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2007 675 Race tires changed geometry of bike

7K views 21 replies 10 participants last post by  Shamrock 
#1 ·
Hello guys, I have been running the 180/55 rear tire using Dunlop Q3's for trackdays. I switched the last track day to the N-tec GPA tires with the 190/60 rear. The supplier told me that the difference in height between the two rears was maybe a millimeter or two. The difference is significant, to the point of (cheap track stands) the Q3 rear giving me about 1/2 inch of clearance from the ground to the bottom of the tire. With the 190 gpa, the rear tire is sitting on the ground while on both stands. The rear of the bike sits so high now it makes the bike very unpredictable in the corners and creates a "wobble" type feel when in tight corners at lower speeds and the bike is extremely twitchy in high speed corners. The bike is so unsettling that I was 3 seconds slower on the GPA tires than I was running on the Q3s. I lifted my forks so that they are flush with the top triple tree, this helped slightly. My rear shock is the stock shock for the 07 675 but the spring has been corrected for my weight.

How many people run the N-tec GPA with the 190/60 rear? What adjustment is there to correct the geometry of the bike while running the GPA so that the rear of the bike isn't so high? Do I have any option other than purchasing a ride height adjustable rear shock?

Any help or suggestions would be greatly appreciated, thanks in advance!!
 
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#3 ·
I have tried a 190/55 rear (not a race tire version however), the rear rim width causes the side of the tire to become almost vertical after a certain lean angle which prevents you from being able to use all of the tire. Once you exceed that lean angle the tire washes out with no warning at all. At least that is how it felt to me. I am considering just running the Michelin evo cup tires as they offer the 180/55 rear.
 
#5 ·
I think you've answered your own query in your original post. it twitchy, unpredictable, wobbly and is costing you 3 seconds per lap. That tyre has to go.

Don't change the bike to suit the tyre. go for the tyre that best suits your bike and your pace.

I used to run 180/55 rear and found it to be ok but a little slow on tip in. I then tried out a 180/60 and have locked it in. it is the right size for me, nice level of flickability (if that is even a word) and hold a steady predictable line in corners. I think if I went any taller in the rear I would also run into issues like yourself.

Perhaps go back to what you are used to or try out a 180/60.
 
#7 ·
I made the switch to the GPA because I stepped up to advanced and most of the guys I have talked to at the track (racers, control riders) said that once I made the move to advanced and I started dropping my lap times another couple of seconds that I would be right on the limit of the Q3s grip. So I went ahead and made the switch. I was going to go with the 180/55 N-tec dunlop slick but was told that the GPA was a better tire offering more grip and that the difference between the 190/60 GPA and 180/55 slick and Q3 was about 1-2 mm. The height is significantly different which obviously caused issues. I now have 2 sets of rims for the bike, so I am going to get another set of Q3s from work and look into a set of slicks as well. Who makes the 180/60 rear? I know tire choice is a personal preference because of the different feedback from different brands of tires and compounds. I basically want something that feels like the Q3s but stickier and that will last more than 2 track days.
 
#8 ·
I run Pirelli Supercorsa slicks. At your pace, you could run an SC3 hard rear and SC2 medium front and you'll have more grip than you know what to do with. Life should be even longer than the Q3. Unlike Dunlops, you can flip the Pirellis backwards when they're about halfway done to even out the wear.
 
#9 ·
I have heard good things about Pirelli from multiple people. I think for the time being I am just going to run the Q3s until they start to slide on me. Once that happens I will make the switch to a 180/55 or 180/60 race tire.

Thank you all for your input.
 
#11 ·
I have heard good things about Pirelli from multiple people. I think for the time being I am just going to run the Q3s until they start to slide on me. Once that happens I will make the switch to a 180/55 or 180/60 race tire.
If it's any consolation, @Hokie ran Q3's in the advanced group until they slid and had the rear step out on him fairly predictably. You'll be fine as long as you're careful.

You can actually calculate how tall the bike is going to stand: the second number is the height of the profile expressed as a fraction of the width. So 180/55 would have a height of 180*55 (god knows in what units). So you can see why 190/60 raised the rear of your bike so much: you have 190*60, waaaay more than 180*55 and then you have the distortion of the narrower rim which (I'm not sure on this) could raise the height even more.
First of all, the tire sizing system is totally messed up. 180 mm width (metric) by 55 height (percentile) on a 17 inch rim (imperial). The real problem is manufacturers aren't consistent. A 180/55 from Pirelli will be slightly different than a 180/55 from Dunlop. The 190 NTEC is actually designed for a 5.5" rear rim, but the Daytona already has flighty characteristics that make set-up hard (i.e. expensive) with such a tall tire. As a rule of thumb with the Triumph, you want to get 180 rears.
 
#10 ·
You can actually calculate how tall the bike is going to stand: the second number is the height of the profile expressed as a fraction of the width. So 180/55 would have a height of 180*55 (god knows in what units). So you can see why 190/60 raised the rear of your bike so much: you have 190*60, waaaay more than 180*55 and then you have the distortion of the narrower rim which (I'm not sure on this) could raise the height even more.
 
#12 ·
I am eventually going to upgrade the rear shock and put some cartridges in the forks. We are a Racetech dealer so I get great pricing on both, fully customer rear shock with hydraulic pre-load adjustment for just over $900 and fork cartridges for under $700. I figure if I put the money into the suspension, the bike will perform better allowing the tires to perform better as well. Once I have the suspension upgraded and feel the Q3s starting to give, I will make the change to race tires. I haven't done any actual races yet, but I am hoping to run at least one Wera weekend to get my license this year. Then focus on having everything set up for next year.

I have some small "sponsorships" from different companies, most notable being a track ambassador for Comet Racing Leathers (great custom fit leathers for a steal!!). Anthony Corbo with BauceRacing has helped me out with Armor Bodies track fairings (awesome guy to do business with!!!!).

I am hoping that next year I will have more substantial backing. So I want to do as much experimenting this year as possible so that I have a solid foundation to start with next year.
 
#14 ·
Here is the tire ranking I've observed in my race organization

1 Michelin
2 Pirelli
3 Bridgestone
4 Dunlop

Dunlops are sometimes referred to as hockey pucks if that says anything. In fact, if the Dunlop vendor weren't such a nice, likable guy I doubt he'd sell a set at all.
If the B'stone rep weren't such a pain in the ass he'd probably sell a few more but they aren't well liked and seem to attract more of the light weight crowd. Michelin and Pirelli are the ticket right now.

All that being said, you need to find what works for you.
 
#15 ·
I have considered going to the michelin evo cups. My sales manager used to race CMRA and Wera and that's what he runs with and he seems to like them. I guess I will just have to try a few different brands and see what I like the most.
 
#16 ·
So a little update on this. I put the Q3s I ran previous to the GPAs on my second set of rims. Noticed during the install that the Q3 front was a 120/60-17 and not a 120/70-17. The GPA front is a 120/70-17. Put the rims side by side and the 120/70 is way taller than the 120/60. With the 120/60-17 Q3 and the 180/55-17 rear Q3 I put down my fastest lap times ever, by roughly 4-5 seconds. So I am thinking that for the time being I am going to stick with the Q3s and continue to run the 120/60 front because the bike felt smooth, predictable and stable in every corner. Not once did it do anything that surprised me.

I think my best option is to just push the Q3s until they become inconsistent or simply start to lack the grip I need. At that point I will start seriously looking at slicks but I believe I am going to stay as close to the Q3 sizes as I possibly can to limit the extent of required upgrades to correct the geometry of the bike to compensate for the tire change.

I appreciate all the input and advice from everyone. If anyone is interested I can be found on instagram using @WICKEDTRIPLE, or on youtube as wickedtriple.
 
#18 ·
I don't know what kind of pace you run but this reminds me of something from few years back. (Since you just moved to race tires I'm sure you're fine. This guy was used to running a race pace on race tires and attempted his pace on street tires)
Our race organization runs all day practice on Fridays. In order do save a few bucks a fellow racer slapped on some quality street tires as a means not to burn up his spendy race rubber. When the bike was trucked back into the paddock it didn't have a single salvageable part remaining...
 
#21 ·
Screw that.....Dunlop have a 180/60 slick. available that works great on my Daytona racer. I've been using the K451 180/60-17 0585 medium+ compound paired with a 120/70 front.

My 2 cents,

Cloner
ABQ, NM
 
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