Drivetrain damage: Tire Size VS. Tire Weight ??

[ojwerks]

Maybe this has been discussed before, but I could not find a specific topic on it.

My current setup consists of 4.10 gears with 295/75R16 Hankook dynapro tires. These tires are a true 33" tall, and weigh in new at 65.5lbs each.

I will soon be upgrading to 4.56 gears, and have about 50% of life left on the hankooks, but when the time to replace comes Im considering a set of 315/75R16 BFG KM2 tires, even though these are almost 2" taller, and almost 1" wider, they actually weigh almost 1lbs less each than my current tires... So if rotational mass plays such a huge factor as some claim it does, my drivetrains should remain just as happy with these "larger" tires? Im i correct or do I have this totally wrong? lol, please give your opinions on the subject.


Picture for attention :sombrero::

 

[comptiger5000]

Rotating weight matters mostly for fuel economy, ride quality and acceleration. It'll only affect drivetrain durability if you're spinning the tires and then suddenly grab traction (more rotating weight will make for a bigger shock load).

Diameter will also effect fuel economy and acceleration (but this can be corrected for via gearing). Larger diameter tires have more leverage against the drivetrain, which makes it easier to break things (gearing doesn't affect this).

 

[4x4junkie]

^^
100% agree.

Is that a Colorado? I'd be a little concerned about the IFS front axle on that with tires bigger than 33", especially if it has the aluminum centersection.

 

[ojwerks]

^^
100% agree.

Is that a Colorado? I'd be a little concerned about the IFS front axle on that with tires bigger than 33", especially if it has the aluminum centersection.

yes sir. i have the same concern for the front axle.. my rear is taken care off, im currently working on swapping in a dana 44 with an eaton locker with 4.56 gears, (stock AAM 8" Diff on colorados only allow 4.10 gears). Obviously front is also going to get the 4.56 treatment. So far ive had zero diff or cv axle related issues, even though ive brocken a front driveshaft before.

 

[Kmrtnsn]

Leverage is also a factor to consider.

 

[Mickey Bitsko]

Can you go to a "P" tire instead of "LT"?,it would save you huge rolling weight, I changed to 4:56's and went from stock 245/75 to 265/75 and got my top end cruising speed back, 4:56's did me well.

 

[charlieaarons]

According to Chris Scott's "Sahara Overland", p.119, , axle/bearing damage begins to be an issue with Landcruisers with 9.00-16s but not smaller (35-36"). Draw your own conclusions from that.

Charlie

 

[jeep-N-montero]

According to Chris Scott's "Sahara Overland", p.119, , axle/bearing damage begins to be an issue with Landcruisers with 9.00-16s but not smaller (35-36"). Draw your own conclusions from that.

Charlie

And this has what correlation to the vehicle in question??

 

[Ducky's Dad]

Based upon the pic of the subject vehicle, I'd be more concerned about front suspension and steering component stress and failure related to the offset on those wheels. Big tires will aggravate that, but the wheels are probably a bigger problem than the tires. Tall tires will also affect braking distances, especially if they are tall AND heavy. And GM front diffs are notoriously troublesome.

 

[Korben]

I wish I could figure out why this is so poorly understood. Rotational mass is almost completely irrelevant to this topic. What does matter is loaded radius and to a small degree unsprung weight. Loaded radius is the leverage ratio, this you are compensating for in part with a gear ratio change, that ratio change however doesn't make your brakes, axles, differential, and ring gear stronger. Unsprung weight is the weight of the tires, axle, etc. this effects the effectiveness of your shocks, this is the only significant effect of a heavier tire. But with let's say 400lbs of unsprung weight 10lbs is minor.
.
Rotating weight alone does not significantly matter for fuel economy or acceleration. This is because the rotating weight difference is very very small in relation to the total weight of the vehicle. Having tires that weight 40lbs more in total is functionally identical in these aspects as putting a 40lb bag in the rig. These are ratio issues not mass issues and are solved by proper gearing.
.
IDK the details with the Colorado but if your brakes and axles can handle the leverage increase then absolutely should be fine.

 

[comptiger5000]

Rotating weight alone does not significantly matter for fuel economy or acceleration. This is because the rotating weight difference is very very small in relation to the total weight of the vehicle. Having tires that weight 40lbs more in total is functionally identical in these aspects as putting a 40lb bag in the rig.

Sorry, but no. That's not correct at all. Rotating weight is felt far, far more than static weight in acceleration and braking, especially when the rotating weight is hanging out on a longer leverage arm (such as the weight in the tread of the tires). That 40 lbs in the tires could easily have the same effect as an extra 100 lbs of static weight in the vehicle. 10 lbs in a driveshaft, however, would be less noticeable, as the driveshaft is a smaller diameter (so that weight ends up carrying less momentum). The only saving grace with weight in the tires is that if the heavier tires are larger diamter, they will turn a few less rpm at a given road speed, which will reduce the amount of increase in inertia from the extra weight.

 

[ojwerks]

wow guys thanks for the replies and opinions... many things to consider. I still have some time to decide this but I might just buy these same 295 Hankooks again and call it a day, the truck behaves very well on them, no reliability issues or strange breakage of anything (with a smart foot of course) and the only reason Id like to go to a larger tire is to have a little more clearance on the deeper rutted trails but I guess that there wont be any real advantage if its going to put my drivetrain (front end specially) at risk..

 

[jeep-N-montero]

wow guys thanks for the replies and opinions... many things to consider. I still have some time to decide this but I might just buy these same 295 Hankooks again and call it a day, the truck behaves very well on them, no reliability issues or strange breakage of anything (with a smart foot of course) and the only reason Id like to go to a larger tire is to have a little more clearance on the deeper rutted trails but I guess that there wont be any real advantage if its going to put my drivetrain (front end specially) at risk..

Have you considered a 255/85r16 km2?

 

[MOguy]

My concern is why is the tire lighter? Is it made of a better material and still a strong durable tire or does it have thinner and weaker construction. I would rather have a stronger heavier smaller tire then a lighter even larger tire that could leave me stranded on the trail.

 

[LR Max]

Complicated question with too many variables. Long story short, its all about stress fatigue. On the front axle, for the most part, its truly rotational ("full float" style axle). In the rear, you'll have axial and lateral forces to deal with.

Either way, your larger tires will reduce the life of your driveshaft components. However I think with this change, the change is marginal considering the tire/wheel package will be lighter. Front axle should be fine since you are mainly cruising around in 2WD. On the front axle, your biggest concern with going to larger tires, is the suspension. Larger tires, even weighing less, will apply more forces onto the IFS and wear out components faster. Also on the front axle, off road, your power steering system will be working harder and the fluid will get hotter. While I don't think it'll have any adverse effects, I'd watch it. I have seen power steering fluid boil when off road. You are like, "ZOMG what do I do!!???1111" and it sucks. Just keep an eye on it but I think with sub 35" tires, it should be fine.

On the rear axle, it should be fine. Just keep the fluid changed as per manufacturers spec and it should be ok. Bad fluid can cause damage since the diff will be working harder with the new gear ratio. If you are concerned about your axle shafts, pull them every couple of years and look for twisting. Stock axles will twist a bit before the give out. I've seen guys paint a straight line on their axle shafts and so when they pull for inspection, they can see if there is any issue.

Of course, changing to synthetic in your diffs and power steering will help out a lot, especially in colder climates, but its not like, the defining thing. Its more for piece of mind.

Overall if you aren't a complete idiot in how you drive, you should be fine. Just keep an eye on things, maybe like, a once a year overall inspection. Don't slam on the throttle all the time and don't tow 20k loads.