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Old 08-23-2011, 12:18 AM   #1
easter bunny
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front tire size question

A friend just picked up an 03 R6. It has a 180 rear which makes sense compared to my 190. But the front is a 120/60 where mine has a 120/70. The crown is visually identical, the added height is purely in the sidewall (i.e. no difference in contact patch).

Is there an advantage to the larger sidewall on a literbike? What happens if I decide to save rotating mass and go 120/60 assuming I compensate with fork height in the triples?
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Old 08-23-2011, 09:47 AM   #2
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Re: front tire size question

The SV's and a few others come with the 120/60 as well. We usually bump them up to a 120/70 when they come in for tires. There arent many sportbikes that come with the 120/60 so going to a 120/70 makes it easier when your tire shopping. The taller sidewall will give you a little breathing room when it comes to running out of tire at lean.

The 120/60 is the same as the 190/50. A stupid tire size that has no real benefit except fender clearance on certain bikes.
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Old 08-23-2011, 10:08 AM   #3
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Re: front tire size question

Thanks for the info. I just looked up my old GSXR and it had a 120/70. Not sure why yamaha decided to changes sizes on the R6, but I'll probably just swap it out and lower the front end.

Maybe. Seems odd to add the weight if there's not a lot of difference. Doesn't look like the larger sidewall gives any added lean angle.
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Old 08-23-2011, 10:42 AM   #4
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Re: front tire size question

If you look at the 2 tires after a trackday you will see the difference. It's not alot but it's enough.
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Old 08-23-2011, 11:29 AM   #5
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Re: front tire size question

Please elaborate.

I'm 90% convinced I'll change it out, but what's the difference? Trying to figure out why Yamaha wouldn't put the 70 on the second gen. New ones come with a 70, but they also updated to USD forks. My 01 had a 70 and conventional forks so there doesn't seem to be much logic to it.
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Old 08-23-2011, 12:30 PM   #6
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Re: front tire size question

I dont know why they didnt do it. Could be they didnt want an issue with fender clearance. Some bikes when we put the 70 on the front make some nasty noises until the sticky goo from the labels is wore off because the clearance between the fender and tire wont clear gravel thats picked up. My guess is thats their main reasoning but it's just a guess.

Going off Dunlop Q2 specs the 120/70 is 4.83 wide while the 120/60 is 4.63 wide. The height difference is 22.8 vs 23.8 for the 70 series.

From the tires I have worked with you will have slightly more "chicken strip" with the 70 series. That means you have a little more breathing room before you run out of tire. The profile will be slightly different as well. I dont know if sidewall angles are different between the 2 but it could make a difference in profile.

Sorry but I'm not one of those really techy guys when it comes to building or fixing bikes. I look at tires, I feel suspension. I ride the bikes and work on making them feel right. Math is great but math doesnt always feel right. Some Techs work by the numbers and on paper they say things will be right. I'm just not that guy. I'm the guy at the track who starts with what I know works then makes little changes one way or another to make it better regardless of what the numbers tell me to do.

I cant give you a scientific explanation other than it works better.

I did run a 125/80 front the other day.... wow. Amazing.
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Old 11-09-2012, 06:33 PM   #7
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Re: front tire size question

After 21 years of riding sports bikes? Choose wisely or die trying! Not a squid!

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Old 11-10-2012, 10:52 PM   #8
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Re: front tire size question

I've been running 120/70 fronts instead of the original size 120/60 on my SV for years. Just like stated, you'll have a little extra chicken strip with the 70. You'll probably want to raise the forks in the triples to compensate for the taller tire.
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