Semi Slicks choice and set up questions

[manga_blue]

These wheels are on the NSW Club website. Might be of interest to you.

Also, Apu, 15x6.5 is the wheel size recommended by most of the R-spec manufacturers for 205/50R15. So nothing wrong with 6.5 s at all.

[greenMachine]

Get some advice from your Yoko supplier re fitment of AO50 205/50 on 8s.

You might also want to check your category rules for motorkanas re the use of semis, ISTR there are some clubs/comps that restrict them. You might be better off with some sticky road tyres in any event.

You should have some toe in at the rear to offset a toe-out movement on compression/roll.

6/6kg worked for me supersprinting the GM in 2B.

I suspect you will have to prioritise kanas and sprints, unless you can switch between two setups.

Finally, don't get too hung up on the tech, and above all set the car up and get lots of seat time. Chasing setup/mods can get confusing - you need to get used to the car, understand how/why how it is behaving, and that only comes with lots of seat time.

[sailaholic]

These wheels are on the NSW Club website. Might be of interest to you.

Also, Apu, 15x6.5 is the wheel size recommended by most of the R-spec manufacturers for 205/50R15. So nothing wrong with 6.5 s at all.

Is that info online somewhere? Emilo tested 8s to be fasted for 205s ...



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[Hellmun]

I'm getting a set of Semis for Motorkhana/Sprint use and I have a few questions around usage and settings...

For reference my NA is a 1.8 turbo, NB 5 speed, Torsen 2, and the suspension and bearings are fresh.

1. I'm looking at some Advan A050 R Specs, soft or medium?

Cannot answer this
2. I'm concerned I could over heat them on hot Perth roads on the way to the venue, is it a problem? I'm not worried about wear as I have a set of road wheels and s-specs. I could change them when I at the venue but that's more work at the end of the day I would like to avoid.

Nope you wont overheat them.
3. I wanted to get some 6ULs but they wont be available until next year, the rim i;m looking at is a Buddy club 15x8 +32, the tyre size is a 205/50. Any thoughts on the sizing suitability wise rim to tyre.

Widest rim possible, with a tyre the same as the rim where possible. 8's and 225's are a common combo on quick cars, perhaps only because they didnt have 9 or 10" rims to mount them on, hellmun and those boys will be able to answer this better.
4. I have read conflicting info about toe in or toe out with semis on a RWD car. In or out?

What end of the car? Read up on how toe in and out works and play with it at the track, What is your HP? under200whpish zero toe front and rear is said to be the fastest because of drag.
5. Spring rates, do I need to raise the rates? Currently I'm running 7.1kg/mm springs front, 5.3kg/mm rear.

You dont need to those will certainly work ok, depending on swaybars you will probably find that setup a little oversteery, because the front is too soft/rear too stiff relative to each other.
6. I'm waiting on brakes coming from the US, I will do the studs then, any issues with running this combo on standard studs for a a few meetings?

Nope.

Thanks in advance
Keets

No worries,
Dann

15*8's were the widest legal rim in supersprints for 2B category, there's a +1" rule on rim width from standard for your model. Club uses this as well (17x7 NB SE rims = 18*8 being largest legal option for NBs). For circuit work I'd definitely go widest rim and tyre possible. Khana takes away a lot of the advantages that affords though thanks to the low speeds and short duration to get heat.

27psi cold is good when at the track ready to go out for a session but for just driving on them to the event I run their hot pressure. The more pressure you take out, the more the tyre deforms and it'll heat up. I run a TPMS on my 6UL's and I found they were warming up and gaining 2-3psi on the expressway on the way home at 26psi. Pump them up to 32psi and they didn't move for me (temp stayed in the 20's instead of hitting 40-50C). I've been driving to/from the track on my R-specs for 5 years now and never had an issue with them degrading or overheating so I wouldn't worry about it. What's more important is that you take them off the car when finished and store them somewhere cold and dark. I keep mine in tyre tote's under a billiard table. Good care is the difference between having semi-slicks that are amazing when bald...and heat cycling them out early so you lose the best bit (Assuming the last event is dry and your not running A048's). I'd hazard there is at least a whole second difference between worn and new V70A's. Soft compound will be a one trick pony, you wont' be able to use them for a trackday unless it's raining. I'd still stick with a really high quality S-spec tyre until your feeling grip limited and want to use a soft compound semi. A cold semi will still give more grip than a cold S-spec...but the S-spec will heat up and probably give you more time at a higher grip level than the medium semi slick.

[manga_blue]

These wheels are on the NSW Club website. Might be of interest to you.

Also, Apu, 15x6.5 is the wheel size recommended by most of the R-spec manufacturers for 205/50R15. So nothing wrong with 6.5 s at all.

Is that info online somewhere? Emilo tested 8s to be fasted for 205s ...[/url]

Just talking about manufacturers' recommended rim sizes, not what Emilio says.

Found it for Toyos: http://www.toyotires.com.au/all-tyres/proxes-r888
Also for Yokies, but only A048 so far: http://www.tirerack.com/tires/tires.jsp ... &tab=Sizes
Also Bridgestone RE11s: http://www.bridgestone.com.au/lib/pdf/M ... PL_RRP.pdf

All saying 6.5". Getting the picture?

[sailaholic]

These wheels are on the NSW Club website. Might be of interest to you.

Also, Apu, 15x6.5 is the wheel size recommended by most of the R-spec manufacturers for 205/50R15. So nothing wrong with 6.5 s at all.

Is that info online somewhere? Emilo tested 8s to be fasted for 205s ...[/url]

Just talking about manufacturers' recommended rim sizes, not what Emilio says.

Found it for Toyos: http://www.toyotires.com.au/all-tyres/proxes-r888
Also for Yokies, but only A048 so far: http://www.tirerack.com/tires/tires.jsp ... &tab=Sizes
Also Bridgestone RE11s: http://www.bridgestone.com.au/lib/pdf/M ... PL_RRP.pdf

All saying 6.5". Getting the picture?

No, I respectfully have to disagree.
They are giving you the test rim width that the tire width was measured on ( tire measurement change slightly depending on the rim width). As you will see from the toyo TEST rim width is always the middle of the approved width range.

The Bridgestone one is alot less clear, but I believe that as the rim size comes straight after the tire width the argument is still valid.

I couldn't load the tire rack link.

I don't expect you to take this on hearsay though so I will scan the book where it explains this. I just have to get said book back off loan.




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[NitroDann]

[manga_blue]

No, I respectfully have to disagree.

No, fair enough. I've seen that recommended range of 5.5-7.5" rim width for 205/50R15 about for years on pretty much all brands. The 6.5" has sometimes been written up as test width, sometimes as recommended width and sometimes measurement width. Probably the meaning of the 6.5 gets lost in translation when it goes to the marketing dept.

What I did want to point out was that the 205 size fits OK on 6.5" rims. That's important for the NA6 guys. As Hellmun said there are a few classes in NSW that limit you to an increase of an inch in width and an inch in diameter. So 15x6.5 is the largest wheel you can put on an NA6. Also, as Apu said, the 15x6.5 is a much more affordable size for the NA8 and NB8A owners. I've run 195/50R15 and 205/50R15 R888s on 6.5" rims in the past and the 205s are definitely quicker. The same set of 205s gave me the same lap times on 6.5" and 7" rims, but the 7" rims were heavier (3.9Kg vs 7.0Kg).

Come to think of it, I've seen 225/50R15 A048s on 6" rims. They're within Yokohama's specs of 6"-8". He was doing very good times at the Island and said they felt fine. That's the super budget option if you can source half worn Porsche 944 Challenge tyres.

[NitroDann]

This is a good thread

Dann

[project.r.racing]

For motorkhanas, unless you are prepared to do a drag racing burnout before every test. Then you are probably better off sticking to road tyres.

Which if you do so, then getting mediums for the track will be the go.

[manga_blue]

I know a few guys have played around with R-Specs on turbo cars for the parking lots around Perth. I recall Simon moving up to Dunlop softs (I think) when the competition started getting serious a few years ago. Warwick comes to mind too. Maybe Okibi could help you with more contacts if you don't have them already.

[Mr. Keets]

Thanks again guys, some great discussion here.

Current wheels are a 15x7+25, but they were over 2K for the set and I had to wait 8 weeks for them so that pushed me further along the "semis on a second set" route

I'm waiting to hear back on the wheels...cheers Managa. The remarks about pressure was really useful as well. The tyre tech was talking abut nitrogen filling the tyres, will that have any effect on cold vs hot pressures?

This conversation has made me think about where I'm going with this...looks like I will go with the soft 205s on 8s, there are no size regs in any of the events I will attend. I will get some seat time and learn how to read the car and become a better driver, maybe get a contact pyrometer down the track.
I'll do as much parking lot stuff next season as I can and maybe a hill climb or two before I get too serious about sprints and stripping out the car. It's a journey..one step at a time I think.

[Hellmun]

Nitrogen would be less important for you as the khana's are too small to generate massive temperature changes. Rule is basically 1psi change for each 10C delta. So in a sprint where you can load the tyre for 5-6 minutes you can go from 20-30C upto 100-120C on a hot day. So about 7-10 psi change with air. Nitrogen follows the same rule , air is mostly nitrogen after all but the benefit is you don't introduce moisture. H2O gets bigger in a gas state VS a liquid state which happens as you introduce the heat. I've never run nitrogen back to back personally but when I read up about it ...it didn't seem that significant. Especially not enough to warrant the carrying around of a gas bottle to the track in-case of rain, cooling conditions or a leak. Though I suppose you could do an initial fill of nitrogen at home, then just contaminate it if required. Then purge again when you get home... also bear in mind you'll want two tyre valves per wheel for completely purging the tyre. 6UL's have two valves for that reason.

[Mr. Keets]

Looks like I've struck a deal on the 6ULs I was after, so I'll get the initial fill with nitrogen.

[geofiz]

Assuming your khana's are ~30 seconds, you'll be struggling to get usable heat in most semi's.

Based on my limited experience with the motorkhanas here in Perth, you don't get much heat into the tyres. The surface at the driving centre is not too harsh on the softer compounds,but at the Midvale Speed Dome it is pretty harsh.

Go the soft compound.