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Post by dave632 on Oct 4, 2016 20:38:00 GMT -7
I was wondering if anyone else has ran into this. Was working on the farm truck looking for some ET since the Rebel 57 is now consistently beating it in ET while MPH is similar. Put some new wider Super tires on it, .240 vs .200 at the same diameter, and lost some ET. Approximately .02 consistently with no loss in MPH. In full size car racing bigger tires = better ET unless the car does not have enough power to run a larger tire. I know less rotating weight helps acceleration but I am not sure that is the answer. I have improved ET with wider rear tires before. I cannot explain this???  |
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Post by SKR on Oct 5, 2016 7:52:36 GMT -7
How's your 60' time look with the smaller tires? I actually like running thinner tires on most of my cars, like you said there is less rotational mass and also less rolling resistance from less contact patch. Just my opinion but if I see no performance loss down low on the track then there is no need for a wider tire. Same MPH could be from the same diameter tire allowing the car top out too early? Interesting topic since there are many variables like durometer, trueness, balance etc... I'd be interested in hearing others thoughts on this as well.
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Post by dave632 on Oct 5, 2016 16:02:06 GMT -7
60' time improved a few thousands with the smaller tire. I can only check the trueness by eye and I can only guess about the balance. Both type tires are fairly soft but I also have no way of testing that.
When I had my Beretta we took about 20 lbs of rotating weight off the car and picked up over .1 in ET. With static weight it took about 100 lbs to make that difference.
Would like to hear others opinions on the subject.
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Post by AJR on Oct 5, 2016 18:09:09 GMT -7
I unfortunately don't have a timing system that will break down my times incrementally like that. I can only look at ET, visual, and sound. I run a narrow tire on almost all of my builds. I definitely have better ET's with a narrow tire over a wider one. I attribute that to less rotating mass as well. I normally run with plenty of down force so traction is not an issue. I have some cars of similar builds where one car likes a bigger tire than the other?? Motor characteristics....magnets....not sure why that is. I just give each one what it likes.
In response to your initial question, I think Sam nailed it. Sounds like the car is having a little bit more trouble getting the larger tire going early and topping out before the end.
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Post by dave632 on Oct 6, 2016 8:45:54 GMT -7
Looks like we agree that the difference in rotating weight is the answer. As long as there is sufficient traction.
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Post by Deleted on Oct 6, 2016 16:27:15 GMT -7
Sgrig has experimented with narrower silifoam tires on narrowed 4 gear rims and they certainly perform better than wide ones.
likewise, some guys have been using narrowed wheels with narrower (in some cases sliced) slip on solid silicone tires to great advantage.
I don't know if diameter is being considered here, but one guy had regular AFX wheels on a 4 gear that was quicker than everyone else.
it wasn't brought to my attention until after the eliminations, which the "illegal" stock 4 gear won and that had to be remedied.
diameter is another factor along with weight.
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Post by AJR on Oct 6, 2016 17:19:30 GMT -7
I was referring to tire diameter when I was talking about some cars liking a bigger tire than others. I should have been more clear. I do know that I need a better timing system to be able to put together this type of info. It is very cool to me to be able to break down a run like that.......not to mention beneficial.
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Post by dave632 on Oct 6, 2016 20:49:46 GMT -7
Diameter was the same on both tires, speed was almost identical with both tires.
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Post by AJR on Oct 7, 2016 7:45:09 GMT -7
This is a very interesting discussion. I am currently running a wider tire on my PSO car, but I am planning on changing that and possibly the diameter before the next race. When I added the braids/shunts, I had to go to a larger diameter tire just to create some space. This car actually liked a smaller dia. tire prior to that. With the addition of the braids the cars performance improved dramatically. So I am wondering if it still likes the smaller tire or not. The wider tire wasn't my intent either, it just ended up that way for the time being. Based on what we are talking about, I stand to gain some ET just by going to a narrower tire without changing dia. We have some cooler weather here this weekend....great for garage slot car testing. I will put some of these theories to the test. I have been waiting on a parts/tire order that should be here today. Wish you guys could come over  . |
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Post by dave632 on Oct 7, 2016 16:12:37 GMT -7
Yes I like theory discussions like this. Used to do it a lot with the full size cars. Seems to be that certain cars benefit from the narrow tires and others do not. Other factors seem to be involved. It would be nice to get together but the distance is large.
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