opinions on fenders good or bad

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ohiofitter
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opinions on fenders good or bad

Post by ohiofitter » Tue Mar 04, 2014 11:17 am

Now i understand your not going to add a extra second to your time by adding fenders, But I'm seeing a lot of online video's of car with a Half fenders. the ones that are wedge shape and put just in front part of the wheels (front and Back). Now I've read the phyicis on fenders but I'm no engeneier so all the data i don't understand all of it. I'm just wandering other than for looks do they honestly help or not. Just looking for opinions :wall:


Plus full body fenders helpfull or not

plus fender skirts ( assumeing you can get the wheel to not rub on them)



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Re: opinions on fenders good or bad

Post by resullivan » Tue Mar 04, 2014 12:55 pm

Let me start by saying that it is highly probable that you do not need fenders to win a scout race. Also, there is a decent chance that, at least at first, you are going to do the fenders wrong and slow your car down. All that being said, just about every "pro" uses them. We are talking about adults that are fighting for thousandths. They have their own test tracks and timers, and buld, run, and test many many cars. This is why I am trying fenders.



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Re: opinions on fenders good or bad

Post by ohiofitter » Tue Mar 04, 2014 1:12 pm

That's what I was thinking re, I don't have a test track just a tuning board. So in a adult league it might be beneficial to have fenders. But know would full body or the half fenders be better. Or again having a test track be the way to answer that.



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Re: opinions on fenders good or bad

Post by resullivan » Tue Mar 04, 2014 1:15 pm

It seems that the smaller the fenders the better. This isn't based on experience, but what I have found on the internet. You just need to be very careful that the fenders do not touch the guide rail.



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Re: opinions on fenders good or bad

Post by FatSebastian » Tue Mar 04, 2014 2:48 pm

ohiofitter wrote:Just looking for opinions
Have you seen this topic yet?



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Re: opinions on fenders good or bad

Post by Speedster » Tue Mar 04, 2014 6:32 pm

ohiofitter, you've been around for a long time. I suspect you win with or without fenders. If they are legal for your races put fenders on. They look COOL !!!



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Re: opinions on fenders good or bad

Post by ohiofitter » Tue Mar 04, 2014 11:20 pm

Thanks for the boost of confidant speedster. And yes we have had a lot of success but I don't think I know it all and I'm in the process of building a car. And its going to have full body fenders and skirts all the way around. I'm sure it's not going to be the fastest car we ever built, but I believe it will be a best in show car



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Re: opinions on fenders good or bad

Post by Noskills » Tue Mar 04, 2014 11:25 pm

I described the issue with fender with my kids and neither wanted the risk. My scout car had fenders and both my kids beat me. I still believe in using them but they are some learning still. My mid-America car will have small fenders.
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Re: opinions on fenders good or bad

Post by MaxV » Wed Mar 05, 2014 9:24 am

Here is the results of an experiment I did showing that there is a very small benefit to fenders:
http://www.maximum-velocity.com/nl/pine ... tm#feature



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Re: opinions on fenders good or bad

Post by LightninBoy » Wed Mar 05, 2014 6:30 pm

So far I've done a lot of research on fenders but only built two cars with fenders. The first car is the fastest I've ever built. The second - well we'll see in a couple weeks. So given that context, here are my opinions on fenders ...

1. Fenders done right help.
2. Doing them right for maximum benefit is an absolute pain in the [censored]. And its not just shaping the fenders - they complicate many aspects of the build and exposes a bunch of fragile parts that a cubby could easily break during the build process. For this reason, we did not put fenders on my clan's cub scout cars even though I'm convinced they help. (The cars I built with fenders are league cars).



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Re: opinions on fenders good or bad

Post by FatSebastian » Wed Mar 05, 2014 8:12 pm

MaxV wrote:Here is the results of an experiment I did showing that there is a very small benefit to fenders:
I really enjoy this kind of testing - very interesting. :thumbup:

Speed is particularly sensitive the CoM placement. How much, and in what direction, did the CoM change when exchanging ballast for fenders? This would be measured most sensitively by the measured weight under the front and rear wheels for each operating configuration.

A small observational sample size, where outliers have been trimmed, is not technically random and the sample standard deviation will tend to underestimate the true uncertainty. Also, the test statistic is the differences in the averages of two populations, which may not be statistically independent. All this means that the observed 0.005 difference might not be a statistically significant difference. (Might you post the raw data, including outliers, for analysis? :mrgreen: )



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Re: opinions on fenders good or bad

Post by MOFAST » Thu Mar 06, 2014 3:15 am

My first car with fenders I did not take away material from the bottom inside area, the car was one of the worst I ever built. It looked great, but was slow.

Since learning to do fenders correctly, our times have improved a bit. It just depends how competitive your racing is. We have a couple of very good builders in our pack, we were the only ones that used fenders, both my boys won by small margins. The fenders helped make that difference.

I think it is better to error on your fenders being too small than too big for sure.



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Re: opinions on fenders good or bad

Post by ODDRacing » Wed Mar 26, 2014 4:32 am

So basically to answer the initial question, yes fenders do make you faster. Not full fenders btw. There's been different tests done and you'll see different times, mostly in the 0.00X which doesn't seem like much. It depends on if you're racing in the NPWDRL, which you win and lose by 0.000X or if you're just looking for your local pack which could be won by 0.0X. Either way, if you want a faster car, build fenders.



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Re: opinions on fenders good or bad

Post by quadad » Wed May 07, 2014 11:28 am

I helped a young Scout speed up his car before his District race recently. We made very small fenders out of balsa, glued the back of aluminum weight pocket tape to them (so they could be easily removed) and tested a graphite car with them first only on the rears and then on all four wheels.

It was pretty obvious that the car was faster. The timer said .01 faster when all four were on, but I would attribute some (guessing up to half) of that to other break-in benefits. I think it is a LOT tougher doing comparisons on graphite lubed cars. With an oil lubed car, you could run a few dozen heats and put the fenders on/off repeatedly and not have to worry near as much about what is changing in your lube.

These fenders only weighed 1.2 grams total, even after sealing/painting them, so the affect on COM, etc., was not measurable. Now these weren't the first fenders I have ever worked on, so I knew about clearance near the body on the bottom, etc. They were also offset from the body and somewhat angled to match the angle (cant) of the particular wheel and not waste material.

There were more lessons learned. I wasn't confident that the taped on fenders would be able to withstand a Scout race handling, stop section, etc. So we took off the tape and glued them on. The glued on fenders had clearance issues (even with a little spacer to substitute for the tape) that the taped on ones didn't. The clearance did look a little precarious once you set the car down and there is weight on the wheels. Without a track however, we could have easily screwed the car up.

I think the long debate over the car being faster with fenders should have ended a while ago (yes, just look at the adult league cars), but I wouldn't suggest them to a novice builder without track access and time to test.



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