Lower performance sneaks up on you - Kawasaki Vulcan 750 Forum : Kawasaki VN750 Forums
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post #1 of 9 (permalink) Old 12-17-2010, 03:32 PM Thread Starter
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Lower performance sneaks up on you

Bike seemed to be running good. Thought it was time to run some Sea Foam thru her. Made a BIG difference. Performance, starting, throttle response, etc. Guess my carbs were SLOWLY gumming up. Will do it more often. Picked up a couple of MPG too.
Next project: over sized tires...........................
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post #2 of 9 (permalink) Old 12-17-2010, 05:36 PM
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Bike seemed to be running good. Thought it was time to run some Sea Foam thru her. Made a BIG difference. Performance, starting, throttle response, etc. Guess my carbs were SLOWLY gumming up. Will do it more often. Picked up a couple of MPG too.
Next project: over sized tires...........................
That Seafoam is good stuff. Oversize tires look cool and will lower your rpms a little on the highway. Probably increase your gas mileage even more still. You may lose a little low end with the oversize tire though. I had a 170/80 on the rear and decided to go back to stock. I could tell a difference in take off acceleration with the stock tire on the rear.
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post #3 of 9 (permalink) Old 12-17-2010, 06:03 PM Thread Starter
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will try to runs Sea Foam thru her monthly.
Looking forward to the new tires soon. Front tire to correct the speedo. Checked it with my GPS and at highway speeds it was 7-8 mph off.
I run her hard here in the desert on the open roads, so the lower RPM with the rear tire will help. I don't take off too fast anyways, so that's not a concern.
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post #4 of 9 (permalink) Old 12-17-2010, 06:41 PM
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I see you live in New Mexico. My dad lived in Las Cruces till he passed away. I always liked it out there. It looks like on some of those straight stretches of road you could really air it out if you wanted to.
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post #5 of 9 (permalink) Old 12-17-2010, 08:13 PM
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Quote:
Originally Posted by Jim8208 View Post
That Seafoam is good stuff. Oversize tires look cool and will lower your rpms a little on the highway. Probably increase your gas mileage even more still. You may lose a little low end with the oversize tire though. I had a 170/80 on the rear and decided to go back to stock. I could tell a difference in take off acceleration with the stock tire on the rear.
Jim on a previous thread another member reported the same results that you have with with the oversize rear tire. I have not gone oversize, and am not disputing your report, just doing the math here.

Mathematically the diameter and the circumference should be almost identical between a 150/90-15 and a 170/80-15 rear tire.

150 mm width X 90% aspect ratio = 135 mm sidewall height. (Tire Diameter =651 mm, Circumference ~ 2046 mm, or 80.55")

170 mm width X 80% aspect ratio = 134 mm sidewall height. (Tire Dia.= 649 mm, Cir.~2040 mm or 80.3")

So the 170/80 tire is actually 2 mm (~ 0.08") shorter than the OEM recommended size.
That`s just over 6mm (1/4") difference in circumference. (Only about 1/3 of 1%. That difference will INCREASE tire rotation for the 170/80 tire by less than 3 revolutions per mile.)

I`m not sure what the tread depth is on a new tire, but a worn out 150/90 will likely be a few mm shorter than a new 170/80 tire. I doubt that most riders could notice a difference in acceleration, engine speed or fuel economy between the two sizes.

Desert Dog, previous discussions on changing tires have noted that the odometer is quite accurate with the OEM 100/90 size while the speedo reads about 10% high. The 110/90 oversize tire almost corrects the speedo, but causes the odometer to now read somewhat low. One member decided he would rather have an accurate odometer, and just perform the simple mental math of subtracting 10% from the speedo to calculate his true speed.

Many members have subjectively reported better traction and handling with the oversize tires. The individual rider will have to decide for himself what tires he likes best, and whether an acurate speedo or odometer is more important to him.

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post #6 of 9 (permalink) Old 12-17-2010, 10:35 PM
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Jim on a previous thread another member reported the same results that you have with with the oversize rear tire. I have not gone oversize, and am not disputing your report, just doing the math here.

Mathematically the diameter and the circumference should be almost identical between a 150/90-15 and a 170/80-15 rear tire.

150 mm width X 90% aspect ratio = 135 mm sidewall height. (Tire Diameter =651 mm, Circumference ~ 2046 mm, or 80.55")

170 mm width X 80% aspect ratio = 134 mm sidewall height. (Tire Dia.= 649 mm, Cir.~2040 mm or 80.3")

So the 170/80 tire is actually 2 mm (~ 0.08") shorter than the OEM recommended size.
That`s just over 6mm (1/4") difference in circumference. (Only about 1/3 of 1%. That difference will INCREASE tire rotation for the 170/80 tire by less than 3 revolutions per mile.)

I`m not sure what the tread depth is on a new tire, but a worn out 150/90 will likely be a few mm shorter than a new 170/80 tire. I doubt that most riders could notice a difference in acceleration, engine speed or fuel economy between the two sizes.

Desert Dog, previous discussions on changing tires have noted that the odometer is quite accurate with the OEM 100/90 size while the speedo reads about 10% high. The 110/90 oversize tire almost corrects the speedo, but causes the odometer to now read somewhat low. One member decided he would rather have an accurate odometer, and just perform the simple mental math of subtracting 10% from the speedo to calculate his true speed.

Many members have subjectively reported better traction and handling with the oversize tires. The individual rider will have to decide for himself what tires he likes best, and whether an acurate speedo or odometer is more important to him.
I'm sure your calculations are accurate. I'm sorry but I should have clarified that I'm talking about my Honda Magna 750 rear tire which is a 150/80-15. I assumed the Vulcan was the same size. I know it made a difference in acceleration from the 170/80 to the 150/80. It's been a little while since I owned my Vulcan and was thinking 150/80 was stock on it as well.
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post #7 of 9 (permalink) Old 12-18-2010, 12:35 PM
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Rather than say bigger or smaller tire here, will say bigger circumfrence or smaller circumfrence.

A tire with a smaller circumfrence will raise rpms over a specific speed, but will have better mechinical advantage to make the bike go "quicker" from rest.

A tire with a bigger circumfrence will lower rpm's at a specific speed, and make the bike a bit slower in take off.

I tend not to trust figures on tires, and would prefer measuring any difference myself before making any statements here, hence the above.

Keep in mind that larger circumfrence tire, if it also means wider...may decrease rpm's at a specific speed...saving you fuel...but the wider tire will add more rolling resistance, using more fuel. The two will likely cancell eash other out.

The only realistic advantage I see in a "larger" tire..and by this I mean wider...is to put more rubber on the road. More rubber increases your available traction and is a good thing.


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post #8 of 9 (permalink) Old 12-18-2010, 03:53 PM Thread Starter
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Thanks for all your input guys. Will weigh it all out after the holidays. Have to break out the ruler too.

Jim, I'm about an hour from Las Cruces. Been there many times. Nice city but too crowded fer me. I like it her in the desert. I go to LC or El Paso when I need a "City Fix"!
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post #9 of 9 (permalink) Old 12-19-2010, 10:50 AM
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Quote:
Originally Posted by Desert Dog View Post
Bike seemed to be running good. Thought it was time to run some Sea Foam thru her. Made a BIG difference. Performance, starting, throttle response, etc. Guess my carbs were SLOWLY gumming up. Will do it more often. Picked up a couple of MPG too.
Next project: over sized tires...........................
I put Seafoam in at every other fill up. I take it with me on trips in a fuel bottle if need be.

Never had any carb problems.


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