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R-Geo "X-Factor" testing and tuning

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#1 JimF


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Posted 11 May 2019 - 01:59 PM

It has taken way too long for me to get around to this but I've finally got some time to report on these variations. It also took some time to test three chassis enough times on two very different tracks with widely varying conditions, to reach any kind of conclusions at all. These impressions were gathered in several sessions over a long preiod of time. The builds were different but stock components were used. I did use a new version of the R-Geo Z-Poid bracket on the last one and this was a major improvent over some prior versions. The two test tracks........


165' 'Hillclimb' at Motown raceway in Modesto. This is really sort of a grandstand Engleman rather what we'd normally think of as a Hillclimb.

  • Although the turns are pretty flat, this is our fastest track in NorCal
  • This track usually has very good bite and never has bad bite

130(?) Kingleman at Fast Track Hobbies.

  • All turns are flat except the finger turn which has modest banking. Gutter lanes are tight.
  • This track has been known to have variable conditions.

Testing was my usual format.......

  • 5 laps to warm up the tires
  • 10 laps at speed noting characteristics, fast lap, slow lap, consistency. Hair laps were discounted.
  • Repeat cycle with each material change. Repeat cycle to re-verify outlier results.
  • First rounds were on a center lane. Best results were repeated on a gutter lane.
  • One difference from usual was that I was not necessarily trying to find the ultimate setup with each but rather to identify differences.

Testing materials used......

  • These are my normal tire choices with the Koford added in just to try them.
  • All cars were geared 9-28 on the Hillclimb and 9-29 on the Kingleman



Bodies tested.....this is somewhat of a different subject and more of a NorCal specific test, but I was trying to "kill two with one" I won't dwell on this.


  • Parma Lola T-163 w/ 1/4" spoiler
  • BPR version of the Kirby TI-22 w 1/2" spoiler
  • JK TI-22 "oldest version" w 1/4" spoiler.




My original X-Factor build posted back in January.


  • This is the stiffest of the three and the most forgiving.
  • This is very stable and easy to drive on both tracks.
  • This chassis was decidedly better with the Lola body.
  • Tires did not affect it very much with the JK 8713 PP being slightly better than the Alpha BFH or the Koford.
  • This chassis was at it's best in center lanes and wider radius turns.
  • I think this chassis is very well suited to faster tracks. This was best with the forks soldered at the apex.
  • If there was a weakness, it was that chassis did not 'turn in' easily on the tightest turns.




Version #2: Goal here was to get better turn in on tight lanes.


  • Forks were floating in front tube but with a lockdown provision.
  • Tested with forks soldered at the apex and not. There was not much difference.
  • Stop tubes changed to round tube rather than the normal square.
  • Major difference was a single .062 "X-Rail" /side rather than two.
  • This chassis has the most flex of the three.
  • This chassis was also at it's best with the Lola body.
  • This chassis showed a decided preference for the Koford tire on the Hillclimb but not much diff on the Kingleman
  • Did get more bite and better turn in in the tighter corners but it was not as forgiving off in the wider turns.
  • Locking/unlocking the forks made no diff on the Hillclimb but did help in the tighter tuns of the Kingleman.
  • Results were that this car was somewhat better on the Kingleman but a push on the Hillclimb.



Version #3:

  • The bracket is a new version that eliminates the need for squaring the bracket face. It is much more square and easier to work with.
  • Two straight .055 rails, .055 forks soldered. Forks soldered at apex. 1/16" shorter wheelbase.
  • In between the other two in flex but flexes to the bracket where the others basically stop at the pan/rail hangers.
  • This car did not offer any advantage with the Lola or the Kirby Ti-22
  • This car had a mild preference for the Koford tire on the Hillclimb but Alpha on the Kingleman.
  • This chassis runs about 3gr lighter than the other two and needed a bit of weight at the nose which I usually don't do.
  • This car was marginally faster on the Kingleman but a push on the Hillclimb and a little more critical to drive than the original.
  • One noticeable advantage of this version was that it could go into the donut on the Kingleman better. Most other turns it was about a push.
  • It could well be that the shorter wheelbase contributed to this result as well.



Generally, the X-Factor is versatile and easy to drive in the "X-Rail" configuration. On faster lanes it is exceptional while on very tight or flat lanes, it needs a little better turn in. I think a 1/16" shorter wheelbase might be better for all versions. It does not seem to be markedly better with unsoldered forks although the bite was slightly better. The kit builds very nicely in the X-Rail or straight rail versions. Of these three specific builds, at this point, I think I slightly favor the straight one although again, the shorter wheelbase may have been the bigger factor.The Koford tire turned out very well on the Hillclimb but less so on the generally slickery Kingleman.


Passing note on the body testing: The JK Ti-22 was tested briefly as shown. This is a NorCal thing but the goal was to try to find another body that is easily available and comparable to the two we generally run in NorCal. Initial impression that this is close to the goal with the short spoiler. I may also need to re-think all the spoiler heights. There will be more to do on this.





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Jim Fowler

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