Our rules allow for a 7 3/8” car. We’ve been cutting our own blocks to get the extra length over the pre-cut blocks and thereby get our weight further up the track. From reading the archives here, most choose a wheelbase between 4 1/2” and 5 1/8”, with the majority of people using a 5” wheelbase. What wheelbase would you use for this car length?
Wheelbase length
- Thread starter Peregrine Racing
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If you move your front wheels back to far the nose of the car will hit the curve on a BestTrack and probably a Freedom... I would use a 5-3/8" to 5-5/8" wheelbase which puts the back at 5/8" from the rear and the front at 1-5/8 to 1-1/8 from the front.
I am not a pro...in fact far from it, but I have read enough to know that the advice given above is sound! The longer wheelbase should help make for a very stable car. If your foundation is solid, you should be able to be aggressive on your COG (however the long WB will work against you on this).
Thanks for the responses and insight. 5k, I’ll try 5.5 for starters and go from there.
The car is cut out, weighted, and ready to drill. My understanding is for using thin wheels, you would not cant the rears at all, such as this |——| and the front dominate wheel would be slightly (1-2 1/2 degrees) canted for steering. Would you cut 1/16th off the dominate front side, 1/16ths off both sides, or no front cut? I know some of you guys no longer cut the front dominate side because of the degree of bend you use, but I don’t think that’s an option with thin wheels.
You can do any of the 3 options you listed depending on your rules and how you want the car to look on the track...
So no cutting at all will work fine as long as you make sure your rears are spaced out enough do they don't hit the center rail.... but your car will not ride with the rear wheels centered over the center rail so you might get it staged centered which may cause some added time to your runs...
Cutting only the DFW side will make your car line up with the track better and you would have less of a staging issue I mentioned above...
Cutting both the DFW and the NDFW back is probably the best method if your rules allow because you car will be staged centered and you can adjust the NDFW (or pin) for a small gap which would help if you get a wiggle.
So no cutting at all will work fine as long as you make sure your rears are spaced out enough do they don't hit the center rail.... but your car will not ride with the rear wheels centered over the center rail so you might get it staged centered which may cause some added time to your runs...
Cutting only the DFW side will make your car line up with the track better and you would have less of a staging issue I mentioned above...
Cutting both the DFW and the NDFW back is probably the best method if your rules allow because you car will be staged centered and you can adjust the NDFW (or pin) for a small gap which would help if you get a wiggle.
Hey, joining in on the axle conversation, what's is the downside of increasing the axle length from front to back to 5 3/4 with the rear wheels at the 5/8 mark from the rear?
Before I get to the update, a word about last years car. We built a beam style car, axle holes drilled with a drill press, 3 wheel rail rider with bent axles all around. Wheels 5/8” from the back and only back 1/4” in front to keep from jarring during stops. 6 cubes behind and I believe 16 in front=roughly .75 COM. Steer was around 2” in 4 feet.
In keeping with the suggestions, I made 5.5”, 5.25”, and 5” wheelbase bodies. The longer two made it to testing tonight. The 5.25” car crashed before I got the rust out (my fault) but the 5.5” made it through. It was around 11 grams, was a bit more stable, same weights behind but 1 cube off the ND side with 2grams of puddy added to the D side. Drilled wheels flat with the SBP and used one bent axle on the DFW. I don’t have three scales but the weighting you see in the third picture was roughly .5 COM. It needed around 8-10” to tame it, but ran pretty straight on the 30’ wood track-no major wiggles. Ran it against last years car and the best it did was maybe 1-2” ahead and lost at least one run. Any progress is good, but we need a car length to be competitive at the next level. Was hoping the ladder, jig and aggressive weighting would pull out the miracle-it’s a lot to ask on a short track. I’m going to build as many as I can with the time I have to see what wheelbase seems to work best and plan to try at least one car on the 3 degree setting just to see how it plays out.
With BSA wheels, part of the benefit of the cant is getting the wheel away from the body correct, so why would this not also benefit a thin wheel car? Would you cant or not? I found some videos of similar looking cars and wheels on YouTube racing at the east coast derby royal class about 7-8 years ago. All had long wheelbases and canted rears. Any other changes you would make with wheelbase or weights? I used the wheels of another car from last year and the same brand straight axles. I have a few different brands that are larger diameter (.093 axles fit the wheel fine) I can try out and see if I can find some speed there. Could also do some fresh wheels with the Ice system and see if that would help as well.
Two things:
1. the car "falls less" because the front wheels reach the transition sooner
2. weight placement (wheels forward means less weight on the FDW and a forward COG)
NOTE: if the front wheels are too far rearward, the car becomes unstable.
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Well, our efforts earned us a trip to the next round. Thanks again for the input so far. I’m still interested in any thoughts you may have to some of the above questions.
I’m curious if anyone has calculated the maximum rearward amount you can put the front wheels before you scrape the front bottom on the rail, coming out of the curve (on a Best Track with a flat bottom)?
I am not a pro, so take this for what it is worth.
It depends ..... There are a number of other variables that need to be considered. Where is the rear axle location? What diameter wheels are you using? What degree bend in the FDW axle? How much steer does the car have? How high were the axle holes drilled?
I do know this, that everything you change on a car has some effect someplace else on that car. We just need to figure out what combination of these variables along with our build style and skill works best for us. Easy as pie ...right?
Welcome to the addiction! 
Rubbing the track isn't going to be your issue pushing your front wheels back; stability will be. Assuming your rear axles are 5/8 from the rear of the car, even 4 3/8 is pushing it.
So 1-5/8 to 1-1/8 inches from the front is the safe range. Optimal peak in that range varies on many factors, but you are trying to balance stability with maximizing the “falling” energy?
Yes ....no ...maybe. I am not trying to be difficult, rather just trying to explain. Yes, ideally the maximum potential energy (falling distance) with stability would generate the best times. However, to generate that stability may require additional steer. This additional steering input then may generate enough added friction that the net result is a slower car.
Clear as mud? The trick is finding the right balance.
Remember, I am not a pro ...but I have stayed at a Holiday Inn Express in the last six months.
LOLYes ....no ...maybe. I am not trying to be difficult, rather just trying to explain. Yes, ideally the maximum potential energy (falling distance) with stability would generate the best times. However, to generate that stability may require additional steer. This additional steering input then may generate enough added friction that the net result is a slower car.
Clear as mud? The trick is finding the right balance.
Remember, I am not a pro ...but I have stayed at a Holiday Inn Express in the last six months.
I really like that answer!
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