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I'm currently running 235/40 (maybe /45) on 17x8.5" wheels with a 40mm offset on my E36 M3. I wanted to consider stepping up to a wider tire until someone asked a great question, "how wide do you want to go".

Well, it's a great question. How does one go about deciding this? For performance considerations, is there too wide a tire? Anyone have guidance, experience, articles, etc that could help me answer this?

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Phil... Now I miss the ITR and the M3!!!
1990 Honda Civic SI

The practical answer for your application without destroying the fenders: Not really.

It usually comes down to a heat-related factor (as in "can't get enough") assuming you don't run into packaging constraints.

Jim

If you go post on Bimmerforums track forum you'll find lots of people who swear a 235 is better than a 255 on track.

I don't buy it. I think they aren't trying hard enough. Wheee!

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Mike Whitney
whit32@gmail.com, 919-454-5445
V10, V8, V8t, I6, I6, V6, F4t, I4, I4, I4, I4, I2, 1, 1

It's possible if the rest of the parameters are goofy (or they are comparing across brands) but I don't buy it either in general.

There was a good bit of chatter last year about using the "new" 275/35-15 Hoosier in colder conditions and how some of the lighter cars couldn't get enough heat into them. In some of those cases, "275" was probably too wide but with a 3000+lb BMW, I don't think that is going to be an issue.

Jim

Probably not an issue in your car since it has HP, but on my Miata I thinks that he 245/15 are too big for my meager hp. The car is real stable, but just does not have enough hp or torque for that size tire. When those go away, I will drop back to 225's or 205's

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1990 Faded Reddish CSP Lite Miata
2002 Electron Blue Corvette Z06
2005 Mazda 6 Wagon
2003 Nissan Pathfinder DTV (Dog Transport Vehicle)

Grassroots did a test that indeed showed you can go too big. They did stock, 1 plus and 2 plus. I don't remember all the details. I know they went up in wheel size. Not sure if they tested using the same wheel. My guess is the weight of a larger wheel and tire does cross a threshold of diminishing returns at some point. Grassroots recorded poorer braking with the largest set up as well as slower course times. Finding that point will take trial and error.

I love Grassroots, but their tire test methodologies are often fairly flawed. Rarely are you going to lose performance on any car over 3000 pounds going to whatever tire will fit in the wheelwell.


--Donnie

If we're talking about the test in this month's GRM, that test wasn't really about changes in tire width as much as it was about changes in sidewall height and the effects of rotational inertia in larger diameter wheels. The 17" wheel and the 18" wheel both ran 225 width tires.

I also agree w/ Donnie on GRM's tire testing methodology. It's a little tortured.

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Tom Freeman
'98 M3/4/5 | '93 Spec3 325i | '12 TSX sport wagon | '03 Tahoe
Team Silver Bullets '91 240SX

What other source would you and Donnie look to for info on tire testing????

Unfortunately, there isn't much. I'd say that if you are interested in their results, then scrutinize what they did very carefully to see if you feel like their methods were similar to how YOU would use the tires. If so, you're probably okay with their results. Even then, find someone who has more experience than you with the type of racing you do in the type of car you have, and ask them their opinions of the results.

But the only true way to be sure is to do your own testing. I understand that isn't possible in everyone's budget, but if your budget is the limiting factor in whether you can test at all then you're probably looking for decent performance tires with really good life. You can usually figure *that* out fairly easily. If you're splitting hairs trying to find that one tire that gives great life and still outperforms other similar tires by some small margin, well, give it up. Work on the driver more and get the tire that fits the budget the best.


--Donnie

Or run in a series with a spec tire...problem solved.

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Jim Pastorius
2008 Silverado VortecMax
1992 Camaro CMC#92
2002 BMW R1150R

2009 3rd Place CMC Mid-Atlantic Championship
2009 CMC Hyperfest Winner

I know Bryan and I don't have unlimited budgets to test tires, but we do a lot of analytics on gearing and weight distribution to tell us what we think would be best. If the tire turns out to be the wrong setup, we suck it up and run it until it's dead and try something else.

With the Crossfire, we have 4 rear sizes we can run, from 235's all the way up to 315's. A lot of the choice does factor on how you drive the car too, thus copying setups I think is not always the best option. It may be a good starting point, but in the end, everyone's setup should be different in order to optimize handling. - AB

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'14 Toyota Sequoia Platinum 4WD
Super Westerfield Bros - '93 Integra - LeChump Du Jour
STX 93 - Scion FR-S

Thats a great point. The most important thing is being comfortable and confident with the car and its characteristics at the limit. Since my goals are to limited to having fun, I don't deliberate as much as some with more competitive goals in mind.

Grassroots' testing may not be perfect. I don't think there is a perfect way given so many performance variables. But I think GRM's anecdotal feedback is valuable enough to not completley discount.

When GRM did their "track tire" test around their go-cart track facility a while back, IMHO, that was their worst test. I simply don't think that was an accurate representation of what a tire really goes through on a road course.

Their auto-x tests are much more representative, however. They're pretty spot on.

I lurk around enough forums that I sometimes pick up feedback from some top level auto-x guys who do have the budget/time to do some more "apples to apples" testing. I also keep an eye on auto-x results from national events and see what the hubbub is when a new tire shows up and performs well.

Neither of those are terribly scientific, but combine that with something like a GRM test, and you'll end up with a little more broadbased data to make your decision from.

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Tom Freeman
'98 M3/4/5 | '93 Spec3 325i | '12 TSX sport wagon | '03 Tahoe
Team Silver Bullets '91 240SX

Hrm. I take issue with the above. That's only important if you are actively working to improve the driver and nothing else. Well, in some cars with some driving styles, it may be that the comfortable way happens to be the fastest way. But in many cases, the comfortable way may not actually be the fastest way around.

For autocross, if you have no ability to do a test and tune, then it probably is. But you should take opportunities at test and tune events to try things not just outside your comfort zone, but WAY outside your comfort zone. And look at the clock. Try lots of random things and keep an eye on that clock. You might just stumble into something that doesn't feel right, but is noticeably faster. And we're out here to go fast, not be comfortable, right?


--Donnie