14 inch tyres and gearing.

[billmoore42]

TBG: Thanks for the reply. I am slowing building up my nerve to do this.

[TBG]

Bill - I don't know if you have seen this - the speeds versus rpm with a 3:1 cwp?

May help you make up your mind and it is exactly what I have now. 2nd gear is a hoot!

[billmoore42]

TBG:

Wow, it looks like 67 mph at 3000 rpm, and 80 MPH at 3500 rpm with a 3.1 differential. This would be a delight, as currently I hate taking the car on the freeway with its 70 MPH + traffic here in California for any length of time.

It looks like I might be looking into getting rid of the rotoflex at the same time, as the work is all in the same area, and why waste my or the shops labor. I replaced the rotoflex couplings a couple years ago, and found it an trying task I may not want to do again. I will talk to the rear end shop that says they have some Lotus experience, and go from there.

[TBG]

Bill - you won't be disappointed! The chart is a bit furry and 80 is actually about 3700 in my car, but still a vast improvement. I have not regretted having the CWP made by the delightful Gordon for one moment though. I did have my doubts reading stuff on here from the unbelievers but it was all tosh in the end!! Good luck and let me know how you get on. D

[1owner69Elan]

Bill Moore:

As I believe you are using "standard" size tires (155/80r13) the gearing on your car with a 3.0 diff will be a bit taller than TBG's (1.65/70r13).

Here are the curves if you fit the 3.0 diff with those tires.

Attached pdf is less fuzzy.

[TBG]

Surely smaller tyres will give lower ratios.........?

[1owner69Elan]

Smaller in width but taller with the 80 profile. (plus ~0.7 inches).

This taller 155/80 tire (while narrower) results in taller gearing. It is the height, not width, that governs this.

[billmoore42]

Thanks everybody for the suggestions. It looks like with my Michelin XAS tires in 155 by 13, I should get around 67 miles per hour at 3000 rpm.

[1owner69Elan]

Thanks everybody for the suggestions. It looks like with my Michelin XAS tires in 155 by 13, I should get around 67 miles per hour at 3000 rpm.

As opposed to ~54 mph @3000 with your 3.77

[billmoore42]

Yes, about 54 mph at 3000 revs. One thing I am realizing is that the Semi Close ratio gear box, with its 2.97 first gear ratio, would be more suitable for this conversion than the earlier close ratio gear box with its 2.51 first gear ratio.

Having a 67 Elan FHC, I am assuming I have the Semi Close ratio box.

[elans3]

Not necessarily. My '68 DHC S/E was specified from new with the close ratio 2.5 : 1 and 3.55 diff, box and still has them, although the semi-close was much more prevalent.

[billmoore42]

Elan3:

Thanks for this, it looks like I will be trying to figure out my cars first gear ratio before anything else happens. The guy at the local differential shop, who has done quite a few British Cars, is hesitant on this one, as he thinks a 3.0 is for V8's.

[TBG]

"as he thinks a 3.0 is for V8's."

Send him over here Bill and I will show him he is wrong!!

[rgh0]

"as he thinks a 3.0 is for V8's."

Send him over here Bill and I will show him he is wrong!!

to many variables for such a simple statement

i.e.
wheel and tyre size
first gear ratio
intermediate gear spacing
car weight
engine torque characteristics


In an Elan all of these can add up to make a 4 speed with a 3:1 diff ratio eminently practical where relaxed high speed cruising is most important compared to the other end of the scale of stop light drag racing performance

cheers
Rohan

[TBG]

True Rohan if drag racing is your thing, but what has happened to me is that 2nd gear is now blistering in acceleration and don't even talk about 1st!!