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Tire Size

Discussion in 'The Garage' started by davey1207, Oct 7, 2011.

  1. davey1207

    davey1207 1981 Yamaha xs400 Special

    Hey guys,

    I'm looking to buy a pair of Vintage Firestone Deluxe Champion tires for my 1981 yamaha xs 400 special. I looked in the manuel for the tire size, and asked a buddy who has the same bike what his tire sizes were. They are different. What is the right tire size I should be buying from this site...

  2. I love those tires. I was going to buy them for my 78 xs 400 but decided to go with a radial. I'm a new rider and wanted a tire that would be more predictable . Do you have 18 alloys? The tires I bought are 100 90/18 rear and 90/90 18 on rear. I know some people go bigger and I would have liked bigger but I went by all the charts as to what maximum tire size was good for my rims. Mine are avon roadrider's.

    My next project is a tx500 with wire wheels which will most certainly have those tires.

    Good luck

  3. davey1207

    davey1207 1981 Yamaha xs400 Special

    That's my problem. I don't know my rim size either. I have mag wheels if that helps. Look in my pictures to see my wheels.

    Those Firestones are sick tho..!
  4. They look like 18" and they should be. It is cast right into the rim on the alloys so mabey they are just dirty and hard to read. Look around your rims I beleive its on the spokes in between the area that is machined. So on the part thats painted black. There will be two numbers I think 2.15 * 18 or something like that. The first number will be different from front to back its the width inside the rim (me thinks). I'd go look at mine and tell you for sure but I'm at work.

  5. Here are a couple snaps of the castings marks on my wheels. If you don't have a manual there are some for download on this site just look around or buy off __-bay. Gotta have a manual. I have two, factory and haynes they will give you all the info.

    Attached Files:

  6. Interesting. AFAIK, the factory size rims for your bike were 18" front and 16" rear - in the U.S., don't know about Canada. That's what my '80 and my son's '81 had. Are there any markings on those rims that say "Suitable For Tubeless Tires"? If so, you don't need tubes. If not, someone may have installed rims from '79 or earlier or Canada specs were different.

    For '80 and '81, with the tubeless tire rim, the factory size rear tire was 120/90x16 - in the U.S. Don't know about Canada. Replacement fronts would be 90/90x18 but you can install 100/90x18 on the rim. That's what I have and so do lots of others.
  7. Hey OliverB

    My bike is a 1978. I was sure what tire size the 81 had I was more just showing where the tire size on the rim was so he could find his rim size. Ya I considered going bigger atleast on my front but only decided to stick with the maximum recomended size because I'm relaitively new to bikes and didn't want to waste the money and regret it after. I also didn't want to get into clearence issues, and when I bought my rubber my bike was still a pile of parts on the ground. So I was being abit safe aswell.

    I do love the look of the bigger tire. My 90/90-18 on front dosen't look as big as I would like. I figured down the road when I had to replace tires I would mabey try bigger.

    As for the markings no mine aren't suitable for tubeless. Are you and your sons bike the rims for use without tube. I wish mine had been.

    On my next build a nice big fat set of the firestones are in order. As big as I can fit :)
  8. Yes, both are so marked and we both run tubeless. On the forum there was some skepticism about the wording of those markings a while ago but I have found since that the wording is straight from the D.O.T. My son's '04 Harley Sportster has the very same wording.

    I am staying with the O.E. sizes on the '79 I will restore this Winter. Yeah, the front tire does look skinny but since mine will be a resto, I will stay with the vintage look.

    There may be clearance issues going with one size larger on bikes '79 or older. Go with the experience of others. With a one size up on the front of my '80, I don't notice any handling problems. My son's '81 had two sizes up on the rear. Looked good but don't think it is wise to do that with the narrow rim.
  9. Ya the smaller dosen't have that same cool look to me. I see your point on handling. Being a new rider I didn't want to build a bike that was going to be difficult to ride either. So my tires should be good.

    Not sure if I helped Davey figure out his tire size though. Hope he found what he was looking for.

  10. XSLeo

    XSLeo XS400 Junkie

    Davy, The size of the tires on your bike is a good place to start. What do the tires say for size?
    Most places that sell tires have charts to crossreference tire sizes. If yours are marked something like 4.00-18 that crosses over to a 110/90-18.
    You might google motorcycle tire size conversion chart.
  11. usmcpedroza

    usmcpedroza XS400 Member

    im also looking to get some of this tires, does any one know the wheel size for spoke drum wheels for my 82 xs400sj?
  12. Pork Chop

    Pork Chop XS400 Junkie

    These are all the rage with the sr400 crowd in Sydney.


    Apparently they are great if you only ride in a straight line but they look tough.
  13. Arclight88

    Arclight88 XS400 Addict


    Off topic alert, but I want to let you know that your latest batch of pictures look great! I like the way you reworked the frame and seat. And the high impact graphics look cool.
  14. 226dark

    226dark 78 2E

    SW MN
    I wanted so so bad the Dunlop K81 and for front would have had to settle for a K70 from Dunlop. The K81 front is 19" so I contacted an ebayer from uk and planned to get the K82 for the 18" rim to match the K81 rear. He has not responded.
    I ended up ordering IRC GS-11 and don't know if anyone has tried those, inexpensive and hope that doesn't mean too cheap. I will have the tires Wednesday and NEXT i will need the bike I saw them on, YEAA! http://www.motorcycleclassics.com/classic-german-motorcycles/hercules-w-2000-zmwz12mazbea.aspx

    Anyway here are some excerpts from a review I read that swayed me away from going big-is-bad look.

    . . . ended up ignoring the advice of the owner's manual, despite my admonitions to everyone else to do so.

    . . . owner's manual is clear -- a 90/90-18 front and a 120/90-18 rear. So I yet again fought off all impulses to try and second-guess the designers, swallowed hard and ordered those sizes.

    most amazing thing is the difference in handling. I hereby state that I will never second guess the tire engineers again. The bike now feels very neutral with the tiny 90 mm wide Lasertec front; the tendency to fall in to turns is completely gone.

    The moral of the story, you already know. Don't second guess the designers. Read the owner's manual and stay with the stock tire sizes (and recommended oil type and weight).

    The review was for Metzler Lasertecs on WebBikeWorld
  15. Pork Chop

    Pork Chop XS400 Junkie

    I have heard good things about the lazertec tyres.

    I have got k81 front 3.0x18 and rear 4.0x18.
  16. 226dark

    226dark 78 2E

    SW MN
    K81 18 incher for front?? Darnit, not in the states it seems :(
  17. davey1207

    davey1207 1981 Yamaha xs400 Special

    thanks for the help and great comments on my bike guys! I still have not ordered the new tires yet but plan on doing so soon. you guys are a big help ALWAYS! I'm gonna post some new pics of my xs400 for ya!

    Attached Files:

  18. davey1207

    davey1207 1981 Yamaha xs400 Special

    i don't know why it uploads upside down sorry!
  19. davey1207

    davey1207 1981 Yamaha xs400 Special

    2nd try at uploading correctly

    Attached Files:

  20. drewpy

    drewpy Excess twin Top Contributor

    that's for the aussies :laugh:
    Jon likes this.

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