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The chain drive sprockets were available with different toothcounts also. The concept is to create an overdive on the front wheels. Masami did this with his yokomos also. It gives the car a different feel, bit like FWD I guess. One explanation I've been given is the ballonong of the rear tires. The narrower front tires (not on an optima, I know) balloon less so at full speed they are smaller in diameter than the rears. A one-way would let them turn faster and not cause a braking effect, but the overdirve on the front will keep it 4WD and actuaaly will pull when the balloning is less: on acceleration.

SWB optima mid belt and optima conversion are the same length belts, stinger upgrade kit or stinger mk2 standard included belts are the same a LWB mid. The stinger used optima diffs I think, while the stinger mk2 used optima mid diffs. And finally , the optima mid/stinger mk2 diffs don't have the overdrive option.

And the belt and pulleys do look like they'd be compatible with the trackmaster. I think I'm going to keep a look-out for a kit

I always though the ballooning of modern buggy tires looks so daft. I understand the concept is rather clever though, as in effect you have variable gearbox ratios.

Mr. Ed, I didn't know the chain drive had different toothcounts available. Then, these may both be for the Optima, which would make sense for a small company to market to such a popular car.

The Optima came with 18 and 19 turn sprockets, and you could use them on both front and rear diffs so you could have overdriven rear as well as overdriven front. At the time I was racing an Optima we were racing on a very low grip surface, so mine was set up with overdriven rear so it behaved more like a rear wheel drive car so it would rotate better in the corners as the front end couldn't understeer with the rear wheels turning faster. Overdriven front would help drag the front out of a corner.

And these pulleys and belt would work fine, you don't need the extra pulley and modified gearbox to convert an Optima to belt drive. My own runner has been converted with just a Mid belt and diffs and has had years of use without any problem. When you consider all the belt is doing is transferring power only to the front wheels and only the lower portion of the belt is under tension you can see that all the small pulley is doing is taking the slack out of the belt.

That makes sense Terry, I remember you saying that awhile back in a post or pm about the belt conversion, that the Optima would run fine with just a belt on the diffs. The 18 one is almost the identical size to the stock one, while the 17s are smaller. So, I guess you could even mix and match llike you said, thanks for the post.

terry.sc wrote:And these pulleys and belt would work fine, you don't need the extra pulley and modified gearbox to convert an Optima to belt drive. My own runner has been converted with just a Mid belt and diffs and has had years of use without any problem. When you consider all the belt is doing is transferring power only to the front wheels and only the lower portion of the belt is under tension you can see that all the small pulley is doing is taking the slack out of the belt.

Even if you forego installing the idler gear in the gearbox, I'm pretty sure the cogs of the belt will rub against the unmodded gearbox as it exits the gearbox, as well as the chainguide floor, probably causing premature wear. Maybe the belt can survive the wear, but there's a reason why the idler gear was included in the conversion kit.

Which do you think is more likely to cause wear on the inside of the gearbox and chain guards. A metal chain that has been tensioned to keep it on the pulleys, or rubber belt teeth that aren't under tension. If it did wear as much as you suggest we would have found plenty of Optimas with the gearbox case and chain guides worn through by the chains.

Unlike the Mid which was designed around the belt drive the Optima belt was an afterthought and the idler pulley takes out the play as the diff pulleys are a little too close for the correct belt tension.

I've run my Turbo Optima without the little white pulley forever. Now, I haven't inspected everything in about a year but last time I checked, everything look pretty darn new.

terry.sc wrote:Which do you think is more likely to cause wear on the inside of the gearbox and chain guards. A metal chain that has been tensioned to keep it on the pulleys, or rubber belt teeth that aren't under tension. If it did wear as much as you suggest we would have found plenty of Optimas with the gearbox case and chain guides worn through by the chains.

You misunderstood my idea of "wear"; I was referring to the belt wearing on the inside as a result of it rubbing the gearbox and chainguide floor; not the gearbox/chainguide wearing. I guess the belt is more durable than I thought, as it's allowed to rub the upper exit channel and chainguide floor without the idler pulley installed and from what you guys are saying, it causes no harm. Oh well, I guess Kyosho Option House was out to lunch when they included the idler pulley in their conversion kit. Oh well, thanks for the info; if I do another Optima belt conversion someday, I'll try it without any modding and see for myself. Sure would save me a lot of time, as I put in a lot of work to fabricate my own belt conversion just like the Option House conversion kit instructions.

Associated included a driver figure and headlights with their kits and they ran great without em

I don't see the problem here, one company has one way of doing the conversion and one company has another idea. Embrace that we have that diversity. One company also didn't survive....which one? The aftermarket one. Maybe their kit worked but not as well. That doesn't automatically mean it wasn't MEANT for this application, just that they had a different way of doing it.

Did we rule out that they were for a stinger?

Anything which rubs will cause unwanted friction, which will be reflected in performace and run times to a degree. It would be like running a car with plain bushes instead of bearings. So it would be best to remove any objects in the way, or fit a roller guide (with bearings) to avoid those obstacles by altering the path of the belt. Any other method would be a bodge imho

gomachv wrote:...

Did we rule out that they were for a stinger?

Kind of; if you want to take my word for it. The belt would be too short for the Stinger.

Ah, gotcha. I was just thinking since the stinger version of the conversion came without the gearbox and idler.....
No such luck.

If you want to use a stinger conversion on an optima you could lengthen the car or get the EDIT: SWB optima mid belt separately.
I don't know if they still are around, but not too long ago someone was offering replacements for both belt sizes on ebay

Mr. ED wrote:If you want to use a stinger conversion on an optima you could lengthen the car or get the EDIT: SWB optima mid belt separately.
I don't know if they still are around, but not too long ago someone was offering replacements for both belt sizes on ebay

As you said earlier, all short-wheelbase versions of the Optima Mid use the same belt as the Optima conversion. I'm using an Optima Mid belt in Barney. I see those on eBay quite often and this seller has plenty; I emailed him a while back to confirm they fit the Optima conversion as well as the SWB. Whoever needs 'em, go get you some.

http://www.ebay.com/itm/Kyosho-OT-89-Optima-Mid-SWB-Drive-Belt-NIP-OT89-/290501222650?pt=UK_ToysGames_RadioControlled_JN&hash=item43a338e0fa