ok, with a 15" rim the diameter is 15" right? if so, i have a tire that measures 195/50/r15 and assuming the tire is off the car what will the diameter be of the wheel now with the tire on it assuming pressure is 30psi. in other words the /50/ means what...the height of the tire measured in what units...mm?

50mm=1.96inches. so now the diamter of the rolling wheel is 16.96inches (not accounting for pressure sag when the wheel is actually on the car.) am i on the right track here?

what im trying to do is figure out what size wheel i should use with a b16 tranny on an ls motor to account for the short gears at the track. i want to hit 104mph in 4th gear at 7000rpm.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by the.hamburglar &raquo;</TD></TR><TR><TD CLASS="quote">ok, with a 15" rim the diameter is 15" right? if so, i have a tire that measures 195/50/r15 and assuming the tire is off the car what will the diameter be of the wheel now with the tire on it assuming pressure is 30psi. in other words the /50/ means what...the height of the tire measured in what units...mm?</TD></TR></TABLE>

50 is the aspect ratio, the ratio of the sidewall height to the tread width.

On a 195/50-15 tire, the tread width is 195 mm. The sidewall height is 195 mm * .50 = 97.5 mm. The outer diameter of the tire is the wheel diameter plus two times the sidewall height.

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by the.hamburglar &raquo;</TD></TR><TR><TD CLASS="quote">what im trying to do is figure out what size wheel i should use with a b16 tranny on an ls motor to account for the short gears at the track. i want to hit 104mph in 4th gear at 7000rpm.</TD></TR></TABLE>

You should get the proper size tires for your CAR, not for the engine or transmission. Meaning, you should get tires whose outer diameter is the same as the stock tires that came on your car. That way, your speedometer and odometer should be accurate, and your tires shouldn't rub on the fender well liners or suspension. What kind of car do you have? (model, version, year)

If you want to change the effective gearing of your car (the ratio between the engine revs and speed), do it by changing the gears, not the tires.

 

thanks, its a 94 civic coupe with a b16 turbo that just blew.

ok anyways if i were to make a pass in the 1/4 with my stock 15" wheels at lets say 90mph at 7000rpm and then i put 22" slicks on which will be a larger diameter tire i might now be able to make a pass at lets say 95mph at 7000 rpm again. i will not have to shift into the terrible 5th gear. how would you do this calculation just for curiosity to see what size tire you would need to make a pass in the 1/4 at 104mph at 7000rpm. im guessing its going to be a big *** tire

 

If you are at 7000 RPM at 90 mph with your stock tires, and you want to know what size tires would put you at 104 mph, the outer diameter of the tire would need to be 104/90 = 1.15556 times as large, or over 15 percent larger. That means the outer diameter would be almost four inches larger. It will almost certainly rub.

Your car came with 185/60-14 tires stock, which have about the same outer diameter as 195/50-15. A tire size that would be about 1.15556 times as large as stock would be 285/50-15, or 355/40-15. And those tires are much too wide to fit on your wheels, of course.

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by the.hamburglar &raquo;</TD></TR><TR><TD CLASS="quote">im guessing its going to be a big *** tire</TD></TR></TABLE>

Yup.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by nsxtasy &raquo;</TD></TR><TR><TD CLASS="quote">

50 is the aspect ratio, the ratio of the sidewall height to the tread width.

On a 195/50-15 tire, the tread width is 195 mm. The sidewall height is 195 mm * .50 = 97.5 mm. The outer diameter of the tire is the wheel diameter plus two times the sidewall height.

</TD></TR></TABLE>

assuming your calculation of sidewall height and not accounting for the sag of the force of the car on the 4 tires:


my car came with those tires but it didnt come with that motor. im pretty sure sir's came with 195/55/r15 using the b16 tranny...

185/60/r14 tire
185*.60=111mmx2 + 14"=8.74"+14"=22.74"
22.74" is the diameter of the wheel and tire on 14" rims

or

195*.55=107mmx2=8.44"+15"=23.44"
23.44" is the diameter of the wheel and tire on 15" rims

22.74/23.44 * 100=97.02 %
they are within ~ 3% of each other.

anyways assuming the sir came with the 195/55/r15...here i am going to find the outer diameter of tire i need to have a trap speed of 104mph (assuming my car is that fast and hopefully will be soon) and still be at 7000rpm on an ls motor with a b16 stock transmission:

given:
195/55/r15 - stock tire size
7000rpm on a b16 tranny will yeild 97.07mph in 4th gear link-

https://honda-tech.com/zerothread?id=1433587

find:
the outer diameter of the tire needed to have a trap speed of 104mph at 7000rpm in 4th gear with the b16 tranny.

soln:
circumference: 2piR=2pi(11.72")=73.64"=1.87043m

1.87043m*7000rev/min=13093.00207m/min=13.093km/min=785.58km/hr

4th gear @ 7000rpm = 97.07mph = 156.21902km/hr

when the wheels rotate at an angular velocity of 785.58km/hr, the crank has an angular velocity of 156.21902km/hr at 7000rpm. so the gear ratio between the two is:

785.58kph/156.21902kph = 5.017:1 is the gear ratio we have

104mph=167.37178kph so,

785.58kph/167.37178kph = 4.69362:1 is the gear ratio we want after the larger tires



5.017/1 = x/167.37178
X = 839.70422kph = 13995.07033m/min

13995.07033m/min
---------------------- = 1.99930m will be the new circumference of the tire i
7000rpm redline need

1.99930m new circumference &gt; 1.53365m old circumference of stock tire


1.99930m=78.71243"

78.71243"=2piR
R=12.52747"
D=25.05495"

using my 15" rim:

25.05495"-15"=10.05495"is the height i will need to gain on the 15" rims or 5.02748" inches on the top and the same on the bottom in order to have a trap speed of 104mph with the b16 transmission at 7000rpm. so the tire size i will need for the 15" rim is:

195*W=5.02748" where W is height of sidewall and will be in inches so ill need to convert to mm.
W=0.02578 "=.65486mm

the tire size i will need is 195/65.486/r15 to trap 104mph with the b16 tranny on an ls motor. now i realize that nobody will ever hit 104mph on street tires so i would have to get a 14" rims with a calculated tire size slick. so it is possibly. the math shows its not going to be such a bigass tire after all!!! and the b16 tranny will be perfect for the ls motor for anyone hoping to do a 12.9second 1/4 like me sometime in the future.

Modified by the.hamburglar at 4:47 AM 11/15/2005


Modified by the.hamburglar at 4:48 AM 11/15/2005


Modified by the.hamburglar at 4:49 AM 11/15/2005

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by the.hamburglar &raquo;</TD></TR><TR><TD CLASS="quote">they are within ~ 3% of each other.</TD></TR></TABLE>

Actually, 195/55-15 is 3.1 percent larger than 185/60-14. 195/50-15 is 0.3 percent smaller than 185/60-14. Which is why 195/50-15 is a better match.

Incidentally, if you don't feel like doing the math yourself, you can use a tire calculator website like this one.

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by the.hamburglar &raquo;</TD></TR><TR><TD CLASS="quote">195/55/r15 - stock tire size</TD></TR></TABLE>

If it's a stock Civic Coupe, it came with 185/60-14. At least, it did in North America. I'm not sure where you are, since you didn't fill in your location in your profile.

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by the.hamburglar &raquo;</TD></TR><TR><TD CLASS="quote">the tire size i will need is 195/65.486/r15 to trap 104mph with the b16 tranny on an ls motor.</TD></TR></TABLE>

That's not correct. If you trap 90 mph with stock size 185/60-14 tires, then you will need tires whose outer diameter is 15.556 percent larger (see above) and you don't need to do all the intervening math; it's a simple ratio, dividing one number by the other.

Outer diameters:
185/60-14 (stock) = 22.74"
15.556 percent larger than that = 26.28"
195/65.486-15 = 25.05"

As you can see, your 195/65.486-15 is nowhere near large enough to cause the actual road speed to rise by 15.556 percent.

 

im from canada and the sir's came with 195/55/r15 tires. its so close it doesnt really matter

and where are you getting the 15% from. can you show me?

 

circle with radius 10 will have a circumference of 2piR=62.83

circle with radius 20................................................ .=125.66

so now that the radius is twice the size the circumference is twice the size so you guess you could do ratios...?

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by nsxtasy &raquo;</TD></TR><TR><TD CLASS="quote">If you are at 7000 RPM at 90 mph with your stock tires, and you want to know what size tires would put you at 104 mph, the outer diameter of the tire would need to be 104/90 = 1.15556 times as large, or over 15 percent larger. That means the outer diameter would be almost four inches larger. It will almost certainly rub.

Your car came with 185/60-14 tires stock, which have about the same outer diameter as 195/50-15. A tire size that would be about 1.15556 times as large as stock would be 285/50-15, or 355/40-15. And those tires are much too wide to fit on your wheels, of course.

</TD></TR></TABLE>

no, according to the chart found here:

https://honda-tech.com/zerothread?id=1433587

the b16 tranny at 7000rpm will move a car at a velocity of 97mph. it doesnt say what tire size is on the car but if you say the car came stock with 185/60/14 then i imagine the the speed is calibrated with those tires which means

104/97=1.072 which means the tires will need to be 7.2% larger. and i had
the initial diameter of the tires at 23.44" (check your calculate link) and i said they needed to be 25.05495":

25.05495"/23.44"= 1.069.....6.9% larger which is close enough because i didnt carry all decimals.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by the.hamburglar &raquo;</TD></TR><TR><TD CLASS="quote">im from canada and the sir's came with 195/55/r15 tires. its so close it doesnt really matter</TD></TR></TABLE>

That's okay - you can do the math using 195/55-15 tires as stock.

The 15 percent came from your statement where you said to assume your car did 90 mph at 7000 RPM when stock. If you change it to 97 mph, you can re-do the math. That (along with the difference in size) is why it's now 7 percent instead of 15 percent.

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by the.hamburglar &raquo;</TD></TR><TR><TD CLASS="quote">the b16 tranny at 7000rpm will move a car at a velocity of 97mph. it doesnt say what tire size is on the car but if you say the car came stock with 185/60/14 then i imagine the the speed is calibrated with those tires</TD></TR></TABLE>

Yes, the speed on the chart would be calibrated with those tires.

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by the.hamburglar &raquo;</TD></TR><TR><TD CLASS="quote">104/97=1.072 which means the tires will need to be 7.2% larger. and i had
the initial diameter of the tires at 23.44" (check your calculate link) and i said they needed to be 25.05495":

25.05495"/23.44"= 1.069.....6.9% larger which is close enough because i didnt carry all decimals.</TD></TR></TABLE>

That makes sense.

However, a tire that is 7 percent larger than stock is still quite big, and has a pretty good chance of rubbing.

 

yeah ok i see where you got the 15% from. i was just using the 90mph as an example until i found the speed chart which said 97mph. on the other hand if a tire that large fits in there then this is a good way to control your trap speeds.

anyways enough about this, the other option is to rev the ls motor past the stock rev limits. what can it safely go up to? 7500?