Rail Riding Question - indenting RR wheel

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scoutdad01
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Rail Riding Question - indenting RR wheel

Post by scoutdad01 » Tue Jan 09, 2018 4:32 pm

Hello all,

New member. I’m attempting to build a RR car for the first time. I’ve read in a few places to ident the block at the RR axle groove 1/16”. Our rules specify a minimum distance between the wheels of 1 3/4” which effectively prohibits this technique.

If I can’t indent the RR axle groove, is a RR car still feasible/beneficial, or will the rear wheel ride as well? I’m planning to bend the forward axle +1.5° and the rear axle -2.5° using the Pro Rail Rider Tool.

Thanks!



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kcarchitect
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Re: Rail Riding Question - indenting RR wheel

Post by kcarchitect » Tue Jan 09, 2018 4:39 pm

scoutdad01 wrote:
Tue Jan 09, 2018 4:32 pm
Hello all,

New member. I’m attempting to build a RR car for the first time. I’ve read in a few places to ident the block at the RR axle groove 1/16”. Our rules specify a minimum distance between the wheels of 1 3/4” which effectively prohibits this technique.

If I can’t indent the RR axle groove, is a RR car still feasible/beneficial, or will the rear wheel ride as well? I’m planning to bend the forward axle +1.5° and the rear axle -2.5° using the Pro Rail Rider Tool.

Thanks!
For what it's worth, after three years of rail riders we've never indented the body. You will probably want to angle both rear axles but in my experience, you don't need more than 1° - 1.5° at the most. The sharper angle just makes it more difficult to fine tune.



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whodathunkit
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Re: Rail Riding Question - indenting RR wheel

Post by whodathunkit » Tue Jan 09, 2018 6:04 pm

Hi scoutdad01, and welcome!
When you say indenting the axle grove.. for the RR Wheel!
Do you mean the for the front dominant wheel.. Or the right rear wheel ?


Most of the time builders will indent the car body by 1/16'' for there front dominant wheel only!
And yes some will also cut a grove around the axle shaft at the body line to help bend the axle at the body line of the front dominant wheel.

( The K house groove as it is called is a slot cut in the axle head like a standard head screw would look..
to where a small standard screw driver can be used to adjust the axle.)

With rail riding you want to keep your rear wheels from rubbing on the rails by letting the rear wheels move out to the axle heads and away from the center rails.
Hope this helps and best of luck!
Whoda.


What type of automobile can be spelled the same forwards & backwards?

Speedster
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Re: Rail Riding Question - indenting RR wheel

Post by Speedster » Tue Jan 09, 2018 6:22 pm

The block measures 1 3/4". Just for an example, I put one of the steel spacers you get with the axle guide behind each of the front wheels and I get a measurement of 1 7/8". You could narrow the distance 1/16" behind the DFW and still have a clearance of 1 3/4". However, if you end up with a distance less then 1 3/4" all you need to do is extend the gap of the raised front wheel and it will pass inspection. If your rules require you to run "4 on the ground", then you will be setting the Non DFW with Negative Cant and Toe-out. That will keep the Non DFW off the rail and will help the DFW. The DFW should be set with Positive Cant and toe-in.
Although I have set cars up without narrowing the car body behind the DFW, I prefer to narrow the body and now do it all the time. I set the rear wheels with 1 1/2 degrees of Negative Cant instead of 2 1/2 degrees. I fear a 2 1/2 degree Cant might mask a rear wheel misalignment. At 1 1/2 degree cant a toe-in or toe-out will still happen. A 1 1/2 degree cant will still lift the rear wheel so it runs on the inside edge - just barely. I use the aluminum Derbyworx tool where you lift the rod to bend the axle. I have to guess where 1 1/2 degrees is because it is not marked but I'm sure I'm very close. Make sure you narrow the car body enough so no part of the wheel, other then the hub, touches the car body.
Best wishes in your race.



scoutdad01
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Re: Rail Riding Question - indenting RR wheel

Post by scoutdad01 » Tue Jan 09, 2018 8:35 pm

whodathunkit wrote:
Tue Jan 09, 2018 6:04 pm
Hi scoutdad01, and welcome!
When you say indenting the axle grove.. for the RR Wheel!
Do you mean the for the front dominant wheel.. Or the right rear wheel ?


Most of the time builders will indent the car body by 1/16'' for there front dominant wheel only!
And yes some will also cut a grove around the axle shaft at the body line to help bend the axle at the body line of the front dominant wheel.

( The K house groove as it is called is a slot cut in the axle head like a standard head screw would look..
to where a small standard screw driver can be used to adjust the axle.)

With rail riding you want to keep your rear wheels from rubbing on the rails by letting the rear wheels move out to the axle heads and away from the center rails.
Hope this helps and best of luck!
Whoda.
Whoda - thanks for the feedback. I was assuming the RR wheel meant rail riding wheel. I was referring to the dominant front wheel. Chalk it up to be being the new guy :idk:



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Re: Rail Riding Question - indenting RR wheel

Post by scoutdad01 » Tue Jan 09, 2018 9:40 pm

Speedster wrote:
Tue Jan 09, 2018 6:22 pm
The block measures 1 3/4". Just for an example, I put one of the steel spacers you get with the axle guide behind each of the front wheels and I get a measurement of 1 7/8". You could narrow the distance 1/16" behind the DFW and still have a clearance of 1 3/4". However, if you end up with a distance less then 1 3/4" all you need to do is extend the gap of the raised front wheel and it will pass inspection. If your rules require you to run "4 on the ground", then you will be setting the Non DFW with Negative Cant and Toe-out. That will keep the Non DFW off the rail and will help the DFW. The DFW should be set with Positive Cant and toe-in.
Although I have set cars up without narrowing the car body behind the DFW, I prefer to narrow the body and now do it all the time. I set the rear wheels with 1 1/2 degrees of Negative Cant instead of 2 1/2 degrees. I fear a 2 1/2 degree Cant might mask a rear wheel misalignment. At 1 1/2 degree cant a toe-in or toe-out will still happen. A 1 1/2 degree cant will still lift the rear wheel so it runs on the inside edge - just barely. I use the aluminum Derbyworx tool where you lift the rod to bend the axle. I have to guess where 1 1/2 degrees is because it is not marked but I'm sure I'm very close. Make sure you narrow the car body enough so no part of the wheel, other then the hub, touches the car body.
Best wishes in your race.
Thanks! I plan on limiting the negative cant to 1.5 degrees based on the feedback from you and kcarchitect. Here's the line from our rules that I am concerned about:

"Inner Wheel Width: Minimum width between wheels is 1 3/4 inches."

I am concerned that the minimum width can be interpreted as not including the gaps since the wheels can be slid up against the body. I understand the logic of narrowing the distance behind the DFW and originally planned to do so, but I am hesitant to do so based on rules interpretation.

When you did not narrow the distance behind the DFW, did you have any issues?



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Re: Rail Riding Question - indenting RR wheel

Post by whodathunkit » Tue Jan 09, 2018 10:32 pm

No problem scoutdad01,
Chalk up my way of thinking that the RR wheel could also be right rear .

Say don't forget about the inside wheel hubs! even though the car block is not 1 3/4" wide..
the inside rims between the front wheels will still be right at 1 3/4" with the hubs pushed up to the car body.
that's if you only remove up to 1/16" and not more. ( the notch is to center the rear wheels over the rail.)
With a stock body block at 1 3/4'' wide with the hubs pushed up to the body your looking at 1 7/8" between inside rims.. give or take a 32nd of an inch.

If the ruling on minimum width will be interpreted .. as from inside rim to inside rim..( and not inside hub to inside hub.) your good to go.
Last edited by whodathunkit on Tue Jan 09, 2018 10:45 pm, edited 1 time in total.


What type of automobile can be spelled the same forwards & backwards?

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Vitamin K
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Re: Rail Riding Question - indenting RR wheel

Post by Vitamin K » Tue Jan 09, 2018 10:40 pm

You can definitely get away with not narrowing the DFW end...especially if you put enough positive camber on the wheel (I like 7-10 degrees, personally).

If you want to get super-technical, you can put a shim on the side of the raised wheel to match the amount removed on the DFW side...you'll keep the same spacing for sure, that way. ;)



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Re: Rail Riding Question - indenting RR wheel

Post by Speedster » Wed Jan 10, 2018 7:10 am

The guide strip measures 1 5/8". The reason for the 1 3/4" clearance is simply so the car will clear the guide strip. In scout racing I think the folks who make the rules are trying to help you and not to look for ways to disqualify you. I suspect the inspector will have some type sample track to see if the car will clear the guide strip. That's all he/she will care about.
Yes, I have had issues with the trailing rear wheel riding the guide strip. I've heard of racers setting a rear wheel with minor toe-out to keep it off the rail. I've never done that. We are required to use the slots and they must stay in their 4 3/8" stock position. We are also (finally) allowed to bend the nail. Test your car without the front wheels on the car. The rear wheels should migrate to the axle heads while rolling the car forward and backwards. You do not want the rear wheels steering the car. With 1 1/2 degree Negative cant on the rears you can adjust any toe from the wheels.
I highly recommend Troy Thorne's book, "Build a Winning Pinewood Derby Car" 2013 addition. It can be purchased from Fox Chapel Publishing. You will learn all the basics in a very short period of time. Keep asking Derbytalk Questions.
Cheers
Speedster



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Re: Rail Riding Question - indenting RR wheel

Post by ironband » Fri Jan 12, 2018 12:48 am

Last year we had a similar situation - 2.5 deg rear axles, 1.5 deg front axle, and no thinning of the front end, though that was just due to poor planning rather than rules concerns.

We solved the problem by gapping the rear wheels with a credit card (about 0.030") and gapping the fdw with the kit box (about 0.015"). It was enough to keep the trailing rear wheels off the rail.

Andre



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