Engine/Transmission (1998.5 - 2002) Increase the wheel size, should I?

[John - K5AWO]

My truck gets the usual 12. 5 mpg or so around town. With the stock wheels and 235 tires on it.

My son is wanting me to put 19. 5" wheels on it with a sportier look :-laf and says that it should give me a bonus of better mpg when driving around empty. he also says that being able to use OTR truck tires will let me run the same set of tires until I die

I have thought about it, it might actually give me a small bonus of running down the highway faster at the same RPMs. Keeping the tach at 2100 or less nets me with 63 mph by GPS.

I just retired last month, and anxious now to hook onto the 34' TT and start a little tour of the USA in nice weather.

Would be nice to run faster than 50 mph with the OD kicked off while pulling that trailer.

The TT is a 34' Avion triple axle and weighs 8200#, bumper hitch style. It is the Airstream style aluminum TT.

Never messed with running big wheels and tires. Would this be a good thing to do? It would help to alter that 4. 10 axle down towards 3. 55 to 3. 7ish effective ratio.

any thoughts from you all?

I noted from the RAM engineers thread that they don't like the idea. They claim that keeping the transmission in the lower gears for a longer period of time will overheat the transmission.

I'm never in that much of a hurry, and I rarely ever use more than about 1/4 to 1/2 throttle to get off the line. I still have the stock exhaust, I can't see me getting any benefit out of a 4" exhaust if I never work the truck hard enough to get the turbo higher than 15 to 20 inches.

It nearly always runs in the 3-6 inches of boost range for me.


John

 

[John - K5AWO]

No thoughts on this? Especially concerning the transmission ?

 

[Coalsmoke]

I missed this first time around John. I'm a standard trans guys, the closest I ever got to working on the autos when working at Dodge was pulling and installing them. However, I honestly cannot see somewhat larger tires causing you to spend an appreciable amount of time in 1st and 2nd given how you use your truck. Now, perhaps if you were running around town all day with 37" tires, then we'd have something to consider. 3rd being direct in your transmission is an excellent gear to be pulling in, so my thoughts would be to have at it with a tire in the 32-33" range.



Now, my thoughts on the 19. 5s, I think its a fine idea, but watch that your rims aren't so heavy that you loose MPG and braking efficiency, as some members here have found. I believe that this is with the aluminum wheels more than the steel ones. Also, keep in mind that Toyo's M-55s are industrial truck tires sized for the pick-up market that will fit on your stock sized rims, and will last a very long time while giving you the performance of a commercial tire. I have run them and feel that their cost is well worth their dependability and durability. Their 255/85/16 is my size of choice. One final thing to keep in mind, if you are wanting an all terrain tire like the M-55 for example, in a commercial compound, they will "sing" to you. To me its music, but some don't like to hear tire or road noises, so keep it in mind when looking at commercial tires.

 

[Road Dog]

The issue with the lower gears is that the torque converter doesn't lock up in first and second. If you turn off O/D then it'll lock in third. If you just kick down to third then it won't lock. Slipage plus less air through the rad (at lower speeds) equals a hotter transmission.

 

[Midnite]

With those 4. 10 gears you'll be just fine going to the taller 19. 5" setup. If I remember correctly 235/85R16 tires are 31" tall, and 245/70R19. 5 tires are 33" tall, so it's not a big difference.

Keep in mind another advantage of the real truck tires is an extra margin of safety towing that big trailer.

Mike

 

[BDaugherty]

While a the 19. 5" tire and wheel combo would look tough, last longer, and have a higher load capacity, I don't think you'll really see any MPG increase. Remember that those 19. 5's are going to be much heavier than a comparable size 16". They will last much longer than your stock type tires, but you still won't be in the range of 22. 5" tires. Also, my experience with 3. 55/auto trucks is that you should stick with a near stock height tire for towing. Too much tire will decrease your overall gearing causing you to downshift more often. I think a torque converter lockup switch would be more helpful for towing than taller tires.

 

[John - K5AWO]

Hi guys, and thank you very much for your time and explicit information.
Sorry to be so long getting back to you, had a couple emergencies around the place that side lined my internet time.

What I am hearing from all of you is go for it, especially since my truck has the 4. 10 axles on it.

A) my son is a big diesel mechanic and he wants me to do this for road safety. ie, POP I won't have to worry about your tires blowing out on you, and they will carry the load much easier.

B) my son has some fancy aluminum wheels all picked out for me, so I don't even get to choose what I end up with ... . :-laf... what do old foggies know anyway, right?

C) I bought the heaviest Torque Convertor that SunCoast makes, it is a 3D TC, and has almost negligible slippage. When Manually shifting from 1st to 2nd, at about 2500-3000 it hits like friggin sledge hammer. Even at 2000, it hits real hard like that. Even with the travel trailer behind it.

Again, thanks a lot for your efforts at educating me. This is why I have been a non-stop TDR member since I bought the truck many years ago. with the knowledge gained on here, I have fixed nearly everything myself. The heavy stuff, I just passed the info on from here and my son or his friends did the work.

You guys are the greatest!!! Oo.

 

[John - K5AWO]

Oh, I forgot to say. Forgot really that I even have it. I bought the transmission Controller from SunCoast so that I can force it into Lockup. It is not on the truck, but shouldn't take too long to put it on.

That would resolve the heating issues in 1st and 2nd gear, would it not?

 

[Coalsmoke]

If safety is your goal 19. 5s will definitely give you good reliability and also better lateral stability. Just keep in mind that you can find safety and reliability in a high end tire without going to 19. 5, that is if budget is an issue. Fancy 19. 5 wheels and tires can carry a bit of sticker shock.

Oh, and we want to see some pictures when you go get the 19. 5s on the truck. I'm looking forward to seeing what you end up with.

 

[John - K5AWO]

:-laf I think that looks has more to do with what my son wants than budget

The truck has been paid for a while now and with the refurb work he did to it, it should outlast my needs for the truck.

In fact, he told me that when I get "too old" to drive it, that he wants it for his stable.

My personal goal is to get the effective gearing where I can run a few MPH faster in 3rd direct with OD off. that would make it more comfortable to pull the trailer around the country on uphill grades.

I will never be one to be in a hurry, and if I hit a steep upgrade and the transmission downshifts..... I just lock the transmission in that gear and keep the RPMs at about 2100-2500 regardless of MPH.

I pay more attention to the EGTs than I do to MPH. When they get up to 1200*, I down shift and get more turbo boost going.

If we spend enough time on the road, I am going to investigate installing the Kelderman air suspension. Going to depend on how rough it rides after I buy the 5th wheel trailer and pull it instead of my '78 Avion TT. The weight will be about the same, but with a 5th wheel, I anticipate a more comfortable ride.

I will definitely upload some pictures when it gets upgraded. right now, she is plain jane stock looking from the outside. Used to be a construction work truck, so it has a few scratches. I have a friend who has offered to repair the right fender (blow out broke it) and then repaint the whole truck for a grand. I don't see how I can pass on that offer.

 

[Coalsmoke]

You will really like pulling the 5ver over the tow behind. Really sits back there nicely and the truck and trailer will pull more as one unit instead of two dogs doing their own thing.

I wish I could get a repaint alone for a grand, that sounds like a good deal if the quality is ok.

 

[John - K5AWO]

I'll be taking pictures of the before, and then the after on the body work and paint job.

Time will tell as to the quality of the end results. He told me that he was going to put several clear coats over the paint so that it would stay shiny instead of that dull off white color it has now.

 

[Coalsmoke]

Sounds good. I think I'll be doing my own paint this summer. There are a few dents and scratches I'd like to take care of.

 

[jelag]

For us there was no MPG change... . we got a harsher ride, but cut tire costs in half, and have safer vehicles because of the added load capacity. .

I posted the following on another thread:::

I run 225/70?/19. 5 on all my trucks... . I've got at least a million miles experience doing this with steel wheels and many trucks... . I started with a F550...

We run new Bridgestone or Michelin on the front and Bandag re-treads on the rear... and have never gotten less than 100K on the fronts and 90K on the rears... The fronts are rib steer tires and the rear recaps are the all season tire used by UPS here in Spokane... .

We ran the F550 for 500K miles, and its gone the other trucks have various mileage with the lowest, the 5500 at 110K miles... .

We currently have 4 trucks doing this... 04 3500 dually, 04. 5 SRW, 05 3500 Dually and 08 5500. . What ever the stock tire that was on the F550 and the 5500 is the tire size we use...

We've never had a blow out, and I can't remember a road hazard but some flats that were repaired...

I can't imagine a 265 on a dually but surly on a SRW 2500 or 3500...

These tires are a little taller and put the speedometer right on compared to a GPS.
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