New Wheel / Tire Tech Ariticle - Errors?

[wret]

I recently posted a tech article to help the uninitiated in their wheel and tire size selections. I’ve received word that there is at least one error. If anyone else can spot any errors or inconsistencies, please point them out and I’ll edit the tech write-up. Thanks.

http://www.dsmtuners.com/forums/showthread.php?postid=792976 - post792976

 

[jtmcinder]

I like the article and hope that it helps to prevent us from having to answer the same questions again and agin, but have at least one quibble. It concerns offsets for 2Gs:

Tire Width Max Offset
225mm 46mm
235mm 41mm
245mm 36mm
255mm 31mm

My quibble is that the offset that you need depends not just on the width of the tire, but also on the diameter. Here's why: on the inside, the first thing that will be hit on a 2G is the vertical link (aka spindle) in the rear. But the vertical link curls over the tire at the top, such that it's at about a 45-degree angle to the tire as it wraps around the corner of a stock-sized tire. So, the smaller the tire (diameter-wise), the less you have to reduce the offset, because the tire will be lower and, hence, farther from the part of the vertical link that wraps around and over the tire.

Example, while a 245/45/17 tire might need a 36mm offset (I'm not really sure, but that sounds about right), a 245/40/17 does not. In fact, my strong favorite street set-up for 2Gs is 245/40/17 on a 17x8 wheel with a +40mm offset.

There are three reasons to maximize offset for the tire that you wish to run. First, it reduces the amount that you have to roll the rear fender lips (if at all). Second, it lowers the stress on the wheel bearings. And, third, it keeps more of the tire under the car, which reduces damage due to stones being picked up and thrown.

All in all, however, a nice tech article. Well done.

- Jtoby

 

[wret]

Okay, just for kicks, try this formula


260 – (D+W)/4 = Max offset mm

D=Tire diameter mm
W=Tire width mm

Conversions:
http://www.sdplastics.com/measure.html

 

[hoffman]

Nice.

I agree with Jtoby also. If you were to take some extra time and figure the rim size to offset conversion for 15s through 18s (since those seem to be the most popluar sizes) it would eliminate alot of the threads that come in here.

Again. Nice job.

 

[wret]

The formula I posted above was a little off. I think it should be like this:

481 – (D + W) / 2 = Max offset mm

Based on that formula I created a table for various wheel and tire size combinations. I am assuming a minimum tire clearance of 4mm. It’s been a long time since geometry/algebra class so maybe someone can help clean up the formula if required.

Can anyone come up with a wheel/tire combination that doesn’t match this chart?

Tire Size MaxOffset
205 35 16 104
205 40 16 93
205 45 16 83
205 50 16 73
205 55 16 63
215 35 16 95
215 40 16 84
215 45 16 74
215 50 16 63
215 55 16 52
225 35 16 87
225 40 16 75
225 45 16 64
225 50 16 53
225 55 16 42
235 35 16 78
235 40 16 66
235 45 16 55
235 50 16 43
235 55 16 31
245 35 16 70
245 40 16 57
245 45 16 45
245 50 16 33
245 55 16 21
255 35 16 61
255 40 16 48
255 45 16 36
255 50 16 23
255 55 16 10
205 35 17 91
205 40 17 81
205 45 17 70
205 50 17 60
205 55 17 50
215 35 17 82
215 40 17 72
215 45 17 61
215 50 17 50
215 55 17 39
225 35 17 74
225 40 17 63
225 45 17 51
225 50 17 40
225 55 17 29
235 35 17 65
235 40 17 54
235 45 17 42
235 50 17 30
235 55 17 18
245 35 17 57
245 40 17 45
245 45 17 32
245 50 17 20
245 55 17 8
255 35 17 48
255 40 17 36
255 45 17 23
255 50 17 10
255 55 17 -3
205 35 17 91
205 40 18 68
205 45 18 58
205 50 18 47
205 55 18 37
215 35 18 70
215 40 18 59
215 45 18 48
215 50 18 37
215 55 18 27
225 35 18 61
225 40 18 50
225 45 18 39
225 50 18 27
225 55 18 16
235 35 18 53
235 40 18 41
235 45 18 29
235 50 18 17
235 55 18 6
245 35 18 44
245 40 18 32
245 45 18 20
245 50 18 7
245 55 18 -5
255 35 18 36
255 40 18 23
255 45 18 10
255 50 18 -3
255 55 18 -15
205 40 19 55
205 45 19 45
205 50 19 35
205 55 19 24
215 35 19 57
215 40 19 46
215 45 19 35
215 50 19 25
215 55 19 14
225 35 19 48
225 40 19 37
225 45 19 26
225 50 19 15
225 55 19 3
235 35 19 40
235 40 19 28
235 45 19 16
235 50 19 5
235 55 19 -7
245 35 19 31
245 40 19 19
245 45 19 7
245 50 19 -5
245 55 19 -18
255 35 19 23
255 40 19 10
255 45 19 -3
255 50 19 -15
255 55 19 -28

 

[jtmcinder]

I can only comment on a few of these.

245 45 16 45

I doubt it. I run 245/45/16s as my race tires and they are on +38s and they are darned closed to the vertical link. I can't see a +45 working.

245 40 17 45

These are my summers. They are on +40s. I doubt that I could get away with a +45. And if I had a brand other than Kumho, I doubt that even the +40s would work. It's that close.

215 50 17 50

This is stock on a premium 1997. The stock wheel is 17x6.5 +46. I think they had more extra space than 4mm.

So, all in all, I don't think that your formula is working. To soften that statement: many people have tried to create such a formula and they have all failed. That's why there are so many lists out there about what works and what doesn't.

Why can't everyone with a 2G just get 245/40/17s on 17x8 +40s and be done with it?

- Jtoby <- unAmerican repressor of personal expression

 

[wret]

Thanks for the feedback.

If anyone could take the time to check the clearance on their set up and post it with their tire size and offset it would be appreciated. Just roll a drill bit over the top side of the tire between the tire and spindle. Also note your degree of tire wear, as a new tire will obviously have less clearance than a worn one.

 

[TSiAWD666]

I'm guessing I'm the one DSMTuners.com member with the 255s, hehe. They fit fine relative to the suspension with a +35mm offset. Seeing as that's the case I'd guess your 245mm calcuation stating a required offset of +36mm is probably a bit off, as there was plenty of room on my older 245mm tires (otherwise I wouldn't have tried 255s).

 

[TSiAWD666]

Oh, your article lists the lug pattern as 5x114.4. This should be 5x114.3. I'd hate for a new guy to freak out that his DSM has a pattern that no aftermarket wheel makers use

 

[wret]

Originally posted by TSiAWD666
I'm guessing I'm the one DSMTuners.com member with the 255s, hehe. They fit fine relative to the suspension with a +35mm offset. Seeing as that's the case I'd guess your 245mm calcuation stating a required offset of +36mm is probably a bit off, as there was plenty of room on my older 245mm tires (otherwise I wouldn't have tried 255s).

Thanks for chiming in. I was hoping for some input from some extreme cases. According to my formula your setup is 1mm less than the max offset for that tire size. Any chance I can get you to check your clearance?

I guess I should check multiple references on specs. Got the 114.4 from vfaq.com. I'll edit to 5x114.3. Thanks.

 

[MNGSX]

Read this



http://www.prostreetonline.com/pso/pages/techtips/showarticle.asp?articleid=9

 

[wret]

Hey, thanks. Good stuff. The problem with his calculator is that he attempts to take diameter out of the equation by stating that one should stay with stock diameter or below. If the control arm runs over the tire at 45° (and it seems to be pretty close), then one mm more tire radius would require 1mm more offset to maintain clearance, all other things being equal.

I found a couple of the setups listed particularly interesting: the 235/45/17's with 44mm offset. One reported rubbing and one reported 2mm clearance. My table suggests that 42mm is the max offset for this tire size (leaving a 4mm clearance).

 

[TSiAWD666]

I would think that would be accounted from the fact that tire manufacturers measurements vary, since there's no real standard as to what their measurements are relative. In light of this there should be a big note in your guide that if you're cutting in close with the estimates you'll need to try it to really be sure a specific tire will fit with a specific rim.

 

[wret]

Good point. I'll add some cautions and disclaimers.