Lowering ST by Rear tire size (Diameter)

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I could not find by searching any info on subject. Maybe did not use the best key words.

Has any of you tried a smaller diameter rear tire to lower the bike a tad ? Maybe a 3/8" to 1/2" ?

I'm sure it would throw the speedometer off more than it already is, but that's my question for today.

:confused:
 
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To lower by 1/2",,, you would need a 1" dia smaller tire,, which is a lot. But it is doable. I lowered the overall drive ratio of my CB's,, and a sports car,, by doing the same thing. This meant my engine was not turning so fast for a given highway speed. Don't worry about your speedometer,, as far as I know,, that comes from the front tire. cat'
 

dduelin

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The ST1300 runs a 170/60 series tire OEM. Tires smaller in overall diameter might be a 55 or 50 aspect ratio in a 180 or 190 width. In theory a 180/50-17 would lower the rear by 12 mm or 1/2". Good luck in your search for a 180/50ZR17.

A smaller diameter rear wheel will increase engine revs per mile so the speedometer and fuel mpg data error will increase. The ST1300 speedometer speed sensor is transmission mounted and measures mph by output shaft rotational speed - the rear wheel.
 

Byron

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Have you already looked into just a lower seat? You might get the lowering you want without the expense of changing the suspension. If you lower the rear you're going to have to lower the front as well.
 
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Sorry for the confusion,,, yes, you are right. In my case mentioned before,, on the CB's and a sports car,, I mounted larger tires too reduce my engine rev's at a given speed. Also,, it is good to know,, that the ST13 senses off the rear wheel. I too am moving to a slightly smaller rear tire in the coming weeks,,, and will be able to see the increased discrepancy on between my speedo and my gps. Currently,, the speedo runs fast by 2-3%,,, and the smaller rear tire will add a %1 to that error. Cat'

Huh???

Would be the opposite. Smaller tires and you need to spin them faster, via higher engine RPM, to maintain the same speed.
 
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Ken Valkyrie
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To lower by 1/2",,, you would need a 1" dia smaller tire,, which is a lot. But it is doable. I lowered the overall drive ratio of my CB's,, and a sports car,, by doing the same thing. This meant my engine was not turning so fast for a given highway speed. Don't worry about your speedometer,, as far as I know,, that comes from the front tire. cat'
Thanks - good point on the speedo
 
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Ken Valkyrie
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The ST1300 runs a 170/60 series tire OEM. Tires smaller in overall diameter might be a 55 or 50 aspect ratio in a 180 or 190 width. In theory a 180/50-17 would lower the rear by 12 mm or 1/2". Good luck in your search for a 180/50ZR17.

A smaller diameter rear wheel will increase engine revs per mile so the speedometer and fuel mpg data error will increase. The ST1300 speedometer speed sensor is transmission mounted and measures mph by output shaft rotational speed - the rear wheel.
Uh-Oh ... dduelin states speedo sensor is trans mounted - then a tire dia. change would increase the speedo error
 
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Ken Valkyrie
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Have you already looked into just a lower seat? You might get the lowering you want without the expense of changing the suspension. If you lower the rear you're going to have to lower the front as well.
I do have my seat in lowest position (for my 28 ish inseam).

I have a Russell Day Long seat, that although they said their new height would be insignificant, it was quite a bit higher on mine for me.
I went to great lengths to remove a good 1 1/2" of excess foam from that seat, I removed it from where the foam met the seat pan,
in order to avoid messing with the seat pocket shape. That worked out very well, but who wants to alter a $800. seat.

I did just lowered the front by slipping the front forks about 3/8" inch. That feels better and gets me a little more flat footed at stops.
see earlier post: "Front Forks Raised" .

I'll take a look around at some tire sizes to see whats available in a 50 aspect ratio.

Thanks guys
 
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My 2 cents on the topic is that the tire size on the sidewall is more of a "nominal" size than exact. You could get 4 tires from different mfrs, all with the same nominal size, and they would all be slightly different in terms of their actual rolling diameter. Years ago I compiled that info on various front/rear tires for the ST1100, all the same nominal size, but different in rolling circumference by as much as a couple inches IIRC. Also, I'm not sure that you could get an exact measurement without mounting the tire on the rim, as they will all "bulge" a bit differently when mounted. You could estimate by standing them all side by side before mounting to get an approximation of the smallest diameter tire and try that one first.
 

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I do have my seat in lowest position (for my 28 ish inseam).

I have a Russell Day Long seat, that although they said their new height would be insignificant, it was quite a bit higher on mine for me.
I went to great lengths to remove a good 1 1/2" of excess foam from that seat, I removed it from where the foam met the seat pan,
in order to avoid messing with the seat pocket shape. That worked out very well, but who wants to alter a $800. seat.

I did just lowered the front by slipping the front forks about 3/8" inch. That feels better and gets me a little more flat footed at stops.
see earlier post: "Front Forks Raised" .

I'll take a look around at some tire sizes to see whats available in a 50 aspect ratio.

Thanks guys
Since you've already lowered the forks you may want to look at a lowered rear shock. You can find more information in this thread.
 

ST Gui

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Ken Valkyrie said:
I'm sure it would throw the speedometer off more than it already is, but that's my question for today.
You are correct sir! It would read an even higher speed than now. It would also affect your gas mileage negatively. Your tach would show more RPM at any given speed than before. (The last bit wouldn't be an induced error.)

By raising the forks in the triple clamps you decrease trail and quicken the steering. It may or many not be noticeable depending on the delta and your sensitivity. Maybe other factors would affect that change such as a bunch of gear on the front end: tank bag gps phone Vulcan etc.

Going to a shorter shock would mean reduced travel in the rear. But if the spring and dampening were sorted better than the stocker you might break even or better in the travel and comfort dept.

A shorter shock instead of a significantly smaller tire means you speedo and mileage and LCD panel wouldn't be affected. Pricier than a tire but maybe a better alternative. That's how I'd roll.

Though if you did find a tire that fit your bill it might tell you if going to a shorter shock is worth the effort for a height change before investing more time and money.
 
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Ken Valkyrie
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Byron & ST Gui - "Thanks" for your input also, all good info.

After searching some tire companies I see what you all say " good luck finding a tire with a smaller aspect ratio" in the ST size. I Couldn't find a 170/55-17.
With my lowered front by slipping the forks and gouging out some foam to lower my seat I'll probably be satisfied, (Ha !!! maybe)
I still may look into a "shorter shock" as ST Gui mentioned.

As you all can see by my age, I need to be planted good at stops, it aids me while my wife is getting on & off and it helps when paddle-ing around in my garage to turn the bike around. I love my ST, handling, ride & performance: so I keep tweaking & modifying it to fit my needs.

Well, enough about me :bow1:
Thanks for your input
 
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I have an 1100, and went from a 70 series to a 60 series tire. I did bump up the width one size, so it only lowered it 1/2 an inch. Between that, my lowered Works shock and Daytona M-Star boots, I can flatfoot the bile. That is with a tall Russell too. I also raised the forks 1/2 an inch.
 
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Lowering the rear suspension without a corresponding lowering of the front shifts the load to the rear tire. This makes the front "light" which you WILL notice in a headwind, near semis, and on bumpy roads. The bike will want to go into a tankslapper and you won't be able to take both hands off the bars at the same time. Ask me how I know.

YMMV.
 
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I could not find by searching any info on subject. Maybe did not use the best key words.

Has any of you tried a smaller diameter rear tire to lower the bike a tad ? Maybe a 3/8" to 1/2" ?

I'm sure it would throw the speedometer off more than it already is, but that's my question for today.

:confused:
smaller tire might have a lighter load capacity - 180/50 or 180/55 get pricey. Dig deep into the closet and find your old platform shoes !!
 
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