• Ciao Guest - You’ve landed at the ultimate Guzzi site. NEW FORUM REGISTRATIONS REQUIRE EMAIL ACTIVATION - CHECK YOUR SPAM FOLDER - Use the CONTACT above if you need help. New to the forum? For all new members, we require ONE post in the Introductions section at the bottom, in order to post in most of the other sections. ALWAYS TRY A SEARCH BEFORE STARTING A NEW TOPIC - Most questions you may have, have likely been already answered. DON'T BE A DRIVE-BY POSTER: As a common courtesy, check back in and reply within 24 hours, or your post will be deleted. Note there's decades of heavily experienced Guzzi professionals on this site, all whom happily give endless amounts of their VALUABLE time for free; BE COURTEOUS AND RESPECTFUL!
  • There is ZERO tolerance on personal attacks and ANY HYPERLINKS to PRODUCT(S) or other competing website(s), including personal pages, social media or other Forums. This ALSO INCLUDES ECU DIAGnostic software, questions and mapping. We work very hard to offer commercially supported products and to keep info relevant here. First offense is a note, second is a warning, third time will get you banned from the site. We don't have the time to chase repeat (and ignorant) offenders. This is NOT a social media platform; It's an ad-free, privately funded website, in small help with user donations. Be sure to see the GTM STORE link above; ALL product purchases help support the site, or you can upgrade your Forum profile or DONATE via the link above.
  • Be sure to see the GTM STORE link also above for our 700+ product inventory, including OEM parts and many of our 100% Made-in-SoCal-USA GTM products and engine kits. In SoCal? Click the SERVICE tab above for the best in service, tires, tuning and installation of our products or custom work, and don't miss our GT MotoCycles® (not) art on the BUILDS tab above. WE'RE HERE ONLINE ONLY - NO PHONE CALLS MADE OR RECEIVED - DO NOT EMAIL AND ASK QUESTIONS OR ASK TO CALL YOU.
  • Like the new V100, GuzziTech is full throttle into the future! We're now running on an all-new server and we've updated our Forum software. The visual differences are obvious, but hopefully you'll notice the super-fast speed. If you notice any glitches or have any issues, please post on the Site Support section at the bottom. If you haven't yet, please upgrade your account which is covered in the Site Support section or via the DONATE tab above, which gives you full site access including the DOWNLOADS section. We really appreciate every $ and your support to keep this site ad-free. Create an account, sign in, upgrade your account, and enjoy. See you on the road in 2024.

Speedometer and Tachometer Error

PerryB

PerryB

Just got it firing!
Joined
Nov 5, 2010
Messages
21
Friends,

I have a 1977 G5 with T3 instruments. Both the speedometer and tachometer seem to be wildly optimistic, as in about 17% too fast. When the speedo says I'm going 60 mph, I'm actually doing only 50 mph. When it says 70 mph I'm only going 59mph.

I've done some calculations and using the standard gearbox and rear drive ratios the engine should be doing 3416 rpm at 60 mph. That's exactly what both instruments show when I'm riding. So I believe that both instruments are way off, both reading too high. I have the stock 18 in. rear rim with a 110/90 tire.

The speedo does not have a trip odometer and does not read in tenths of a mile, only whole miles, so it's difficult to check if the odo works accurately.

Has anyone had an experience like this? Is there some fix? Could I have a side car rear drive that's lowering the gearing so much that my actual speed is 17% off?

PerryB
 
Speedometers on the old Guzzis have always been optimistic. Tach is usually pretty close. At an indicated 70 MPH in 5th, the tach should read about 4,000 RPM. If RPM is much higher then you may very well have sidecar gears. Other options are GPS based speedometers which have been covered as replacements on this forum.
 
Thanks for the replies.

I counted the teeth on my ring gear (it's the correct 7/33) and also used Guzziology to find the ratio for the speedo drive gear at the transmission output shaft. From that and from measuring the circumference of the rear tire, I concluded that the speedo cable should rotate 1679 revolutions per mile. On the outside of the speedometer itself there's a small sticker that says 1610 revolutions per mile, so even if everything is working correctly the rear drive and speedo gearing is over 4% too fast for the way the Veglia calibrates the stock instrument.

With the speedo reading 17% too fast I knew that I should investigate further. I cracked open both tach and speedo last weekend and was able to tighten the watch springs on both instruments until they read correctly. After some trial and error I was able to get both tach and speed to read correctly. The odometer, which has no adjustment since it uses fixed gears, remains optimistic.

I knew everyone was losing sleep over this one, so I thought I'd post an update!
 
You must log in or register to reply here.
Back
Top