Motor RPM per tire size

[2qmedic]

Greetings, hope everyone had a joyous Easter, remembering the day with all spirtual respects and enjoying family gatherings with all the little ones.
And it never hurts to find the prize egg!!!

I did a search and have not found what I'm looking for.

It has been posted before on the RPM difference between the 205-60 & 205-65 rear tire at highway speed.

Does any one have the info?

Thank you much,

[John Schmidt]

This is from the link below, comparing at 3000 rpm there's very little difference.

RPM with 205/60 R 16's      RPM with 205/65 R 16's 
              3000                                  2908


http://www.dakota-truck.net/TIRECALC/tirecalc.html

[2qmedic]

This gives the tire revolutions per mile of which I have.

What I was looking for was the motor RPM difference at high way speed.

Thanks

[R J]

This gives the tire revolutions per mile of which I have.

What I was looking for was the motor RPM difference at high way speed.

Thanks

Don't understand what you are asking if ya don't have the rear end ratio, but try this one and see if it tickles yur inerds.   LOL.

http://www.tacomaworld.com/forum/tirecalc.php

[John Schmidt]

What I was looking for was the motor RPM difference at high way speed.
Thanks

Hey, do you suppose if you multiplied the final transmission gear ratio of .805 X the two wheel rpm's....you might get the corresponding engine rpm??? So...3,000 at the wheel = 2415 for the engine. And 2908 at the wheel = 2340 for the engine. That's 75 rpm difference at the engine for the different tire sizes. You disregard the final drive ratio because it's the same for either situation.

Be interested if someone disagrees with my suggestion, which has worked for me in the past but I may have overlooked something. I don't hold my self out as the know all/end all when it comes to such things. 

"This gives the tire revolutions per mile of which I have."
No, that's revolutions per minute...not mile.

[2qmedic]

Yea, I played around with the math alittle also.
I see that there is a 3% reduction in the tire revolutions per mile, I wonder if that also equals a 3% motor rpm reduction?

ie 205-60 = 3000 rpm @ 60 mph
   205-65 = 2910 rpm @ 60 mph   
                (3000 - 3% = 2910)


This would seem logical, but for some reason just doesn't seem correct.
If memory serves (and sometimes it dosen't), I was thinking there was a approx 200 rpm difference between the 2 sizes at 65 mph.

[John Schmidt]

Another approach; one mile=63,360". The circumference of the 205/60 is 80.69", the circumference of the 205/65 is 83.23".  So, by dividing 63,360 by each circumference, you get 785.23 revs. per mile of the 205/60 and 761.27 revs. per mile for the 205/65. Essentially a 24 revolution per mile difference between the two sizes. I wouldn't concern myself with that so much as the handling difference along with possible extra clearance issues. The engine rpm difference at speed is inconsequential so the issue boils down to personal preference on size, handling, and clearance/mounting. As I see it, it's not going to make a big difference in economy, however it will sit you just under an inch higher with the 205/65 assuming nothing else is changed.

[Bobbo]

This is from the link below, comparing at 3000 rpm there's very little difference.

RPM with 205/60 R 16's      RPM with 205/65 R 16's  
             3000                                  2908


http://www.dakota-truck.net/TIRECALC/tirecalc.html

"This gives the tire revolutions per mile of which I have."
No, that's revolutions per minute...not mile.

If a 205/60 R 16 tire was turning at 3000 RPM, the vehicle would be traveling at 229 MPH!!      

[roboto65]

Ok what I want to know is for the front what size tire to take the 5 mph over that I show do I go up in size or down. Yeah sorry for the highjack LOL

[Mildew]

The Electra glide Harleys have an 18" wheel. Thats a 20 mph difference from the 16" at 65 mph.

[2qmedic]

I know it would be;
-1" taller tire = 1/2" taller axle height = 1/4" taller seat height
-possible clearance concerns (not likely cause I'm a light weight)
-slight handling difference if any,
-small motor rpm difference.

But it is the Motor RPM difference that I want to get a handle on...is it going to change anything, probably not, but it's just what I want to figure out.

[John Schmidt]

I was just giving him an RPM comparison. I think he's too hung up on the engine speed differential between the two tire sizes. It's not that big a deal and I've spent more time on the entire issue than I normally would....but it's been raining here today. My feelings....just pick a tire you like; a 205/55, /60, or a /65, just not worth the worry 'cause it ain't gonna wear the engine out any faster or save you a noticeable amount of gas. Pick one, mount it, and ride already. 

[2qmedic]

Yep, its an answer that I want to know - call me hung up on it or what ever???
ain't gonna make a difference in anything,
I like to figure out these things and just want to know

[Bone]

If you want bigger tires, divide your old tire diameter by your new tire
diameter. This tells you what your NEW RPM will be.



FOR EXAMPLE, if you want to switch from 32" tires to 35" tires, you
divide 32/35 = 0.9143. So, your NEW RPM = 0.9143 times your OLD RPM.

[Mildew]

It would be nice to cruise at 2800 rpm instead of 4000.

[2qmedic]

FOR EXAMPLE, if you want to switch from 32" tires to 35" tires, you
divide 32/35 = 0.9143. So, your NEW RPM = 0.9143 times your OLD RPM.

Well, I'll be running over 100 miles today before I get back to the house.
I'll record what the rpm is at different speeds and come back and figure accordingly.

Stay tuned, more to come...

[Mildew]

Actually my bike runs the best over 3000 rpms. I can really feel the help it's getting after 2900 or so. I think it's suposed to run just the way it is with the 60 or 55. I've known some people to run 70's. No need for an extra gear or the taller rubber. The valks 5th gear is taller than the Harleys 96 CI 6th

[Rio Wil]

Unless I screwed something up, just take the number of tire revolutions per mile and multiply by 3.333  (while in 5th gear) and you will have engine rpm.  Assuming you do the number of tire revolutions in one minute, it will equal rpm.  A tire that turns 800 per mile will be 2666 rpm, a tire that turns 750 per mile will be 2499 rpm.   The idea is the overall drive train  gear ratio times the revolutions per mile (and the revolutions are done in one minute)