If there is an existing thread on this, please let me know.

I have an 89 fxrt with stock 80" and 5spd. I tend to do a lot of hwy riding in the 85-100mph range for long distances. I have some engine work planned, but wanted to drop the RPMs down a bit in 5th. Currently I'm running about 4krpm at 80mph.

Other than replacing the tranny with a 6spd, what are my options? I've been told I could replace the front 32t pulley with a 31t. Are these made? I'm trying to preserve as original a bike as I can and still accommodate my riding needs. I'd like to avoid stuff like a belt size change.

Thanks in advance.

 

Going from a 32t to a 31 is doing just the opposite that will gain you rpm's on the highway.You want to go up in tooth count, each tooth you go up will lower your rpms 3% but it will also give you 3% less torque coming out of the hole. If you don't want to change the belt then don't go more then one tooth.

 

You have a "need" to ride 100MPH?

 

Wear ear plugs! They cost pennies and are the cheapest tuning aid known to mankind. There are two simple ways of raising gearing: either via the compensator, with a suitable longer primary chain; swapping the rear pulley to the International spec 61T, with shorter belt. Don't do both!

 

If your turning 4000k @80 I think someone already made changes your gear ratio. Have you owned the bike since new. Before you change anything you need to find out what gear ratio currently have. There are gear ratio calculators on the net. Open your primary and count the teeth on both sprockets and then count your trans pulley and your final pulley and plug in the numbers.once you find what you have then go forward.

 

Completely stock '89 should be turning 3627 at 80mph.

 

Thanks for the good info. @98Hotrod..... What makes you think it's been changed? Should it be lower or higher?

 

Based on my experience and my 98 fatboy 4k put me at aprox 95mph.

 

I agree, stock gearing gives around 22mph per 1,000rpm. Softail gearing is taller than the other big twins. If you are getting only 20mph per that suggests to me a change in compensator, probably to 21T from 24T.

 

just stumbled on this thread...I run the 61T on my 88 FXRp.

requires loosing the belt guard and swapping to the shorter softail belt.

15% overdrive, been using it over 20 years.

can;t remember exact rpm/mph.... 75 MPH is about 2800 rpms

OP if you want exact stock gearing/rpm/mph chart, then google:

28_RatiosMpg

Mike