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ultimoptima

Optima Mid Arb Kit

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Hi All,

Just having a look through the spec of my Optima Mid Custom Special and wondered why it wasn't originally supplied with an Anti Roll Bar kit? Does anyone have any comments about how differently it handles with as opposed to without? I might try and pick up a set if it's worth the upgrade?

Thanks in advance

David

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The anti roll bar kit was in the Turbo Mid kit as one of the differences between the Turbo and standard Mid, but I can't think of anyone who raced with one. One look at the design of the mounts and thin wire used it is obviously just there for show with very little effect on handling. The short wheelbase of the original Mids also makes them more suitable for an anti roll bar to help tame the twitchy handling, which isn't needed on the longer wheelbase Custom models.

If you are looking for one just to add all the period correct options then go for it, if you are considering adding it to improve the handling don't bother it won't make any difference.

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Back in the day, tracks were real loamy and rougher than they are today. At least US tracks. We used to take the roll bars off as they limited suspension travel.

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I was going to ask about the diffs actually. When I got my first Ultima (when it was released) it had a gear diff, when I got my Ultima Pro it had a ball diff (considered an upgrade?). When I've read articles about ball diffs people always say they're more work, wear out faster etc. In the spec for my Optima Mid Custom Special, I got the feeling Kyosho made a big deal about having factory assembled gear diffs. Are the ball diffs an upgrade. Where any of the Mid's supplied with factory ball diffs or is it Option House only?

Also, there were one way diffs available too. I'm guessing these do what it says on the tin, but how does it make the car react, front, rear or both?

I need to get one of those hardened spur gears, What's the part number?

Many Thanks

David

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Where any of the Mid's supplied with factory ball diffs or is it Option House only?
The Turbo Optima Mid Special came with ball diffs, as well as every other option available at the time, all others came with gear diffs. If you are planning on vintage racing with your Mid you might look at ball diffs as a tuning aid, if you aren't racing they aren't worth bothering with at all. Kyoshos ball diffs were a bad design, Kyosho didn't use diff washers in them, so when the diff balls wear a track into the outdrive plates you have to source a new set of diff internals to fix them. They need a lot of regular maintenance to remain smooth and to do that on a Mid involves a complete strip down of the whole car to split the gearboxes.

None of my Mids, even when I raced them, ran with the ball diffs.

Also, there were one way diffs available too. I'm guessing these do what it says on the tin, but how does it make the car react, front, rear or both?
Yes there is a front one way option. It replaces the front diff and means that under normal driving it is rear wheel drive, but under hard acceleration the front diff locks solid to give you four wheel drive. It makes the steering very twitchy when you turn in to a corner, and you can't brake hard as you only have rear wheel braking so it spins out. With the front axle locking solid under acceleration it means it understeers more coming out of the corner than with the ball diff. On high grip tracks without hard braking I ran a one way, low grip surfaces I ran a front gera diff.
I need to get one of those hardened spur gears, What's the part number?

Kyosho never made a hardened spur gear, and there's nothing wrong with the kit one. Kyosho didn't upgrade any of the gears in the Mid.

The one gear known to wear was the idler gear and the popular upgrade was a Tufnol version sold by SRM Racing who have long since gone. RW Racing, Wasp and other third party companies made alternative spur gears, usually to convert it to the more popular 48dp size gear teeth.

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Right, I've done some shopping and have bought front and rear ball diffs, some spare gearbox cases (as spares) and a pair of OT-47 uprights (I read your other post about your setup Terry). I'd like to try and buy a front one way diff at some point just to experiment with. It'll be nice to have all the diff options to choose from. The front one way makes me curious because I can't really get my head around it, does it just have oneway bearings in it?

I need some education with regard to the gearing. What are my options for upgrading the idler gear apart from finding an old SRM Racing on eBay or is it not worth worrying about? Also, I've seen different coloured spur gears fitted and have seen RW Racing still supply spurs, is there an advantage to running 48dp apart from the availability of pinions?

Thanks

David

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The front one way makes me curious because I can't really get my head around it, does it just have oneway bearings in it?

Yes, the front diff is replaced with a housing that contains two one way bearings, with an outdrive in each side. It means the only time it is 4wd is when the rear wheels slip or spin. It makes the steering very direct, and you need pretty good reactions to stop it spinning out, and a lot of suspension geometry tuning to get it balanced. If you do fit one remember you can't really use the brakes any more as it will swap ends.

What are my options for upgrading the idler gear apart from finding an old SRM Racing on eBay or is it not worth worrying about?
There isn't any option, although considering there are thousands of Mids running around perfectly fine with the standard gears there isn't any need to upgrade it.
Also, I've seen different coloured spur gears fitted and have seen RW Racing still supply spurs, is there an advantage to running 48dp apart from the availability of pinions?
Way back then we didn't have the internet, so our choice of pinions was what was available locally. 48dp was pretty much standard and 0.6 module pinions were only used on the Mid and no other car at the time. replacing the spur gear gave you use of the full range of 48dp pinions that racers had, instead of having to be stuck with the kit pinion. I used the standard spur as I ordered the range of 0.6 module pinions from Kyosho as I only had the bigger 32dp pinions after racing an Optima and Ultima.

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