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Message started by barry68v10 on 04/21/07 at 15:52:20

Title: Theoretical speed/rpm, 5-speed tranny
Post by barry68v10 on 04/21/07 at 15:52:20

OK, as promised here's my calculations, someone please confirm or deny...

Primary reduction gear = 1.81 based on 67/37 tooth gears
Final drive ratio = 2.9565 based on 68/23 tooth pulleys
5th gear ratio = .884 based on posted tranny specs
Stock tire = 140/80/15 w/5.51 inch width, 4.4 inch tire sidewall height, 23.819 inch tire height, 74.829 inch tire circumference, 846.272 revolutions/mile

Putting it all together it looks like this:

846.727 revolutions/mile*2.9565 final drive ratio*.884 5th gear ratio*1.81 primary reduction ratio = 4005.489 rpms @ 60 MPH (because we used wheel rotations/mile, 1 mile/min = 60 mph to convert to proper units)

Did I miss something here? (I realize the actual tire size may be different than stated due to manufacturing vs. theorectical specs)

Title: Re: Theoretical speed/rpm, 5-speed tranny
Post by barry68v10 on 04/21/07 at 15:53:57

So, the bottom line looks like:

REAL close to 15 mph/1000 rpms in 5th gear w/stock tires...

Title: Re: Theoretical speed/rpm, 5-speed tranny
Post by Rockin_John on 04/23/07 at 23:27:55

I don't get the same numbers as you on some points.

We're good up to the tire circumference= 75.83 but then it goes off... from there is should be 75.83"/12 = 6.32' ft/rev. 5680'/6.32' = 898.73 rev/mi

Then 898.73 x 2.956 x .884 x 1.81 = 4250 engine revolutions per mile. If you deside to do that mile in a minute, then it becomes 4250 rpm ;)

Just for fun, lets figure mine on my '99 chopper:

It is also a 5-speed so... the primary is the same, and I have stock belt @ 68/23 = 2.956; but I'm running a huge 140/90 rear tire that is approx 25." dia. so... it rolls over 6.54'/rev... 5680/6.54 = 868.5 rotations/mi.

868.5 x 2.956 x .884 x 1.81 = 4102 rpm @ 60 mph

So... I'm cranking 150 less rpm @ 60 mph.

My '87 is running the lower primary 68/36 = 1.889, but higher top gear than the '99, ('87 top gear = .875) and the same rear tire size as yours. So it's math would be:

898.73 x 2.95 x 1.889 x .875 = 4382rpm @ 60mph

Believe it or not, I can actually feel the difference between those 280rpms at 60 mph. But man 5th gear is gutless for passing on the '99. Third is kind of cool though, because it will wind up past 70mph on entrance ramps! Then drop into fourth and blend in with traffic. ;-)

I'm pretty happy with the belt drive ratio with the 5-speed and the big 140/90-15. It works with my 250+ pounds and the engine doesn't seem to labor badly even cruising at 70mph. At 55-60mph it is just putting along. I see no reason for a chain with my big rear tire.

Title: Re: Theoretical speed/rpm, 5-speed tranny
Post by justin_o_guy on 04/24/07 at 08:09:51

And just who MAKES your big rear tire? Hmmmm?

Title: Re: Theoretical speed/rpm, 5-speed tranny
Post by Rockin_John on 04/24/07 at 15:15:42

justin_o_guy wrote:

And just who MAKES your big rear tire? Hmmmm?

I suppose you are asking about the Dunlop 140/90-15
I mis-identified? HMMMMM???? I ask, becuse I also have a Cheng-Shin (sp?) 140/90-15 that is a bit wider, and about a half inch shorter.

And why is it I get the feeling your question is asked in the spirit of a spelling flame? You'll just have to pardon my Dyslexia.

The math remains the same. The Dunlop on the back of my chopper is pretty close to 25" dia.

Title: Re: Theoretical speed/rpm, 5-speed tranny
Post by barry68v10 on 04/24/07 at 16:13:11

John, I've discovered your err. 1 mile = 5280 feet, not 5680...Other than that I just simplified the conversion by using time instead of distance, knowing that you cover 1 mile/min at 60mph.

Title: Re: Theoretical speed/rpm, 5-speed tranny
Post by barry68v10 on 04/24/07 at 16:15:53

You made me look though :o

Title: Re: Theoretical speed/rpm, 5-speed tranny
Post by Rockin_John on 04/24/07 at 16:48:10

barry68v10 wrote:

You made me look though :o

And I can tell how I came to err such... I forgot that the standing quarter mile is 1320 ft. and not 1420 ft. How I could forget a factoid which I knew by heart as a young drag racing fan is surprising to me.

Must be early onset of old-timer's disease. Might as well get that one early too... I've had the onset of every other old age ailment already. 51 years young, and had a heart attack at 43. Takes me an hour; a cup of coffee, and two pain pills to get moving in the morning; due to all my musculoskeletal aches and pains.

Title: Re: Theoretical speed/rpm, 5-speed tranny
Post by Rockin_John on 04/25/07 at 00:01:05

Corrected calculations:

Barry's Savage...

23.82" dia. rear tire = 74.8" / rotation... 74.8"/12= 6.23' /rot. 5280/6.23= 847 rot/mi

847 x 2.96 x .884 x 1.81 = 4011revs @ 60 mph = 4011rpm
(slight difference in my calculations from not carrying decimals out as far.)

My'99:

25" x 3.14 = 78.5"/12 = 6.54' / rotation 5280'/6.54' = 807 rot/mi

807 x 2.96 x .884 x 1.81 = 3822revs @ 60 mph = 3822rpm
--------------------------------------------------------------------------
My '87:

23.82" dia. rear tire = 74.8" / rotation... 74.8"/12= 6.23' /rot. 5280/6.23= 847 rot/mi

847 x 2.96 x .875 x 1.89 = 4146 rev/mi @ 60mph = 4146rpm

So really, the difference between what my '99 and '87 are turning is a bit more than 300 rpm @ 60mph. I can feel the difference, and like it. If I were considerably lighter the temptation of sprockets and higher ratios would be irresistable to me, but as it is...

Title: Re: Theoretical speed/rpm, 5-speed tranny
Post by justin_o_guy on 04/25/07 at 00:47:50

Noo, I wasn't picking on you at all.I didnt even notice anything misspelled. I was & am genuinely curious, Because, I want to gear as high as I can without doing the chain mod & that rear tire looked like a good one for that. here's the thing tho. I need a tire that sticks pretty good & I have seen the mileage reports you have made. I hope they are sport touring & not just touring. Thanks for responding.

Title: Re: Theoretical speed/rpm, 5-speed tranny
Post by Rockin_John on 04/25/07 at 10:39:14

justin_o_guy wrote:

I want to gear as high as I can without doing the chain mod & that rear tire looked like a good one for that. here's the thing tho. I need a tire that sticks pretty good & I have seen the mileage reports you have made. I hope they are sport touring & not just touring. Thanks for responding.

Sorry about misunderstanding...

From what I can tell, the Dunlop 404 @ 140/90-15 fits within the swingarm, belt and fender clearances of my 1" lowered rear chopper -just barely- and only because a couple of the fender brace / sissy bar bracket bolts have been removed to keep them from rubbing the sidewall.

Now that I've put the digital calipers on the Cheng-Chin (sp?) and realize that it is a couple of mm wider and about 1/2" shorter, I wouldn't recommend trying to put one of those on the Savage. I'll probably take that new one I got cheap off eBay and trade it at the independant cycle shop towards another Dunlop 404. I think it (the 404) is the biggest thing in both width and diameter that could safely be stuffed under a stock Savage.

Title: Re: Theoretical speed/rpm, 5-speed tranny
Post by justin_o_guy on 04/25/07 at 10:52:05

Thanks, I have a couple of Rolodex cards in the file I use for notes on parts & sources. When I actually need the stuff I grab the Rolodex & see what I have for clues.. I just added Dunlop 404..

Title: Re: Theoretical speed/rpm, 5-speed tranny
Post by barry68v10 on 04/25/07 at 14:38:00

Quote:

My '87:

John, carefull with those 87 numbers. There have been a few changes. Top gear ratios are different AND the front and rear pulley sizes are different. There's a post around here somewhere that highlights those differences...

Title: Re: Theoretical speed/rpm, 5-speed tranny
Post by barry68v10 on 04/25/07 at 14:40:46

Ohhh, Okay. John, I see you accounted for the primary reduction gear and top gear on the tranny, but unless I'm mistaken, the 87 had different size front and rear pulleys which will change the 2.96 ratio...

Title: Re: Theoretical speed/rpm, 5-speed tranny
Post by Rockin_John on 04/25/07 at 17:33:28

barry68v10 wrote:

Don't think so... the belt is the same one, and both the pullys are too: Much to everyone's regret... otherwise there would be at least a couple of gearing options with the belt; which there aren't.

Good try though... You made me look ;-)

Title: Re: Theoretical speed/rpm, 5-speed tranny
Post by barry68v10 on 04/25/07 at 18:27:45

Touche'

Yes, I see now that someone suggested that there were a few different size pulley's, but someone else looked up part numbers and verified they've always been the same.

I stand corrected, sir.