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Originally Posted by guitarterry
This question is kind of for metrompg but would like anybodys input. Has anybody checked out the difference in fuel economy in say the 12, 13 and 14, maybe even bigger ties all at the SAME RPM, for example, 12 inch tire at 3000 rpm and 55 mph versus 14 in tire at 3000 rpm and 55 mph, especially since the 12 inch should be alot lighter and narrower, even less sidewall to flex. ( assuming we arnt going into expensive low profiles.)
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The 12 inch would have the most sidewall if your keeping tires of the same diameter for each rim size. The weight of the rim depends largely on the material and style. If the engine is going the same rpm with all of them then there should be a very small difference between their efficiencies. The biggest reason to change tires to a taller size is the gearing change it provides. The reason for skinnier tires is to reduce frontal area.
If your not changing the tires to reduce frontal area or improve gearing, then there is no point in the change except for looks, which obviously dont help with FE.
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I think this is very informational. I drive a metro cause i put alot of over the road miles on my car. so the RRC figures according to yourself dont affect me as much. I have yet to have one person come up with a reason the 12's wouldnt be the best. This could be a good opportunity. it cost 1k to make one gear cause of r&d. what if somebody made 100 top gears. instead of using a tranny with a bad first gear to get a good top gear, drop in a new top gear and get the best of all worlds.
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People have given reasons for the 12s not being the best, you just choose not to listen. The biggest reasons are availability since virtually no vehicles run them anymore and lack of choices when you do find them. No demand means no products.
Same reason no one is going to R&D and mass produce a new top gear for the metro. Its not worth the investment if its going to take the rest of your life to sell the 100 gears you had made. You could probly get a 1 off made, but like others have said, thats not cheap.
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wow so u know the 14 inch out performs the 13 or 12. even if the engine effiencies are taken OUT of the equation thru gearing. (please, why are u going on a gearing tangent, the idea is the engine will be turning the same.) I thought u just said that aero was more important than LRR at speeds over 20 mph. Plus as right of right now i dont know the LRR of the 12 or 13.
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Ok, in case you havent realized it yet, tires ARE gears. If you change the tires you change the gears, get it? If the engine is turning the same speed, the only changes will be marginally better for a skinnier tire (like the 145/82/12) or a LRR tire, like the bridgestone mentioned above. I would venture to guess that the wider 14" tire would perform almost identical to the skinnier 12 inch tire, since it makes up for its RR with less frontal area and vice versa for the 14.