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buck n duck

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Posted: 07/29/21 07:32am Link  |  Quote  |  Print  |  Notify Moderator

Has anyone replaced the factory 235/80R17 with 255/80R17? It looks like they are 1.2" taller and .7" wider. If so do you have plenty of space between the rear wheels?


Brian

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Posted: 07/29/21 08:31am Link  |  Quote  |  Print  |  Notify Moderator

You have to maintain the proper distance between the Duals to prevent sidewalls from touching, which is BAD.
Some add bigger tires by adding a spacer between the wheels. I think I'll keep my OEM size.


2018 Chevy 3500HD High Country Crew Cab DRW, D/A, 2016 Redwood 39MB, Dual AC, Fireplace, Sleep #Bed, Auto Sat Dish, Stack Washer/Dryer, Auto Level Sys, Disk Brakes, Onan Gen, 17.5" "H" tires, MORryde Pin & IS, Comfort Ride, Dual Awnings, Full Body Paint

Durb

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Posted: 07/29/21 08:38am Link  |  Quote  |  Print  |  Notify Moderator

I have 1" spacing between tires on my 235/80 tires. This is at 55 PSI and unloaded. Going to a larger size will reduce that to a little over 1/4" unloaded. Seems like that spacing would be perfect for catching rocks and grinding them into the sidewalls.

There is a dually that roams around our town that has monster tires that stick out around 5" past the wheel wells. I assume he has special wheels or spacers.

The 1.2" taller calculates out to 4%. That is 4% less acceleration and braking performance.

n0arp

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Posted: 07/29/21 09:13am Link  |  Quote  |  Print  |  Notify Moderator

Over on a Cummins-specific forum, lots of people are running 255s and as long as they keep adequate pressure in them, they don't come near touching. Personally I wouldn't, but plenty of people do. There are several threads on it over there. Some run quarter inch spacers. There are a few people who go all the way to 285s with a 1" spacer, which is getting dangerous.

If you want a bigger/wider tire, you really need to replace the wheels with something like DDC or American Force forged, and be sure to consider the weight carrying capacity. The 17x6" isn't wide enough to put a 255 on, at least according to most manufacturers I've seen, who call for a 6.5" minimum width. Some chain, or more reputable tire shops might refuse to mount them.

You could also go to 19.5s. I'm running 245/70r19.5 on 19.5x6.75" wheels. For other reasons, they're equally annoying to get mounted.

* This post was edited 07/29/21 09:36am by n0arp *


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Cummins12V98

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Posted: 07/29/21 10:00am Link  |  Quote  |  Print  |  Notify Moderator

Taller tire means less towing capacity.


2015 RAM LongHorn 3500 Dually CrewCab 4X4 CUMMINS/AISIN RearAir 385HP/865TQ 4:10's
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n0arp

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Posted: 07/29/21 10:05am Link  |  Quote  |  Print  |  Notify Moderator

Cummins12V98 wrote:

Taller tire means less towing capacity.


If you're talking about gearing, yes, but the impact here is relatively minimal. Otherwise, a proper wheel/tire combination could be taller and still (theoretically, for the weight police here) increase towing capacity by increasing the payload capacity.

235/80r17 = 31.8" (factory size on DRW)
255/80r17 = 33.1" (discussed here)
275/80r18 = 33.2" (factory 18 on SRW)
285/60r20 = 33.0" (factory 20 on SRW)
245/70r19.5 = 33.3" (what I run, and mentioned above in this thread)

So all things considered, going to the 255/80r17 will provide the same final drive ratio as a factory SRW with the same drivetrain/gearing. I don't consider that a big deal. Use AlfaOBD to reprogram the tire size if you want all the shift points, etc to be exact.

You could go up to a 35" with your 4.10s, and be right at 3.73 which is a very common ratio sold on Rams that tow heavy.

* This post was edited 07/29/21 04:54pm by n0arp *

SweetLou

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Posted: 07/30/21 07:26am Link  |  Quote  |  Print  |  Notify Moderator

Cummins12V98 wrote:

Taller tire means less towing capacity.
But you can go faster to where you are towing [emoticon] (Mushroom cloud)


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Cummins12V98

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Posted: 07/31/21 09:51am Link  |  Quote  |  Print  |  Notify Moderator

SweetLou wrote:

Cummins12V98 wrote:

Taller tire means less towing capacity.
But you can go faster to where you are towing [emoticon] (Mushroom cloud)


COOL!!! That means my real top speed of around 103 may be 105 or so.

whjco

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Posted: 08/01/21 06:53pm Link  |  Quote  |  Print  |  Notify Moderator

buck n duck wrote:

Has anyone replaced the factory 235/80R17 with 255/80R17? It looks like they are 1.2" taller and .7" wider. If so do you have plenty of space between the rear wheels?


Is your truck a 4 x 4? If so, you'll need to replace all six tires as they must all be the same size.


Bill J., Lexington, KY
2006 Starcraft 2500RKS 25' Travel Trailer
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ksss

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Posted: 08/02/21 07:40am Link  |  Quote  |  Print  |  Notify Moderator

I think even a 4X2 needs the same size for the ABS to work correctly.


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