16 vs 18 inch rear wheels

Picasso said:

I have the stock 16 inch rear wheel on my 81 GL 500 , how much more speed on the top end would you get with the 18 inch wheel? How about difference in gas mileage? And are the only ones available the reverse Comstar in silver? No black?

Thanks, Picasso.

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Hi,



The metal finish CX wheels are (plain) "Comstars". The black ones are "reverse Comstars".



In Europe we got reverse Comstars on the standard model 1981. Last year for this model was 1982. The first years (1978 - 1980) that model had plain Comstars. 18" rear on all of them.



The Custom, Deluxe and GL models had reverse Comstars from the beginning (1979, 1979 and 1981). 16" rear on all.



The Euro and Turbo models had a different design, 18" rear with brake disc.



I don´t think you´ll gain much top speed with an 18-incher.



I own 1981 European spec standard models and have never been able to touch red in fifth. I had a Deluxe some years ago and with that one I was pretty close. But then again did the instruments on that one play their own games... So I´m not sure how fast it was.



What you´ll get with a 18-incher is marginally (but noticeable) lower revs (some few %). Maybe also marginally better mileage, but certainly not much.



I tried an 18-incher on one of the GL 500:S I owned many years ago. As a "fulldresser" it looked kind of strange with that thin rear wheel.



Sture

Yeah you'll actually have a little less power due to gearing change.



However, 18's just look better

marshallf3 said:

However, 18's just look better



In spoked I'd say yes, but with reverse comstars I kind of like the difference of having the 16 in the rear, I also think it holds a wider tire.

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Going slightly off topic, maybe - anyhow...



I´m going the other way around with one of my -81 standard models.



I´ve prepped that one for a serious trip abroad with m´lady in the future (next summer???). As a 130 / 90 x 16 rear can carry a higher load than the 4.00 x 18 that´s on as original, I put a 16-incher on that one to test. It´s revving a tad higher, which may even be a good thing once fully loaded. Maybe I´ll do a 650 clutch gear swap - the parts are on another of my bikes, right now.



The bike stands there in the garage with a triple bypass done only 50 kms back. KONI rear shocks to handle the unevitable overload, progressive front fork springs are in there since before, a TAROZZI fork brace will go on before we go. A new rear tire will be on too.



A standard model 500 is only allowed to carry 170 kg or so. I know our weights already and together with what we´ll be needing, luggagewise, there´ll be at least 70 kg more than what´s allowed.



The bike can handle it (did a similar trip with my son, riding pillion (similar weight) 7-8 years ago). Rough eastern-European roads - no problems, not one single bottoming out - but at speed on German Autobahn I wasn´t so confident - the rear ran rather hot, being seriously overloaded. I´m sure the 16-incher will add some margin..



Sture

InWeldingWeTrust said:

@cxsture

Thats a very valid point. For additional capacity, look to fit the american MT90-16 tyre size as a lot of 130/90-16 tyres will have a load rating as low as 67 (307kg) wheras MT90-16 will likely be either 74 (375kg) or 80 (450kg)

MT90-16 is near as dammit identical to the metric 130/90-16 so clearance problems should not be an issue. This is in effect a toughened tyre spec intended for old school baggers so is right at home carrying you, your passenger, and luggage

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Thanks, IWWT!



I´ve been wondering about the difference between MT90-16 and 130/90-16. From some manufacturer´s chart these two seem to have almost identical dimensions, so I was thinking MT90 was something special, probably for Harleys and such.



I have an almost spanking new Metzeler ME 77 130/90 on a spare rim, already, but may very well try a MT90, if necessary.



The front tire (3.25 - 19) has load rating 54 (212 kg) and the 130/90 rear has 67 (307 kg). Together they will be good for 519 kg, if ideally distributed.



The bike weighs in @ 220 kg, naked but filled. Me, m´lady, luggage and all will be at least 260 kg. Totally, with some margin, just under 500 kg. But - most of it will no doubt be carried by the rear wheel. Worth thinking about!



Sture