Tyre size for GS450 (how wide / tall can you go)

[Guest]

Hi All!

It breaks my heart to ask for this, as this topic has been asked a Million of times, but for the life of me I cannot find exactly what I'm looking for in this forum.

Background:
I'm putting together a GS450 (84) which I bought in pieces. The tyres are old and need replacing, but I really want wider, and taller ones than what's on it now. I know that a thinner tyre handles better than a wide one, but aesthetically thin tyres don't tickle my fancy if you know what I mean. See the image below where it looks like a bicycle wheel!

It has the star shaped mag rims, both 18 inch front and rear.

Question:
How wide and tall can I go without getting into trouble? I'm currently looking at purchasing:

• Front: 100/90-18
• Rear: 120/90-18

But can I go beyond these measurements and still be OK?

Screenshot 2020-04-01 at 12.52.34.jpg

[Nessism]

How wide are the wheels? A 120/90 rear can be used if the wheel is 2.15" or wider, although it's pushing the limits. For the front a 100/90 is best to keep the proper steering feel.

[LAB3]

^^^^^ Agreed, that's the max

[Gorminrider]

"star shaped" rims? 18"? I suspect you have 1981 rims from a GS450E or, a GSX400E or some other 1980-1981 .......These are 1.85x18..90/90 18 Front, 100/90 18 rear is what they want...110 is ok -120 would be a gamble I wouldn't take for aesthetics...But I'm not sure about YOUR swingarm, being an '84...

The GS450 went through big changes in 84 and the wheelbase is longer, the rims and tires fatter. I'm interested that the '81 wheels fit ok...

If you want a fatter look I'd find a set of rims that ARE from the 84 or MAYBE a 1980-81 "T". These are 2.15x17 rear and you can mount 120 on them though IT'S a tight fit against the swingarm they came with.... Or, spoked wheels from 83 OR even the 16" rim from an L...really room for fat there!

[Guest]

Yes - good questions. I thought the star shaped mag rims were all the same.

They measure:
- Front = 60 mm (2.36 inches)
- Rear = 68 mm (2.68 inches)

I measured with the calipers on the outside of the rim. Should it be the inside?

I also measured the swing arm where it starts to narrow, and that is 127 mm (5 inches).

Pictures of how I measured to make sure I did it the right way (tyre that sits on the rear now is 3.5 / 18).

Screenshot 2020-04-01 at 17.39.13.jpg

[Gorminrider]

....yes, those are 80-82nrims from an "E"..yes the INSIDE measure is the one you want to consider per the left picture...and yes, 3.5X18" is a tire for the 80-82 rims you are using...there's certainly room in the 84 swingarm for larger tires ...

It's up to you whether you want to try what in essence might be Balloons on those rims....(which by the way are for Tubed tires...)but I'm pretty conservative with tires so you'll have to consider if the underlying argument is really valid or just pedantry. Consult widely.

[Nessism]

The rim size will be cast into the wheel.

[Guest]

Good news and bad news. Good news is that I found the measurement cast into the rim (thanks Nessism). The bad news is that they are thinner than I expected.

Front = 1.60 x 18
Rear = 1.85 x 18

So what is the verdict. How wide / tall would you go on that?

Will 90/90 be OK for the front, and 110/90 rear?

[Guest]

even the 16" rim from an L...really room for fat there!

Will that 16 inch rim fit onto my E model without any modifications? I have actually found one on eBay at a reasonable price. It's 16 x 2.15:https://www.ebay.de/itm/Orig-Hinterr...kAAOSwiLZeOAD7 It's in German though, but maybe you can see from the pictures it is the right one.
I actually think I need to change out the rear rim, as the brake drum lining looks really bad (deep cracks etc.).

[Nessism]

Good news and bad news. Good news is that I found the measurement cast into the rim (thanks Nessism). The bad news is that they are thinner than I expected.

Front = 1.60 x 18
Rear = 1.85 x 18

So what is the verdict. How wide / tall would you go on that?

Will 90/90 be OK for the front, and 110/90 rear?

Yes. I think that will be your best bet.

[Gorminrider]

Will 90/90 be OK for the front, and 110/90 rear?

as I said in an earlier post, these are ok on the 18" rim. In fact, I have a 110/90 18 on MY rim, which is the same as pictured. But it's nothing fancy...generic street tire.

Will that 16 inch rim fit onto my E model without any modifications?

I can only say,I expect so. I don't have any 16" rims of this year, but seeing as your 80-81 star-shaped rim fit your 84 and seeing as a 17" starshaped rim does fit my 81 gsx400E (because I have a T too) I strongly suppose the star-shaped rims are pretty much "swappable"..same brakes too.

The Sprocket, however, is another thing....you will want to check the ratio . i'd say, All the bikes mentioned have about the same HP and 6 speed transmission. To get the best out of them, with the different diameter tires, the ratios will vary.
Goto CMNSL and read the part description. gear teeth are often noted. Try to stick to the original "match" of hp versus speed versus engine rpm if you can, whichever wheel you use. That is, check the front engine sprocket of the 84 engine against the 81 engine's. If they are the same, you are likely ok with the 16" rear sprocket IF you can say that the engine itself is not radically different in other ways...it's worth thinking about....
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