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Questions about guide setup and wheelbase


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#1 Mattb

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Posted 14 August 2017 - 08:25 AM

While the cars we race aren't very technical or cutting edge, I have always wondered what most racers consider the optimum setup  for guides and wheelbase.   Several questions:

 

Is there a preferred distance from the front axle to the front of the guide or to the guide post?

 

How high for the front wheels, barely touching the track?  

 

Is there an advantage to a longer wheelbase over a shorter wheelbase for handling?

 

thanks for your replies and opinions.

 

mattb


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#2 Dominator

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Posted 14 August 2017 - 11:47 AM

Hi Matt,

As for guide lead (center of front axle to center of guide post) most will build using 15/16" or 1" (with a 3-15/16" or 4" wheel base) Sometimes 7/8" on a high speed track. A 1" guide lead is more forgiving and A 15/16" Guide lead will be a little snappier out of the turn.

Front axle height will depend on your rules. IRRA for coupe, can am, and F1 require a front clearance of .015 with a .750 minimum diameter front. With the chassis laying flat use jig wheels or turn down some Parma 29 crown gears to .720 (.750 - .015x2 = .720). I prefer to use .710 jig wheels on the front as I tend to have more material ahead of the front axle on my builds.

Speaking for retro or scratchbuilt cars, you want the front tires to touch and roll. If you take the body off and set the car in the slot on the track the rear tires should lift slightly when you push down on the guide post. Add or remove guide spacers as needed.
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#3 kvanpelt

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Posted 14 August 2017 - 12:13 PM

Dominic, I'm a bit confused by your post.

 

If you have more material in front of the axle, don't you need bigger jig wheels to get more clearance because of the rake of the chassis?



#4 kvanpelt

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Posted 14 August 2017 - 12:18 PM

LOL. never mind. I blame it on the drugs!!!!


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#5 Dominator

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Posted 14 August 2017 - 01:00 PM

No problem Kevin lol

A motor is only as fast as the chassis it's in.
 
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#6 Kevin Donovan

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Posted 14 August 2017 - 03:47 PM

I don't race scratch built cars but I have wondered about this question of guide lead. If you look at a more modern style Car like a flexi or Eurosport, the chassis itself serves as the contact points where front wheels used to. On these chassis the contact points are even with, or sometimes ahead of the guide making for zero, or even negative guide lead. HO and 1/32 cars are running similar setup. Have you ever experimented with this on your handmade cars?

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#7 Dominator

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Posted 14 August 2017 - 05:38 PM

Hi Kevin,

KVP can explain a little better than I can as I haven't run scale cars in about 9 years now. Basically with stamed or scale type chassis you want to set the guide height the same as you would for a scratchbuilt. The only difference is you want the front of these chassis to touch just a little in the corners. The faster the car, the more important the spacing is as more down force is being applied to the nose of the car.

Judging from the stamped chassis you have in the bottom picture the one on the left looks good with spacing where the one in the middle looks like it needs .005-.010 more. You want to pick up a little rubber but too much means you might be dragging on the straight.

A motor is only as fast as the chassis it's in.
 
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#8 Half Fast

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Posted 14 August 2017 - 06:11 PM

Front axle height will depend on your rules. IRRA for coupe, can am, and F1 require a front clearance of .015 with a .750 minimum diameter front. With the chassis laying flat use jig wheels or turn down some old 29 crown gears to .730 (.750 - .015x2 = .750). I prefer to use .710 jig wheels on the front as I tend to have more material ahead of the front axle on my builds.
 

 

 

Dom-

 

Perhaps I'm off my Meds too but could you explain that statement

 

Cheers


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#9 MSwiss

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Posted 14 August 2017 - 06:31 PM

Yes, Dom must of posted that in a hurry.
 
He needs to proof read that and repost.
 
I think some of those numbers should be .720".
 
Also, among other things, 29T's are about .719 - .721" in dia., so you won't be turning those down to .730"

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#10 Kevin Donovan

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Posted 14 August 2017 - 08:01 PM

My question wasn't about guide spacing, but if you ever build handmade chassis with real short guide lead to mimic the modern cars like I showed. Just wondering how that would work, or is there a rule that specifies a certain guide lead for the handbuilt classes?

#11 Dominator

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Posted 14 August 2017 - 08:34 PM

Sorry about that incorrect posting guys. I went back and correct my original post with the correct math.

The Parma 29 crown gears are .720-.722 in diameter. The Go Fast or Red Fox are closer to .710.

A motor is only as fast as the chassis it's in.
 
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#12 Half Fast

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Posted 14 August 2017 - 08:46 PM

" .710 jig wheels on the front as I tend to have more material ahead of the front axle on my builds."

 

Dom- This was the statement I did not understand, what did you mean by more material?

 

Thanks


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#13 JerseyJohn

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Posted 14 August 2017 - 09:05 PM

" .710 jig wheels on the front as I tend to have more material ahead of the front axle on my builds."

 

Dom- This was the statement I did not understand, what did you mean by more material?

 

Thanks

Bill the front clearence as measured and built with standard jig wheels is .015 directly below the axle. Most cars have chssis that are built with the center section or pans that extend beyond the axle center line. Now with the chassis pitched down because the rear is .050 any thing in front of the axle will be below .015 oops. iF  you dont want to go crazy measuring etc. use the standard 720 jig wheels. When done mount all 4 of your normal sized racing tires and take a .015 gauge and check you clearence from the front most part of the chassis. if its too low just adjust your height by resetting your axle/.

Another thing to keep in mind. as your rear tires wear the nose will raise a tad Also lets say you have 825 rears on and your alittle low in the front. try 815 tires. they will raise the front pitch up a  few thou and are large enough for tech


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#14 kvanpelt

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Posted 15 August 2017 - 10:38 AM

My question wasn't about guide spacing, but if you ever build handmade chassis with real short guide lead to mimic the modern cars like I showed. Just wondering how that would work, or is there a rule that specifies a certain guide lead for the handbuilt classes?

 

Kevin, the majority of this thread was headed toward the retro car class.

 

Retro rules require CanAm front wheels of .750 x .225 and must support the chassis with front clearance of .015 and rear clearance of .050 with low down-force bodies. Add the 100gram minimum weight limit, huge .8125 rear tires and in-line motor configuration, we are talking about a whole different animal than modern flexi or spring steel chassis. Most cars are built with the wheel base and guide leads mentioned above, anything too different, shorter or longer usually doesn't work very well.

 

I would agree with Dom regarding the guide setup of the chassis pictured. Certainly racing accidents may have altered the rubber build up on those cars, but a good blueprinted chassis with proper guide spacing will have the rubber build up more evenly across the front of the chassis and along the outside edge, the length of the pan.

 

Especially with Falcon motors, it is a very fine balance between handling well and scrubbing too much speed. 



#15 Dominator

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Posted 15 August 2017 - 05:14 PM

So here is an example of what I meant earlier about more material ahead of the axle. Both cars below have a 15/16" Guide lead, 4" wheel base, and .815 rear tires. Both have .050 clearance on the rear. Because the second chassis overall material length is longer (from the front edge of the brass nose to the rear axle) it changes decreases the amount of clearance in the front. Is it alot? Not really but its something to be aware of when building.

20170815_165606.jpg

20170815_170141.jpg

20170815_170223.jpg
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#16 Half Fast

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Posted 15 August 2017 - 06:01 PM

Thanks Dom/JJ Got it.

 

Cheers


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#17 Jim Lange

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Posted 16 August 2017 - 12:26 PM

Questions about guide length and wheelbase have been discussed in the past. Some well known builders have very strong feelings that short wheelbases and guide lengths do not work well in most cases. Which I disagree with. But like I've stated before, most people don't take the time to learn how to drive a short car properly. Once you do, they are much faster than the long car. On chassis's I build, my standard guide length is .700 for C/A and F1 on a Gerding. For flat track racing I go to .850. It is true that the short car is less forgiving, both in driving and setup, but it is definitely faster. As far as the material forward of the front axle on the picture shown ... the long one must still maintain .015 clearance in the front. With the additional length, the front must be raised to get the proper clearance. Also, any weight forward of the front axle reduces the weight on the rear. Small little details all add up in my book. That's my .02. 


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#18 Mattb

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Posted 16 August 2017 - 01:38 PM

So a simple answer for a simple slot car is a little longer wheelbase is usually a little easier to drive than a shorter wheelbase?  The guide out front of the front axle by 3/4 - 1 inch makes for a better handling, easier to drive car?    Provided it is a simple flat brass chassis is car or tube frame, but not some hinged wonder?

That the driver talent is average at best and not super racers?


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#19 Jim Lange

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Posted 16 August 2017 - 08:43 PM

Yes Matt, you are correct. Keep the front overhang to a minimum, as low and light as you can and still make tech. Good luck and build away.







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