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Speed up that Horse? For those of you that do not know, I race Lawn Mowers with the United States Lawn Mower Racing Association. I compete at the top level of Lawn Mower racing, the Sta-Bil Lawn And Garden Mower racing Series. I race the #M37 Cool Rides Online mower in the C/P Class. After Several inquiries as to speeding up tractors I decided to do a write up on just this subject. So letÃ¢â‚¬â„¢s speed up that Horse! Put a 6Ã¢â‚¬Â pulley on your engine, and a 4Ã¢â‚¬Â pulley on your tranny and you will boost the speed of your tractor to approx 10MPH... But that isnÃ¢â‚¬â„¢t enough...LETS GO FAST! WHOOAAAAA BIG RED! You did not think it was going to be that easy did you! First thing, before we talk about gears and pulleys and revs and all that jazzÃ¢â‚¬Â¦.lets look at a few things! LIKE SAFETY! Your tractor is a tractor, not a go-cart! Tractors are made for working, not flying around the neighborhood. There for, many of the components on your tractor were neither designed for , nor are they correct for High speed applications! First of these being the brakes! Higher speeds are much harder on brakes. That little band brake that will flip you out of the seat at 7mphÃ¢â‚¬Â¦wonÃ¢â‚¬â„¢t do much more than make some smoke at 30 MPH! On USLMRA Racing mowers we upgrade to some pretty serious Disc Brakes, some of us running front & Rear brakes so that we can safely Whoa up our trick PonyÃ¢â‚¬â„¢s! Next is Wheels; Now compared to most, WHÃ¢â‚¬â„¢s have some strong feet, but speed is hard on wheels! On our sanctioned class racers we upgrade to some pretty stout stuff! Along with wheels comes steering; That wobbly gobbly thing we call a Ã¢â‚¬Å“Good Strong Front endÃ¢â‚¬Â is not near stable enough for high speed application. One of the biggest things is Stability; A USLMRA Prepared Class racer sits as low as 4Ã¢â‚¬Â Off of the ground, has a 38Ã¢â‚¬Â tracking width, and weighs in the neighborhood of 300-350 pounds, give or take. With our tractors sitting 3 times or more than that up, several inches narrower, and two or three times the weightÃ¢â‚¬Â¦..things get interesting REAL quick! Having a 600 or more pound tractor land on you can get way past dangerous in less than a heartbeat. Now that we have considered how unsafe this venture can beÃ¢â‚¬Â¦why else DONÃ¢â‚¬â„¢T we want to make changes to the gearing of our tractor? How about your engine? More than likely, without some major modifications, that K91 is NOT going to pull a doubled up gear ratio! How about your tranny? WH trannies are NOT models of efficiency. They may be great for the job they were intended, but when it comes to high speed application they would not be your first choice, or secondÃ¢â‚¬Â¦.or 23rd? Over speeding them can have catastrophic effects on them, to the point of actually blowing them apart. Do you really want to do that to your 50 Y/O treasure? Finally there is the subject of the purpose of your tractor. If you ever connect any type of attachment or implement to your tractor you DO NOT want to speed it up! Plain and simple here gents, without re-engineering and re-gearing your transaxle, you cannot speed up one gear without speeding up all of them. Tractors are made for working, and Wheel Horses are capable of some simply amazing feats when you consider the amount of work they get done for the size of engines they have. The minute you start increasing speed you decrease the amount of work your tractor can do. And as far as mowers or snow blowers go go, excessive speeds on rotating attachments can be fatal, for the attachment and the operator! You start speeding it up, forget about dirt work, snow pushing or all that other Ã¢â‚¬Å“TractorÃ¢â‚¬Â stuff with your now very poorly designed Go Cart! SO just so we are clear, if you decide to proceed beyond this pointÃ¢â‚¬Â¦ I AM ABOUT TO SHOW YOU THE EASIEST AND QUICKEST WAY TO MAKE YOUR TRACTOR USELESS AND WORSE YET....SPILL YOUR BEER!! Now that you have decided to ignore my very intelligent and worthy cautions.....lets get to the fun! You can slightly Ã¢â‚¬Å“boostÃ¢â‚¬Â the speed of most tractors without any major ramifications...so for youthat want to make your 7MPH Horses go a whopping 9MPH...or get really out there and hit the double digits at say 12MPH!! here is the goods! Making your tractor faster is relatively simple, it takes a little bit of math, some minor mechanical ability and fabrication skill. The speed of a tractor has 3 basic elements; The speed of the engine, the overall gear ratio and the size of the tires. Now immediately someone is going to tell me I forgot the SIZE of the engine. In theory the engines size or power does not determine how fast the tractor will go but rather how long it will take it to get to that speed! In actuality, if you do not have enough engine to get the thing rolling in the first place...the amount of time it takes to reach top speed is exactly never! We are going to focus on the second element only. The engine build is an entirely different subject, and I am going to assume most of us already have our tires. So what you guys really want to know is, how to manipulate your gear ratio. Simply put, the overall gear ratio of a tractor is a comparison between how fast the engine turns and how fast the axle turns. The fewer revolutions your engine makes for every revolution of the axle, the faster your tractor goes. The overall ratio on a WH is broken into 2 sections. The primary, or belt drive, consists of the engine pulley, the belt and the transmission pulley. The final drive, or trans-axle, consist of.....you guessed it...the trans-axle! To find your overall Drive Ratio you Multiply your primary ratio by your final ratio. To speed up your tractor, you must change one of these ratios. As I said earlier, there is nothing you can do about the trans-axle ratio without re-engineering the whole thing. The primary drive however, we can whoop the hell out of that! How much speed you gain will be determined by how much you change that ratio..most of us would prefer to know how much speed we are going to get before we buy the pulleys. So NOW we are getting to what you really wanted to know. I know....Rooster just shut up and tell me what size to get! OK..A 6 on the engine and a 4 on the tranny...happy now? If you want to know how I got those numbers...read on. To determine your pulley sizes you need a formula...and here it is... Top Speed = (Engine RPM * Tire Diameter) / (Gear Ratio * 336) SO lets break that down a little.... Engine RPM: I usually govern Ã¢â‚¬Å“workingÃ¢â‚¬Â engines around 3500...so we will just use that #. Tire Dia: This is the actual measured Height of your rear tires...not what is printed on the sidewall. For argument, we ar going to use 23Ã¢â‚¬Â 336: This is a constant derived from the circumf...ohhh you donÃ¢â‚¬â„¢t care...just use the number! Gear ratio: This is the thing we are working with...remember... To find your overall gear ratio takes another formula.... Overall Gear ratio= Primary Ratio * Final Ratio Primary Ratio= Transmission Pulley/ Engine pulley SOOOOOO I believe most WHÃ¢â‚¬â„¢s have a 4Ã¢â‚¬Â engine pulley and a 6Ã¢â‚¬Â tranny Pulley Gear Ratio= (Trans Pulley/Engine Pulley)*Final Ratio ANDDDDD Top Speed = (RPM*Dia)/(((Trans Pulley/Engine Pulley)*Final Ratio)*336) We now have the complete formula for figuring speed. So lets plug our numbers in here... I believe most WHÃ¢â‚¬â„¢s have a 4Ã¢â‚¬Â engine pulley and a 6Ã¢â‚¬Â tranny Pulley, and the final gear drives best my research shows on manual tranyyÃ¢â‚¬â„¢s is 24.6/1. Top Speed=(3500*23)/((( 6/4 )*24.6)*336) 80,500/(( 1.5 *24.6)*336) 80,500/((36.9)*336) 80,500/ 12,398.4=6.49 MPH So, the speed of a Manual transmission Wheel Horse Tractor with 23Ã¢â‚¬Â tall tires, at 3500 RPM is about 6 ½ MPH...more or less depending on how many beers you have had. Now Ã¢â‚¬Â¦.I still have not told you how to make it faster.... Simply change the pulleys... Bigger on the engine or smaller on the tranny makes you faster. Smaller on the engine or bigger on the tranny makes you slower...but you can pull more How much faster is simply a matter of how drastic of a change you make. To make this easier, I have made a calculator for you to use....Wheel Horse Speed Calculator Insert your Pulley sizes, tire Diameter and engine speed and it will figure your Overall Gear ratio and top speed for you. So now we are all done! Oops....wait....your clutch doesnÃ¢â‚¬â„¢t work anymore....dangit. HereÃ¢â‚¬â„¢s an Idea...since your clutch and belt are made to work with a 4Ã¢â‚¬Â & 6Ã¢â‚¬Â pulley....use those sizes, only put the 6Ã¢â‚¬Â on the engine and the 4Ã¢â‚¬Â on the tranny....where have I heard that before? We still have a belt guard issue, which on many tractors is also a belt guide issue...which must be addressed. I am sorry to tell you, but I have not devised any other way than making a new belt guard? As for the issue of attachments, all hope is not lost. You can buy Ã¢â‚¬Å“SteppedÃ¢â‚¬Â sized pulleys. So your drive pulley would be the 6Ã¢â‚¬Â and your attachment pulley what ever size the original was.