Wheel and tire change - check my math for me!

I think I now have an accidental degree in tirenometry or wheelgebra... whatever advanced math it takes to figure out what happens when changing wheel specs and tire sizes.

I'm trying to determine how much further out the new wheel and tire setup will be.

Current; Stock:

• Wheels - 20" Limited
• Wheel width - 7"
• Wheel offset = 15mm
• Tires - 245/60/20

Planned:

• Wheels - 17" TRD Pros
• Wheel width - 7"
• Wheel offset = 4mm
• Tires - 285/70/17

Assuming those specs are accurate, my math says...

• 245s to 285s = 40 mm or 1.6" wider
• 15mm offset to 4mm pushes the wheel out 11mm or .433" more than stock.
• .433" (additional offset) + .8" (half of additional tire width) = 1.23"

NET: 285s on the TRD Pros will be 1.23" further out.

Does that sound right?

 

Yes, your math is correct. Congrats'. You're a genius.

 

Can you please tell me why is this important to you? Are you trying to figure out if you will have any rubbing? Or concerned about the looks.

 

Fair question! Mainly the look/stance. Pushing the tire out 1.2" is getting pretty close to being outside the fender. I'm just not a fan of tires poking beyond the fenders on otherwise stock/mild builds.

 

Just a thought, If you get TRD ORP (17 x 7.5 +15) wheels they still provide a decent poke and they are within spec to run 285/70R17 tires.

Vs TRD Pro wheels are not approved to run 285/70R17 tires and since TRD Pro (17 x7 +4) wheels are skinny the tires don't look wider to my eyes.. Both 4runners have 285/70R17 tires.

 

Thanks guys. If only I liked the TRD ORP wheels... I just really don't.

These could work - 17 x 7.0 x 15mm. Not 7.5" wide, but the 15mm is 2/3 of the battle.

Could have them media blasted and powder coated a bit darker, e.g., medium gunmetal gray (gloss)...

 

Go to "willtheyfit.com" and play around with different wheel and tire specs. I have a '23 Limited with 275/55-20s on the OEM 20x7 / +15mm offset wheels, planning on going with 17x7.5 / +15mm offset Sequioa wheels once I get them back from powdercoating ("signal brown" to match the redwood interior). I'm going to run 265/70 ATs, have new TPMS sensors / black lug nuts / different wheel center caps to complete the package.

 

Thanks @bronzestar1. Clearly, I didn't pass that wheelgebra class, because my math is different from WillItFit.com's math. But I'm not convinced I'm wrong. I mean, if the new wheel has a 4mm offset, that's 11mm more offset. So, right there the outer edge of the wheel is .43" farther out. Right? Then, the 285 is 40mm wider. That's 1.6" wider, add half of that to the .43" and the outside tire is 1.2" farther out. Right?

I can't see how the site it is getting to that "poke" number. Well, unless I'm misunderstanding what poke means.

 

stock wheels are +15mm and +4mm though...

 

That's what I used - my current OE Limited 20s are +15. I used 17" ORPs - 7.5" wide, +4mm. What am I missing?

 

I'm pulling this out of my ass but is it the backspacing? Your math assumes all the width is going out, right? Depending on the rim some could be going towards the center

 

I don't think so. The 285 is 1.6" (40mm) wider than the 245. I added .8 to the 11mm of increased offset - from 15mm to 4mm - .433" That nets 1.2"

I'm waiting for the reply, "Dude, that's not how it works. You take the..." to make it all better. ;-)

 

Oh I dont have that. I specialize in thin air guesses that are right so long as nobody has proof otherwise

 

Those really are the best.

 

FWIW, Here's a 285/70/17 on a -6mm offset wheel. It's pretty flush with the fender flare. Your setup should end up 1 cm further in, so it should be fine.

 

Here's more reference photos for OP.

17x7 +4 (TRD Pro 'SEMA' wheels)
285/70/17 Nitto RG's

vs

17x8.5 -12 RRW wheels
285/70/17 Nitto RG's

 

I believe "poke" on willtheyfit.com is referring to the wheel only. Not the tire. Which is certainly counterintuitive...

285/70/17s work nicely on the TRD Pro 'sema' wheels (17x7 +4.)
The tires will not be outside of the wheel well.

If you change your mind wanted them to "poke" outside the wheel well, you would have to add spidertrax 1.25" spacers.

This is fairly common and there are plenty of photos of this setup.

I like a little "poke" personally

 

A 285/70 should be ok on a 7.5" wide wheel, but IMO it's too wide of a tire for a 7" wide wheel. Will a 285 fit on a 7" wheel? Yes. Should you run a 285 on a 7" wheel? No.

 

Yeah you’re not wrong. it’s outside of most tire manufacturers approved wheel size for 285/70/17. Many people do it without issue though.

I believe a safer option is 275/70/17 for a 7” wide wheel. Definitely worth considering if you’re buying wheels specifically to run 285s

 

Damn - you guys are awesome. These pics help a lot. This definitely seems like one of those math vs real world don't always align situations.

One of the reasons I'm sweating the width, is that this truck is supposed to stay stock - just a tiny lift and some 33s... you know, stock... ish. Tires at or outside the fender line just change the vibe. I know that 285s on 7" wheels is outside the spec, and I may drop to 275s. But, it doesn't bother me that much... maybe as much as it should. Getting Discount Tire to mount them might be an issue... I should check.

I shattered the rule on my '84. These are FJ40 wheels - 15x5s with 33/10.50/15s. I think that's 265mm wide on a 5" wheel. But that setup has been popular for decades. Okay true, it's a 2,700 lbs truck that wouldn't exactly kill it on a slalom course.

 

Yeah tire shops may give you a little grief. If you tell them it’s a 7.5” wide wheel I don’t think they’ll bust out a tape measure to disprove you xD

@kmeeg made a great point earlier about wheel width. Crazy how much of a difference it makes visually.

Ime the wider wheel allows the tire to deform over obstacles and find grip too. This was an unexpected benefit for me. Also the wider track width makes the rig feel more stable when off camber. This was another pleasant surprise.

Personally I moved away from the TRD wheels because
1. Too narrow. 8.5” is ideal for most 285/70/17 tires.
2. Not enough offset and I didn’t want to run spacers

The RRWs fit the bill for me.

 

Well damn. I thought 7.5" was the minimum in-spec width. It would appear 7.0" is cool with BFG (I'm a BFG AT fan).


Finding a wheel I like that keeps the factory look isn't easy. Toyota made sooo many 17x7 wheels (6x139.7) but just a couple 17x7.5.

 

There ya go! I'm surprised that a 7" rim width is "approved" for a 285, but there it is!

 

These guys make PRO replica wheels that are 8" wide:

https://www.fnwheels.com/store/product/fn-wheels-fx-pro/

 

Anyone that gets these wheels will have to get new lug nuts, since they specify conical seat lug nuts. I believe the OEM lug nuts are mag seat style, so they won't work on these particular wheels.

 

I like those FN wheels, except for the 0 offset. If my math (here we go again) is right... 0mm vs. +15mm = .60" farther out. Add 1/2 the additional tire width (245mm to 285mm), convert that 20mm to 'merican... that's .8". So, the 285s on the FN wheels would be 1.4" further out. That's too much for my fancy Limited (that I told myself would stay mostly sorta stock).

 

I think it be would nearly flush.

0.6" more "poke" than the OEM TRD Sema wheels.
0.8" less "poke" than my RRW wheels ^

This might be one of the best options around to keep the factory look.

Thanks @Thatbassguy
I'll likely be recommending these wheels to ppl in the future.

 

Check tire manufacturer spec sheet.

BFG KO2 spec sheet -


Falken spec sheet -



Toyo Open Country spec sheet -

 

Well that is some consensus isn't it. Dammit. It's never simple. I do like the FN 17x8s. I'm gonna play with a straightedge, plumb bob, and abacus and see where I land.