RA car questions - Side rail design

General discussions for car and semi-truck racers.
pgosselin
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Re: RA car questions - Side rail design

Post by pgosselin »

Yep. But try not to get any on the wheel tread. You may want the extra grip there.

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Re: RA car questions - Side rail design

Post by rpcarpe »

If allowed, shave off the BSA lettering from the outside of the wheel, and get it nice and smooth with 400-1000 grit wet/dry. A good graphite rub on the DFW will help. Keep the rears off the rail by increasing the gap on the DFW or narrowing the REAR of the car (1/16-1/8").

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Re: RA car questions - Side rail design

Post by CallMeChris »

So I've finally gotten home from work and we are working on the cars...run into a major problem though. We will be racing on a different track this year and no one can tell me the name brand, construction, or side rail/center rail. Looks like we will be doing plain cars and not narrow the front or rear since we just don't know. Also plan on making them a 3 wheel straight runner instead of a RR so it should do ok on whatever track they throw at us.

This is our first year to do narrow cars so we are using a LOT of what we find on here. Take a look at this and let me know your thoughts. Here is our progress so far...

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As you can see right now we are at .6 oz for just the body and 4.7 with the tungsten cubes added. Do we need to get rid of more wood or do ya'll think it will be ok after paint and tires are added. I've got tungsten putty to fine tune with at the end. I know I can leave one of the cubes out but the more weight in the cubes and the less in wood the better, right?

Shape look ok? We are leaving it at stock wheel base...our old track was MURDER on the extended wheelbase cars when they came to a stop at the end and like I said above since I don't know what we are getting into this should be a safe bet to make.

Any other comments or concerns, post them up. We have done PWD for a few years now but this is the first time to do one with nothing but speed in mind! :mrgreen:
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Re: RA car questions - Side rail design

Post by rpcarpe »

If NOT allowed to lighten your wheels, you're going to be in trouble.
BSA wheels and axles weight about .5oz.

Great progress on the car. What did you use to create the weight pockets?
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Re: RA car questions - Side rail design

Post by CallMeChris »

A 1/4" fostner bit in my drill press. I tried to let Conner do it but that was just a little much for him and if you look closely in the first pic you can see where it got into the side of the car just a tiny bit. We have been able to sand it out pretty good and it's smooth where the wheel will ride so I guess it's good enough.

This is an RA car, not a BSA car so the wheels are different. Guess I need to weigh them and see.

What should I shoot for with the body and weights....4.3 oz or so if my wheels and axles are .5. That would put me at 4.8 give or take before paint and tungsten putty.
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Re: RA car questions - Side rail design

Post by Stan Pope »

Since I know what kind of track my pups will be racing on, I plan for 0.15 to 0.20 trim weight to adjust the CM location. The needed adjustment is usually forward.

Since you are entering a vast unknown, it would be a shot in the dark. With the weight and car body as shown and without trim weights, your CM will be about 0.5" forward of the rear axles (if tungsten cubes are toward the back of the cavity) to 0.7" forward (if tungsten cubes are toward the front of the cavity.) At these CM's a straight runner will rattle all over the track as the car nears the finish line. Up until it comes loose, it will be fast, an the rattling will lose only to the fast cars (the ones whose builders knew (or guessed right about) the kind of track to run and knew how to set up for it.

If you can wait until race day and find out what kind of track you will run on and still have a half hour to finish the tuning, then you can assume center rail, set up to run the rail and then adjust to run straight if you find you are running in a trough!
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Re: RA car questions - Side rail design

Post by CallMeChris »

I won't have a chance to tune the car the day of the race I don't think...would we be beIst setting it up.as a rail rider and going with it. If we get it tuned at say 2" for 4' and the track happens to be a side rail would we lose more speed than a straight runner rattling around?
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Re: RA car questions - Side rail design

Post by Stan Pope »

CallMeChris wrote:I won't have a chance to tune the car the day of the race I don't think...would we be beIst setting it up.as a rail rider and going with it. If we get it tuned at say 2" for 4' and the track happens to be a side rail would we lose more speed than a straight runner rattling around?
Run Straight!

But ...

Would you have time to screw on the weight between arrival at venue and start of inspection?

If so, you can
1. indent both wheels 1/16" at one end of the car. On a track with a center rail, this is the front; on a trough, this is the back.
2. set the car up to run perfectly straight, forward and backward. Test over a yardstick to assure that rear wheels don't rub. Test in a trough to assure that rear wheels don't rub.
3. on a center rail, narrowed end is front; on a trough, narrowed end is rear. Screw on the weight accordingly!
Stan
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Re: RA car questions - Side rail design

Post by CallMeChris »

But how do I decide which end to indent? We were going to be racing a side rail but now no one knows anything besides it's a 4 lane track.
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Re: RA car questions - Side rail design

Post by Stan Pope »

CallMeChris wrote:But how do I decide which end to indent? We were going to be racing a side rail but now no one knows anything besides it's a 4 lane track.
Okay, so now you know you will be racing in a trough, not with center rail!!! Right???

YES:

That narrows it down enough!

Majority DT opinion says, "Run straight in a trough."
It also says "keep your rear wheels off the sides!" To do this, narrow the rear.

If the track starts steep and finishes with a gentle slope or level, make the rear heavier than the front... ratio of about 4:1. (scale under front wheels reads one ounce, scale under rear wheels reads 4 ounces!)

NO:

re: "But how do I decide which end to indent?"
Pick an end.
In a trough, run with weight attached to narrow end and wide end is front of car.
On a rail, run with weight attached to wide end and narrow end is front of car.

Since you are aligning to run straight, forward and backward, you may swap which end of the car is the back by just swapping where the ballast is attached!
Stan
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CallMeChris
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Re: RA car questions - Side rail design

Post by CallMeChris »

Gotcha, makes sense now. I do not know if it's going to be a side rail or center rail though. Our track for the last few years has been side rail but no one can tell me what the new track will be other than it will be 4 lanes instead of 2. Do they even make a 4 lane side rail?
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Re: RA car questions - Side rail design

Post by rpcarpe »

Yes,
SuperTimer offers 4 lane edge-guided tracks.
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Re: RA car questions - Side rail design

Post by CallMeChris »

We got the cars finished today. Since I couldn't find out which track they will be running on we were forced to build a generic car that hopefully will perform decent on either track. Both cars are set up as a 3 wheeled straight runner. If the track turns out to be a center rail it should be easy enough to tune for a rail rider the night of the race. Races aren't for another month but I work on the river and just left this afternoon for work. I get home in 28 days...1 day before the races! Lol. Anyways, both cars are 4.9 oz and will be brought up to 5 oz with tungsten putty at weigh in. Thank you everyone for all of your help to get us to this point!


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Re: RA car questions - Side rail design

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Re: RA car questions - Side rail design

Post by CallMeChris »

Thought I would give a quick update...after a few schedule changes and more changes we finally ended up racing Friday night on our own old wooden 2 lane side rail track. We had a major problem when 2 days before the race the Perry the platipus car was dropped from about 6' up. It bent the right rear axle so the tire was under the car and messed up the wood around where the axle goes. I smoothed it all the best I could and we prepared a spare axle and fixed it up as best we could. We also had an issue when we got to the races and the cars wouldn't go on the track. We pushed the rear axle back as far as we could but that made the cars rear wheels not fit on the track...had to get creative with a razor blade right before the race and cut some off of the front of the car to move the rear axle up on the track!

For the races there were 5 age groups...1st grade, 2nd grade, 3rd grade, 4th grade, and 5th grade and then an overall race with the first place winners from all groups...all races were double elimination. I thought this was my oldest sons last year but we are good to get for one more year for him! My youngest won first in the 3rd grade age group with a speed of 126.4 mph...I was super happy with that after our repairs we pulle off! My elder son won first in the 4th grade age group, first overall, was undefeated for the whole night, and had the fastest speed of the night at 131.36 MPH!



All in all a great night for the boys!
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