2nd Gen Non-Engine/Transmission 215 to 235 tires

[rschwiesow]

I just put 235 on my 99 3500 from 215 but I have done allot of looking through the treads and have seen allot of talk about the speedo correction units. Also that the dealer can re-program the PCM? I have a gps and found that the speedo says 65 mph but actually doing 70 so I have a 7. 14% difference. The reason I went to higher tire was for improve mileage. I now have a 135,000 on the truck and have averaged 16 mpg with no load. But at the same time the dealer has put 5 yes 5 new transmission and yes it is a auto. I do not haul anything except a truck camper 30% of the time. I had a TST but took it off and seen my transmission problem go away and even seen better MPG. My question is what is the truth can the dealer make the changes or am I better to purchase the correction unit?

 

[BillGotthelf]

I think if you read the posts in here EVERYONE who has an auto is told to get the trans upgraded because it will not handle much more power than stock levels. If you got the tst powermax box you could add up to 60% more hp than stock. Don't blame the trans. Also with the larger tires you may develop a rubbing between the dualie tires which in extreme cases can cause tire to blow out at speed. As the load increases the tires squat and the sidewalls rub together. This rubber on rubber creates high temps and the potential for blowouts-not good if your hauling your camper.

 

[rschwiesow]

Thanks for the reply.



I guess I should explain a little more in detail about the history of this truck. I kept this truck stock from the day I picked it up in Jan 99 until I reached a 105000 miles. The first transmission went out at 23000 the second at 42000 and the third 68000 the forth at 69000 bad transmission from dealer. and the final transmission was replaced at 98000 and have had no problems sense then. I put the TST after 100000 miles on that was recommended by Cummins to improve MPG. This did not work and seen the transmission slip so of it came. I got the Idea for the taller tires from the treads. As far as I can read that the 99 yr is the only yr that 215 were put on the dully. All years after that were 235 and the same rims are used. If this is correct rubbing should not be an issue unless someone can tell me different. I just joined TDR last month and cant get enough information. I was bound to get rid of this truck but I like it to much with the camper. I am learning about the transmission mods and I Live in Wisconsin so I need information on who to go to in this area?

 

[stownsend]

215's??

You were running 215's? What's stock? I would think that with 235's you are closer to the stock speedo calibration than with the 215's.

 

[rhelms]

I put the 235's from my '02 on Dad's '94. We drove 'em together for a few miles, talking on the cel phones, to verify the speedo change.



The difference on the '94 running 235's (it is calibrated for 205's) is 5 mph.



Pop's has a habit of driving 5 mph over the limit, I suggested he start driving the limit or he'll be paying a lot more than the cost of the calibration in speeding tickets.

 

[willyslover]

215's were the stock size tire until the disc brakes came out in 01. 5 and then they went to 235's. . the rims have a deeper ofset to accomidate... however running 235's on the old rims is just fine as long as it's 235x85x16... and have a stiff side wall... I ran several sets this way. . on my old rig and friends...

I would get the programer sold out of several places [get a copy of any JP magazine or 4 wheel off road and they are listed in the ads. ]... I would not have the dealer touch your rig !!

 

[rschwiesow]

Thanks for the input I really appreciate it. I will be buying a converter this week. With the math calculations I just added

2 MPG by going to 235x85x16. I am really pleased with the performance. The next Item on the list is to update the transmission.

 

[dcochran]

In fact the 235's became stock on the Y2K 3500's which have the rear drum brakes. DC in their infinite wisdom however, neglected to add some width to the rear fenders and, as a result, the outer tires extend beyond this "protective" fender and even mudflaps are hard pressed to completely block debris comming off the rear wheels.

 

[pwr2tow]

rschwiesow,

I was thinking of adding 235/85 tires to my dually and I would like to ask you a question.



1. When your going 65 MPH out of overdrive in third gear locked up what RPM's are you turning? I would need the corrected speed from you GPS to read 65 MPH.



2. Did you notice any decline in performance while towing with the bigger tires?



If you or anyone could help me on this I would greatly appreciate it.



Thanks,

Ron

 

[monkfarm]

switch

There is a switch (I have no idea where it is) that adjusts the speedo, but I think it is for the difference between the 1500, and the other trucks (3500) included. So yours is probably already adjusted. I found this out because the puke dealership where I bought it (Lakeville Dodge--Lakeville, MN) had no clue that the switch existed. It turned out mine was switched wrong (Chrsler Winona (Winona, MN)) found the problem.

Other then that there is a device that will adjust your speedo, but I cannot remember what it's called and how it does it (about $150. 00) Maybe someone else can help us out remembering, or you could do a search forums for speed adjustment.

 

[Ncostello]

To stay along the same lines as this topic, can I install LT265-75R-16's on my 99 2500? It has the factory steel chrome wheels. I have 245's on it currently. I found a good deal on 4 Goodyear Wrangler ATS's that were on a 2001 2500 4x4 (360 V-8) with the factory aluminum wheels. They only had a few hundred miles before he put on mudder tires. I didn't want to screw up the speedo... and I would like to lower my rpms just a hair on the highway.

 

[time1]

I have an excel sheet that I got of the net several years ago. I don't know who the original author is. It allows you to play the what if game with respect to different tire sizes and rear end ratios. I am sure that there are no viruses in the file and there are no macros to cause cause problems. If any one is interested please email me directly and I will gladly send a self extracting file for you to play with.