Topic: Rubbing rubber with K81s

[brooze72]

I recently installed some new Dunlop K81s (TT100) on Goldie & I used a 4.10x19 on the front as I read that the "V" profile on this tyre was equivalent to the original 3.25x19.  While it does fit the rim fine, it's definitely a wider tyre.  I could hear a faint whirr when I rode & it was a little louder when leaning into a right hand turn.  Investigation showed that there was some slight sidewall rubbing on the inner brake line loop bracket holder welded to the fender on the inside & I guess there is a little tyre shift/flex when cornering that causes the volume increase.  I wasn't able to bend the bracket further away from the tyre, so I took the wheel off & used an angle grinder to remove a little material.  Rear 4.50x18 is no problem. Don't know if this is just an issue with the 500 fender width (I tried 2) but be aware to check this if you use the K81s.  Hope the picture helps make this clear where the problem was.

[HondaMan]

Well, 2 things:
1. The 4.10x19 size actually crosses to the 3.50x19 equivalent, so it will be a tight fit on a 500/550 front.
2. Check your wheel bearings, and spoke tightness. A small amount of flex when side loaded is normal, but not much. With the bike on the centerstand and the wheel pointed straight ahead, push firmly (sideways) against the metal rim, between the forks, and note how far it moves, and if it has any looseness at all. There should not be any perceptible movement, except for bending of the spokes.

Finally: run at least 35-38 PSI in the trigonometric tires. They are not made to run at the tire pressures of the older label on the bike. Their smaller tire patch (when vertical) requires the air pressure strength to provide the linear handling they can give, and the lack of roll-over when pushed to their sidewalls.

Of course, all this presumes they are really trigonometrics, and not just re-numbered metrics: I recently saw some from Cheng Shin that were labelled "K81" in the 4.10 and 5.10 size on a CB650C, and they were nothing more than round-profile tires with "K81" molded on them, and a similar-looking block tread pattern. Certainly not sidewall-racing tires... 

[brooze72]

Thanks, Hondaman, for the tip about running higher pressures, I will boost them today.  As far as I know they are actual Dunlops, is there a way to tell by these pictures?  I have checked the wheel bearings,  but hadn't thought about the spokes, another job to do.

[Old Scrambler]

Dunlop usually means Dunlop but you can never be sure in this modern world.

I have new K81s on order for my CB750...............hope they fit.

[brooze72]

Hopefully the 750's have a wider front fender, Old Scrambler, or did they use the same original 3.25x19s as my 500?

I didn't find any loose spokes altho you can play quite a range of notes by pinging them with a wrench.  I guess  that means there is unequal tension on the spokes, or is it normal?
Raised the air pressure & took it out for a snort up & down the street this evening, all seems quiet now, no rubbing.

[HondaMan]

Thanks, Hondaman, for the tip about running higher pressures, I will boost them today.  As far as I know they are actual Dunlops, is there a way to tell by these pictures?  I have checked the wheel bearings,  but hadn't thought about the spokes, another job to do.

Is the top picture a shot of the front tire? If so, they appear to be a round-section tire with added middle rubber thickness. I have seen some similar in a local bike tire shop, not sure of the brand (but they weren't labelled with the proud 'Dunlop' letters on the sidewalls), but they did not have the high-tack rubber of my old K81 set. The ones I saw have that classic K81 tread pattern and same deep rubber tread, but the carcass is not the cross-laid ribbed pattern (which you can see inside the tire). The "old" K81 trigonometrics were a VERY pronounced Vee shape, with a narrow middle tread and wide sidewall treadss, nearly twice as wide as the middle tread width. I'm not sure if I can scan an old photo I have of them on my 750, but if I can, I'll post it here later. I sure don't remember them looking that rounded (?).

[brooze72]

Yes it is,  Not sure if you can see the writing on the sidewalls in the pics. #2 says "Dunlop Roadmaster TT100" & #3 has "Made in Japan " & "K81". Maybe they changed/updated the profile or Bike Bandit & me were ripped off by some knock off company. Here is the sticker from the rear tire.

[HondaMan]

Yes it is,  Not sure if you can see the writing on the sidewalls in the pics. #2 says "Dunlop Roadmaster TT100" & #3 has "Made in Japan " & "K81". Maybe they changed/updated the profile or Bike Bandit & me were ripped off by some knock off company. Here is the sticker from the rear tire.

Ah, I see the clue here: the tire is an "85" profile, according to the label in the picture. This is a wider, squatter profile with less top height. In other words, it is more round-looking than the traditional Vee profile. The original ones came also in the "standard" profile and the "85" profile. The "85" was used for heavier bikes, as it carried more load and rolled over to the side a little less on hard cornering, but also resulted in a smaller tire patch on the side. Interesting!

[brooze72]

Boy, it's nice having your input & experience here, thanks again Mark.  So does the wider "85" profile have a lower speed rating than the Standard profile? (not that it would matter to my kind of riding)  It seems this is a borderline size for the 500. I hope Old Scrambler was aware of this when he ordered his K81s or does it matter for the 750 as it is a heavier bike?