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 tire size flip flop
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Nightwatchman
Male Standard Member
135 Posts


Littleton, CO
USA

Honda

Shadow Spirit 750

Posted - 09/07/2012 :  2:52 PM                       Like
Would it be considered unwise to put a 170/80/15 rear tire where there was once a 160/80/15?

SkootchNC
Male Advanced Member
1062 Posts
[Mentor]


raleigh, north carolina
USA

Harley-Davidson

road glide

Posted - 09/07/2012 :  4:26 PM
quote:
Originally posted by Nightwatchman

Would it be considered unwise to put a 170/80/15 rear tire where there was once a 160/80/15?



it's "only" 10mm. BUT..... (and there is always a but) there are two very important things you must find out first.....
1) RIM width.... will the 170 tire's bead fit into your rim (look up the tire manufacturer site, and read the charts)
2) width of your swing arm/fender.... you MAY... or may not have enough room

Plus... you need to look at "load rating" ... not all tires carry the same load, even within a "family"

an example of a tire chart: (for informational uses, I selected the Dunlop Elite-3).

http://www.dunlopmotorcycle.com/tir...lite-3-bias/
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scottrnelson
Advanced Member
6950 Posts
[Mentor]


Meridian, ID
USA

Honda

XR650L, 790 Adv R

Posted - 09/07/2012 :  5:07 PM
Many tire manufacturers list what rim sizes may be used with which tires.

I'm familiar with the Ducati 17 inch rims that were 4.5" and 5.5" wide. The 4.5" rim took a 160 and was too narrow for a 170 tire. The 5.5" could take a 170 or a 180 and I've used both sizes of tires on that size rim.

Putting a 170 on a 4.5" rim would squeeze it a bit too much, distorting the shape of the tire. You would be likely to get less cornering traction from the wider tire in that particular case.

Also, pay careful attention to how much room you have. Way back in the 80's when I had a Yamaha RZ-350, it came with a 110/80-18 rear tire. The local Yamaha shop convinced me to replace that with a 120/90-18 when it wore out. That wasn't just one size bigger, but two sizes bigger and although the tire didn't touch anything when the bike was at rest, at speed it grew larger and rubbed the swingarm at the center of the tire. It actually wore a grove in the metal of the swingarm matching up with the center groove of the tire. It took me a while to figure out why the bike suddenly had a limited top speed, and why there was much more smoke behind me than normally comes out of a two-stroke engine. At least I learned a lesson from that stupid move.
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Daddio
Male Advanced Member
775 Posts
[Mentor]


Calera, AL
USA

Suzuki

Bandit 1250

Posted - 09/07/2012 :  6:56 PM
That will also affect your speedometer reading. If your speedo used to say 50 mph you will now be going about 53 mph actual and still read 50 mph on the speedo.
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James R. Davis
Male Administrator
17378 Posts
[Mentor]


Houston, TX
USA

Honda

GoldWing 1500

Posted - 09/07/2012 :  7:18 PM Follow poster on Twitter  Join poster on Facebook as Friend  
I really dislike being a killjoy, but ...

Your bike was designed starting with the tires. Your suspension and tires are a closely interactive and tightly designed system. (By the way, the fact that your speedometer will be off demonstrates the tie-in to total bike design.)

Anyway, there might be a really good reason to change the tires the way you want to, but you apparently don't have any idea what the change will cause - in handling, for example. Thus, it does not seem like you start with that reason.

I know of no 'really good reason' to do as you want (and apparently the designers of your bike didn't either).

I can tell you that whether or not there is a safety issue, if you have an accident and your insurance company (their lawyers) find out that you have non-standard tires on the bike, you will have a VERY HARD time winning a claim against them if they can show that the tires were in any way causative. Is it worth it?
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kacinpa
Male Advanced Member
802 Posts
[Mentor]


Lansdale, PA
USA

Triumph

Sprint GT

Posted - 09/07/2012 :  8:05 PM
quote:
Originally posted by Daddio

That will also affect your speedometer reading. If your speedo used to say 50 mph you will now be going about 53 mph actual and still read 50 mph on the speedo.



I don't understand why changing the rear tire size would change the speedometer accuracy. Isn't the speedometer driven by a sensor on the FRONT wheel?

NOT that I think going with a different size tire than the manufacturer recommends is a good idea, I just don't see how the rear tire size would make the front tire's rotations per mile change.
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Nightwatchman
Male Standard Member
135 Posts


Littleton, CO
USA

Honda

Shadow Spirit 750

Posted - 09/08/2012 :  12:41 AM
Something about it didnt seem quite right to me... thats why I asked you all... thank you!
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SkootchNC
Male Advanced Member
1062 Posts
[Mentor]


raleigh, north carolina
USA

Harley-Davidson

road glide

Posted - 09/08/2012 :  6:28 AM
quote:
Originally posted by kacinpa
[br
I don't understand why changing the rear tire size would change the speedometer accuracy. Isn't the speedometer driven by a sensor on the FRONT wheel?

NOT that I think going with a different size tire than the manufacturer recommends is a good idea, I just don't see how the rear tire size would make the front tire's rotations per mile change.



It depends on HOW your bike determines speed.

If your speedometer gets the imput from the front wheel..... then changing rear tire size has no effect.
If the input comes from the transmission.... then changing tire (overall) diameter will effect speedo readings
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Daddio
Male Advanced Member
775 Posts
[Mentor]


Calera, AL
USA

Suzuki

Bandit 1250

Posted - 09/08/2012 :  7:04 AM
Thanks Skootch
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Indiana Randy
Moderator
2118 Posts
[Mentor]


Fort Wayne, Indiana
USA

Honda

2000 Magna V4 750

Posted - 09/09/2012 :  7:47 AM
I went up one size on the rear of my bike because I thought it would 'look better'. And it Did, IMO. However, it changed the handling of the bike. It felt like the bike was now falling into tight turns and silly as it sounds, felt like I was always riding slightly down-hill.

Although a one up tire size will most likely 'fit' your bike, my advice is to stay with the original tire size.
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kacinpa
Male Advanced Member
802 Posts
[Mentor]


Lansdale, PA
USA

Triumph

Sprint GT

Posted - 09/09/2012 :  7:47 PM
quote:
Originally posted by SkootchNC

quote:
Originally posted by kacinpa
[br
I don't understand why changing the rear tire size would change the speedometer accuracy. Isn't the speedometer driven by a sensor on the FRONT wheel?

NOT that I think going with a different size tire than the manufacturer recommends is a good idea, I just don't see how the rear tire size would make the front tire's rotations per mile change.



It depends on HOW your bike determines speed.

If your speedometer gets the imput from the front wheel..... then changing rear tire size has no effect.
If the input comes from the transmission.... then changing tire (overall) diameter will effect speedo readings



Indeed. But the Shadow Spirit 750 - the bike in question - has the speedometer connected to the front wheel. So in this particular case no change to reported speed would be noted.
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Nightwatchman
Male Standard Member
135 Posts


Littleton, CO
USA

Honda

Shadow Spirit 750

Posted - 09/11/2012 :  3:27 PM
Gosh it seems that a different tire size would be extremely unwise! Looks like my very limited selection of tires will remain limited. Oh well....
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