Wheelbase on modified class

[JCovert]

What is considered when selecting a wheelbase. How extended is practical? I'm assuming bringing the DFW back would allow for stability when wanting COM farther back towards the rear and If I'm following correctly some post COM as 1/2", meaning 1/2" in front of rear axles. I guess I've just heard/read much info on extending wheelbase as much as possible but have seen many cars not following that line of thought.
Accidentally posted same Q in building tips.

 

[W racing]

The shorter the wheelbase the more agresive you can get with the COM. Because a shorter wheelbase will put more weight on the DFW than a long wheelbase for the same COM. 5" is a good starting point.

 

[JCovert]

Cool thanks. It appears that the rear wheels are always set as far back as possible and then wheelbase is a product of how forward the DFW is placed, correct? Is this a process of trial by fire or are you using some equation/calculations to derive the location needed based on the COM desired. If the later is being used can you advise some resources/info that would help me get the ball (wheels) rolling.
- Thanks, J.

 

[W racing]

Always place the rear wheels as far back as the rules allow.

You can build a few cars and measure the COM until you get it correct. Or you can use a spread sheet to calculate the weight on the front wheel each component has then add them all together. From this you can get the COM.

Weight on Front Wheel = (Weight * COM)/WB

SUM these for all components and you will get the weight on the front wheel. Rear axles and whels add 0 weight ot the front wheel as thei CON is zero. THen to calculate overal COM solve the equation for COM using the weight on the FW and WB.

If you use that equation for the same COM of the car and diffrent wheel basis you will see that weight on the front wheel is less as the WB increases for a given COM.

 

[Quicktimederby]

???? That doesn't work for me. The longer the WB the more aggressive I've been able to get with the COM. The longer the WB the more stable the car can be with less steer. On My Unlimited and Eliminator cars my WB's are long, in fact all of my cars are much longer WB than the standard. Yes even more than the 5inches most like. For the way I set up and build my cars it works for me. If were I have my COM where its at on a short wheel base car I wouldn't be able to control it with any amount of steer.

The shorter the wheelbase the more agresive you can get with the COM. Because a shorter wheelbase will put more weight on the DFW than a long wheelbase for the same COM. 5" is a good starting point.

 

[W racing]

When given a choce between 5 3/4 -vs- 5 WB it is a tough call. For a novice either choice is correct. However as they race and watch the top finishers they will re-think a lot of things. Top racers can win with multiple WBs as there is a lot more to a car than WB. On any given day the winner's WB may vary from the previous winner.

If you can however make a car stable at 5" WB at the same COM you were racing at 5 3/4" WB previously you now have more weight pressing down on the DFW. You can bleed that weight of by forcing the COM back. If the car is stil stable you have just gained potential energy and lost nothing.

 

[renegade]

I have to agree with Quicktime on this one. The longer the wheelbase the more aggressive I can be on the com with my cars.

???? That doesn't work for me. The longer the WB the more aggressive I've been able to get with the COM. The longer the WB the more stable the car can be with less steer. On My Unlimited and Eliminator cars my WB's are long, in fact all of my cars are much longer WB than the standard. Yes even more than the 5inches most like. For the way I set up and build my cars it works for me. If were I have my COM where its at on a short wheel base car I wouldn't be able to control it with any amount of steer.

The shorter the wheelbase the more agresive you can get with the COM. Because a shorter wheelbase will put more weight on the DFW than a long wheelbase for the same COM. 5" is a good starting point.

 

[Guest]

I have to agree with Quicktime on this one. The longer the wheelbase the more aggressive I can be on the com with my cars.

???? That doesn't work for me. The longer the WB the more aggressive I've been able to get with the COM. The longer the WB the more stable the car can be with less steer. On My Unlimited and Eliminator cars my WB's are long, in fact all of my cars are much longer WB than the standard. Yes even more than the 5inches most like. For the way I set up and build my cars it works for me. If were I have my COM where its at on a short wheel base car I wouldn't be able to control it with any amount of steer.

The shorter the wheelbase the more agresive you can get with the COM. Because a shorter wheelbase will put more weight on the DFW than a long wheelbase for the same COM. 5" is a good starting point.

I have to agree as well with QT and Renegade............longer is better! Not too sure if that holds true on wide wheel cars, but on the razor wheeled cars I think it does! /images/boards/smilies/wink.gif

 

[OPARENNEN]

Quicktime is absolutely correct. Also in respect to wheel base, the longer the wheelbase, the shorter the veer. The shorter the wheelbase the longer the steer. While building and testing our new Street Rod class (which has a much shorter wheel base), I started testing the veer at 10 inches, then 12, then 14. Each time the time decreased. My testing board is only 24 inches wide, and the cars are over two inches wide. I finally set the 2 cars completely to the right, and set the steer completely to the left. Achieved the best time. So I took one car and still increased the veer even more, and again the time was better. I will see how they do in Feb, but I believe one of them may break 3.0 With all of this said, I should add that I stacked the weight as far to the rear as pollible, all behind the rear axle. I think this may also have affected the amount of veer required, but I am not sure.

???? That doesn't work for me. The longer the WB the more aggressive I've been able to get with the COM. The longer the WB the more stable the car can be with less steer. On My Unlimited and Eliminator cars my WB's are long, in fact all of my cars are much longer WB than the standard. Yes even more than the 5inches most like. For the way I set up and build my cars it works for me. If were I have my COM where its at on a short wheel base car I wouldn't be able to control it with any amount of steer.

The shorter the wheelbase the more agresive you can get with the COM. Because a shorter wheelbase will put more weight on the DFW than a long wheelbase for the same COM. 5" is a good starting point.

 

[quadad]

Opa, you have coined a new term "VEER" !!! Unless you were talking football, and we were not catching it.

More seriously, I would like to add a couple of other points to this conversation.

- You can go up to 5 3/4" wheelbase (fully extended wheelbase) on adult league cars if that suits your building style and not be worried about it because league tracks slow the cars down before they hit something (i.e. don't have to protect the front wheels like on a typical Scout race track). My razor wheel cars are typically this WB.
- There are inherent advantages to short and extended wheelbase cars on different parts of the track (e.g. standard wheelbase cars can be faster through the transition, extended wheelbase cars with lower COM give you more energy to start with).
- While we all have favorites, there is no magic wheelbase for any class, any can be made very fast. A number of racers here are extremely competitive with 5" WB cars (I am NOT one of them) which is close to being 'in the middle'.
- "W"'s equation above and the suggestion to build a sample is a good starting point when planning a new setup. Remember though that the more aggressive COM you are planning for means you have to more aggressively pack the weight into the back packet and this can be a challenge.
- At the end of the day its all about how everything works together, the WB, the horizontal and vertical COM, your drift, and ALWAYS, the quality of your alignment and your parts and their prep.
- Key is building and testing, preferably on a similar-to track. That is where you will really understand how the elements all work best together.

 

[OPARENNEN]

Veer, Steer, Drift = all the same to me. i.e. Movement to the NDW side. For those who didn't understand some of my posts, that is what I mean. And when I quckly enter a response, who knows what I might say.
Advantages of Age. Just try to interpret.

 

[OPARENNEN]

One point on wheel base - as the front axle placement moves backwards, that pushes the overall weight backwards. Personally, I have tried 4.BSA, 5.0 and 5.5 == After all my testing, I prefer 5.0

 

[quadad]

Opa, it's no fun if I can't give you a hard time !!

I don't agree on your last point though. If the rears are at the same location (e.g. 5/8" from the back), the car with the lowest COM has the most potential energy. At that point, the location of the front wheels doesn't matter.

 

[OPARENNEN]

Opa, it's no fun if I can't give you a hard time !!

I don't agree on your last point though. If the rears are at the same location (e.g. 5/8" from the back), the car with the lowest COM has the most potential energy. At that point, the location of the front wheels doesn't matter.

You may be right, I just seem to always get the best results with 5, at least on SS and Unlim. On SS I have tried 5.5 and my own tests keep taking me back to 5. On Unlim, in last race, identically preped wheels turned in very close times, one with 5 the other with 5.5. The 5 turned my fastest time, but the 5.5 turned the best overall average. So ?????

Don't know about SP or Elim, none of my cars ever do well in that class.

 

[W racing]

Moving the DFW back (and the raised wheel if it is present.) changes the COM of the car if you calculate COM as the balance point of the car in front of the rear axles.

For my COM calculations I disgard the weight of any wheels that are touching the ground. As they are supporting the car. I only count the weight of the raised wheel.

 

[JCovert]

Thanks for the feedback. I was a little surprised by the "just make a decision and learn from it" approach. Ultimately the location of the DFW will have a very measurable effect given the weight bearing down on it. I think the less weight on it, the less "veer" I can achieve. The more weight bearing down on it the more veer I can achieve. The weight bearing down on the wheel is a result of the center of mass and distance away from that mass I choose to place the wheel. Is this along the correct lines?

 

[W racing]

The weight on the front wheel is a factor of the chosen WB and the COM. With COM being measured from the rear axle. It is easy enough to add two sets of holes for the front axle and go between them. It is somewhat more difficult to change the COM of the weight.

For a first car the fully extended wheelbase is likely the best approach. Assuming you are league racing. Scout races you need to back off the front wheels by a 1/4" to prevent damage from the stop section.

I always look at the winner circle. The top three cars will show if they extended their wheelbase or not.

That being said anyone able to finish in the top three might be able to get away with something a less experince builder could not. Or they might win despite a poor design choice as they are just that good.

One car actually placed all of its added weight above the axle line and won lots of races that way. I chalked that one up to the builder being good.

So the work is to figure out what the top builders are doing and then decide if you want to follow them or not. Would their choice work for you...

 

[JCovert]

Thanks for the info W, noticed your Com vs. DFW weight post as well, very helpful.