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Discussion Starter · #1 ·
it has been commonly said that a wheel with a smaller diameter holds an advantage over a wheel with a larger diameter. It is said that the larger wheel has a larger overall rotational mass since the mass of the wheel is further out. Sure that is true....But your forgetting one very important factor! The TIRE.

In this comparison I used a 14.5lb 16" ROTA Grind vs a 15.5lb 19" Centerline RPM

225/50/16 vs 215/35/19....side by side these two tires have an equal outer diameter. However their weight is significantly different. The 16" tire adds a noticeably more weight vs the 19" tire. Hence making the 'lighter' 16" wheel HEAVIER than the 19" wheel.

I feel that the added weight of the larger tire outweighs the benefit of the smaller diameter rim size and its lighter weight.

I tested my observations @ cougarfest on the drag strip.

16" tire = kumho V700 @25psi
19" tire = BF goodrich KDW @27.5psi

Observations.

16" tires had superior traction. However netted me a best of 14.8 @ 92.2 mph (only twice) 2.23 60ft
19" tires had less traction. however allowed for higher rpm launch. netting me a best of 14.7 @ 92.5mph (3-4 times) 2.23 60ft

16" tires where much less consistent than the 19" tires. So I will leave the ETs out of the following results and concentrate solely on Trap Speed, which would most directly indicate hp vs weight. In my test. The weight of the tire/rim assembly would directly affect end avg trap speed.

16" wheel/tire netted an avg of 90.7 trap speed.
19" wheel/tire netted an avg of 92.1 trap speed.


I thought i would share my observations. Please feel free to add your input.
 

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I ran my car at the track 3 times at Fest.. each with my heavy 19 inch rims which weigh in at a hefty 55lbs a corner mounted and I ran all 3 runs at consistantly the same speed/time and whatnot - I found it odd, but perhaps it just confirms your therory? I have KDW GForce tires too.. I figured I'd have some fluctuation on my runs but all 3 were exactly duplicates of the first run with only my reaction times getting better because I was finally figuring out the tree.
 

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Discussion Starter · #3 ·
your runs being consistent is exactly what should have happened. Especially considering you have an ATX. Unfortunately rim weight has nothing to do with the consistency of your runs. Had you changed to my 19s for example (a good 20lbs Lighter per wheel) I am sure your times would have improved significantly
 

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There is also the option of reducing the profile of the 16" tire, giving you a smaller diameter which would effectively make you final drive ratio higher.
 

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Or you could also check on different tires and weights. I was seriously suprised when GMK had me pick up the two wheels, side by side. The 16"s were VERY heavy, as compared to the 19"s. I'm glad that the track proved the theory we put together that night. :thumbsup:

Now, I have tire weights of every tire we sell (because of shipping calculations) -- so I guess its time I start searching thru the DB to find the lightest 19/18/17 tires... ;) I have a new selling point...

E1
 

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Discussion Starter · #7 ·
Yes E1. Please find out that for me. That would rock.

Also see if you can find the weights of the 2 tires I listed also.


Sonza, if you lowered the tire profile on the 16" wheel that would give you in essance shorter gearing no? Which I understand is fantastic for autox, but in the drag you would have to shift more times. (any benefit?)

I have noticed that alot of the SCCA race cars & Japanese race cars have been using 18" or even 19" wheels with a 'low' profile tires.
 

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Originally posted by: GrandMasterKhan
your runs being consistent is exactly what should have happened. Especially considering you have an ATX. Unfortunately rim weight has nothing to do with the consistency of your runs. Had you changed to my 19s for example (a good 20lbs Lighter per wheel) I am sure your times would have improved significantly
next year ;)
 
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