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So I'm facing a few problems with choosing new tires. Of course I'm not overly concerned about what tire I go with, but more or less the size and the proper gearing that best suits my driving.

Here's what I'm facing...

Going with the 315/70R17 compared to 35x12.5R17.. will there be any noticeable differences between the two tire sizes with regards to power loss or gas mileage? 35x12.5R17's are a bit larger in diameter, and have almost an inch on the 315/70R17's in terms of width but with the difference between the two, should lean more towards one or the other? I know the greater the surface area the better the off road traction, but for on road driving would the increased surface area worsen my gas mileage with the wider tires?


Also another question, the two tires I'm leaning towards (Trail Grapplers, and General Red Letters if it matters) are both VERY heavy tires. I guess these heavier tires suck the power away. With the heavier tires would I benefit going from 4.11's to 4.56's? I'm going to be wheeling a decent amount, but with going off to college I'll also be doing a TON of driving, so I'm wondering if the 4.56's would be a bad choice.

What I'm trying to do is be able to retain the most power possible, while getting the best gas mileage possible and still having a very capable offroad tire. I'm well aware that you give and you take but I'd like to find a fine median that I would hopefully benefit from the most with the setup I'll be running.

And yes, I do realize I'm just crazy and over thinking things but that's never been a bad thing (at least not yet anyways) :D
 

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I know the greater the surface area the better the off road traction, but for on road driving would the increased surface area worsen my gas mileage with the wider tires?
What brings you to that conclusion? I don't know your specific application, but that isn't necessarily a fact in all situations, or even most situations.

It's a fairly common "assumption" by most 4x4 drivers that wider is better, but personally I don't believe so. Read this article, it's a very interesting review on the subject.

http://www.expeditionswest.com/research/white_papers/tire_selection_rev1.html
 

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What brings you to that conclusion? I don't know your specific application, but that isn't necessarily a fact in all situations, or even most situations.

It's a fairly common "assumption" by most 4x4 drivers that wider is better, but personally I don't believe so. Read this article, it's a very interesting review on the subject.

http://www.expeditionswest.com/research/white_papers/tire_selection_rev1.html
That article sounds like it was written by a college student who hasn't been exposed to the real world. If he was even remotely correct in his assumptions, we'd be all riding on 5 inch wide tires...

To the OP - I can't image a BIG difference in gas mileage between the two sizes you mention. As far as gearing, do the math and see what axle ratio is going to get you as close to stock overall gearing as you can get if that's your target. For a vehicle as modified as would be necessary to run 35's, I'd imagine that running shorter gearing would be preferred (shorter than stock overall gearing) to aid in crawl ratio. Tire weight is going to affect acceleration and larger/heavier tires will reduce mileage. there is no way around this.
 

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That article sounds like it was written by a college student who hasn't been exposed to the real world.
Luckily, he posed up his bio so you could know someting about who wrote it.
http://www.expeditionswest.com/about_us/owner_profile.html

Who knows, it might be all blow, but it's more substantial than the experience you've offered up to make your case for being so superior.

This is particularly relevant to this thread, because if the OP sticks with a narrower tire, he can shed unnecessary weight, and rolling resistance, therefore saving fuel and retaining on road manners, without assuming he's sacrificing a lot of off road ability.
 

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Luckily, he posed up his bio so you could know someting about who wrote it.
http://www.expeditionswest.com/about_us/owner_profile.html

Who knows, it might be all blow, but it's more substantial than the experience you've offered up to make your case for being so superior.

This is particularly relevant to this thread, because if the OP sticks with a narrower tire, he can shed unnecessary weight, and rolling resistance, therefore saving fuel and retaining on road manners, without assuming he's sacrificing a lot of off road ability.
Did you look at the vehicles on that site? I don't see any skinny tires on any of them. Besides, we're dealing with just a couple of choices the OP asked us about. Not enough difference to nit pick about width, weight, etc.

And, that article has the caveat of not including deep sand or mud. I don't know how many people drive on gravel and get stuck. The article also dismisses the fact that tire width may mean the difference between the tire spinning in the air and being wide enough to grab something.
 

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For one thing no you are not crazy or over thinking. Lots of options. Anyway, go with red letters they look more road friendly. They are both heavy tires but if you add weight along with big treads that's a lot of extra rolling resistance. Or take a hit on performance and get an AT. I know tirerack.com and discounttirezone.com list the weights.
 

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Simple physics: given a set tire pressure a wider or narrower tire does not affect the size of the contact patch with the road, only the shape of it. A wider tire has more grip left-right, a narrower tire more grip front/back.

Wider tires work better off-road as they can grip over a wider surface on uneven terrain. Wider tires work best on sports cars as they help lateral grip. A narrower tire will work best on slick surfaces where traction is limited, such as snow.

The reason that this can't be taken to extremes (as one poster suggested that we'd all be on 5 inch wide tires) is that you need enough surface and air pressure to hold up the vehicle and keep the sidewall at the right height/geometry to control the vehicle (thats another story) as well as being able to fit in a wheel well.

Larger and heavier tires take more power to turn and are harder to brake as well. They also put more stress on suspension components. Gearing can take care of the power part of the equation only in that you will turn more rpm for a given turn of the wheel, which will cost fuel but maintain the 'sense' of power/acceleration. A beefier suspension can take care of the up/down momentum of a heavier tire/wheel. Better brakes are needed to keep the braking properties close to stock. This last part is often forgotten, but probably the most important...
 

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Going with the 315/70R17 compared to 35x12.5R17.. will there be any noticeable differences between the two tire sizes with regards to power loss or gas mileage? 35x12.5R17's are a bit larger in diameter, and have almost an inch on the 315/70R17's in terms of width but with the difference between the two, should lean more towards one or the other? I know the greater the surface area the better the off road traction, but for on road driving would the increased surface area worsen my gas mileage with the wider tires?
315/70/R17 = 34.4x12.4 R17 Sidewall = 8.7 inch Radius = 17.2 inch Circumference = 108.0 inch Revs/mile 587
318/72/R17 = 35.0X12.5 R17 Sidewall = 9.0 inch Radius = 17.5 inch Circumference = 110.0 inch Revs/mile = 576

Front wheel well needs to be trimmed. I will go to 4:56's to run 35's but that's just me. And my rig is no longer a DD. I'm going with Goodyear Wrangler MT/R with Kevlar side walls.


Trail Grapplers look OK for rocks to me.
Red letters look like sand tires to me.
your rig is also not on a DD path , you may need to buy a Volkswagen Beetle to DD. your rig will no longer be a fuel efficient vehicle( if it ever was).

http://www.tacomaworld.com/forum/tirecalc.php?tires=315-70r17-318-72r17

 
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