2015 Championship Edition re-fit Racer/Runner

[JasonB]

Actually, the wide axles swing the wheels front/back, the pivot is farther in. By increasing the arm and plunging the pivot point inside the wheel (like a B4), it corrects the geometry from this issue.

So you're saying the scrub radius is correct using these extra-wide arms with short axles and B4 wheels? Is this documented somewhere? My B2 wheels seem to have a much lower offset than the B4 wheels, but I haven't measured.

[JasonB]

With the two usual super fast guys not present this week, I TQ'd and very narrowly missed first place of seven in this weeks club race.

NOW! I didn't see any replies to my question above to tonight, and this had me thinking today. So tonight I had some spare time and I measured the B2 wheels and B4 wheels I had for the sake of comparison. I believe B2 wheels are the same offset as the 3pc. CE wheels that came on my car. I'm not claiming anything about my caliper or even my ability to measure, so consider these rough values. I could not find the dimensions anywhere online, despite over an hour of searching the forum and google. Maybe someone reading this can confirm or correct me here. Before someone comments about it: MY BACKSPACING MEASUREMENTS are done form the lip of the rim to the outer race of the front inner wheel bearing. MY WIDTH MEASUREMENTS are done from outer lip surface on either side of the wheel. I took pictures if anyone wants to see.

RC10B4 wheel: 25.2mm wide, 12.1mm backspacing (-0.5mm offset)
RC10B2 wheel: 19.5mm wide, 5.0mm backspacing (-4.75mm offset)
Measured also the width difference between RC10CE front axle and new 6801 associated axle which is +5.75mm

-4.25mm (difference in offset)+5.75 (longer axle)= +0.5mm
This 4.25mm dfference in wheel offset is clearly slightly less than the 5.75mm length increase of the axle; hence the scrub radius is changed very slightly (probably within the range of measurement error though) with the new 6801 associated axles.

Now, let's take for consideration the arms being that same (assuming?) 5.75mm longer instead? Now the B4 wheel is used, so the EFFECTIVE offset or the distance from kingpin to wheel center is reduced. Not trying to knock a new RC10 product but as far as I can tell, lengthening the arm only increases the track width and "fixes" nothing about the geometry when using B4 wheels. This change in scrub radius could alter steering for better or worse; do I know from testing? No. I only know the theory: You are making the scrub radius more negative (or as you said, putting the steering axis further "inside the wheel". Does this result in better performance? Has anyone tested it back-to-back yet? The people who designed the car know both theory and no doubt they have tested it, and their solution comes close to maintaining the original steering performance of the car with a wider front wheel installed. Is there a clear benefit to having more a more negative scrub radius on the RC10?

[JK Racing]

I dont know anything about scrub radius, I am far from an engineer

What I do know is the B3 wheel retains the width of the B4 and the backspacing of the CE/B2...best of both worlds if running stock axles. Same with B3 rear wheels , width of B4/modern, perfect back spacing for RC10. The re-re worlds rear wheels are narrow like the original RC10 worlds and B2 wheels.

My theory on the GT Wide axles being used by AE in the re-re worlds? 1) it was seen here that we were doing it already, 2) no re-engineering and making new parts...dig into an already existing parts bin and bag it up. (also, the re-re rear wheel is a parts bin pull from the Thunder Tiger Phoenix BX II buggy)

[JasonB]

Actually, the wide axles swing the wheels front/back, the pivot is farther in. By increasing the arm and plunging the pivot point inside the wheel (like a B4), it corrects the geometry from this issue.

Then you say:

I dont know anything about scrub radius, I am far from an engineer

Ah ha! You DO know the concept because you just described it a couple posts back!
http://en.wikipedia.org/wiki/Scrub_radius

I'm actually really surprised that nobody commented on my scrub radius comments. Maybe I should put it in its own thread? Has anybody actually crashed those shapeways front arms or are they all on shelf queens? At this point, nobody is discussing so I feel like buying the new long arms just to test and at the same time find out if it's a positive or negative performance difference (from the changed scrub radius ONLY, I would use short axles) by doing A-B-A a couple times.

Are the various RC10 wheel offsets and exact sizing published anywhere on the site? I can't find them.

[rcgerber]

Jason, looking at the link you provided, the scrub radius changes no matter what you change to be able to run B4 wheels and 2.2 tires. The only way to not change the scrub radius and run 2.2 tires is B2 rims (which are hard to come by). If you want to use the easier to find B4 wheels your two options both widen the track with so you can accommodate the larger back space of the B4 wheel. Since the kingpin is stationary, the GT axle option adds positive scrub radius from stock, while the longer arm adds negative scrub radius from stock. In my experience the positive scrub radius tends to create push which isn't something you want in a rear motor car. So the longer arm is the better option in terms of handling if you want to run B4 wheels.

[JK Racing]

Brian has run the wide arms and test crashed them in the B1M thread. That was Thursday night, I was too busy to drop by and take some video.

Oh...B2 wheels, Duratrax Evader BX front wheels are pretty much identical in offset and size. Yes, they take the same bearings as AE as well.

[JasonB]

Jason, looking at the link you provided, the scrub radius changes no matter what you change to be able to run B4 wheels and 2.2 tires. The only way to not change the scrub radius and run 2.2 tires is B2 rims (which are hard to come by). If you want to use the easier to find B4 wheels your two options both widen the track with so you can accommodate the larger back space of the B4 wheel. Since the kingpin is stationary, the GT axle option adds positive scrub radius from stock, while the longer arm adds negative scrub radius from stock. In my experience the positive scrub radius tends to create push which isn't something you want in a rear motor car. So the longer arm is the better option in terms of handling if you want to run B4 wheels.

Thanks for chiming in, that's exactly what I was hoping to hear! Now I'm much more eager to test the difference for myself.
Still, by my measurements the scrub radius change with the longer axles is very minimal (.5mm) so I believe Associated took the correct approach with the rere worlds kit.

Brian has run the wide arms and test crashed them in the B1M thread. That was Thursday night, I was too busy to drop by and take some video.

Oh...B2 wheels, Duratrax Evader BX front wheels are pretty much identical in offset and size. Yes, they take the same bearings as AE as well.

I'm in love with his B1M project and plan to do something similar in the near future. I have ordered the shapeways longer arms and will see how I like the change on my racer. I must admit, with so few people racing on the shapeways parts I'm still a little worried about their durability. Thanks for the info on the Duratrax Evader wheels, though if they are narrower like B2 wheels then will modern buggy front foams/tires fit correctly?

[JK Racing]

Fit, yes...correct, meh...depends on your definition. 2wd buggy front tires have grown wider and wider. Some tires develop a 'crown' when using the narrow wheels. It depends on how well you can trim up the insert and which tire. I recently gave in and went to the re-re front axles and B4 front wheels, just to ensure I am getting a tire fitting the wheel correctly. It was also time, most my other tires were getting worn to the point of becoming 'practice' tires anyways...something with less grip that forces you to be a better driver

[JasonB]

This week we had a low turnout... especially in 17.5 buggy, so they ran the stock buggies with the mod buggies.
I changed upper shock mounting holes and went to 35wt front shock oil, but otherwise the same setup as I had been running. The speed difference on this track layout was apparent only in that the mod cars could easily clear the big doubles, while us stock guys have to get a really good run up to avoid landing on the crest and bottoming out hard. I won stock easily and was competitive with most of the mod guys. If not for a big "OOPS!" crash which was my fault and getting run into once, I would have had 3rd easily

[JasonB]

Fit, yes...correct, meh...depends on your definition. 2wd buggy front tires have grown wider and wider. Some tires develop a 'crown' when using the narrow wheels. It depends on how well you can trim up the insert and which tire. I recently gave in and went to the re-re front axles and B4 front wheels, just to ensure I am getting a tire fitting the wheel correctly. It was also time, most my other tires were getting worn to the point of becoming 'practice' tires anyways...something with less grip that forces you to be a better driver

I notice my proline electron rears have a definite crown on the worlds wheels. When the track is wet, they come off with only the center 2/3 of the tire gummed up with clay.

Less grip is great for practice, but sadly I have found that when I get used to running my old tires (on my new buggy at least) I get comfortable with that level of grip... then I don't try to push as hard when I DO have the grip. This is frustrating; I don't want to always be buying new tires (wearing the good ones out in practice) much less doping the tires up for every practice run.

[JasonB]

A few horrific crashes with 8th scale newbies on the track resulted in a broken CF front CE tower, among other things
This prompted me to rebuild the front end with fredswain's shapeways arms and Niki's bb spring adapters. Also changed to an aluminum B4 top shaft (the kind that still takes the spacer) and avid triad slipper to shave drivetrain mass. I've added about the same amount of weight with the front arms, bb spring adapters and a new battery cup. Lots of new parts on this old car now As soon as my new set of short axles arrives It'll be ready; I should be running it in practice this weekend and club racing next week

[JasonB]

Am I the first one to break one of the 3d printed arms? I didn't get to do my ABA test, so I guess I'll buy another pair of them.

Made it through a couple hours of practice last week including a practice where Dakotah crashed me on accident with his 8th scale. Today I ran two heats with three moderate crashes, and finally broke in the main at tonights club race. I'd say at this point they might be similar in strength to the vintage plastic stock black/long arms (having broken many of those in the last year).

[JasonB]

The new replacement shapeways arms showed up last week and they are substantially different from the ones I had before. Maybe I will contact them about this...
1. The pin holes did not require drilling, the pins pushed through easily and they are perhaps even a little sloppy in the holes.
2. The surface finish is nicer/much smoother.
3. The nylon itself seems to be a different type. As I broke the arms apart from each other last time I was able to flex them back and forth exactly 4 times before the webbing snapped. This time, I was able to flex them only one time.

Last week I managed to turn the fastest lap for stock buggy. Qualified second and finished 2nd of 10.

[JasonB]

I have the car pretty much what I would call 'dialed' without having changed caster or rear toe/anti squat. After racing back-to-back with both cars numerous weeks it's clear now that:
-The car has slightly more understeer in general with the shapeways extended arms vs regular long arms. I swapped both arms and ran it at the same static camber and toe settings. I feel the car is more stable and planted on corner entry with the longer arms, so I am going to keep running them for now.
-I can drive my B5M significantly faster (between .5 and 1 second per lap on three different tracks).
-The RC10 takes substantially more effort to drive 'at the limit' than the B5M does.
I'm going to keep running the RC10 on indoor clay during the winter whenever I need a challenge... and for nostalgia sake. I absolutely intend to continue trying different things in the future, including caster, anti-squat and rear toe.
Now that summer is upon us, outdoor season is ramping up. A friend has a nice DIRT outdoor track, I recently found another gold pan car, and I have piles of CE parts so I may build another CE racer specifically for this soft outdoor stuff

[SLIDER]

Thanks for the update! Sounds like you got old school hustling pretty good! Have you had anymore issues with the Shapeway arms breaking? I ordered a set for the front and rear my RC10! The rear set of arms snapped apart on the 1st flex, the front arms took 4 or 5 before they came apart!