Tire clearance w/245/70/19.5 tires?

[Heartbeat Hauler]

I am about due for new tires on my '01 dually and I am considering 19.5" wheels & tires. If I do go this way I was wondering about 245/70/19.5 tires as opposed to the 225/70/19.5. I know the 225's will fit, but not sure about the 245's on the front. All stock suspension (height-wise). Any input out there?

JP

 

[RayMich]

According to my calculations, the 225/70R-19.5 tires should fit with no modifications. the 245/75R-19.5 tires will be very close in size to the 285/75R-16 tires. They may require a little trimming, and very little raising of the torsion bars (if any) as long as you mount them on wheels having the stock offset dimension of +28 mm. (BTW - Rickson sells 19.5" steel wheels with +28 mm offset.)

Here are some dimension of all 3 tires compared to the 265/75R-16 tires that come with the 3500SRW and do NOT require any changes if mounted on wheels with stock offset dimension.

If you get wheel with ZERO or NEGATIVE offset, you will very likely require trimming and cranking of the T-Bars with all of these tires.

 

[RayMich]

JP,

I just realized that you have a dually; my comments about wheel offset were with respect to the 2500HD and 3500 SRW, so they will not apply to dually wheels. Here again, you will want wheels with offest as close as possible to the offset on the stock front wheels on your truck.

The tires sizes should be correct. So hopefully that should help.

As for the larger tires on a dually, you will probably need spacers for the rears unless the new wheels already take that into account.

Sorry for the confusion.
_________________________
EDIT:
Here is a size comparison between the OEM LT215/85R-16 vs the LT245/70R-19.9 tires.

 

[Heartbeat Hauler]

Sorry Ray. A little slow gettin' back to you with a response.....:errr:

I have looked at the specs on the 245/70/19.5 tires and realized that they were close to the 285/75/16s. I was also aware that the 285s usually require some trim work to the front. My hope is that even though the 245/70/19.5s are the same height as the 285/75/16s, they are 4 sizes smaller (width-wise) and may not rub. I don't really wanna do any suspension changes if I don't have to. I know I could just stay with the 225s, but if I'm gonna do this I'd like to do it the way I would like it.

Whadda ya think?

BTW, thanks for the visuals, I always do better with pics.....:thumbsup:
JP

 

[RayMich]

According to my calculations, if you keep the stock offset for the front wheels, you will need very little trimming and probably no suspension changes by going to the 245/70R-19.5 - Wheel offset can make you or break you with any tire/wheel change.

You are going to want to have a minimum of 0.50 inch clearance from rubbing when the wheels are turned to the angle where you get the smallest clearance to any component in the wheel well. Typically the low clearance points are around the bumper valance as well as the plastic fender liner on the LH side around the park brake cable. (check both sides to make sure) You may have to force the park brake cable back and tie it down to the body. Some times it may be necessary to also tie back the plastic fender liner itself. I would use some type of wire tie rather than plastic ties which will eventually stretch and break. Make sure you check your clearances with the truck on the ground with full weight on the suspension. After you make your adjustments, drive it over some bumps to see if you have any dynamic pinch points.

Here is a direct size comparison between the 285/75R-16 vs the 245/70R-19.5 tires.

Note that the unloaded diameter of the 245/70R-19.5 is a little bit taller, but the diagonal, which is what cause the bulk of the rubbing problems when turning, is a little shorter than the 285 tire.

Keep in mind that these figures are NOMINAL dimensions. Different tire makes may slightly deviate from these figures, but these will get you in the ball park. You should always check the tires and wheels mounted on the truck, before you make your final decision.

Let us know what you decide.

Good luck.

PS: don't forget that going to the larger 245/70R-19.5 tires and wheel will cause your speedometer/odometer to read approximately 8.5% too slow. In other words, when the speedometer indicates 60 MPH you'll be going around 65 MPH.

 

[Pepperidge]

he's got EFI live though...so he'll be able to compensate...

 

[RayMich]

he's got EFI live though...so he'll be able to compensate...

That's great.

I didn't see EFILive in his sig. That why I mentioned the speedo cal.

 

[Heartbeat Hauler]

he's got EFI live though...so he'll be able to compensate...

:yesnod:

That's great.

I didn't see EFILive in his sig. That why I mentioned the speedo cal.

I am just using it for "diags" :ihih: right now. I will get one free tow tune, and I would kinda like to do everything done at once. That is some really good info and diagrams. I appreciate it Ray.:thumbsup:
JP