How do I Lower RPM @ Highway speed HELP! : V-Twin Forum: Harley Davidson Forums

1990heritage · 09-22-2009, 04:53 PM

I do not have a tach but i think i must be turning close to 5000rpm at 70 mph. There is a bunch of vibration but the main concern is to reduce rpm. I have been thinking of changing the transmission and rear wheel pulley. I think the oem is 32 & 70. I have found 34 & 65
available. Has anyone done this? if so, is there a drive belt change needed as well? Is there a decrease in rpm that makes this transition worth while?

rob71458 · 09-22-2009, 05:26 PM

I would be willing to bet you are not any higher than 3500 rpm at 70mph. I could see changing one of the pulleys but not both. Your bike would become a dog, unless you have lots of torque on tap.

Y2K · 09-22-2009, 05:46 PM

If you're turning 5K @ 70 mph your clutch is slipping.

Taller gearing or an aftermarket overdrive trans can get you there but having enough power to pull taller gears becomes an issue,even with a TC88" let alone an 80" Evo.

aka_matt · 09-23-2009, 03:58 PM

stock gearing in those is about 24mph/1000rpm... or about 3000 @ 72... r u sure ur in 5th gear? if u make the gearing any taller, u'll be stalling it (or slipping the clutch real bad) at every take off and have no power to move that heavy bike...

1990heritage · 09-23-2009, 04:43 PM

Quote:

Originally Posted by rob71458

I would be willing to bet you are not any higher than 3500 rpm at 70mph. I could see changing one of the pulleys but not both. Your bike would become a dog, unless you have lots of torque on tap.

I bought this bike about 4 weeks ago. It has a S&S E Series Carb. with a K&N High flow and Harley turn out exaust and a EVL-3020 Comp Cam. This bike does have Balls.

Z-Man747200 · 09-23-2009, 04:58 PM

I did this on a rice burner a few years ago (rear sprocket only) and it worked fine but the point remains that if you are up to 5 grand at 70 mph, you have other fish to fry...my .02.

rob71458 · 09-23-2009, 08:21 PM

Quote:

Originally Posted by 1990heritage

I bought this bike about 4 weeks ago. It has a S&S E Series Carb. with a K&N High flow and Harley turn out exaust and a EVL-3020 Comp Cam. This bike does have Balls.

You never said what size engine you have. Saying it has balls means nothing, it's your oppinion not a fact. You also say it revs to high, but have no way to back that up eather. Buy a tach and see where your revs really are first. It is a fact if you gear any bike "higher", it will decrease the torque output to the wheel which will affect the performance.

ponderopa · 09-23-2009, 10:54 PM

Maybe the vibration is your issue, making the rpm's seem high. Maybe a motor mount problem?

wdgld · 09-24-2009, 08:15 AM

5000rpm at 70?

No frikkin way, unless as previously mentioned, you have clutch slip issues.

1997bagger · 09-24-2009, 11:21 AM

If your rpm's at 70 is a fact, an 8 speed would be the only way to go to get your engine speed down to 3500 @ 70 mph

yeehaw · 09-24-2009, 02:59 PM

8 speed hahaha that's funny bagger. Before I rebuilt my 80" I had 34 on the trans shaft and 61 on the back, and a 5 speed trans. On deceleration the top of my belt rubbed on the jack shaft inner primary, due to the trans pulley being a bit taller. I didn't care it just was annoying, it sounded like a squeak. However, I used my bike on the highway most of the time. Off the line was a bit sluggish, but like I said I used it on the highway. Since then I am running, balanced flywheels, 9.5:1 comp., stock heads (re-worked), ev27 cam, S&S reed valve, 42 mikuni, and 2 into 1 thunder headers. Significant improvement in torque verses stock displacement. I now have a 6 speed trans., 32 on the trans pulley and 65 on the rear. I do not spend much time in 6th unless I'm up around 65 or so. I'm happy with the changes I made but, I'm set up for highway. Just my 3 cent nickel.

yeehaw · 09-24-2009, 03:00 PM

I forgot to mention my bike is a softail a little lighter than a bagger.

qtrracer · 09-24-2009, 06:21 PM

If you bought it second hand are you certain that the pulleys are still the oem items? The trans pulley may have been changed to a smaller one thereby increasing rpm's and making it seem like it has more "balls".

jtmurph00 · 09-25-2009, 04:54 AM

Go to Bakers website, they have an RPM calculator on there, pretty handy, just put in what you've got. I had to go to a 70 tooth rear to run a narrow belt so I put a 34 tooth in front. According to them it comes out to within 100 RPMs the same.

1990heritage · 09-28-2009, 04:28 AM

Quote:

Originally Posted by qtrracer

If you bought it second hand are you certain that the pulleys are still the oem items? The trans pulley may have been changed to a smaller one thereby increasing rpm's and making it seem like it has more "balls".

Good Point!! I will be getting the bike on the lift tonight and i will start counting.