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What are the pros and cons of switching a 120/60 front to a 120/70 front? I have heard that the 70 turns in slower than a 60 (makes sense) but the 70 is more stable and helps to protect the rim edge better. Anything else? Thanks.

 

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My advice would be to go with the 70-series if you ride on the street...I've seen a fair amount of tweaked rims from 60's (though granted the people with the dinged rims weren't the types to closely monitor tire pressure /images/icons/laugh.gif). Any difference in steering can be compensated for by raising/lowering the forks in the triple clamps to suit your preference.

Then again, I live in NY, which could explain a lot...

-nominal_squid-
SMUSA #11
 

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Put the OEM Specified tire size on it. A rim made for a 160 tire will be protected fine by a 160 tire, a rim made for a 170 would probably do better with a 170. If you are racing, or riding in a controlled enviornment, you can fol around with different sizes to get specific results but on the street, probably better off going with spec.

 

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Stick with the OEM size: A lower profile has less rubber available for gripping the road. If you want quicker steering, lower the front or raise the rear....

Scott /images/icons/smile.gif

 

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i noticed in the specs for sportbikes, tire size is always listed but not the rim size. for instance if on a f4i and an r6 both the front and rear rim are the same size then if you wanted you could easily change the front tire of the r6 to a 70 or the other way around and change the f4i to a 60, if both manufacturers have the same size rim and if that rim fits either size tire equally well then i guess it'd be up to the rider whatever he felt more comfortable with, right? wrong? if someone could clear this up for me. of course unless the tire size has more to do with the rim size, such as suspension set up, how the weight is ditributed along the bike etc...then of course its best to go according to the specs. i hope this doesnt sound confusing, could someone clear that up for me? thanks
 

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changing the profile changes the rolling diameter, which of course changes the ride height... and will affect stability/quickness of steering... it will also make your speedo error increase unless you have one that uses a sending unit on the trans output shaft (like the new gixxers).

 

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catsis - thanks
i also wanted to clear up that i hope my post didnt sound like a wiseguy comment, i had no intention of coming across that way. im honestly probably the least informed person there is about bikes. and i really am curious about tire/rim size topics. on that note i was wondering if someone knows where one could find listings of each bikes rim size since the tire size is always listed but never the rim size. also do the f4i, gsxr600 and the r6 have the same size front and back rim? and while im asking all this, i hope this last question doesnt tip the scale against me but how is it that some manufacturers give you the option of the size tire you want on the rim, such as the aprilias rsvmlle's spec it says you can choose between a 180 or 190 rear tire? i know i said there was going to be only one more but i was also wondering when suzuki decided to change the rear tire on the gsxr750 from a 190 to a 180 did the rim size also change along with it? thanks for bearing with me.
 

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<blockquote><font size=1>In reply to:</font><hr>

it will also make your speedo error increase unless you have one that uses a sending unit on the trans output shaft (like the new gixxers).


<hr></blockquote>

Actually, that's a poor system as far as compensating for gearing changes and rolling diameter. The sensor will read the same regardless of the fact that you went up 3 teeth in the rear, down 1 in front, changed your tires or whatnot. Better is to read off the wheel or rear brake rotor - Gearing changes won't affect how that sensor reads. Even better to read speed off the front wheel - Most people stick to stock sizes there, and there's no gearing to change.

<blockquote><font size=1>In reply to:</font><hr>

also do the f4i, gsxr600 and the r6 have the same size front and back rim? and while im asking all this, i hope this last question doesnt tip the scale against me but how is it that some manufacturers give you the option of the size tire you want on the rim, such as the aprilias rsvmlle's spec it says you can choose between a 180 or 190 rear tire? i know i said there was going to be only one more but i was also wondering when suzuki decided to change the rear tire on the gsxr750 from a 190 to a 180 did the rim size also change along with it? thanks for bearing with me.

<hr></blockquote>

Ok - The size tire you should choose is most related to the size of your rim 5.5 inch should be about a 180, 6 inch should be a 190. The reason you might get an alternate fitment is because a tire can often work well on a slightly larger rim - 180 on a 6" (like the Aprilias). In general, though - You want to run the smallest tire that gives you enough grip for best (fastest) handling. Hence the 180 on the larger rim.

As far as different manufacturers putting the same tire sizes on bikes in the same class - It makes sense that they are all working off a nearly identical set of requirements so they would choose the same tires to fit. So 600s will often use 170s - They steer faster than 180s and grip plently well enough for the motor's output. As long as there's 'enough' grip, going up a size only hurts - Unless you're only concerned with 'pose points.'

The short answser is you should stay with whatever tire sizes and profiles the manufacturer recommends. You could experiment ONE size on any direction, but it's been my experience that I've always ended up back at the stock size.

Hope that helped!

Scott /images/icons/smile.gif


 

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You can easily see that the F4i does not have the same rim size front and back. The rear rim is much wider than the front as a quick visual inspection will show. I assume that the same is true of the R6 and GSXR. I havent really looked at the other two but I think I would have noticed if they were the same. The same rim will allow for some variation in tire size, but not much, you could not swap front and rear tires (also, I doubt that the forks themselves would have enough clearance to even fit the rear tire between them.).

Yes, there are other considerations than rim size, but that's why they use different rim sizes - so the proper size tire will fit! What makes a proper size tire does have to do with weight distribution, traction distribution, turn in properties, suspension properties and probably other things that I can't think of off-hand. Use the OEM - again unless you have a specific problem to solve for a specific set of circumstances, and you really know what you are doing.

 

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jxL&scotteq and everyone else thanks for all the help and info. really appreciate it.
 
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