Topic: help needed changing gear ratio 500/4

[rockadoo]

I have been reading some previous posts but can't seem to find an answer to my particular question. It seems everything I read was about making their bike quicker. I want to bring my revs down, my cruising speed up and improve my fuel economy . If I remember right my bike is revving somewhere in the 6k range at (indicated 60 mph) I know the speedometer is optimistic ( it lies). I'm not concerned about quick acceleration, I just want to cruise at a comfortable 65 mph. with the revs preferably at or under 5000 rpm. I am running a 16" rear wheel. I was considering using an 18t front, but don't know what to use for a rear sprocket. Any constructive input is appreciated.

[Muckinfuss]

Whatever you do, change only one at a time.  A quick gut check here says the primary sprocket is the easiest to swap with perhaps the most available choices.  A larger primary sprocket can give you less chain wear as well, all things equal.  Just be careful you don't place your shift points outside of the power band.

[dave500]

the 500s clutch rod prevents you going larger than 18 front,it runs frighteningly close,i dont think youll get a smaller rear sprocket that will clear the hub?

[Retro Rocket]

Going back to an 18inch rear rim will definitely help....

[Powderman]

The total height of the rear tire needs to be taken into consideration. Just going from a 16 to an 18 may not change anything at all if the 16 has a big fat tire on it and the 18 a standard type. You need to know the difference in circumference or total height to do calculations with.

[Retro Rocket]

The total height of the rear tire needs to be taken into consideration. Just going from a 16 to an 18 may not change anything at all if the 16 has a big fat tire on it and the 18 a standard type. You need to know the difference in circumference or total height to do calculations with.

Agreed, but after having bought plenty of 750's with 16 inch wheels and changed them back to stock, i am yet to find a 16 with tire that matched the height of the stock 18 with tire.... Maybe one of the members that has both can put them side to side, i've never seen a tire that was 2 inches taller on a 16 inch rim...

[rockadoo]

I have a 120/90 16 tire on the rear, a quick eyeball is about 3.5 inches from outer edge of the rim to the highest point on the tread. I don't know what the dimensions are for a stock wheel.  I had found a stock rear wheel assembly cheap, but I dropped the ball and it was gone.

the 500s clutch rod prevents you going larger than 18 front,it runs frighteningly close,i dont think youll get a smaller rear sprocket that will clear the hub?

Will I have to be concerned running the 18 front sprocket?

[scottly]

I am running a 16" rear wheel. I was considering using an 18t front, but don't know what to use for a rear sprocket. Any constructive input is appreciated.

What size sprockets, front and rear, are you currently using?

[rockadoo]

I'm running stock, which is 17 and 34 I think!

[becken]

On my 76 550F I'm running Lesters with 16" rear and also have the original wheel and tire. Last time I had the rear wheel off I inflated the original and stood them side by side. The 139/90-16 was about 1/2" shorter than the original tire. Does anyone know the width of the 16" Lester as I'm thinking of going to a narrower tire?

[rockadoo]

if that was a typo of 139? It's probably 130 mm width. that equals 5.11 inches. Standard 16" wheels were mostly 5 inch. the old tire sizes back in the day would have been listed as 510x 16

[Bankerdanny]

assuming a 120/90 tire on both (~ 4.25" sidewall), the diameter of an 18" wheel and tire is about 8% larger than the diameter of a 16" wheel and tire (83.2" diameter vs 76.9" diameter).

So if you are turning 6k rpms in 5th at at 60mph, then changing to an 18" tire should drop RPM's to about 5,500.

[becken]

if that was a typo of 139? It's probably 130 mm width. that equals 5.11 inches. Standard 16" wheels were mostly 5 inch. the old tire sizes back in the day would have been listed as 510x 16

Sorry, that was a typo, should be 130. I'm thinking of going to a 120 for my next tire but only if the rim is the proper width. I'll wait until it's time for a new tire and pull it off and measure the rim at that time.