Based upon some information in another thread, I have a question. How much would increasing your tire size from stock 245's to a much larger size (say 315s or 325s) increase your egts while towing on an LLY with a tuner (say for example a Hypertech on level 3)?

Say for example you did the same pull twice towing the same weight, but once with 245's and once with the larger tires. Assume somewhat hilly terrain, with some flat areas too.

Anyone have any experiences or estimations? I'm not looking for a egt temp , but an estimated difference in the temps during the two tows. A lot, not a lot, etc?

i just towed a est 11k friday! ive done this trip may of times and i personaly liked the whole feel of the truck much better with the 315 and 40hp tune vs stock. the truck seemed to pull much better at 73mph with the tune and larger tires than with 245's and stock tune as far as egts go i am sure they were higher in the hills but lower on the flats. thats just a wild gues. my engine temp went down while towing at a steady 73mph. so going by that i am asumeing the egts werernt all that bad! then again i doing have gauges so i cant tell you for sure.

swap from 31570/17 to 265/70/17.

temp drop for certain. towing 9k# cargo trailer with lotsa wind drag. up hills, with the 315's i was watching temps like a hawk.

drop to 265... very anecdotal evidence.... but i think 150-200* ish. probably because of the new gearing. when you tow heavy up a hill, and you see egt's rising and you start getting worried right when it shifts into 4th. rpm's go up high and the egt's start cooling real fast. not sure why the temps drop when that happens, but my rpm's are about 10% faster now.

big enough difference that i would feel comfortable just taking out the gauge with the 265's (low 1200's max), but not a chance with 315's (slowing down at about 1400).

<< Quote:
Originally Posted by TheMonkey
very anecdotal evidence.... but i think 150-200* ish. probably because of the new gearing. when you tow heavy up a hill, and you see egt's rising and you start getting worried right when it shifts into 4th. rpm's go up high and the egt's start cooling real fast. not sure why the temps drop when that happens, but my rpm's are about 10% faster now.



In my other thread that I posted a link to above, another person I was talking with was seeing high egts with the same programmer I have but I had 245's and he had 325's, so I would think he was seeing a lot hotter temps, wouldn't you?>>

very much so. my gearing difference between 265 & 315 is about 10%. i would think that 245 to 325 would be a bigger change in temps than what i'm seeing.

That is what I was thinking. So possibly the truck with the 325's could have been easily seeing 200-300 degrees higher egts than mine with 245s. That makes me feel better. If you read my posts in this thread you can see what I was concerned about.

http://www.dieselplace.com/forum/showthread.php?t=38937

Thanks for your help.