Got Punch?
#1
Got Punch?
So in another thread a few of us were kind of discussing tires size vs performance. I mean we all know that huge tires on an xj can be compensated by gearing, right? Well somewhat.
Gearing only compensates for the added ratio change by going with larger tires. So basically by putting 40's on your truck that came stock with 30's you just caused a severe gear ratio change. One rotation of a 30" tire is equal to 94.2 inches. One rotation of a 40" tires equals 125.6inches. Thats a 25% increase in wheel speed. So to compensate for that we go with bigger gears.
And thats it. What gearing does not compensate for is horse power loss of heavier rotational masses. Well I knew this but not to the extent of what it actually is.
There are several different formulas out there you can look up if you want to figure just how much horse power you are losing. If I have time later I may get them for you. Now there are two important robbers of HP. One is weight, which we already know, and two is the distance the weight is front the center axis. The second factor is the major one.
Here is one article I found interesting. And this is with a small sportscar.
Now with this small car we are talking only a slight increase in tire height and 20lbs per tire. Equals out to a loss of about 55hp! Thats a huge amount. So when you are talking the weight of 40's plus the dana 60's required to run them. You are looking at a 25% increase of vehical mass. And by my rough calculations a loss of over a hundred horse!! Again, I knew it was a lot, but did not realize how much.
So in simple terms you just through out the old inline 6 and put in a VW motor with a webber carb..LOL
Now that you only have 135 hp turning your 40's just make certain you gear it enough to get over the huge boulders
Now of course your motor does not lose any crank hp. It still puts out the spec amount at the crank. But what it loses is what it puts to the ground. And that is where the fun starts.
Anyways, before you just go big. Consider also what you are giving up? Now sometimes I think getting 37" tires and dana 60's would be awesome! But I have to give up my hill antics which I enjoy. My umph and great wheel speed on some muddy hills and such. Not to mention my cruising 75mph with the Cruise on!
Well we are not racing right? Does it really matter? No, it all depends what you are doing with your rig. If your rock crawling then you just need enough umph to get over the rocks. You won't win any races thats for certain. But thats okay just put a sign out that says (Don't follow me!) You wont make it. LOL
Gearing only compensates for the added ratio change by going with larger tires. So basically by putting 40's on your truck that came stock with 30's you just caused a severe gear ratio change. One rotation of a 30" tire is equal to 94.2 inches. One rotation of a 40" tires equals 125.6inches. Thats a 25% increase in wheel speed. So to compensate for that we go with bigger gears.
And thats it. What gearing does not compensate for is horse power loss of heavier rotational masses. Well I knew this but not to the extent of what it actually is.
There are several different formulas out there you can look up if you want to figure just how much horse power you are losing. If I have time later I may get them for you. Now there are two important robbers of HP. One is weight, which we already know, and two is the distance the weight is front the center axis. The second factor is the major one.
Here is one article I found interesting. And this is with a small sportscar.
Originally Posted by "stretch"
Ugh, I keep trying to resist posting to this thread.
Can't do it anymore.
The average 20" wheel is 35lbs. The stock 16" wheel combination WITH tires is 39.4 lbs. So you're almost as heavy before even mounting tires! I tried looking up tire weights, and realized that no respectable manufacturer makes the size you would need. So you're forced to buy **** tires. Kuhmo doesn't even make the "MX" in a 20" size because no respectable performance driver would be on 20's. But their 712's are available in SUV sizes, and the 255/35/20 is 30lbs. T1-S's also come in that size, but no smaller width. These are essentially SUV tires, they're heavy because they're designed to support a lot of weight. Falken doesn't even make Azenis in a size over 17" because again, no respectable racer (autocrosser) would use wheels larger than that.
The only reason to run large wheels is to run large brakes, and the 3's brakes are completely adequate for track use (when used with track pads) even under 16" wheels.
Anyway, back to weights. You're going to run 35lb wheels with 30lb tires, totally 65lbs compared with 39.4lbs stock. This is not like adding a 200lb subwoofer in the trunk (which is pretty stupid), this is far worse. The thing about wheels is you have to spin them, and that takes much more effort than it does to move an object that isn't spinning. You're dealing with the polar moment of inertia.
I won't bother explaining it since I doubt you care (and Crossbow already touched on it), but here are some numbers for you.
In fact, just for fun I looked up how much straight-line performance you'd lose by switching from 16" wheels to 20" wheels if the wheels weighed the same. It'd be about like adding 200 static weight to the car, which would take an additional 11ft-lbs of torque (roughly 15hp @ the rev limiter) to compensate and get the same acceleration as a stock car. That's bad enough.
But no 20" wheel is as light as the stock 16's. Your combination will weigh 65lbs, remember?
That's like adding nearly 800lbs of static weight to the car. Think about that number. That's almost 30% of your car's entire weight. In order for the car to accelerate like it did STOCK, you'd have to gain back 42ft-lbs of torque over the ENTIRE rev range. At the rev limiter, you'd need to be making 55 extra horsepower. Not gonna happen without forced induction. So basically, you'll need to supercharge your car to keep pace with a stock Mazda3 on 16" wheels.
Bling bling though, right?
Now you know why people with big rims get laughed at. Clowns wear big shoes too, but they're supposed to be funny.
Oh, and that's assuming you get the tires to fit in the first place, and then manage to make it over a pothole. You should aim to keep the volume of air in a tire constant when plus-sizing, which is why you should always upgrade to a wider wheel and wider tire when plus-sizing (a reason why Porsche uses hollow spokes!). Due to fender size constraints, you can do neither, and your brand new $4000 wheels will be bent in no time. The sidewall on 35 profile tires has to be very soft to be compliant, and your car will look like the rims are touching the ground. You know the look- like the tires are low on air. Take a turn and it looks like the rim scrapes, hit a pothole and the rim breaks. Utterly stupid looking.
Oh, and I almost forgot to mention- that extra 800lbs of equivelant weight that you're adding to the vehicle? You're going to have to slow it down, too. Good thing the Mazda3 has awesome brakes, cause you're going to need every ounce of them to stop your car in just routine traffic.
Ugh, I keep trying to resist posting to this thread.
Can't do it anymore.
The average 20" wheel is 35lbs. The stock 16" wheel combination WITH tires is 39.4 lbs. So you're almost as heavy before even mounting tires! I tried looking up tire weights, and realized that no respectable manufacturer makes the size you would need. So you're forced to buy **** tires. Kuhmo doesn't even make the "MX" in a 20" size because no respectable performance driver would be on 20's. But their 712's are available in SUV sizes, and the 255/35/20 is 30lbs. T1-S's also come in that size, but no smaller width. These are essentially SUV tires, they're heavy because they're designed to support a lot of weight. Falken doesn't even make Azenis in a size over 17" because again, no respectable racer (autocrosser) would use wheels larger than that.
The only reason to run large wheels is to run large brakes, and the 3's brakes are completely adequate for track use (when used with track pads) even under 16" wheels.
Anyway, back to weights. You're going to run 35lb wheels with 30lb tires, totally 65lbs compared with 39.4lbs stock. This is not like adding a 200lb subwoofer in the trunk (which is pretty stupid), this is far worse. The thing about wheels is you have to spin them, and that takes much more effort than it does to move an object that isn't spinning. You're dealing with the polar moment of inertia.
I won't bother explaining it since I doubt you care (and Crossbow already touched on it), but here are some numbers for you.
In fact, just for fun I looked up how much straight-line performance you'd lose by switching from 16" wheels to 20" wheels if the wheels weighed the same. It'd be about like adding 200 static weight to the car, which would take an additional 11ft-lbs of torque (roughly 15hp @ the rev limiter) to compensate and get the same acceleration as a stock car. That's bad enough.
But no 20" wheel is as light as the stock 16's. Your combination will weigh 65lbs, remember?
That's like adding nearly 800lbs of static weight to the car. Think about that number. That's almost 30% of your car's entire weight. In order for the car to accelerate like it did STOCK, you'd have to gain back 42ft-lbs of torque over the ENTIRE rev range. At the rev limiter, you'd need to be making 55 extra horsepower. Not gonna happen without forced induction. So basically, you'll need to supercharge your car to keep pace with a stock Mazda3 on 16" wheels.
Bling bling though, right?
Now you know why people with big rims get laughed at. Clowns wear big shoes too, but they're supposed to be funny.
Oh, and that's assuming you get the tires to fit in the first place, and then manage to make it over a pothole. You should aim to keep the volume of air in a tire constant when plus-sizing, which is why you should always upgrade to a wider wheel and wider tire when plus-sizing (a reason why Porsche uses hollow spokes!). Due to fender size constraints, you can do neither, and your brand new $4000 wheels will be bent in no time. The sidewall on 35 profile tires has to be very soft to be compliant, and your car will look like the rims are touching the ground. You know the look- like the tires are low on air. Take a turn and it looks like the rim scrapes, hit a pothole and the rim breaks. Utterly stupid looking.
Oh, and I almost forgot to mention- that extra 800lbs of equivelant weight that you're adding to the vehicle? You're going to have to slow it down, too. Good thing the Mazda3 has awesome brakes, cause you're going to need every ounce of them to stop your car in just routine traffic.
So in simple terms you just through out the old inline 6 and put in a VW motor with a webber carb..LOL
Now that you only have 135 hp turning your 40's just make certain you gear it enough to get over the huge boulders
Now of course your motor does not lose any crank hp. It still puts out the spec amount at the crank. But what it loses is what it puts to the ground. And that is where the fun starts.
Anyways, before you just go big. Consider also what you are giving up? Now sometimes I think getting 37" tires and dana 60's would be awesome! But I have to give up my hill antics which I enjoy. My umph and great wheel speed on some muddy hills and such. Not to mention my cruising 75mph with the Cruise on!
Well we are not racing right? Does it really matter? No, it all depends what you are doing with your rig. If your rock crawling then you just need enough umph to get over the rocks. You won't win any races thats for certain. But thats okay just put a sign out that says (Don't follow me!) You wont make it. LOL
#3
To you. To me its interesting how weight affects hp. And it explains a lot of things I notice on the trail. It also can aid in building what you want in an xj.
Pointless was your post
Pointless was your post
#5
So roughly speaking for every 10lbs of rotational mass you add you lose about 3hp on a 4wd.
That's a big difference. Especially if you are even slightly concerned about mpg.
#7
Originally Posted by holycaveman
To you. To me its interesting how weight affects hp. And it explains a lot of things I notice on the trail. It also can aid in building what you want in an xj.
Pointless was your post
Pointless was your post
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#8
Im not reading all that, but my big tires and axles never stopped me from trying the gnarliest of hillclimbs. But yes, bigger tires do suck up power, not just from the diameter, but because of rolling weight, and the further out from the wheel hub, the more that weight is going to effect power. Doesn't take math and forumals to figure that out.
experience> some numbers you found on the internet
experience> some numbers you found on the internet
Last edited by ktmracer419; 09-05-2012 at 10:13 AM.
#9
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not gonna lie, i read it all.
some good info in there. you should reference this to all the people who start threads asking if 33s on stock gears will slow their jeep down
this is also why i laugh at people who claim they didn't notice a loss in power when throwing on 35s with stock gears. come on, get real.....
some good info in there. you should reference this to all the people who start threads asking if 33s on stock gears will slow their jeep down
this is also why i laugh at people who claim they didn't notice a loss in power when throwing on 35s with stock gears. come on, get real.....
#10
Im not reading all that, but my big tires and axles never stopped me from trying the gnarliest of hillclimbs. But yes, bigger tires do suck up power, not just from the diameter, but because of rolling weight, and the further out from the wheel hub, the more that weight is going to effect power. Doesn't take math and forumals to figure that out.
experience> some numbers you found on the internet
experience> some numbers you found on the internet
Expierence I had on the trail to know this by the way The re search I had to look up to confirm what I knew.
Been competing off road since 1992.
Last edited by holycaveman; 09-05-2012 at 10:35 AM.
#11
No, its an engine turning a weight. Its exactly the same thing.
And by the threads on here I see about performance and or fuel economy it should be taken into consideration. Especially since its the cheapest way to gain engine effiecency.
And by the threads on here I see about performance and or fuel economy it should be taken into consideration. Especially since its the cheapest way to gain engine effiecency.
#12
Anyways to some this can be important information. For others like ktmracer with a purpose buit truck not so much.
#13
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Originally Posted by holycaveman
No, its an engine turning a weight. Its exactly the same thing.
And by the threads on here I see about performance and or fuel economy it should be taken into consideration. Especially since its the cheapest way to gain engine effiecency.
But two way different vehicles, with two different intentions... apples to oranges...
#14
But what I would take in to consideration is what to buy tire wise.
Say for instance you were looking at purchasing a set of boggers. The two you are looking at were the 35x14.5x 15 or the 35 x 10.5 x 15's. If you run the weight difference its about 15lbs per tire heavier for the wider tire. So now translating that into hp if you get the wider set of boggers you will lose about 18-20hp. To me that is definitely worth considering whether I really want those super wide boggers? Not to mention the extra rim weight?
Then if you compromised and went with a set of 33in km2's you may save over 30hp? These simple differences in tire choice can pay out huge on the performance side. What is a super chargers gain in hp? 30%? Well this little choice here just got you half of that!
I will search tonight and get some real formulas and numbers if possible. Just very interesting. I always like to look at every aspect when building or adding on something.
Last edited by holycaveman; 09-05-2012 at 11:17 AM.