# Wheel size and efficiency



## 3dplane (Feb 27, 2008)

Ioku!
While that works good from a fuel efficiency standpoint in a ICE car, EVs don't benefit at all from low motor rpm. Actually the motor in EVs have to be kept at a "happy" higher rpm where their efficiency is greater due to reduced current draw. (Most people only use second and third gear.) Now as far as rolling resistance goes sure the larger diameter tire should be more efficient.
Barna.


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## DVR (Apr 10, 2008)

I agree, The ratios of the g/box are there to keep the motor in a range where it's happy. but a larger wheel shouls handel road irregularities better and therefore be more efficient.

I think...


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## ww321q (Mar 28, 2008)

I had a 1984 4x4 Nissan with 36" tires . In 5th gear it would not accelerate at all on the freeway . ....................J.W.


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## 3dplane (Feb 27, 2008)

The original poster stated same weight between the tires in comparison.I have a 1994 mazda protege. the rpm is about 2500 at 50-55mph with 13" tires.I could use more diameter for better mpg. but would not put "mud truck" wheels on there to achieve it......Barna.


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## DVR (Apr 10, 2008)

ww321q said:


> I had a 1984 4x4 Nissan with 36" tires . In 5th gear it would not accelerate at all on the freeway . ....................J.W.


within reason, a vehicles acceleration is a function of available power and gear ratios. not the tire size. If you want to design a vehicle i to go a certain speed with a certain size tire, you select a gear ratio to efficiently achieve that. If you then mess around with the tire size the original ratios will be incorrect and inefficient. Those same tires with the correct ratios would be efficient.


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## ww321q (Mar 28, 2008)

well said DVR ! On the EV I'm building I am even changing the ring and pinion gears to make use of 4th and 5th gears in the trans. Only $162 for that truck. Now the hard part calculate the right gear ratio J.W.


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## Carroll_1 (Dec 18, 2007)

Here's a link to a RPM / Speed spreadsheet I've used. http://www.landiss.com/files/mphvrpm.xls


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## ww321q (Mar 28, 2008)

That your good looken S-10? J.W.


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## dataman19 (Oct 7, 2009)

If you are retaining the OEM transmission - have you considered your speedometer calibration when changing physical tire size?
..
I know this may be a little off topic - but the speedometer is required in almost all regulatory jurisdictions. And an accurate one will keep the blue lights from chasing you around.
..
dataman19


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## DIYguy (Sep 18, 2008)

woa... hold on here...babalouie...lol. If you want to compare efficiency of wheel size that's kewl... but what has it to do with gearing etc?... when figuring out such things...one must eliminate the influences of other items...or minimize them as much as possible. In other words.... if you want to compare two wheels of different sizes... you need to change the gearing to eleminate it as an influencing difference, right? unless I'm misunderstanding your intent....?

I'm thinking you want to get to the issues of rolling resistance based on diameter, weight of rim vs tire influence etc.... yes/no? (don't ask me the for the answer though! lol)


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## Woodsmith (Jun 5, 2008)

Wheel diameter has to be factored in with the gear ratio. It is the final 'gear' before rotational motion is converted to linear motion.

However, if the overall ration of motor to road is the same then a larger diameter wheel will have less rolling resistance, allowing for tyre tread pattern, tyre pressure, tread width etc.


As an aside why is Dataman 19 resurecting year old threads all over the forum?
(never mind, probably searched and came up with lots of questions.)


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