Diameter vs Weight of Tire?

[carlomagne]

Would a heavier tire be more of an issue than the diameter in regards to gear searching at higher speeds and also the initial acceleration from stop?

33 x 12.5 Toyo Open Country MT (smaller diameter but heavier tire)
vs
295-305/70 Cooper STT Pros (larger diameter but lighter tire)

Thanks in advance.

 

[Bumbo]

Not really sure... Its probably a really complex equation because it isn't as simple as that...

I think what matters is where weight is in relation to the diameter of its rotational axis...

This is why its better to have smaller rim than one that is larger, even for the same size tire. Having the bulk of the weight closer to the center axis has less torque / centrifugal force which helps with handling/braking...

I find un-spring weight to be really noticeable between my street rim/tire setup and my off-road set...

How much weight are we talking about here?

 

[UnderFire]

Those are both really heavy tires, the 10lb difference in weight probably won't make a big difference, I'd think that the added rolling resistance from the Toyo's being a full inch wider than the 295 coopers would be the biggest factor. A good option that a lot of people overlook is the Mastercraft MXT, made by cooper still, but usually runs a whole lot lighter than other similar MT tires. For instance, the 295/70R17 is only around 58 pounds, compared to the STT pro at 66.

 

[carlomagne]

Maybe a taller tire like 285/75/17 would be better since there would be less of a footprint?

 

[m85476585]

Once you get the tire up to cruising speed, the weight doesn't matter much. You could have solid metal tires, and once you get them rolling they would just keep going with about the same amount of power from the engine as a regular tire. Rolling resistance and tire size will have a bigger impact on gear hunting at highway speed.

 

[carlomagne]

Once you get the tire up to cruising speed, the weight doesn't matter much. You could have solid metal tires, and once you get them rolling they would just keep going with about the same amount of power from the engine as a regular tire. Rolling resistance and tire size will have a bigger impact on gear hunting at highway speed.

Since rolling resistance (wider tire) and tire size (for my example, a taller tire) will have a bigger impact on gear hunting, which of the 2 would hunt less?

The wider tire would be heavier than the taller tire due to the different brand/model tire I would be getting. The weight would affect initial acceleration (and probably stopping power) and that's why I included that as a factor as well.

 

[wanderMT]

Taller tire changes your final drive ratio a little higher (lower numerically). I think that would be more noticeable than 10# - I think final ratio is too high stock.
Can go smaller diameter and save weight.:hiding:

 

[Bumbo]

Taller tire changes your final drive ratio a little higher (lower numerically). I think that would be more noticeable than 10# - I think final ratio is too high stock.
Can go smaller diameter and save weight.:hiding:

You can keep the diameter and still save weight... Tall tires are good.

I run a 255 and love it, going 275 285+ just isn't for me.

A smaller contact patch works better anyways on and off road unless you are building a dune runner.

 

[jrm]

lots of 5th gen

Maybe a taller tire like 285/75/17 would be better since there would be less of a footprint?

owners are going the 255 75/80 17 route. That cooper sst in 255 80 17 is a nice looking tire..

 

[VTNick09]

This can get into a very detailed conversation. Long and short it depends. Somethings sometimes overlooked but to keep in mind.

Heavier tire will effect cv axles, bearings, bushings, gear, etc. causing premature wear.

Taller tire with less weight wont have as much effect as that but will cause fitment issues depending on lift situation, and gearing which can throw off speedo.

 

[TrdinOhio]

This question could get into the realm of needing to be talked about on a physics forum...
Also I am going to speculate as to your specific answers as I'm not totally sure but...
To keep it simple heavier tires will cause slower acceleration from a stop. You are adding unsprung weight. Adding unsprung weight will decrease acceleration when talking about tires and wheels due to rotating mass. Example: a car that weighs 2500 lbs and has 100lbs in wheels and tires will accelerate quicker than a 2500 lb car with 300lbs in wheels and tires.

As far as gear hunting on the highway I think both weight and size potentially could effect gear hunting. I believe the weight could potentially cause more gear hunting but that's just a guess.
Here's why I think that: Gear hunting is the transmission shifting from say 5-6-5-6-5 etc. your throttle input, vehicle speed, load, RPMS, all effect transmission shifting. A transmission shifts up when governor pressure ( vehicle speed ) exceeds throttle pressure within the transmission. A transmission downshifts when throttle pressure exceeds governor pressure. By adding heavier tires OR taller tires you could be changing the internal pressures of the transmission or the input signals that the trans receives. Hydraulic transmissions are no longer made in the U.S. but the theory is generally the same but now done using electric shift solenoids that GET INPUTS FROM THE ECU ( engine computer ). Mainline pressure also plays a roll as mainline pressure is build up by the transmission pump which is RPM controlled. Mainline pressure is the source pressure for the whole transmission including the valve body, torque converter and all clutches. Toyota likes to use an electronically controlled 1/2 lock of the torque converter that's dependent of many factors and inputs but seems generally pressure controlled for the most part. Adding heavier or larger tires could also effect these inputs or pressures.

 

[DeepSea]

What tire are or did you decide on? This is the same question I've faced every time I look for new tires. Each manufacturer has completely different specs for exact size and weight in their respective tire sizes. Another big consideration is load rating. BFG KM2 is one of the few tires left in a "D" rated tire (285/70R17) as most are "E" now which equates to stiffer & heavier

 

[1engineer]

This question could get into the realm of needing to be talked about on a physics forum...
Also I am going to speculate as to your specific answers as I'm not totally sure but...
To keep it simple heavier tires will cause slower acceleration from a stop. You are adding unsprung weight. Adding unsprung weight will decrease acceleration when talking about tires and wheels due to rotating mass. Example: a car that weighs 2500 lbs and has 100lbs in wheels and tires will accelerate quicker than a 2500 lb car with 300lbs in wheels and tires.

As far as gear hunting on the highway I think both weight and size potentially could effect gear hunting. I believe the weight could potentially cause more gear hunting but that's just a guess.
Here's why I think that: Gear hunting is the transmission shifting from say 5-6-5-6-5 etc. your throttle input, vehicle speed, load, RPMS, all effect transmission shifting. A transmission shifts up when governor pressure ( vehicle speed ) exceeds throttle pressure within the transmission. A transmission downshifts when throttle pressure exceeds governor pressure. By adding heavier tires OR taller tires you could be changing the internal pressures of the transmission or the input signals that the trans receives. Hydraulic transmissions are no longer made in the U.S. but the theory is generally the same but now done using electric shift solenoids that GET INPUTS FROM THE ECU ( engine computer ). Mainline pressure also plays a roll as mainline pressure is build up by the transmission pump which is RPM controlled. Mainline pressure is the source pressure for the whole transmission including the valve body, torque converter and all clutches. Toyota likes to use an electronically controlled 1/2 lock of the torque converter that's dependent of many factors and inputs but seems generally pressure controlled for the most part. Adding heavier or larger tires could also effect these inputs or pressures.

You were right on up to the highway option. Larger diameter will be the culprit of gear hunting at highway speeds. Reason: You have already accelerated the unsprung mass from rest so now it's just keeping it rolling. The tire size now will be the issue because of torque, or lack thereof. So rule of thumb is weight is the problem around town, diameter is the problem on the highway.

 

[Unner]

I've been reading about this a lot lately since I'm due for tires soon. I know more weight and diameter are negative, but I'm having a hard time finding a way to quantify it. I'll probably go up one size to a 255/80/17. That'll be .6" taller than my current tire, and 11 lbs heavier. I don't think it'll be too bad. I also can't read about tires anymore. The perfect tire doesn't exist so I'll need to make compromises somewhere.

 

[1engineer]

I've been reading about this a lot lately since I'm due for tires soon. I know more weight and diameter are negative, but I'm having a hard time finding a way to quantify it. I'll probably go up one size to a 255/80/17. That'll be .6" taller than my current tire, and 11 lbs heavier. I don't think it'll be too bad. I also can't read about tires anymore. The perfect tire doesn't exist so I'll need to make compromises somewhere.

You are correct as a perfect tire does not exist. Another rule of thumb to remember: adding 10 lbs of unsprung weight is equivalent to adding 100 lbs to the vehicle as far as efficiency calculations go.

 

[Unner]

What do you mean by efficiency calculations exactly? I've heard 1:20, 1:12, 1:10, 1:6, 1:4, 1:2, pretty much every ratio comparing unsprung weight to sprung weight. No one can ever provide a mathematical calculation (neither can I) as to which one is most right and why though. 1:10 seems a little high to me. I've been a believer in the mid range estimates, something like 1:5 ish.