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small or big tires

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Old 12-15-2008, 07:09 AM
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kingpin123
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Default small or big tires

i was wondering if smaller or bigger tires will give me more top end speed?

and also if thinner or wider tires would give me more top end speed?

which ones will give me more top end??
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Old 12-15-2008, 09:16 AM
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Default RE: small or big tires

bigger tires will give you more top end but less low-end. the narrower and lighter they are, the more top and low end you will get.
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Old 12-15-2008, 09:36 AM
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Default RE: small or big tires


ORIGINAL: kingpin123

i was wondering if smaller or bigger tires will give me more top end speed?

and also if thinner or wider tires would give me more top end speed?

which ones will give me more top end??
Smaller tires will sacrifice your top end speed. But smaller tires will help acceleration due to a couple of factors: less weight to accelerate, and the reduced diameter combined with less weight means less moment of inertia. And reduced moment of inertia = faster acceleration.

Larger tires, ones with larger diameters, will give a higher top speed, that is if you have the torque to turn those wheels for the gears you have. But, as a direct converse of smaller tires, larger tires will have more weight and more moment of inertia, thus, you will sacrifice your acceleration.

Now, tires with a higher moment of inertia will help you control the RC's flight attitude while in mid-flight after a jump. Gas it and you can pitch the nose up. Hit teh brakes, and you can pitch the nose down. Using the moment of inertia of teh wheels in mid flight can allow you to control your RC such that you can even land on all four wheels. I know I can do this very easily for nitro RCs, since they are 4wd and the proportion of teh RC chassis to teh body is such that teh wheels are much larger, but in gassers, the 2WD will only give you half teh amount of the moment of inertia control. Moreover, the mass of teh wheels in relation to teh rest of the RC is not like that of nitros, thus it is much harder to control the flight attitude of a gas RC.

As for skinny versus wide tires, skinny tires are great for top speed for a couple of reasons.
First and foremost is you reduce the road contact area and thus the amount of rolling friction incurred. (This is assuming the tire is relatively stiff enough and not running flat. A flat tire is the worst offender of rolling friction.)
Second, the thinner tires at speed present less of a crossectional area for teh sake of aerodynamic drag. Wide tires only add to the cross sectional area.
Now, skinny tires , since they have less of a road contact area, will not be useful in hard acceleration. The tires will break free and spin out more easily than what wider tires would. So if you are in loose dirt or other conditions where you want grip, you want wide tires. Or if you want great grip under hard acceleration, such as drag racing, you want wide tires to the powered wheels. That is why top fuel drag racing rails have massive rear wheels (the powered wheels) but tiny skinny frunt wheels (they are only there to steer, since they do not power teh rail, it only makes sense that they do not contribute to rolling friction and aerodynamic drag)
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Old 12-15-2008, 11:14 AM
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Default RE: small or big tires


ORIGINAL: SAVAGEJIM


ORIGINAL: kingpin123

i was wondering if smaller or bigger tires will give me more top end speed?

and also if thinner or wider tires would give me more top end speed?

which ones will give me more top end??
Smaller tires will sacrifice your top end speed. But smaller tires will help acceleration due to a couple of factors: less weight to accelerate, and the reduced diameter combined with less weight means less moment of inertia. And reduced moment of inertia = faster acceleration.

Larger tires, ones with larger diameters, will give a higher top speed, that is if you have the torque to turn those wheels for the gears you have. But, as a direct converse of smaller tires, larger tires will have more weight and more moment of inertia, thus, you will sacrifice your acceleration.

Now, tires with a higher moment of inertia will help you control the RC's flight attitude while in mid-flight after a jump. Gas it and you can pitch the nose up. Hit teh brakes, and you can pitch the nose down. Using the moment of inertia of teh wheels in mid flight can allow you to control your RC such that you can even land on all four wheels. I know I can do this very easily for nitro RCs, since they are 4wd and the proportion of teh RC chassis to teh body is such that teh wheels are much larger, but in gassers, the 2WD will only give you half teh amount of the moment of inertia control. Moreover, the mass of teh wheels in relation to teh rest of the RC is not like that of nitros, thus it is much harder to control the flight attitude of a gas RC.

As for skinny versus wide tires, skinny tires are great for top speed for a couple of reasons.
First and foremost is you reduce the road contact area and thus the amount of rolling friction incurred. (This is assuming the tire is relatively stiff enough and not running flat. A flat tire is the worst offender of rolling friction.)
Second, the thinner tires at speed present less of a crossectional area for teh sake of aerodynamic drag. Wide tires only add to the cross sectional area.
Now, skinny tires , since they have less of a road contact area, will not be useful in hard acceleration. The tires will break free and spin out more easily than what wider tires would. So if you are in loose dirt or other conditions where you want grip, you want wide tires. Or if you want great grip under hard acceleration, such as drag racing, you want wide tires to the powered wheels. That is why top fuel drag racing rails have massive rear wheels (the powered wheels) but tiny skinny frunt wheels (they are only there to steer, since they do not power teh rail, it only makes sense that they do not contribute to rolling friction and aerodynamic drag)

i said it plain and easy. you basically just turned it into as essay
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Old 12-15-2008, 12:54 PM
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Default RE: small or big tires

wow thanks for all the advice. so what would be your best choice for wheel choice if drag racing on asphalt?
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Old 12-15-2008, 01:22 PM
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Default RE: small or big tires

Slicks for sure, really wide and very tall tires for the read if 2WD, and small skinny one on the front.

If you have 4WD, go with slightly wider ones on teh read and slightly narrower ones on teh front. When accelerating, teh center of mass of teh RC will shift rearward thus placing more force on teh rear wheels (by way of the same action that eventually leads to a wheely, with teh assistence of the engine's torque on teh rear axles). But in 4WD, make sure all 4 wheels have the same diameter.
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Old 12-15-2008, 01:27 PM
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Default RE: small or big tires


ORIGINAL: scarletboa


i said it plain and easy. you basically just turned it into as essay[:@]
Well, I was just tying to explain why larger diameter wheels give more top speed and why smaller diameter tires kill top speed.

Also, smaller diameter tires give more torque at teh wheel in addition to better acceleration.
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Old 12-15-2008, 04:19 PM
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Default RE: small or big tires

here's some slicks i use for tarmac on my fgbaja, the monster slicks on the back and truck rear slicks on the front
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Old 12-16-2008, 07:58 AM
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Default RE: small or big tires

is that a 2wd or 4wd baja you have there?

do you have the part number for those slick you have on the front and back?

do you drag race with it and how do you hold up against 2wd gassers?
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Old 12-16-2008, 08:23 AM
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Default RE: small or big tires

Guys, don't forget rotating mass. Tall wheels is not what he wants for drag racing. Small wheels and lower gearing to compensate for the reduction.

Or at least, lets say more importantly lighter wheels.
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Old 12-16-2008, 10:54 AM
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Default RE: small or big tires


ORIGINAL: kingpin123

is that a 2wd or 4wd baja you have there?

do you have the part number for those slick you have on the front and back?

do you drag race with it and how do you hold up against 2wd gassers?
It's 2wd, 2speed. 28.5 reed ported oneills, 813 carb and jetpro
I don't drag race just got them for tarmac bashing to save my knobbies, i know a couple of guys with 5b's with road tires and have seen em run, cos of the 2speed it'd be no contest.

for drag racing i'd say they'd be the bomb if the set up is right....with my gear ratios and motor i was breaking one tire out off the line and ballooning badly as it would just hit max revs as soon as it let go...i've a 4plate locking diff now but haven't tried it yet but that'll fix 1 wheel getting loose. you do need to get them warm though with a standing burnout.
Foxy these tires balloon at high revs like real drag tires so even though they weigh a bit more you can gear for off the line and they'll grow giving you taller gears at high revs like the top fuel guys[8D]
I'll weigh em later compared to fr and rear truck slicks.

it's hard for me to say how they would be on a standard baja i can only tell you what they're like with my set up, without enough power and having to gear a single speed to compensate they might well be too heavy for good starts off the line
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Old 12-16-2008, 08:00 PM
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Default RE: small or big tires


ORIGINAL: Foxy

Guys, don't forget rotating mass. Tall wheels is not what he wants for drag racing. Small wheels and lower gearing to compensate for the reduction.

Or at least, lets say more importantly lighter wheels.
Absolutely correct! And that was one of my major points I was trying to say in what turned out to be my essay.

Lighter wheels with larger diameter is okay so long as the meat of that wheel mass is closest to the hub, thus a smaller moment of inertia. Now, if you have a heavy wheel, it is very possible for the heavier wheel to have the same moment of inertia as a smaller wheel. It is all in how close to the hub the meat of the wheel mass is.

Lets take two wheels that weight the exact same. Lets say both wheels in this example are 1lbf each. Lets also assume that both wheels have exactly the same diameter. Let one wheel have most of its mass in the tire treads, therefor the weight is focused furthest away from the hub. Let teh other wheel have teh meat of its mass as close as possible to the hub, say on the inside of the of the rim. The wheel with the weight focused on teh tire treads will have a much higher moment of inertia and will thus hurt acceleration. The one with the weight focused more to the hub will be much easier to accelerate.

Now a smaller diameter tier will in general have a significantly smaller moment of inertia than a larger diameter tire for the very same reason: The mass is closer to the hub. But an exception is if a smaller diameter tire has its weight focused on teh tire treads and teh larger diameter tire has its weight focused as close as possible to the hub.

I hope this explanation of physics was not too hard for the casual RC fan, I absolutely tried to stay away from going into physics equations and calculations in my examples.
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