Rooster 191 #1 Posted December 17, 2011 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 let’s speed up that Horse! Put a 6†pulley on your engine, and a 4†pulley on your tranny and you will boost the speed of your tractor to approx 10MPH... But that isn’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 jazz….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 7mph…won’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 Pony’s! Next is Wheels; Now compared to most, WH’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 “Good Strong Front end†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 4†Off of the ground, has a 38†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 weight…..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 be…why else DON’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 second….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 “Tractor†stuff with your now very poorly designed Go Cart! SO just so we are clear, if you decide to proceed beyond this point… 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 “boost†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 “working†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 23†336: This is a constant derived from the circumf...ohhh you don’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 WH’s have a 4†engine pulley and a 6†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 WH’s have a 4†engine pulley and a 6†tranny Pulley, and the final gear drives best my research shows on manual tranyy’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 23†tall tires, at 3500 RPM is about 6 ½ MPH...more or less depending on how many beers you have had. Now ….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 doesn’t work anymore....dangit. Here’s an Idea...since your clutch and belt are made to work with a 4†& 6†pulley....use those sizes, only put the 6†on the engine and the 4†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 “Stepped†sized pulleys. So your drive pulley would be the 6†and your attachment pulley what ever size the original was. 5 Share this post Link to post Share on other sites
littleredrider 409 #2 Posted December 18, 2011 That calculator is pretty cool. I changed the pulley's around on my ranger, according to that it's doing almost 20. When I had the 23" tires on it 25!! Feels much faster than that tho, guess cause there isn't a whole lot around yah.... Share this post Link to post Share on other sites
Sparky-(Admin) 21,350 #3 Posted December 18, 2011 Good post! I have a 656 with the engine drive pulley upped by 1". I left the rear pulley stock, its no speed demon but is a bit quicker than the rest of my machines. Mike.......... Share this post Link to post Share on other sites
Trouty56 567 #4 Posted December 18, 2011 I'll bet that is fun racing those tractors....cool information too. Share this post Link to post Share on other sites
KC9KAS 4,741 #5 Posted December 18, 2011 This is a very interesting, well written post. I love your sence of humor AND knowledge! I watched the videos of the races, and I realized very early there were more than just "speed" modifications. Although I enjoyed watching "lawn-mower" demolition derbys, this seems much less destructive on the machines......unless you "crash". Share this post Link to post Share on other sites
Hydro 131 #6 Posted December 18, 2011 Excellent post!! Really well written. Great info if we want to. :thanks: Share this post Link to post Share on other sites
fireman 1,021 #7 Posted December 18, 2011 Great write up! Share this post Link to post Share on other sites
Rooster 191 #8 Posted December 20, 2011 This weekend I am beginning the build on the B-11 "Race Horse" that I will be running iin the Sta-bil Series next year. I will be posting pics as I build it as well so all those with the questions...stay Tuned, lol! Share this post Link to post Share on other sites
71_Bronco 1,072 #9 Posted December 21, 2011 Very cool write up. I assume some tractors & trans are safer to "speed up" than others? Share this post Link to post Share on other sites
Rooster 191 #10 Posted December 21, 2011 Very cool write up. I assume some tractors & trans are safer to "speed up" than others? If I was going to speed one up, I would do it to something with dual rear tires. The increase width greatly improves the stability. The tranny isn't really going to make a difference until you start making engine changes. Some difference yes, but most WH trannys are similar in nature. The Puller fellas have told me the 8 Pinion 8 Speed are the stoutest? Hydros, I think your pretty much limited on those, over driving a hydro unit doesn't do much more than over heat it. Now that is Most Hydro's I am familiar with. I have not really worked on a WH Hydro, so they could be something different? I dunno? If you start Speeding them up very much over....I am gonna say 12-15 MPH, then you really need to look at Re-purposing that Machine. A tractor that will run that fast is not going to have any grunt left for working, so you have really built more of a "Tractor Looking Go-Cart" than anything else. At that point you need to start looking at Lowering that machine for stability, adding some pretty good brakes, a tetherd kill switch so that if the driver falls off the engine dies. Chasing a 15 MPH machine is ALOT different than a 7MPH machine, and imagine a 5 or 600 pounds at 15MPH hitting something or someone. Share this post Link to post Share on other sites
71_Bronco 1,072 #11 Posted December 21, 2011 I have an RJ on my plate for a resto after I finish my Bronco. It will be my fun driving tractor, and was thinking about upping the drive pulley. Duals in the back are on my mind, so that would help. Not trying to make a speed demon out of it, just trying to get a little more "get-up-and-go" out of it. Share this post Link to post Share on other sites
SousaKerry 501 #12 Posted December 21, 2011 Well ya all know of my little C-251 project (Wisconsin V-4) well them old V-4's only turn about 2400 RPM so according to the calculator with stock tires I need about an 8 inch pulley on the motor to do 13.3 mph 98% of drivers when on a snowy road and heading for a ditch yell "Holy S#$%" the other 2% are from Michigan and say "Hold my beer and watch this" 1 Share this post Link to post Share on other sites
Rooster 191 #13 Posted December 21, 2011 I have an RJ on my plate for a resto after I finish my Bronco. It will be my fun driving tractor, and was thinking about upping the drive pulley. Duals in the back are on my mind, so that would help. Not trying to make a speed demon out of it, just trying to get a little more "get-up-and-go" out of it. Which RJ...that speed Calculator only works for the WH Manual trans. The Smaller RJ's had that whats it trans....lol....I cant remember the name of it?? Also, I dunno how much gearing up those little engines will be able to pull? Well ya all know of my little C-251 project (Wisconsin V-4) well them old V-4's only turn about 2400 RPM so according to the calculator with stock tires I need about an 8 inch pulley on the motor to do 13.3 mph 98% of drivers when on a snowy road and heading for a ditch yell "Holy S#$%" the other 2% are from Michigan and say "Hold my beer and watch this" Whats the C-251 Project? We call that "A rednecks Last words..." LOL Share this post Link to post Share on other sites
71_Bronco 1,072 #14 Posted December 21, 2011 Rooster, the RJ I have is an RJ-58, with the gearbox (3 forward gears, 1 reverse). Prolly gonna try the tractor first with the stock pulley to see how well it goes and then go from there. Share this post Link to post Share on other sites
littleredrider 409 #15 Posted December 22, 2011 If you have the 8-speed tranny, you can still have the get up and go and the pull a house down low gear. When I had the 13 horse on the ranger and 6-12 tires, I had a 3.5" I think on the motor and a 2" on the tranny. Hauled a$$ up the road but would still pull my crew cab at an idle in low gear.. Share this post Link to post Share on other sites
Rooster 191 #16 Posted December 22, 2011 Also, I have never sped up a wheel horse tranny...so I cannot tell you how well they will like it or not..... Share this post Link to post Share on other sites
Rooster 191 #17 Posted December 22, 2011 Some of you guys are using the speed calculator wrong...sorry, I am not a document builder. REPLACE the blue numbers with your numbers. Do not add them to the boxes below ;) Share this post Link to post Share on other sites
baerpath 517 #18 Posted December 25, 2011 Works fine compared the sled speed(we have agitonics on the sled) to the chart speed came up almost exact for the 20hp (10.46 mph) Sled says between 11 and 12 usually I use this to pick a belt when we change pullies http://www.csgnetwork.com/pulleybeltcalc.html Duane Share this post Link to post Share on other sites
Wheel Horse Kid 105 #19 Posted December 25, 2011 That is some great information! Thanks for sharing. I used to have a little Toro 8-25 rider and I doubled the size of the pulley on the transmission and I probably 2x if not 3x the speed of it. That was a blast to drive around in the snow! Anyways, thanks again for sharing! Share this post Link to post Share on other sites
zieg72 209 #20 Posted December 25, 2011 Now that I changed the theme I found this post, thanks so much for the calculator. I am looking for 10-11 mph out of my 520H, hoping to not hurt the Hydro in doing it, mainly for a quick trim when the grass needs some attention or a little more ground speed when pushing snow. Share this post Link to post Share on other sites
TT-(Moderator) 1,131 #21 Posted December 25, 2011 The information above doesn't actually apply to hydro tractors. Wheel Horse made the 520-HC models faster by changing the gearing after (beyond) the hydro unit. If it was as simple as changing two pulleys and a belt, I'm sure they would have just done it that way. That doesn't mean that speeding up the input shaft of the pump won't increase the ground speed of the tractor, but I don't believe that's the "correct" way. :confusion-shrug: Share this post Link to post Share on other sites
zieg72 209 #22 Posted December 25, 2011 The information above doesn't actually apply to hydro tractors. Wheel Horse made the 520-HC models faster by changing the gearing after (beyond) the hydro unit. If it was as simple as changing two pulleys and a belt, I'm sure they would have just done it that way. That doesn't mean that speeding up the input shaft of the pump won't increase the ground speed of the tractor, but I don't believe that's the "correct" way. OK maybe someone will chime in then about the hydro units, I definitely don't want to ruin anything Share this post Link to post Share on other sites
can whlvr 993 #23 Posted December 25, 2011 im no expert on the hydro unit per say,but i would not play with any of mine that way,jm2cents,i have a 13 honda on a 300 series and can tell you its my faster tractor,i used the hp engine pulley which i think is a little smaller than the 10,s and bigger,i think without looking Share this post Link to post Share on other sites
c161rat 185 #24 Posted December 26, 2011 Rooster, Where on earth did you get the idea to write this thread???? Very well written and I will use this info when it comes time to pull the rat back into the garage. By the way does anyone know the shaft size of an 8 speed tranny off a 161???? I am almost sure the engine shaft is 1.125" but am not sure of the tranny shaft size. Thanks again Rooster!!!!! Share this post Link to post Share on other sites
TT-(Moderator) 1,131 #25 Posted December 26, 2011 An 8 speed input shaft is 5/8" & very short. (not always easy to find a pulley that has a set screw that properly lines up with the center of the key. 3 & 4 speed input shafts are 3/4" - and they're short too. Note - information provided above is guaranteed to be 100% accurate - unless I'm wrong. :ychain: Share this post Link to post Share on other sites
