I hit it!!! Theoretically.

Just messing with the top speed calculator and with my 18" wheels and 7K redline that chips allow, I can "theoretically" hit 201 mph with a stock 5th gear; and a lot more hp. lol

http://www.catherineandken.co.uk/sti/tyres.html

 

Hey Todd... 'sup?

How does a 17" wheel-size possibly affect top speed?

Did you take into account outside tire diameter?

Keith

 

Hey Keith! How goes it down under in O town?

My understanding is the bigger the wheel the less revolutions the gears/wheels have to make so it is like adding a higher gear(lower gear ratio) with using bigger wheel. So if 5th gear is .850 and you go from a 16" to 18" wheel that same gear is like .750, or so. Not real numbers, just example of theory.

I assume the calculator takes uses the tire/wheel data to compute the outside diameter of the wheel/tire.

 

you also need to take into account clutch slippage. Typically it is not more than 10% for a very good clutch.

 

hmm...I find this extremely hard to believe on stock gearing. My '87 951 with a 6950-7000 redline will do 145-148mph in 4th gear at the limiter. This is on 225/45/17 and 255/40/17 tires.

On 225/35/18 and 285/30/18 it goes a little slower. The 17's are taller by a bit (18's are right at 24.7" tall). So unless your running like a 225/40/18 and 285/35/18 or something biggger then that, I find it VERY hard to believe.

I've calculated 183mph on stock 951 gearing. My S2 with turbo trans runs at about 135-140 in 4th at 6480. Thats with my 18's.

Let me ask you this, what's your speed at 7k rpm, in 2nd and 3rd? Mines 70 and 107.

 

Here you go http://www.924.org/Downloads/PorscheTrans1.xls

 

Todd,

Well the problem is that when using larger diameter wheels, you tend to use lower-profile tires, so the overall circumference does indeed remain the same, and therefore no increase in top speed.

In order to increase the circumference by ¼ (for example) you'd have to increase the OUTSIDE tire diameter by the same fraction... and then it wouldn't fit in the wheel arch, -front OR rear.

Keith

 

In some cases.

Some good searching on this very forum on this topic.

https://rennlist.com/forums/944-turb...h-what-hp.html
https://rennlist.com/forums/944-turb...ak-200mph.html
https://rennlist.com/forums/944-turb...n-a-951-a.html

 

It also is talking in a "perfect world" there is no account for the friction of the air on the car "At speed" . These scales are not even a waste of time because there is never that perfect world for example I did one of the scaling for my quarter mile time on one of my race cars and it said 8.9ish and when test it was a 9.53ish. Just my 0.02 cent these things are a waste of time


costas

 

two words - aerodynamic drag

 

Yeah thats right. I measured a 6.7 1/4th mile when I was running with my Nikes, but when I changed to Adidas, I got a 7.35

 

Glad to see you are out of jail.

 

Scaling error or driver error???

 

True, but I am pretty sure even with lower profile tires on my 18's, they're still a larger diameter than the old 16". My 16" were 55 profile and 18" are 45.

 

I will have to get back to you on that as I try not to run it out to 7K that often. lol

IIRC at the stock redline (appx 6,500) I would be about 100-101 in 3rd.