van vs truck

[Canine]

The 2000 van we have,pulls this 9500 lb camper much better than the 1997 4x4 pulled the 6000 lb camper we had.The same engine and drive train.I think it must be tire size.The truck had 265/75/16 tires and the van has 235/75/15.More torque?

 

[29chico]

The 2000 van we have,pulls this 9500 lb camper much better than the 1997 4x4 pulled the 6000 lb camper we had.The same engine and drive train.I think it must be tire size.The truck had 265/75/16 tires and the van has 235/75/15.More torque?

It can only be the tire size if the gear ratio in the differentials of both vehicles are the same. 

A 265/75/16 is 32 inches in diameter, the 235/75/15 tire is 29 inches in diameter.

A 4x4 truck may well weigh  a more than a 2wd van as the van does not have the 4wd parts.

I am a bit concerned by your towing a 9500# camper with a rig with that has the 235/75/15.  Those size tires are associated with lighter duty vehicles that most folks refer a half ton.  Do you know what your gross combined weight rating on the van is?

 

[LeeRevell]

A larger tire diameter gives better torque.  Exactly why dragsters have large rear tires.  So that doesn't apply to your van vs. the truck.

 

[Big Country]

Tire size has a significant effect on overall gear ratio, 29Chico is correct, different tire diameters will have an effect on towing.

 

[highdesertranger]

tire size effects your final gear ratio, nothing more, nothing less.
Rear Axle
Gear Ratio tire size
24" 26" 28" 30" 32" 34" 36" 38" 40" 42" 44"
2.18 1831 1690 1570 1465 1373 1293 1221 1157 1099 1046 999
2.50 2100 1938 1800 1680 1575 1482 1400 1326 1290 1200 1145
2.74 2301 2124 1973 1841 1726 1625 1534 1545 1381 1315 1255
3.08 2587 2388 2218 2070 1940 1826 1725 1634 1552 1478 1411
3.23 2713 2504 2326 2170 2035 1915 1809 1714 1628 1550 1480
3.50 2940 2714 2520 2352 2205 2075 1960 1857 1764 1680 1604
3.73 3133 2892 2686 2507 2349 2212 2089 1979 1880 1790 1709
3.90 3276 3024 2808 2621 2457 2312 2184 2069 1966 1872 1787
4.10 3444 3179 2952 2755 2583 2431 2296 2175 2066 1968 1879
4.56 3830 3536 3283 3064 2873 2704 2554 2419 2298 2189 2089
4.88 4099 3784 2513 3279 3074 2894 2733 2589 2460 2236 2139
this ^ is your rpm.
you can see that as your tire height gets bigger your rpm goes down. highdesertranger
highdesertranger

 

[highdesertranger]

I don't know why that chart is all screwed up. the first column is axle gear ratio, the second column is your rpm for 24" tires the third column is for 26" and so on. dang cut and paste. highdesertranger

 

[Canine]

Whatever it is,there is a big difference.Maybe the old truck just had a weak motor?I would think a smaller tire would increase the torque.But I've been wrong before.

 

[LeeRevell]

Whatever it is,there is a big difference.Maybe the old truck just had a weak motor?I would think a smaller tire would increase the torque.But I've been wrong before.

Smaller tire increases rotational speed, bigger tire increases torque.  Same as with gearing.

 

[29chico]

Smaller tire increases rotational speed, bigger tire increases torque.  Same as with gearing.

So are you saying that switching to taller tires on the drive wheels, that have a larger outside diameter, will help a vehicle pull a heavy load from stopped easier?

 

[NeedAnEscape]

A smaller tire gives more torque, A larger tire gives more speed.

 

[29chico]

A larger tire diameter gives better torque.  Exactly why dragsters have large rear tires.  So that doesn't apply to your van vs. the truck.

The reason that dragsters run wide , tall and slick tires is all bout getting the maximum area of rubber on the asphalt via having a wide, long (the result of having a tall tire) & continuous (the result of having no tread grooves) tire footprint to provide max traction.

 

[LeeRevell]

A smaller tire gives more torque, A larger tire gives more speed.

We will just have to disagree.  At least until dragsters get tiny tires and Indy cars get big meats.  Look at your bicycle's gears.  Or your transmission.  "Low" gear is bigger for torque to get started, "high" gear is smallest.  It's all in the ratios.

 

[minimotos95]

The taller the tire the numerically lower the gearing, the lower the RPM at speed. Shorter tire bigger gear ratio, higher RPM quicker acceleration
Same reason people complain about tall knobbies with stock gearing on dual sport motorcycles. The decrease in torque makes it easier to stall compared to the stock height tire.
Increasing the tire size increases how much torque the tire has over the sprocket not the other way around.

 

[29chico]

We will just have to disagree.  At least until dragsters get tiny tires and Indy cars get big meats.  Look at your bicycle's gears.  Or your transmission.  "Low" gear is bigger for torque to get started, "high" gear is smallest.  It's all in the ratios.

Many years ago an associate of mine put huge tall tires on the back of his work truck thinking that by lowering the cruising rpm of his motor he would get better fuel mileage.  He did not get better fuel mileage as the tires, besides being really tall, were really wide with mud & snow tread. 

The truck had a four speed manual tranny that had a granny gear first setup where one would usually start out in second gear except on a steep hill or with a heavy load.  He found out really quick that he had to start out all of the time in granny gear as second was too tall with the tall tires.  If your thinking were correct he should have found that starting out in second gear was easier with the tall tires.

What matters with tire diameter and overall gear ratio is tire roll out.  Roll out is how far a tire will travel in one revolution.  A taller tire will roll farther in one revolution than a shorter one.  It always takes more energy to go a greater distance.

 

[highdesertranger]

taller tires do not give you more torque. they are like adding an overdrive, lowers the gear ratio. if you go to big performance will suffer. then you will have to regear the axle ratio to make up the difference. remember gear ratios are kinda confusing for non-mechanics. the lower the numerical ratio the higher the gearing and vice versa, the higher the numerical ratio the lower the gearing is. taller tire are lowering the numerical ratio. highdesertranger

 

[LeeRevell]

Many years ago an associate of mine put huge tall tires on the back of his work truck thinking that by lowering the cruising rpm of his motor he would get better fuel mileage.  He did not get better fuel mileage as the tires, besides being really tall, were really wide with mud & snow tread. 

The truck had a four speed manual tranny that had a granny gear first setup where one would usually start out in second gear except on a steep hill or with a heavy load.  He found out really quick that he had to start out all of the time in granny gear as second was too tall with the tall tires.  If your thinking were correct he should have found that starting out in second gear was easier with the tall tires.

What matters with tire diameter and overall gear ratio is tire roll out.  Roll out is how far a tire will travel in one revolution.  A taller tire will roll farther in one revolution than a shorter one.  It always takes more energy to go a greater distance.

Speed is NOT in the equation.  On motorcycles, a larger rear sprocket improves low end torque and off road performance.  A bigger tire does the same.  Smaller gears or tires improve the high end speed, but reduce torque.  Simple mechanics.
Look at your basic farm tractor - much larger rear (driven) wheel, for low end torque and stump-pulling power.  Same with 4X4 trucks.  But they are no good for higher highway speeds.  Again, simple mechanics.  And personal experience verifies this.

 

[highdesertranger]

ok the motorcycle with the larger rear sprocket it does improve low end torque because it raise your numerical gear ratio. a taller tire on the other hand lowers your numerical gear ratio therefore lowering your torque. this is common knowledge, do a search the 4x4ers all know this and the charts are all over the internet, to bad mine came out screwed up. as far as a farm tractor goes the ring and pinion has like a 30 to 1 gear ratio(meaning the pinion turns 30 times to turn the ring gear once), way lower than anything in a street vehicle, the large tires are for crop and ground clearance. Lee you are right on the motorcycle sprockets, but wrong on the tire size. highdesertranger

 

[29chico]

Below is the first line of the text from a gear ratio calculator for 4x4 enthusiasts.


Bigger tires can help you crawl up those slick rocks, look cool, and rob you of power.   


Link:

http://www.4lo.com/calc/geartire.php

 

[skyl4rk]

Speed is NOT in the equation.  On motorcycles, a larger rear sprocket improves low end torque and off road performance.  A bigger tire does the same.  Smaller gears or tires improve the high end speed, but reduce torque.  Simple mechanics.
Look at your basic farm tractor - much larger rear (driven) wheel, for low end torque and stump-pulling power.  Same with 4X4 trucks.  But they are no good for higher highway speeds.  Again, simple mechanics.  And personal experience verifies this.

Bigger tires with larger circumference increase speed at the same rpm.  If you want low end torque, get a bigger rear sprocket or reduce the diameter of the tire/wheel.

 

[29chico]

Speed is NOT in the equation.  On motorcycles, a larger rear sprocket improves low end torque and off road performance.  A bigger tire does the same.  Smaller gears or tires improve the high end speed, but reduce torque.  Simple mechanics.
Look at your basic farm tractor - much larger rear (driven) wheel, for low end torque and stump-pulling power.  Same with 4X4 trucks.  But they are no good for higher highway speeds.  Again, simple mechanics.  And personal experience verifies this.

Please explain how you think that I made a statement about speed being in the "equation".  I did use the word speed in reference to a four speed transmission.  My focus in the post that you replied to was about the forces involved in getting a vehicle underway from a dead stop.

How can a smaller outside diameter tire improve high end speed when at a given RPM it goes a shorter distance than a taller tire that has a larger outside diameter and greater circumference?  Speed is defined as distance traveled over time, the M in RPM defines the time.

This whole issue goes back to the fact that majority of folks erroneously use the term "high gears" in reference to vehicle performance when in fact the final drive gear ratio for going farther and faster at a given driveshaft RPM will be represented as having a lower number. 

I think that we can agree that most vehicle enthusiasts would would agree with the statements that "a 3.0 final drive ratio are high gears for the freeway" and "a 4.11 differential ratio are low gears for pulling a load".   A 4.11 reduction gearset  would be properly expressed in engineering terms as 4.11 to 1 ratio.