Set back for 151" track - 3 or 3.5"?

[DigitalFusion]

I have spent hours and hours searching, and cannot seem to find an answer to this. When setting back for a 151, is it back 3 or 3.5? Math says 3.5 (151-144 = 7 | 7 / 2 = 3.5) but I see a lot of posts saying 3".

 

[Snowmixer]

Technically, you would also need to take into account what size (diameter) drivers and rear wheels you will be using, as a larger diameter has a larger circumference, and therefore will take up more of the track, leaving less room for the setback.

 

[DigitalFusion]

Stock drivers and stock rear wheels, that should be 3.5", right?

 

[Snowmixer]

Yes, 3.5 inches does sound correct for stock drivers and rear wheels. If it were me, I would try to remove the springs/shocks from the skid and move rear wheel track tension adjusters to the middle of their travel, then put the skid and track into the tunnel (you'll have to at least temporarily install drivers so the track has something to hang onto in the front). Then tension the track towards the rear until you see about what you want as far as approach angle (keeping in mind to move the skid suspension arms up to where they would normally be during normal riding), and try to mark the mounting arm locations on the inside of the tunnel. This may not be possible, because the new holes might end up halfway off the steel doubler plate in the tunnel, but at least then you'll know where they should go and can hopefully find a way to drill from the outside of the tunnel to get them in that location.

It's possible that some people opted to move only 3" back to avoid drilling on the edge of the doubler plate, or possibly to leave more room for track adjustment, and finally, if they moved the skid down as well as back, this will also take up a little more space. Add those variables to the fact that a 151 track may not actually measure 151 inches, the 3" setback may have been a necessity for some just to get it to fit, which is why I would try to mock it up with the actual track you are going to use before drilling any holes.

I have used some CAD software to draw up the stock Phazer MTX skid vs. driver location complete with driver, idler, rear wheel, front rail arc and skid rail tip-up, and moving the skid directly back 3.00 inches would yield a theoretical track length of 147.8837 inches. It is likely that a 3.5" setback would get much closer to 151, but for reasons mentioned above maybe 3.0" has worked better for some. You could always just aim for 3.25! Hope this helps!

 

[DigitalFusion]

For those of you who are parents out there, or maybe even remember being read the book "If you give a mouse a cookie", you'll understand how my night went. I am going to do the 151 conversion because I found a good deal on a track, which arrived the other day.

Then I decided that since I have the skid out for the conversion, I might as well pull my skid rails to send off for powder coating.

Then I decided since I had to pull the hyfax off the rails, I might as well get the duponts to replace them.

Then I read that you need a fully clipped track for dupont slides.

Then I figured if I am going to clip the track, I might as well get extrovert drivers.

Next thing I know I ordered clips, the tool, a new boost gauge, and some duponts and my wallet is $500 bucks lighter and I still have no idea what I am doing for drivers and how it will effect all of this!

 

[blueironranger]

I would just go 3”, mainly because the 144” hardly uses any of the adjuster at all on mine, my current 144” freeride actually has the adjusters backed off completely! With 3” setback you would be in the middle of the adjustors, allowing for a looser track if your running extroverts.

 

[blueironranger]

Seen your other post, definitely go 3” if you go with 9 tooth drivers, 2.5” would be enough with 9 tooth drivers. 8 tooth is stock.

 

[DigitalFusion]

So, I am finally getting around to trying to do this. I must be doing something wrong because both 3" and 3.5" and down 1" put the hole in the middle of the seam of the plate inside the tunnel? Were poeple just running it like this, or am I measuring wrong?

I have the skid installed in the stock locations. I put some painters tape down and made a line with a level from the center of the front bolt. I then measured back both 3" and 3.5" from the center of the bolt with a caliper. Then, I went down 1" vertically from both of those marks. Either one ends up overlapping the edge of the plate inside the tunnel.