Does increase on car wheel size reduce engine rpm at high speeds?

[umairc2]

My car which has a 1.5 engine . The wheel size are 14", which are factory wheels. If I upgrade them to say 15 would that reduce the engine rpms? Does it affect the transmission in any way?

[ali454]

The rpms will decrease only if you are able to recalibrate the speedometer according to the bigger tire you put which i doubt is possible.

Bigger tire means less revolutions for same speed as compared to a smaller tire.
The thing you can do is calculate the speed error and find the difference in speed and try driving it at that speed.

For example changing a tire size from 185/65/r14 to 195/65/r15 will give an error of aprox 7kmph. Meter will show 120kmph but ur actual speed will be 127kmph. You can drive at 113kmph so as to maintain ur actual speed of 120kmph.

This is the only way i could think of to keep rpms low.

[HellsGuardian]

a larger tyre in simple words decreases your overall gear ratio so you travel faster on same rpm. Use this site to calculate the difference between oem size and the size under question.

https://www.tacomaworld.com/tirecalc

It is recommended not to go above or below 3% change in diameter from oem size.

[mzahid]

Increased tyre diameter increase fuel consumption in stop and go driving. While decrease fuel consumption on steady speed highway drive.

[sunny221185]

No they cant reduce. If u have a wider tyre, for example 195 (wider) on your Car no matter how big the tyre is 14 or 15". The Friction between the Asphalt and the tyre will be increased. So your Top Speed will be decreased if your engine has not enough power. If you have 14 or 15" Tyres your rolling scope could be higher or smaller. So it shows u a fault speed on your speedometer.

[sunny221185]

Increased Tyre DIAMETER doesnt increase the fuel consumption only wider tyres bcz of the increased friction between asphalt an tyre.

[mzahid]

Increased diameter require more torque in typical first gear driving .... more fuel consumption ... experienced it personally with same width tyres.

[mzahid]

kmph reading will be lesser than actual, while rpm reading will be accurate.

So to maintain same actual speed you need lower rpm.

[sunny221185]

Exactly

[sunny221185]

Brother can i ask wich tyre sizes u had that u noted a bigger fuel consumtion? Normally when u incresae the diameter also the tire will be wider but than u smaller the percent of the hight to stay at a gud rolling scope or like brother "hellsguardian" already mentioned in the 3%

[mzahid]

Old times .. I shifted from 175-R13 to 175-R14 (Baleno) ... increase in fuel consumption is felt when driving too much in rush areas.

Simple formula Torque = Force (Tyre width) x MomentArm (Tyre Dia)
For more torque you need more engine power and hence more fuel.

On highways it actually improved fuel consumption while light foot. I even achieved mileage of 19-20

[sunny221185]

I agree with your argument brother. No need to calculate . But didnt thought somebdy will notice that little on more fuel but maybe u noticed your fuel in a book . Or simply 14" was to much for a baleno. Thanks Brother.

[HellsGuardian]

Guys fuel economy depends how bigger is the size and how wider is the tyre. If you are increasing size in one step the mileage difference would be very little and will also depend on usage e.g city drive or highway drive. Now another import thing is that brand and tyre type. Some tyres have lower rolling resistance, in such case you MAY get increase fuel economy buy going one up size.

But if tyre type and brand is same, then size that lies within 3% difference wont have much affect on mileage. Any more than that, and you will get reduced mileage due to more friction of tyre. Apart from mileage, going above 3% change also is not good for suspension system and braking distance may actually increase. For best results, stay less than 3% difference if you want best economy, health of suspension and braking of car.

[sunny221185]

I think everything is said otherwise the starter from this discussion will sell his car an walk​ . We can also talk about Alloy Wheels and Steel wheels and so on. But i think he got his answer.

[umairc2]

Thanku so much brother
Actually i have civic exi 2005. Exi come with 14 and vti come with 15 so if i install 195/65/15 on exi then what will happen.. I think speedometer nd odo will not work correctly? Coz vti is 1.6 nd exi is 1.5. So which size is best for Exi? 195/65/15 or195/60/15

[HellsGuardian]

If you want to go with 15" then you have following options, listed best to worst

185/60R15
195/60R15
185/65R15
195/65R15

Yes VTI comes with 15" size but i think you should stick to your rim size i.e 14" and find better profile like 195/65/R14

[umairc2]

Ok but if i maintain 14 inch diameter by using the less side wall tire e.g 195/55/15 on 15" rims.. is it better or not?

[HellsGuardian]

yea its fine but expect a little less economy due to increased width. 195/55R15 is good looking profile for your car

[umairc2]

Hmm thanku brother but more width means more grip...

[HellsGuardian]

grip factor for such small increase is very little, its more of a look thing i would say