Jongbloed 15x10 On Track Car

[rwh11385]

2. stretch isn't always bad. GRM has proven, pretty scientifically I might add, that a 225 rival on a 15x8 is no faster on a track than a 205 rival on a 15x8. A 225 rival on a 15x9 on the other hand was significantly faster. Think about it. Stretching a tire has a "triangulation" effect on the sidewalls i.e. instead of bending to flex, the sidewall is forced to compress or extend, and can actually increase the contact patch.

Hey man... we don't need your science or facts here. We have the Google machine to show how stupid 205s look on 8" wide wheels, even if the actual picture is 195s and you may have personal experience with track-worthy 205s fitting fine.

Wow - bonkers. That rear wheel looks like a spare in comparison.




I have no need for that much (going the 15x8 route likely with 205's) but pretty neat.

[RoccoB517]

Just a quick update. I found an absolutely killer deal on a sticker set of 245/40r15 Hoosier R6's so I picked them up. So unfortunately no 275/35 for now. They are being mounted now, so as soon as I get them back I'll test fit and take some pictures for you folks.

The positive side to all of this is that I will run these 245's, then switch to 275 at some point during the season, then we will have some data to compare lap times, handling, and adverse effects on the flimsy chassis between the two different sizes on these 15x10's.

[robgoesvroom]

Thought I'd update as well -had a quarter life crisis and decided to buy an S2000 as my "daily driver". Also I'm spending money on "maintenance" items to get it road worthy.

Going to be performing a headgasket change on the S52 also, so don't hold your breath - you can expect a voltex wing mounted on my E30 soon.

Does anyone recommend any machine shops out in the LA area for headwork?


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[Apps]

Stretching a tire has a "triangulation" effect on the sidewalls i.e. instead of bending to flex, the sidewall is forced to compress or extend, and can actually increase the contact patch.

I don't wish to join the scuffle but thought I'd clarify a common misconception.

Stretching a tire or going to a wider tire size increases the cornering stiffness of the tire. Cornering stiffness estimates the slope of the lateral force vs slip curve in the linear regime. It actually doesn't have very much to do with contact patch size, but definitely affects vehicle handling and can affect contact patch shape.

For example, different rim widths can be considered between the front and rear of the vehicle to change the understeer gradient or balance.

The contact patch size has nearly total dependence upon the pressure and load. Another example, if you change tire widths but retain the same pressure and the corner load does not change the contact patch area will be constant - Area = Force/Pressure.

I'm sure this seems illogical since all race vehicles tend to prefer as wide as possible (or allowable by the regulating body). This is true, but what you don't see is the lower pressures they are running.

They can get away with this because the load carrying capacity of a tire generally increases as the contained volume increases. So, for the same vehicle a wider tire at the same diameter can be safely run at a lower pressure (need to have in-depth knowledge of the specific tire before arbitrarily lowering the tire pressure).

I'm sure this is far more then you ever wanted to hear about tires...hopefully it makes sense.

[Wh33lhop]

You should probably just buy some.

If I was comfortable spending the money I would have already. Probably some 9s.

[RoccoB517]

Sorry, I've been too busy working on other people's cars to do anything to my own. It might be another month.

[lambo]

Anyone have updated pics of these things?

You should probably just buy some.

[Wh33lhop]

Anyone have updated pics of these things?

[GThomas]

Wow - I just looked on tirerack and they don't list the 225/45/15 RS3 anymore. Are they really discontinued or just introducing a new high performance street tire? I have a feeling miata and autox people will be upset

Yeah, I need some for next season. I planned on getting the RS-3 Version 2's this year but they have been gone for a month of so now. I called Tirerack but they didn't really have any info. Hopefully some new stuff will come out in Feb/March.

[z31maniac]

I suspect it's because it's winter and they will be back in stock in the spring.

[robgoesvroom]

Yeah they both used to come in 225/15. I'd pick the rs3 over the rival but iirc they're both discontinued.

Wow - I just looked on tirerack and they don't list the 225/45/15 RS3 anymore. Are they really discontinued or just introducing a new high performance street tire? I have a feeling miata and autox people will be upset

[Wh33lhop]

Hey wait, there's another 225 street tire in 15" other than RS3s? I just looked on tire rack and didn't see a 225 Rival. I need another set of street tires soon!

Yeah they both used to come in 225/15. I'd pick the rs3 over the rival but iirc they're both discontinued.

[tinkerputzer]

Those are the only 225/15 offerings iirc. Of those i'd take the rs3 hands down.

In that test from grm they only tested the 225 rival against itself on different width wheels. The earlier part of the test was all 205's.

[robgoesvroom]

2. stretch isn't always bad. GRM has proven, pretty scientifically I might add, that a 225 rival on a 15x8 is no faster on a track than a 205 rival on a 15x8. A 225 rival on a 15x9 on the other hand was significantly faster. Think about it. Stretching a tire has a "triangulation" effect on the sidewalls i.e. instead of bending to flex, the sidewall is forced to compress or extend, and can actually increase the contact patch.

Hey wait, there's another 225 street tire in 15" other than RS3s? I just looked on tire rack and didn't see a 225 Rival. I need another set of street tires soon!

[AWDBOB]

many 205

such 8"

so stretch

wow







Your wheels look awesome though, OP! I almost went with the Jongbloed since their 15x8 offset is similar to that of the 6ULs (because Miata), which suites the iX quite nicely.