Tire/Wheel Help

[sdwindansea]

Well, we are two and a half weeks away from picking up our SMB in Fresno. It is an E350 RB diesel with the SMB 4x4 conversion. We have not done anything else customized as far as the 4x4 system goes. Also we have elected (at least for now) to stick with the factory wheels (16 x 7) and tires (245/75/R16) in order to save some upfront money. Also, I was told you get almost no credit for swapping the tires/wheels, so I figured I would put some initial wear and tear on them.

I have always been under the impression that this was something I can easily upgrade later, especially if I don't change the size of the wheels. Of course I'm now having some second thoughts and some questions. I should preface this by stating that I'm pretty dumb when it comes to tire/wheel size combinations and the effect on the vehicle, speedometer, etc. So, here are my questions...

1 - Will I have any problems upgrading to a 285/75/R16 tire later on (or a 27/75/R16)? Will these fit on the current rims? Will any type of speedometer recalibration be necessary?

2 - Will I have any problems airing down the stock 245/75/R16 tires for beach/washboard driving?

3 - Assuming I never want to upgrade to 17" wheels, are there any limitations to my current situation that I'm not considering? This does not include the appearance of the exterior van initially

Thanks for the help/advice.

[jage]

This is my favorite online "Converter" because it give you a graphic too.
http://www.miata.net/garage/tirecalc.html

You don't have to do this by hand, but so you understand what is going on with the numbers:
245 - this is the "section width" in millimeters. Divide by 25.4 to get how many inches wide your tire is.

75 - this is not a measurement, but a percentage. It is percentage of the width, in this case 75%. What it means is your sidewall (the rubber) is 75% as tall as the tire is wide. So it depends on the tire width.

R16 - simply the rim size. A 16" rim.

To get total diameter you have to use all these numbers, but the calculators will do that for you (I included another one below).

So any tire with an R16 number will fit on your 16" rims. It's probably safest to stick within an inch or two of width wider then your current tire but when you get closer you can actually worry about that. There are plenty of sizes so picking tires and/or rims later is not a problem.

Going up to 17s is no problem there is just more space, but the spec will be R17 for the last number.

For just one tire and no graphics try:
http://www.s-series.org/htm/calc/tiresizeconv.htm

[Jeffrey]

SD, I hate to tell you this, but it is almost assured that you will want larger tires SOON. And those stock wheels only go so far. Fortunately, they can be had locally when you are ready.

I was sure that 33's were going to be just fine until I visited SMB and looked closer. The size, weight and performance of a 350 Ford with SMB 4x4 really uses the 35"s well. And having just spent a bit of time on rough rocky trails in low 4x4, they really helped. I've got 31's on my Land Rover, but the big guys just kept rollin' on.

[sdwindansea]

Thanks Jage and Jeffrey - another couple questions.

Is there any advantage to getting new tires/wheels now (before pickup) as opposed to locally later on?

I know the larger tires are better off road, however, what about on road use? The SMB will also be my daily driver, so I'm guessing it will ultimately see about 80% on road and 20% off road use.

Am I missing anything else in my thought process?

[Jeffrey]

SD, you're on the right track.

There is something very nice about picking up your van all ready with the wheels/tires of your choice. One less future big hassle to eliminate. Plus, SMB will calibrate the speedo, which is a valuable service to get.

Daily driver and still 20% off road use? More power to you. I wish I had that ratio!

[sdwindansea]

Thanks again Jeffrey - I'm waiting for some specs/pricing from Greg at SMB. The biggest advantage to not getting the tires yet is that we don't have a trip planned for several months so I can wear out the factory tires a bit. Plus, that is a lot of money I don't have to pay right away which should help the vehicle registration fees in CA a little bit (although not enough to make that a real reason).

I realized my 80/20 ratio is way off. For some reason I was day dreaming of our past trips down to Baja.

[jage]

I'd say warranty might be an issue. I don't know what SMB is doing these days but with Discount Tire refusing to work on vehicles with spacers, having the tires put on by a company that will honor their warranty might be worth it to wait.

[sdwindansea]

Thanks Jage - that is a good point. I've never changed the wheel/tire size on any of my past vehicles. Is there a lot involved in doing this, besides recalibrating the speedometer? Are there many tire shops that will do this?

I currently drive a Chevy Avalanche Z71. It has 17" wheels and is equipped with 265/70/R17 tires (Bridgestone A/T). This has been fine for everything I've ever wanted to do (on road travel, moderate off road, mud, snow, beach driving, etc).

Since I will probably never take my SMB in conditions more "extreme" conditions than those where my Avalanche has gone, what tire size and wheel size would people recommend? Also, remember that a large majority of time will be spent on pavement. Finally, I don't want to spend even more money because I'm forced to change gearing, braking become inadequate, etc.

Thanks again...this is my final hurdle before picking up the van in 2.5 weeks.

[jage]

2.5 weeks to go, you're a little late to be thinking about gearing!

The SMB 4x4 comes with 4.10 gears. The 35" tire package may be different, but I doubt it (Jeffery do you know?)

The 4.10 gears are well suited to the 285/75/16 tires which makes me think you're going to be a little high in the revs department, but it looks like less than 10%... still I'd take it easy on the hammer and top speed until you get new tires. Probably nothing to worry about Ford probably makes factory vans with this combination (4.10 are as stock option and those tires are a stock size.)

I think I read somewhere on here that speedo calibration is a chip on the tranny, some thread about 4x4 lo registering the wrong speed. Any dealer or superchip owner should be able to program a new calibration.

I'd go with your original plan and run the stock tires. Take it easy a bit and upgrade when you're ready. If you're ready by the time you get home from SMB you haven't lost much over doing it there. If not you can probably live with the stockers a long time. You'll have time to consider rims and tires, even other sizes, while you own the van.

You can also keep your eyes open for deals on used tires. Guys who wheel are changing up all the time and sometimes a good deal comes up on just what you need. I saw a set of 35s with 80% tread for $200 yesterday and was almost tempted to lift my Jeep 2" more just to take advantage of the deal!

[kenkillsr]

I have to agree with Jage ["below"] on taking delivery with stock tires/wheels.
In fact, I just replaced my oe tires in kind.
If I ever decide to change sizes, I'll be keeping the same diameter, [rev. per mi.] as nearly as possible trading up to 17's or 19.5's strictly for the increased weight carrying capacity.

Ken


"I'd go with your original plan and run the stock tires.
Take it easy a bit and upgrade when you're ready.
If you're ready by the time you get home from SMB you haven't lost much over doing it there.
If not you can probably live with the stockers a long time.
You'll have time to consider rims and tires, even other sizes, while you own the van.
You can also keep your eyes open for deals on used tires.
Guys who wheel are changing up all the time and sometimes a good deal comes up on just what you need.
I saw a set of 35s with 80% tread for $200 yesterday and was almost tempted to lift my Jeep 2" more just to take advantage of the deal!"