81 GS450T Rear Wheel/Tire Specs/Swap

[Guest]

Hey guys; I have an 81 GS450T, and I was wanting to upsize the rear to an 18 or 19" wheel. I tried searching and got a little lost. Can I swap over a rear wheel from a similar-year GS450S or GS450E (which I believe had the 18" rear) without changing any of the braking/chain components? My bike will be due for brakes and tires over the winter, but I'd like to retain as much of the OEM-spec components while also having a little lower profile tire in the rear. Also I see the GS450S rear tire size is listed as 3.50-18. How does that size compare to a 120/80-18, for example? Or do I just roll with the 3.5-18? Thanks for your help!

[pete]

I've never looked into this, but I would think if the drum brake shoes are the same part number for both the T and E/S models, then the hub would be the same. The swingarm part number would give the same indication but I wouldn't be surprised if it's different without being an issue.

I run a 100/90-18 on the rear of my 450E and it's a good size.

The big question with the swap is if the swingarm isn't the same is the spacers etc. and you may need to have some made to fit.

I'm not a guru on wheel or swingarm swaps but those are the things I would take into account as an absolute minimum, hopefully someone a little more knowledgeable can share a few more tips and pointers.

Oh, I guess you probably need to take into account any difference in overall diameter to ensure you still have clearance between the top of the tyre and the mudguard etc.

[Gorminrider]

it should be fine to switch rims....I can do 18->17 on the '81 GSX400 models ( I have E and T) and they are identical to '80,'81 GS450s to look at...I think the engine+carbs pretty much the only difference excepting the speedometer ( KMH in Canada)

on my E 18" rear rim (1.85x18 TT) and

tires to fit being"3.50s x18 or 3.75s x18 TT"

110/90 18 is the metric size that works well...it's a narrow-looking tire and you won't even know you are going around a corner...quite a lighter feel than than the fatter tires...

[pete]

You sure on the 110/90-18? I ran 100/90-18 front and 110/90-18 rear for a while and found the profile too pinched and tip in to corners got a bit iffy, just didn't feel stable. That was running 32 psi in both.

When I went back to 90/90-18 front and 100/90-18 rear it was spot on and the tip in is much more stable. I now run 36 psi front, 38 psi rear after a very long and in depth conversation with a tyre guy on why I was wearing through the centre of my rear tyre so fast.

Not saying you're wrong by the way, just my experiences

[Steve]

Hey guys; I have an 81 GS450T, and I was wanting to upsize the rear to an 18 or 19" wheel.

I know there are some of the smaller bikes out there that use an 18" wheel, have not heard of any with a 19" on the rear.

..., but I'd like to retain as much of the OEM-spec components while also having a little lower profile tire in the rear.

Not sure how going with a larger rim is going to get you a lower profile. A lower-profile tire will likely get you less rubber on the road, given the relatively skinny rims.

Also I see the GS450S rear tire size is listed as 3.50-18. How does that size compare to a 120/80-18, for example? Or do I just roll with the 3.5-18? Thanks for your help!

The conversion is simple math. A 3.50 tire is 3.5" in width, which is 88.9mm. Modern tires are available in numbers divisible by 10, so you would go to a 90. Not too many rear tires available in a 90, so you woule likely look for a 100. The older tires usually had a taller profile of 100%, meaning that the distance from the bead to the tread is 100% of the distance across the sidewalls. Most newer tires come with a 90% profile, so you would be looking for a 100/90-17 (or 18). A 120 tire might fit in the swingarm, but will make the bike handle rather slow. The 80% profile will make it even worse. Contrary to automotive 'wisdom', putting wider tires on a bike does not give it more traction or make it handle better. The wider tire will be squeezed onto a narrow rim, which pulls the tire into a tighter curve, acutally putting LESS rubber on the road. An 80% profile tire will be even worse, with its shorter sidewall.

Is there anything wrong with your current 17" rear, or are you just going for a "look"?

.

[LAB3]

I've never looked into this, but I would think if the drum brake shoes are the same part number for both the T and E/S models, then the hub would be the same. The swingarm part number would give the same indication but I wouldn't be surprised if it's different without being an issue.

I run a 100/90-18 on the rear of my 450E and it's a good size.

The big question with the swap is if the swingarm isn't the same is the spacers etc. and you may need to have some made to fit.

I'm not a guru on wheel or swingarm swaps but those are the things I would take into account as an absolute minimum, hopefully someone a little more knowledgeable can share a few more tips and pointers.

Oh, I guess you probably need to take into account any difference in overall diameter to ensure you still have clearance between the top of the tyre and the mudguard etc.

Rear brake sizes can get very strange! On my 450txz the brake shoes are larger diameter than the 450tx.

If I where to give swapping rims a try, the first thing I'd do is check part numbers on all the hardware. If they match, you're golden, if not you could find a small project like that nickel and diming you to death!

[Gorminrider]

You sure on the 110/90-18? I ran 100/90-18 front and 110/90-18 rear for a while and found the profile too pinched and tip in to corners got a bit iffy, just didn't feel stable. That was running 32 psi in both.

When I went back to 90/90-18 front and 100/90-18 rear it was spot on and the tip in is much more stable. I now run 36 psi front, 38 psi rear after a very long and in depth conversation with a tyre guy on why I was wearing through the centre of my rear tyre so fast.

Not saying you're wrong by the way, just my experiences

sure, Pete. I know how you ride (My front tire on the E right now is a Shinko tourmaster 3.0 x18) ....I run 28-30 psi front and rear! depending on the weather..without any massive load on the rear... but I expect the tires to wear the centre first no matter what: the curves on my routes are not extreme and the sharpest corners I normally find are the street corners. I don't whip 'round those very fast - I'm adverse to the risks of getting tangled in the baby-carriage on my right or the left-turner suprising me on the left...or the slipper sewer grate, the crosswalk lines..all of that.

I'm a little puzzled by your tire-guy but I don't know how heavy you are... I'd expect a too-high pressure to cause more wear in the centre- It's reducing the amount of tread on the road if you consider a hard perfect circle, there's only a single contact point...but there's an optimal tire profile for every ride and rider I guess...to me , looking down, it's roughly a tire not-squashed...but not hard-as-a-rock-riding-on-it's-tip-toes either- I like to have some rubber on the road when it's a wet or dodgy surface...I can even get paranoid and let a pound out in the rain.... but I expect it's not so performance oriented...the rims will wander over the tire a little if it's pushed to the centripetal limits

Just an aside, maybe a lower profile than the "90" would help ..having less sidewall to shift?
Modern street bikes (and fancy cars too) seem to trend to this though I haven't researched it that way...while the dual sports and dirt bikes seem to have the same profiles our old "all-rounder" bikes do.

[pete]

Ah ok, less pressure would possibly solve that tip in weirdness I felt.

I won't pretend to be able to explain how the tyre guy did, but it made sense at the time.

Basically, an under inflated tyre will end up not with more tread on the road, but the centre will start pushing inwards, resulting in two shoulders if you like taking the most of the wear, and it starts tearing the tyre tread.

Over inflated will definitely do the centre more, but what he saw with my tyre wear indicated under inflation.

He demonstrated by forcing a bare tyre not mounted on a rim around the floor, and you could see what the centre of the tyre did and it was bulging in.

The symptoms I gave him was a worn centre, but when he looked and showed me, there was also a bunch of scalloping just outside of the centre, and that tearing of the tread from under inflation is what causes that.

I hope I've done some justice to his explanation there

I've not figured out the formula he uses to come up with the numbers, but it's definitely based on bike/rider weight and maximum load rating of the tyres. For my Kat, he suggested 38/38 psi and so far that feels good.

Anyway, make of it as you will, I was surprised that I was able to jump on with the pressure increases and feel it was good to go without taking too long to adjust to it either.

[Ktsteuart]

Yeah just trying to change the look up a little. I think the 100/90/18 is pretty close to the factory size and I’ve heard good things about the Shinko 712s. I’ll do some hunting on google to see if the rear brake/sprocket stuff is compatible. Thanks guys!

[Gorminrider]

sure, shinkos are an ok tire all-round...

While my engine is a little different, I'll still say:

Don't forget that while the E and S will probably have a slightly different rear sprocket than the T, (2 teeth less?) this is because the E/S tire is a bit larger diameter. The bikes will all spin the motor about the same per mph and your chain adjustment shouldn't be a problem.