My '71 ironhead came stock with a 19 tooth primary socket. I would like to increase the size to lower RPM's at freeway speeds. How big can i go before there is a problem with clearence etc.

 

My 1970 XLCH came with a 19, I was told that the XLH that year came with a 20. I was also told (1971) that the 19 was gone for Sportsters that year, pretty interesting.

 

Sorry, replied too quick, I put a 22 on mine (1970), that was about as big as I could stand,I would think a 23 would be tops.

 

23 is it!

 

I wouldn't go over a 22. Going up 3 teeth on the front sprocket is a huge change.

 

I have ridden about 40k miles on a 22 tooth, over half of them interstate miles, with no complaints. Personally, I think getting the bike going with a 23 would suck, especially two-up.

 

i run a 23 front and 51 rear no problems, im 240 lbs and take the ol alot of the time no problem ( i do have a little motor work ! )

 

23/51 is, in my experience, an ideal setup. Reasonable acceleration and low hiway RPMs. Myself and my two local IronHead riding buddies all run this combination; as well as a bunch on another IronHead forum.

With an o-ring chain you do have to grind some metal from the sprocket cover. With a regular chain i think you would be good to go.

 

The OP stated his 'original primary sprocket' came as a 19T. I see everyone overlooked that and assume he is talking about his transmission sprocket. (Which must be the case here)
The original primary sprocket is a 34T.

The original transmission sprocket is a 19T. (for 1970-71 XLCH)
Original trans sprocket for a 1970-73 XLH was a 20T.
Original trans sprocket for 1973 and later (all models) was a 21T.

The ideal set up for gearing with the Sportsters of these years is having the drum brake 51T on the rear wheel and a 23T trans sprocket.
This is highway gear and runs well out on the open road. It has enough gear down low to get you around town without bogging down too.
Really, it is the absolute best compromise of gear to be had on a Sporty.......... pg

 

You're right - I was thinking 48 rear (late model Ironhead) when I said 22 max on the front sprocket.