2005 CRF450X Street Supermoto Gearing
  • What size rear sprocket

    39t
    0
    No votes
    40t
    1
    50%
    42t
    0
    No votes
    other
    1
    50%
     
    Total votes: 2
  • thormx88yz1
    Posts: 12
    Joined: Mon Jul 16, 2012 3:03 pm

    2005 CRF450X Street Supermoto Gearing

    by thormx88yz1 » Thu Sep 06, 2012 6:47 am

    I have a big bore stroker 510cc CRF450X that I am in the process of converting to Sumo, and am looking for some gearing insight.

    I have ordered a 14t front sprocket +1 from the stock 13, and am now trying to decide how small I want to go in the back. I am debating between a 39t, 40t, or 42t. The 39t will give me a top speed 104.3 MPH at 9000 RPM, and the 42t will have a top speed of 96.9 MPH with the supermoto wheels and tires, and the 40t at 101.7 MPH.

    My question is, will the motor be lugging too hard in the low gears? I can always swap the 13t stock front back in place of the 14t to give me more accel, so I think I want to err on the tall side. I am leaning towards a 40t.

    Any insight or opinions appreciated.
  • thormx88yz1
    Posts: 12
    Joined: Mon Jul 16, 2012 3:03 pm

    by thormx88yz1 » Thu Sep 06, 2012 6:50 am

    Also, is there any detriment with going way small in the back other than killing accel? For example, chain/sprocket wear, chain rubbing, etc. I will be riding on the street for the most part, with probably 25% highway, so I want to have a comfortable cruising RPM at ~70 MPH.
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    crfsonly
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    by crfsonly » Thu Sep 06, 2012 8:21 am

    you won't be able to go small enough in the rear sprocket to affect chain wear. you may be able to answer your question using our sprocket/RPM calculator:

    http://crfsonly.com/howto/gearing/motor ... ulator.php

    ken
    OEM Parts for Honda - Yamaha - Suzuki - Kawasaki: http://yeltrik.com
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  • thormx88yz1
    Posts: 12
    Joined: Mon Jul 16, 2012 3:03 pm

    by thormx88yz1 » Thu Sep 06, 2012 9:13 am

    Thanks for the reply Ken.

    I used the Gearing Calc to get the general idea of where I want to be, which I think is going to end up being the 40t. That was if it is too drastic, I can go back to the 13t up front and have effectively the same gearing as 14t/43t.
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    gal8x
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    by gal8x » Thu Sep 06, 2012 12:22 pm

    That is exactly what I did. I am holding on to my new 14T and will use it when I replace my 40T with a 43T. that will be when the chain needs replacing.
    2005 CRF450X (plated)
    "Can't never could do anything"
  • thormx88yz1
    Posts: 12
    Joined: Mon Jul 16, 2012 3:03 pm

    by thormx88yz1 » Fri Sep 07, 2012 5:22 am

    gal8x wrote:That is exactly what I did. I am holding on to my new 14T and will use it when I replace my 40T with a 43T. that will be when the chain needs replacing.


    Thanks for the info! Would you not benefit more from the 13/40 since both sprockets are smaller = less weight and rotating mass?

    What speed does your bike cruise at? and are you on a 17" wheel with this set up?
  • User avatar
    gal8x
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    by gal8x » Fri Sep 07, 2012 8:49 am

    thormx88yz1 wrote: Thanks for the info! Would you not benefit more from the 13/40 since both sprockets are smaller = less weight and rotating mass?

    I’m not sure. I like the ‘angle-of-attack’ of a 14. I would prefer a 15 but I will always use a cases saver. I dont race so weight is not a factor. The 13T is the OEM and is warn (I Know it will degrade the chain faster). The 40T is a very light grade aluminum, I don’t expect it to last long. I can get a 43T in steel that looks bad azz…
    http://www.crfsonly.com/catalog/product ... cts_id/634
    so when the time comes that is what I plan to do. I think if I powder coat the supporting spars black, the chain will give the allusion it is floating off the hub.

    thormx88yz1 wrote: What speed does your bike cruise at? and are you on a 17" wheel with this set up?

    18” 90/120
    With the 14/40 setup she would cruse 75 mph at 62++ rpm. I have not been on the highway since converting to the 13/40. On the back roads it really likes 50-55 (third gear). My issue is my front tire simply will not true correctly. The Honda dealer could not do it and I am better than they are.
    2005 CRF450X (plated)
    "Can't never could do anything"
  • thormx88yz1
    Posts: 12
    Joined: Mon Jul 16, 2012 3:03 pm

    by thormx88yz1 » Fri Sep 07, 2012 9:03 am

    gal8x wrote:
    thormx88yz1 wrote: Thanks for the info! Would you not benefit more from the 13/40 since both sprockets are smaller = less weight and rotating mass?

    I’m not sure. I like the ‘angle-of-attack’ of a 14. I would prefer a 15 but I will always use a cases saver. I dont race so weight is not a factor. The 13T is the OEM and is warn (I Know it will degrade the chain faster). The 40T is a very light grade aluminum, I don’t expect it to last long. I can get a 43T in steel that looks bad azz…
    http://www.crfsonly.com/catalog/product ... cts_id/634
    so when the time comes that is what I plan to do. I think if I powder coat the supporting spars black, the chain will give the allusion it is floating off the hub.

    That looks cool, but I am probably just going to end up getting a steel JT sprocket off ebay as they are only $31 and some change shipped. I am on a fairly tight budget as I intend on putting the bike up for sale once it is complete and hopefully street titled, and I also have to believe this design would be stronger than the thin-spoked style one.

    thormx88yz1 wrote: What speed does your bike cruise at? and are you on a 17" wheel with this set up?

    18” 90/120
    With the 14/40 setup she would cruse 75 mph at 62++ rpm. I have not been on the highway since converting to the 13/40. On the back roads it really likes 50-55 (third gear). My issue is my front tire simply will not true correctly. The Honda dealer could not do it and I am better than they are.


    Too bad I don't still live in Clear Lake or I could have sold you my front wheel!

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