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This is interesting. Based largely on what I read here in the forums I recently changed from a 180/60 rear tire to a 180/70 on my GL1800. Two reasons: first it was said it would correct my speedo error, which was an actual 73 mph on my GPS when my speedo read 75 mph. Secondly, it was said it would help to get it up onto the centerstand.

Well, it did correct the error....but in my opinion, made it worse. Now, at 75 mph my GPS shows 76-77 (bounces back and forth). Two things affect me mentally about this: first it was always comforting to know that at 75-76 mph on the freeway that I was safe speedwise. Now I'm running over that limit; just effects my mental attitude.

Secondly, it was always comforting to know I was getting about 39-40 mpg (but in actuality was kidding myself). Now I'm getting 36-37 mpg and no better. Again, it's a matter of mind over matter (or reality). Technically a large diameter should give better mileage but that's the best I've done in 1600 miles on the new tire. Sometimes I'd rather be fooled, especially when my Harley friends tell me about the 43-45 they are getting on their Ultra Classics (with permium fuel of course).

As to the center stand, well, I haven't tried it yet but will in the next few days; it's been 12,000 miles on my last oil change; it's starting to change color from goldish to a dark brown; is time.

BTW, when I put the new rear tire on, the old tire (Elite 3) had 14,600 miles and was cupped quite a bit despite religously maintaining pressure; it had lots of tread left and should have gone another 2-3,000 miles. My current front tire with 10,000 miles is still super duper.

Next tire I'm going back to the 180/60.
 

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A larger diameter tire will affect overall gearing and it takes more power to turn. Most likely the culprit in your gas mileage concern.
 

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cycleman wrote:
A larger diameter tire will affect overall gearing and it takes more power to turn. Most likely the culprit in your gas mileage concern.
More torque.. but not more power... and the lower calculated gas mileage (as correctly pointed out in the original post) is a figment of the speedo change.. not a reality..
 

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sandiegobrass wrote:
More torque.. but not more power... and the lower calculated gas mileage (as correctly pointed out in the original post) is a figment of the speedo change.. not a reality..
Exactly. The best way to check mileage would have been to set up the GPS for a trip from point A to point B, record how far it is, and then measure how much fuel it takes to drive that distance at a set speed (as measured on the GPS) with the old tires.

Then, repeat the exact same test with the new tires and see the difference.

The GPS is not affected by speedometer or odometer error. Both the speedometer and the odometer are affected by the tire diameter. The larger the tire, the more error (reading low) that the speedometer AND the odometer will read.

A 180/70 tire is approximately 6% larger in diameter than a 180/60 tire. Therefore, when calculating your new mileage, multiply your measured mileage by 1.06 before doing the equation to get the MPG. That should give you a bit more accurate representation.
 

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Does an 1800 use the rear wheel drive to measure distance. On my 1100, my GS and all my prior bikes the front is used to measure for the odo and speedo?
 

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1800 Goldwing has a lot more horse power then a HD that is the reason for lower gas mileage:toast:.
 

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fgh wrote:
Does an 1800 use the rear wheel drive to measure distance? ....
I am not an 1800 guy.. so not the best person to answer but my answer assumes yes.. my understanding it there isa speed sensor on the output shaft.. Maybe Kit or another 1800 person can confirm..
 

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Keep in mind that with the 60 rear tire, we are reading more miles than is reality. With the 70 tirewe are reading closer to real miles traveled. So ifwe got better mileage with the 60, it is only becausewe were getting an inflated odometer reading. There is no reason mileage would go up with a 70 series rear tire, becausewe are reading a more realistic number of miles to the gallon of gas used.

:walker:
I find it harder to put the GL1800 up on the center stand with the 70 rear tire. I also found that the tire would just touch the ground when up on the center stand, making it harder to do a inspection for nails and road debris. I solved this by making up some simple 1/8 thick spacers that I have attached to the center stand "feet". Just adding 1/8 inch to the center stand makes the bike roll up and also off the center stand quite easy. Also the tire now clears the ground by 5/8 inch for inspections.
The biggest advantage I enjoy with the 70 series tire is the added clearance while leaning in the twisties. Also, not all 70 series tires are the same. After much research I have found that the Bridgestone G850 Exedra gives me the best performance under all riding conditions. The 70 series rear tire, tread wear is only good for about 10,000 miles. After several G850's, the excellent performance throughout the tire life, for me, makes this my tire of choice. But I am always looking!!!!!!:madeyes:
 

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sandiegobrass wrote:
fgh wrote:
Does an 1800 use the rear wheel drive to measure distance? ....
I am not an 1800 guy.. so not the best person to answer but my answer assumes yes.. my understanding it there isa speed sensor on the output shaft.. Maybe Kit or another 1800 person can confirm..
Yes that is where it is at, on the right side of the bike. Kit
 

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Looks like the questions have been bantered about so i'll leave that be . Instead just a :waving:Hello from over the hill in San Antonio.
 

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The rear tire I am running now (we won't get into that)is about 5% larger circumference than the 180/60. I still get the same fuel mileage as before using the odometer so I am actually getting about 5% better gas mileage with a larger tire.
 

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Twelve thousand miles on an oil change seems rather lengthy to me. Even if it's a synthetic unless it was done in a fairly short period of time.
 

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Interesting thing about speedo/odo on the 1800.

I investigated it quite carefully and determined that my speedo was out by 4.8%, compared to the GPS, this was an average of a number of readings on different trips.

The odo was also out, but not by the same percentage, only about 3%.

After I fitted a SpeedoHealer and set the correction factor to -4.8% I checked the speedo again, both with the GPS and a stopwatch over a measured 10km on the Trans Canada.

The speedo was right on the money, at an indicated 100kph the 10km should take 6 mins, which is what I got +/- 1 sec.

Now the odo is corrected by the same factor, so it is -1.8% out.

Presumably, when Honda put in whatever factor to convert sensor pulses, the factors must be slightly different for speed and distance. It makes sense that the speedo would read a little higher than the odo, so as not to break the laws that say a speedo must never read less than actual speed.

I don't think the speedo acuracy is such a big deal, except that my truck and the wife's van both read correctly using the same GPS, so I wanted the bike the same.
 
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