XR100 Tire and Tube Questions

Discussion in 'Mini Racing' started by yuengling910, Sep 11, 2018.

  1. yuengling910

    yuengling910 Well-Known Member

    I recently purchased an 03 XR100 to turn in to a mini moto bike for kart tracks and possibly some flat track.

    I found an XR80 front wheel so I can run 16s on the front and rear. I bought a pair of BT45s in 100/90/16.

    When I mount the rear tire, which direction should I mount it in? Should the arrow be pointing towards the front or should I flip it around on the rear?

    I read that I can use 3.25/3.50-16 tubes. Does this sound right for both wheels? It looks like the rear wheel is slightly wider.

    What is a good starting tire pressure for these tires?

    Any tips for mounting the tires and tubes? I have a NoMar but have never mounted a tubed tire.

    Thanks!
     
  2. FZ1guy

    FZ1guy Hey...watch this

    Mount the rear tire in the correct rotation. Mount the front tire backwards. That size tube should work.
    Inflate the tube just slightly and mount the tire just as you would any tire. Be careful not to pinch the tube with the spoons. Get the valve stem exactly centered, you can do this after the tire is on the rim. Start with 17-18 psi for minimoto. Rim locks are a good idea, but not required.
     
  3. ChouDawg

    ChouDawg Well-Known Member

    I run Pirelli Sport Demon 110/90-16 tire on my XR100 with 16"x1.6" rims front/rear. I'm using STI Heavy Duty Tubes 90/100-16. In inches I think this translates to ~3.5/4.0-16.

    https://www.americanmototire.com/sti-heavy-duty-tube-90-100-16-tr-6/

    Mounting a street tire on a skinny dirtbike rim is by far the most painful thing in the world. Heating the tire up will help (black trashbag out in the sun or a heat gun), lots of soapy water and as FZ1guy mentioned inflating the tube slightly helps keep it from getting pinched/torn. I run between 20-22 psi with my tires.

    As far as direction goes, I'll have to disagree with FZ1guy here. Since both your tires should be "front" tires I would mount the front normal and the rear flipped; personally I mount both the same way. The tread pattern is designed for both water and grip (more so water dissipation) so on the rear you'd want it to be reversed to simulate a "back" tire tread pattern.
     
  4. FZ1guy

    FZ1guy Hey...watch this

    Actually, I believe you are correct. Rear tire mounted backwards. Really, I don't think it makes much difference.
     
    ChouDawg likes this.
  5. ChouDawg

    ChouDawg Well-Known Member

    Ah cool glad I didn't get that wrong. I never ride in the wet and have never had an issue in the dry so I agree it's probably no big deal either way unless you're racing minis professionally.
     
  6. TurboBlew

    TurboBlew Registers Abusers

    where did you get the idea for a 100 sized tire? The 110 is a better tire. in the BT45. To get them to fit better on the front...lace a rear 1.6 rim to the front hub. Rim is $30 new from Honda.

    There are HD 16" tubes. Better for running lower pressures without pinching. Running a beadlock? No way. Make sure you put air in the tube and powder to keep it from pinching. Balance with spoke weights.
     
  7. yuengling910

    yuengling910 Well-Known Member

    That's what I was thinking about the direction of the front. I'll just mount the rear, backwards.

    I'm not sure exactly where I got the idea to run the 100's. I spent a few hours googling somewhere along the way that's what I ended up with. You guys running 110's front and rear? This is all just for some cheap(er) fun, so I'll give the 100's a try before I try to unload them for a set of 110's.

    So I can just buy a 16x1.6" rim and use the hub and all the spokes to lace it up, or would I need to get new spokes as well? Is this necessary if I'm running the 100's? Should I try to exchange the standard tubes for some HD tubes like the ones posted?

    What else do I need to know about setting this thing up? I have new OE brake shoes for front and rear, new brake cable, replaced all swingarm/linkage bushings, new 20w fork oil, new steering head bearings, new chain and sprockets (XR80 - 420 pitch), hand guards and have been going over it, fixing everything that I can find. It has been turning into more of a project than I had expected.

    Thanks for the help.
     
  8. noles19

    noles19 Well-Known Member

    I've been using bt45s for years and can't remember worrying about the direction of the tire before, to be honest.
    I use 16.5 psi front and rear.
    the 110/90 is the best tire front and rear.
    the oem are the best brake shoes.
     
    sharky nrk likes this.
  9. yuengling910

    yuengling910 Well-Known Member

    I'm trying to set up a return for the 100 tires and will order some 110/90/16's. Will this fit on the XR80 front wheel or do I definitely need to get the 1.6" rear rim for it?
     
  10. FZ1guy

    FZ1guy Hey...watch this

    I thought I heard the 110 front scraped the forks. Right or wrong?
    I run 100 front / 110 rear
     
  11. ChouDawg

    ChouDawg Well-Known Member

    Not certain but I think you can re-use the XR80 front spokes and just swap out the rim but I might be wrong since the rim widths are different. If they're not the same then you would probably have to order some from Buchannan or similar. I have 1.6" front/rear on my bike but bought it that way so unfortunately cant tell you what spokes to use.

    Regarding the 100/110 debate, I saw similar discussions. To some the 100 was a godsend because it allowed them to turn in quicker for others the 110 allowed for more front end grip without running off the edge. For me the 110 Pirelli rubs on my forks but not enough to hinder performance or cause an issue, just rolling around with the engine off in neutral.

    Another thing I recall about tire size is the 100 width tires for both Bridgestone and Pirelli only come in H speed rating; the 110 width is available in a V speed rating. Most people recommend the BT-45V, the tread is the same so I'm not sure if speed rating is the only difference. However, people seem to swear by it and many will even tell you NOT to buy the H rating tire. With how blazing fast XR100s are I don't see why 130 mph (H) to 149 mph (V) really matters. I can only guess the compound on V rated tires is better. The load rating goes from 54 to 59 between tires sizes but again is irrelevant on the bike we're talking about.

    As far as changing tubes I would just leave what you have and swap them out later unless you're concerned about getting a flat while racing. Regarding the 110 on a 1.4" rim it does fit, my buddies XR100 has this setup with an XR80 front. Interestingly enough his bike doesn't rub and mine does, most likely due to the wider rim.
     

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