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Discussion Starter · #1 ·
Has anyone gone from the stock 60 to a 70 series tire on the front? If I'm doing the math right, on a 120 size tire (the stock size on my bike), the 70 series would be 12mm taller, right? How does that affect handling? do you need to a taller tire on the rear to keep the same weight dist. on the bike?

mike
 
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The manufactures also have cicumference specs, which are more acurate tha just the aspect ratio(60 or 70 series).
 

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I put a 70 series on my 800 and raised the forks to compensate. If you go to sportrider.com they have an article in their tech section about this subject.
 

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Discussion Starter · #4 ·
Thanks, guys. Very helpful, as always.

Mike
 

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Discussion Starter · #5 ·
Here's the link to the article on changing ride height to compensate for a different tire. I haven't found anyone who can give me the tire circumference data for Diablos ("I'd have to go measure" is the best they'll say), so I think I'll be taking a tape to the tire store next time... Emails to the tire companies may prove helpful, but so far they've been pretty slow to respond.

At least now I know I can set up my baby for a free 70 series diablo from the pirelli folks w/o goofing up the suspension too much. I'm planning on adding a revalved 748 shock this winter as well, so the fewer other variables I add, the better.

http://www.sportrider.com/tech/146_0202_geek/
 
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A tape measure won't do any good unless the tire is mounted on the correct width wheel, and filled to the correct pressure.

Raising the forks in the tree is an alternative, but may change the rake/trail of the front end geometry.
 

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-------snip-----------
I haven't found anyone who can give me the tire circumference data for Diablos
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I have a Diablo booklet, says:

120/60-17 on a 3.5" rim : 594mm (23.39") Diameter

120/70-17 on a 3.5" rim : 609mm (23.98") Diameter

So, to keep the same ride height at the front, you would need to raise the forks 0.30" in the triples. If you do that, the tire will then only change the trail from OEM 102mm to 105.4mm.

Make sure you've got clearance, you definitely don't want the tire hitting anything at full compression.
 

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The differnce above will also make any front mounted speedos more acurate (the speedo will read 2.5% lower--and closer to reality--for a given speed based on my math).

Do the super bikes not use a 70 profile front? Obviously a completely different bike but.....
 

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Hi, folks. Just had to deal with this today. Went from a 120/60-17 on the front to a 120/70-17. On the Dunlop web site they give the diameters of both tires. Doing the calculations gave me a difference of about 12 mm in circumference. According the the article on the Sport Bike site, I should raise my forks by this amount. However, I don't really notice that much difference in the way the bike feels so I may not mess with it. The only clearance issue is the new tire is verrrrrry close to the fender. This is a Monster 620 and you know about the flexi-fenders on those! (Can't quite figure how to deal with that.)
 

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Discussion Starter · #10 ·
12mm sounds about right. Dunlop says the 120/60 stock D205 on my bike is 22.95" in diam. Diablo says its 70 series is 23.98" so you end up with a front a hair over 1/2" "taller" in radius.

It looks like the Diablos run tall. I'm waiting to hear back from Dunlop on the exact #, but it looks like the stock Dunlop 205 on the rear is about 24.8" in diameter. The Diablo 160/60 is 25.31". So all in all, the front ends up 1/4" higher than stock with the Diablo 70 series front and 60 series rear.

Sorry if this thread bored the sh*t out of everyone -- it was better than working, at least for me, and I learned a bit about tires in the proces....

mike

mike
 
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