Tire Weight or Diameter?

[Hokiefyd]

I have a vehicle that takes a P235/65R17 tire, and am looking to put new tires on it. I'm looking at the P235/65R17 and the P245/65R17 size. And I'm looking at two different tires here, one in the P235/65R17 size, but a different tire if I elect to go with the P245/65R17 size.

The P235/65R17 is 29.1" tall, has a 9.5" section width, and weighs 32 pounds.

The P245/65R17 is 29.6" tall, has a 9.6" section width, and weighs 31 pounds.

I'm not interested in the differences in the performance of the two tires for this discussion; I'm interested in which tire would be preferable in terms of load on the vehicle/suspension, etc. You typically want to minimize unsprung mass to minimize load on the suspension. And taller tires generally add load to the drivetrain. These two are not normally at odds like this; the larger tires are typically the heavier ones. But in this case, the "larger" tire is barely larger to begin with, and the weight is actually a pound less.

Which should I consider to be the most critical here: tire diameter or tire weight? I don't want the discussion to turn into a vehicle or tire brand discussion, but let's just say that this is a 4-door SUV with 4-wheel independent suspension that doesn't see severe duty, but does ocassionally go off the pavement and tow.

 

[CapriRacer]

Hokie,

Seems to me you started off with only one set of criteria - load on the suspension - and that had an obvious answer. Then followed up by saying your vehicle has some special uses, implying that there was an additional set of criteria that ought to be considered.

This leads me to think you are trying to get us to agree with your choice without giving us the benefit of all the information available on the subject.

I think I am going to refuse to give you an answer until I get the entire picture.

 

[Deltona_Dave]

The diameter is more of an issue. The taller/larger diameter of the tire, the less it rotates for a given distance. This may upset the speedometer calibration and the ABS sensors.

IMHO,
Dave

 

[eljefino]

Sounds like the smaller tire needs reinforcement to make its load range, while the larger is more "natural". I'd go with the 245.

What are you more concerned about with towing, wrecking your drivetrain or stability at speed? Do you have the tallest gearing available in your truck?

 

[Hokiefyd]

Originally Posted By: CapriRacer
Seems to me you started off with only one set of criteria - load on the suspension - and that had an obvious answer. Then followed up by saying your vehicle has some special uses, implying that there was an additional set of criteria that ought to be considered.


I was trying to say that it's a typical SUV with typical use. Mostly on-pavement travel, but ocassional gravel roads and light towing. So I was trying to say that there are no "special needs" here: it's a typical suburban SUV application.

Originally Posted By: CapriRacer
This leads me to think you are trying to get us to agree with your choice without giving us the benefit of all the information available on the subject.


No, I don't know which is the more critical factor: tire weight or tire diameter. I have not yet made a choice; I was hoping you guys could help me prioritize which is more important.

Originally Posted By: CapriRacer
I think I am going to refuse to give you an answer until I get the entire picture.


The only reason I "withheld" anything is because I know how polarizing the mention of brand names becomes on this board. I was trying to give you as much "usage" information as I could while still occluding the make/model of vehicle and make/model of tires considered. I will give you whatever information you think is helpful in answering my question.

Thanks!

 

[Hokiefyd]

Originally Posted By: eljefino
What are you more concerned about with towing, wrecking your drivetrain or stability at speed? Do you have the tallest gearing available in your truck?


Because the SUV originally came with 235/65R17s, I don't want to put too much additional strain on the system with taller tires. At the same time, I'd also prefer to keep unsprung mass to a minimum. As far as I know, there was only one set of gears available. The towing package (which this SUV does not have) comes with a few coolers, but no different drive ratio. I shouldn't have mentioned towing at all. It might tow a jet ski or U Haul trailer here and there, but it's not an everyday thing.

 

[Zaedock]

You will probably not even notice a 1 lb weight and .25" height difference.

If you're worried about load on suspension components, the tires weight would be more important than diameter.

 

[Hokiefyd]

Thinking more about it, anyone who also reads the "Vehicles" forum on here knows I've bought my parents' 2005 Acura MDX. So I'll just out with all of it.

It's a 2005 Acura MDX. OEM tire is the Michelin Cross Terrain SUV, which is highly liked by most MDX owners. My local Sam's Club stocks the Cross Terrain, but in the P245/65R17 size. This is the OEM tire for the Chev/GMC Trail/voy, and those owners also really like the Cross Terrains.

Sam's Club does not stock the Cross Terrain in the correct size, and since I prefer to buy in-stock tires at retailers, the P235/65R17 tire that Sam's DOES stock is the BFGoodrich Long Trail T/A Tour. It seems like a good tire. When I compared the two in the store (the 235/65 BFG and the 245/65 Michelin), I noted that the BFG felt heavier. So I went home and looked it up and sure enough: the BFG is a pound heavier. (It felt like more than a pound.)

So that's everything. Thank you for your replies so far, and thank you in advance for your forthcoming answers.

 

[suspiciousmind]

I'd just look at all the online reviews on the two choices and pick one from what I could gather from user input of their actual experiences. When I buy a set of tires, I usually do a month's worth of research beforehand....I'm always happy with my choices so far.

 

[ARCOgraphite]

You'll notice the taller tire but not the unsprung mass in a mid-large suv. There are so many variables on a different tire selection that the issues you are concerened about would get swamped by tire design differences - but not the the larger diameter(circumference). DO you feel the gearing is currently short and would benefit by a taller gear? I easily notice tire dia changes on my Yaris and my old, very cammy, Suzuki Aerio - both MT. The aerio would be "dead" with 55 series but absoultely came alive with non-stock 45 series on the front. Now, on a V6 or larger SUV which tend to be geared too short (in the asian models at least) I think you would benefit by the slightly larger dia. tire. Forget about unsprung mass - and concentrate more about finding the sweet spot for tire pressure.

 

[440Magnum]

Originally Posted By: Hokiefyd
Thinking more about it, anyone who also reads the "Vehicles" forum on here knows I've bought my parents' 2005 Acura MDX. So I'll just out with all of it.

It's a 2005 Acura MDX. OEM tire is the Michelin Cross Terrain SUV, which is highly liked by most MDX owners. My local Sam's Club stocks the Cross Terrain, but in the P245/65R17 size. This is the OEM tire for the Chev/GMC Trail/voy, and those owners also really like the Cross Terrains.

Sam's Club does not stock the Cross Terrain in the correct size, and since I prefer to buy in-stock tires at retailers, the P235/65R17 tire that Sam's DOES stock is the BFGoodrich Long Trail T/A Tour. It seems like a good tire. When I compared the two in the store (the 235/65 BFG and the 245/65 Michelin), I noted that the BFG felt heavier. So I went home and looked it up and sure enough: the BFG is a pound heavier. (It felt like more than a pound.)

So that's everything. Thank you for your replies so far, and thank you in advance for your forthcoming answers.



There's not enough physical difference (weight and diameter) between those two tires to matter one whit. One pound is probably maybe 2% or less of the total weight of the tire mounted on a wheel, so it will just never matter in practical terms. The diameter, IMO, will have more effect in skewing your speedometer and effectively lowering the final drive ratio a bit- but again its not going to be a big effect at all.

I would also add that they're both SUPERB tires. I absolutely love the Long Trail T/A Tours that are on my daughter's 99 Cherokee, and will be putting them on my 01 when the (hard as rock, and about as grippy as rock in the rain) Uniroyal Laredos are worn out. I love the way the Laredos work in the dry, but they give up far too much in the wet.

And just remember- when you read reviews of the Long Trail T/A tour, remember that there was a previous BFG tire called the "Radial Long Trail T/A" that was an OEM tire that they sold in other sizes for aftermarket use and was very, very mediocre. The "Long Trail T/A Tour" is a completely different animal and is far better.

 

[Hokiefyd]

Originally Posted By: ARCOgraphite
Forget about unsprung mass - and concentrate more about finding the sweet spot for tire pressure.


I'm starting to feel that way. In addition, I checked and the OEM Cross Terrain size is only 28.9" tall, so the P245/65R17 version of that tire actually represents a 0.7" change in tire diameter, compared with the OEM tire anyway.

 

[d00df00d]

I agree with the others who posted that the diameter should be more of a concern than the unsprung/rotating mass. The fact that your vehicle is a "typical SUV" (i.e. a big lumbering thing

) means that one pound per corner shouldn't make much of a difference; however, the fact that it's a 2005 Acura means that a difference in overall diameter could significantly affect the ABS and stability control systems.

IMO: get the right size, load rating, and speed rating first, and then worry about mass.

 

[RiverWolf]

+whatever on the diameter.

The Honda/Acura AWD system uses difference in rotation speeds to activate the rear axle. Not a problem with 4 new tires, but what about your spare? If it's full size you need to replace it as well. If it's a space saver, you'll want to pick a tire that most closely matches the OEM tire; I think I remember the tolerance being .25". The Honda/Acura AWD system is not built for the continuous duty that would be caused by running the spare with off sized tires.

I have to ask. Why the objection to ordering a tire that's not in stock? Never heard that one before.

-Brent

 

[Hokiefyd]

Originally Posted By: RiverWolf
I have to ask. Why the objection to ordering a tire that's not in stock? Never heard that one before.


I've had a situation before when I needed a replacement tire due to a road hazard. In this case, I bought the tire at Sears, and Sears normally stocked that tire. So I was able to have the vehicle fixed immediately. With a special order tire, the vehicle might be down for 3-5 days. With it being our main family vehicle, I want to minimize any interuption if a problem does arise.

 

[440Magnum]

Originally Posted By: Hokiefyd
Originally Posted By: RiverWolf
I have to ask. Why the objection to ordering a tire that's not in stock? Never heard that one before.


I've had a situation before when I needed a replacement tire due to a road hazard. In this case, I bought the tire at Sears, and Sears normally stocked that tire. So I was able to have the vehicle fixed immediately. With a special order tire, the vehicle might be down for 3-5 days. With it being our main family vehicle, I want to minimize any interuption if a problem does arise.


I think the same way you do about that... but to play devil's advocate: there's no guarantee that they'll have that tire in routine stock 6 months from now anyway. Granted, if they stock it now its more LIKELY they'll keep it stocked, but you never know.

 

[bepperb]

I did notice my sisters "nice" Acura has a donut, my "base" 4cyl Highlander has a full size spare.

Watch out on reviews of the long trail tour. They really have only been around for about 3~4 years tops, but plenty of people give mistaken reviews of other tires from longer than that ago.

I think you'd be happy either way on the Mich vs BFG. For me, it'd come down to price which in my size is about a 60 dollar a tire difference.

 

[Hokiefyd]

This thread has turned into commenting on the tire choices and vehicles, which is fine (but what I wanted to avoid in the beginning). I do see a clear trend from the responses: the size here is more important than the weight.

The Michelin Cross Terrain SUV is an obscenely expensive tire. About $190 each from Sam's Club in this size. The BFGoodrich Long Trail T/A Tour is about $145. Michelin does have a $70 instant savings going on now through Christmas, so that brings the price down to $173 each, or about $30 more expensive than the BFGs.

I have noticed that a good many reviews of the Long Trail T/A Tour are mostly likely really reviews of the older Radial Long Trail T/A. And interestingly, the performance of the Cross Terrain SUV tires seems to vary wildly with the size, because it's almost strictly an OEM tire, so the performance characteristics among the various sizes seem to differ as much as they would if they were different tire models all together. Indeed, the tread pattern of the Cross Terrain SUV tire in the two sizes I'm considering is quite a bit different; you'd think they were different tire models.

In the P235/65R17 size, the Cross Terrain SUV is OEM on the Acura MDX, and no other vehicle (that I know of). In the P245/65R17 size, it's OEM on the Chev/GMC Trail/voy SUVs. MDX and Trailvoy owners both pretty universally praise the Cross Terrain. My parents really liked the OEM set that came on the MDX, and wish they'd put them on when they replaced the tires a year or two ago. But many MDX owners report getting 70, 80, even 100 thousand miles out of a set, and most report decent all season traction as well. Being an OEM tire, I'm sure that fuel economy will also be at least as good as the BFGoodrich, and at $35/tire, the difference in fuel economy might be enough to pay for itself over the LONG life of the tires. Even if it doesn't, it looks like the more favorable ride of the Michelins will suit our needs best.

 

[Hokiefyd]

Another reason I like to buy in-stock tires is because I can look at the DOT code when I buy them, to ensure a recent tire. That's harder to do with warehouse-supplied tires.

I don't know, I think I'm favoring the BFG Long Trail T/A Tour at this point. Sam's stocks 'em, will probably continue to stock 'em, and looks to be every bit as good of a tire compared with the Michelin CT SUV. I had read a ton of good reviews on the Michelins, but I'm finding more that report winter performance declining after the 1st or 2nd season. The BFGs might be more consistent in that regard.

Decisions, decisions.

 

[meep]

we have an 02 mdx. that off-the-line throttle snap is touchy. I'm actually considering 245/65-17 at next change. Having done this with a p-finder that was one size too small, there is a small difference in feel. I think it will be an improvement.

The mdx is a gas pig, and it has short gearing. a slightly increased dia, while the trip computer will show a slight drop in mpg, will actually yield a slight increase in real world mpg, I suspect.

IF you actually use the 4-lock, beware... it is only rated to 155 ft/lbs per rear wheel, 310ft/lbs total. It's not a real lockup, and can slip. so if you use the 4-lock on a boat ramp and experience front wheel slip, I would add this--- a larger dia tire will *slightly* lessen the power that the rear can put to the ground by a few percent.

M