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Tyre issue?

Discussion in 'Technical and Troubleshooting Torque' at netrider.net.au started by hopeless, Jun 16, 2015.

  1. Ok so a stupid question probably. I have a Pirelli MT66 route tyre on the rear of my FZX750. Size is 150/90/15. The bike as standard came with 140/90/15. The tyres were put on by previous owner before I picked it up.

    Now up until recently I've been really happy. But with all the drizzle in North Brissy lately I'm finding the tyre lets go really easy in the wet under acceleration. For example, this morning I filtered through to the front and there was another bike there, plenty of room and the lights changed so I gave it a little twist, away from everyone Like a tiny twist, and it let go, not dangerous, but it now has me a bit concerned when cornering. Its has happened a few times when I just accelerate normally when wet.

    I can only find positive reviews of the MT66. They seem to be designed for cruisers, and My bike is not quite a cruiser but not a sports either. Is this the wrong tyre for my bike maybe???

  2. you will find it more slippery at intersections
    oil , white painted lines and that sort of shit
    • Agree Agree x 3
  3. things that come to mind:
    your bike doesnt weigh enough for the tyres
    your tyres dont have enough tread
    your tyres are set at the wrong pressure
  4. Your wrist is too heavy.
    • Like Like x 1
  5. i dont get it
  6. What, a heavy wrist?

    You need more than 250cc of raw throbbing power to experience heavy wrist syndrome.

    • Funny Funny x 1
    • Informative Informative x 1
  7. ahh, i understand now.
    yeah when i twist my wrist i only have to worry about the front coming up
  8. we are talking about bikes now Mat
    • Funny Funny x 3
    • Disagree Disagree x 1
  9. You don't want your rubber letting go when it gets wet.
    • Like Like x 2
    • Agree Agree x 2
  10. Cheers mate, I was thinking about the weight bit myself. Tyre is also 1 size bigger than standard.
    Tyres are new so stacks of tread, not the issue
    Pressures are as recommended by the manual. But that is for the original tyres

    Nope, no more extra throttle than normal start up, I am fairly timid in the wet.:p
  11. going from a 140 to a 150 has a bigger effect on handling and tyre choice than it does grip. if the tyre really is a cruiser tyre then it will work best with an extra 100kg and 25 degrees less lean angle.
    read up on load ratings and speed ratings to get a better idea of which tyre would suit you
  12. Yeah I'll do that but there's a lotta life left in the tyre and being broke it will be a while before its replaced. I'll just take care for now I guess.

    My main concern is it affects the way I ride in the wet, I found I had to force myself not to stiffen up in wet corners and roundabouts, which is stupid I know.
    • Agree Agree x 1
  13. Quick check shows its the wrong tire for my bike. 74 rating is for a 375kg bike. Mine is only 220 wringing wet.
    H speed rating at 130 would never happen either
  14. You're looking at it wrong, although it's an easy logical error to make. For starters you forgot your own weight. :D
    You also have two tyres. :D

    74 rating is for 375kg max load at max pressure on that one tyre. You have 220kg bike plus xxkg rider weight distibuted across two tyres, front and rear. Assuming hypothetical 80kg rider weight and perfect 50/50 front to rear weight distribution you have (220+80)/2 = 150kg load on each tyre, and therefore 375-150 = 225kg margin for that tyre.

    The original 140/90/15 tyre for your bike seems to have a 70 rating, ie 335 kg, which gives 335-150 = 185kg margin instead. Which doesn't seem too bad to me.

    Obviously these load figures are not real life, your rear weight bias is almost undoubtedly more than 50% of total weight so the calcs will come out a fair bit different.

    In which case, even if we assume as much as 200kg rear load the actual load on the tyre seems to be between 1/2 and 2/3rds max load with either of those tyres.

    For comparison, on my motarded 450x rear tyre is 66 rating (300kg @ 41psi) for a bike that weighs ~130kg fully fuelled. Using the 50/50 and 80kg rider assumptions yields (130+80)/2 = 105kg load, and a 195kg margin.

    For further comparison, the OE offroad knobby tyre on my bike is rated 71 (345kg), which gives 345-105 = 225kg margin.

    Hope this helps.
  15. It is more than likely a hard compound tyre too, good for longevity, not so great for grip..

    You could play around with pressures, but too low a tyre pressure doesn't necessarily equal better grip in the wet.
  16. Interesting. I had assumed static weight. I might drop a couple of psi and see Ifit helps.What I find odd is that there are no reviews complaining about wet weather traction, so its gotta be me, right?
    it is probably a hard compound as longevity is a strong selling point.
  17. It's more than likely more than one thing. It could be weight of the bike, hard compound tyre, too higher pressure, the rubber may be old and hard (even if it is a brand new tyre, you don't know how long it's been on a shelf or how it was stored), suspension may be worn causing the tyre to do more work. Or, it could be that the roads are just very slippery after rains in your area??
    • Agree Agree x 1
  18. bobthekelpybobthekelpy might be onto something as another factor.

    There will be a code on the sidewall of the tyre that can tell you when it was made. Google it up, you'll find it.

    Found it for you!

    Also from Pirelli;
    Dedicated to Custom, Cruiser and Touring motorcycles, this tyre ensures excellent comfort, easy steering and high mileage.
    • Like Like x 1
  19. I've been suspicious of Pirelli cruiser type tyres since a mate with a GS550 Custom (whatever the suffix was) stuck one on the back and then started complaining his clutch was slipping. It was only when I followed him round a wet roundabout one day that we realised that the slip wasn't in the clutch :eek:. Says something for the GS's stability that it didn't just dump him.

    So I'd guess that your problem has nothing to do with going up a size which, frankly, I'd be surprised if you could feel on something as primitive as the FZX, and everything to do with it being a crappy hard compound Pirelli. Not that I can offer any positive suggestions for alternatives.

    The positive reviews may reflect the fact that it's a cruiser tyre and cruisers don't get ridden in the wet much.
  20. Cheers guys. I think I'll just have to keep taking it easy in the wett till its time for a new one.
    Thanks for that info PatB, good to hear its not just me.