Topic: Gear ratio 18-48 or 17-48

[HondaMan]

My K8 sprocket on the front is a 15 and on the back is a 41....make any sense???  Oh ya the back tire a 17" rim too...

The K8 used the 630 chain size, so the teeth are different from the earlier models. The ratios are about the same, though.

[HondaMan]

The smaller diameter rear tire would act like a bigger rear speocket and increase your RPM for a given speed.

So my 48 tooth sprocket is actually acting like say a 52 tooth becasue of the smaller tire ?

The stock tire (4.00) on the stock rim (18") makes about 26" diameter. The 17" wheel with 130/100mm tire makes about  27.25" diameter. This should make the RPM about 3850 in 5th at 60 MPH if you have 18T/48T. Stock setup yields about 4000 RPM at 60 MPH. Changing to 17T/48T should yield about 4175 RPM at 60 MPH (stock tires).

These RPM numbers vary a little, depending on tire wear, brands, and tire pressures. And clutch condition.

[mwohlenhaus]

you also have to remember that 130 is the width not the height.  width has no effects on anything other than increased drag and traction.

[HondaMan]

What? I got the 130/110 backward?
Shame on me.   

[eldar]

SCOUT, that is the factory gearing for the K8. Pretty decent ratio really. It is more of a top end setup. Ratio is something like 2.73  the K0 was 2.8 or so. Dont care to get to into math! if I was to do a 530 conversion, I would go with 17/47. As it stands, with my 630 set up, I run about 4800 rpm at 70mph. Not too bad really.Still not even tapping my mains fully probably. Still gotta get my idle mix set one of these years! I can spin the fatty a little even with this gearing but once tuned, I should be able to smoke it a little!

Just to add, I have the 17in rim and  130/90 tire

[K8 Scout]

  Thanks Eldar.... I'm ok with factory...seems to be running great with this gearing, so until I need to replace chain and sprockets, I'm just going to leave it alone....might even sell the K8 as I was offered $2200.00 canadian for the old girl and I got a line on a 2003 HD anniversay sportster with only 1900 kms for 7000 

[cbjunkie]

meh.

K8 - HD Sportster...

what's the difference?

[Andrew Foss]

my 76' 750F runs about 6000rpm at 80 mph. i was originally planning on putting a taller sprocket set there to bring down the rpms, but the engine really seems to "settle in" right about there (runs smoother than cruising at higher or lower rpms). unfortunatly, the charging system boils out the battery when you go 80 for about four hours straight. how does the F gearing compare to other bikes??
-andrew

[GroovieGhoulie]

my 76' 750F runs about 6000rpm at 80 mph. i was originally planning on putting a taller sprocket set there to bring down the rpms, but the engine really seems to "settle in" right about there (runs smoother than cruising at higher or lower rpms). unfortunatly, the charging system boils out the battery when you go 80 for about four hours straight. how does the F gearing compare to other bikes??
-andrew

The F was geared shorter with a 17/48 sprocket, which approximates the original (and perfect IMO) K0 ratio.  Also, 4th and 5th are a little shorter than the K 4th and 5th, giving more "punch", but making for higher RPMs while cruising.  The F had a higher redline than the K, so the shorter gears could still wind up and not run out of revs.

[dusterdude]

meh.

K8 - HD Sportster...

what's the difference?

nah,im not gonna touch that.

[ProTeal55]

So where should someone turn to purchase a new rear sprocket ?
I am looking for something in the 45 tooth and lower range I would think....

[cbjunkie]

ha-ha - i knew i'd get a bigole fish with that one...

[HondaMan]

So where should someone turn to purchase a new rear sprocket ?
I am looking for something in the 45 tooth and lower range I would think....

The HONDA genuine sprockets are exceedingly hard to beat. They have tapered teeth and a 0.5mm oversize base circle for long chain life, smoother power transition (spell that "lower losses"), and better, truer chain direction running. They are also very hard steel, and they are drilled out for lightness, almost as light as an aluminum sprocket. (AL won't last as long, often are not truly round or concentric, and have square-cut ANSI teeth that dislike the misalignments that come from big throttle openings.     ).

[ProTeal55]

Are these available at my local dealer - or should I look to somewhere on the net ?

[Ernie]

i have a 550 k and i just wish there was a transmission mod to add a sixth or seventh gear or just make fifth gear a higher ratio,now that would be sweet

[HondaMan]

i have a 550 k and i just wish there was a transmission mod to add a sixth or seventh gear or just make fifth gear a higher ratio,now that would be sweet

The 550 will pull up to 4 less teeth on the rear without much trouble, if the engine's in good shape. You might want to add +2 degrees to the spark timing in the process, then run on premium gas. Make sure you're using the D7 heatrange plugs. Also, run at least 32 PSI in the tires, or your gas mileage will actually drop a little. If the tire(s) will accept it, run 34 PSI (check the sidewall for ratings).

This is what we used to do for the couples where the guy was riding a 750 and his girl was riding a 500/550, and they toured together. It works out well.

[DarkRider]

So after reading all of the above that is saying my K4 should have the 18/48 combo correct? Now say i want to get max punch ouf of my bike mostly for in town riding would i be better off with the 17/48?

[nteek754]

Hey guys  check out the post  differance between the 750 KandF oops

[Zip]

I went from 17/48 to 18/48 to 18/45 to bring the revs dpwn on the highway (70+mph).  The engine felt way too busy previously.

Zip

[nteek754]

Hey all, been runnig  18 48 for  hmmm 30 years now  (yup go ahead call me an old timer) also a 16 inch rear 130 now the 16 doesnt change it much at all in fact I wouldnt of really noticed if  sister hadnt been runnig a 17 for a while and  side by side  with her  accilerating just a smigin the engines would harmonize we didnt bother  asking each other what the revs were cause of tach error cause it is so minnor but as far as someone saying  that 18 48 was too tall I disagree I think its just perfect for all around rideing  and I put an average of  10,000 a season yup if I was going to go 1/8th mile dragging I would put my 17 tooth on but not for everyday rideing  and on the other hand if I wanted 70 mpgs I'd put a 43 on the back but what a hondog around town  I just love smokin them 1200 harleys  sorry Barry  and a few others  names I wont mention lol this year I guess I am cheating a bit  running a 1973 750 K kerker pods and oh yeah its an 836  its a pretty sweet sleeper  but in all fairness for the last three decades  been running stock 736

[HondaMan]

So after reading all of the above that is saying my K4 should have the 18/48 combo correct? Now say i want to get max punch ouf of my bike mostly for in town riding would i be better off with the 17/48?

Sorry 'bout the delay: I've been under the car hoods again...   

I really like the 17/48 combo in commuter driving. I have to ride 20+ miles one way to work, half in stop-go traffic lights and half on interstates at up to 80 MPH. The 17/48 lets me ride 1 gear higher than "normal" in the t'lights areas, which helps keep the engine a little cooler and not so busy. It does wind a bit more on the highway, but the throttle response is better, too, in high gear. It pulls about 128 MPH tops in 17/48 in nearly any conditions, about 131 tops in 18/48 on a flat, windless road. I've always felt the 18/48 was more for Honda's warranty benefit and for those who wanted a little less noise at 55 MPH, which happened right about the time the K3 came out. On mine (in 18/48 trim), I always could get better MPG at 55 MPH, 2-up, loaded in 4th gear than in 5th gear. I had to get up to 62 MPH to stop "rowing" through gears in hilly country this way, and 65+ to get the same MPG that I got at 55 MPH in 4th. That's my observations that lead to my "overgearing" position. I've also found that the K4-K6 owners I've ridden with also had similar results, but those bikes only made about 40 HP on the ground.

Guys I know who added cams with slightly more duration (not more lift) would get better results in the 4000 RPM range with the 18/48 combos in high gear, heavily loaded. Now that mine is rebuilt with something like this (.020" less lift than stock cam, but +4 degrees duration on the intakes, stock on the exhaust side), I really notice a strong difference in the 3k-4k range in high gear with the 17/48 setup. Of course, mine is a hemi, too....

[cbjunkie]

that's the most helpful post on this topic yet - thanks Hondaman...

[Ernie]

i have a 550 k and i just wish there was a transmission mod to add a sixth or seventh gear or just make fifth gear a higher ratio,now that would be sweet

The 550 will pull up to 4 less teeth on the rear without much trouble, if the engine's in good shape. You might want to add +2 degrees to the spark timing in the process, then run on premium gas. Make sure you're using the D7 heatrange plugs. Also, run at least 32 PSI in the tires, or your gas mileage will actually drop a little. If the tire(s) will accept it, run 34 PSI (check the sidewall for ratings).

This is what we used to do for the couples where the guy was riding a 750 and his girl was riding a 500/550, and they toured together. It works out well.

wow thats very helpfull thnx Hondaman

[DarkRider]

So with that said the 17/48 combo would bring my K4 closer to the performance of a K0?

[GroovieGhoulie]

So with that said the 17/48 combo would bring my K4 closer to the performance of a K0?

Yes.  The engine will still be detuned, but it'll have more "pep".