tire size adjustment for 295 toyo mt

[CookD]

I just got a smarty jr. and want to adjust for my 295 toyo mts but I don't have a gps. If you have done this what size did you input to get speedo set? Toyos website says 33. 5.



Thanks guys



Dale

 

[cerberusiam]

Every truck seems to vary a little so its not the same for every application. In order to get the speedo with 1 mph of a GPS on my truck I used 32. 8 as a tire size. If you measure the tire as it sits on the ground it is right at 33". I had to back it down some more to get things close as I have them.

 

[AH64ID]

On my truck I use 31. 25 for my toyo 285's. Thats about . 5" shorter than the advertised rolling radius of 31. 7. . The 295 MT is advertised at 32. 6, so I would start at 32.

 

[EArp]

I apologize for a dumb question, but I don't know alot about tires. From my understanding the tires have 3 numbers. For example, P265/70/R17. My question is, I thought the first number is the WIDTH of the tire and the middle number is the HEIGHT of the tire. So why would you need to adjust the speedometer if you are only going to a wider tire?

 

[brods]

My 285/75-17 Toyo AT tires work well at 32. 8. They are listed at 33. 8" tall. I came across this by trial and error, but there is a way to figure it. Forget the advertised diameter or loaded radius as neither one work out right.



Use the Toyo chart revs per mile and work backward. For the 285/75 the revs per mile are 614.



5280' in a mile divided by 614 revs per mile = 8. 5993 feet per revolution. 8. 5993 feet is the effective loaded rolling circumference of the tire.



8. 5993 divided by pi (3. 1416) = 2. 7373 feet diameter. 2. 7373 feet times 12" in a foot = 32. 8471" diameter.



Simplifying the math gives 20,168 divided by revs per mile = the tire diameter in inches to enter into the smarty.



Just punch in 20,168 into a calculator and then divide by the revs per mile from the tire manufacturer's chart.



According to the Toyo MT chart the 295/70-17 has 619 revs per mile... . so the “rolling” diameter to be entered into the smarty is 32. 58". Try starting there and adjust as needed.

 

[cerberusiam]

I apologize for a dumb question, but I don't know alot about tires. From my understanding the tires have 3 numbers. For example, P265/70/R17. My question is, I thought the first number is the WIDTH of the tire and the middle number is the HEIGHT of the tire. So why would you need to adjust the speedometer if you are only going to a wider tire?

You are correct, the first number is the tread width. However, the second number is the sidewall height expressed as percentage of tread width. Wider tires are generally taller given the casing construction is the same.



Don't assume tread width is what you measure on the tire either. It may or may not be what the manufacturer uses to rate the tire size. Tread width in itself is a function of the casing construction and the actual facing may not be accurate. Single biggets reason why 2 tires with the same size rating from different manufacturers will almost invariably have a different rolling height.

 

[Road Dog]

The first number is the section width -- the widest part of the tire. The second is the aspect ratio -- the ratio of sidewall height to section width (as a percentage). The third is the rim diameter. As brods described, the revs per mile is the best starting point. It changes as the tires wears too.

 

[Regcabguy]

Using Smarty I had to adjust tire size to 31. 10" to correct the odometer with my 285-70-17 Toyo AT's. Pressure is 55 psi and they're mounted on stock rims. Thank God for GPS.

 

[EArp]

Thanks for your responses guys. That clears things up for me. I was wanting a bigger (taller) tire for my truck as well. I was thinking of a 285/75/17 on my stock rim. However, based on you guys educating me, i'm wondering if I go to that size if it'll be too big? If any of you guys happen to have a pic of a tire that size on one of our trucks i'd love to see it.

 

[cerberusiam]

Thanks for your responses guys. That clears things up for me. I was wanting a bigger (taller) tire for my truck as well. I was thinking of a 285/75/17 on my stock rim. However, based on you guys educating me, i'm wondering if I go to that size if it'll be too big? If any of you guys happen to have a pic of a tire that size on one of our trucks i'd love to see it.

A 285/75/17 is comparable in height to the 295/70/17, at least in the Toyos. Slightly wider than stock but right at 33" tall. Toyo makes that tire in an AT design and it should be an excellent choice for a good all around tire. The only draw back is it rated slightly less for weight than the 295 but unless you are at max towing weights all the time it should not matter.

 

[Road Dog]

I was wanting a bigger (taller) tire for my truck as well. I was thinking of a 285/75/17 on my stock rim. However, based on you guys educating me, i'm wondering if I go to that size if it'll be too big? If any of you guys happen to have a pic of a tire that size on one of our trucks i'd love to see it.

If you want to go taller then keep the width the same and go to a higher aspect ratio. For example, a 265/85R17 is taller than a 265/75R17 (if it exists). The other thing is P is passenger and LT is light truck (more belts and a load rating). A P265/75R17 will be a little smaller than an LT265/75R17.

 

[EArp]

A 285/75/17 is comparable in height to the 295/70/17, at least in the Toyos. Slightly wider than stock but right at 33" tall. Toyo makes that tire in an AT design and it should be an excellent choice for a good all around tire. The only draw back is it rated slightly less for weight than the 295 but unless you are at max towing weights all the time it should not matter.

Can I run a 295 without it rubbing?

 

[cerberusiam]

Can I run a 295 without it rubbing?

Yep, thats what I am running on the stock rims. You can go up to a 305 tire without rubbing issues if you use the correct back spaced rim.

 

[Paddy McMahon]

If I set the tire size at 33 on my smarty the actual speed is slower by about 2-3mph. I believe air pressure has a significant effect on the diameter of the tire as well-40psi vs. 60psi can be as much as 5/8 inch in diameter of the tire. I have entered 32. 5 inches and seem to be pretty close to actual speed.

 

[CookD]

Thanks for all the replys, I found that with my 295 on stock rims tire pressure at 50 front and 40 rear 32. 85 put me right on by borrowing a gps and by watching the mileage markers on the side of the road. The 295/70/17 and the newer 285/75/17 I think are the perfect size for the third gen trucks for looks and no rubbing!

 

[Regcabguy]

Thanks for all the replys, I found that with my 295 on stock rims tire pressure at 50 front and 40 rear 32. 85 put me right on by borrowing a gps and by watching the mileage markers on the side of the road. The 295/70/17 and the newer 285/75/17 I think are the perfect size for the third gen trucks for looks and no rubbing!

My friend has the 285-75-17 Toyo AT's on his '05. They are 14# heavier than my 285-70-17 AT's. Nice tire. He's got 23,000 on them with no rotation or rebalance(lazy fool) plus a 1000# Callen camper. I'd say he'll get 40,000 safe no maintenance miles out of them.

 

[AH64ID]

My friend has the 285-75-17 Toyo AT's on his '05. They are 14# heavier than my 285-70-17 AT's.

That was what ultimately made me choose the 285/70... the 285/75 is 19lbs heavier than stock, where the 285/70 is only 5lbs heavier than stock.

 

[Regcabguy]

That was what ultimately made me choose the 285/70... the 285/75 is 19lbs heavier than stock, where the 285/70 is only 5lbs heavier than stock.

Yeah,he and I carry campers on our rigs all the time,so the additional sidewall is appreciated. I'm getting his soon as he's decided to upgrade to 35" Toyo MT's. No tire spending for quite awhile for me.

 

[KHousworth]

I just put on Toyo Open Country A/T Load range E, each tire holds 3750 lbsI think. I have loaded my truck very heavy once in a while, so i decided I would get them and run them at 80 psi. They handle good and look great.

Local dealership here in Milledgeville, GA. reset my comp. for free with the right revolutions per mile for my truck. Gotta love cust. service.

 

[CAPN Harley]

toyo mt's

I have the toyo mt 295/70/17s on my dwr and they look great. I had to put 2 and 1/2 inch spacers on the back but no rubbing and can carry any load. Oo.