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3.55 ring & pinion???

PostPosted: Sat Feb 16, 2008 4:57 pm
by vagt6
I've been told that 3.55 ring and pinion sets may be available for Spridgets. This would seem to be a good alternative to installing a 5 speed or overdrive, IMHO.

The 3.55 gears would fit, but they're apparently rare. Probably could find some in the UK somewhere. These engines are fairly torqey and I don't think the reduced final drive ratio would be a problem. In fact, I'd love it. This would seem to be the way to go, IMHO. Cheaper than OD. Not easy to install, but certainly cheaper with the same or better reduction in RPM than OD.

Do any of youse guys have knowledge of the 3.55 gearset??

Re: 3.55 ring & pinion???

PostPosted: Sat Feb 16, 2008 7:24 pm
by admin
Hmmmm...interesting thought. Likely eBay is the best source. Not sure how many were produced. Love to hear if you find one and get it installed, and how you like the result. Keep us posted!

Re: 3.55 ring & pinion???

PostPosted: Sun Feb 17, 2008 1:36 am
by KenR
You could try Autogear in the UK. P/N CWP037
http://autogear.co.uk/product/search.ph ... ter=Search

Listed as 162 pounds, not sure about Sterling or not...

Re: 3.55 ring & pinion???

PostPosted: Sun Feb 17, 2008 4:01 pm
by vagt6
Yes, I saw that just today on the British Car Forum. 3.39 ring & pinion set for 162.50 quid (British pound sterling), converts to about $318 US plus shipping. Pricey. I imagine the shipping wouldn't be real cheap, but I don't know for sure how much it may cost to ship a small package that weighs about 10 lbs. or so?

Victoria British sells a new 3.70 ring & pinion set for $299.99, with Vicky Brit warranty.

Question: 3.39 sounds like it would make the car a far better highway cruiser, but with a stock ribcase gearbox and a nicely sorted 1275, would a ratio like 3.39 be sluggish? Isn't first gear pretty low in the ribcase, though??

Anyone drive a Spridget with a final drive ratio like 3.39ish? For example, a five-speed with OD???

Re: 3.55 ring & pinion???

PostPosted: Sat Feb 23, 2008 2:19 am
by Charlie Tolman
The 3.55:1 ratio most likely has differential gear teeth count of 32 / 9. With 23" diameter tires, at 60 mph, engine speed is near 3100 rpm.

However, the ratio closest to a 3.39:1 is 44 / 13, or 3.3846:1. Is this the teeth count for this ring and pinion set ? At 60 mph, 2970 rpm. Does your engine have enough horsepower at 3000 rpm for cruising, with this gear set ?

Fifth gear in the Datsun 210 transmission has a ratio of 0.846:1.
With a 4.22:1 diff gear, the net reduction would be 3.57:1. (Close to 3.55)
With a 3.90:1 diff gear, the net would be 3.30:1. With 23" diameter tires, at 60 mph, the engine speed would be just under 2900 rpm.

First gear in a rib-case transmission is 3.20:1.
With a 3.55:1 diff gear, the overall reduction in first gear is 11.4:1.
With a 3.3846:1 diff gear, the overall reduction is 10.8:1.
These two values should be compared to the standard 1275 numbers, with a 3.90 diff gear, with a first gear overall reduction of 12.5. Yes, the 3.55 and 3.38 diff gears would give sluggish performance in first gear. Acceleration would be about 10% to 15% less.

Charlie Tolman
H/P 40



Charlie Tolman

Re: 3.55 ring & pinion???

PostPosted: Sun Feb 24, 2008 3:59 pm
by vagt6
Thanks for the math, Charlie, good stuff.

With stock or near-stock 1275 engine, 3.70 sounds like a good compromise to me.

--Mark

Re: 3.55 ring & pinion???

PostPosted: Mon Feb 25, 2008 6:51 pm
by Charlie Tolman
The 3.55 differential gear set mentioned above might have a tooth count of
39 / 11 = 3.5454.

Charlie T.

Re: 3.55 ring & pinion???

PostPosted: Wed Nov 24, 2010 4:54 am
by opplee

Re: 3.55 ring & pinion???

PostPosted: Tue Sep 13, 2011 10:15 pm
by regularman
I have a 3.55 and it would work well with just a straight 4 speed. Its a 39:11 and I think I got the last set that Vicky Brit had. They were a bear to set but they fit in the old 39:10 pumpkin just fine. I wanted a higher gear and I got it. I was told that this was used as a "big track" gear set for places like Daytona. That is all I know about them. I was also told this was the gear set that was used in some of the Lotus 7 kits.
I set my midget up for cruising. I have 175/70/13 tires and a Datsun 5 speed in mine as well. 60@2750, 65@3000, 70@3200

Re: 3.55 ring & pinion???

PostPosted: Thu Sep 15, 2011 2:01 pm
by vagt6
I finally decided to install a stock (3.91) ring and pinion in the diff when we rebuilt it. Got the gears from a used Midget, they looked like new.

With the Datsun 5 speed, the stock diff gearing of 3.91is great. 5th gear is .82 ratio and I rev about 3200RPM at 70 MPH. I practically never cruise that fast, though. Most of my driving is 60MPH and lower and I avoid Interstate Highways like the plague, anyway.

In fact, most of my driving is 45 MPH or slower. Just what the Midget was designed for!

Thanks to all for the great input, as always.