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Got my 235 / 85's mounted!

Matt Bachand

Matt Bachand

Depends on the 6.5
Messages
5,330
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26
Location
Worcester, MA
Figured I'd share.

Went from 225/75 to 238/85's, they seem to be the exact same width, just a good couple inhces taller.

No rubbing, front end wise (as expected), and the gap between my rears remains the same at around a little over an inch.

I couldn't be happier with the gear reduction either.

It's about a 7% circumference gain (from a tire calculator website), and I do notice its not so ultra-torque at the line, BUT, This allows me to easily do 50-55 without shifting out of 3rd. IT feels so good to be able to do that without the engine winding up too high, and eliminates a 'rock and a hardplace' I had before where I wanted to get out of 3rd to avoid the high RPM's, (2500+) and dump into OD while about to climb a hill.

I've yet to use OD with them, but i'm a well trained dog on the highway, I have no problem cruising along in the right lane doing 50ish.

The height gain is obvoius too from looks, and from hopping in and out of the rig. I can tell i'm sitting taller.

The rear especially fills my wheelwells up now.

Wish my camera was never stolen and I'd post pix.....

Couldn't be more happier with my choice.

I'll have to tackle that VSS box soon to correct my speedo/Odo.

I was worried about the rear's rubbing, I hope this post helps someone else so their is absolutely no need to worry.

They measured close to the same width (around 8) as my olds, but its always tough to tell when they aren't mounted

So proud of the truck i bought her a few cans of rustoleaum gloss black, and hit the wheel wells and frame)

Not to mention tire-shine. Juiced them old skins up good.

I can't stop looking out the window at the truck now. LOL.
 
Good for you Matt, glad you finally got the new ones on. Just so you know, I've been running a 7% correction factor (285s in place of stock 245s) on my last 3 trucks for a combined 185k miles and never reprogrammed for it. I'm so used to it now I'd just confuse myself if it read right!):h
For figuring mpg I just multiply x 1.07 every time and I've never failed to calculate a tankfull in all that time...
 
btfarm said:
Good for you Matt, glad you finally got the new ones on. Just so you know, I've been running a 7% correction factor (285s in place of stock 245s) on my last 3 trucks for a combined 185k miles and never reprogrammed for it. I'm so used to it now I'd just confuse myself if it read right!):h
For figuring mpg I just multiply x 1.07 every time and I've never failed to calculate a tankfull in all that time...
Click to expand...

That means your truck has 100,045 miles on her! Congrats on breaking the 100k! :)

Reprogramming is merely for the TCC to lock up at appropriate speed. If it was reprogrammed, (which is easy to do on the 6.5 takes about 1/2 hour, just a few jumpers to move/solder) the TCC would lock up earlier, which may just make the benefit that much better for me, as I'm heavy, 9200-10k always...
 
Matt Bachand said:
That means your truck has 100,045 miles on her! Congrats on breaking the 100k! :)
Click to expand...
Nah... only from a warranty standpoint. Since it only has that many "rolling" miles I can't count it.):h Kinda like air speed Vs ground speed in an airplane.
Actually the odo will turn up 95k tomorrow or Sunday.
At 700+ miles/week, it won't be long to the magic # ;)
 
Matt Bachand said:
That means your truck has 100,045 miles on her! Congrats on breaking the 100k! :)

Reprogramming is merely for the TCC to lock up at appropriate speed. If it was reprogrammed, (which is easy to do on the 6.5 takes about 1/2 hour, just a few jumpers to move/solder) the TCC would lock up earlier, which may just make the benefit that much better for me, as I'm heavy, 9200-10k always...
Click to expand...
Not neccesarily. 3.42 geared trucks lock-up in OD at roughly 53-54 MPH, and 4.10 trucks lock-up at roughly 44-45 MPH and 3.73's lock-up right in between around 49 or so from what I have found. On the diesels GM was worried about lugging and the turb unspooling so lock-up is a function of RPM more so than speed on the 6.5.
 
Yes, 235s rock!!! Congrats.

On both my trucks the 235s were PERFECT size for the speedo. Checked with GPS.

Also I think the 235s are mileage champs. Report back on that as well :)

... I switched to 17s (265/70R17-E) which look good, but are harder on mileage for sure even thought the diameters are the same as the 235s.
 
Pillow said:
Yes, 235s rock!!! Congrats.

On both my trucks the 235s were PERFECT size for the speedo. Checked with GPS.

Also I think the 235s are mileage champs. Report back on that as well :)

... I switched to 17s (265/70R17-E) which look good, but are harder on mileage for sure even thought the diameters are the same as the 235s.
Click to expand...

That's because of the wider width. More rolling resistance.
 
Pillow said:
Yes, 235s rock!!! Congrats.

On both my trucks the 235s were PERFECT size for the speedo. Checked with GPS.

Also I think the 235s are mileage champs. Report back on that as well :)

... I switched to 17s (265/70R17-E) which look good, but are harder on mileage for sure even thought the diameters are the same as the 235s.
Click to expand...


Hard to say what it will do to my mileage, as now on the highway I defanately get a 'hum' from my rear outer's... Noise is a byproduct of inefficiency, as is heat. These tires have a lot more of a m/s pattern than ribbed. That alone can't help mileage. For a set of 6 tires costing 180bux total, they really are in spectacular shape.

2 are super beefy, brand new looking, but have to be at least 3-4 years old judging by the slight amount of 'dry rot' in the tread.

The other 4 were on some old D-Max'ers 5th wheeler, where 1 brake must have been working more than another, as the only reason he replaced all 4, was because one tire started to look worn.

= Score for me.

My TCC was locking up on me right around 49 with the new skins, exactly as you say 3.73's should be. Speedo was at its 45ish spot.

It's almost like the TCC is constantly adjusting its ratio of 'grab'? I can almost hold 2k rpm, and my speed increases gradually, but not in ratio with rpm's.

I never really paid close detail on other vehicles before on how this works.

When TCC does lock up, its clear as day, acting exactly like another shift.

Was getting highway runs at around 16mpg. City 12-14ish.

Of course i'll post about my new mileage findings.

Big difference here too, is the main reason I put these skins on was to be able to keep it in 3rd instead of going OD into bogmode. That May hurt me, or it may help me. If I have a decent highway run, I'll have to go 65or so to get near 2krpm in OD.

Aerodynamics is not a friend of my truck.
 
Go deal Matt!
I wondered when I bought my 225's if I should have gone to the 235/85/16's instead. Also wondering in the future I wanted to go maybe 22's with a 305/40/22. With these the height will be 32"! I was thinking a gear change will be neccessary when (if) that time comes. Sorry got more to ramble but the misses is rambling about a roach in the corner.....:mad2:
 
ak diesel driver said:
with 3.42 your geared pretty high probably sluggish till you get the rpms up.
Click to expand...

I know this wasn't 'geared' :) towards me, but in my opinion, from recent ratio change, these engines don't have much problem moving empty vehicle weight in low gears, 1,2,3 etc. Its the overdrive gear where they seem to have bogging issues.

Even now with my new size, in 3rd doing under 1500rpms, the engine doesn't feel bogged one bit under acceleration. Perhaps that is due to the TCC NOT being locked. In fact, that must be it. Its the OD bog that seems to have a bogging effect, to the point where the engine wants to downshift instead of accelerate.
 
Matt, sounds like you got a good deal on some new skins. If you wanted you can run a 265/75 on the front to help support your heavy truck and plow, there roughly the same height. I've done that before, you just cant rotate them to the rear though.

GJF said:
Go deal Matt!
I wondered when I bought my 225's if I should have gone to the 235/85/16's instead. Also wondering in the future I wanted to go maybe 22's with a 305/40/22. With these the height will be 32"! I was thinking a gear change will be neccessary when (if) that time comes. Sorry got more to ramble but the misses is rambling about a roach in the corner.....:mad2:
Click to expand...

I'd go with 275/45/22's, the 305's are a royal pain in the ars, dont ask me how I know.
 
midniteplowboyy said:
Matt, sounds like you got a good deal on some new skins. If you wanted you can run a 265/75 on the front to help support your heavy truck and plow, there roughly the same height. I've done that before, you just cant rotate them to the rear though.



I'd go with 275/45/22's, the 305's are a royal pain in the ars, dont ask me how I know.
Click to expand...

My 285's almost rub my mudflaps now, anything wider may or may not. Its been my experience that tall and skinny tires perform best for what I do.

I did well i think too on the cost. I just looked at the local craigslist everyday searching for 235 85 until i found em.

Didn't even bother trying to beat up the asking prices. Wish I had my camera still. Truck looks badass now.
 
I just put 265/75/16s on my 2000. No clearence issues course my back was a little sore cause I was too cheap to pay 100$ for mount and did them myself with tire irons. Damn I'm gittin old. Got Pro Comp AT extremes for 700$ to my door.
 
I would go get some 19.5's. . . 245/70R19.5 they come in 12ply F 14ply G 16 ply H load ranges.

Mike
 
Matt Bachand said:
I know this wasn't 'geared' :) towards me, but in my opinion, from recent ratio change, these engines don't have much problem moving empty vehicle weight in low gears, 1,2,3 etc. Its the overdrive gear where they seem to have bogging issues.

Even now with my new size, in 3rd doing under 1500rpms, the engine doesn't feel bogged one bit under acceleration. Perhaps that is due to the TCC NOT being locked. In fact, that must be it. Its the OD bog that seems to have a bogging effect, to the point where the engine wants to downshift instead of accelerate.
Click to expand...

You need a chip that seems to change all that:D
 
I just put new skins on mine; 285-75-16 on the rears and 305-75-15 on the front. They are about the same height as Matt's 235-85-16 at 33". They made a HUGE difference in the truck and how it performs. The cruise RPMs have slowed down about 200-300 RPMS across the power band and the truck doesn't seem to be working as hard. Overall, I am extremely happy with the size and it looks a hell of a lot better. I have been meaning to get pics up, but haven't had a chance to. I'll try and get some pics up later today.
 
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