129" vs 137" upper bogie size differences

[jetpilot785]

I have a buddy of mine with a 129" short track ZR 7000 he just picked up used. He installed a 8.5" JT stealth 4th wheel kit similar to mine but I'm running the SR Viper LTX SE with the 137" and his track is too tight IMO. I was curious if anyone knows why the 129" runs larger bogies on the upper scissor arm than the 137"? He is going to bring it by this week for me to take a look at and see if I can't figure something out and get the track a little looser. I was thinking of maybe putting the smaller bogies on that the LTX used to get a little more length out of the track. I was also thinking of maybe machining the rails and/or stops to get more throw on the adjustment. Has anyone had any experience with this situation?

I haven't seen the two side by side yet so I don't know if it's even doable yet. Just throwing this out there to get some insight before I start messing around and making it worse or having to spend money to replace stuff I f%#k up lol.

 

[saskieXTX]

The 129 users 7.5in kit. If he got 8.5in then they are to big and would cause the track to be to tight.

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[jetpilot785]

Insee

The 129 users 7.5in kit. If he got 8.5in then they are to big and would cause the track to be to tight.

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I'm seeing that on JT's site but I'm wondering what the differences between the skids that one can use 8.5" wheels and the other needs 7.5" wheels but the 129" also uses 7" scissor idlers as opposed to the 6.5" on the 137". Any idea why?

 

[saskieXTX]

If I had to throw out a guess. Geometry...track angles etc. I'm no suspension expert lol

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[fxnytrortxkid]

They make offset axles to run the larger wheels. The larger wheel allows the sled to roll easier and hence faster. If he put 8.5" wheels on stock axle he will have issues

 

[TD Max]

The bigger wheels on a straight axle would hang too far below the rails ------_