Top speed?

[Frenco99]

Ok guys, I have a 88 na 944 on stock 215 tires. I've been wondering.. I know this will hurt my acceleration points, but will wider tires increase top speed? Such as an 255 or 275 width tire?

[marre94487]

Physically, since it will be heavier with more rim and tire mass it will increase rotational force needed to turn the wheel and technically that would rob top speed as well as acceleration just like you brought up. Adding meaty tires is usually accompanied with suspension (or/and power) upgrades to give the car a set up to decrease the disadvantage of rotational mass as much as possible. Wider tires keep the vehicle more steady in the corners with more contact surface to the road and the usually accompanied suspension upgrade will cooperate and aid the beefy tires to stick its bigger contact surface to the road as well. Aerodynamical downforce modifications/upgrades are also a good combination with wider wheels. So as far as running stock with wider tires goes, physically I cannot see any pefromance beeing gained.
Hope I helped answer your question, apart from perfomance wider tires make our cars look like proper racers, gives an aggresive appearance. Cheers and good luck with your wheel searching!

[ckelly78z]

Depends on the aspect ratio. The 215 represents how many mms it is from the lip of the rim, down the sidewall, across the tread width, and back up the other sidewall to the other lip of the rim. If you have a 50 series tire, 50% of that 215 mms is used up by the two sidewalls so your tread width would be 107.5 mm wide. This also means that each sidewall would be just shy of 54 mms. from that you can figure out the circumference of the tire and how far it will travel with every revolution. A 255 40 series tire would have 102 mm of sidewall so each sidewall would only be 51 mms (alot shorter).

By changing the height of the tire, it will effectively change the gear ratio, and provided you have the horsepower to push it, would make you go faster if the tire was taller.....not likely with a N/A 944 with 153 HP.

[v2rocket_aka944]

No
The 944 is drag limited, by aerodynamics...tires don't have a whole lot to do with it. There is plenty of gear left when the 944 hits an air-wall.

a 944NA should be able to get to at least 130, maybe 140, depending on your actual power output...a 951S, with 100 more HP, will crack 160.

Is your car a racecar? Because if you're hitting top speed you should probably gear down and run smaller tires to accelerate better...there aren't a lot of tracks that allow a 150hp car to get up to 140mph

If its a street car, I will say, don't do it. But when you do try it, make sure everything is well bolted on and secured!
Driving a 944 with good-shape tires (rated for the speed), good suspension, etc way past 100mph is about as dramatic as a dog farting itself awake from a nap.
It just gets louder from wind and engine noise, but it doesnt shake or anything crazy.

Find a nice straight, preferably downhill, section of "closed highway", just after sunrise (headlights up will slow you down), and go for it...

[Tervuren]

When you hit 5th gear. five miles later, you might of picked up another 8 MPH. Another 5 miles, maybe a little more. 5th is for fuel economy, and the engine runs out of torque to push against the friction. As you shorten the ratio with a smaller tire, it has mechanical advantage, but you run out of torque sooner, so it sort of balances out, providing you haven't tuned the car for more top end.

For all practical purposes, the top speed is the top of 4th gear, its just "a little extra" after.

[333pg333]

btw...how often do you do 140mph or whatever these cars wind out to? Is it a track car? Even then, very rare to be hitting the rev limiter in top gear.

[Frenco99]

I don't top out often at all, just curious about how to increase it as I've had some run ins with c4 corvettes and mustangs. Really just wanted to know if I could "hang" if it even go to that point. But I will be tracking it soon to answer your race car question

[v2rocket_aka944]

a c4 corvette will pull your doors off in a straight line race.
along with any 90s+ v8 mustang.
you can pull on or at least keep up with most v6 mustangs up til 2010 or so (whenever they got rid of the 4.0)`

[Tervuren]

Originally Posted by 333pg333

btw...how often do you do 140mph or whatever these cars wind out to? Is it a track car? Even then, very rare to be hitting the rev limiter in top gear.

You limit out well before the rev limiter. Your rear wheels would have to be off the ground, or sitting on rollers, to hit the rev limit in top gear.