Hello From Central Jersey

[bobc]

hello all my name is bob i work for a small townshp in nj i love this site and have been visiting for over a year great info and stories.i have a problem and need some advise.my town is currently looking to purchase a new granite tandem axel 16yrd dump 6sd auto 350-400 hp dealer we talked to says 502 ratio rears (with the new engines )will be fine we want 606s or lower. truck will be used for snow plowing

,salting and hauling dirt to the landfill our current trucks all have 534s or lower truck will very rarely see speeds over 45mph could you go wrong by specing to low of a gear? we have quite a bit of hills in town and dont want a dog well not that kind thank you your opinions are greatly appreciated

[Barry]

Hi Bob...welcome to BMT!! I'm not too knowledgeable about ratios, but I'm sure someone here will have some good info for you!

[maxidyne237]

what size tire?

[bobc]

what size tire?

not sure ill try and find out tomorrow,i do know it will have 18k front and 52k rears and registered for 70,000. our newest truck a 06 volvo garbage truck with 400hp,22.5 tires,auto and 5.34s is lazy till she gets rollin thanks.

[bulldoggin']

[dak49]

Bobc, welcome to BMT.

I just did the math and with 6:06 gears the engine would have to turn about 2290RPM @45 That's using a low-pro 22.5 tire and a direct drive transmission. If you have an over drive trans then it would be closer to 1695RPM. That would be with a .74 overdrive trans. You would really need to know the correct tire size (RPM =rev's per mile) most tire manufactures can give you that info. I was using a 504 tire RPM (for a low pro 22.5) A bigger tire will have a lower tire RPM and a smaller tire would be higher.

The way to figure it is like this:

take the speed that you want to run (cruise) in this case I used 45 then multiply that times the trans high gear ratio if its an over drive, if not use 1 (or just skip that one) then times that by the rear ratio times tire RPM. Then devide by 60

Example

45x1x6.06x504=137440.8 devide that by 60=2290.68 engine RPM.

speed x trans top gear ratio x tire RPM = devide by 60= engine rpm @ indacated speed

I hope that helps you and maybe a few others, let us know what you decide to go with.

Dak49

P.S. a direct drive trans has a 1to1 ratio that is why if you use the gear ratio you would need to use 1.

[bobc]

thanks for the info i just talked to the dealer friday and expressed our conserns.he says since mack has dual reduction rears the 502s will realy be closer to a 537? when compaired to a volvos rears btw the tires are going to be 24.5s

[dak49]

thanks for the info i just talked to the dealer friday and expressed our conserns.he says since mack has dual reduction rears the 502s will realy be closer to a 537? when compaired to a volvos rears btw the tires are going to be 24.5s

Good Grief, where do people come from?? He is right the Mack rears are dual reduction, but 5:02 is 5:02 not 5:37. anyway after I did the math it works out to about 1875RPM at 45 MPH. Again, that's assuming a direct drive transmission. Do you have any idea how many gears the trans will have? That will make a big difference as well. For example, if its a 6 speed direct it should have plenty of low end power, if it has 4 speeds, it could be another dog, no pun intended.

It sounds to me like the dealer is trying to sell what he would want and not what you need, or want. One last thing, if it won't run much faster than 45, I would think resale wouldn't be very high either though, unless someone just wanted it for off road use.

Good Luck, and keep us posted as to what you wind up doing.

Dak49

[dak49]

Bob, I just reread your original post and seen that you are going to use a 6 speed, I would think with the 5:02's it wouldn't be a problem on take off, but

if the Volvo is slow, then I'm guessing the Mack would be as well. I think the 6 speed would have a low enough lo gear to get it started pretty fast, but with 70,000 pounds it could be kind of slow.

I wish I could be of more help sir.

Good Luck and keep us posted as to how everything works out.

DaK49