Derby Talk

Just messing around in the shop today, and thought I'd give it a shot. Still have some final sanding to do, but pretty happy so far. Any/All critique welcome...

There's still an awful lot of wood left in there!

Don't know where the cut limit, before losing any/all rigidness is, lol. I really do have a problem with jumping right in on new stuff, without knowing exactly what it is that I'm doing!

I used stock wheelbase on this (leaving some wood in the rear), since I figured this would be a good test mule to try my first full-length/full wheel surround balsa fenders. I know that the balsa top will add some strength, but since I don't have any on hand, I played it safe.

Ok.....put it on a diet and took off was much wood as I think could possibly come off. Did I go too far, not far enough yet, or about where a ladder chassis should be? I know it was pretty fragile taking it this far with a dremel and a file! lol

I've raced very nicely with side rails that thin (and missing the middle cross piece) with nothing covering 'em to give them strength. Since I think that you will be reinforcing with some kind of covering, you should do great! If anything, you may find that the front end is lighter than you want.

Just a little info that might be of interest.
A piece of 1/32" Balsa the size you would need to cover the top weighs 1.82 grams. It has a typical density of about 160 kg/m3.
A piece of 1/32" Basswood the size you would need to cover the top weighs 3.16 grams. It has a typical density of 560 Kg per cubic metre.
If you're concerned about flexing or breaking, the Basswood might be a better choice.
It appears you cut off the back. If you are considering moving it to the front I'm not sure it will clear the curve on the Best track. I'll check it out and let you know.

That is excellent information! I will be going to the closest hobby town in next few days, and they have a very good selection of both woods. As far as the rear cut off, this car will never see a track and is just a "learning" build, so for sure not putting it on the front. It will be a shelf queen. I want to finish the chassis, then do the fenders, then paint it. Not sure if I'm going to weight it and do wheel/axle work or not at this point.

FWIW, I did check again to make sure a car with a shifted wheelbase (cut off the back and move it to the front) would clear the curve on a Best track and it does clear. It's very close. If the Derbyworx Jig was used to drill holes I think the front would scrape. Maximum Velocity did a test a short time ago on a shifted wheelbase car and the difference was in the .000 range for the better.

I'm eager to see the finished car. Might we see pictures of the build?

Speedster wrote:FWIW, I did check again to make sure a car with a shifted wheelbase (cut off the back and move it to the front) would clear the curve on a Best track and it does clear. It's very close. If the Derbyworx Jig was used to drill holes I think the front would scrape. Maximum Velocity did a test a short time ago on a shifted wheelbase car and the difference was in the .000 range for the better.

I'm eager to see the finished car. Might we see pictures of the build?

Thanks Speedster, very good info to have on file!

Hopefully someone replies very soon as I need some advice before cutting this out!


QUESTION: When sticking with a stock wheelbase, is the rear weight pocket layout better to be centered with the rear axle (symmetric with the front rear pocket), or better like pictured below? If no response with the hour, it will be getting cut like it is. If that's not preferred, then I guess I will just have to cut another, lol.

I have not tried that. I prefer to keep the weight tight up against the rear axle.

Regarding your first ladder - you'll want to give yourself more room between the rear axle spar and the first spar forward from the axles. Basically, you'll want to make that weight pocket bigger to give you more weight placement options. I'd argue that that is the whole point of building an ultra light chassis. Going two rows of weight in front of the axle is usually not the best.

Thanks for the timely reply! lol

I added some meat to the front of the car (from 3/8" to 1/2"), pulled the rear rear weight pocket in to an equal distance of the axle centerline, and added 1/4" to the front rear weight pocket (is that enough, or more needed)?

I am very new to cube weighted cars, so this point baffles me a little "Going two rows of weight in front of the axle is usually not the best". I've been finding/reading that with rear wheels not pushed back to 5/8", that 12 cubes behind the axle is too much. So with that said (having less weight behind rear axle), not sure where the rest of the weight can go, besides in the front rear pocket, which will be more than 2 rows?

Gtdhw wrote: I am very new to cube weighted cars, so this point baffles me a little "Going two rows of weight in front of the axle is usually not the best". I've been finding/reading that with rear wheels not pushed back to 5/8", that 12 cubes behind the axle is too much. So with that said (having less weight behind rear axle), not sure where the rest of the weight can go, besides in the front rear pocket, which will be more than 2 rows?

I always go 12 cubes behind the axle. Even with a stock wheelbase.

What I meant by "Going two rows of weight in front of the axle is usually not the best" is this. With the ultralight frame you are building, you will be able to add 4oz or more cubes to the car. This means, after you put one row of 6 cubes in front of the axle and two rows of 6 behind, you'll have 6+ cubes to place. Where you place those last 6 cubes makes a difference in the speed and stability of the car. Rarely, do I find, that its best to simply add another full row of 6 cubes, because there won't be enough weight on the DFW. So that means you'll need to add more weight to the DFW side, going 3 maybe even 4 cubes deep. However, your weight pocket in your first pictures you shared looks likes its only big enough to hold two rows in front of the axle.

LightninBoy, you have put me back to Square One. I thought 1 1/2 ounces was the preferred weight behind the rear axle for a stock wheelbase car. There is a 2 ounce block available. Did you ever use it? Is there any advantage/disadvantage of dealing with all those individual 1/4" cubes if your intent is to use 2 ounces? Do you shift the wheelbase if allowed? Is a ladder chassis the absolute best design for a car if speed is your only goal?
Would you show us one or more of your cars with a stock wheelbase and how it is weighted?

Ok, so for now, I put the stock wheelbase on the back burner, and this is attempt #2. Front weight pocket is still made tight for 2 rows, but early testing showed that the "extra" weight will need to be in the next pocket forward to get a 15g DFW weight (12g if all weight stays in the rear pockets). This is just the mock-up stage, and the fenders will come back off to be paired and final shaped/sanded/rail clearance'd, but I'm having a blast (even if I'm not doing anything right! lol). Pine chassis, thinned basswood undercarriage, balsa fenders, & thinned balsa "hood". With virgin wheels/axles, the car comes in @ 24g. Hoping to get it down to 23g after shaping the fenders better. Weights should be coming in today....

(How long has Stan been telling every one this?)

Stan Pope wrote:There's still an awful lot of wood left in there!

Now there's some Derby Talk Trivia for ya!
Seem's i ran across a web site were some one said... Stan said this very thing to them.

The car is looking good Gtdhw.