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Old 07-21-2013, 10:30 PM   #31 (permalink)
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What I got from the conversation, was in keeping the total rotational diameter the same (or within 2%) and adding weight is not worthwhile. Keeping weight the same, and adding rotational diameter, is beneficial.

And as for regearing transmissions, it may not be as difficult as it seems, but definitely more difficult than getting a larger tire. I imagine it's difficult to reasonably change gearing for the better under most circumstances.

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Old 07-22-2013, 01:27 AM   #32 (permalink)
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If you change tire overall diameter, regardless of how, it alters things other than just gearing. Ride height and roll centre location are both altered with an alteration in tire diameter. Small changes may not be readily apparent but that doesn't mean they don't have an effect.

If you want to change the tires and wheels in order to try to reduce polar moment of inertia or overall weight fine, but it should be done while keeping the overall diameter as close to OEM as possible.
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Old 07-22-2013, 03:49 AM   #33 (permalink)
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Quote:
Originally Posted by mcrews View Post
False.
The 2/10% error in size is within the margin of error. If you have followed any of the multiple threads on taller tires, we all agree that you need to be atleast 5% increase to accurately explain the increased mpg.
I'm not talking about 0.2% but 2%. With the margin of error (the biggest being 2% larger, the smallest being 2% smaller) the real difference can be as high as 6%. How can you argue that? Calculate yourself.

In that case, the biggest tire has lower mpg so it goes in the wrong direction (due to the weight). The point was that 2% gearing change can very well change things at 0.1 mpg.

Quote:
Originally Posted by mcrews View Post
shoulda, woulda coulda......you paying the bill for new gears?????
MANY members here use taller tires to improve mpg by lowering the rpm at cruise. Please see my threads on my Infiniti Q45 245/45/18 stock to 245/50/18. Same improvement on my KIA Sportage 235/60/16 stock to 235/70/16
No passive-aggressiveness please. I was talking about how it should be ideally not what you ought to do.
Of course you can improve mpg with the tires but changing the differential ratio and keeping the same tire size will be more beneficial (no, I don't tell you to do it).
My initial question was "why tall tires" ?
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Last edited by HypermilerAX; 07-22-2013 at 03:54 AM..
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Old 07-22-2013, 08:59 AM   #34 (permalink)
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Tire diameter comments-
Tall tires can be a cheap way to re-gear however there are prices to be paid in performance due to the added weight and the added distance the weight is from the hub center. For example, on my 2002 Celica I went 10% taller in tires with brand new 205/65/16 Michelin Energy Savers AS (205/50/16 stock). This was a stopgap solution and is working for now, but if money were no option this is not the route I would have gone. This tire swap cost me -$200, aka the tires needed replaced and I would have paid $200 more for the “correct” low profile size. The performance on the car is notably slower, more so than simply the 10% gear change would have affected, but the car is still fast enough for me.

My final drive is in the transaxle requiring a compete tear down to go from a 4.53 to a 4.3X or 3.94. Thus I cannot justify changing that gear, a $500 part and probably $500+ install as I can get a completely rebuilt transmission with this gear already installed for $2000. Better to spend the extra and get a fresh gearbox along with the final drive swap.

When my current tires or transmission wear out (whichever is first), my plan is to buy smaller 15” wheels, get stock sized lrr tires, and get a rebuilt transmission with the 3.94 final drive.

Tire weight comments-
On my truck, I have both light 255/85/16 mud tires on light wheels and heavy 285/70/17 road tires on heavy wheels. Probably a 30lb per wheel difference, 20lbs in the tires and 10lbs in the wheels. Exact same 33” diameter. The truck is noticeably slower on the heavy tire heavy wheel combo, much slower than just throwing 120lbs in the back. It seems crazy but I have found so far that my light Cooper Discoverer AS knobby tires get better MPG than the heavy Michelin LTX MS2 on short trips. Note that this is on a giant truck and we are talking a huge increase in wheel and tire weight. I cannot yet comment on long trips as I try not to take my truck on long trips if the car will suffice. Best MPG mod I have found.

Last edited by aardvarcus; 07-22-2013 at 09:05 AM..
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Old 07-22-2013, 12:02 PM   #35 (permalink)
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Quote:
Originally Posted by freebeard View Post
Is the wheel centered on the hub or the lug bolts?
Thanks, freebeard, for this question. It forced me to more rigorously answer the question of center bores. And I discovered that the Miata and Prius wheels I had been listing are 54.1 center bore, while the 1992-2000 Civics were 56.1mm. If I understand correctly that means the Civic wheels can safely be installed on the Miata or Prius (which ring spacer/adapters) but the Miata and Prius wheels cannot be installed on the Civics. The Mini's are a perfect fit. And there are a slew of VW wheels with 57.1 center bores.

Sorry I was mistaken before about a couple of those wheels... perhaps goes to show you don't know what you don't know, always be skeptical, check and recheck specs.
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Old 07-22-2013, 12:24 PM   #36 (permalink)
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Right. You can use ring adapters to use a larger-bore wheel but not smaller.

Quote:
Originally Posted by California98Civic View Post
Here is my list of possible wheel swaps for 5th/6th gen Civics like ours, from my car's garage site:

Possible wheel swaps for gearing/weight advantages:
13" Civic VX 8 spoke (higher RPMs but only 9.7 lbs.)
14" Civic HX 8 spoke (approx 11 lbs)
15" Mini Cooper R81 Imola 7-hole (12.1 lbs)
15" Mini Cooper R86 star-spoke (15 lbs)
15" Mini Cooper R96 7-spoke (13.8 lbs)
15" Enkei Classic J-speed (14.1 lbs)
15" Acura Integra GSR (94-95, 16lbs)
Other size specs: Offset 35-45; bolt patter 4X100; lug size 12mmX1.5; hub center bore 56.1mm.
Popular wheels for the Fit, that would mostly work for you as well. Note that my minimum diameter is now 15" instead of your 13/14.
Enkei RP-F1 (15" = 9.5 lb) $225 @ tirerack
Kosei K4R (15" = 10.7 lb) $144 @ tirerack
Konig Helium (15" = 11.2 lb) $89 @ discount tire, $88 @ good-win-racing.com (source for weight)

Helium is where I'd go today, and I'm sorely tempted. My stock 16" rims are a decent 17 lb, but this would be a big reduction.
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Old 07-22-2013, 02:27 PM   #37 (permalink)
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1. If you have not read the many posts on taller tires and the ABA tested results, comments about % really carry little or no factual basis. They are just your opinion.
5% is the threshold. Under that and you are at the manufacturer's margin of error. Over that and you will see gains that are verifiable.
2. No one on this forum would do what the mag did. Wrong forum. So long drawn out discussions on the numbers from the mag are pointless. Except for the EXCESSIVE weight on the 19in rims/tires. Adding weight is pointless in an mpg environment.
3. While I agree that exceeding eom specs can be unhealthy for wear and tear. (See my multiple comments on lowering kits on this forum, a 5% increase in tire diameter is NOT destructive. With 270k miles on my infiniti Q45, I can say that a taller tire was not a problem.
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Old 07-22-2013, 04:18 PM   #38 (permalink)
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54.1 => 56.1mm. That's 1mm of material on each side. Would you take it off the hub or the rim?
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Old 07-22-2013, 04:50 PM   #39 (permalink)
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I did a pretty thorough tall tire test 2 years ago with my xB. 17" wheels/tires that were 12 lbs. heavier on each corner fared worst in testing against lighter similar diameter and shorter diameter tires. The difference was 0.3-3.7 mpg with cruise control at 35 mph, 1.2-3.2 mpg with 25-40 mph P&G, and 1.5-2.4 mpg at 55 mph highway cruising.
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Old 07-22-2013, 04:55 PM   #40 (permalink)
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Quote:
Originally Posted by freebeard View Post
54.1 => 56.1mm. That's 1mm of material on each side. Would you take it off the hub or the rim?
I wouldn't put a 54.1mm center bore wheel (like the 1990-1993 Miata) onto a 56.1mm hub plate (like my Civic). Having read a bit more now, I know some of the risks and wouldn't modify either surface for fear of compromising the hub, the wheel, or ending up with dangerous vibration from a poorly balanced wheel. But I understand rings can be used to adapt, for example, a 57.1mm center bore to a 56.1mm hub plate. A one millimeter ring, and I guess its done. That seems more acceptable. Still, best is a direct OEM quality fit. Clearly.

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