how much does wheel and tire size effect speed?

so, background. tomos motor on a puch frame project. i got 2 in mind that this effects.

lets start with the first one. now lets assume i am putting an a35 on my monza which has 17 inch rims and very large tires. i think 3.00 or 3.25 rear. optimally i would like a 31 tooth front sprocket but lets assume i only have a 27 front. i think the smallest rear i can go with is a 25 and that would have to be custom made. now tomos SPEED GEARING is 31x20. and like moderate speed gearing would be 27x22 right? and the gearing i am expecting to be able to reach is 27x25 or maybe 31x25 so...

31x20 = 1.55

27x22 = 1.23

31x25 = 1.24

27x25 = 1.08

so keeping in mind the much larger wheel diameter how do i find out if a 25 rear will be small enough? what is the dext step in the formula?

i also have another project that will be an a55 on a magnum with mbx wheels (18 inches). now i know i can get a 32 rear, would have to have anything smaller custom made. i can use whatever formula to figure out if that extra 2+ inches helps enough.

i assume that wheel diameter has to have a fairly significant role in speed so i am hoping it will make a large difference.

Re: how much does wheel and tire size effect speed

i think you'd be best off working the whole problem backwards. Start w/ your tire/wheel combos circumferences and see what effect it has on RPM at the speed you want

example : a 17x2.25 gazelle is 23inches tall(diameter) so its 6.018 feet per revolution. it seems like a lot of math but once you put it all down on paper its easy to see

Re: how much does wheel and tire size effect speed

or basicly a taller tire will get you more top speed and a smaller rear will be better for hill climbing

Re: how much does wheel and tire size effect speed

What crackstar said. Do some calculations, it's actually not that complicated.

Let's say you have a wheel that is 17" and has a 1" tyre on top of it.

That means the diameter is 457.2mm (=2R). 2PIR = 23.141592654*228.6mm = 1436.34mm per revolution covered (That's 1.43634 meter per revolution)

Now do the same with the wheel you're replacing it with, and you can see the difference and calculate what gear you will need.

Re: how much does wheel and tire size effect speed

weight of the wheels is far more important that wheel size harold size can always be compensated for using gearing.

a drop in a lbs or 2 from a rim/tyre combo can and will produce noticeable acceleration gains.

Re: how much does wheel and tire size effect speed

ok we are getting there. but i still dont know the whole equation. i need a longer equation.

like rpm x wheel diameter x gearing = ????mph anyone know how to do that? i think i might need to know main gear teeth too.

Re: how much does wheel and tire size effect speed

I just realised, I have a program for that Harold. Download it here:'s%20Puch%20Calculator.exe

I belive I already translated it once, for this forum. I'll look that up for you.


Copied from wiki :P

Spoel-/uitlaattiming = Transfer-/Exhausttiming

Timing (In degrees)

Portheight (in mm)

Deckheight (in mm)

Stroke (43mm standard)

Con. rod length (90mm standard)

Inlaattiming = intake timing

Timing (in degrees)

Intakeheight (in mm)

Pistonlength (At the longest point, in mm)

Deck (in mm)

Stroke (43mm standard)

Con. rod length (90mm standard)

Poortbreedte = Port width

True width (in mm)

Portmap width (in mm)

Bore (in mm)

Snelheid, toeren = Speed, RPM

Speed (In KM/H)


Front sprocket (In number of teeth)

Rear sprocket (in number of teeth)

Internal gearing (Leave it the way it is for Puch)

Tire radius (In meters. The length that the tire rolls for one revolution, if you catch my drift)

Informatie = Information

Place the radio button at the variable that's unknown. (The variable you want to calculate)

Re: Translation

jesus fucking christ that is complicated. i think i am looking for an uncommon simple formula. like the solution to a high school algebra word problem lol....

if harold is going 45mph on a bike with 27x25 gearing on a 16 inch wheel, how fast would he go with the same gearing on a 17 inch and 18 inch wheel.

solve for x =P

lol fucking math.

Re: Translation

Well, you can do that pretty easily with the Puch calculator.

It isn't as complicated as it looks. You just fill in the gearing, the speed and the wheel circumference and press "Bereken". Then check the radio box on the gear you want to change and change the wheel diameter to the wheel diameter you will be using.

Re: Translation

If you got the torque to pull it off, weight dosn't matter and so on, you would go faster in relation to how much bigger the wheel is. Like as a percentage.

But that's not how it works in real life.

I've added 1/2 an inch in tire (2.75 from 2.25) and gained 4 MPH... on a shitty scooter with a lot of torque.

Re: Translation

what i want to know is how big of a effect tire width will have on top speed. less tire on the road = less friction right?

Re: Translation

here is a simpler wiki for gear inches:


More accurate is something called Gear Inch, which combines gear ratio with wheel diameter (this is overall diameter, including the inflated tire) to calculate how far your bike will travel for one revolution of the crank. Since almost all modern bicycle chains adhere to the

Re: Translation

put it on and play with it simple

Re: Translation

naw its not simple lol. i have to have custom rear sprockets made at 50$ a pop. i want to get it right ahead of time. if a 25t is gonna be too big i am going to have to pay even more for a super custom offset one.

how much does wheel and tire size effect speed?

Harold, my bike has MB5 wheels, 18", and i run 16 x 36 gears. Doggy off the line but it goes low to mid 50's with my 210 pound ass on it. tempted to put a 17t on front and have a speed run with the GPS. I used a 420 chain with the stock puch sprocket with no issues. I didn't even have to JB weld the sprocket on, lol.

how much does wheel and tire size effect speed?

If you had a 17 inch wheel and switched to an 18 inch wheel. you will travel aproximately 3.14 inches more per wheel revolution.

Re: how much does wheel and tire size effect speed

You have to make some assumptions before you make the calculations.

Assume 10,000rpm

Then figure reductions thru the gears in the gearbox

then knowing the drive sprocket speed determine the reduction (or multiplication) between the drive sprocket and the rear wheel sprocket.

This will give you the rear wheel rpm. Calculate the circumference of the rear wheel tire and multiply it times the rpms it is going. (remember to convert the wheel circumference to feet and decimal feet.)

Divide this out to determine speed over the ground in miles per hour.

Then by using different sprocket ratios you can figure out the over the ground speed with the same engine rpm.

You will have to discount wind resistance as the speed changes and whether the engine can pull the speed desired.

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