Hello All,

As can be seen from my questions about rear ends, I am building a pullin' truck. I have built all kinds of FoMoCo powered race cars, and built motors of all kinds for many different kinds of competition and work, but I have never built a pulling truck before. My question is concerning gearing:

How does one determine the best tire speed to gear for? I know that my buddy's geared for ~24 MPH when running teh engine at 7000 RPMs. I also know that he is spinning his tires quite a bit faster than most of his competitors, and is doing quite well in teh 5500 and 6500 lbs. classes. He claims that his increased speed gives him more momentum to pull farther. I understand his theory, but if one gears to go too fast then he is loosing possible mechanical advantage as well as risking too much tire spin (assuming the motor will turn the tires that fast without bogging). So, as I see it, the HAS TO BE a happy medium between all of these factors that determines what the optimal tire speed is. . . So, I guess my question is: How do you "professional" pullers determine what tire speed to gear for.

Thanks a bunch,
Nathan

 

i'm building a stock truck pulling truck and I have the same question I will probally gear it to go 30 MPH in 4 low First gear with a automatic C6 at 6500 RPM My engine should be able to do that because it is a 514 that has over 600 horse and 600 torque Some of the modified trucks I have talked to run a 4 speed and pull in 4th gear and have special pulling transfer cases that I dont know the gear ratio they are and they run military rear ends with 6.72 gears and have 512 bowties under the hood and have 850 horse
The problem is you have to find the perfect gear so you dont spin to much and you can get some speed going I have knot figured out that gear ratio yet

 

The more tire speed the better. The more pulling force the better. The more horsepower you have the more you can have of both. If you had 2000 horsepower you could have 50 MPH tire speed and still maintain plenty of pulling force. In other words, horsepower is the name of the game. As for choosing the correct gearing I would say just make sure your rearend is geared low enough that first gear low range is plenty slow enough and if you feel you need to go faster then you can use higher gears in the transmission and/or high range in the transfer case to adjust.

 

Bus Driver,

Thanks for the response. However, I am building a 2WD pullin' truck, and due to the lack of a transfer case (and several other factors), I need to have a good way of determining the right ratio the first time around. Once I figure out how to determine this, I will mismatch tranny/rear end gear ratios, and tire heights to get it right.

Now, I must say that I do not fully agree with your assesment of the situation: I do not think that the more tire speed the better. The main reason for my objection to this is traction. Say we have a pulling truck set up like your example: 2000 horsepower, and geared for a tire speed of 50 MPH. Now, how in the world are you going to get all of that power to the ground? In a pull you do not shift, and any engine (speaking of 5xx and smaller V-8s) that produces that much power will likely have a somewhat narrow rpm range in which it makes that power. So, one would have to launch this truck at an RPM that would undoubtly shock the tires to the point that there would be NO WAY of hooking up on dirt pulling a sled. So, we are back to where we started, needing a happy medium between all of the variables.

PLEASE, feel free to correct anything that I have said that is falacious. I am not trying to argue or start a fight , simply trying to work this stuff out . . .

Respectfully,
Nathan

 

>Bus Driver,
>
>Thanks for the response. However, I am building a 2WD
>pullin' truck, and due to the lack of a transfer case (and
>several other factors), I need to have a good way of
>determining the right ratio the first time around. Once I
>figure out how to determine this, I will mismatch
>tranny/rear end gear ratios, and tire heights to get it
>right.
>
>Now, I must say that I do not fully agree with your
>assesment of the situation: I do not think that the more
>tire speed the better. The main reason for my objection to
>this is traction. Say we have a pulling truck set up like
>your example: 2000 horsepower, and geared for a tire speed
>of 50 MPH. Now, how in the world are you going to get all
>of that power to the ground? In a pull you do not shift,
>and any engine (speaking of 5xx and smaller V-8s) that
>produces that much power will likely have a somewhat narrow
>rpm range in which it makes that power. So, one would have
>to launch this truck at an RPM that would undoubtly shock
>the tires to the point that there would be NO WAY of hooking
>up on dirt pulling a sled. So, we are back to where we
>started, needing a happy medium between all of the
>variables.
>
>PLEASE, feel free to correct anything that I have said that
>is falacious. I am not trying to argue or start a fight
> , simply trying to work this stuff out . . .
>
>Respectfully,
>Nathan



You have the right idea because if you spin off the line you are not going to do that good that is why I'm going to gear my truck high so the engine will have to work and hopfully not spin until the 300 ft mark or so and weight has a lot to do with the power when pulling you have to have everthing perfect to get all the power to the ground so you do good I have seen people pull stock trucks with 600 to 700 horse and they were mud drag trucks and they did bad because they had to much power for the weight they had so they spun

 

You have a couple of good points there. I didn't know you were doin' 2 wheeler and wouldn't have a transfer case. That will make it more difficult to change your ratios so that you can adjust on the fly. I guess I can't say too much about how to get it right on the first try. You'll need advice from experienced 2 wheeler pullers for that. I imagine that is probably why you started the post as opposed to in order to get advice from a novice like me, but I thought I'd pipe up anyway.

As for being geared too high and shocking the tires, I also see your point there, but I'm not sure it is much of a concern. Generally, most good pullers are setup for relatively high engine speeds and ground speeds at the end of the track. They avoid shocking the tires by riding the clutch a bit at the starting line. Probably less adviseable for a daily driver, but if you're talking about a dedicated puller there are clutches that will take the abuse. Besides on a dedicated machine you gotta expect to abuse parts like clutches etc. if you're gonna win.

At any rate good luck to ya'.

Neil

 

Hey All ..ShaZam here:

here's my set-up I don't think it'll help much because I pull 4 wheel drive but any info is better then none.
1978 4X4 Dana 60 front 4.55 gears Corp. rear 4.56 gears NP 435 Tranny with a 3.34 2nd gear And a NP 208 2 to 1 cast iron transfer case.I run 35" Tires in Super Stock and 34" in Mod.
Wheel Speed for my Pulling truck goes as follows.
6800 Rpm's 23.3 Mph
7200 Rpm's 24.6 Mph
8000 Rpm's 27.4 Mph

I pull in Low Range 2nd gear and this is what I learned this last season about tire speed and traction.

If I slipped my Clutch to the 100' mark on a good tight track and let everything get going with out spinning the tires I'd turn 6800 Rpm's all the way to the end and then I would spin out at the end. But I'd be really close to the 300' mark.

If I did everything the same but say got on it at the 75' mark I'd turn 7200 Rpm's and wouldn't finish that close to the end.

And let's say I just lost all since of reason and got on it right out of the hole,I'd turn 8200 Rpm's and I'd be lucky to make it to the 200' mark.

So I build a motor that will turn 8000 to 8500 Rpm's with out blinking and eye, And I have to learn to play with the throttle and keep it between 6800 and 7200 to be competative.

So the Keys to doing well is this.
Find out where your motor makes it most Torque and H.p. set your sights in the middle of the two, that will be your target Rpm.
Get yourself a real good Slipper Clutch. ( Mcleod or Crower )
and learn how to use it.
And I did a lot better at 23 Mph the I did at 27 Mph So I'd have to say 23 Mph is the target wheel speed.

If your going to use a Automatic Tranny look at getting a 3000 to 3500 Rpm Stall Converter. And build a motor with at least 850 to 950 H.p to be competative. With a Stick you could get by with 750 to 850 H.p.

Hope this helps

 

Shazam,

Thanks a bunch for the post. It has some good info in it that will indeed help. The fact that you did better at 23 mph rather than 27 further supports my thoughts on the matter.

Now, you touched on the idea of a slipper clutch. I honestly hadn't even thought of that! My experience is in drag racing and I am very new to the world of truck pulling. I have hooked up with a buddy that runs in local classes here in central KY, and most all of these guys run solid hub metallic clutches (which are identical to what I used to run in my 4-speed drag cars). They don't slip the clutch at all (which isn't really conducive to that design anyway), and launch hard and let the engine "fall back" to its torque peak. This makes okay sense on the onset, but they all seem to spin too much off the line (despite the fact that most of them do full pulls). So, the idea of a slipper clutch makes a bit more sense. . .

Thanks Again,
Nathan

 

Well Nathan :

I slip my clutch off the line alot to help the truck hook to the track.I've been told by other Puller that there's time My truck never spins it's tires till the end of the track or after a full pull the guy's would say.. Ya we knew you where out of here with it that time .. ShaZam never spun a lug of dirt all the way ..

Getting the tires to hook to the track is the biggest secret to getting it out the end .