Hi guys!
I have a 2010 JCW WC 50 and I have changed most of the mechanical parts under the hood. Not sure what the car is pushing but it must be more than 225hp.
I don't want to sit here and list all the modifications I've made.
I'd like your expert advice for getting as much grip and handling as possible on the car for handling in turns but mostly acceleration since it can spin it's wheels in 3rd gear.
So the question is do you get more grip with a wider tire or with a larger diameter tire?
17"225 or 18"215?
Thanks!

 

traction is better with more side wall give, so going to 18" would make it worse. A good tire is paramount, I found michelin PS the best so far, I'm at 215 width and atleast your HP , hitting dyno saturday, was 219HP with stage 1, now stage 2 catless.

I have an auto so I only loose traction off the line and sometime going into 2nd.

Coworker has 20" on a 600+ HP camaro and 315 or 325 wide and spins them in pretty much any gear, he does much better with 15" slicks.

 

Thanks for the reply!
I currently have Michelin Pilot Super sports 215 on my 17".
So based on what you are saying it would probably be best to get a wider tire, but shouldn't make much difference.
I wish someone super technical could help out.

 

I'm no expert but if you are racing in competition, I think you would loose acceleration coming out of a turn with the larger tires. I went from 15 inches to 17 on my Mini and due to the increase weight and larger tires, the decrease in acceleration was very noticeable. I finally settled on 16 inch for mine.

 

Hey thanks for your input.
My issue is not with acceleration, I have plenty of acceleration. My issue is transferring the torque and POWA to the ground as efficiently as possible.

 

A wider tire increases grip in cornering and decreases it in acceleration and braking. A softer tire compound increases grip in all situations. For street driving the Bridgestone RE 71R is about as sticky as you can get without risking frequent punctures. More air pressure is good for cornering, worse for acceleration.

A limited slip differential will move power to the wheel with more grip.

A larger diameter tire will not provide more grip but can lessen wheel spin by effectively making the final drive taller. This will also raise the center of gravity and compromise the grip when cornering. Changing the differential and/or transmission gearing would be more effective.

Suspension components and adjustments are going to be a compromise between cornering speed and grip while accelerating.

Any of these changes will change the effectiveness of the other changes so getting the best combination can take a whole lot of testing, and you're ultimately limited by the front tires having to both steer and accelerate.

The best specific advice would come from someone who has done what you are trying to do; ideally with the same car and same personal preferences as you.

Good luck.

 

Ps. Racers make these changes at every track they visit, and even during a race. Engineers who are good at it are in great demand.

 

OP does not specify which make and model of tire he is currently using. 225 vs 215 vs 195, etc, means little compared to the difference of any OE Mini tire vs a real sticky street tire, like an RS3 or Z2 Star Spec. Given that OP has an LSD and can't put 225hp down, I'm guessing the current tires are garbage.

As noted, flexible sidewalls are exclusively good for straight line traction in a drag scenario (as well as comfort on the street). Start turning though, and you want the lease compliant sidewalls possible.

There are also plenty of lightweight 16s and 17s that won't increase unsprung weight noticeably. I think 18s look silly on R56s, and also prefer the slightly greater sidewall (for protection) and cheaper cost of 16" and 17" tires in general.

On other cars, I have enjoyed going to tires with smaller OD than stock for the gearing advantage. I would never willing go to a larger diameter tire, particularly on "just" a 225hp car--that won't solve your traction issues, and will make the car less snappy.

The Z2* comes in 225/45/16, which is a nice short tire with a great contact patch. Alternatively, I'd go 235/40/17, which is shorter than the slightly narrower 225/45/17.

 

Personally I'd go lighter on the throttle at lower rpm but that isn't what was asked.

 

Ha, agreed. It's not an on/off switch.

 

I did post the tires, but I can repost them here.
215 17 45 Michelin pilot super sports.
I used have Rspec tires and they were better in all scenarios.
So based on what you guys are saying it wont make much difference at all changing the tires regardless. Wider or Larger.
Only difference is in the turns.
I thought the wider the better because more rubber to the ground. I guess I was wrong.

 

Wider just changes the shape of the contact patch, not the area. Again, narrower is better for straight-line acceleration and braking, wider is better for cornering.

The RE 71R Bridgestone is closer to an R tire than a street tire. It won't last nearly as long as the Super Sport though.

 

Nothing matters except sheer mechanical grip. That is only achieved with a larger wider contact patch. Wider is better. Spacers also help widen the wheel track.

 

Derp, sorry, totally missed that. You can't get much better than PSS, honestly, especially for the street. I would look into 235/40/17s, I guess. The Star Spec in that size is a full 1" wider in tread than the PSS, at the expense of comfort and longevity (and noise over time).

The contact patch widens, but doesn't get any larger, as hsautocrosser points out. I wouldn't call spacers a noticeable difference in anything besides cosmetics (though I am a fan).

 

A 10 inch wide contact patch is larger than a 7 inch wide contact patch.
Mechanical grip is developed with laterial forces acting on the contact width of a tire. Period.
The wider the tire the more mechanical laterial grip produced in a corner. Porsche figured this out early on in 1970's & then offered a "wide trac" spacer options for street cars to improve handling

This is why winning race cars have huge staggered tire/wheel fitments!!!
Observe pic and it will become clear to even the most novice wannabe racer.




WRONG:
The contact patch widens, but doesn't get any larger, as hsautocrosser points out. I wouldn't call spacers a noticeable difference in anything besides cosmetics (though I am a fan).[/QUOTE]

 

[/QUOTE]

Sorry, but you're statement that wider = larger is blatantly incorrect according to science. Here's one source, a bit more definitive than a picture of a period race car: http://www.roadandtrack.com/car-cult...-tire-patches/

You are correct that widening the contact patch (which changes the patch but does not enlarge it) helps in the corners, obviously.

 

As an engineer friend of mine pointed out in similar circumstances: Go back to the units.

Tire pressure is measured in pounds per square inch, obviously. The weight of the car (or on one corner of it) is measured in pounds. The area of the tire's contact with the road is in square inches. See where this is going?

If you use the same air pressure in a wider tire as in a narrower tire, you get pretty much the same size contact patch. It will be wider, but less deep. (The stiffness of the tire carcass and sidewalls affects that, of course, so it's not exactly the same, but it's close.)

Spacers do have an effect on traction, though. The further from the CG of the car the contact patch is, the better "leverage" it has, which gives it slightly better mechanical grip. It's not a huge effect, but it is noticeable.

 

Did you already have a stiffer bushings on front arms , Powerflex ? I use almoust same mods. but Quiafe LSD and powerfex bushing reduced lots of torq.steering and made the my MCS a more sharp handle.I run 215/45/17 Contisports.

 

This is only strictly true if the tire was very flexible, like a balloon. For real tires the tire stiffness enters the equation and bigger/wider tires do indeed give a larger contact. This is why drag racers run monster big tires at very low pressure. On a mini id expect a oversize tire would have more ill effects on handling that their worth in straight line traction. Even if you are drag racing the mini you need to consider if the added traction trades against the added rotating inertia.

 

Hmmm so your saying to change bushings. Noticable difference? Is there a downside?
I changed the engine mount once but it wa too much vibration in the cabin.
I like where this thread is going!!

 

Since you are in Toronto, as ambient temperatures get colder, typically in the 40-45° Fahrenheit range, summer performance tires lose a noticeable percentage of traction as their tread compound rubber properties change.

 

Agreed but my issue is in full summer 30 Celsius.
I believe that the Pilot Super sports are not the best.

 

Narrower tires are better for straight line acceleration and braking? How come drag cars run wide tires on the drive wheel?

Wider tire, given the same tire at the correct settings, should yield more contact area. The other thing is tire compound.

If I were you I would give some 235 r comps a try. Imo you'll probably need some body work to prevent from running.

I have heard mixed reviews on re71. They're grippy but doesn't last long. Your call.

Ps: r comp tires are generally wider than high performance summers at the same size (ie. 225 on both tires doesn't have equal physical width)

 

The width shrinks and the diameter grows dramatically after the dragster launches. You can find slow motion video of it on youtube.

Put 8000hp in a mini and you too will need huge tires to launch it. Not merely wide tires, huge tires.

Load and air pressure mostly determine the area of a contact patch. Believe what you want. I'm sticking with the race tire engineers.

 

Yes the width shrinks then I still don't understand why they need wide tires in the first place.

In his case, he is losing traction in 3rd gear. He needs a wider tire so it shrinks less to get more traction.

Of course tire pressure and load changes contact patch, but if in this scenario they're running the same tires, wouldn't the wider tires get more bite?

I understand drag tire engineers wants to reduce drag from tires after the launch, but here he doesn't even have enough tire contact to begin with.

I am not hating. Sorry if my previous reply sounds like a hate post