1. Some members were not receiving emails sent from XJbikes.com. For example: "Forgot your password?" function to reset your password would not send email to some members. I believe this has been resolved now. Please use "Contact Us" form (see page footer link) if you still have email issues. SnoSheriff

    Hello Guest. You have limited privileges and you can't "SEARCH" the forums. Please "Log In" or "Sign Up" for additional functionality. Click HERE to proceed.

Tire question

Discussion in 'XJ Technical Chat' started by NACHOMAN, Mar 22, 2006.

  1. NACHOMAN

    NACHOMAN Member

    Messages:
    139
    Likes Received:
    1
    Trophy Points:
    18
    Location:
    Milan N.Y.
    I've ordered and recieved a new set of tires for my '82 750 seca. I opted for stock sizes in the Metzler Lasertec line. The PO had cheapo Chen Shin tires fitted in larger than stock sizes, specifically a 110/90-19 up front. I know on my earlier Yamahas using a larger tire decreases traction due to changing the tire shape to fit the skinny rim. The small amount I rode the bike before teardown was plauged with poor handleing, do you think the tire size was to blame? Perhaps it was a combination of size and cheapo tires.

    Second question: The cheapo tires didn't hold air very well, do these rims require tubes?

    Any insight greatly appreciated. 8)
     
  2. Robert

    Robert Active Member

    Messages:
    7,479
    Likes Received:
    9
    Trophy Points:
    38
    Location:
    Ventura CA
    First, Chen Shin is CHEAP junk. They are round, they do hold air, but they are the crummiest tires in existance, heck a starving Ubangi could make a better tire. Best not to buy them unless you can live with the lousy performance they WILL give. So that should answer your first question. Second, your stock rims are designed to be tube-less. You can fit them with tubes but it is rather pointless unless your rim is so badly pitted from corrosion you have no other option (at which point I would recommend replacing the rim anyway). There you go!
     
  3. NACHOMAN

    NACHOMAN Member

    Messages:
    139
    Likes Received:
    1
    Trophy Points:
    18
    Location:
    Milan N.Y.
    That was funny!!

    What do you think about the oversize angle?
    Squeezing the tire to fit is supposed to chage the shape of the tire with adverse affects.

    Ubangis crack me up.... :p
     
  4. Robert

    Robert Active Member

    Messages:
    7,479
    Likes Received:
    9
    Trophy Points:
    38
    Location:
    Ventura CA
    Well... your analysis of "less traction with larger tire" is not quite in keeping with popular opinion unless you run it with WAY too much air pressure (not a good idea). A larger tire will have a larger "footprint" or contact patch, simple enough. Squeezing the tire is not a term I am familiar with so I'll give you my best guess at what you are asking. There is limited room in the caboose of our fine steeds and there has been much discussion about how much meat you can try to cram into it without detriment. A rule of thumb I was taught years ago is you can run one size wider or narrower than stock. In application this has served me fairly well. The problem I have run into has been the aspect ratio. Stock tires have a 70 percent aspect ratio which gives good response with an acceptable amount of harshness in the handling characteristics. I once ran stock 70-14-195 radials on my truck. No problems. Then I ran across a set of 60-14-205. Problems started with the tires rubbing with maximum deflection in the steering. Ok, bought a set of 70-14-195 and the problem went away. The tread width was just too wide to clear any possible contact points in my tire well (60 series were a poor choice too, my motor was taching higher as well to reach speed and that sucked up a lot of gas). Here is the break down, 70 refers to the ratio of side wall height, in percent, to contact patch width, in my case 195 mm. In this case my side wall should be 136.5 mm high. The lower the ratio (65, 50), the shorter the side wall height, the better the handling performance, and the harsher the ride feedback. You need to make sure that the tread width is narrow enough to clear the swing arm with an eye on the sidewall aspect ratio. Don't go too low or you’re liable to run into contact issues and lousy highway performance. If I remember right (here I go again, apologies before hand), Dunlop has a little tutorial on tire size information (I'll bet others do too). Check them out and bone up on the details. Hope this helped, not sure if I answered your question.
     
  5. NACHOMAN

    NACHOMAN Member

    Messages:
    139
    Likes Received:
    1
    Trophy Points:
    18
    Location:
    Milan N.Y.
    The thing I have been told is when you squeeze a tire that is too wide onto the rim, it changes the profile. In other words, the curve of the tire becomes more aggressive. While this makes the bike "tip in" easier, it makes it harder to stand up after the curve. Race profile tires typically have a more aggressive curve. I was just wondering if anyone has experienced this first hand. I believe it would affect the handleing more on the front tire, than the rear. My front was a 110/90-19 which I believe is 2 sizes wider than the 3.25-19.
     
  6. Robert

    Robert Active Member

    Messages:
    7,479
    Likes Received:
    9
    Trophy Points:
    38
    Location:
    Ventura CA
    I'll have to defer, never monkeyed with my tires. Anyone?
     
  7. woot

    woot Active Member

    Messages:
    1,244
    Likes Received:
    3
    Trophy Points:
    38
    Location:
    <a href="http://maps.google.com/maps?q=44.777479+-
    Well - you're both right from what I understand of it.

    There are two more numbers to think about. What size rim the tire was made for and how much do they mean that.

    If the tire was made for a 3" rim and you put it on a 2.5" rim then the beads are pulled together. This twists the tire and changes the profile of the tire.

    If you change the tire and make it more angular you loose some of the footprint width. If you make it too angular you can't use the outside edge becuase you hit hard parts before you can get out there. Meaning that you'd have been better to have had a shallower profile and used more of a contact patch to get more rubber on the road.

    The idea is that you can just throw a larger tire on and that if it fits you've got a larger contact pad. It probably is larger, but it's unlikely a linear function. Adding 10mm doesn't mean you're getting an extra 100mm of fooprint from my understanding.

    Furthermore the twist put on the tire - that's fine for us but that compounded with hugesidewall flex on bigger bikes might lead to premature failure possibly in the most spectacular ways.

    Then there is a question of tire profile and stability. The bike might not respond well to a drastic change in profle - of course between brands (of the same size) this changes...

    In the end - I said all kinds of things that could go wrong - but I tend to quiety side with Robert at times that a little change is unlikely to really hurt - not with the non-agress frames. On the other hand, I don't change from what I use because I'm happy with the results and really have a need to even put some changes into the system there.

    It's a balancing act - I tend to be harder nosed about it when people aren't as familiar with the issues... it is a bit of a personal thing, where you have to weigh up the changes both good and bad. I'm not one to rant about the good changes because everyone will do it without considering the bad.

    :)

    So I think you're both right.

    RE: Fronts and Rears

    I don't think the front tire fits the maxim although there don't seem to be alternatives out there... the real problem is the rim size... if you were going to really go sporty you'd have to do a front end swap. I'd be very hesitant to change the front tire size... the rear on the other hand I agree is less of an issue.
     
  8. woot

    woot Active Member

    Messages:
    1,244
    Likes Received:
    3
    Trophy Points:
    38
    Location:
    <a href="http://maps.google.com/maps?q=44.777479+-
    One other thought about pinching a tire - when you pinch the tire it doesn't have to uniformly change shape across the profile. It will flex where it is easiest to flex... it might flex in two soft spots rather than across the center. I'm not sure what you'll get for a profile - certainly it might not be what you expected... :D
     

Share This Page