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A question for the grip gurus


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As you would expect, my s15, like all others, likes to oversteer. It's not really a problem and I actually love the way it handles so far, but I'm trying to make it the best it can be. So if I were to run a larger tire/wheel combo on the rear, would this improve the oversteer on cornering? I've currently got 225 on 8J all round but after it's gone to the panel shop, i'm thinking 255 on 9J front and 275 on 10J rear, because i'm greedy.
And while i'm here, how does tire profile affect handling? From what I understand, a larger sidewall (within reason) gives the tire more flex when cornering and this produces more grip (with the proper camber). I'm wondering if a 16" wheel would be better for [grip] track days than a 17".

Oh, and one last thing: can anyone recommend some good grip tires? I'm thinking that since i'm not going to be burning them anymore, I'm willing to spend a bit more money on a good set of tires (provided it's actually worth it). Looking for good daily performance tires (under ~$250ea) and some good semi-slicks (under ~$400ea).

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big tip, good quality will always outperform size, but your wallet and life expectancy of the tyre will suffer

 

that said, wider will always give you more grip on like for like tyres and the difference between a 16 and a 17 tyrewall wise won't improve that much so stay on 17s imo

 

most of my cars have had 215 and 225 tyres and gripped fine, it all comes down to fine tuning your suspension setups!

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big tip, good quality will always outperform size, but your wallet and life expectancy of the tyre will suffer

Yeah, that's why i'm looking for some good quality tyres. Like I said, I'm willing to spend a little more since i'm not going to be turning them to smoke. Are there any you would recommend?

the difference between a 16 and a 17 tyrewall wise won't improve that much so stay on 17s imo

 

mmk, cheers

most of my cars have had 215 and 225 tyres and gripped fine, it all comes down to fine tuning your suspension setups!

I see tire/wheel choice to be the first and easiest step to get the most out of the car. Other than that, i'm keeping it pretty basic with coilovers (7/4.5 spring rates) and adjustable arms for alignment, both of which i'm initially setting up according to what's suggested by MCA. Once I actually start getting some track time, then I'll get to start on the fine tuning.

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Smaller tire wall (low profile) [note opposite is true for larger tire wall]

Pros: Better handling as less wall flex, therefore better stability and cornering

Cons: Feel the effects of the road a lot more (less comfort)

 

So I would say your statement is not entirely correct. Plus, there are better ways to manage handling like sway bars for instances which reduces the cars roll. More than that, understanding how to shift the cars bodyweight around is even more valuable.

 

255 and 275? That's fairly huge. I guess the idea is, larger front tyres = less understeer and larger rears tyres = less oversteer. However I am not clear on the perfect ratio. How is your car handling currently? Oversteering too much? Look at it as a function of your car and it's power to weight.

 

Tyres I would look at:

Nitto NT01 and Advan AD08R. Maybe even Hankook RS3 or Federal RSR

 

For semis:

Toyo R888

Bridgestone RE55

Hankook Ventus TD Z221

Advan A050

 

Lastly, I usually go to tirerack to check out tyre reviews. Note all the prices there are in US and the shipping doesn't make it cheap to buy from there.

http://www.tirerack.com/content/tirerack/desktop/en/homepage.html

Edited by volt_bite
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Smaller tire wall (low profile) [note opposite is true for larger tire wall]

Pros: Better handling as less wall flex, therefore better stability and cornering

Cons: Feel the effects of the road a lot more (less comfort)

So a 17" would be the better choice over a 16" then?

 

So I would say your statement is not entirely correct. Plus, there are better ways to manage handling like sway bars for instances which reduces the cars roll. More than that, understanding how to shift the cars bodyweight around is even more valuable.

 

255 and 275? That's fairly huge. I guess the idea is, larger front tyres = less understeer and larger rears tyres = less oversteer. However I am not clear on the perfect ratio. How is your car handling currently? Oversteering too much? Look at it as a function of your car and it's power to weight.

 

I'm not going to look at sway bars until i actually have a good idea of how the car handles and understand the more intricate details of things like how the bodyweight shifts.

 

And yeah, that is the idea. Am I going in the wrong direction here? To be realistic, i may have to go smaller, say 235/255, but I'll have to see what magic my panel guys can do and what sort of clearances i have to work with.

 

I'm very comfortable with how it handles currently, the oversteer has not yet been something that causes me to lose control. I just feel like it could be better. The ratio will come down to trial and error I guess; the fine tuning.

As for power:weight, I was under the impression that you are on relatively little power when cornering. From my understanding (please correct me if i'm wrong) you brake up to the corner then more or less coast in and power on as you exit. I guess I thought that power and handling were completely separate. If (when) I end up going for more power, is this going to change the cornering characteristics?

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When it comes to sizing, 16 and 17 doesn't make a HELL a lot of difference. If you are staying the same rolling diameter, then yes your tire wall sizing will change. If you want the same tire wall size but different sizes, then your RD will change. See what I am getting at? Other than that, it comes down to price, sizing (availability). I mean, on top of that you have caliper & disc clearance especially for the fronts.

 

So just stick to 17s. The only reason why I would go 16s is because of price of the tyre I want but 17s and 18s are common enough anyway.

 

I did a gymkhana day before and after sway bars and you can most definitely feel the difference between the two. The car will roll like no tomorrow under stock sway bars and cause your car to oversteer. Funnily enough, some drifts run no sway bar! Go ahead and try it but it's definitely worth doing.

 

Yeah going too big has its issues. Too wide and the front and you just scrub on lock anyway. Too wide on rear is relatively ok but pointless if you don't have the power required to maximise the grip potential.

 

Hmm last bit, think of this. When you are powering into a corner with a lot of speed, you need to brake hard under acceleration which if you don't have good enough brakes and grip, you will understeer into the corner. If you have good low end power, you can power out of the corner quickly especially if you have good grip which means faster times (hopefully).

 

Keep in mind I am not an expert but that is what I've learnt over the years (despite my car being under build lol).

Edited by volt_bite
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Racing: Your either braking, or accelerating. If your coasting, then your losing time. Brake hard before the corner, then accelerate through the corner.

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From memory the basic for cornering is to brake hard in a straight line to wash off the speed, and then accelerate smoothly out of the apex (following your driving lines).

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Definitely. Too many people (including myself) tend to spend big on items they don't need. The best way is to try it out and set up the car to how you want it. Obviously still helps to get some advice though.

 

Just make sure you do all the usual servicing before and after track work to take care of your car.

 

Greg on here use to raise his silvia for grip. I think there are a few others around still too but their builds are pretty wild.

Edited by volt_bite
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What Marshall said, this is also a helpful technique for making your tyres last longer than the others on the track and also skinnier tyres at the front because you're never trying to get them to do two things at once.

 

-Braking on the straight -washes off speed, transfers weight on to the front tyres.

 

-Turning in- As you're lifting off of the brakes, line up your apex, use all that weight now at the front to get the optimal steering response and turn in keeping the throttle partially open.

 

Accel out- As you hit your apex and start to straighten the wheel, accelerate out. The pressure of your right foot on the throttle should match the angle of your steering, the straighter you get, the more the weight evens out, the more grip you have, the more power you can apply until WOT.

 

255 in a decent tyre would be more than sufficient for an s15 <350hp to really enjoy the track and learn in.

 

Achilles ATR let me down when they got hot after a couple of runs, they got slippery and developed understeer even using a much slower approach.

 

Federal 595 rs-r have been good so far tread wear is pretty drastic, but for a tyre with that much grip, I didn't expect anything less. They hold up pretty well in the rain too. That's with 255/35/18 18x9 on each corner

Edited by DonkeyKong
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i normally run 18 inch wheels on my s15 (235/45/18) . a few months back i got a set of 17s and put the same brand new federal 595 tyres on 235/45/17 and couldn't be leave how much traction i lost . it went from a twitchy grip machine to drift setup

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235 up the front is plenty.

 

You need to be able to turn your car...I run 225 federals and have very very little understeer...a better tyre would reduce it.

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Can anyone recommend a good daily driving tyre that will outperform the achilles atr? Or is there pretty much a big solid line between daily street tyres and "ultra high performance" street legal race tyres?

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If you want to fix your oversteer problem, forget tyres and just go straight to a front swaybar.

Read carroll smith books if you want to learn how the suspension works and how changing things affects performance.

I have 255 semis all round, mca reds, arms etc and front swaybar made the most noticeable difference at barbs.

Edited by VFR15
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Dont waste your time with 16s. Rubber choice and cost is sheet. 18s are the best value for money these days.

 

Get decent offset wheels that will allow a 245/265 combo without scrub or stretch.

 

Use an ADO8R or an NT05 if your budget cant stretch for the yokes. Both great high performance street tyres that can handle track stints and still have a reasonable life span.

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Agree with 18's. That's what I'm looking at and especially with those tyre sizes too because they are common in a 45 profile.

 

If you got over steer issues. a different front to rear tyre width will help. Changing the ride height to be slightly higher front wise will help. Finer throttle control will help. Sway bar adjustment might help but that depends more on how much loading you are exerting on the outer tyres during the corner. Coilover damper setting will help with regards to sway bar setting.

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  • 2 months later...

If you can be bothered going to a race engineer //it's expensive I know// you can get your suspension geometry set up and wheel weights professionally loaded properly. Most aftermarket bits after fiddling with you height and what not will throw out the individual weight loading on each tire. So sorting the geometry and alignment and damper configurations is must!

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Balance will benefit you the most. A square or close to square set up will be the best option. I would run a 255 all round or a 245/255 Front to Rear.

Too much bigger on the rear and you will increase understeer.

 

Read books and get seat time you will get a much better understanding than anything you read on the internet

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