Any one yet to put 17" 6ul's on an nb.

[Mr Sexy]

I was waiting for all the oldies to start crawling out of the wood working, rambling on about the benefits of 15" wheels

I loved my set of stock racing hearts but unfortunately buckled them on a fairly large put hole, I really liked how the 17's would slightly lift the car up a little. They also filled the arches alot nicer.

I'v been on the hunt for a nice set of wheels for my se for ages, there doesn't seem to be much around in the 16-17 department, I thought these might of been a decent option but seems not.

[KevGoat]

Any mention of 17's is always a minefield ....

[Mr Sexy]

Cheers for the advice guys. Had a long hard think, I am going to leave this issue for a while and bite the bullet on getting my se running properly. I'm nearly at the stage of being able to run an aftermarket esc and getting a tune so I'm going to focus on getting that sorted. Once this is sorted it will be time for new wheels.

[chrons_rotary]

Bit of a revival, but I am considering buying a set of 17x9 +45 6ULs for my NA8 track car.
Yes, I know, 15" are better, and I have a set of 15x9 currently, but I am planning on running in WTAC clubsprint class and the widest 15" AD08R are 205/50.
With 350+whp planned, I don't see the 205s being as useful as a set of 245 or 255 on the 17s.

Any thoughts or suggestions?

[ninerwfo]

Hi Chrons,
I am just about to pull the trigger on these http://www.koya.com.au/cars/sf02-17%E2%80%B3-semi-forged-custom-fit/

Koya SF02.JPG

Koya SF02, 17x9, 4x100 PCD, custom offset from 15-37 (I am choosing 15), load rated to 850kg, and weight approx 7kg, depending on the offset you choose. Very good value, even compared to the legendary 6ULs. I will be running these with 255/40-17 tyres, either Nitto NT01, or the new Achilles ATR-K sport. They will fit like this compared to the stock SE wheel/tyre package:

Chart1.JPG

Chart2.JPG

Note that with a 15 offset, this will not be a road-legal fitment for two reasons (i) the rims are more than 1 inch wider than stock, and (ii) the track has been widened by more than 12mm each side. So these are my track wheels. But I could have just as easily chosen a road-legal fitment with these same wheels, by getting a 17x8 rim with a 28mm offset (40-12). That would look like this:

Chart3.JPG

Chart4.JPG

I have absolutely agonized over doing this, because it goes against the inviolable MX5 law: "Thou must only run 15s"!!! And yep, I know that the overall rolling diameter is 40mm larger than stock. But here are my reasons:
- I got advice from both Paul at Option1 garage, and the maker of my coilovers, MCA,
- I have modified the inner guards to maintain the correct suspension travel and wheel droop specified by MCA,
- all the 250+hp cars on the big US forum say "run as wide as you can fit",
- 255/40-17 is a very common size, so tyre choice is awesome. Every brand semi slick has this size. Also 2nd-handies are easy to find. I have just bought a set of 50% worn Federal 959s from a Honda Integra dude for $25 a corner,
- there are hardly any 15" tyres out there that are over 225 wide,
- the SEs in the Prodsports series run 17s - check out google images.

I am in no way discounting the rich knowledge of guys like Lokeil etc. I agree that 205, or 225 is all you need for an MX5 normally, but what about if it is a very high-output car? The fact is that with the new breed of turbos like the Borg Warner EFRs, 300hp-plus cars are becoming more common, and all the data from the US (back-to-back lap comparisons, G-plots, etc) is indicating that for high-power cars, wider is better. But if you are running 15s, as far as I know in Australia, the only really wide option you are left with is a Hoosier slick at $400+ a corner - just not practical for me.

So my track wheels will be 255/40-17 on an ET15 wheel.

[Lokiel]

^
You have valid non-aesthtic reasons for wanting 17" rims, more grip needed for high-powered car, and the cost of wide 15" tyres, so I'd never diss that.

At 7kg per rim, these rims are nearly 1kg heavier per rim than 6UL 15x10s, not a problem acceleration-wise with a high-powered car but an issue on lesser cars. Will still be harder on brakes/rotors and handling but you'll need to accept that for additional grip needed.

[ninerwfo]

Yep, exactly right Lokiel, unsprung weight is pretty much what is keeping me up at night as I get closer to making the purchase! Maybe it is because I am a trackday hack - but I cannot really tell much difference between my 20KG road wheels (some chrome monstrosities), and my current 16kg track wheels (Lensos). So my mental gymnast is telling me that if I am struggling to notice 4kg per corner, then hopefully 1kg per corner should dissolve... at least that is what I tell myself to get to sleep.

[Magpie]

As the poster stated this is track decision. As long as the car can meet the clubsprint rules then there are no issues. Rules have changed for 2017!

If the car is grip limited then the only choice is wider wheels for wider rubber. Consider the power output and what size wheels are run on, for example a S2000. Clubsprint cars it is not uncommon to run 10" rims or bigger. The trade off is increased unsprung weight and the associated increased stresses on suspension components.

If my car was grip limited I would have gone to a 16x9 to run wider AD08R's

[Magpie]

In addition to my previous post the decision can also be put in the context of a cost/benefit analysis.

As this is a track based decision the benefit will be measured by time (not exhaustive)

1. Is the driver consistent enough to be used as a measure for time?
2. Is the car at a point where the only change being made will be the tyres whilst testing is being undertaken?
3. Has the car been dríven by a 'Stig' type character to give an opinion on the overall setup of the car?
4. Is the testing going to be done on the same day and in almost the same conditions?
5. Data logging to generate G plots to compare tyres

Now to look at the alternatives for the money to be spent to improve time. Assume $4.5k for 2 complete sets tyres/rims and $0.5k for track time to test - total $5k. Again not an exhaustive list.

1. At least 6 full days of track AND professional coaching with MR Tuning
2. Carbon fibre roof/doors
3. MCA Gold suspension (maybe)
4. Over 350mins of track time at SMSP
5. 5 x entries in clubsprint for WTAC (assuming no price increase, excludes practice day, tyres, accommodation...)
6. 40 hours of dyno tuning
7. Logging dash/PDM setup
8. 3,500 ltrs of E85
9. 700 on line simulations using ChassisSim (allowance made for setup costs)

So it is more a question of where would the money be best spent to get the time you want.

If you are aiming for a top 5 shootout in WTAC Clubsprint, based on 2016 results you will need to be at least 1:40. Top 20 you need at least 1:45. These times rule me out

I improved by 3 seconds between my 2015 and 2016 times. The changes to the car were from 6.5" rims to 7" and a few extra RWHP. So where did the 3 seconds come from, more than likely from seat time and a little due to the rim change. Therefore for me the best use of $5k would be on driver training as I'm not chasing 1/10's rather full seconds. When I get to the 1/10's I will think of another rim/tyre combo.

[rascal]

Yep, exactly right Lokiel, unsprung weight is pretty much what is keeping me up at night as I get closer to making the purchase!

Don't sweat it. Given your projected hp, you will improve lap times way more from having the extra grip of the larger, wider rims/tyres than any minor detriment of a 1kg heavier rim..

[kalt]

I cannot really tell much difference between my 20KG road wheels (some chrome monstrosities), and my current 16kg track wheels (Lensos).

Were both on same tyres and tyre pressures, or different tread pattern and pressures? You should be able to discern the steering weightiness, but if you had less grippy tyres on the 16kg wheels then that may negate any improvement in laptime expected from less unsprung weight.

Like that little taco girl says you need to have both lighter wheels and grippy tyres- same time.

[MattR]

Pfft, nothing a set of spacers won't fix.....