Semi Slicks choice and set up questions

[Mr. Keets]

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?

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.

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.

4. I have read conflicting info about toe in or toe out with semis on a RWD car. In or out?

5. Spring rates, do I need to raise the rates? Currently I'm running 7.1kg/mm springs front, 5.3kg/mm rear.

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?

Thanks in advance
Keets

[NitroDann]

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

[manga_blue]

1. I'm looking at some Advan A050 R Specs, soft or medium? Speak to the motorsport tyre guy. Usually soft for motorkhana and medium for sprints, so you may have to decide which you want most.

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. I personally hate driving on R-specs. My usuall tracks are at least 2 hours away so I always change at the track if I drive there. If it was just a short trip I'd put up with it, unless it was really wet.

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. 205s fit fine on 7s and 8s.

4. I have read conflicting info about toe in or toe out with semis on a RWD car. In or out? Zero front and back. Have a look at Emilio's set up guide on hs 949 racing site. For motorkhana without a long travel to the track I'd think about going to slight front toe out for faster turn in.

5. Spring rates, do I need to raise the rates? Currently I'm running 7.1kg/mm springs front, 5.3kg/mm rear. 7/5 is about the minimum for track work. That will work until you're fighting for championships.

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? No, you're just going to have to drive within the capabilities of the brakes you've got.

[manga_blue]

BTW, thanks for unusually sensible and relevant questions.

[NitroDann]

[Mr. Keets]

Thanks for the replies guys, great advice

1. Compound. I'll have a chat with the tyre tech before I go forward

2. Drive or change at the track. I'll see how they feel, I have a 4X4 to carry tools etc so it can be done

3. Rim /tyres size. Mmm more fender work and expense for the 225. More thinking to be done there I think.

4. Thinking about the front mainly, the car makes around 230RWHP, I had a look at Emilio's set up page...I cant beleive I missed that. Looks like a little toe out on the front and see how we go

5. I'll leave the rate alone for the time being, one change at a time I think. I have a 28mm tubular Racing Beat on teh front and standard on the back. Accoring to FCM's calculaotr I'm at 61% FRC

6. Ill leave the studs until I do the brakes

[plohl]

I have 8" 6uls with 225s and didnt need to roll the guards. My car isn't that low though, maybe 110mm to seams.

My alignment is 2° camber, 5.5° caster at the front, 2.5° camber rear and 0 toe all round.

Sent from my SM-N9005 using Tapatalk

[Magpie]

205/50 on 7" 6UL's with -2 deg camber will rub the guards on a NA6 if you drop the height too low (90mm F and 95mm R at the pinch welds)...

Spring rates will depend (among other things) on your sprung/unsprung weights. Rims/tyres of different brands could weigh differentley and hence change the sprung/unsprung weight.

Think about your bumpstop as this is what will be used when going around a sharp corner.

If worried about overheating just make sure you set your tyre pressure when they are cold. As a good starting point R Spec's like about 30 psi hot (stand back from flames) so start at about 27 cold.

Soft/med depends on race type. Generalising, soft for sprints, med for longer track sessions. Also a 195 tyre will heat up faster than a 225 (generally speaking).

[Jeo]

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

[manga_blue]

5. I'll leave the rate alone for the time being, one change at a time I think. I have a 28mm tubular Racing Beat on teh front and standard on the back. Accoring to FCM's calculaotr I'm at 61% FRC

61% on an NA sounds pretty stiff at the front. It might be good if you're driving lots where you stand on the brakes and rotate the car around the fronts but very understeerish on circuits. Driving style does come into it too. I run 10/7 with OEM bars on an NA8 to give me around 55%, which is how I like it - just a little bit taily.

[manga_blue]

I have 8" 6uls with 225s and didnt need to roll the guards. My car isn't that low though, maybe 110mm to seams.

My alignment is 2° camber, 5.5° caster at the front, 2.5° camber rear and 0 toe all round.

Sent from my SM-N9005 using Tapatalk

Virtually identical set-up to mine, except I run 15X7s with 205s. Works for me.

[Magpie]

Just a question, when you used FCM's calculator did you also input the actual car weights etc or did you use the defaults?

Also the simple FCM calculator does not allow you to input unsprung mass, however if you do a consultation with FCM this information is needed.

[manga_blue]

I use the earlier FCM spreadsheet. That lets you play around with unsprung weights, variable sway bar arm lengths, etc

[Mr. Keets]

Thanks guys

-Car is 110m to the pinch weld and I've already lipped the front and back, 3° on the front. Minor rubbing
-The wheels I'll be running are 6.7Kg...by no means lightweights but the 6ULs are on backorder and I don't want to trash my Car Make Corns wheels (4.7Kg)
-27C cold, check
-The idea of using a narrower tyre to get the heat up quicker makes sense, the runs I will be making around around 1:15-1:20...hopefully less, so the softs look like a better bet, 205 on an 8 unless the tyre tech gives me a better plan or I find some other wheels
-Yup, right now it's a bit more a of a parking lot car than circuit, I'll see how we go and if i get understeer I can source a narrower front bar. I'm expecting to have to make changes by going wth the R-Specs anyway...I can see this little car heading towards a stripped interior next year and me buying another daily driver
-The bumpstops are 30mm medium density front and 35mm soft density rear
-I did the full consult with Shaikh, I didn't have the real numbers but I did give him details a/c, full interior, Roll bar, wheels etc. The unsprung weights will be different, 2Kg plus the delta on the tyres each corner.

Thanks for the set ups too,

[Apu]

What wheels do you have on your car? Mine are 15x6.5 and I run 205s, wheels are 5.5kg each. You can get well made cast alloy wheels without busting the bank.