My '79 FLH 80" Classic came from the factory with a 22/47 final drive sprocket combination. It always seemed like the old shovel was under a lot of stress when running at interstate highway speeds, so I put a 23 tooth sprocket on the tranny. Solved one problem ( better top end, lower RPMs, less strain on the motor) and got another. Does anybody know how much the bigger tranny sprocket throws off my speedometer? By the way, on my first shakedown breakdown run after changing the tranny sprocket, the speedometer froze at 85 mph and stayed there. Probably 'cause the old gal hadn't been pushed that hard in 31 years! Anybody have a used, original HD clock with about 28,000 miles on it?

 

Welcome to HDF.

You can work that out, by simply using the difference in number of teeth. So at 85mph on your speedo (while it worked!) you would actually be travelling at 85 x 22/23 or 81mph. Not a lot different as I doubt if the speedo is as accurate as that in the first place!

If you want to keep at a posted speed limit, just add 10% and you should be fine, for example 44mph on the speedo in a 40 limit. That should take account of the original 'accuracy' plus an adjustment for change in gearing!

Can't help with a replacement speedo. My Evo's batwing started out life the same colour as yours and came off a similar bike.

 

Get an inexpensive gps like a tom-tom (or borrow one for an hour) and check your speedo against it. Easy & cheap.

 

Sell it! The bike is getting ready to send you to the bank.

 

Too late Badwhine, this bike has already sent me to the bank. Can't quit now. Thanks for the speed calculation formula, Graham. Good to know I'll actually be UNDER the posted speed limits rather than over.

 

I know this is old as dirt, but I feel I should point out (for anyone that comes across this old thread while searching ratio topics as I have) that the math is wrong posted above.

The OP is really traveling @ 23/22 of the original speedo's displayed speed, as he went UP in tooth count on his FRONT sprocket. So really doing more like 89 MPH...

 

my 79 shovel came with 22 trans and 51 rear wheel. i changed the trans to 24 teeth and it was big differance. my speedo was front wheel driven.

 

Be careful when going big on the front sprocket ... It's not uncommon to have interference issues with the inner primary.

 

Antone know the STOCK (OEM) tooth counts in the primary/secondary on a 79 FLH?

I'm assuming it's 22/37 and 22/51 (which is about a 3.89:1 final)? But unable to find the exact info to back up my assumption.

Trying to work some different theoretic ratios out in my head as I'm needing to change the gearing on this one I've got.

 

May not show when ride solo,
2 up and or loaded is when it'll show,