Tires. Is wider always better?
#16
My pirelli 205's are so easy to lock up in front. Tires DEFINITELY affect braking. Good thing i have a set of sp8000's coming soon which are wider.
Let me run down the rest.
He says the car now feels more sluggish and his fuel mileage is down with these wider tires.
944 had a set of 17" boxter wheels with 255's in the rear. My car did seem alot peppier with the 15" 225/50/15 race tires on the factory rims all around.
Even my good year 215's were wider than the pirelli 225 rears...
I have zr p7000 supersport, which grip very well laterally. Better than my good year eagle gt2's.... Yet it took a lot more effort to lock up the good years. The pirellis are a good 2 inches narrower.
oh, the good years were 215/60/15 while the pirellis are 205/55/16
I also have to wonder about the current mania for giant rim sizes. Looks or performance? I suspect the former is the biggest factor.
__________________
Best Car Insurance | Auto Protection Today | FREE Trade-In Quote
#18
Thinking outside da' bun...
Lifetime Rennlist
Member
Lifetime Rennlist
Member
Joined: Apr 2002
Posts: 11,529
Likes: 470
From: Dayton, Ohio
One other thing you need to keep to keep in mind is the wider and larger you go, the heavier your rims will likely be, unless you are like 930Rocket running those bigass magnesium BBS wheels I get a woody for every time I see.
I think keeping weight down on the rims should be as much a concern as any. For most of us, 3-4 pounds extra on each wheel probably wont mean much. If you are on the track or something Im sure it will.
Im pretty much speaking out of my bunghole though. I dont know for sure.
I love Fuchs.
I think keeping weight down on the rims should be as much a concern as any. For most of us, 3-4 pounds extra on each wheel probably wont mean much. If you are on the track or something Im sure it will.
Im pretty much speaking out of my bunghole though. I dont know for sure.
I love Fuchs.
#19
Luis, it depends on the application. In general, yes. As Dave correctly points out there are time the answer is no, snow, ice and heavy rain are some of them. Wider tires also have much more tendancy to follow the road surface or tram.
UD - to be honest even a professional driver will not likely notice 3-4 pounds per wheel. I had held that view for a long time and recently saw an interview with Michael Andretti confirming that. On a street car you are unlikely to notice 20 pounds per wheel if all things were equal (yeah, here comes someone to disagree). What people do notice when they go bigger is that the car is harder to turn (more contact patch) and that is "feels" a little sluggish. Geo has correctly pointed out why people think it feels sluggish.
__________________
Best Car Insurance | Auto Protection Today | FREE Trade-In Quote
UD - to be honest even a professional driver will not likely notice 3-4 pounds per wheel. I had held that view for a long time and recently saw an interview with Michael Andretti confirming that. On a street car you are unlikely to notice 20 pounds per wheel if all things were equal (yeah, here comes someone to disagree). What people do notice when they go bigger is that the car is harder to turn (more contact patch) and that is "feels" a little sluggish. Geo has correctly pointed out why people think it feels sluggish.
__________________
Best Car Insurance | Auto Protection Today | FREE Trade-In Quote
#20
He put on the wrong size tires. 195-65-15 were sized for 6 inch wide tires. 215-60-15 were sized for 7 inch tires. He could have gone to 205-60-15, but not 215-16-15 on 6's. The tires are much too big and the problems he experienced are what happens with a wider than normal tire on a narrow rim. Who every told him to go to that size tire was doing him a disservice. Any competent tire installer could have told you this information.
Chris F.
924S 190K
Chris F.
924S 190K
#21
On a street car you are unlikely to notice 20 pounds per wheel if all things were equal (yeah, here comes someone to disagree).
#22
Originally Posted by chris924S
He put on the wrong size tires. 195-65-15 were sized for 6 inch wide tires. 215-60-15 were sized for 7 inch tires. He could have gone to 205-60-15, but not 215-16-15 on 6's. The tires are much too big and the problems he experienced are what happens with a wider than normal tire on a narrow rim. Who every told him to go to that size tire was doing him a disservice. Any competent tire installer could have told you this information.
Chris F.
924S 190K
Chris F.
924S 190K
#23
I'll join the disagreement on weight, I'm far from an expert driver but I could feel the 2 lb difference between my Fuchs and my PDs. I doubt the difference is enough to be measurable but the car feels much more nimble with the lighter wheels.
FWIW, there's actually a difference in "weight" between a 15 pound 15" wheel and a 15 pound 18" wheel (yes, you read it right), both wheels have a little weight at the center and most of their mass toward the outside (near the tire). The 15" wheel has most of its mass 7" from it's axis while most of the 18" wheel's mass is an inch and a half further out, the same weight has more leverage and thus more inertia.
Think of it this way, there are some among us with lightened flywheels and cranks and it takes quite a bit of work to do these mods (at least the flywheel is easy to get to in a 944 ) for a pretty small gain, wheel weight the same effect on the on the drivetrain that the weight of the crank or flywheel have but wheels are much easier to swap.
FWIW, there's actually a difference in "weight" between a 15 pound 15" wheel and a 15 pound 18" wheel (yes, you read it right), both wheels have a little weight at the center and most of their mass toward the outside (near the tire). The 15" wheel has most of its mass 7" from it's axis while most of the 18" wheel's mass is an inch and a half further out, the same weight has more leverage and thus more inertia.
Think of it this way, there are some among us with lightened flywheels and cranks and it takes quite a bit of work to do these mods (at least the flywheel is easy to get to in a 944 ) for a pretty small gain, wheel weight the same effect on the on the drivetrain that the weight of the crank or flywheel have but wheels are much easier to swap.
#24
Dave, were the tires the same model, size, and age? That would make your car feel much more nimble. Could also be a placebo effect.
My car is running without a front sway bar right now, and it "feels" better, but I know it's really driving worse.
My car is running without a front sway bar right now, and it "feels" better, but I know it's really driving worse.
#25
I just ran some numbers on the amount of angular inertia that wheels and tires add to a car, and it probably isn't enough to feel with a butt dyno. The inertia involved in accelerating a 1400 kg car and driver consists of about 99.5% linear inertia and 0.5% angular interia from the wheels/tires (not including drivetrain.) Changing to a larger diameter wheel of the same weight may reduce your acceleration rate by 0.1% to 0.2%. If the wheel is heavier, the biggest change is in the additional linear interia, not the additional angular interia.
Dave, the flywheel is a different case. If you accelerate your car from 0 to 100 mph, the wheels accelerate from 0 to 1300 rpm. In the same period the flywheel is accelerated from about 3000 rpm to 6500 rpm three times, and back down twice. The inertial changes of the flywheel are much greater than those of the relatively slowly rotating wheels.
Dave, the flywheel is a different case. If you accelerate your car from 0 to 100 mph, the wheels accelerate from 0 to 1300 rpm. In the same period the flywheel is accelerated from about 3000 rpm to 6500 rpm three times, and back down twice. The inertial changes of the flywheel are much greater than those of the relatively slowly rotating wheels.
#26
I'll throw one more factor into the mix. Heat. And it's the most important.
Tires achieve best grip within a temperature range, that optimal range varies for different tire types. A typical DOT R tire needs to be in the 180-200F range. Slicks hotter, streets colder. Check with manufacturer for specifics.
Here is a simple rule of thumb (words to live by):
a) Tires are too big when you can't get into the temp range. In that scenario a narrower tire will be faster.
b) Tires are too narrow when you are running too hot. In that scenario a wider tire will be faster.
There are also other factors that affect tire temp such as tire pressure, alignment, driver technique, ambient temps, etc. Those factors must be understood and adjusted appropriately.
Tires achieve best grip within a temperature range, that optimal range varies for different tire types. A typical DOT R tire needs to be in the 180-200F range. Slicks hotter, streets colder. Check with manufacturer for specifics.
Here is a simple rule of thumb (words to live by):
a) Tires are too big when you can't get into the temp range. In that scenario a narrower tire will be faster.
b) Tires are too narrow when you are running too hot. In that scenario a wider tire will be faster.
There are also other factors that affect tire temp such as tire pressure, alignment, driver technique, ambient temps, etc. Those factors must be understood and adjusted appropriately.
#27
Originally Posted by Luis de Prat
A guy from another forum has a 1986 944 NA with 15" phone dials. When he bought the car, it had 195 65 15 sized tires on it. He later realized that the factory size was 215 60 15 and put on a new set of tires in this size.
He says the car now feels more sluggish and his fuel mileage is down with these wider tires. Since I've never used smaller sized tires on my cars, I wonder if the handling gain (as in preventing understeer/oversteer) is enough to give up the advantages of a more narrow tire, if any.
Anybody?
He says the car now feels more sluggish and his fuel mileage is down with these wider tires. Since I've never used smaller sized tires on my cars, I wonder if the handling gain (as in preventing understeer/oversteer) is enough to give up the advantages of a more narrow tire, if any.
Anybody?
According the pontiac grand prix wider is better! LOL
#28
Originally Posted by Peckster
Many people buy tires more for looks than performance imo. But you'll have a hard time convincing them their fat tires don't make their car handle better. These things are so subjective, unless you have a professional or very experienced driver who can test different tires on the same car and compare lap times.
I also have to wonder about the current mania for giant rim sizes. Looks or performance? I suspect the former is the biggest factor.
I also have to wonder about the current mania for giant rim sizes. Looks or performance? I suspect the former is the biggest factor.