SOLTRA

Howdy, folks! As a total noob just embarking on his first tractor build (see my intro thread), the first question I have is with regards to gearing. I am building for the modified class, but having zero experience, I have no idea what average speed is in that class. I can calculate the appropriate pulley and sprocket sizes for the target speed, but what is the target?

FWIW, I tossed the 11hp Briggs and Peerless 800, and am building using a Briggs OHV 15hp, Peerless 700, and probably 18" tires. 

Actually, since we're on the topic of the Peerless- I have a three-speed model. I'm under the impression that only two gears are used during the races- is this true? I have to doublecheck, but I think the lowest gear is too deep to be particularly useful, anyhow...

the average speed in mod id say would probablly be around 40 km/h... Either a 700 series gear box or the 3 speed models are the most used in just about any mod out there.

The 15hp ohv is a good start for a motor but id suggest to keep an eye out for a v-twin mower engine that would make you competative with most of our mods on the track now.

Thanks for that! I'll have to hit the calculator, armed with the tranny's ratio numbers. I can shoot for 40 or so in high gear ar 3850 (I'll check rules again). Odd question from a total noob- Do guys shift during the race? I know that no gears can be removed, just wondering if I should devise a lockout or gate that leaves, say, 2nd and 3rd available. Also (and forgive me if this has been covered)- While removing "gears" is a no-no, I have read that if the reverse chain were to fail on the 700, it could well mean the death of the tranny. Since the reverse chain is not technically a "gear" per se- can/should I remove it?

As for the engine, I'll keep my eyes peeled. I DO have an 18hp horizontal twin available to me, but I'm not sure how/if I could legally use it. For now, I'm going to keep things somewhat simple and design the drivetrain around the 15. Thanks for your help!

We do not normally shift during racing. And the reverse chain has to stay. Welcome to mower racing.

yes unfortanitly the reverse chain has to stay, but i have been racing for about 5yrs now and have not had one go or have seen one go in our club. (yet)

Also you do not have to have a gear lock to keep it for going into any higher gear than what you need but if you feel more comfortable with one then it is up to you. But remember sometimes it is nice to have that choice for longer and shorter tracks.

Okay- now that I think about it, I can see why it's likely unnecessary to shift while racing. 40 km/h is not as fast as I had expected the average to be, so you don't need to gear up from zero to race speeds. 

For the reverse thing, I'll just put in a new chain while I have the 'case apart. I haven't opened it up yet, but I think I read somewhere that it's a #40 or #41 chain. Common as mud.

Most guy run in third gear usually. I forget what size pulleys and sprockets I use. If I remember tomorrow I'll measure them

im pretty sure its a #40 chain

You need to figure out wear you would like to top out. You  do not want to still be pulling at the end of the straight as you will hurt coming off the corner. You need to run out of revs just after the start finsih line to have the power to come off the corners.

My current set up is 8 to 4.5 and 13 to 35 in third gear.

If you don't have a bunch of pullies or sprockets then buy an adjustable pulley for your tranny and play at the track with different sizes. Normally they will adjust from 4.5 to 6 in. Do not go under 4 as you will not have enough belt wrap around the tranny pulley and you will either distroy the belt or dramatically shorten it's life due to slippage.

Thanks for the tips! Gearing may take a bit more pondering than I had thought. I have no problem figuring out ratios and projected speeds, but have never raced before. When to "peak" is a bit of a head-scratcher.

No matter, I have larger and greater things to figure out first. I keep seeing references to the "tunnel" but don't have a clear picture of what it is and how it applies to me. I think my chassis does not feature a tunnel per se. Framerail depth is about 2 1/2", give or take. Rules like not being able to mount the seat lower than the tunnel is a mystery in my case.

I have built a new front axle beam (with fixed caster and KPI angles) and am leaning towards keeping the steering gear, but replacing the column and wheel. It will indeed be strong enough- I'm new but not a fool!

Also- I saw a rule stating that you cannot drill your brake rotor. What if it's drilled/slotted from the factory? I have a pitbike rotor and a go kart rotor to choose from. Both will use a hydraulic caliper.

You need to post some pictures..

Since my last post I have moved up to an 8 to 4, 14/40 gear. You will need to open up your 700 and see which is the 25/25 gearset and that will be your race gear as it is the strongest.

The tunnel is on old school tractors like mine. Basically you have to put your foot OVER the tunnel to get on it to drive. The newer chassis are called WALKTHROUGH because you can slide your feet through the chassis to sit down.

All new tractors are walk through.

DO NOT keep the steering gear. It was meant for 10 mph. You will strip it. Be safe and build direct steering.

For a baseline on your axle I would suggest no more than 10 degrees positive caster and 10 degrees of King Pin Angle.

From what I gather. the drilling rule only applies to people making their own brake disc. Factory machined cooling in brake discs would be exceptable.

PLEASE used hydraulic brake. Do not trust manual.. some might diagree but they have TERRIBLE fade and I have actually spit chunks of pad off manual brakes. Once you go hydraulic you set and forget and also give other racers peace of mind that you will not plow into them because you have no brakes.

You WILL need a twin or at least an 18 hp single to keep up in this class..

You know, it's funny. On my forum, I always push for pics, yet I haven't posted pics here yet. I'll try to get to it this weekend.

For the steering, I will be replacing all the crappy factory rod ends with some higher quality units. The steering gear itself might actually be worthwhile, I will address that later. Believe me, I'm not into killing myself. For the brakes, they will be hydro. I use hydro for all my projects, including the little go kart I built for my kids. I used the front braking system from a Yamaha Virago 250.

The engine thing is a bit annoying-  I traded up from the factory 11hp Briggs flatty to a 15hp Briggs OHV and was pretty happy about that. I guess I will keep my eyes peeled.

I haven't gotten around to opening up the tranny yet, but as it is a 3-speed, I am assuming 3rd gear is as high as it gets...

Oh- I see. Then I guess I do need a tech's opinion. The seat bolted directly to the fander unit, which was one solid piece, and bolted to what you see.

I hate that you can't go back and edit later! Anyways, that was supposed to be FENDER unit. The fender unit was a large unit that I cut in half lengthwise, thinking that I would spread the fenders to cover the tires now that a wide axle has been installed, and then fill the void by welding in some sheetmetal. I am re-thinking that now, as most of the builds I see do not have the fenders covering the tires.

Here's a couple more pics. #1 shows it dead stock. #2 is after the rear axle swap. Both show the fender unit clearly.

Take a look at this build thread.

http://www.heymow.com/index.php?topic=11932.0

That's a nice build! The chassis is basically the same as mine, with the exception of the overall shape. Mine is simply rectangular, there are no side projections. (Running boards unbolt).

Seeing as it's legal for those guys, can I assume it's okay for SOLTRA? That thread also showed a pic of another built oldie, where the builder made a cutout in the fender unit to lower the seat a couple inches. I'd like to do that, too. If I have interpreted the rules correctly, I can't get the rearend much lower. The axle passes through the frame just below centre.

I'd still wait for a word from one of the techs as to seat locationing.