1988 Excel SE Diff now £50

[LotusElan17]

Standard diff, appears to be good although I never actually drove the car, £80.
Carrier plate also available £20.

David 07908185755
Enfield North London

[LotusElan17]

Now £50 to clear, nothing wrong with it, feels tight, just trying to clear my garage for next project. If you are running an Excel SE, and I presume most people on here do, then it must be worth buying as a spare.

[jeff.fenton]

If you have a non SE car and run 205 50 15 tyres, putting in a SE diff will bring your speedo reading back nearer correct, ask me how I know.

[jpm6591]

Jeff,
I have a non SE car on 215-15-15 tyres and am a bit confused wih your comment on speedo.
I drove down a major industrial road, spot on 40 mph only to get flashed as it was a 30mph zone.
Ticket stated 40mph on notice of prosecution, when does speedo lose accuracy?

[AndyC]

Most speedos are set to read up to 10% higher than reality (indicated 44mph = really doing 40mph) that way the manufacturer cannot be accused of causing you to speed. There will always be some inaccuracy, so the 10% covers it, even almost worst case scenario.

If you run 205 50 15s instead if 215 50 15s the side wall will be 5mm shorter (aspect x width, 50% of 10mm reduction in width), with a tyre that's circa 300mm radius that's 1.5%, so your speedo should read 1.5% higher than it would have done on the correct size tyres. Csan't be bothered to due exact calcs but there are sites out the just for that if yo wish to get it accurate.

The SE diff Vs 160 BHP diff is 4.1 Vs 3.9, so the SE diff gives 0.2 more rear wheel rotation for the same prop shaft rotation than a 160 BHP one would. That's 0.2 in circa 4.0 (can't be bothered to do the exact based on 4.1) or, approx 2%, so your speedo (driven by the output shaft on the gearbox) would read circa 2% lower for a given vehicle speed with an SE diff in place of a 160 BHP one.

Do both tyres and diff and you get
1.5% higher due to tyres.
2% lower due to diff.
Net speed reading 0.5% lower overall than when left factory.


Other factors do play a big part, tread depth (starts at circa 7mm, legal limit is more than 5mm less than that), inflation of tyres (higher pressure for given tyre means effective bigger rolling diameter), tyre stiffness of wall (stiffer means bigger rolling diameter).

[jeff.fenton]

Smaller tyres will make the speedo read faster than you're going,(safe, reads 70, going at 65 mph app.), higher diff ratio will make it read slower than you're going,(not safe, reads 70 going at 75mph app.),they help to cancel each other out leaving speedo reading nearer to correct. Changing from 215 50 15 to 205 50 15 reduces rolling circumference, you go less miles for the same indicated speed. Changing from std.(4.1:1) to SE.(3.9:1) you go more miles for same indicated speed,(higher ratio equals lower numbers). Hope that helps,(and Really hope I'm right). Sorry to hear about your N.I.Prosecution, good luck.

[amarshall]

Most speedos on cheap cars are allowed to read up to 10% higher than reality

but not allowed to read any lower at all.

I've found that the speedo on my Excel, at least, is 100% accurate at all speeds above 15mph (allowing for needle wobble).