A little math formula

Discussion in 'General VFR Discussions' started by Outboard John, Dec 25, 2015.

  1. Outboard John

    Outboard John New Member

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    I have getting closer to pulling the trigger on a set of PR4's for my Multistrata. Now I used to think that my VFR was a little tall, so I've flipped the triangles and dropped the front 10mm, better now. Well tall is relative. The VFR feels tiny after purchasing the MTS last year. Any way back to the tires. The MTS uses 190/55 and 120/70 17's. So I got to thinking about the side wall aspect ratio to width and what difference it would make in over all tire height. I found a formula online to calculate this and it's kind of interesting (at least if your vertically challenged). Goes like this, rim size (17) + 2x aspect ratio (that's 50 on the 190/50) x width(190) /25.4 in this example the tire height is 24.48 which compared to the 190/55 is about 3/4" shorter (25.22) not huge, but 3/4" there, the difference on the front tire is about an inch (the 60 verses the 70) ,then drop the front a few mm, shave the seat a bit and it all starts to add up, and this, is the shit you can do when you retire to keep yourself from watching too much Judge Judy. Lol!
    P.s. Didn't do well at math in school, so if I f...d this up, please correct me so my bs doesn't go any further.
    John
     
  2. Outboard John

    Outboard John New Member

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    Well, I've had it pointed out to me by my best friend and past tire sales man, that I would only reduce the height by half of what I thought I would since we are talking about the over all height of the tire, half of the savings would be on the top, half on the bottom. Not all at the bottom (lowering the bike) like I first thought. Oh well.
     
  3. RVFR

    RVFR Member

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    I've done this math for sports cars, not motorcycles, thing was in the auto world was to keep the tire height, as in today's world it's all about the rim. ei; take a MR2 from the early 90s, they had 14" rims now to add 19" or 17" you had to do some creative math to get them tires so they would fit. Now with Motorcycles a fender clearance issue isn't a problem. I can see you lowering a 1/2" with a profile adjustment if they are made. I now ask at what cost to handling may come about? Most tires want a certain contact patch to work like they should. Does this foul that up?
     
  4. Outboard John

    Outboard John New Member

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    Good point, I really don't know. I should probably get involved in my Ducati forum and see if anyone there has first hand experience with this. It just doesn't feel like home over there yet.
     

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