Extended wheel base vs short wheel base (rail riders)

[whodathunkit]

Are extended wheel base rail rider cars faster then the short wheel base rail rider cars?

If we look at the extended wheel base and how it helps the car track better
& how rail rideing helps the short wheel base car in the same way.

The shorter wheel base car should have longer to fall on the incline due to set back wheels.
Where the extended wheel base would not transition as well on the incline,however should track better in the flat.
Where the short wheel base car would tend to get the death rattle if the cog was pushed back to far.
So could the extended wheel base car be faster if set up to ride the rail as well.

Just some thoughts running in my head, that i'd to like hear your thoughts on as well.

Whoda.

[sporty]

Over the years, Many have come to ask this question.

I have seen people make some very fast stock wheel base cars and I have seen people make very fast extended wheel base cars.

Yes, a shorter wheel base car should be faster. But so few are good at making them be faster then a extended wheel base.


Over the years, since I have built plenty of both. But I always seemed to be able to get the extended wheel base faster. But have built a few stock wheel base cars, that ran the same speed as extended wheel base.


The great debate is, really, comes down to builder skills !


I on the other hand, thought, that since a extended wheel base car sits a little farther up the track / higher. that it gave a advantage over a stock wheel base car. It's a small amount in the rear wheels. but I felt it's enough to do well over a stock wheel base car.

But the stock wheel base does drop sooner and does better, but seems to loose some on the flat.


As for RR, I think that its easier to tune a extended wheel base car, than a stock wheel base. But those who are pretty good at tuning stock wheel base cars, are pretty darn fast ~!

Sporty

[Speedster]

I think this all has to do with COM and tracking. Both cars would have their rear wheels in the exact same place assuming a 7" overall limit. On the stock BSA car you simply cut off the extra wood in the back and move it to the front. If I may quote Doc Jobe. "No matter where the COM starts on the circular arc track, it will reach the horizontal run about the same time. This is to be expected because of the similarity of the circular arc track to the Cycloid of Constant time". If it is true a longer wheel base car will run straighter than a short wheel base car than the longer wheel base car always has the advantage in that department. If the COM is exactly the same on both perfect cars than the cars should be lined up with each other when they reach the horizontal run. The long wheelbase car might be a bit ahead because it is running more true. The long wheel base car, running straighter, would win the race. My question would be, Can you have as an aggressive COM on a short wheelbase car as you can on a long wheelbase car? If not, the short wheelbase car has no chance of winning. I'm going to guess a short wheelbase car can never win a race against a long wheelbase car, all other things being perfect. Am I close?

[FatSebastian]

I think that its easier to tune a extended wheel base car, than a stock wheel base.

I also concur with Sporty's assessment.

[Stan Pope]

This is a really interesting question since several aspects come into play.

Case 1: The stock wheelbase may be shifted in the car body so that the rear axles have the same location as on an extended wheelbase car.

The perfectly built standard wheelbase car should win over the perfectly built extended wheelbase car. The reason is that as the cars enter the curvature, the front wheels lift slightly, causing a small lift in the CM. The location of the axles and the shape of the track define the path followed by the CM.

The extended wheelbase car's front wheels lift earlier in the run than the stock wheelbase car's, meaning that the CM path of the extended wheelbase car is shallower ... less steep during the descent.

Case 2: The stock wheelbase must conform to the original block locations relative to the nose of the car.

This case requires a trade-off between steeper path from case 1 and increased slope length for the extended wheelbase car. I don't know which prevails in this case, but I suspect that the increased slope length for the CM of the extended wheelbase car is a bit superior.

In both cases, the advantage is so small that I would not trust anyone's on-track comparisons without many, many replications.

There is one more physical aspect which might tip the scale in favor of the stock wheelbase design: If DFW weight is a critical design factor (and many believe that it is), then the stock wheelbase design places the CM closer to the rear axle for a given DFW load.

[FatSebastian]

The perfectly built standard wheelbase car should win over the perfectly built extended wheelbase car. The reason is that as the cars enter the curvature, the front wheels lift slightly, causing a small lift in the CM. [...] In both cases, the advantage is so small...

Instead of numerous trials, could the magnitude of this effect be mathematically quantified? As you imply, I might have expected it to be close to negligible.

[Stan Pope]

The perfectly built standard wheelbase car should win over the perfectly built extended wheelbase car. The reason is that as the cars enter the curvature, the front wheels lift slightly, causing a small lift in the CM. [...] In both cases, the advantage is so small...

Instead of numerous runs, could the magnitude of this effect be mathematically quantified? As you imply, I might have expected it to be close to negligible.

Depending on their attention to detail, one of the available sims might be able to quantify the effects. The sims I know of include Jobe's and Lastufka's. I don't know for sure if either includes the parameters under discussion.

[whodathunkit]

Thanks for your thoughts guys.

This is a really interesting question since several aspects come into play.

Stan, I thought so myself but just had to ask the guestion.

[Speedster]

Question Gentlemen. When allowed, why do I see so many extended wheelbase cars?

[sporty]

Question Gentlemen. When allowed, why do I see so many extended wheelbase cars?

Because, It's the prefered way to go fast.

Easier to tune. More weight placement options.

Sporty

[Speedster]

More weight placement options. Sporty, that sentence has me asking the question again. Can you weight a long wheel base car and not be able to weight a standard wheel base car the same way? If this is true, and I suspect it is, a standard wheel base car is at a disadvantage from the start. You have weighted one of your cars with a 3/8" CM. Is it possible for a standard wheel base car to run with this set up or would it be far to unstable?

[sporty]

I have ran a standard wheel base car with a 3/8th weight balance point, and it was not easy, much tuning,. tricky but can be done, but found that the car ran slower, with that balance point. 4/8th and 5/8ths worked better for me for a stock wheel base.

Sporty

[Stan Pope]

I have ran a standard wheel base car with a 3/8th weight balance point, and it was not easy, much tuning,. tricky but can be done, but found that the car ran slower, with that balance point. 4/8th and 5/8ths worked better for me for a stock wheel base.

Sporty

This is interesting! Shortening the wheelbase while holding the rear axle to CM distance constant adds weight to the DFW which should make the car more stable and allow the car to hold the rail with less toe-in. Then moving the CM further from the rear axle adds even more weight to the DFW allowing even less toe-in.

Understanding your results is gonna take some serious study!

How rough was the track and rail on which you accomplished the comparison?

[sporty]

It's hard for me to recall, since its been almost 2 years ago, since I was building stock wheel base cars in the adult racing world.

But as I said, the best performing stock wheel base cars, were at 4/8th or 5/8th. less than that and I had tuning issues.


Sporty

[Noskills]

I just built an extended front end car with the standard wheel base with a 7/8th in COM. My daughter's car this year will be very similar (same COM, wheels, axels and prep) but with an extended wheelbase. I will let you know who wins in the open race. I kind of hope its her as my wife will give me a hard time for beating my daughter!
Noskills