I'm not sure if this question fits best here or the ECM/tuner section. If no one can help I'll try asking over there. There is a thread currently in the Touring section on this subject, but I thought I would post these questions here in case someone has done it or has feedback of any kind on this mod.

I'm contemplating replacing the 66T IDS rear pulley on my '07 FLHX with a 68T IDS Sportster pulley (#40518-08 for the Japanese market). It is reportedly identical except the bearing, which can be replaced with the proper part (#40670-06). My questions involve how well everything else on the bike will work after this change:

1. Will cruise-control operation be affected by gearing-down the bike in this manner?

2. How about the 6th-gear light?

3. The speedometer is now 2½% fast and will be even more inaccurate with this mod. Can the speedo be calibrated using the HD Digital Technician (dealer) software?

4. If the speedo can be re-calibrated, will this affect cruise, the 6th-gear light, or anything else?

I've known one person with an '08 who's done this without problems, but he has TBW and a totally different ECM configuration. Has anyone done this mod on an '07 or have feedback from anyone who has? If so, were there any adverse side-effects?

 

I've since found out that the DT (dealer) software will not make speedo adjustments, but TTS and the new DynoJet PowerVision will. Two from another forum have installed '07 68T non-IDS XL pulleys on their '07 FLH's and neither have had 6th-gear-light or cruise problems, so I guess all but one of my questions have been answered. I would like to know how much the speedometer is affected by the change.

 

The change is a matter of simple arithmetic. By using a 68T instead of your 66T the speedo change is 68/66 = 1.03, or 3% lower.

So when travelling at 60mph on your speedo you will actually be travelling at 60 x 66/68 = 58.23mph. However your speedo is designed to read 0-5% fast, so it is quite possible the change will balance that out and your speedo reading will be more accurate than originally!

If you have a satnav it probably has a speed readout, so you can check. I suggest you forget the speedo until the bike is back on the road, you may not need to do anything. Hope that helps!

You can change the gearing of your primary without affecting your speedo.

 

I figured about 3% based on that calculation, but thought diameter difference would be the more-accurate method. Perhaps it is in fact the same.

My speedo is about 4% fast now, and my understanding is that since the bike will be going slower with a sprocket change than before the speedo will actually be less accurate. For example, if I am going 62.5 mph indicated for an actual speed of 60mph now, changing the rear sprocket will make the bike travel less distance than before, thus travel at a lower speed, and if 3% is the calculation it should be going around 58 mph with the mod.

I have a GPS and that is how I'm figuring my speedo error. I've also done some timed runs between highway mileage markers with the same result. Changing primary gearing isn't something I want to hassle with, and even the rear-sprocket change is something I'm thinking isn't really necessary. If I thought my speedo would change toward being more accurate I would probably do it, however. If less-accurate I probably wouldn't.

 

Quite right! The diameter is directly related to the number of teeth. Makes life easier for calculating such things!


You're quite right. I should've thought that through!

Changing the gearing on these things is very worthwhile and worth the effort!

What is so frustrating is that on the later bikes it is so difficult to make decent changes to the primary, as that is the best place to make changes.

 

A note.
Changing the primary ratio will impact the 6th gear light.
Changing ratios after the trans will not.
Speedo matrix(VSS calibration) and 6th gear logarithm are separate.