Difference in Top Speed

[Bazetech]

Just wondering about putting a 16T countershaft sprocket on. What kind of a top end increase could a person expect? I do alot of highway to get to the dirt and want to calm the R's when traveling at 70mph for extended periods. Thanks.

[sebastacruz]

From what i gather it may not be a great idea to run a 16t. I thought about it for awhile too and after reading that, with a case saver, the chain still would have enough slop when properly adjusted to nick the case. Bad news.

-You could always go down 3 in the back, ya? Same difference:excuseme:

[vash]

I use a 13/45 to 15/45 setup. Works well.

I was going at about 160-170KMH for an hour about a month ago and she didnt feel too wrung out, but then i had earplugs in.

[motopsycho650]

Oh lets see how well I remember this. Start by finding your current gear ration (not really "the" gear ratio, but for this purpose...).

Mine is 14 / 48 = .292. My top speed is 95 MPH up here in the altitude. Now figure out the new gear ratio, i.e 16 / 48 = .333. Now, cross multiply, i.e:

(current max speed * new ratio) / current ratio = new max speed

95 * .333 = 31.635

31.635 / .292 = 108.34 mph (theoretical new top speed)

[XR650L_Dave]

It may make your chosen cruising speed a skosh less buzzy, but I do not think you will gain top speed by gearing up from stock.

Dave

[Kenzo]

It may make your chosen cruising speed a skosh less buzzy, but I do not think you will gain top speed by gearing up from stock.

Dave

yup ?

unless u have the HP to bounce it off the rev limiter with the stock final gearing...raising the gearing just reduces the rpm at any given speed.

when i geared down to a 14T from a 15T there wus no significant change in top speed...only the rpms it wus turning.

[rdjohnson55]

HRC ran 14/45 for BITD and 15/47 for Baja

[motopsycho650]

It may make your chosen cruising speed a skosh less buzzy, but I do not think you will gain top speed by gearing up from stock.

Dave

I 100% disagree. With 14/48 gearing, the counter shaft sprocket is turning 3.42 times per rotation of the rear wheel. If you change to 15/47, the counter shaft sprocket ratio changes to 3.13 rotations per rotation of the rear tire. Just like changing diff gearing in a car/truck, it will change top speed, provided the engine has the HP. And yes, cruising speeds will need less RPM's.

For fun, say the rev limiter keeps the counter shaft at 10,000 rpm (hypothetical number). With 14/48 gearing the rear wheel will be doing 2920 RPM. With 15/47 gearing, and the same 10,000 RPM's from the counter shaft, the rear wheel will be turning at 3130 RMP.

Plug 15/47 into my formula instead of 16/48, and my 95 mph top speed should increase to approx. 103.78 mph

[Kenzo]

It may make your chosen cruising speed a skosh less buzzy, but I do not think you will gain top speed by gearing up from stock.

Dave

I 100% disagree. With 14/48 gearing, the counter shaft sprocket is turning 3.42 times per rotation of the rear wheel. If you change to 15/47, the counter shaft sprocket ratio changes to 3.13 rotations per rotation of the rear tire. Just like changing diff gearing in a car/truck, it will change top speed, provided the engine has the HP. And yes, cruising speeds will need less RPM's.

For fun, say the rev limiter keeps the counter shaft at 10,000 rpm (hypothetical number). With 14/48 gearing the rear wheel will be doing 2920 RPM. With 15/47 gearing, and the same 10,000 RPM's from the counter shaft, the rear wheel will be turning at 3130 RMP.

Plug 15/47 into my formula instead of 16/48, and my 95 mph top speed should increase to approx. 103.78 mph

...from my calculations u only 50% disagree.

?

[Bazetech]

I saved your formula for future use. I used to have all of that kind of info way back but have lost it over the years. I'm thinking of simply dropping the rear about 4 or 5 teeth. Just to ease the RPM's while traveling at 65-75 for extended periods.

[motopsycho650]

1 tooth change on the counter shaft sprocket = about 2.5 teeth change on the rear sproket.

If you simply add a larger counter shaft sprocket, or shrink the drive sprocket that much, you'll probably have to alter the length of the chain. I've heard that 15/47 gearing can be done with the stock chain.

[XR650L_Dave]

I 100% disagree. With 14/48 gearing, the counter shaft sprocket is turning 3.42 times per rotation of the rear wheel. If you change to 15/47, the counter shaft sprocket ratio changes to 3.13 rotations per rotation of the rear tire. Just like changing diff gearing in a car/truck, it will change top speed, provided the engine has the HP. And yes, cruising speeds will need less RPM's.

For fun, say the rev limiter keeps the counter shaft at 10,000 rpm (hypothetical number). With 14/48 gearing the rear wheel will be doing 2920 RPM. With 15/47 gearing, and the same 10,000 RPM's from the counter shaft, the rear wheel will be turning at 3130 RMP.

Plug 15/47 into my formula instead of 16/48, and my 95 mph top speed should increase to approx. 103.78 mph

On a stock XR650L, or one with the standard mods, it does not have the power to pull a higher top speed by gearing up. Pretty much no matter what you do, the out-of-the-box top speed is it until you add some power.

Dave

[gmc454]

Just bought my pig, stock gearing and feel like 5th bogs at 65,

Maybe an altitude issue 7500'? or is it carb issue? PO had rejetted for a range of 8-10k ft but have not pulled carb to see what is actually in there. Hopefully time this weekend.

Thinkin of goin to a 14t as I am happy cruising right at 65 on highway to get around. I am thinking with a 14t It would not run too fast to sustain some mileage at 65

any thoughts?

[Kenzo]

Just bought my pig, stock gearing and feel like 5th bogs at 65,

Maybe an altitude issue 7500'? or is it carb issue? PO had rejetted for a range of 8-10k ft but have not pulled carb to see what is actually in there. Hopefully time this weekend.

Thinkin of goin to a 14t as I am happy cruising right at 65 on highway to get around. I am thinking with a 14t It would not run too fast to sustain some mileage at 65

any thoughts?

14/45 works for me at sealevel for 65-70mph indicated but that's only for 45-60 minute runs every once in a while...? the stock 110 link chain works for both 14T & 15T sprocket :banghead:

yup, check ur jetting, make sure ur airbox is opened up w/ a gud airfilter and a free flowing exhaust...anything to help it breath ?

[Bazetech]

Any ideas where to locate a 40 tooth rear sprocket? I have looked but to no avail. Mostly I am more interested in lowering the R's that it's screaming at when doing 70+. Just because of how far I have to go to get anywhere to rideyou know. Thanks.

[gmc454]

14/45 works for me at sealevel for 65-70mph indicated but that's only for 45-60 minute runs every once in a while...? the stock 110 link chain works for both 14T & 15T sprocket :banghead:

yup, check ur jetting, make sure ur airbox is opened up w/ a gud airfilter and a free flowing exhaust...anything to help it breath ?

Workin on the aftermarket list unfortunately funds are not so readily available... Not ready for pipe, would pull snorkel but don't want to have to re jet each step of the way.

first on the list is bigger tank, which brings me to my next question

What kind of impact on mileage will I see?

This will be used to commute maybe 60/40 street/dirt.

[Beyond The Pale]

Once you get into the regime where air resistance is the primary for of drag, the required power scales at velocity to the third power. As long as you are not bouncing on the rev limiter in top gear the gearing has little to do with top speed. It's all horsepower.

[hondacrf150f1]

I ran 15-45 gearing with 17" wheels for quite a while. It was a great set-up but i ended up going to 15-40 for peace of mind at higher speeds. I hated revving this shit outa the motor at 60 MPH. The gearing change gave me maby 2-3 MPH top speed. from 103 to 106 on flat ground. It wasnt really worth looseing all that bottom end power, but it keeps the revs down at highway speeds. And Yes the bike tops out at about 6900 RPM's with this gearing at something like 106-107 MPH, with lower gearing it will pull right to the rev limiter at 8250 RPM's.

[Kenzo]

FWIW the L w/ stock gearing (and wheels) ain't get'n the pizz rev'd outta it at 70mph indicated... ?

chit u chud drop in a real cam & high comp piston and ur STILL no abusing the bike at 70mph indicated