Tire size VS Spare Tire VS AWD madness... [Archive] - Honda Element Owners Club Forum

: Tire size VS Spare Tire VS AWD madness...


ndp
02-24-2004, 08:01 PM
Well, having cruised the archives for a week I feel the need to open yet another discussion on tires.

I want to upgrade the tires on my E. The stock ones bite: They are noisy and have lousy traction. I have been looking at a number of options but I keep getting hung up on the size. There are, as many of you are painfully aware, very few tire options in the stock size. However, changing tire sizes presents a problem with changing tire diameter. Once you depart from the stock tire size itís virtually impossible to get the exact same diameter.

With the AWD system in the E the dealer (and Honda customer support) made it clear that all four tires be the exact same size and have identical tread patterns. No problem. But, then there is the spare. The spare isnít even the same size as the stock tires.

Consider:

The stock tires are 215/70R16 which, in theory, are 27.85 inches in diameter and turn 724 revolutions per mile.

The spare tire is a 145/90R16 which, in theory, is 26.28 inches in diameter and turns 768 revolutions per mile. Thatís 1.57 inches smaller than the stock tires! I measured this difference my self and that number seems pretty close to accurate (although I didnít do a rolling circumference measurement test)

My problem: I want to upgrade to 225/70R16ís or even to 235/60/R17ís these add .5 and .25 inches to the tire diameter respectively.

What happens if/when I get a flat? According to Honda (and the dealer) the spare should cause the AWD to activate and, assuming I am on pavement, cause the driveline to self destruct in short order.

But is that actually true? The stock arrangement already has a significant difference in the size of the main tires and the spare. Will the extra half-inch really matter???

To add to the confusion, different tire manufacturers claim different diameters for tires of the same ďsizeĒ

For example: A 215/70R16 should be 27.8 inches, but Yokohama claims their Geolander H/T-S G051 in that size is actual 28 inchesÖ So will that cause problems?

Has anyone had experience with upgraded (larger) wheels/tires and running the spare to get home? On an AWD model?

Xenon-E
02-24-2004, 09:21 PM
No. I upgraded to 235's and got a flat. Put the spare on. Drove 20 miles. No problems.....

paulj
02-24-2004, 09:31 PM
Actually, the dual pump RT4WD unit has a thermal cutout. If you spin the tires too long the system reverts to front wheel drive only. So even if the mismatch in tires activates the rear wheel drive (don't know if the speed difference is enough to do that), it will cut out after a bit.

I too worried about larger tires and spare tire size, until I realized that the temporary spare is significantly smaller. So at least for temporary use, a mismatch in tire size doesn't bother Honda engineers.

paulj

Pimpn E
02-25-2004, 06:34 AM
The spare is simply there so you can *limp* somewhere for a tire repair. It is not meant to be driven the remainder of a trip at 70 mph down the highway. The difference in size will not matter if the speeds are kept down, it's kept off the drive wheel and repairs are made ASAP.

Slowhand
02-25-2004, 09:26 AM
I used the spare and it "felt" so funny, I pulled off the road twice to check that the lugs nuts weren't loose. I've used that scissors jack for the last time, too. Took me so long to jack it up, I went out and bought one of those aluminum racing jacks - the hydraulic ones.

Bill in Houston
02-25-2004, 11:08 AM
[quote:de5836558d=" "]<snip>The stock tires are 215/70R16 which, in theory, are 27.85 inches in diameter and turn 724 revolutions per mile.

The spare tire is a 145/90R16 which, in theory, is 26.28 inches in diameter and turns 768 revolutions per mile. Thatís 1.57 inches smaller than the stock tires! I measured this difference my self and that number seems pretty close to accurate (although I didnít do a rolling circumference measurement test)
<snip>
To add to the confusion, different tire manufacturers claim different diameters for tires of the same ďsizeĒ

For example: A 215/70R16 should be 27.8 inches, but Yokohama claims their Geolander H/T-S G051 in that size is actual 28 inchesÖ So will that cause problems?

Has anyone had experience with upgraded (larger) wheels/tires and running the spare to get home? On an AWD model?[/quote:de5836558d]

It's probably better to compare revolutions per mile than sizes on some tires. Somehow, as you found, the actual tire can be fairly different from what the nominal size tells you. You may be able to find a tire that is supposedly larger or smaller that has the same revs per mile, and therefore have more options. Also revs per mile helps you figure out speedometer error.

Bill

ndp
02-27-2004, 03:02 PM
It's probably better to compare revolutions per mile than sizes on some tires. Somehow, as you found, the actual tire can be fairly different from what the nominal size tells you. You may be able to find a tire that is supposedly larger or smaller that has the same revs per mile, and therefore have more options. Also revs per mile helps you figure out speedometer error.


I agree completely. However the data from manufacturer, when available is different from the theoretical calculation.

Consider, if I run the computation for revs per mile (RPM):

5280 / ((width*aspect)*2 + RimDiameter)

(assuming all units in feet )

For the stock size of 215/70R16 I get tire diameter of 27.8 inches and 724 RPM. Checking Yokohama's data sheets for the exact same size tire I get a diameter of 28 inches, which is larger than the theoretical value. Yet, Yokohama also claims that the tire turns 742 RPM! This would indicate a smaller diameter tire.

Yokohama has a top notch data sheet: They also report the static radius of the tire under load (12.7) and note that the RPM value is for a loaded tire.

I think this actually makes sense. All properly inflated radials have a bulging sidewall between the rim and the ground. This compression lowers the effective radius of the wheel, and thus changes the actual values for RPM.

I guess the lesson here is that doing the calculations for tire size, tire diameter, and RPM are good for rough comparison purposes only. Depending on the individual tire - especially with regards to sidewall construction - the actual effective values may be quite different!

I made a table, just because I had to totally geek out on this. Check it out at:


http://carbon.oce.orst.edu:8080/tires/

ndp
02-27-2004, 03:10 PM
Did I mention that Goodyear doesn't supply any of the data for the tire under load?

Some how, I am not suprised...

Bill in Houston
02-27-2004, 03:42 PM
[quote:09c5696265=" "]I guess the lesson here is that doing the calculations for tire size, tire diameter, and RPM are good for rough comparison purposes only. Depending on the individual tire - especially with regards to sidewall construction - the actual effective values may be quite different!
[/quote:09c5696265]

Right-o.

Let us know what you land on. The Geolandars looked like the best replacement to me when I poked around. Hoping to not have to buy new tires for at least 2 more years, though.

Bill

Moto
02-27-2004, 03:46 PM
No. I upgraded to 235's and got a flat. Put the spare on. Drove 20 miles. No problems.....

I assume it does not rub?

And what are the specs? Rim diameter and aspect ratio (i.e. 235 65 16s or....?)

paulj
02-27-2004, 04:50 PM
So the temporary spare gets 768 revolutions/mile. Given that it is runs at 60 psi, it probabably has little bulge, and the number needs little adjustment.

The stocksize (at least for the Geolanders) gives 742 rpm, v 724 for the unadjusted stocksize.

The difference between the full size tires and the temporary spare is still there, just smaller. We still don't have any criteria for judging how big of difference is harmful to the drive system - other than the fact the Honda engineers accepted the use of the temporary spare.

paulj

ndp
02-28-2004, 10:25 AM
So the temporary spare gets 768 revolutions/mile. Given that it is runs at 60 psi, it probabably has little bulge, and the number needs little adjustment.

The stocksize (at least for the Geolanders) gives 742 rpm, v 724 for the unadjusted stocksize.

The difference between the full size tires and the temporary spare is still there, just smaller. We still don't have any criteria for judging how big of difference is harmful to the drive system - other than the fact the Honda engineers accepted the use of the temporary spare.


Right, well I made three 30 minute phone calls to Honda of North America in which I tried to get them to answer this question. The 1st person I spoke to seemed to understand the question and said, "Whatever, run the 225/70R16's you'll be fine". The 2nd person didn't want to help and was basically an *&%^*&^%@. The third person wanted to help, but couldn't get her head wrapped around the question.

Basically I was asking: On a 4wd E, what is the allowable difference in size between the temporary spare and the rest of the wheels? What is the engineering data on this?

I am positive that the Honda engineers know. They have a design spefification and product testing results that contain this information. I suspect the difference is linked to wheel speed....

alberta
02-29-2004, 10:51 AM
I am buying a new AWD 5 speed and the dealer may agree buy the stock tires or rims and tires from me.
The 5 speed turned about 3800 RPM at 60 MPH. Needlessly fast Iam thinking cause I do lots of highway driving and don't care too much if I lose a bit of excelleration.

I am confused when I read here that bigger tires are reported to turn more RPM.

I asked a tire dealer (though I amy not have been speaking to there most experenced person) about 18" rims and bigger tires to reduce RPM. He said yes to 18 " rims but that I would then need to go narrow profile tires to keep the speedo the same. But to drop highway RPM I will have speedo error and this I can live with.

So can sombody clear up my confusion?
Any advice on a long wearing and quite tires to reduce RPM...

LMN_OP
02-29-2004, 01:34 PM
[quote:79e31cbc04=" "]
The 5 speed turned about 3800 RPM at 60 MPH. [/quote:79e31cbc04]

Are you sure you are shifting to 5th gear?
OR may be you meant 80 mph?

paulj
02-29-2004, 10:19 PM
A couple of points regarding high rpms at highway speeds:

- the Element has no problems cruising at 80 mph (I did quite of bit of this across North Dakota and Montana this fall)

- the rpm's may seem high, but only in comparison to the larger US v6 and v8s. The 2.4L 4 cyl has peak power up in the 4000 rpm range.

- switching to larger tires (larger overall diameter) will lower the rpm's a bit (for a given highway speed), but may not improve gas mileage. With larger tires, the Element sits higher, and develops more wind resistance.

paulj

Bill in Houston
03-02-2004, 11:29 AM
[quote:a47cc84673=" "]- switching to larger tires (larger overall diameter) will lower the rpm's a bit (for a given highway speed), but may not improve gas mileage. With larger tires, the Element sits higher, and develops more wind resistance.[/quote:a47cc84673]

So true. Thanks for posting so I didn't have to.

Alberta, get the Odyssey. :D

drphun
03-24-2004, 10:26 AM
[quote:fb0d833a85=" "]
I am confused when I read here that bigger tires are reported to turn more RPM. [/quote:fb0d833a85]

Bigger tire is less RPM. It is bigger around, so it goes around fewer times to go the same distance.