Does tire size affect HP????
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PLATINUM SPONSOR
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Does tire size affect HP????
We get asked a lot about tire size and how it affects HP. Yes you will lose a little HP because of larger tires, but that is not the main reason performance suffers. It has more to do with your RPM band and how changing tires size move where you are at in the rpms at a certain speed.
Check out this video to learn more.
Check out this video to learn more.
Fleet Mechanic
Joined: May 2018
Posts: 1,765
Likes: 502
Same here. You aren't going to lose HP because of tire size, but of course it has an impact on the 'seat of the pants feel'. I didn't realize that was a thing people didn't realize was happening...
Hotshot
Joined: Jul 2013
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how much HP/.TQ will I loose on my 37's on 22.5's. I think I started with 450. then added Banks derringer which added 60. then added DFS780 which claims another +20 at 2000RPM. Then I added meth injection which is good for another 10% to 15%. so 450+60+20+45=557. but I added 37's on 22.5's so am I back too 450. I think I spent a lot of money to wind up back where i started.
Lead Driver
Joined: Nov 2005
Posts: 5,219
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From: Kaysville Utah
I can tell you go from stock 275/65R20's ( 34.1" tall) to 295/65R20 ( 35.4" tall cost me 1 mpg
Going from 295/65R20 ( 35.4" and 11.5" wide) to 35x12.5r20 with a slightly more aggressive tread cost me another 2 mpg
So it's not just how tall the tires are, but also how wide and how heavy
Going from 295/65R20 ( 35.4" and 11.5" wide) to 35x12.5r20 with a slightly more aggressive tread cost me another 2 mpg
So it's not just how tall the tires are, but also how wide and how heavy
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PLATINUM SPONSOR
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Bigger tires do in fact hurt HP and can lower MPG... even if you re-gear. Also the extra air drag from sitting higher in the air will also cost hp and MPG.
The main point of the video is realizing how moving your RPM band will GREATLY affect hp. This changes depending on mods/engine/etc but Here is a general example.
70mph with 31s at 2000 rpms vs 70mph at 1500rpm with 37" tires is going to be about a 200hp LOSS in power at the same speed.
So yes, you will feel a HUGE difference in power, but it is not simply because of the bigger tires. It is because you changed where you will be at in the RPMS. Re-gearing will fix that issue, but you still have the extra rotational mass and air drag (which is not as big of a deal).
The main point of the video is realizing how moving your RPM band will GREATLY affect hp. This changes depending on mods/engine/etc but Here is a general example.
70mph with 31s at 2000 rpms vs 70mph at 1500rpm with 37" tires is going to be about a 200hp LOSS in power at the same speed.
So yes, you will feel a HUGE difference in power, but it is not simply because of the bigger tires. It is because you changed where you will be at in the RPMS. Re-gearing will fix that issue, but you still have the extra rotational mass and air drag (which is not as big of a deal).
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Logistics Pro
Joined: May 2011
Posts: 4,832
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From: Maine
Bigger tires do in fact hurt HP and can lower MPG... even if you re-gear. Also the extra air drag from sitting higher in the air will also cost hp and MPG.
The main point of the video is realizing how moving your RPM band will GREATLY affect hp. This changes depending on mods/engine/etc but Here is a general example.
70mph with 31s at 2000 rpms vs 70mph at 1500rpm with 37" tires is going to be about a 200hp LOSS in power at the same speed.
So yes, you will feel a HUGE difference in power, but it is not simply because of the bigger tires. It is because you changed where you will be at in the RPMS. Re-gearing will fix that issue, but you still have the extra rotational mass and air drag (which is not as big of a deal).
The main point of the video is realizing how moving your RPM band will GREATLY affect hp. This changes depending on mods/engine/etc but Here is a general example.
70mph with 31s at 2000 rpms vs 70mph at 1500rpm with 37" tires is going to be about a 200hp LOSS in power at the same speed.
So yes, you will feel a HUGE difference in power, but it is not simply because of the bigger tires. It is because you changed where you will be at in the RPMS. Re-gearing will fix that issue, but you still have the extra rotational mass and air drag (which is not as big of a deal).
I'll wait.
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PLATINUM SPONSOR
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Same thing happens with wind drag from sitting higher in the air, although very minor.
The biggest issue is moving where you are at in the RPM band at a certain MPH. Which can make 200hp less of useable HP
Useable HP is all the matters. And larger tires will give you less useable HP
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PLATINUM SPONSOR
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If you change your tire size, then it will change where you are at in the RPMs based on a certain speed. Which great affects how much useable HP you have available at that speed.
This happens to be a 7.3 dyno graph, because that is what is in the video. But that is not important. 6.7s will suffer from the same issue.
If you want to take a step further... the red line is a modified stock size turbo and blue is a larger turbo. You can see a similar issue with having less available HP at a certain speed also happens with a larger turbo. Same thing happens again with bigger injectors with larger nozzles. Now add bigger tires + bigger inj + bigger turbos + stock gears and you will have a hot smokey mess.
Logistics Pro
Joined: May 2011
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From: Maine
I'm not arguing that there will be less HP to the ground. Shifting, RPMs, gearing, tire size all affect the final transfer of power from the engine to the ground.
But.... it doesn't change how much power the engine makes.
But.... it doesn't change how much power the engine makes.
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PLATINUM SPONSOR
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I don't like to play semantics, I am just here helping people understand their trucks better and how certain mods will affect overall driveability and useable hp (useable HP would be how much force is applied against the road to propel your vehicle forward). When you are struggling to tow a big hill after putting bigger tires on a truck or have slower times at the track... you will notice you have less usable HP.
Re-gearing helps, but it does not solve everything. You will still lose useable HP from wind drag and extra rotational mass from a heavier and taller tire.
Here are a few more links to a similar subject with actual dyno numbers. I have also dynoed it myself and found similar results.
[URL unfurl="true"]https://jalopnik.com/see-how-big-tires-can-change-wheel-horsepower-1825922567
[URL unfurl="true"]https://www.carthrottle.com/post/how-does-wheel-size-affect-performance/
Re-gearing helps, but it does not solve everything. You will still lose useable HP from wind drag and extra rotational mass from a heavier and taller tire.
Here are a few more links to a similar subject with actual dyno numbers. I have also dynoed it myself and found similar results.
[URL unfurl="true"]https://jalopnik.com/see-how-big-tires-can-change-wheel-horsepower-1825922567
[URL unfurl="true"]https://www.carthrottle.com/post/how-does-wheel-size-affect-performance/
FTE Legend
Joined: Mar 2017
Posts: 31,795
Likes: 9,122
From: Western NY
The way I understand it, and I'm no expert, but when you increase tire size enough, you take the engine out of its effective powerband (RPMs) by affecting the gear ratio. Taller tires rotate less for the same distance as smaller tires... so it drops the engine RPMs... because the engine is no longer in the RPM powerband (lower revs) as designed by the factory, it will use more power to keep the truck moving, use more fuel and accelerate slower (plus taller tires are wider and heavier, more rolling resistance). To bring the RPMs back up to where they were and bring the factory performance back, you need lower (bigger ratio) gears to accommodate for taller tires...
FTE Legend
Joined: Mar 2017
Posts: 31,795
Likes: 9,122
From: Western NY
I don't like to play semantics, I am just here helping people understand their trucks better and how certain mods will affect overall driveability and useable hp (useable HP would be how much force is applied against the road to propel your vehicle forward). When you are struggling to tow a big hill after putting bigger tires on a truck or have slower times at the track... you will notice you have less usable HP.
Re-gearing helps, but it does not solve everything. You will still lose useable HP from wind drag and extra rotational mass from a heavier and taller tire.
Here are a few more links to a similar subject with actual dyno numbers. I have also dynoed it myself and found similar results.
[URL unfurl="true"]https://jalopnik.com/see-how-big-tires-can-change-wheel-horsepower-1825922567
[URL unfurl="true"]https://www.carthrottle.com/post/how-does-wheel-size-affect-performance/
Re-gearing helps, but it does not solve everything. You will still lose useable HP from wind drag and extra rotational mass from a heavier and taller tire.
Here are a few more links to a similar subject with actual dyno numbers. I have also dynoed it myself and found similar results.
[URL unfurl="true"]https://jalopnik.com/see-how-big-tires-can-change-wheel-horsepower-1825922567
[URL unfurl="true"]https://www.carthrottle.com/post/how-does-wheel-size-affect-performance/
