80mph speedometers.

[SteveD]

I have one, or at least one is in the mail.

Can anyone provide some info on these please.

[Garnet]

I have one, or at least one is in the mail.

Can anyone provide some info on these please.

When someone says "it's in the mail", be carefull, there is another parts to that saying.

[SteveD]

I have one, or at least one is in the mail.

Can anyone provide some info on these please.

When someone says "it's in the mail", be carefull, there is another parts to that saying.

Yeah...but I said it, not the seller! It's a recent ebay acquisition, which I bought for it's reported better accuracy.

I'm after why they were used, which models...any other info really.

If I was to go 180kph, would it break the needle off, or will it act like a speed limiter 'cause I'll be scared it may?

[dougie]

I believe they were on models during the gas crunch when the U.S. highway speed limit was 55 mph.
Don't know if it will break when you go faster than 80.

[Major Softie]

It's a recent ebay acquisition, which I bought for it's reported better accuracy.

I'm after why they were used, which models...any other info really.

If I was to go 180kph, would it break the needle off, or will it act like a speed limiter 'cause I'll be scared it may?

They are eighty-five mph speedometers. They were used because of a government mandate during the oil embargo of the late 70's. They were intended to reduce speeding both for safety and fuel savings. Research proving that 85 mph speedometers would actually result in lower speeds was, as far as I know, non-existent. Only 2 years after the rule was instituted, the NHTSA recommended removing the rule, but it took longer than that for them to disappear.

Speedometer accuracy rules in the U.S., for whatever reason, are based on a percentage of total overall range, so, if the rule is 3%, on an 85 mph speedometer it is 3% of 85 - on a 160 mph speedometer it's 3% of 160, and that applies over the entire range.

So, yes, an 85 mph speedometer is more accurate. They were used on every model of every U.S. vehicle from 1980 until they went away, whenever that was. I think that varied with various manufacturers, and models. They were on everything for at least 3-4 years, but they were still around a lot longer than that.

The speedometer is not supposed to be harmed by going faster than 85 mph. I've never heard of anyone who knows that they harmed one by going high speeds, but that doesn't mean it's never happened. Still, it's not anything I'd worry about.

The biggest advantage to my mind (besides better accuracy) is that they are much easier to read because they haven't crammed 160 mph worth of numbers onto the face of the dial. Despite those two advantages, they were very unpopular, so I imagine they are much cheaper than higher range speedometers

[SteveD]

Thanks Softie. That's good info. Cheers

[moosehead]

I have the 85PMH speedo on my 82 RS. Measured against my GPS its extremely accurrate...last I looked it was knock on in MPH to GPS reading.

Over 85...no problem...it just sits there or little beyond

My problem is we're KPH in Canada so have to look closley for the KPH numbers.

I think someone on the board said these speedos were the most accurrate but I didn't know why...oil embargo and US regs explains it!

[Jean]

The explaination about accuracy over total range is why they are more accurate...
Their effect was not what the government committee imagined it would be, tho. DUH.
I have one in my '78 van, and it's no problem...It doesn't want to go over 80 anyhow!!

The serious thing to consider is "DOES it MATCH the ratio of your rear-drive?"
Speedos are matched to the gearing there since they are driven off the output of your gearbox.
Doesn't matter if it's 85 or 160.mph...gotta match or accuracy is just smoke.

[moosehead]

I think Steve has an 81 RS so his gear ratio to speedo should be OK for the 85MPH speedo.

[Jean]

If the bike is a Canadian edition and he's getting a US speedo, the ratio might NOT be the same!
They shipped different ratios to the US vs. the Euro-models, so it's always a possibility it is different.

According to my BMW parts book ( The FAT little Auxiliary Catalog) , a CDN version could have either a 2.91 or a 3.00 rear ratio. the US edition came with 2.91 only (unless someone changed it out later).
In 1981, there WAS an official CDN version, too. It's listed separate from the US version.