Wheelbase Lengthening Inquiry

[Panther6834]

A few months ago, I posted (in the "General Tech" section) an inquiry about lengthening a wheelbase to 329mm, specifically for a build I was considering. In the thread, I mentioned a few chassis possibilities. Some responding agreed with certain choices, and gave suggestions how to lengthen the wheelbase to my needed length, while others gave additional suggestions and/or have reasons why certain chassis wouldn't work for my project. In the end (at that point in time), I decided on using the VP VS4-10 rails & VFD trans, asking with TRX4 portal axles...though, I still haven't purchased anything for that build, and maybe that's a good thing. Now, a few months, Axial releases the SCX10.3, and I need to reevaluate my project's possibility. I'm looking for some help/suggestions, to see if what I'm proposing can be done using the SCX10.3, or whether I should return to my original idea. I realize few people have received their SCX10.3, but I'm hoping that those who've already received theirs, and have started their build, will be able to help..

The most important thing for the build I am proposing...and, simultaneously, the biggest problem...is in extending the wheelbase of whatever chassis is used. My original idea was to move the rear shock tower back (to keep the shock in as close to the same position as possible), and use longer upper & lower links, as well as a longer driveshaft. However, the split-rail design of the SCX10.3 opens an entirely new possibility, and one that could prove to possibly be the best option.

To those who've received their SCX10.3, and are already building theirs should, try to
visualize what I'm saying. Here's my idea:

The front end would remain unchanged, with one minor exception. In order to lengthen the wheelbase as I'll describe, I'd need to cut a piece off the front of each rear rails, between the 1st & 2nd holes (based on the image in the manual, there are 10 holes at the front of each rear rail). The front of the skid would attach to the front rails using the piece I cut (to 'compensate' for the rear rails being moved further back). As for the 'pin' on each side of the skid, near the front (just behind the screw), that would be left "hanging", as there'd be no real rail for the front 'pin' to insert into.

Speaking of those 10 holes at the front of each rear rail, this is where I need some help. Specifically, in order to make this work...or determine if it's even possible...I need to know the center-to-center measurement of the spacing between those 10 holes. I'm assuming that the spacing remains the same between each of the holes, as 4 holes per trail appear to be used in building the chassis (as described in the manual). Example, from front-to-rear of the rear rails: screw through hope #1, skid pin through hope #2, skid pin through hope #4, and finally screw through hope #5. It's because of this that I believe the holes are equally spaced. So, what is the spacing between these holes?

Getting back to the rear of the skid, depending on the hole spacing, the rear rails would be slid back the number of holes needed to achieve the necessary 329mm wheelbase. The rear skid screw would go through the proper hole on the front rails, followed by whatever rear rail hole creates the required wheelbase, and then into the screw hole at the rear of the skid...plus, the 'pin' in front of the rear screw would insert into the appropriate hole on the rear rails.

Finally, so as to structurally stabilize the front & rear rails to each other, I'd drill holes through the front & rear rails, closer to the rear of the front rails, and attach them together using a shorter screw & nut with threadlock. Alternately, instead of using nuts & threadlock, I could add an additional cross-brace, and, using screws the same length as those going into the skid, screw the screws into the cross-brace, which would also provide additional structural-stability to the frame. Going with either option, between the front & rear rails, as well as the skid, each side would use 3 screws, instead of the usual 2 screws.

As for the rear suspension, I'd need to get upper & lower links that were 16mm longer than stock. Since I'd already be going with steel driveshafts front & rear (such as MIP), I'd just need to get a rear driveshaft that could handle being 16mm longer than stock. In this configuration, 100% of the front geometry would remain the same. As for the rear, the rear shocks, and rear upper links, would still be mounted at the exact same angle as stock...and, the change to the rear lower links & rear driveshaft would be so minimal, it shouldn't have any change in performance, or operation.

Is my idea a "good" idea? Is it "doable"? If it could work, it would finally give me the needed 329mm wheelbase is need to complete the project I originally proposed a free months ago. Honestly, I think it should easily work. What are people's thoughts? Positive, or negative, I'm listening.

~ More peace, love, laughter & kindness would make the world a MUCH better place

[Topher Builds]

Regarding the links, it wouldn’t be as simple as stretching them by 16mm since the geometry is triangular and the link itself is on the hypotenuse. You could whip up Pythagorean’s theorem to find the true length that C needs to be extended in order for B to be +16mm after solving for A, by measuring. I think A is close to 40mm with a quick measure.

For the sake of steering geometry you’ll want to keep everything up front as similar as possible, without changing the upper or lower front link mounts, in an effort to maintain the steering and axle swing geometry. This may be possible with some drilling and problem solving in just the rear end.

[Panther6834]

Originally Posted by Topher Builds

Regarding the links, it wouldn’t be as simple as stretching them by 16mm since the geometry is triangular and the link itself is on the hypotenuse. You could whip up Pythagorean’s theorem to find the true length that C needs to be extended in order for B to be +16mm after solving for A, by measuring. I think A is close to 40mm with a quick measure.

For the sake of steering geometry you’ll want to keep everything up front as similar as possible, without changing the upper or lower front link mounts, in an effort to maintain the steering and axle swing geometry. This may be possible with some drilling and problem solving in just the rear end.

Regarding the front, I wouldn't be keeping everything "as similar as possible"...it would be 109% stock, 100% identical. As for the rear, and what you said, my excuse is, "I hadn't yet had my morning coffee, and my brain wasn't working yet". That excuse does work, right?

Seriously, though, I had completely forgotten about taking the the angle of the rear links into consideration. Comparing moving the rear shock towers further back (what I'd be doing if I went with the VS4-10 rails), and lengthening the rails (what I'd be doing if I went with the SCX10.3), I really prefer lengthening the rails. When 1:1 vehicles are "stretched" (such as stretched limos), that's exactly how they do it.

So, in terms of scale accuracy, I'd think that the SCX10.3 idea would also be better. My primary concerns are structural stability, as well as the angle of the rear shock, from shock tower to axle. That last point is why I was reluctant to go the VS4-10 route...and, work the release of the SCX10.3, I'm VERY glad I didn't wish into getting the VS4-10 rails & VFD trans. Overall, tho, do you think my chassis lengthening idea would work?

~ More peace, love, laughter & kindness would make the world a MUCH better place