October 2010 Issue, MX5 Tire Test: Grassroots Motorsports forum: Grassroots Motorsports Magazine

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Sept. 14, 2010 7:14 p.m. HiTempguy HalfDork

I am really, REALLY confused about this.

I understand the idea to add lightness, but why were the LIGHTER rims tested with narrower tires? It just doesn't add up. What would have been REALLY awesome would have been having tire weights + rims weights separate, allowing us to come to our own conclusions about the weights. Instead, I'm told a 255/40R17 on a heavy rim, a 245/40R17 on a light rim (and its never mentioned why a 255 was not ran), and then the 18" rim combo (which didn't surprise me in the slightest, as weight was being moved further along the diameter of the rim). Furthermore, the slightly smaller diameter may have played a large factor depending on how your autox course was setup.

Did it just come down to time? Almighty dollar? I would have thought the penalty (weight wise) for running a 1cm wider tire would be vastly negated by how light the Kosei's are. Which leads to another question, of why weren't the Kosei's just bought in the first place? Obviously all things being equal, it would be crazy to not go for the lightest available option (given a specific price point, but Kosei's are DIRT cheap for what they are)!

I'm more curious than anything, I'm sure there is a solid reason behind it. This issue was solid, and I REALLY liked all of the articles in it
Sept. 14, 2010 7:36 p.m. triumph5 HalfDork

Gotta fill the pages between the ads, regardless of the inconsistencies in any article.
Sept. 14, 2010 8:03 p.m. M030 HalfDork

In reply to triumph5:

That's not really fair. I defy you to find another magazine that's as unbiased, or as thorough in their testing processes as GRM.
Sept. 14, 2010 8:15 p.m. HiTempguy HalfDork

M030 wrote:

In reply to triumph5:

That's not really fair. I defy you to find another magazine that's as unbiased, or as thorough in their testing processes as GRM.

I agree, I don't think it came down to that. At most, I figured they were offered the first set of rims (free is best, no?) and then figured they should test a lighter offering. I am still just curious to hear why their methodology was not as "sound" as usual.
Sept. 14, 2010 9:34 p.m. David S. Wallens Editorial Director

Because what you're watching is the development of a race car, and sometimes you do have to follow your gut. Based on some math and prior experience, we thought that the C3 wheels would be the answer--plus the price was right. (The Koseis would have cost about $500 more.) Initial testing showed that the car was faster, but wasn't perfect. So we tried some other setups--a bigger setup and a lighter one.

Are we finished testing? Nope. We're going to campaign the car in 2011 with another trip to Nationals planned. (And sorry for the short answer, but it's late and I'm tired--the Donger needs sleep.)

On a related note, we do need to redo the heavy vs. light wheel test. We did one several years ago on a Miata. Maybe the smooth site worked against us, but the data showed no real difference. We were all blown away by the results.
Sept. 14, 2010 10:07 p.m. Javelin SuperDork
Redo the lightweight wheel test but on something more powerful/heavier than a Miata, like maybe a Mustang. I think that will allow you to have actual measurable results, plus be easier to do with identical tire sizes and plus sizing wheels.

For example:
- Stock 17x7 w/ 245/45/17
- Light 17x7 w/245/45/17
- Ultra-Light 17x7 w/245/45/17
- Replica (Heavy) 17x7 w/245/45/17
Then take the "light" wheel (probably a RPF01) and do:
- Light 17x7 w/245/45/17
- Light 18x7 w/245/40/18
- Light 19x7 w/245/35/19
Doesn't have to be those sizes, but do you see what I'm saying? Exact same width and brand of tire for all wheels, do a weight test with 3-4 sets of different model wheels in the same size, and then do an identical wheel test with different rim diameters.

Although a Miata 13"/14"/15"/16"/17" would be interesting as well. I do think it's not powerful enough and handles too well to really show a measurable difference.