Given you calculate with wheel diameter in meters, the speed will be in meters per second. Multiply with 60 and divide with 1000 to get kph.
The factor 3.02 (used by tyre companies) is used in stead of pi to compensate for the wheel not being a perfect circle when rolling.
Calculating top speed using the figures from the first post:
wheel diameter (rim + side walls) : 19*2.54 + 2*(28.5*35/100) = 68.21 cm
drive ratio (gear ratio * final drive) : 0.833*3.62 = 3.015
Stick the formula in an excel sheet and you can play with rim size, wheel size and final drive to see how it affects your speed in different gears.
(ahhh, this brings me back to the long gone days of bmwe30.net where guys used this to see what final drive they would need to reach 100 kph in 2nd gear)
Very cool but wouldnt hp have anything to do with it? So if a stock m6 will do 338kph approx 210mph what about an m6 with 50 extra horsepower and maybe 50lbs ligher. I would think the weight of the car and horsepower have some consideration, no?
Very cool but wouldnt hp have anything to do with it? So if a stock m6 will do 338kph approx 210mph what about an m6 with 50 extra horsepower and maybe 50lbs ligher. I would think the weight of the car and horsepower have some consideration, no?
To keep it simple so we donīt hijack the thread; no. Go ahead and tune your car to 1000hp, or 2000hp. With the wheel diameter and drive ratio above, at 8250 rpm you would still be doing what speed?
338 kph.
You would, however, get to 338 kph very, very quickly
But yours is modded. What would you say top speed of a stock M6 with speed limiter removed to be? Or maybe M6 with basic mods like intake/exhaust? Is there a formula for top speed b/c i heard standard vets can do 200mph and with just a V8 i'd think our V10's should be able to go much faster.
The amount of cylinders a car has does not have any bearing on its ability to hit a given maximum speed; but the power that engine produces does factor in. There are stock Corvette V8 engines that produce allot more power and torque than the S85 V10 engine found in the M6's so don't let the amount of cylinders fool you. The horsepower, transmission gearing, final drive ratio, wheel diameter, mechanical drag, aerodynamic drag and weight are what factor in; plus I may be forgetting a few.
Quote:
Originally Posted by landski
To keep it simple so we donīt hijack the thread; no. Go ahead and tune your car to 1000hp, or 2000hp. With the wheel diameter and drive ratio above, at 8250 rpm you would still be doing what speed?
338 kph.
You would, however, get to 338 kph very, very quickly
I know you said you wanted to keep your explanation simple but that is a little oversimplified. Top speed will be affected by the power that is made and where in the rev range it is being made. Allot of vehicles do not have enough power to reach the mechanical drive limit of their transmission gearing, final drive and tire height. Also with the M6 if you are making more power in the upper rev range than you will probably be able to continue to accelerate while in 7th gear past 8250 rpms which will of course mean that your top speed achieved is higher.
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Last edited by rocket5979; 27th September 2011 at 13:18.
Back to the OP's original purpose of this thread, which I can only assume is to develop some sort of tech information database about the M6. Attached is a .pdf document that has allot of VERY in-depth technical info for the S85 powertrain and DME. While the title says it is for the M5 all engine information applies to the M6 as well. Enjoy.
Edit: Well I tried to attach the 15MB file but the forum didn't let me. Strange. I will try to figure out some other way to post it.
Just some random info that may be good to include in the first post. Engine control module, also referred to as the DME Control unit, is the Siemens MS_S65. Stock compression ratio for the S85B50 V10 engine is 12.0:1. The firing order is 1-6-5-10-2-7-3-8-4-9. The 7 speed SMG III transmission is officially deemed the SMG Getrag 247. The reverse gear ratio is the same as first gear 3.985:1.
I know you said you wanted to keep your explanation simple but that is a little oversimplified. Top speed will be affected by the power that is made and where in the rev range it is being made. Allot of vehicles do not have enough power to reach the mechanical drive limit of their transmission gearing, final drive and tire height. Also with the M6 if you are making more power in the upper rev range than you will probably be able to continue to accelerate while in 7th gear past 8250 rpms which will of course mean that your top speed achieved is higher.
I believe it was sufficiently explained. Our cars are powerful enough to reach red line in 7th gear (in stock form a bit of a struggle, mildly tuned; comfortable). So then power is not the limiting factor for top speed in stock form. It is engine rpm. Maybe you can increase red line to 8400 rpm, but thatīs not gonna do a lot. Do you wanna have the S85 turn faster than that? Wheel size isnīt gonna bring much either. Adding hp is gonna do zilch for top speed on a stock car (M6).
Changing drive ratio is the key to increasing top speed on the M6, and then hp comes very much back into play. But from what I have read on this forum, this is a very rare mod on these cars. Drive ratio mods are anyway mostly done to increase acceleration for the sacrifice of top speed.
I threw that formula into a spreadsheet for people to play with so you can see for yourselves.
I believe it was sufficiently explained. Our cars are powerful enough to reach red line in 7th gear (in stock form a bit of a struggle, mildly tuned; comfortable). So then power is not the limiting factor for top speed in stock form. It is engine rpm. Maybe you can increase red line to 8400 rpm, but thatīs not gonna do a lot. Do you wanna have the S85 turn faster than that? Wheel size isnīt gonna bring much either. Adding hp is gonna do zilch for top speed on a stock car (M6).
Changing drive ratio is the key to increasing top speed on the M6, and then hp comes very much back into play. But from what I have read on this forum, this is a very rare mod on these cars. Drive ratio mods are anyway mostly done to increase acceleration for the sacrifice of top speed.
I threw that formula into a spreadsheet for people to play with so you can see for yourselves.
As I said before, what you stated was a bit on the oversimplified side of things. How is tire height "not going to bring much" when the formula you posted even incorporates it? If I rotate a 24" tire (75.36" uncompressed circumference) to 2,803rpm's that will achieve a speed of 200mph. Now change that to a 26" tire (81.64" uncompressed circumference) and rotate to that same 2,803rpm's and we achieve a speed of 216.7mph. Seems like tire height plays a role in top speed to me. It changes the overall "drive ratio" just like changing a gear in a transmission does and just like changing rear differential gears do. The only difference is that usually with a larger diameter tire you will encounter more parasitic drag due to the resulting higher mass of said tire. So this means that, again, horsepower will come into play to turn that heavier tire. Also if I go from achieving a maximum top speed with a max rpm of 8250rpm's to 8400rpm's, because I am making enough power to pull the car that high, then that is actually a pretty significant difference. It is roughly 2% which sounds small but when speaking in terms of top speed a difference of almost 4mph is pretty large.
Shoot look at the top speed achieved by Russramz in his M6 on the Autobahn some years back. He "only" hit 206.3mph verified by GPS and that was with all of the modifications done to his car at the time. Your spreadsheet assuming that a stock M6 will hit 210mph based upon gear ratios alone is real optimistic. The reason for this is because horsepower does indeed play a factor even with the M6 and so does drag. The car didn't have enough power to accelerate anymore due to drag and thus stayed at a constant rpm lower than the redline of 8,250. By the calculation according to your very own spreadsheet his car was revving to 8,100rpm's while in 7th gear at 206.3mph. I doubt he was only revving that high because he had a piece of carpet stuck under the gas pedal or just didn't feel like going any faster so it must have been something else...... He wasn't anywhere close to stock during that run if I remember correctly.
I am not trying to slam your post because it does have technical merit, but I think it was just too oversimplified.
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where guys used this to see what final drive they would need to reach 100 kph in 2nd gear)
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