 tire and the difference in lower rpms is hardly noticeable. Then I added the front scootworks pulley and with both larger tire and pulley bikd will start to reve at 75mph. Then I added a rear scootworks pulley in adition to the front sw pulley and the larger tire and now i'm very happy with the results. Now I can cruise at true 80mph without the buzzing and can clearly see the vehicles behind me on the rear view mirrow. I recomend to upgrade to the 1700 but if you decide to stay with a 900 then i will recomend the pulleys over a taller tire due to it's a one time expense over a tire that needs to be replaced often.


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post #10 of 17 (permalink) Old 07-04-2011, 05:11 PM
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Quote:
Originally Posted by pacomutt View Post
At 60 MPH, with the standard tire, the engine will turn 3510 times to go a mile, or 3510 RPMs. Since 70 MPH is 1.1667 times greater than 60 MPH, or 16.67% greater, then the engine will be turning 4095 RPM at 70 MPH with the standard tire (or any tire!). This equates to what most of us with tachs see at 70 MPH indicated.
With the non-standard 170/80/15 tire, the RPM's to achieve 70 actual MPH will be 3970, and with the non-standard 200/70/15 tire, the RPMs at 70 actual will be 3922.

The difference between the standard tire and the 200/70/15 tire is a 4.2% reduction in engine RPM to achieve the same highway speeds. This compares favorably with the aftermarket pulleys which offer a 5.9% reduction in highway RPMs over the stock setup.
I agree with Ron. I have Pirelli Night Dragon tires, a 200 rear and a Scootworks rear pulley. The reduction that I saw and felt, is almost perfect for my needs. I can't state exact numbers because I don't trust the tach, speedometer and GPS readings to be completely accurate. But at approximately 70 mph on the GPS, I'm seeing a tach reading of about 3800.

As V Twin says above, at 75 mph, the bike starts getting a little buzzy again. If I find that I'm doing a lot more freeway riding, I'll probably install the Scootworks front pulley as well.

As for modifications, I did not need any to install the 200 rear tire. It fits fine with either all stock pulleys or with the Scootworks rear pulley installed. It would not work in combination with a Scootworks front pulley and stock rear pulley. I like the looks and handling of the Pirelli tires and I'll probably continue to use the 200 on the rear, even if I go to a Scootworks front pulley.

2010 Vulcan 900 Classic LT
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