pulley ratios

1971 Views 7 Replies 5 Participants Last post by BudC., Mar 11, 2005

gizmo#137

Discussion Starter · Mar 6, 2005

has anyone change they front pulley in order to drop the RPMs? at 70 mph i am turning 3000rpms. i have a SB single speed with a 225/60/15 rear tire. mj

Save

1 - 8 of 8 Posts

Pulley Ratios

Gizmo#137;

I have a single speed 97 clutch Boss with a 38 tooth front. It seriously drops the RPM's @ cruise, but being a clutch, gives up a lot in how much I have to slip it to get it going from standstill.

Mountain Boss Hoss applied a "Frame Loop Mod", to change the left aft downtube to accomadate the larger front pulley.

I'm sure Tom or Roger would be happy to explain it to you, and it would probably really benifit a single speed auto. I understand they are set up @ the Harley dealer on Beach Street if your in Daytona.

my 2 cents.

Ride Safe

HAWK88
Jack Phillips

See less See more

Save

Dean

· #3 · Mar 6, 2005

Pulley Ratios

gizmo

I am in the process of that mod right now. I have a 98 SB 350 w/ a SS automatic trans. I purchased the larger pully from Mountain BH and was told they could do the "frame loop" or I could machine the outer flange of the pulley. I opted to have the pully machined, and everything seems to fit. The other problem you will need to address is the old Gates belt will be too small. You will need to go to the new Kevlar belt, which is larger. You will need to make some modifications to the rear wheel adjusters. I can't speak about preformance because I live in Cleveland OH (snow and cold), and only rode the bike about five miles from the shop to my house.

Sorry I can't be more help right now, but when it stops snowing I'll give it the freeway test

Dean

Save

HAWK88

· #4 · Mar 6, 2005

pulley

Dean;

Not positive but you may need to change the rear pulley to accomidate the new (and much better) Gates belt and front pulley. I recall some previous threads about this, but couldn't find one quickly for you.

I'm sure Mountain could, and would be happy to advise you.

Ride Safe!

HAWK88
Jack Phillips

Save

BudC.

· #5 · Mar 6, 2005

Pulley Ratio

Gizmo, You need to count the cogs on your existing pulley to see if it is worth the change. I have a 1996 Boss Hoss that had the 1998 auto single speed tranny installed when I bought it. With the 29T cog on the transmission and an Avon 250 tire ( I think much shorter than your car tire ) I was only getting about 13 mpg. ( don't remember the RPM ) I made my own frame loop mod and tried a 38T cog. That seemed to kill too much of the bottom end. I went back to a 36T cog and I have been very pleased. The mileage jumped up to around 19 to 20 mpg. But with the shorter tire, I am still running around 3000 rpm at 70 mph. I rode it 2600 miles in 5 days last year to Daytona and it was very smooth at that RPM. I was worried about slowing the RPM's down too much for fear of slipping the convertor ( building heat ) at slower cruising speeds around town. I ordered the exact replacement pulleys at a local industrial supply shop for a fraction of what the dealers charge. I did go thru Mountian Boss Hoss for the belt because I could not find the correct size thru the industrial suppliers. I have done alot of mod's to my bike and this was by far the best. If you are only running 3000 rpms at 70 and you slow it down much, you may find like I did that it really kills the low end punch. I did not have to change anything with the rear pulley on mine.
Bud C.

See less See more

Save

gizmo#137

Discussion Starter · #6 · Mar 8, 2005

pulley

thanks to BUD - JACK - & dean i send all of you a PM... my front pulley has 32 t & rear has 76t OD on front is 6.25. with 3/16 clear to frame. i can take off a good 1/8 off the outside rimto give me 1/4 in clearence
DEAN do you know the OD on the 36t or the 38t pulleys? make &part#of the larger belt?
new question i need a lay out view of the rear axle right side... my mounting bracket for the caliber rubs the rotor ,, it seem a spacer is missing plus the cal is not centering on the rotor i have re place the outer pad once in 4000miles and it need it again, the outer piston are not working so today i rebuld the caliber(new O-rings) i use two flat washer on each mounting bolt to get the rotor center better that when i saw the mounting bracket was rubbing the rotor. so i quit for the day..

Save

Glenn B

· #7 · Mar 9, 2005

Gizmo,
Also check the support arm that has two heim joins on the ends. Those rust up inside and they do not allow the brakes to work properly.

Dean,
Mountain Boss Hoss had told me that if I converted to the new belt on my 98 and changed the front pully than the back would be fine and didn't need to be changed. I am still running the old gates belt. Changed my rear pully this fall but that is due to the teeth having worn down by approx. 1/3 from high mileage.
Glenn

Save

BudC.

· #8 · Mar 11, 2005

Pulley Questions

Hey Gizmo, I tried sending you the RPM / speed information you request in the last PM. But for some reason, I am not able to PM you anymore. They will not leave my outbox, I have tried twice. I found some of my old calculations from when I was changing things up. With my 34T / 74T pulleys and Avon tire, my calculated RPM at 70 mph was 2950 rpm's. The tach registers around 3050 to 3150 rpm. For every two teeth that I went up on my front pulley, my RPM's only dropped about 250 in my calcualtions. A car tire with the larger circumference really made the RPM's drop in my calculations.
Bud C.

Save

1 - 8 of 8 Posts

This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.

Top Contributors this Month