Ten inch tire diameters for Z50R bikes

Discussion in 'Tech Area' started by preventec47, Apr 11, 2019.

  1. preventec47

    preventec47 Member

    Apr 1, 2019
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    The largest available tire to fit the stock 8 inch rim is 16.6 inches diameter. ( Carlisle XTRAC )
    and 4.7 inches inflated tire width on stock rims for said tire.

    What are some diameters of 10 inch wheel and tire combos so I can get an idea of how much
    additional clearance needed. Smallest and largest where the inflated tire width does not
    exceed five inches.
    I assume the inflated width of 10 inch tires on the 2.5 inch wide rims is going to be less.
    I see on EBAY two sources of the 10x2.50 rims at about $75 each including shipping.

    There are no other easy choices or sources of 10 inch tires are there ? I define easy
    as not needing to change drum hubs to disk hubs and change out the rest of the brake
    system for disk operation.

    As far as weight goes....Is it likely that narrower 10 inch aluminum wheelsets with tires
    are lighter than steel 8 inch stock wheelsets ?

    !2 inch tires are beautiful but it seems they cannot be used on drum brake systems.
    and require swap of front forks and hubs for disk brakes. Is that correct?
    #1 preventec47, Apr 11, 2019
    Last edited: Apr 11, 2019
  3. racerx

    racerx Administrator
    Staff Member Administrator

    Jul 10, 2005
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    Good luck finding accurate installed dimensions for any of these tires, regardless of flavor...8, 10 or 12 inch. There's a world of difference between the nominal & real-world sizes and the nominal specs are scarce enough. 12-inch is becoming more popular and that carries the same issues as newer car tires; you're limited to the same tire diameter which translates into shorter sidewalls. As for wheel & hub weight specs, if there are any they're among the best-kept secrets in the biz, in the past 2 decades I've seen exactly...none.

    With 10" tires, I've seen them as short as ~53" circumference and as tall as ~61". That's a diameter range of ~17-20". Stepping up to 12-inchers, on a CT70, doesn't change much except sidewall height; there's only so much real estate. The tallest 10-inch tires 120/90-10 cause some issues...reduced suspension clearance and loss of chain adjustment range. Any taller and you'll have to start re-engineering the rolling chassis. A lot of guys like low-profile tires. I'm indifferent...don't care one way or the other, in terms of aesthetics. In practical terms, shorter sidewalls have some big drawbacks. And the small diameter tires to which we are restricted mean harsher ride quality and more impact being transmitted into the rolling chassis, i.e. potential for bent rims, tweaked hubs, bent shock mounts etc. Tire sidewalls are a a critical part of the suspension of these little bikes. The stiffer the sidewalls, the more work has to be done by the suspension and real suspension components are really expensive.

    IMO, you should start by setting an overall goal. From there, it'll be time to consider practical parameters...like suspension clearance, at full compression. If a tire makes contact with any part of the chassis at full compression (i.e. bottomed-out), or sooner, the wheel will lock...and disaster will follow. I'd also consider the wheel & hub combo. Stock hubs can be used, as long as the wheels selected have the matching bolt pattern. CT70 hubs are okay, but not all that great and leave you stuck with some compromises. Up front, the speedo drive can be handy it's also cheap; but, you're limited to ~56" tire circumference, if you want accurate speedo input. There are aftermarket speedo drives but, any mechanical drive is only accurate with one, specific, tire diameter. Out back, the rubber-mounted sprocket assembly is a huge plus, far better than the rigid-mount of the Z50. On the other hand, it's kinda sloppy, does eventually wear out and leaves you married to CT70 (4-post) sprockets.

    If you want lightweight wheels, go for stamped rims, such as split rims from G`Craft, Kitaco, et al, if you can find them. If you want strong rims, opt for castings...which will be heavier. There's even more weight difference between tires. Stock Trailwings are among the lightest tires, tubeless road tires, with reinforced sidewalls can easily weigh more than twice as much. There is some disagreement as to which is "better". Lightweight rims + tires make the suspension more responsive, at the cost of less "gyroscopic effect" at speed, i.e. straight-line stability, at speed. These little bikes are inherently twitchy. What's your priority list? How fast do you plan on rolling along and for how many miles at a shot? How are your local roads...smooth or cratered?

    As for brakes, take your pick. As long as the hub fits the wheel and the brake plate matches the hub, all you need are the proper length spacers and a solid brake stay, to prevent the brake plate from rotating when you grab a handful of brakes. Braking power is pretty much the same from the Z50 up to the CT110...same size brake shoes. An hydraulic disc brake, on the front, is a good upgrade for 50mph+ road use.

    I'm cutting this here as the topic is a can of worms. It's not impossible to sort through, by any means. When building a custom bike, rolling chassis mods involve a lot of "roll-your-own" elements. The high-end parts market is extremely thin in the US of A, always has been. Most owners make their choices based on appearances and price; naturally, that's where the vendors have things covered..which makes sense. I mean, who in their right mind would stock items that cannot be sold quickly enough to pay for themselves? So, I'll repeat my basic approach...set a goal, then your top priorities (including a budget); the rest of the project will more or less dictate itself from there.
  4. preventec47

    preventec47 Member

    Apr 1, 2019
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    since buying my 1st Z50 nearly 2 weeks ago, In my research I have located a very good
    deal on a 2nd Z50 that will be there for the taking for a long time. (stashed in a relatives
    storage shed). On top of my rocket powered Z50R (125cc) which for health reasons
    dictates that I make mods to tame the beast,
    I've identified for the 2nd Z50 another objective. I want to make it as light as possible.
    The specs for the Z50R indicated a 108 pound weight and I would like to shave ten
    pounds off that weight.
    Wheels and tires would seem to be a good place to start.
    1. Possibly narrow spoked alloy rims with narrow tires,
    2. Maybe swap some steel components in the front fork for aluminum.
    3. Get rid of fenders of course
    4. See if aluminum swingarms of std size might be a pound or two lighter than the
    OEM steel original.
    5. Swap rear shocks for alum strut and make it a hardtail
    Thats all I can think of short of turning the under-stressed parts of the frame into swiss cheese.
    ( though for relatively big bucks I note that G-craft and maybe WeBike have replacement
    aluminum frames.... I am not that desperate... or wealthy ). Still interesting to think about.
    I've been involved with aviation nearly all my life and I am obsessed with weight and pure engineering design.

    The goal would be to have a mild mannered 50cc automatic appreciably LESS than 100 pounds.

    Maybe this is a waste of time as there may well be off the shelf pit bikes for peanuts that
    meet the same weight and performance parameters with zero effort and probably lower cost.
    As I said, this is a way back burner project and in my travels for my priority project I
    would like to pick up as much info as possible, I am asking all the vendors for the weight
    of their products and all dimensions and performance info and many seem offended.
    What the heck ! What kind of world is it where salesmen no longer need
    to know the details of the products that they sell. How is it possible that a manufacturer
    cannot tell you what the alloy of aluminum is being used? Well it must be an alloy
    they are ashamed of in my opinion. ( actually the market seems like one ripe
    with opportunity for a super detail oriented vendor )
    Dont even mention "SHOCKS" ... I dont want to talk about em.
    BTW---- BIG THANKS RACERX for all the info.
    #3 preventec47, Apr 11, 2019
    Last edited: Apr 11, 2019

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