A "smaller" rear hub on a KX500 to run a tiny sprocket? Does it exist?

[radeenshemirani]

Here's a gnarly question for y'all:
I drag race a 2001 Kawasaki KX500 2 stroke. Currently looking for some more top speed. With 16/38 gearing it tops out just under 100MPH, and currently need it geared well into the 120s as I am letting off and shutting the bike off around 1000 feet. 

Here's my issue: I talked to a few custom sprocket shops and the smallest sprocket they said I could fit on my bike was a 36t sprocket, and that wasn't even guaranteed. They claimed that they wouldn't recommend me paying for anything under 37 because they couldn't guarantee that it would work. Now, there is a solution, albiet an expensive one. Something called a "Quick Change Barnes Style Hub". Basically a hub with a tiny outer flange that would let me run sprockets into the low 20s. Issue with this is, the hub alone is over 600 dollars. Tie in a wheel, lace kit, and bearings and I am looking at over 1,000 bucks JUST in my rear wheel. Keeping in mind I am only about 750 bucks in this ENTIRE bike, does anybody know of a solution that would let me run somewhere around a 32t sprocket? Is there a Kawasaki hub with a smaller I.D that I could run and lace onto my existing rim? Or am I screwed with buying this expensive flat track hub that will let me finally get this bike into the 10s? 

ANY help is appreciated!

[highmarker]

taller tire maybe? or possibly taller primary gear set from a different model or year bike or quad. keep searching because I doub't your breaking new ground, somebody has delt with it before. Drag roadrace speed record  etc.

[radeenshemirani]

58 minutes ago, highmarker said:

taller tire maybe? or possibly taller primary gear set from a different model or year bike or quad. keep searching because I doub't your breaking new ground, somebody has delt with it before. Drag roadrace speed record  etc.

Running a 28" tall tire so thats out of question. Modifying the trans is a possibility as the KX5 trans is close ratio. I'd have to talk to someone who knows these transmissions, maybe run a primary gear set out of a KLR? 

Talked to a bunch of flat track guys and they all said *Quick Change Barnes Hub* which I REALLY don't want to have to do, but if it's a necessity I could. I've seen a few top speed/bonneville KXs and they run their own custom hubs, which is my dilemma. 

[ossagp]

I had an 83 kx500 that I took to the drags.  No Hd's with license plates got close to it in time.  13.23 and it was topped out at 96 in what felt like it was halfway down the strip.  Now mine was tuned.  It had a 15 tooth countershaft and the stock 43 tooth sprocket that it came with.  my tire was a carlisle dirt track tire,  not nearly 28 inches high.  Smaller carb than yours (38mm mikuni vm type).  Stock pipe.  the tire spun easily and the front wheel was off the ground a lot (stock suspension).  some of my times were up in the 14's that day because of spin,  wheelying corrections,  or as in the first run when it was coldest I backed off due to getting a ringing pinging noise (we retarded the spark so much that we had to push start it) on pump gas.  After retarding the spark we had a gain from just over 93 mph at the big end to the 96 that it ran everytime after that.  all that to tell you that you need to turn yours IMO before you go spending a lot on wheels.  you can get down to 40 on an old drum type kx wheel,  as sprocket specialists did one for me later to use on the ice.  (well over 100 mph on clear icey lakes was a snap).  you can also find any wheel off a street bike and get well under 40,  but yours is winding out and going flat WAYYYYYYYYY too soon.   Among other things, likely richer than heck and the float hasnt been set since it saw the factory.  But if you are hell bent on a barnes or kosman wheel and want to pay even 600 remember me!!!  

[radeenshemirani]

14 hours ago, ossagp said:

I had an 83 kx500 that I took to the drags.  No Hd's with license plates got close to it in time.  13.23 and it was topped out at 96 in what felt like it was halfway down the strip.  Now mine was tuned.  It had a 15 tooth countershaft and the stock 43 tooth sprocket that it came with.  my tire was a carlisle dirt track tire,  not nearly 28 inches high.  Smaller carb than yours (38mm mikuni vm type).  Stock pipe.  the tire spun easily and the front wheel was off the ground a lot (stock suspension).  some of my times were up in the 14's that day because of spin,  wheelying corrections,  or as in the first run when it was coldest I backed off due to getting a ringing pinging noise (we retarded the spark so much that we had to push start it) on pump gas.  After retarding the spark we had a gain from just over 93 mph at the big end to the 96 that it ran everytime after that.  all that to tell you that you need to turn yours IMO before you go spending a lot on wheels.  you can get down to 40 on an old drum type kx wheel,  as sprocket specialists did one for me later to use on the ice.  (well over 100 mph on clear icey lakes was a snap).  you can also find any wheel off a street bike and get well under 40,  but yours is winding out and going flat WAYYYYYYYYY too soon.   Among other things, likely richer than heck and the float hasnt been set since it saw the factory.  But if you are hell bent on a barnes or kosman wheel and want to pay even 600 remember me!!!  

I ran a 12.5 shutting the bike off at the 1000' mark. Running 16/38 gearing with a flat track rear tire. And I run 95 octane in it to avoid the pinging you describe because I experienced it also.

 

My bike was cutting out probably around 98mph. IIRC the 80s KXs had a wider ratio trans than the newer ones 

[Jimmy boy]

I used to run a 81 YZ 465 w/ 16/40 gearing . 105mph was as fast as it would go. My best time was 008 reaction and 12.05.

[ossagp]

I have owned three of them,  the first one being the only one that went to an actual quarter of mile.  The transmissions were not so different.  The later ones came with a 46 tooth rear sprocket and the same 14 on front that mine did.  Do the math on your gearing and you will see it is a good 17 percent higher than I was using, not to toss in your taller tire.     Mine just sang itself out about halfway and you could roll the throttle way back and still maintain the 96 I was getting.  all on pump gas and I actually had an extra head gasket in that one to keep it from hammering the pistons apart for ice racing.   if yours is cutting out it is too rich.  but you do what you have to in order to make it live.  If you are happy with the tune you have it in,  all the better.  If I had ever taken mine back with the higher ice gearing and a street tire (I had plenty of those wheels that must be rare where you are,  still do as indicated) I am confident that I would have easily gotten 10 mph faster with the engine just like it was.  Even the 40 tooth would have helped.  The liquid coolers were just a bit faster. 

Anyway,  if you want taller gearing it isn't as hard as you indidate.  just look to the street bikes for a wheel.  

[ossagp]

6 hours ago, Jimmy boy said:

I used to run a 81 YZ 465 w/ 16/40 gearing . 105mph was as fast as it would go. My best time was 008 reaction and 12.05.

I had a yz490 (technically I guess I still do since my friend who bought it from me hasnt ever finished paying me back).  Exhaust port raised up about .045 and transfers about 25, decked down cylinder to make the compression back and rounding the "bend" on the squish It would beat any of my KX's.  That engine was maybe my favorite.  If I see an IT version of it reasonably I think I will buy it and put some USD's on the front and a disk on the back.  I have two CR500's.  both 87's.  Both stock cylinders.  They wont catch the 490 in a straight line either.  

[radeenshemirani]

19 hours ago, ossagp said:

I have owned three of them,  the first one being the only one that went to an actual quarter of mile.  The transmissions were not so different.  The later ones came with a 46 tooth rear sprocket and the same 14 on front that mine did.  Do the math on your gearing and you will see it is a good 17 percent higher than I was using, not to toss in your taller tire.     Mine just sang itself out about halfway and you could roll the throttle way back and still maintain the 96 I was getting.  all on pump gas and I actually had an extra head gasket in that one to keep it from hammering the pistons apart for ice racing.   if yours is cutting out it is too rich.  but you do what you have to in order to make it live.  If you are happy with the tune you have it in,  all the better.  If I had ever taken mine back with the higher ice gearing and a street tire (I had plenty of those wheels that must be rare where you are,  still do as indicated) I am confident that I would have easily gotten 10 mph faster with the engine just like it was.  Even the 40 tooth would have helped.  The liquid coolers were just a bit faster. 

Anyway,  if you want taller gearing it isn't as hard as you indidate.  just look to the street bikes for a wheel.  

About the transmissions; that's actually good to know. Was gonna start doing some research on swapping out gears from older KX5s

 

theres always a possibility that my tune is off. I've noticed after I let off at 90something MPH the bike does some serious surging. It runs amazing, but has the surging issue which indicates to me there's some carb work to be done.

 

is it even possible to put a street wheel/hub on the bike? Willing to bet the ID of the hub to sprocket bolt pattern is smaller on that than the KX5s hub.

 

Thank you again for the info 

[ossagp]

Yeah, the whole idea of getting a hub off of a streetbike is that the sprocket mount is going to have a smaller diameter.  Just take a look at the medium sized street bikes and you see them running stock gearing with less than 40 teeth.  I think I would look for a sportbike wheel and plan on going from the larger 6 series chain down to a 5 series like the kx has.   that way you can get  a wider rim.  No reason to use any of the wheel parts on your kx.   back end off a wreck from the late 80's on should do nicely.

I think you are on your way to a fun project,  and that there is some tuning to get yours making hp up into the 9k range.  Look over at some of the products offered to mini sprint racers etc,  I would consider tossing the valve linkage and opening it up and locking it open,  and play with raising the port timing as a future step.  get the back lower and stiffer,  and I bet you get a second off of it soon.   

[radeenshemirani]

2 hours ago, ossagp said:

Yeah, the whole idea of getting a hub off of a streetbike is that the sprocket mount is going to have a smaller diameter.  Just take a look at the medium sized street bikes and you see them running stock gearing with less than 40 teeth.  I think I would look for a sportbike wheel and plan on going from the larger 6 series chain down to a 5 series like the kx has.   that way you can get  a wider rim.  No reason to use any of the wheel parts on your kx.   back end off a wreck from the late 80's on should do nicely.

I think you are on your way to a fun project,  and that there is some tuning to get yours making hp up into the 9k range.  Look over at some of the products offered to mini sprint racers etc,  I would consider tossing the valve linkage and opening it up and locking it open,  and play with raising the port timing as a future step.  get the back lower and stiffer,  and I bet you get a second off of it soon.   

If I use the entire assembly off of an older streetbike, that means I would need the entire wheel setup, axle, brake caliper and mount for the swingarm, etc? Would the hub fit inbetween the swingarm? Id have to do some measuring before I actually buy a wheel. And I can shorten and lengthen my chain for the smaller rear sprocket, I already have 3 or 4 chains for different sprocket setups depending on where I ride the bike.

I have always wanted to get the bike dyno tuned. There's definitely improvements to be made, I tuned it the best I can on my own doing passes in my busy neighborhood.

Whats this about keeping the powervalve open? Wouldn't that kill bottom end power?

Edited April 10, 2017 by radeenshemirani

[ossagp]

For a long time they didn't come with power valves.  working on the assumption that if you need lower end on a drag bike,  flattrack bike etc, something is wrong.  FYI my hondas would skin my kx's for low end.  made similar hp at 1000 rpm less,  go figure, huh.  Easiest thing to do is to get some bearing sizes and go from there on the wheels.  sprockets and disks can be cut down to make spacers if you want.   It's a cake walk.  fyi the barnes and Kosman hubs generally require adapters to fit your axle too.   if you have a motorcycle salvage yard, I would head over with your wheel or a measuring tape.  Look at what has the disk and sprocket around the same distance apart as yours.  

[radeenshemirani]

6 hours ago, ossagp said:

For a long time they didn't come with power valves.  working on the assumption that if you need lower end on a drag bike,  flattrack bike etc, something is wrong.  FYI my hondas would skin my kx's for low end.  made similar hp at 1000 rpm less,  go figure, huh.  Easiest thing to do is to get some bearing sizes and go from there on the wheels.  sprockets and disks can be cut down to make spacers if you want.   It's a cake walk.  fyi the barnes and Kosman hubs generally require adapters to fit your axle too.   if you have a motorcycle salvage yard, I would head over with your wheel or a measuring tape.  Look at what has the disk and sprocket around the same distance apart as yours.  

I mean, no it isnt neccesary, its definitely nice though, haha. I launch out of second, with the throttle nearly pinned and releasing/feathering out the clutch, hillclimb style. Helps the transition when "powerband" kicks in. One of the photographers at my track has a picture of me with the front wheel coming up in the air as the bike hit powerband in second. Yeah, chances are ill take one of my spare KX5 hubs to my local motorcycle salvage yard and do some measurements. Even if I can find a hub that has the same width but different bearing sizes I can buy the axle assembly also as long as it fits through my swingarm. And yes, the Barnes style hub requires a new axle, bearings, etc. 

[ossagp]

12 hours ago, radeenshemirani said:

I mean, no it isnt neccesary, its definitely nice though, haha. I launch out of second, with the throttle nearly pinned and releasing/feathering out the clutch, hillclimb style. Helps the transition when "powerband" kicks in. One of the photographers at my track has a picture of me with the front wheel coming up in the air as the bike hit powerband in second. Yeah, chances are ill take one of my spare KX5 hubs to my local motorcycle salvage yard and do some measurements. Even if I can find a hub that has the same width but different bearing sizes I can buy the axle assembly also as long as it fits through my swingarm. And yes, the Barnes style hub requires a new axle, bearings, etc. 

The barnes is a really easy one to put on.   I bought extra adapters blanks for that,  spin them to width.  Like a lot of things,  it is easier to put spacers behind the the sprocket and brake disk than make the wheel narrower.   But the barnes or kosman (kosman  hubs are harder to find,  but PRETTY when you consider the work).  Axle diameter again,  nothing to it.  You can machine off the bottom of the slot and lose nothing as far as strength goes for riding purposes.  You can have collars or bushings made if you end up with a smaller axle.  The barnes just uses a stepped adapter to fit and existing axle which you can do for any wheel actually.  FYI best time on the air cooled kx came with a third gear very boring nearly lug off in third launch.  the following two shifts were about 3 heart beats apart and then you wait to get to the end.  I don't know why I didn't take that one back, lowered and with a street tire.  and some higher gearing.  

[turbo dan]

Seems like you should be turning a few more RPM if you're topping out with the current gearing.  My KDX tops out at an indicated 90 MPH with 15/46 gearing.  I don't think it's running more than 9500 RPM, tops.  I also don't know what your overall gear ratio is but I don't think they would be running a shorter top gear on the 500.  Those are desert bikes and they often run into the 100's without drastic measures.

I wonder if the powervalve is fully operational.  That's got a center valve in the main port and two drum valves operating four sub ports.  Lots of stuff going on.  Makes more sense to make sure you're getting 100% out of the motor rather than it does rigging up a different rear wheel on a bike thats signing off 3000 rpm early.

[turbo dan]

I'm actually looking at a 1994 issue of Cycle World magazine about a team green Baja KX500.  Running 16/42 gearing and topping out at 115.  On a stock size knobby tire.

You're definitely missing revs.  If 16/42 was getting them 115, 16/37 would get you 128 assuming drag is not a limiting factor.

Edited April 12, 2017 by turbo dan
added math!!!!!!

[crazyal426]

16/38 and just under 100mph?  You have an engine problem.  Low compression or KIPS is not opening.

[Greta Fauchi]

On 4/10/2017 at 11:14 AM, radeenshemirani said:

About the transmissions; that's actually good to know. Was gonna start doing some research on swapping out gears from older KX5s

 

theres always a possibility that my tune is off. I've noticed after I let off at 90something MPH the bike does some serious surging. It runs amazing, but has the surging issue which indicates to me there's some carb work to be done.

 

is it even possible to put a street wheel /hub on the bike? Willing to bet the ID of the hub to sprocket bolt pattern is smaller on that than the KX5s hub.

 

Thank you again for the info 

As far as swapping transmissions, here you go. Just need to join to view it.

A bit of machine work on the clutch hub, I believe a bushing or spacer too and you have a wide ratio k5. See the transmissions on fleabay by the dozens.

 

If you're dragging/modding/looking to squeeze every pony out of that machine, the site I linked is the place to be. K5 specific info on fixing the closed throttle surge (super easy, just a modified bolt to stop the pv from "over closing"), timing, tuning, lectrons, porting, wheels and hubs, a really trick looking intake setup to stop reversion, blah blah. 

http://www.kxriders.com/forums/index.php/topic,11029.0.html

Edited April 15, 2017 by Jethrobolas

[crazyal426]

The end short answer to the KLR gears, no, it won't work.  Fix your engine, the gearing you are running you should have very tall legs and it sounds like your engine is not making the juice.

[radeenshemirani]

On 4/14/2017 at 3:43 PM, crazyal426 said:

16/38 and just under 100mph?  You have an engine problem.  Low compression or KIPS is not opening.

Sorry for such the late reply. School and priorities, etc etc typical excuses

 

Definitely not low compression. Engine has less than 30 hours and kicked over 170 psi. I am thinking of taking it to my local dyno that does 2 stroke dynos 

On 4/15/2017 at 6:30 AM, Jethrobolas said:

As far as swapping transmissions, here you go. Just need to join to view it.

A bit of machine work on the clutch hub, I believe a bushing or spacer too and you have a wide ratio k5. See the transmissions on fleabay by the dozens.

 

If you're dragging/modding/looking to squeeze every pony out of that machine, the site I linked is the place to be. K5 specific info on fixing the closed throttle surge (super easy, just a modified bolt to stop the pv from "over closing"), timing, tuning, lectrons, porting, wheels and hubs, a really trick looking intake setup to stop reversion, blah blah. 

http://www.kxriders.com/forums/index.php/topic,11029.0.html

Thank you for the link!

I do have the closed throttle surge, so I will definitely look into that. Thank you